AND METHOD FOR PRODUCING SAME

Technical Field

The present, invention relates to a metal colloidal solution that uses, as a protecting agent for metal nanoparticles , a polymer that contains a polyacetylalkylenimine N-oxide segment and a hydrophilic segment or a polymer that contains a hydrophobic segment in addition to the aforementioned two segments, and a method for producing the metal colloidal solution. It also relates to the aforementioned polymers and a method for producing the polymers.

Background. A t

Metal nanoparticles are nanoparticles having a particle diameter of one to several hundred nanometers and a significantly large specific surface area.. Metal nanoparticles having such properties are drawing much attention from various fields and there is a high expectation for use in electronic materials, catalysts, magnetic materials, optical materials, various sensors, coloring materials, and medical exa.mina.tion.

Printed wired boards and semiconductor devices are mainly produced through photolithographic processes that include a series of complicated production steps. Under such circumstances, a printable electronic device productio technology is drawing attention. A printable electronic device production technology involves preparing ink compositions by dispersing recently developed metal nanoparticles in media, forming patterns by printing using the ink compositions, and assembling the patterns into devices.

This technology is called printed electronics. Printed electronics offer prospects for roll-to-roll mass production of electronic circuit patterns and semiconductor elements and economical efficiency since the technology is suited for on-demand production, simplification of processes, and resource conservation. The technology is also expected to pave the way toward low-cost production processes for display devices, light-emitting devices, IC tags (RFIDs) , etc. Conductive material inks used in the printed electronics can contain metal nanoparticles of gold, silver, platinum, copper, and the like. Due to economical reasons and ease of handling,

I development of silver nanoparticl.es and inks containing the silver nanoparticles has preceded.

Silver in form of nanometer-order particles exhibits a significantly large specific surface area and an increased surface energy compared to bulk silver. Silver nanoparticles show a strong tendency to fuse with each other to lower the surface energy. As a result, particles fuse with each other at a temperature far below the melting point of bulk silver. This phenomenon is called a quantum size effect (Kubo effect) and presents an advantage of using silver nanoparticles as a conductive material on one hand. On the other hand, the strong tendency of metal nanoparticles to fuse with each other impairs the stability of the metal nanoparticles and degrades storage stability. In order to stabilize the metal nanoparticles, the metal nanoparticles need to be protected with a protecting agent that prevents fusion.

Typically, nanomaterials (compounds having a size on the nanometer order in general} are produced through special processes owing to their size and tend to be expensive. This has inhibited spread of the nanomaterials. In order to produce metal nanoparticles at low cost, a liquid phase reduction process that does not require special equipment such as vacuum process chambers is advantageous . A liquid phase reduction process is a process for obtaining metal nanoparticles by causing a metal compound to react with a reductant in a solvent. According to a known technology, reduction is performed in the presence of a compound, called, a dispersion stabilizer or a protecting agent in order to control the shape and particle size of the metal nanoparticles to be generated and to achieve a stable dispersion state. The protecting agent is often a polymeric, compound designed to have a functional group (such as a tertiary amino group, a quaternary ammonium group, a heterocyclic group having a basic nitrogen atom, a hydroxy! group, or a carboxyl group) capable of coordinating with a metal particle (for example, refer to PTL 1).

As discussed above, in order to produce metal nanoparticles that are expected to undergo desirable low-temperature fusion, an appropriate protecting agent that controls the shape and. particle size of the metal nanoparticles and stabilizes the dispersion is used. However, a protecting agent functions as a resistive component for bulk metal and lowers the conductive performance. Depending on the amount of the protecting agent used, a desirable low-temperature sintering property (the property that the specific resistance of a thin film obtained by firing a thin film of a metal-nanoparticle-containing conductive ink at a temperature in the range of 100 deg C to 150 deg C is on the 10 ^" ° ohm-centimeter order) may not be exhibited. From the viewpoint of designing a conductive material, the protecting agent is required to exhibit an ability to produce small particles, an ability to stably disperse these particles, and an ability to rapidly detach from the particle surfaces during sintering so as not to inhibit fusion between the metal nanoparticles . From the viewpoint of production of metal nanoparticles, the protecting agent is required to exhibit an ability to facilitate purification and. separation of metal nanoparticles produced. The protecting agent desirably exhibits all these abilities. Examples of the protective agents disclosed so far include commercially available polymeric pigment dispersants such as Solsperse (trademark, produced by Zeneca) and FLOWLEN (trademark, produced by Kyoeisha Chemical Co., Ltd.}, polymers that have a pigment-compatible group (amine) in a main/side chai and two or more salvation segments, and copolymers that have polyethylene irnine segments and polyethylene oxide segments. However, these dispersants rarely achieve all of the desired abilities described above and further improvements are needed (for example, refer to PTL 2 to 4) .

[Citatio List]

[Patent Literature]

[PTL 1] Japanese Unexamined Patent Application Publication No. 2004-346429

[PTL 2] Japanese Unexamined Patent Application Publication No. 11-080647

[PTL 3] Japanese Unexamined Patent Application Publication No. 2006-328472

[PTL 4] Japanese Unexamined Patent Application Publication No. 2008-037884

Summary of Invention

[Technical Problem]

An object of the present invention is to provide a. metal nanoparticle-protecting polymer to which various properties, such as an ability to control metal nanoparticles , igh dispersion stability, a good low-temperature sintering property, and ease of purifying and separating metal nanoparticles , are intentionally adjusted and imparted so that a more practical electrical conductivity is exhibited. A metal colloidal solution and methods for producing the metal nanoparticle-protecting polymer and the metal colloidal solution are also provided,

[Solution to Problem]

The inventors of the present invention have already disclosed (refer to PTL 4) that a binary system polymer in which a polyalkylenimine segment containing polyet ylenimine is linked with a ydrop ilic segment containing a polyoxyalkylene chain and a ternary system polymer in which a hydrophobic segment such as an epoxy resin is linked, to the binary system polymer are useful for producing metal nanoparticles. However, according to the technique disclosed in PTL 4, the properties described above have not been sufficiently achieved. Based on further investigations, the inventors have found, that it is effective to use a novel acetylated N-oxide-based polymer obtained by acetylating a primary amine portion or primary and secondary amine portions in the polyaikylenimine segment and then oxidizing a tertiary amine portion into an N-oxide, and made the present invention .

In other words, the present invention provides a metal nanoparticle-protecting polymer that includes, in a molecule, a polyacetylalkylenimine N-oxide segment (A) obtained, by acetylating a primary amine portion or primary and secondary amine portions in polyalkylenimine and then oxidizing mainly a tertiary amine portion; and a hydrophilic segment (B) . The present invention also provides a method for producing the metal nanoparticle-protecting polymer, a metal colloidal solution that contains metal nanoparticle-containing composite bodies dispersed in a medium, the composite bodies being prepared by using the metal na oparticle-protecting polymer as a protecting agent, and. a method for producing the metal colloidal solution,

[Advantageous Effects of Invention]

A metal colloidal solution obtained in the present invention exhibits a good low-temperature sintering property. The conductive performance at low temperature is excellent since the protecting polymer used in the present invention readily detaches from the surfaces of the metal nanoparticles at low temperature . Moreover, the size of the metal nanopar icles obtained in the presence of this particular protecting polymer is sufficiently small, monodisperse, and narrow in particle size distribution. Thus, the storage stability is also high. This is because the acetylated structure uni s and N-oxide structural uni s in the protecting polymer protect the metal nanoparticles well and the ydrophilic segment or the hydrophobic segment in the polymer causes the particles to disperse in the medium. Thus, the dispersion stability of the dispersion is not impaired and the dispersion retains a stable dispersion state in a solvent for a long time.

In the present invention, in producing a metal colloidal solution, metal nanoparticles are obtained by reduction and, in the following purification and separation step of removing impurities, composite bodies constituted by metal nanoparticles and the protecting polymer easily settle and become separated by a simple operation of adding a poor solvent to a dispersion of the composite bodies. This is achieved due to strong association force of the protecting polymer. Since complicated steps and elaborate condition settings are rarely needed, this method is industriously advantageous.

Moreover, the metal nanoparticles in the metal colloidal solution obtained, in the present invention have a large specific surface area., high surface energy, and plasmon absorption, which are the characteristics of metal nanoparticles. In addition to these characteristics, the dispersion stability and storage stability can be efficiently exhibited because the polymer dispersion is of a self assembly type. Thus, the metal colloidal solution has various chemical, electrical, and magnetic properties required of the conductive paste or the like and can be used in a wide variety of fie.1ds , sueh. as cata.1ysts , e 1ect.ronic ateria1 s , magnet ic materia1s , optical materials, various sensors, coloring materials, and medical examination use.

Description of Embodiments

A metal nanoparticle-protecting polymer of the present invention is a polymeric compound that has a polyacetylalkylenimine N-oxide segment (A) and a hydrop ilic segment (B) or a polymeric compound that has the polyacetylalkylenimine N-oxide segment (A) , the hydrophilic segment (B) , and a hydrophobic segment (C) . A dispersion (metal colloidal solution) of metal nanoparticles protected with a protecting polymer having such a structure has high dispersion stability and good conductive properties and exhibits various functions of metal -containing functional dispersion derived from metal nanoparticles such as coloring, catalyzing, and. electrical functions .

Since the polyacetylalkylenimine N-oxide segment (A) in the protecting polymer of the present invention contains acetylalkylenimine units and n-oxide units that can form coordinate bonds with a metal or a metal ion, the polyacetylalkylenimine N-oxide segment (A) is a segment that can immobilize the metal as nanopar icles. When the metal nanopar icles obtained in the present invention are protected, with the protecting polymer to form, composite bodies and the composite bodies are produced and stored, in hydrophilic solvents, a metal colloidal solution obtained can exhibit excellent dispersion stability and storage stability due to incorporation of the polyacetylalkylenimine N-oxide segment (A) and the hydrophilic segment (B) that exhibit hydrophilicity in the solvents.

From the viewpoint of industrial production, a simple purification and separation method for composite bodies prepared by protecting metal nanoparticles with the protecting polymer, the metal nanoparticles being produced by dissolving or dispersing a. metal compound in a medium and reducing the metal compound in the medium is a critical process. Preferably, this purification and separation method involves settling achieved by adding a poor solvent such as acetone to the solution after the reaction. The acetylalkyleniraine units and. N-oxide units in the protecting polymer of the present invention have nigh polarity and thus promote rapid association of the metal -nanoparticle-containing composite bodies. Accordingly, settling easily occurs while blocks of large associated particles are formed.

A metal colloidal solution which is a dispersion of metal nanoparticle-containing composite bodies or a conductive material obtained by using the metal colloidal solution to form a conductive ink is printed on or applied to a substrate. In the subsequent sintering step, the acetylalkylenimine units and the N-oxide units in the protecting polymer easily decouple from the metal nanoparticle surfaces even at low temperature because coordinate bonds between the units and the metal are weak. As a result, a good low-temperature sintering pro erty is exhibited .

The particle size of the dispersed bodies (composite bodies) in the metal colloidal solution of the present invention is dependent not only on the molecular weight of the protecting polymer used and the degree of polymerization of the polyacetylalkylenimine N-oxide segment (A) but also on the structure and compositional ratios of the components constituting the protecting polymer, namely, the polyacetylalkylenimine N-oxide segment (A) , the hydrophilic segment ( B ) described below, and the hydrophobic segment (C) described below.

The degree of polymerization of the polyacetylalkylenimine N-oxide segment (A) is not particularly limited. At an excessively low degree of polymerization, the protecting polymer may not exhibit sufficient ability to protect metal nanoparticles. At an excessively high degree of polymerization, the size of the composite particles constituted by the metal nanoparticles and the protecting polymer may become excessively large, thereby degrading storage stability. Accord.irigly, in order to enhance the metal nanoparticle immobilizing ability and prevent generation of gigantic dispersed, particles, the number of alkylenimine units (degree of polymerization) in the polyacetylalkylenimine N-oxide segment (A) is usually in the range of 1 to 10,000, preferably in the range of 5 to 2,500, and most preferably in the range of 5 to 300.

The polyacetylalkylenimine N-oxide segment (A) can be easily obtained by acetylating the alkylenimine portion in the polyalkylenimine segment, which is the precursor of the polyacetylalkylenimine N-oxide segment (A) , with an acetylating agent and then oxidizing the acetylated. portion by bringing the acetylated portion, into contact with an oxidant. A segment constituted by polyalkylenimine may be any commercially available or synthesizable segment. From the viewpoint of industrial availability, the segment, is preferably constituted by branched. polyethylenimine or branched, polypropylenimine and more preferably branched polyethylenimine .

In the case where a hydrophilic solvent such as water is used to prepare a metal colloidal solution, the hydrophilic segment (B) in the protecting polymer of the present invention exhibits high compatibility with the solvent and retains storage stability of the colloidal solution. In the case where a hydrophobic solvent is used, the hydrophilic segment (B) having strong intramolecular or intermoiecuiar association force helps form cores of dispersed particles. The degree of polymerization of the hydrophilic segment (B) is not particularly limited. In the case where a hydrophilic solvent is used, the storage stability is degraded at an excessively low degree of polymerization and aggregation may occur at an excessively high degree of polymerization. In the case where a hydrophobic solvent is used, association force among dispersed particles becomes insufficient at an excessively low degree of polymerization of the hydrophilic segme t (B) and the compatibility with the solvent is not retained at an excessively high degree of po1ymerization . From thiese viewpoints, the degree of po1ymerx zat ion of the hydrophilic segment (B) is usually 1 to 10,000, preferably 3 to 3,000, and, based on ease of production, more preferably 5 to 1,000. When the hydrophilic segment is a polyoxyalkylene chain, the degree of polymerization is particularly preferably 5 to 500,

The hydrophilic segment (B) may be any segment composed of a hydrophilic polymer chain that is commercially available or synthesizable . In the where a hydrophilic solvent is used, the hydrophilic segment (B) is preferably composed of a nonionic polymer since a highly stable colloidal solution is obtained.

Examples of the hydrophilic segment (B) include polyoxyalkylene chains such as a polyoxyethylene chain and polyoxypropylene chain, polymer chains composed of polyvinyl alcohols such as polyvinyl alcohol and partially saponified polyvinyl alcohol, polymer chains composed of water-soluble poly (meth) acrylic acid esters such as pol yhydroxyethyl acrylate, po1yhydroxyethy1 methacrylate, dimethy1aminoethyl acry1ate, and dimethylaminoethy1 methacrylate, hydrophi1ic-substituent-containing polyacylalkylenimine chains sueh as po1yacety.1ethylenimine, po1yacety1propy1enimine , po1ypropiony1ethy1enimine , and po 1 ypropiony1propy1enimine , and polymer chains composed of polyacrylamides such as polyacrylamide, polyisopropylacrylamide, and polyvinylpyrrolidone. Among these, polyoxyalkylene chains are preferred since a highly stable colloidal solution is obtained and the industrial availability is high. In the present invention, the protecting polymer may further contain a hydrophobic segment (C) . In particular, when an organic solvent is used as a medium for the metal colloidal solution, it is preferable to use a polymer containing a hydrophobic segment (C) as a. protecting agent ,

The hydrophobic segment (C) may be any segment composed of a residue of a hydrophobic compound that is commercially available or synthesizable . Examples of the hydrophobic segment (C) include those composed of residues of polymers such as polystyrenes, e.g., polystyrene, polymethylstyrene, po1ychloromethy1styrene, and polybromomethylstyrene, water-insoluble poly (meth) acrylic acid esters, e.g., polymethyl acrylate, polymethyl methacrylate, poly (2-ethy1hexy1 acry1ate), ard poly (2-ethyIhexyl ethacry1ate) , and hydrophobic-subs tituent-containing po 1 yacy1a1ky1enimines such as polybenzoylethylenimine, polybenzoylpropylenimine, po1y (meth} acry1oy.1ethy1enimine , po1y (meth} acry1oy.1propy1enimine , poly [N-{3- (perfluorooctyl ) propionyl } ethylenimine ] , and poly [N-{3- (perfluorooctyl ) propionyl } propylenimine ] ; and residues of resins such as epoxy resins, polyurethanes , and polycarbonates. The hydrophobic segment (C) may be composed of a. residue of a single compou d or a residue of a compou d obtained by preliminarily reacti g two or more different types of compounds. The hydrophobic segment (C) preferably has a structure derived from an epoxy resin and more preferably has a structure derived from a bisphenol A-type epoxy resin since a protecting polymer can be easily industrially synthesized and a metal colloidal solution obtained therewith exhibits nigh adhesion to a substrate when printed or applied.

The degree of polymerization of the hydrophobic segment (C) is not particularly limited but is usually 1 to 10,000, and preferably 3 to 3,000 and more preferably 10 to 1,000 if the hydrophobic segment (C) is a polystyrene, a poly (meth) acrylic acid ester, a hydrophobic-substituent-containing polyacylalkylenimine , or the like. When the hydrophobic segment (C) is composed of a residue of a resin such as an epoxy resin, a polyurethane, a polycarbonate, or the like, the degree or polymerization is usually 1 to 50, preferably 1 to 30, and more preferably 1 to 20.

The metal nanoparticle-protecting polymer of the present invention may be made by allowing an acetylation agent to react with a. precursor compound (I) which is either a compound having a polyalkylenimine segment and a ydrophilic segment (B) or a compound having a polyalkylenimine segment, a hydrophilic segment (B) , and a hydrophobic segment (C) , and then, treating the resultant product with an oxidant. Alternatively, an acetylating agent may be used during performance of a reaction for preparing a precursor compound (I) from a polyalkylenimine segment and a hydrophilic segment (B) and then the resulting product may be treated, with an. oxidant. According to any of these methods, an as-designed protecting polymer can be easily obtained . A process disclosed in PTL 4 and Japanese Unexamined Patent Application Publication No. 2006-213837 can be directly used to produce the precursor compound (I) .

After the precursor compound (I) is obtained, the nitrogen atoms of the primary amine portions or primary and secondary amine portions in the polyalkylenimine segment are acetylated. Alternatively, during the process of producing a precursor compound (I) by using a polyalkylenimine segment and a hydrophilic segment (B) , the nitrogen atoms of primary amine portions or primary and secondary amine portions in the polyalkylenimine segment are acetylated. The acetylation reaction is performed by adding an acetylating agent that has an acetyl structure (CH3-CO-) . Subsequently, the nitrogen atoms in the acetylated polyalkylenimine segment are oxidized. Oxidation is conducted by adding a compound having a peroxide structure (-0-0- or -N-0-) to an aqueous solution of the acetylated precursor compound (I) , Examples of the compound having a peroxide structure include hydrogen peroxide, metal peroxides, inorganic peroxides and salts thereof, organic peroxy compounds, and organic peroxides and salts thereof .

, common industrial acetylating agent ca be used as the acetylating agent . Examples of the acetylating agent include acetic anhydride, acetic acid, dimethylacetamide, ethyl acetate, and chlorinated acetic acid. Among these acetylating agents, acetic anhydride, acetic acid, and dimethylacetamide are particularly preferable from the ^' viewpoints of availability and. ease of handling-.

When the polyalkylenimine segment is derived from a. branched, polyalkylenimine compound, primary, secondary, and tertiary amines are contained homogeneously and at random. When this polyalkylenimine segment is reacted with any of the acetylating agent described above, one acetyl group is offered per nitrogen atom in the primary amines and/or secondary amines while leaving the tertiary amine un-acetylated. In other words, the acetylation reaction proceeds on the primary amine and the secondary amine that have higher quantitative reactivity with the acetylating agent used. The acetylation ratio for the acetylation reaction in terms of the acetylation ratio of the primary amine and secondary amine is investigated. As a result, it has been found that a protecting polymer having- good electrical conductivity, dispersion stability, and an ability to facilitate purification and separation is obtained when 5 to 95 mol% of the primary amines or 5 to 95 mol% of the primary amines and 5 to 50 mol% of the secondary amines in the polyalkylenimine segment are acety1ated .

Next, nitrogen atoms are oxidized. When hydrogen peroxide is used as an oxidant, an industrially available 30-50 mol% hydrogen peroxide solution is usually used. Examples of the metal peroxides include sodium peroxide, potassium peroxide, lithium peroxide, magnesium peroxide, and zinc peroxide. These peroxides are highly available and can be used as the oxidant . Examples of the inorganic peroxides and salts thereof include persulfuric acid., percarbonic acid, perphosphoric acid, perchloric acid, Oxone (registered trademark by DuPont, oxidant mainly composed of potassium hydrogen persulfate} , ammonium persulfate, sodium persulfate, potassium persulfate, and sodium percarbonate . Examples of the organic peroxy compounds and organic peroxides and salts thereof include peracetic acid, perbenzoic acid, m-chloroperbenzoic acid, benzoyl peroxide, tert-butyl peroxide, 1, 2-dimethyldioxirane, and Davis reagents (2- (phenylsuitonyl) -3-a.ryloxaz.i id.ine) . These may also be used as the oxidant. Among these oxidants, a 30% hydrogen peroxide solution, ammonium persulfate, Oxone, and peracetic acid that are highly available, easy to handle, and less expensive are preferable.

The oxidants described above can give one oxygen atom for one nitrogen atom. he one-on-one reaction is assumed to occur with tertiary and. secondary amines. However, some complexity is expected in reaction with primary amines. That is, primary amines may go further than reacting ¾ ⁷ it.h one molecule of the oxidant and may undergo reaction with a next molecule of the oxidant. The amount of the oxidant, to be added, was studied, based on these assumptions. As a result, it n was found that a protecting polymer that has good conductivity, dispersion stability, and an ability to readily separate on purification is obtained by adding the oxidant in an amount corresponding to 0,5% to 95% of the number of all nitrogen atoms in the polyalkyleniraine segment in the precursor compound (I).

Especially when the polyalkylenimine segment is based on a branched polyalkylenimine compound, the primary, secondary, and tertiary amines are evenly and randomly contained. When these amines are reacted with an oxidant, the tertiary amines turn into amine oxide (C-N ⁺ (0 ^" ) (-C)-C) only. The secondary amines undergo a further reaction with an amine oxide (C-HN ^"f (0 ^~ ) -C) depending on the reaction condition and turn into hydroxylamine (C-N (OH) -C) and its oxidized form, nitron (C=C-N ⁺ (0 ^" ) -C) . The primary amines may turn into hydroxylamine, (C-NH(OH) ) , nitroso (C-NO) , and nitro (C-NO2) . Due to these possibilities, the protecting polymer obtained is assumed to contain these structures although the amounts thereofmay.be small .

The metal nanoparticle-protecting polymer of the present invention contains a hydrophilic segment (B) and, optionally, a hydrophobic segment (C) in addition to the polyacetylalkylenimine N-oxide segment

(A) that can stabilize the metal nanoparticles . As discussed above, the hydrophilic segment ( B ) exhibits strong association force in a hydrophobic solvent and high compatibility with a hydrophilic solvent, and the hydrophobic segment (C) exhibits strong association force in a hydrophilic solvent and high compatibility with a hydrophobic solvent. Moreover, it is presumed that when the hydrophobic segment

(C) contains an aromatic ring, the pi electron of the aromatic ring interacts with the metal and contributes to stabilization the metal nanoparticles .

The ratio of the number of moles of the polymer constituting the chain of the polyacetyla.lkylen .mine N-oxide segment (A) to the number of moles of the polymer constituting the chain of the hydrophilic segment

( B ) , that is, the molar ratio (A) : ( B ) , is not particularly limited. The ratio is usually in the range of 1: (1 to 100} and preferably 1: (1 to 30} from the viewpoints of the dispersion stability and. storage stability of a metal colloidal solution obtained. When the protecting polymer also contains a hydrophobic segment (C) , the ratio of the number of moles of the polymer constituting the chain of the polyacetylalkylenimine N-oxide segment (A) , the number of moles of the polymer constituting the chain of the hydrophilic segment (B) , and the number of moles of the polymer constituting the chain of the hydrophobic segment (C) , that is, the molar ratio (A) : (B) : (C) , is usually in the range of 1: (1 to 100} : (1 to 100} and preferably in the range of 1 : (1 to 30) : (1 to 30} from the viewpoints of the dispersion stability and storage stability of the metal colloidal solution obtained. The weight-average molecular weight of the metal nanoparticle-protecting polymer of the present invention is preferably in the range of 1, 000 to 500., 000 and more preferably in the range of 1,000 to 100,000.

The protecting polymer of the present invention is dispersed or dispersed in various media and used in production of metal colloidal solutions . The material used as the media is not particularly limited and the dispersion may be of an oi1 /water (0/ ) system or of a water/oi 1 (W/O) system. The medium may be selected according to the metal colloidal solution production process and/or usage of the metal colloidal solution. For example, a hydrophilic solvent, a hydrophobic solvent, a mixed solvent containing hydrophilic and hydrophobic solvents, or a mixed solvent that contains other solvent in addition to the foregoing as described below may be selected and used. When a mixed solvent is used, the amount of the hydrophilic solvent is adjusted to be larger than that of the hydrophobic solvent for an O/W system and the amount of the hydrophobic solvent is adjusted to be larger than that of the hydrophilic solvent for a W/O system. The mixing ratio is not particularly limited since the ratio depends on the types of the solvents used. In general, for an O/W system, the volume of the hydrophilic solvent is preferably 5 times or more large* than that of the hydrophobic solvent and for a W/O system, the volume of the hydrophobic solvent is preferably 5 times or more larger than that of the hydrophilic solvent.

Examples of the hydrophilic solvent include methanol, ethanol, isopropyl alcohol, tetrahydrofuran, acetone, dimethylacetamide, diraethylformamide, ethylene glycol, propylene glycol, ethylene glycol monomethyl ether, propylene glycol monomethyl ether, ethylene glycol dimethyl ether, propylene glycol dimethyl ether, dimethyl sulfone oxide, dioxirane, and N-methylpyrrolidone . These can be used alone or in combination.

Examples of the hydrophobic solvent include hexane, cyclohexane, ethyl acetate, butanol, methylene chloride, chloroform, chlorobenzene, nitrobenzene, methoxybenzene, toluene, and xylene. These can be used alone or in combination.

Examples of other solvent that can be used by being mixed with a hydrophilic solvent or a hydrophobic solvent include ethyl acetate, propyl acetate, butyl acetate, isobutyl. acetate, ethylene glycol monomethyl ether acetate, and propylene glycol monomethyl ether acetate .

The metal nanoparticle-protecting polymer may be dispersed in a medium by any method. Typically, the metal nanoparticle-protecting polymer is easily dispersed by leaving- the polymer to stand still or by stirring at room temperature . If needed, an ultrasonic treatment or a heat treatment may be carried out. In the case where the protecting polymer is not readily compatible with the medium due to its crystallinity or the like, the protecting polymer may be dissolved or allowed to swell in a small amount of a good solvent and then dispersed in a desired medium. It is effective to employ an ultrasonic treatment or neat treatment during this process.

A mixture of a hydrophilic solvent and a hydrophobic solvent may be prepared by any mixing method and mixing order, etc. Since the compatibility of the protecting polymer with various solvents and the dispe s ibil ity of the protecting polymer differ depending on the type, composition, and other factors of the protecting polymer, the solvent mixing ratio, the order of mixing the solvents, the method for mixing the solvents, mixing conditions, and the like may be appropriate selected based, on the purpose.

According to the method for producing the metal colloidal solution of the present invention, metal ions are reduced in the solution or dispersion of the protecting polymer to form metal nanoparticles. The source of the metal ions may be a salt or an ionic solution of a. metal. The source of the metal ion may be any water-soluble metal compound, for example, a salt of a metal cation and an acid group anion or an acid group anion containing a metal. For example, metal ions that have metal species such as transition metals are preferably used..

The transition metal ion can be smoothly coord.ina.ted to form a complex irrespective of whether the ion is a transition metal, cation (M ⁿ⁺ ) or an anion (ML _x ^n~ ) constituted by a halogen bond . In this description, a transition metal refers to a transition metal element in 4 to 12 groups and 4 to 6 periods of the periodic table.

Examples of the transition metal cation include the cations (M ⁿ⁺ ) of the transition metals such as monovalent, divalent, trivalent, or tetravalent cations of Cr, Co, Ni, Cu, Pd, Ag, Pt, Au, and the like. The counter anion of the metal cation may be CI, NO ₃ , SO ₄ , or an organic anion of a carboxylic acid.

An anion in which a metal is coordinated with a halogen, such as a metal -containing anion (ML _x ^n" ) , e.g., AgNOs, AuCl ₄ , PtC-u, or CuF ₆ , can also smoothly coordinate to form a complex.

Of these metal ions, the ions of silver, gold, and platinum are preferred since these are spontaneously reduced at room temperature or under heating into nonionic metal nanoparticles . In the case where the metal colloidal solution obtained is used as a conductive material, silver ions are preferably used to develop electrical conductivity and prevent oxidation of a coating film obtained by printing or applying the metal colloid l solution.

The number of metal species to be contained may be two or more. In such a case, salts or ions of plural metals are added either simultaneously or separately so that the metal ions of different species undergo a reduction reaction in a medium and metal particles of different species are generated. Thus, a colloidal solution that contains plural species of metals can be obtained.

In the present invention, metal ions may be reduced by using a reductant .

The reductant may be any of a variety of reductants . The selection may be made based on the usage of the metal colloidal solution obtained, metal species contained., etc. Examples of the reductant. include hydrogen, boron compounds such as sodium borohydride and ammonium borohydride, alcohols such as methanol, ethanol, propanol, isopropyl alcohol, ethylene glycol, and propylene glycol, aldehydes such as formaldehyde, acetaldehyde , and propionaldehyde , acids such as ascorbic acid, citric acid, and sodium citrate, amines such as propylamine, butylamine, diethylamine, dipropylamine, dimethylethylamine, triethylamine , etnylenediamine, triethylenetetrami e, methylaminoethanol , dimethylaminoethanol , and triethanolamine, and hydrazines such as hydrazine and hydrazine carbonate. Among these, sodium borohydride, ascorbic acid, sodium citrate, methylaminoet anol , and dimethylaminoethanol are preferred due to high industrial availability and ease of handling.

In the method for producing a metal colloidal solution of the present invention, the ratio of the metal ion source to the protecting polymer used is not particularly limited. For example, when the total number of the nitrogen atoms constituting the polyacetylalkylenimine N-oxide segment in the protecting polymer is assumed to be 100 mol, the amount of the metal is usually m t e range of i to 20, 000 mol, preferably in the range of 1 to 10,000 mol, and more preferably in the range of 50 to 7,000 mol.

In the method for producing a metal colloidal solution of the present invention, the medium in which the protecting polymer is dispersed or dissolved may be mixed with a metal salt or an ionic solution by any method. For example, a metal salt or an ionic solution may be added to a medium in which the protecting polymer is dispersed or dissolved or vice ^' versa, or a protecting polymer and a metal salt or ionic solution may be simultaneously fed to a separate container and mixed. The mixing method is not particularly limited and may be stirring.

The reductant may be added by any method. For example, a. reductant may be directly added or a reductant may be dissolved or dispersed in an aqueous solution or other solvent and then mixed. The order of adding the reductant is not particularly limited. A reductant maybe preliminarily added to a dispersion or solution of a protecting polymer or a reductant may be added to the protecting polymer together with a metal salt or an ionic solution . Yet alternatively , a solution or dispersion of a protecting polymer may be mixed with a metal salt or an ionic solution and then a reductant may be added thereto after several days or several weeks.

In adding a metal salt or an ionic solution thereof used in the production method of the present invention to a medium in which the protecting polymer is dispersed or dissolved, the metal salt or ionic solution thereof is preferably added either directly or in the form of an aqueous solution irrespective of whether the system is O/ or W/O. In the case of metal ions of silver, gold, palladium, platinum, and the like, the metal ion coordinates to the acetylalkylenimine or N-oxide unit in the polymer and then spontaneously reduced at room temperature or under heating. Thus, leaving the metal ions to stand still or stirring the metal ions at room temperature or under heating gives metal nanopart. icles and a metal colloidal solution which is a dispersion of composite bodies of metal nanoparticles protected with the protecting polymer. However, in order to efficiently reduce the metal ions, a reductant is preferably used as discussed above and a metal colloidal solution can be obtained by leaving the ions still or stirring the ions at room temperature or under heating. During this process, the reductant is preferably used as is or prepared into an aqueous solution in advance. The temperature at which heating is conducted differs depending on the types of the protecting polymer and types of the metal, medium, and reductant used, for example. Generally speaking, the temperature is 100 deg C or less and. preferably 80 deg C or less.

Metal nanoparticles precipitate as a result of reduction of metal ions described above and, at the same time, surfaces of these particles are protected with the protecting polymer that stabilizes the particles. The solution after the reduction contains impurities such as the reductant, counter ions of the metal ions, and the protecting polymer not contributing to the protection of the metal nanoparticles and thus cannot perform sufficiently as a conductive material. Accordingly, a purification step of removing the impurities is needed. Since the protecting polymer of the present invention has high protecting- performance, a poor solvent can be added to the solution after the reaction to efficiently settle the composite bodies constituted by metal nanoparticles protected with the protecting polymer. The settled composite bodies can be concentrated or isolated through centrifugation or the like. After concentration, an appropriate medium is added to control the nonvolatile content (concentration) to suite the usage of the metal colloidal solution and the resulting product is used, in various usages .

The metal nanoparticle content in the metal colloidal solution obtained in the present invention is not particularly limited. However, if the content is excessively low, the properties of the metal nanoparticles in the colloidal solution are not sufficiently exhibited. If the content is excessively high, the relative weight of the metal nanoparticles in the colloidal solution is increased and the stability of the colloidal solution is anticipated to be poor due to the imbalance between the excessively large relative weight of the metal nanoparticles and. the dispersing ability of the protecting polymer. Moreover, from the viewpoints of reducing capacity and coordinating capacity of the acetylalkylenimine N-oxide units in the protecting polymer, the nonvolatile content in the metal colloidal solution is preferably within the range of 10 to 80 mass% and more preferably within the range of 20 to 70 mass%. The metal nanoparticle content in the nonvolatile matter is preferably 93 mass% or more and more preferably 95 massl or more in order for the colloidal solution used as a conductive material to exhibit satisfactory electrical conductivi y.

The size of the metal nanoparticles contained in the nonvolatile matter in the metal colloidal solution obtained in the present invention is not. part.icula.rly limited. In order for the metal colloidal solution to exhibit higher dispersion stability, the metal nanoparticles are preferably fine particles 1 to 70 nm in particle size and more preferably 5 to 50 nm in particle size.

Generally speaking, metal nanoparticles several ten nanometers in size have characteristic optical absorption induced by surface plasmon excitation dependent on the metal species. Accordingly,, whether metals are present by taking a form of nanometer-order fine particles in the solution can be confirmed through measuring the plasmon absorption of the metal colloidal solution obtained, in the present invention. Moreover, it is possible to determine the average particle size and the distribution width by using a transmission electron microscope (TSM) image of a film obtained by casting the solution .

The metal colloidal solution obtained, in the present invention stays stably dispersed for a long time in all types of media and thus the usage thereof is not limited. The metal colloidal solution finds its usage in various fields including catalysts, electronic materials, magnetic materials, optical materials, various sensors, coloring materials, and medical examination uses. Since the metal species and the ratio thereof to be contained are also easily adjustable, the effects desired for the usage can be efficiently exhibited. Moreover, since the solution stays stably dispersed for a long time, the solution can withstand long-term use and long-term storage, which makes the solution highly useful . Moreover, the method for producing the metal colloidal solution according to the present invention does not require complicated steps and. elaborate condition settings and. is thus a highly advantageous industrial process,

EXAMPLES

The present invention will now be described in further detail by way of examples which do not limit the scope of the present invention. Unless otherwise noted, "%" means "massl" .

The instruments and measurement methods employed in the examples below a.re as follows:

^X H-NMR: AL300 produced by JEOL Ltd., 300 MHz

Particle size measurement: FPAR-1000 produced by Otsuka Electronics Co., Ltd.

Plasmon absorption spectrum: UV-3500 produced by Hitachi Ltd.

Confirmation of structure of protecting polymer through ^X H-NMR

About 3 mL of a protecting polymer solution was concentrated and thoroughly dried under a reduced pressure. The residue was dissolved in about. 0.8 mL of an NMR measurement solvent such as a 0.03% tetramethy1 si 1ane-containing deuterated ch1 oroform, fo ^' examp1e , the resulting solution was placed in an NMR measurement sample glass tube 5 mm in outer diameter and a ⁱ H-NMR ₁ spectrum was acquired by using a nuclear magnetic resonance absorption spectrum, analyzer, JEOL JNM-LA300. The chemical shift delta was based, on. tetramethylsilane as a reference substance.

Particle size measurement by dynamic light scattering

A portion of a metal colloidal solution was diluted with purified water and the particle size distribution and average particle size were determined with. FPAR-1000 concentrated-system particle analyzer produced, by Otsuka Electronics Co., Ltd.

Measurement of metal content in nonvolatile matter by t ermogravimetric analysis

About 1 mL of the metal colloidal solution was placed in a glass sample jar and concentrated by heating on a boiling water bath under a nitrogen stream. The residue was further vacuum dried at 50 deg C for 8 hours to obtain nonvolatile matter. Into an aluminum pan for thermogravimetry, 2 to 10 mg of the nonvolatile matter was accurately weighed. The aluminum pan was loaded in EXSTAR TG/DTA6300 tiermo-gravimetry/differential thermal analyzer (produced by Seiko Instruments Inc. ) and heated from room temperature up to 500 deg C at a rate of 10 deg C per minute under an air stream to measure the weight loss caused by heating. The silver content in the nonvolatile matter was calculated from the following equation:

Metal content (%} = 100 - weight loss (%)

Measurement of resistivity of metal thin film obtained from metal colloidal solution

Onto an upper part of a 2.5 X 5 cm clean glass plate, about 0.5 mL of a metal colloidal solution was added dropwise and a coating film was formed by using a bar coater No. 8. The coating film was air-dried and then heated in a hot air drier at 125 deg ^' C and at 180 deg C for 30 minutes to form a fired coating film. The thickness of the fired coating film was measured with an Optelics C130 Real Color Confocal microscope (produced by Lasertec Corporation) and the surface resistivity (ohms per square} was measured with Loresta-EP MCP-T360 low resistivity meter (produced by Mitsubishi Chemical Corporation) in accordance with Japanese Industrial Standard (JIS) K719 "Testing method for resistivity of conductive plastics with a four-point probe array" . The thickness of the coating film was substantially constant at 0.3 micrometers under the above-described conditions and the volume resistivity (ohm-centimeter) was calculated from the equation below based on the thickness a d the surface resistivity (ohm per square) :

Volume resistivity (ohm-centimeter) = Surface resistivity (ohm per square) X thickness (cm)

Synthetic Example 1: synthesis of tosylated polyethylene glycol monomethyl ether

In a nitrogen atmosphere, a chloroform solution (30 mL) containing 9.6 g (50,0 ramol) of p-toluenesulfonic acid, chloride was added dropwise to a mixed solution containing 20,0 g (10.0 mrnol) of methoxypolyethylene glycol [ n=2, 000] , 8.0 g (100.0 mrnol) of pyridine, and 20 mL of chloroform under stirring and ice cooling for 30 minutes. Upon completion of the dropwise addition, the resulting mixture was stirred for 4 more hours at 40 deg C. After completion of reaction, 50 mL of chloroform was added to dilute the reaction solution. The diluted reaction solution was then washed sequentially with 100 mL of a 5% aqueous hyd.rochlo.ric acid solution, 100 mL of an aqueous saturated sodium hydrogen carbonate solution, and 100 mL of a saturated saline, dried over magnesium sulfate, filtered, and concentrated at a reduced pressure. The solid matter obtained was washed, with hexane several times, filtered, and dried at 80 deg C at a reduced pressure. As a. result, 22.0 g of a tosylated product was obtained.

The measurement results of ¹ H-NMR (AL300 produced by J ^' EOL Ltd., 300 MHz) of the product obtained are as follows:

Results of ^X H-NMR (CDC1 ₃ ) :

Delta (ppm) - 7.8 (d, 2H, J = 7.8 Hz, tosyl group), 7,3 (d, 2H, J = 7.8, tosyl group), 4.2 (t, 2R, J = 4,2 Hz, sulfonic acid ester vicinal), 3.6-3.5 (m, PEGM methylene) , 3.4 (s, 3H, methoxy group at PEGM chain terminal), 2.4 (s, 3H, tosyl group methyl)

Synthetic Example 2 : synthesis of polyethylenimine-b-polyethylene glyco 1 copolymer

In a nitrogen atmosphere, 19.3 g (9.0 iranol) of tosylated polyethylene glycol obtained in Synthetic Example 1 and 30,0 g (3.0 ramoi) of branched polyethylenimine (ΕΡΟΜΙ ^' SP200 produced by Nippon Shokubai Co., Ltd.) were dissolved at 60 deg C and mixed by stirring. To the resulting solution, 0.18 g of potassium carbonate was added and the resulting mixture was stirred at a reaction temperature of 120 deg for 6 hours. After completion of the reaction, the product was diluted with a THE solvent and concentrated at a reduced pressure at 30 deg C after removing the residue. A solid product obtained was again dissolved in a THF solvent and heptane was added to the resulting solution to again settle the residue. The residue was separated by filtration and concentrated at. reduced pressure. As a result, 48.1 g of a pale yellow solid product was obtained (yield: 99%) .

The results of ¹ H- MR and ⁱ³ C-NMR (AL300 produced by JEOL Ltd., 300 MHz) and results of elemental analysis of the resulting product are as follows.

Results of ^! H--NMR (CDCI3) : Delta (ppm) = 3.57 (br s, PEGM methylene) , 3.25 (s, 3R, methoxy group at PEGM chain terminal) , 2.65-2.40 (m, branched PEI ethylene) .

Results of ¹³ C-NMR (DMSO-de) :

Delta (ppm) = 39.9 (s) , 41.8 (s) , 47.6 (m) , 49.5 (m) , 52.6 (m) , 54.7 (m) , 57.8 (m) (branched PEI ethylene up to here) , 59.0 (s) , 70.5 (m) , 71.8 (s) (PEGM methylene and terminal methoxy group up to here) .

Results of elemental analysis: C (53.1%) , H (10.4%) , N (19.1%)

Synthetic Example 3: synthesis of polyethylenimine-b-polyethylene glycol-b-bisphenol A epoxy resin

In 100 mL of N, N-dimethylacetamide, 37,4 g (20 mraol) of EPICLON AM-040-P (produced by DIG Corporation, bisphenol A-type epoxy resin, epoxy equivalent : 933) and 2.72 g (16 mmol) of 4-phenylphenol were dissolved and 0.52 mL of a 65% ethyltriphenylphosphonium acetate ethanol solution was added to the resulting solution. The reaction was carried out in a nitrogen atmosphere at 120 deg C for 6 hours. The resulting product was allowed to cool and added to a large quantity of water dropwise. The deposits obtained were washed with a large quantity of water. The residue was dried at a reduced pressure and a modified bisphenol A-type epoxy resin was obtained as a result. The yield of the product was 98% . The integrated ratio of the epoxy group was investigated through 'H-NMR measurement . It was found that 0.95 epoxy rings remained per molecule of the bisphenol A-type epoxy resin and that the product was a monofunctional epoxy resin having a bisphenol A skeleton.

The measurement results of ¹ H-NMR. (AL300 produced by JEOL Ltd. , 300 MHz) of the monofunctional epoxy resin obtained are as follows:

Results of ¹ H-NMR (CDCi ₃ ) :

Delta (ppm): 7.55-6,75 (m) , 4.40-3.90 (m) , 3,33 (m) , 2.89 (m) , 2.73 (m) , 1.62 (s)

To a methanol (150 mL) solution of 20 g (0.8 mmol) of the polyethylenimine-b-polyethylene glycol copolymer obtained in Synthetic Example 2 , an acetone (50 mL) solution of 3.2 g (1.6 mraol) of the modified epoxy resin was added dropwise in a nitrogen atmosphere and the mixture was stirred at 50 deg C for 2 hours . After completion of the reaction, the solvent was distilled away under a reduced pressure, and the product was further dried at a reduced pressure. As a result, a polyethylenimine-b-polyethylene glycol-fo-bisphenol A-type epoxy resin was obtained. The yield was 100%.

The measurement results of ^:! H--NMR (AL300 produced by JEOL Ltd., 300 MHz) of the product obtained are as follows:

Results of \H-NMR (CDC1 ₃ ) :

Delta, (ppm) = 7.55-6.75 (ra) , 4.40-3.90 (m) , 3.60 (m) , 3.25 (s) , 2.70-2.40 (m) , 1.62 (s)

Example 1: synthesis of protecting polymer (1-1)

Acetyiation reaction: synthesis of acetylated compound (1-lA)

In 270 raL of N,N-dimet ylacetamide, 19,3 g (9,0 mmol) of tosylated polyethylene glycol obtained in Synthetic Example 1 and 30.0 g (3.0 mmol) of branched polyethylenimine (EPOMIN SP200 produced by Nippon Shokubai Co,, Ltd.) were dissolved in a nitrogen atmosphere and 0,18 g of potassium carbonate was added thereto. The resulting mixture was stirred at a reaction temperature of 120 deg C for 6 hours. After completion of the reaction, the solid matter was removed, the product was concentrated at a reduced pressure at 70 deg C, and a mixture of 200 mL of ethyl acetate and 600 mL of hexane was added to the residue to obtain deposits. The deposits were separated and diluted with a THF solvent. The residue was removed, and. the product was concentrated at a reduced pressure at 30 deg C. A solid product obtained was again dissolved in a THF solvent and heptane was added thereto to again settle the residue. The residue was separated by filtration and. concentrated at reduced pressure. As a result, 7.8 g of a pale yello solid product was obtained (yield: 98%) ,

The results of ^X H-NMR and. ¹³ C- MR (AL300 produced, by JEOL Ltd., 300 MHz) of the resulting product are as follows.

Results of ⁱ H-NMR (CDCI3) :

Delta (ppm) = 3.57 (br s, PEGM methylene) , 3.25 (s, 3H, methoxy group at PEGM chain terminal), 3.16 (m, 2H, methylene group next to acetyl N) , 2,65-2.40 (m, branched PEI ethylene) , 1.90 (br s, 3H, acetyl group of primary N) .

Results of ⁱ³ C-NMR (DMSO-d ₆ ) :

Delta (ppm) = 22.9 (s) (acetyl group of primary N) , 39.9 (s) , 41.8 (s) , 47.6 (m) , 49,5 (ra) , 52.6 (m) , 54,7 (ra) , 57,8 (m) (branched PEI ethylene up to here) , 59.0 (s) , 70.5 (m) , 71.8 (s) (PEG methylene and terminal methoxy group up to here) , 173.4 (m) (acetyl group}.

Calculation of the integrated ratio of the 1.90 ppm peak attributable to acetylated primary amines in the branched polyethylenimine in ¹ H-NMR measurement suggested that 11 mol% of the primary amines in the branched polyethylenimine were acetylated.

Oxidation reaction: synthesis of acetylated N-oxide

In 100 mL of pure water, 37,7 g (N equivalent : 531 mmol) of the acetylated compound (1-lA) obtained by the synthesis described above was dissolved. To the resulting mixture, 5.16 g (53.1 mmol, 10 moil- in terms of N equivalent) of a 35% hydrogen peroxide solution was slowly added while the mixture was stirred in an ice bath, and oxidation reaction was conducted, for 5 hours. A protecting polymer (1-1) that had a hydrophilic segment and a pol yacetyiethylenimine N-oxide chain was quantitatively obtained as a product.

The results of ¹ H-NMR and ¹³ C-NMR (AL300 produced by JEOL Ltd., 300 MHz) of the resulting product are as follows.

Results of ^I-NMR (DMSO~d ₆ ) :

Delta (ppm) = 3.6 (br s, PEGM methylene), 3.3-3.2 (m, N-oxide ethyl 25 (s, 3H, methoxy group at PEGM chain terminal), 3.16

(m, 2.H, methylene group next to acetyl N) , 2,9 (m, N-oxide ethylene) , 2.7-2.4 (m, branched PEI ethylene), 1.90 (br s, 3H, acetyl group of primary N) .

Results of ¹³ C--NMR (DMSC-d ₆ ) :

Delta (ppm) = 36.0 (m, N-oxide ethylene), 39.0 (m) , 41.8 (s) , 43.0 ( , N-oxide ethylene) , 46.0 (m) , 48.0 (m) , 51.0 (ra) , 53.0 (m) , 56.0 (m) , 59,0 (s), 63.0-68.0 (m, N-oxide ethylene) , 70.0 (m) , 71.5 (s) ,

173.4 (m) (acetyl group).

According to the ¹ H-NMR. measurement , the tertiary amine peaks at 2.40 to 2.55 ppm, which lie in a higher-magnetic-field side among the branched PEI ethylenes at 2.40 to 2.70 ppm, were decreased and. the integrated ratio thereof was decreased accordingly. However, the peaks of secondary amines at 2.55 to 2,60 ppm and the primary amines at 2.60 to 2.70 ppm remained substantially the same. The ¹³ C--NMR measurement results also showed, that although the tertiary amine peaks at 51.0 to 56.0 ppm were decreased, the primary and secondary amine peaks at 39.0 to 51.0 ppm remained substantially the same. It is assumed, based on the integrated ratio of the NMR measurement, that about 10% of all nitrogen (N) ato s in the precursor compound, we e oxidi zed and turned into N-oxides .

Example 2: synthesis of protecting polymer (1-2)

Oxidation reaction: synthesis of acetylated N-oxide

In 100 mL of pure water, 37.7 g ( equivalent: 531 mmol) of the acetylated compound (1-lA) obtained in Example 1 was dissolved. To the resulting mixture, 25.8 g (265.5 mmol, 50 mol% in terms of N equivalent) of a 35% hydrogen peroxide solution was slowly added while the mixture was stirred in an ice bath, and oxidation reaction was conducted for 5 hours. A protecting polymer (1-2) that had a hydroph.il ic segment and a polyacetylethylenimine N-oxide chain was quantitatively obtained as a product.

The results of ¹ H- MR and ¹³ C-NMR (AL300 produced by JEOL Ltd., 300 MHz) of the resulting product are as follows.

Results of ^X H-NMR (DMSO-d ₆ ) :

Delta (ppm) - 3.6 (br s, PEGM methylene), 3.3-3.2 (m, N-oxide ethylene), 3.25 (s, 3H, methoxy group at PEGM chain terminal), 3.16 (m, 2H, methylene group next to acetyl N) , 2.9 (m, N-oxide ethylene) , 2,7-2,5 (m, branched PEI ethylene), 1.90 (br s, 3H, acetyl group of primary N) .

Results of ⁱ³ C-NMR (DMSO-d ₆ ) :

Delta (ppm) = 36.0 (m, N-oxide ethylene), 39.0 (m) , 41.8 (s) , 43.0 (m, N-oxide ethylene) , 46.0 (m) , 48.0 (m) , 51.0 (m) , 53.0 (m) , 59.0 (s), 63.0-68.0 (m, N-oxide ethylene) , 70.0 (m) , 71.5 (s) , 173.4 (m) (acetyl group) .

According to the H-NMR measurement, the tertiary amine peaks at 2,40 to 2.55 ppm, which lie in a higher-magnetic-field side among the branched PEI ethylenes at 2.40 to 2.70 ppm, vanished, the peaks of secondary amines at 2.55 to 2,60 ppm. and the primary amines at 2.60 to 2.70 ppm were decreased, and the integrated ratios thereof were decreased accordingly. Similarly, in the ^lj C-NMR measurement, the tertiary amine peaks at 51.0 to 56.0 ppm vanished and the primary and secondary amine peaks at 39.0 to 51.0 ppm were decreased. It is assumed, based on the integrated ratio of the NMR measurement, that about 50% of all nitrogen (N) atoms in the precursor compound were oxidized and turned into -oxides.

Example 3: synthesis of protecting polymer (1-3}

Oxidatio tion: synthesis of acetylated N-oxide

In 100 mL of pure water, 37,7 g (N equivalent: 531 mmol) of the acetylated compound (1-lA) obtained in Example 1 was dissolved. To the resulting mixture, 46,4 g (477,9 mmol, 90 mol% in terms of N equivalent) of a 35% hydrogen peroxide solution was slowly added while the mixture was stirred in an ice bath, and oxidation reaction was conducted for 5 hours. A protecting- polymer (1-3) that had a hydrophilic segment and a polyacetylethylenirnine N-oxide chain was quantitatively obtained as a product.

The results of ¹ H-NMR and ¹³ C- R (AL300 produced by JEOL Ltd., 300 MHz) of the resulting product are as follows.

Results of ^! H-N R (D SO-d ₆ ) :

Delta, (ppra) = 3.6 (br s, PEGM methylene) , 3.3-3,2 (m, N-oxide ethylene), 3.25 (s, 3H, methoxy group at PEGM chain terminal), 3.16 (m, 2H, methylene group next to acetyl N) , 2,9 (m, N-oxide ethylene) , 2.7-2.6 (m, branched PEI ethylene), 1.90 (br s, 3H, acetyl group of primary N) .

Results of ¹³ C-NMR (D SO-de) :

Delta (ppra) = 36.0 (m, N-oxide ethylene) , 39.0 (ra) , 43.0 (m, N-oxide ethylene) , 46.0 (m) , 48,0 (ra) , 53.0 (ra) , 59.0 (s) , 63.0-68.0 (m,

N-oxide ethylene), 70.0 (m) , 71.5 (s) , 173,4 (m) (acetyl group).

According to the ^X H-NMR measurement, the tertiary amine peaks at 2.40 to 2.55 ppm, which lie in a higher-magnetic-field side among the branched PEI ethylenes at 2.40 to 2.70 ppm, vanished, and the peaks of secondary amines at 2.55 to 2.60 ppm and the primary amines at 2.60 to 2.70 ppm substantially vanished. Similarly, in the ¹³ C-NMR measurement, the tertiary amine peaks at 51.0 to 56.0 ppm vanished and the primary and secondary amine peaks at 39,0 to 51.0 ppm substantially vanished. It is assumed, based on the integrated ratio of the NMR measurement, that about 90% of all nitrogen (N) atoms in the precursor compound were oxidized and turned into N-oxides.

Example 4 : synthesis of protecting polymer (1-4) Oxidation reaction: synthesis of acetylated compound (1-4A)

In 270 mL of N,N-dimethylacetamide, 19,3 g (9,0 m ol) of tosylated polyethylene glycol obtained in Synthetic Example 1 and 30.0 g (3.0 mmol} of branched polyethylenimine (EPOMIN SP200 produced by Nippon Shokubai Co,, Ltd.) were dissolved in a nitrogen atmosphere and 0.18 g of potassium carbonate was added thereto. The resulting mixture was stirred at a reaction temperature of 140 deg C for 6 hours. After completion of the reaction, the solid matter was removed, the product was concentrated at a reduced pressure at 70 deg C, and a mixture of 200 mL of ethyl acetate and 600 mL of nexane was added to the residue to obtain deposits. The deposits were separated and diluted with a THF solvent. The residue was removed and the product was concentrated at a reduced pressure at. 30 deg C. A solid product obtained was again dissolved in a THF solvent and heptane was added there to again settle the residue. The residue was separated by- filtration and. concentrated at reduced pressure. As a result, 8.0 g of a pale yello solid product was obtained (yield: 98%) ·

The results of H-NMR and. ¹³ C- MR (AL300 produced, by JEOL Ltd., 300 MHz) of the resulting product are as follows.

Results of ⁱ H-NMR (CDC1 ₃ ) :

Delta (ppm) = 3.57 (br s, PEGM methylene) , 3.25 (s, 3H, methoxy group at PEGM chain terminal), 3.16 (m, 2H, methylene N next to acetyl N) , 2.65-2.40 (m, branched PET ethylene), 1.90 (br s, 3H, acetyl group of primary N) .

Results of ⁱ³ C-NMR (DMSO-d ₆ ) :

Delta (ppm) = 22.9 (s) (acetyl group of primary N) , 39.9 (s) , 41.8 (s), 47.6 (m) , 49.5 (m) , 52.6 (m) , 54.7 (m) , 57.8 (m) (branched PEI ethylene up to here) , 59.0 (s) , 70.5 (m) , 71.8 (s) (PEGM methylene and terminal methoxy group up to here), 173.4 (m) (acetyl group).

Calculation of the integrated ratio of the 1.90 ppm peak attributable to acetylated. primary amines in the branched polyethylenimine in ¹ H-NMR measurement suggested that 30 mol% of the branched PEI ethylene primary amiΠΘ3 JGIG cLCΘtylated.

Oxidation reaction: synthesis of acetylated -oxide

An acetylated N-oxide was synthesized by the same oxidation reaction as in Example 1 except that 39.6 g (N equivalent: 531 mmol) of the acetylated compound (1-4A) obtained by the aforementioned synthesis was used instead of 37.7 g of the acetylated compound (1-lA) . As a result, a protecting polymer (1-4} that had a hvdrophilic segment and a polyacetylethylenimine N-oxide chain was quantitatively obtained as a product ,

The same results as those in Example 1 were obtained from the ^X H- MR and ^1J C-NMR (AL300 produced by JEOL Ltd., 300 MHz) measurements of the resulting product.

Example 5: synthesis of protecting polymer (1-5)

Oxidatio tion: synthesis of acetylated N-oxide

An acetylated N-oxide was synthesized by the same oxidation reaction as in Example 2 except that. 39.6 g (N equivalent: 531 mmol) of the acetylated compound (1-4A) obtained by the aforementioned synthesis was used instead of 37.7 g of the acetylated compound (1-lA) . As a. result, a protecting polymer (1-5) that had a hvdrophilic segment and a polyacetylethylenimine N-oxide chain was quantitatively obtained as a product. The same results as those in Example 2 were obtained from the ¹ H-NMR and ¹³ C-NMR (AL300 produced by JEOL Ltd., 300 MHz) measurements of the resulting product.

Example 6: synthesis of protecting polymer (1-6)

Oxidation reaction: synthesis of acetylated N-oxide

An acetylated N-oxide was synthesized by the same oxidation reaction as in Example 3 except that 39.6 g (N equivalent: 531 mmol) of the acetylated compound (1-4A) obtained by the aforementioned synthesis was used instead of 37.7 g of the acetylated compound (1-lA) . As a result, a protecting polymer (1-6) that had a hyd.rophil.ic segment and a polyacetylethylenimine N-oxide chain was quantitatively obtained as a product. The same results as those in Example 3 were obtained from the ¹ H-NMR and ¹³ C-NMR (AL300 produced by JEOL Ltd., 300 MHz) measurements of the product.

Example 7: synthesis of protecting polymer (1-7)

Acetylation reaction: synthesis of acetylated compound (1-7A)

In 45 g of chloroform, 9.98 g (N equivalent: 145 mmol) of the acetylated compound (1-4A) obtained in Example 4 (the polyethylenimine-b-polyethylene glycol copolymer with 30 mol% of primary amines acetylated) was dissolved. To the resulting solution, 1.48 g of acetic anhydride was slowly added under stirring at 30 deg C to conduct acetylation reaction for 2 hours. After completion of the reaction, the product was treated with a strong alkali and the residue obtained thereby was filtered. The product, was concentrated, at a reduced pressure and 10.5 g of a pale yellow solid product was obtained as a result (yield: 99%) .

The results of ^i- MR and ¹³ C-NMR (AL300 produced by JEOL Ltd., 300 MHz) of the resulting product are as follows.

Results of ^! H--NMR (CDC1 ₃ ) :

Delta ippm) = 3.57 (br s, PEGM methylene) , 3.25 (s, 3H, methoxy group at PEGM chain terminal) , 3.16 (m, 2H, methylene group next to acetyl N) , 2,65-2.40 (m, branched PEI ethylene) , 2.11 (br s, 3H, acetyl group of secondary N) , 1.90 (br s, 3H, acetyl group of primary N) .

Results of ⁱ³ C-NMR (DMSO-d ₆ ) :

Delta (ppm) =21.4 (s) (acetyl group of secondary N) , 22.9 (s) (acetyl group of primary N) , 39.9 (s) , 41.8 (s) , 47.6 (m) , 49.5 (m) , 52.6 (m) , 54,7 (m) , 57.8 (m) (branched PEI ethylene up to here) , 59.0 (s) , 70.5 (m) , 71.8 (s) (PEGM methylene and terminal methoxy group up to here), 173.4 (m) (acetyl group).

Calculation of the integrated ratios of the 1.90 ppm peak and 2.11 ppm peak respectively attributable to acetylated primary amines and. acetylated secondary amines in the branched polyethylenimine in ¹ H-N R measurement suggested that 58 mol% of the primary amines and 11 mol% of the secondary amines in the branched polyethylenimine were acetylated..

Oxidation reaction: synthesis of acetylated N-oxide

An acetylated N-oxide was synthesized by the same oxidation reaction as in Example 1 except that 43.4 g (N equivalent: 531 mmol) of the acetylated compound (1-7A) obtained by the aforementioned synthesis was used instead of 37.7 g of the acetylated compound (1-lA) . The reaction was conducted for 24 hours and. a protecting polymer (1-7) that had a hydrophilic segment, and a polyacetylethylenimine N-oxide chain was obtained as a product. The same results as those in Example 1 were obtained from the ^! H--NMR and ⁱ³ C-NMR (AL300 produced by JEOL Ltd., 300 MHz) measurements of the product.

Example 8: synthesis of protecting polymer (1-8) Oxidation reaction: synthesis of acetylated N-oxide

An acetylated N-oxide was synthesi zed by the same oxidation reaction as in Example 2 except that 43.4 g (N equivalent: 531 mmol) of the acetylated compound (1-7A) obtained by the aforementioned synthesis was used, instead of 37.7 g of the acetylated compound (1-lA). The reaction was conducted for 24 hours and a protecting polymer (1-8) that had a ydrop ilic segment and a polyacetylethylenimine N-oxide chain was obtained as a product . The same results as those in Example 2 were obtained from the H-NMR and. ¹³ C- MR (AL30Q produced by JEOL Ltd., 300 MHz) measurements of the product.

Example 9: synthesis of protecting polymer (1-9)

Oxidation reaction: synthesis of acetylated N-oxide

An acetylated N-oxide was synthesized, by the same oxidation reaction as in Example 3 except that 43.4 g (N equivalent: 531 mmol) of the a.cety1ated. compound ( 1 -7A) obtained by the aforementi oned synthesis was used instead of 37.7 g of the acetylated compound. (1-lA) . The reaction proceeded slowly and took 24 hours. As a result, a protecting polymer (1-9) that had a hydrophilic segment and a polyacetylethylenimine N-oxide chain was obtained, as a product. The same results as those in Example 3 were obtained from the 'H-NMR and ¹³ C-NMR (AL300 produced by JEOL Ltd., 300 MHz) measurements of the product .

Example 10: synthesis of protecting polymer (1-10)

Acetylatio tion: synthesis of acetylated compound (1-lOA)

In 45 g of chloroform, 9.98 g (N equivalent : 145 mmol) of the acetylated compound. (1-4A) obtained in Example 4 (branched. PEI ethylene with 30 mol% of primary amines acetylated) was dissolved. To the resulting solution, 2.96 g of acetic anhydride was slowly added under stirring at 30 deg C to conduct, acetylation reaction for 2 hours. After completion of the reaction, the product was treated with a strong alkali and. the residue obtained thereby was filtered. The product was concentrated at a reduced pressure and 11.0 g of a pale yellow solid product was obtained as a result (yield: 98%) .

The results of ¹ H-NMR and ¹³ C~NMR (AL300 produced by JEOL Ltd., 300 MHz) of the resulting product are as follows.

Results of H-NMR (CDC1 ₃ ) : Delta (ppm) = 3.57 (br s, PEGM methylene) , 3.25 (s, 3R, methoxy group at PEGM chain terminal) , 3.16 (m, 2H, methylene group next to acetyl N) , 2.65-2.40 (m, branched PEI ethylene) , 2.11 (br s, 3H, acetyl group of secondary N) , 1.90 (br s, 3H, acetyl group of primary N) .

Results of ¹³ C-NMR (D SO-de) :

Delta (ppm) =21.4 (s) (acetyl group of secondary N) , 22.9 (s) (acetyl group of primary N) , 39.9 (s) , 41.8 (s) , 47.6 (m) , 49.5 (m) , 52.6 (m) , 54.7 (m) , 57.8 (m) (branched PEI ethylene up to here) , 59.0 (s) , 70.5 (m) , 71.8 (s) (PEGM methylene and terminal methoxy group up to here) , 173.4 (m) (acetyl group) .

Calculation of the integrated ratios of the 1.90 ppm peak and 2.11 ppm peak respectively attributable to acetylated primary amines and acetylated secondary amines in the branched polyethylenimine in ¹ H" MR measurement suggested that 88 raol% of the primary amines and 22 moll of the secondary amines in the branched polyethylenimine were acetylated-

Oxidation reaction: synthesis of acetylated N-oxide

An acetylated N-oxide was synthesized by the same oxidation reaction as in Example 1 except that 47.4 g (N equivalent: 531 mmol) of the acety1ated compound ( 1-10A) obtained by the aforementioned synthesis was used instead of 37.7 g of the acetylated compound (1-lA) . The reaction proceeded slowly and took 72 hours . As a result, a protecting polymer (1-10) that had a hydrophilic segment and a polyacetylethylenimine N-oxide chain was obtained as a product . The same results as those in Example 1 were obtained from the ^l H-NMR and ¹³ C-NMR (AL300 produced by JEOL Ltd., 300 MHz) measurements of the product .

Example 11: synthesis of protecting polymer (1-11}

Oxidation reaction: synthesis of acetylated N-oxide

An acetylated N-oxide was synthesized by the same oxidation reaction as in Example 2 except that 47.4 g (N equivalent: 531 mmol) of the acety1ated compound ( 1-10A) obtained by the aforementioned synthesis was used instead of 37.7 g of the acetylated compound (1-lA) . The reaction was conducted for 72 hours and a protecting polymer (1-11) that had a hydrophilic segment and a polyacetylethylenimine N-oxide chain was obtained as a product . The same results as those in Example 2 were obtained from the tH-NMR and ^1J C-NMR (AL300 produced by JEOL Ltd., 300 MHz) measurements of the product.

Example 12: synthesis of protecting polymer (1-12)

Oxidation reaction: synthesis of acetylated N-oxide

An acetylated N-oxide was synthesized by the same oxidation reaction as in Example 3 except that 47.4 g (N equivalent: 531 mmol) of the a.cety1ated. compound. ( 1 - 10A} obtained. by thie a forement ioned. synthesis was used instead of 37.7 g of the acetylated compound (1-lA) . The reaction proceeded slowly and took 120 hours. As a result, a protecting polymer (1-12) that had a hydropnilic segment and a polyacetylethylenimine N-oxide chain was obtained, as a product. The same results as those in Example 3 were obtained from the Ή-NMR and ¹³ C-NMR (AL300 produced by JEOL Ltd., 300 MHz) measurements of the roduct .

Compa.rat.ive Example 1: synthesis of protecting polymer (1 ' )

Acetylation reaction : synthesis of acetylated compound (I'-A.)

In 45 g of chloroform, 9.98 g ( equivalent: 145 mmol) of the acetylated compound. (1-4A) obtained in Example 4 (the polyethylenimine-b-polyethylene glycol copolymer with 30 mol% of primary amines acetylated) was dissolved. To the resulting solution, 7.40 g of acetic anhydride was slowly added under stirring at 30 deg C to conduct acetylation reaction for 2 hours. After completion of the reaction, the product was treated with a strong alkali and the residue obtained thereby was filtered. The product was concentrated at a reduced pressure and 12.0 g of a pale yellow solid product was obtained, as a result (yield: 92%).

The results of ^X H-NMR and. ¹³ C- MR (AL300 produced, by JEOL Ltd., 300 MHz) of the resulting product are as follows.

Results of Hl-NMR (CDC1 ₃ ) :

Delta (ppm) = 3.57 (br s, PEGM methylene) , 3.25 (s, 3H, met oxy group at PEGM chain terminal), 3.16 (m, 2H, methylene group next to acetyl N) , 2,65-2.40 (m, branched PEI ethylene) , 2.11 (br s, 3H, acetyl group of secondary N) , 1.90 (br s, 3H, acetyl group of primary N) .

Results of ⁱ³ C-NMR (DMSO-d ₆ ) :

Delta (ppm) =21.4 (s) (acetyl group of secondary ) , 22.9 (s) (acetyl group of primary N) , 39.9 (s) , 41.8 (s) , 47.6 (m) , 49,5 (m) , 52.6 (m) , 54.7 (m) , 57.8 (m) (branched PEI ethylene up to here) , 59.0 (s) , 70.5 (m) , 71.8 (s) (PEGM methylene and terminal methoxy group up to here) , 173.4 (m) (acetyl group).

Calculation of the integrated ratios of the 1.90 ppm peak and 2.11 ppm peak respectively attributable to acetylated primary amines and acetylated secondary amines in the branched polyethylenimine in ^X H-NMR measurement suggested that 96 mol% of the primary amines and 98 mol% of the secondary amines in the branched polyethylenimine were acetylated .

Oxidation reaction: synthesis of acetylated N-oxide

An acetylated N-oxide was synthesi zed by the same oxidation reaction as in Example 2 except that 55.7 g (N equivalent: 531 mmol) of the acetylated compound (I'-A) obtained by the aforementioned synthesis was used instead of 37,7 g of the acetylated compound (1-lA) , The reaction proceeded slowly and took 120 hours. The resulting product was subjected to ⁱ H-NMR and ^1J C- R measurements (AL300 produced by JEOL Ltd., 300 MHz) and the results showed, that, a small amount of a target acetylate N-oxide was obtained.

Example 13: synthesis of protecting- polymer (2-1)

Synthesis of acetylated compound (2-1A)

To a methanol (150 mL) solution of 18,2 g (1.25 mmol) of the acetylated compound (1-4A) (branched PEI ethylene with 30 mol% of primary amines acetylated) obtained in Example 4, an acetone (50 mL) solution of 3.2 g (1.6 mmol) of a modified epoxy resin, which was a onofunct ional epoxy resin having a bisphenol A skeleton synthesized in Synthetic Example 3, was added dropwise in a nitrogen atmosphere, and stirring- was conducted at 50 deg C for 2 hours . Upon completion of the reaction, the solvent was distilled away under a reduced pressure and the residue is vacuum-dried. As a result, a polyacetylethylenimine-b-polyethylene glycol-b-bisphenol A-type epoxy resin was obtained. The yield was 100%.

The results of ^X H-NMR (AL300 produced by JEOL Ltd., 300 MHz) of the resulting product a.re as follows.

Results of ¹ H-NMR. (CDC1 ₃ ) :

Delta (ppm) - 7,55-6.75 (ra) , 4.40-3.90 (m) , 3.57 (br s, PEGM methylene) , 3.33 (m) , 3.25 (s, 3H, methoxy group at PEGM chain terminal} , 3.16 (m, 2H, methylene group next to acetyl N) , 2.89 (m) , 2.73 (m) , 2.65-2.40 (m, branched PEI ethylene) , 1.90 ibrs, 3H, acetyl group of primary ) , 1.62 (s) .

Calculation of the integrated ratio of the 1.90 ppm peak, of the acetylated primary amines of the branched polyethylenimine in the ¹ H-NMR measurement suggested that 30 mol% of the primary amines of the branched polyethylenimine were acetylated.

Oxidation reaction: synthesis of acetylated N-oxide

An acetylated N-oxide was synthesized by the same oxidation reaction as in Example 2 except that 3.9 g (N equivalent: 531 mmol) of the acetylated compound (2-1A) ob ained by the aforementioned synthesis was used instead of 37.7 g of the acetylated compound (1-lA) . As a result, a protecting polymer (2-1} that had a hydrophilic segment, a hydrophobic segment, and a polyacetyiethylenimine N-oxide chain was quantitatively obtained as a product.

The results of "H-NMR of the resulting product are as follows. Results of ^X H-NMR (DMSO-d ₆ ) :

Delta (ppm) - 7.55-6.75 (m) , 4.40-3.90 (m) , 3.6 (m, PEGM methylene) , 3.30-3.20 (m, N-oxide ethylene) , 3.25 (s, methoxy group at PEGM chain terminal) , 3.16 (m, 2H, methylene group next to acetyl N) , 2.9 (ra, N-oxide ethylene), 2.73 (m) , 2,65-2.40 (m, branched PEI ethylene), 1.90 (br s, 3H, acetyl group of primary N) , 1.62 (s) .

According to the ^X H-NMR measurement, the tertiary amine peaks at 2.40 to 2.55 ppm, which lie in a higher-magnetic-field side among the branched PEI ethylenes at 2.40 to 2.65 ppm, vanished., the peaks of secondary amines at 2.55 to 2,60 ppm and the primary amines at 2,60 to 2.70 ppm were decreased, and the integrated ratios thereof were decreased accordingly. It is assumed, based on the integrated ratio of the NMR measurement, that about 50% of all nitrogen (N) atoms in the precursor compound were oxidized and turned into N-oxides.

Example 14: synthesis of silver colloidal solution using protecting po1ymer ( 1 - 1 ) of Examp1e 1

To a 1 L reactor, 180 g of pure water, 13.5 g of an aqueous solution of the protecting polymer (1-1) obtained in Example 1, and 113 g (1.27 mol) of N, N-dimethylaminoethanol were added, one after next and. stirred to prepare a mixed solution of a protecting polymer and a reductant . In a separate container, 72.0 g (0.424 mol) of silver nitrate was dissolved in 120 g of pure water. The resulting aqueous silver nitrate solution was added, dropwise to the reactor at room temperature for about 30 minutes and the mixture was stirred at 40 deg C for 4 hours. Upon completion of the reaction and cooling,. 1.4 L (about three times the volume of the reaction mixture} of a poor solvent, acetone was added thereto and the resulting mixture was stirred for 5 minutes and left to stand still for about 1 hour. Composite bodies constituted by silver nanoparticles and the protecting polymer separated by settling as a result. After the supernatant was removed, the deposits generated were separated by centrifugation . The separated paste-like deposits were washed with 80 g of pure water and thoroughly dispersed. The remaining acetone was distilled away. The product was concentrated, at a reduced pressure until the nonvolatile content was about 60%, As a result, 77.0 g of an aqueous silver colloidal solution was obtained (46.2 g in terms of nonvolatile matter, yield: 96%) . Results of the thermal analysis (Tg DTA) showed that the silver content in the nonvolatile matter was 96.3%.

Example 15: synthesis of silver colloidal, solution using protecting po1ymer ( 1 -2 ) of Examp1e 2

In this example, 76.0 g of an aqueous silver colloidal solution (45.5 g in terms of nonvolatile matter, yield: 95%) having a nonvolatile content of about 60% was obtained as in Example 14 except that 14.7 g of an aqueous solution of the protecting polymer (1-2) obtained in Example 2 was used instead of 13.5 g of an aqueous solution of the protecting polymer (1-1) obtained in Example 1. Results of the thermal analysis (Tg/DTA) showed that the silver content in the nonvolatile matter was 96.2%.

Example 16: synthesis of silver colloidal solution using protecting po1ymer ( 1 - 3 ) of Examp1e 3

In this example, 76.7 g of an aqueous silver colloidal solution (46.0 g in terms of nonvolatile matter, yield: 95.8%) having a nonvolatile content of about 60% was obtained as in Example 14 except that 15.9 g of an aqueous solution of the protecting polymer (1-3) obtained in Example 3 was used instead of 13.5 g of an aqueous solution of the protecting polymer (1-1) obtained in Example 1. Results of the thermal analysis (Tg/DTA) showed that the silver content in the nonvolatile matter was 95.8%.

Example 17: synthesis of silver colloidal solution using protecting polymer (1-4} of Example 4

In this example, 76.8 g of an aqueous silver colloidal solution (46.1 g in terms of nonvolatile ma.tt.er, yield: 96%) having a nonvolatile content of about 60% was obtained as in Example 14 except that 14.2 g of an aqueous solution of the protecting polymer (1-4) obtained in Example 4 was used instead of 13.5 g of an aqueous solution of the protecting polymer (1-1) obtained in Example 1. Results of the thermal analysis (Tg/DTA) showed that the silver content in the onvolatile ma11e r was 96.2%.

Example 18: synthesis of silver colloidal solution using protecting polymer (1-5) of Example 5

In this example, 76.0 g of an aqueous silver colloidal solution (45.6 g in terms of nonvolatile matter, yield: 95%) having a nonvolatile content of about 60% was obtained as in Example 14 except that 15.3 g of an aqueous solution of the protecting polymer (1-5) obtained in Example 5 was used instead of 13.5 g of an aqueous solution of the protecting polymer (1-1) obtained in Example 1. Results of the thermal analysis (Tg/DTA) showed that the silver content in the nonvolatile matter was 96.4%.

Example 19: synthesis of silver colloidal solution using protecting polymer (1-6) of Example 6

In this example, 76.0 g of an aqueous silver colloidal solution (45.6 g in terms of nonvolatile matter, yield: 95%) having a nonvolatile content of about 60% was obtained as in Example 14 except that 16.5 g of an aqueous solution of the protecting polymer (1-6) obtained in Example 6 was used instead of 13.5 g of an aqueous solution of the protecting polymer (1-1) obtained in Example 1. Results of the thermal analysis (Tg/DTA) showed that the silver content in the nonvolatile matter was 95.9%.

Example 20: synthesis of silver colloidal solution using protecting poI ymer ( 1 -7 } of ExampIe 7

In this example, 76.0 g of an aqueous silver colloidal solution (45.6 g in terms of nonvolatile matter, yield: 95%) having a nonvolatile content of about 60% was obtained as in Example 14 except that 15.5 g of an aqueous solution of the protecting polymer (1-7) obtained in Example 7 was used instead of 13.5 g of an aqueous solution of the protecting polymer (1-1) obtained in Example 1. Results of the thermal analysis (Tg/DTA) snowed that the silver content in the nonvolatile matter was 96.1%.

Example 21: synthesis of silver colloidal solution using protecting po1ymer ( 1 - 8 ) of Examp1e 8

In this example, 76.0 g of an aqueous silver colloidal solution (45.6 g in terms of nonvolatile matter, yield: 95%) having a nonvolatile content of about 60% was obtained as in Example 14 except that 16.7 g of an aqueous solution of the protecting polymer (1-8) obtained in Example 8 was used instead of 13.5 g of an aqueous solution of the protecting polymer (1-1) obtained in Example 1. Results of the thermal analysis (Tg/DTA) snowed that the silver content in the nonvolatile matter was 96.4%.

Example 22: synthesis of silver colloidal solution using protecting polymer (1-9) of Example 9

In this example, 76.0 g of an aqueous silver colloidal solution (45.6 g in terms of nonvolatile matter, yield: 95%) having a nonvolatile content of about 60% was obtained as in Example 14 except that 17.8 g of an aqueous solution of the protecting polymer (1-9) obtained in Example 9 was used instead of 13.5 g of an aqueous solution of the protecting- polymer (1-1) obtained in Example 1. Results of the thermal analysis (Tg/DTA) snowed that the silver content in the nonvolatile matter was 95.9%.

Example 23: synthesis of silver colloidal solution using protecting polymer (1-10) of Exam le 10

In this example, 75.1 g of an aqueous silver colloidal solution (45.1 g in terms of nonvolatile matter, yield: 94%) having a nonvolatile content of about 60% was obtained as in Example 14 except that 16.9 g of an aqueous solution of the protecting polymer (1-10) obtained in Example 10 was used instead of 13.5 g of an aqueous solution of the protecting- polymer (1-1) obtained in Example 1. Results of the thermal analysis (Tg/DTA) snowed that the silver content in the nonvolatile matter ¾/as 96.1%.

Example 24: synthesis of silver colloidal solution using protecting po1ymer ( 1 - 11 } of ϋxamp1e 11

In this example, 74.3 g of an aqueous silver colloidal solution (44.6 g in terms of nonvolatile matter, yield: 93%) having a nonvolatile content of about 60% was obtained as in Example 14 except that 18.1 g of an aqueous solution of the protecting polymer (1-11) obtained in Example 11 was used instead of 13.5 g of an aqueous solution of the protecting polymer (1-1) obtained in Example 1. Results of the thermal analysis (Tg/DTA) showed that the silver content in the nonvolatile matter was 95.9%.

Example 25: synthesis of silver colloidal solution using protecting po1 ymer ( 1 - 12 } of Examp1e 12

In this example, 76.0 g of an aqueous silver colloidal solution (45.6 g in terms of nonvolatile matter, yield: 95%) having a nonvolatile content of about 60% was obtained as in Example 14 except that 19.3 g of an aqueous solution of the protecting polymer (1-12) obtained in Example 12 was used instead of 13.5 g of an aqueous solution of the protecting polymer (1-1) obtained in Example 1. Results of the thermal analysis (Tg/DTA) showed that the silver content in the nonvolatile matter was 96.1%.

Example 26: synthesis of silver colloidal solution using protecting po1ymer ( 2 - 1 ) of Examp1e 13

In this example, 75.2 g of an aqueous silver colloidal solution (45.1 g in terms of nonvolatile matter, yield: 94%) having a nonvolatile content of about 60% was obtained as in Example 14 except that 15.7 g of an aqueous solution of the protecting polymer (2-1) obtained in Example 13 was used instead of 13.5 g of an aqueous solution of the protecting polymer (1-1) obtained in Example 1. Results of the thermal analysis (Tg/DTA) showed that the silver content in the nonvolatile matter was 95.6%.

Comparative Example 2: synthesis of silver colloidal solution using protecting polymer (1 ' ) of Comparative Example 1

In this example, 77.6 g of an aqueous silver colloidal solution (46.6 g in terms of nonvolatile matter, yield: 97%) having a nonvolatile content of about 60% was obtained as in Example 14 except that 21.0 g of an aqueous solution of the protecting polymer (1 * ) obtained in Comparative Example 1 was used instead of 13.5 g of an aqueous solution of the protecting polymer (1-1) obtained in Example 1. Results of the thermal analysis (Tg/DTA) showed that the silver content in the nonvolatile matter was 95.5%.

Comparative Example 3: synthesis of silver colloidal solution using a compound of Synthetic Example 2

In this example, 76.0 g of an aqueous silver colloidal solution (45.6 g in terms of nonvolatile ma.tt.er, yield: 95%) having a nonvolatile content of about 60% was obtained as in Example 14 except that an aqueous solution prepared by dissolving 3.5 g of the compound obtained in Synthetic Example 2 in 9.5 g of pure water was used instead of 13.5 g of an aqueous solution of the protecting polymer (1-1) obtained in Example 1. Results of the thermal analysis (Tg/DTA) showed that the silver content in the nonvolatile matter was 96.2%.

Comparative Example 4: synthesis of silver colloidal solution using a compound of Synthetic Example 3

In this example, 76.8 g of an aqueous silver colloidal solution (46.1 g in terms of nonvolatile matter, yield: 96%) having a nonvolatile content of about 60% was obtained as in Example 14 except that an aqueous solution prepared by dissolving 4.1 g of the precursor compound obtained in Synthetic Example 3 in 9.5 g of pure water was used instead of 13.5 g of an aqueous solution of the protecting polymer (1-1) obtained in Example 1. Results of the thermal analysis (Tg/DTA) showed that the silver content in the nonvolatile matter was 95.8%.

The acetylation ratios of the primary and secondary amines and the N-oxidation ratio resulting from the oxidation reaction obtained by subjecting the protecting polymers of Examples 1 to 13 and Comparative Example 1 to NMR measurement are shown in Table 1. The resistance of metal thin films and the average particle size were measured as described above by using the silver colloidal solutions obtained in Examples 14 to 26 and Comparative Examples 2 to 4 , The amount of acetone used in the settling treatment during synthesis and the time taken for the treatment are shown in Table 3. The silver colloidal solutions obtained were left to stand for one week at room temperature (25 to 35 deg C) and the stability of the solutions was evaluated from the appearance . The results are shown in Tables 2 and 3. In Table 2, O.L. means overload.

The results show that good electrical conductivity, dispersion stability, and ease of purification and separation are exhibited when protecting polymers in which the primary amine acetylation ratio is 5 to 95 mol% and/or the secondary amine acetylation ratio is 5 to 50 mol% in the polyalkylenimine segment and the N-oxidization ratio is 0.5 to 95% are used.

[Table 1]

With the protecting polymer (primary amine acetylation ratio: 96%, secondary amine acetylation ratio: 98%} of Comparative Example 1, the oxidation reaction was conducted for a long time, i.e. , 120 hours, but the oxidation reaction little proceeded. NMR measurement results found that the N-oxidization ratio was not. more than 5% and. that the N-oxidation does not proceed on polymers having high acetylation ratios such as that of Comparative Example 1.

[Table 2] Specific resistivity of silver thin film fired for 30 minutes

Protec ing

polymer (micro-ohm cm}

125 deg C 180 deg C

Example 14 1-1 17.6 8.3

Example 15 1-2 11 , 5 7.7

Example 16 1-3 10.9 7.1

Example 17 1-4 5.5 3.5

Example 18 1-5 4.4 3.2

Example 1 1-6 6.5 4.1

Example 20 1-7 5.4 3.4

Example 21 1-8 3.9 3.0

Example 22 1-9 5.5 3.3

Example 23 1-10 8.8 5.6

Example 24 1-11 9.1 6.6

Exam le 25 1-12 8.3 6.2

Example 26 2-1 30.5 9.0

Comparative

1 ^! 0. L . 91

Example 2

Comparative Synthetic

579 16.6

Example 3 Example 1

Comparative Synthetic

0. L . 115

Example 4 Example 2

[Table 3]

Amount of

acetone used Stabi lity ime Average

(relative to (room

taken for particle

volume of temperature , settl ing size (nm)

reaction 1 week) solution} Example 14 3 times larger 1.0 hour 39.5 No deposits

Example 5 3 times larger 0.5 ho rs 42.1 No deposits

Example 16 3 times larger 0.5 hours 39.5 No deposits

Example 17 3 t imes 1arger 0.5 hours 24.1 No deposits

Example 18 3 times larger 0.5 hours 25.5 No deposits

Example 9 3 times larger 0.5 hours 23.6 No deposits

Example 20 3 times larger 0.5 hours 27.5 No deposits

Example 21 3 t imes 1arger 0.5 hours 22.7 No deposits

Example 22 3 times larger 0.5 hours 26.5 No deposits

Example 23 3 times larger 1.0 hour 38.5 No deposits

Example 24 3 times larger 1.0 hour 41.1 No deposits

Example 25 3 t imes 1arger 1.0 hour 39.8 No deposits

Example 26 3 times larger 0.5 hours 32.1 No deposits

Deposits in

Comparati e Undetect

5 t imes 1arger 4 hours large

Example 2 able

quantities

Comparative

5 times larger 4 hours 9 Q n No deposits Example 3

Deposits in

Comparative

5 times larger 8 hours 31.0 small

Example 4

q antities