FIELD

[0001] The present disclosure relates to monomers, oligomers and polymers useful as additives for adhesive and/or sealant compositions, and particularly to one drop fill ("ODF") sealant compositions for liquid crystal display applications. The present disclosure permits assembly of liquid crystal display ("LCD") panels with little to no migration of the sealant composition into the liquid crystal, or vice versa, during LCD assembly and/or curing of the sealant composition.

BRIEF DESCRIPTION OF RELATED TECHNOLOGY

[0002] The ODF process is becoming the mainstream process in the assembly of LCD panels in display applications, replacing the conventional vacuum injection technology to meet faster manufacturing process demands, in the ODF process, a sealant is dispensed on a first electrode-equipped substrate to form a frame of a display element. Next, liquid crystals are dropped inside the formed frame. In the next step of the assembly, another electrode-equipped substrate is joined to the first electrode- equipped substrate under vacuum. Then, the sealant undergoes a curing process, either by a combination of UV and thermal or by a thermal only process.

[0003] The ODF process has a few problems in that the sealant material in the uncured state comes into contact with the liquid crystal during the assembly process. Migration of the sealant material into the liquid crystal or migration of the liquid crystal into uncured sealant material can reduce electro- optical properties of the liquid crystal. Hence, design of sealant materials that show good liquid crystal resistance (i.e., less contamination) is paramount. Unfortunately, it remains a challenge.

[0004] Until now, despite the desire to provide curable resin systems with low sealant migration into neighboring liquid crystals, and vice versa, a suitable solution has not provided.

SUMMARY

[0005] The present disclosure relates to curable compositions, including additives that provide adhesive and/or sealing performance. In one aspect, the inventive curable compositions may be useful as ODF sealant compositions with improved performance. [0006] According to the present disclosure, in one embodiment a curable composition includes a curable resin, a polyamide additive, and a curing agent.

[0007] According to the present disclosure, in another embodiment a curable composition includes a curable resin, a star polymer additive, and a curing agent. The star polymer additive includes a core formed from a network of cross-linked polymers and a plurality of linear polymer chains (arms) extending from the core.

[0008] According to the present disclosure, in yet another embodiment a curable composition includes a curable resin, a comb polymer additive, and a curing agent. The comb polymer additive consists of a main chain with two or more three-way branch points, and linear side chains extending from each branch point.

[0009] According to the present disclosure, in still another embodiment a curable composition includes a curable resin, a repetitively branched dendrimer additive, and a curing agent.

[0010] According to the present disclosure, in still yet another embodiment a curable composition includes (a) a curable resin functionalized with groups selected from maleimide, epoxy, (meth)acrylate, vinyl ether, vinyl acetate, nadimide, itaconimide or mixtures of any two or more thereof, (b) an additive whose volume expands with an increase in temperature, and (c) a curing agent. The additive provides at least 2 times improved viscosity slump resistance from a first, lower temperature condition to a second, higher temperature condition compared to the curable composition without the additive. The temperature range within which these two temperature conditions may be found are about 25°C to about 65°C.

[0011] According to the present disclosure, a method of synthesizing a star polymer is provide that includes providing (meth)acrylate such as t-butyl acrylate, injecting an initiator to create a mixture, and injecting a ligand such as tris[2-(dimethlyamino)ethyl]amine to the mixture to form the star polymer core. In embodiments, the method of the present disclosure achieves (meth)acrylate conversion (from (meth)acrylate to a core network of cross-linked polymers) of greater than 85 percent. Then, to the core, adding (meth)acrylate such as n-butyl acrylate and additional ligand to form the arms, and isolating a resulting star polymer. In embodiments, the method of the present disclosure also achieves (meth)acrylate conversion (from (meth)acrylate to a plurality of linear polymer chains) of greater than 85 percent.

[0012] According to the present disclosure, a method of imparting improved viscosity slump resistance to a curable composition includes providing a curable resin selected from: an epoxy-functionalized resin, a (meth)acrylate-functionalized resin, a vinyl ether-functionalized resin, an oxetane-functionalized resin, a cyanate ester-functionalized resin, a maleimide-functionalized resin, a nadimide-functionalized resin, a itaconimide-functionalized resin, or mixtures of any two or more thereof, providing a curing agent, and adding an expandable viscosity modifier additive, where the volume of the expandable viscosity modifier additive expands with an increase in temperature. The expandable viscosity modifier additive provides at least 2 times improved viscosity slump resistance from first, lower temperature condition to a second, higher temperature condition compared to the curable composition without the additive. The expandable viscosity modifier additive provides a greater viscosity index compared to the curable composition without the additive, sometimes to a level approaching 1.0, and in some cases to a level greater than 1.0 (meaning that the viscosity increases at higher temperatures). The temperature range within which these two temperature conditions may be found are about room temperature (25°C) to Tonset of curing, which will depend on the nature and identity of the reactive constituents in the composition. In one specific application, the Tonset may be about 65°C. The viscosity index ("VI") is the ratio of viscosity at a higher temperature divided by the viscosity at a lower temperature. Ordinarily with the inventive curable compositions VI is less than 1.0, though sometimes it is greater than 1.0.

[0013] Other features and advantages of the present disclosure should become apparent in light of the following description of non-limiting embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

[0014] FIG. 1 is an exemplary graphical representation of several curable resin systems containing additives compared to a curable resin system without the additive.

[0015] FIG. 2 is an exemplary graphical representation of several curable resin systems containing additives compared to a curable resin system without the additive.

[0016] FIG. 3 is an exemplary illustration of a synthesis of block copolymers used to form various additives.

[0017] FIG. 4 is an exemplary illustration of a synthesis of a star copolymer additive.

[0018] FIG. 5 is an exemplary illustration of gel permeation chromatography ("GPC") results and a nuclear magnetic resonance ("NMR") spectroscopy spectrum of a star copolymer additive.

[0019] FIG. 6 is an exemplary illustration of the synthesis of a hyper branched polymer additive. DETAILED DESCRIPTION

[0020] Viscosity is a measure of resistance to gradual deformation by shear stress or tensile stress. For liquids, it corresponds to the informal concept of "thickness." For example, at ambient temperature honey has a much higher viscosity than water.

[0021] Cure behaviors of different thermoset resin formulations fit a similar profile in that upon the application of heat, the resin viscosity drops initially, passes through a region of maximum flow (where the resin viscosity continues to drop), and then begins to increase as chemical reactions increase the average length of the polymer network being formed and the degree of cross-linking between constituent monomers and/or oligomers. The viscosity increase continues until a continuous three- dimensional network of monomer and/or oligomer chains is created. This transformation is known as gelation.

[0022] In one aspect of the present disclosure, an additive that maintains high viscosity of the ODF sealant composition and reduces in practice penetration of the sealant composition into the liquid crystal (or vice versa) during LCD assembly and/or curing of the resin is disclosed. These additives exhibit viscosity slump resistance, both (1) reducing the initial resin viscosity drop, and (2) reducing the viscosity drop during the region of maximum flow. These features are particularly desirable in ODF sealant compositions.

[0023] Additionally, the additives increase in volume with an increase in temperature. For example, the additives of the present disclosure may coil at lower temperatures and then expand at increasing temperatures.

[0024] In embodiments, the additive may be used in an amount of about 0.1 to about 20 percent by weight of the curable composition. In embodiments, the additive may be used in an amount of about 0.1 to about 10 percent by weight of the curable composition. In embodiments, the additive may be used in an amount of about 0.1 to about 5 percent by weight of the curable composition.

[0025] These additives may also be referred to as "gelling agents."

[0026] As noted above, according to the present disclosure, a curable composition includes a curable resin, a polyamide additive, and a curing agent.

[0027] In one aspect of the present disclosure, the polyamide additive has the structure:

where: R is an alkyl linkage from about 1 to about 20 carbon units or an aryl linkage; and n is about 1 to about 50.

[0028] In some embodiments, polyamide additives are aliphatic based, providing improved solubility characteristics. In embodiments, R is an aliphatic chain containing one or more Oxygen atoms, Sulfur atoms, and/or Nitrogen atoms.

[0029] In some embodiments, the polyamide additives are aromatic, where R is an aromatic ring such as a furan, benzofuran, isobenzofuran, pyrrole, indole, isoindole, thiophene, benzothiophene, benzo[c]thiophene, imidazole, benzimidazole, purine, pyrazole, indazole, oxazole, benzoxazole, isoxazole, benzisoxazole, thiazole, benzothiazole, benzene, naphthalene, anthracene, pyridine, quinolone, isoquinoline, pyrazine, quinoxaline, acridine, pyrimidine, quinazoline, pyridazine, cinnoline, phthalazine, 1,2,3-triazin, 1,2,4-triazine, 1,3,5-triazine (s-triazine), and the like.

[0030] Examples of polyamide additives include: Crayvallac ^® SF, Crayvallac ^® 60P, Crayvallac ^® 60X, E00075, and the like, manufactured by Arkema (King of Prussia, PA) and BYK-R 605, BYK-R 606, BYK-R 607, BYK 425, BYK 428, and the like, manufactured by BYK Chemie (Wallingford, CT).

[0031] Crayvallac ^® SF is reported by the manufacturer to be an amide-modified hydrogenated castor oil rheology modifier, available as an "off white" powder, with an enhanced tolerance to temperature and solvent strength. Compared to other hydrogenated castor oil based rheology modifiers, Crayvallac ^® SF is reported by the manufacturer to be more tolerant to strong solvents and high processing

temperatures due to the presence of its amide. Using a Malvern Mastersizer S laser particle size analyzer, the manufacturer reports the particle size to be between about 4 pm to about 20 pm.

Additionally, using differential scanning calorimetry (DSC), the melting point of Crayvallac ^® SF is between about 130°C to about 140°C and its density at 25°C is about 1.02 g/cm ³ .

[0032] Crayvallac ^® 60P is reported by the manufacturer to be a solid powder wax consisting of fine particles of oxidized polyethylene. It is mainly used in industrial and maintenance coatings where its primary function is to provide pigment suspension without any increase in the apparent viscosity.

Typical applications of Crayvallac ^® 60P are epoxy primers, vinyl primers, anti-fouling paints, road marking paints and chlorinated rubber coatings. Using a Malvern Mastersizer S laser particle size analyzer, the manufacturer reports that the Crayvallac ^® 60P's particle size is less than about 7 pm, and its density at 25°C is about 0.93 g/cm ³ .

[0033] Crayvallac ^® 60X is reported by the manufacturer to be a waxy solid paste consisting of very fine droplets of oxidized polyethylene dispersed in xylene, having a density at 25°C of about 0.87 g/cm ³ . [0034] E00075 is reported by the manufacturer to be a polyamide based gelling agent dispersed in an acrylate resin. More specifically, the manufacturer reports that E00075 is a mixture of Crayvallac ^® SF (approximately 20%) and acrylate resin (approximately 80% 4-tert-butylcyclohexyl acrylate).

[0035] BYK-R 605 is reported by the manufacturer to be a solution of polyhydroxycarboxylic acid amides, typically used for plastic applications such as vinyl ester and epoxy resins, unsaturated polyester resins, and gel coats to reinforce the rheological effectiveness of pyrogenic silica. For example, BYK-R 605 is reportedly used in unsaturated polyester resins, epoxy and polyurethane systems to reinforce the three-dimensional network structure of the silica or phyllosilicates through additional bridges, thereby enhancing the thixotropy. Its density at 20°C is about 0.93 g/cm ³ .

[0036] BYK-R 606 is reported by the manufacturer to be a liquid polyhydroxy carboxylic acid ester. The manufacturer reports that it reinforces the hydrogen bonds of the silica and phyllosilicates, resulting in increased thixotropy. Its density at 20°C is about 1.01 g/cm ³ .

[0037] BYK-R 607 is reported by the manufacturer to be a solution of amine functional oligoamides.

The manufacturer reports that it reinforces the network developed by a thixotrope, ensuring that the network does not break down, as it usually would, when amine hardener is added. BYK-R 607 reportedly enables hydrophilic fumed silica or clay additives to be used alone in two-component epoxy systems. Its density at 20°C is about 0.98 g/cm ³ .

[0038] BYK 425 is reported by the manufacturer to be a solution of urea modified polyurethane. Its density in Ibs/US gal at 68°F is about 8.68. BYK 425 is typically solvated with polypropyleneglycol.

[0039] BYK 428 is reported by the manufacturer to be a solution of a polyurethane with a highly branched structure. Its density in Ibs/US gal at 68°F is about 8.76. BYK 428 is typically solvated with water and/or ethoxylates.

[0040] Polyamides generally are macromolecules with repeating units linked by amide bonds. They may occur in nature or be synthesized. Examples of naturally occurring polyamides are proteins, such as wool and silk. Synthesized ones may be made through step-growth polymerization or solid-phase synthesis yielding materials such as nylons, aramids, and sodium poly(aspartate). These latter polyamides are commonly used in textiles, automotive applications, carpets and sportswear due to their high durability and strength.

[0041] The polyamide additives used in the present disclosure can be added, for example, to a curable resin, such as a curable resin selected from a maleimide-functionalized resin, a nadimide-functionalized resin, an itaconimide-functionalized resin, or mixtures of any two or more thereof, with a curing agent, to form an inventive curable composition, such as an ODF sealant composition. [0042] In another aspect, the star polymers include a core formed from a network of cross-linked polymers and a plurality of linear polymer chains (arms) extending from the core.

[0043] With an increase in temperature, the star polymers can increase their hydrodynamic radii and, as a consequence, their volume. Higher molecular weight star polymers with longer (and higher molecular weight) arms may provide an increase in volume change per increase in temperature.

However, a star polymer with too high of a molecular weight (i.e. approximately 600 kDA) may be tricky o dissolve to form a solution. Accordingly, the star polymer additives used in the present disclosure achieve a balance between high volume change and solubility.

[0044] In embodiments, the star polymers have a core : arm ratio, based on molecular weight, of between about 1 : 20. In embodiments, the core: arm ratio is between about 5 : 15. Thus, in some embodiments, the molecular weight of the core can be about 10 to 20 times greater than the molecular weight of the plurality of linear polymer chains extending from the core.

[0045] In embodiments, the plurality of polymer chains are acrylate polymer chains, which provide consistent interaction between the star polymer additive and the functionalized curable resin.

[0046] In embodiments, the acrylate polymer chains are linked to the core by a reaction with an a- bromo-ester. In embodiments, the core is formed by copolymerization of block copolymers linked by P- 1,6-hexanedio! diacrylate-P', and P and P' are each copolymers that may be the same or different.

[0047] Some of the more notable characteristics exhibited by star polymers of the present disclosure are their unique viscosity modifying properties compared to linear analogues of identical molecular weight and/or monomer composition. In addition, star polymers exhibit lower melt temperatures and lower crystallization temperatures than comparable linear analogues.

[0048] Generally, the star polymers have smaller hydrodynamic radii than linear analogues of the same molecular weight. In the present disclosure, a hydrodynamic radius is the radius of an equivalent hard sphere for the molecule under observation.

[0049] The orientation of end polar groups (e.g., hydroxyl or carboxylic acid) may affect the viscosity slump resistance. Polar groups at the end of the linear polymer chain arms (i.e., the outer shell of the star polymer) oftentimes contribute to improved viscosity slump resistance, while polar groups at the interior portion of the star polymer and connected to the core do not routinely exhibit improved viscosity slump resistance.

[0050] In some embodiments, an end of at least one linear polymer chain further away from the cure is capable of hydrogen bonding via a hydroxyl group. [0051] In some embodiments an end of at least one linear polymer chain closest to the core is bound to the core by hydrogen bonds.

[0052] In one aspect of the present disclosure, a star polymer additive having a core formed from a network of cross-linked polymers and a plurality of linear polymer chains extending from the core is included with a curable resin functionalized with groups selected from maleimide, epoxy,

(meth)acrylate, vinyl ether, vinyl acetate, nadimide, itaconimide or any two or more thereof, and a curing agent to form an inventive curable composition.

[0053] In still another aspect, the comb polymer additive consists of a main chain with two or more three-way branch points, and linear side chains extending from each branch point.

[0054] The comb polymer additives may be chosen from a host of materials, commercially available examples of which may be sourced from Evonik Industries (Essen, Germany), Arkema (King of Prussia, PA) and Chemtura (Middlebury, CT). The following comb polymers are commercially available from Evonik: VISCOPLEX ^® 3-160, VISCOPLEX ^® 3-162, VISCOPLEX ^® 3-200, VISCOPLEX ^® 3-201, VISCOPLEX ^® 3- 211, and VISCOPLEX ^® 3-220, and promoted to adjust the viscosity index of gasoline used in engines.

Cray Valley also has a polyfarnese polymer that can be used as a comb polymer.

[0055] An example of a comb polymer structure of the present disclosure is illustrated below.

[0056] In embodiments, at least two linear side chains extending from different branch points are identical.

[0057] In embodiments, all the linear side chains extending from the branch points are identical.

[0058] In embodiments, at least two linear side chains extending from the branch points are different.

[0059] In embodiments, all the linear side chains extending from the branch points are different. [0060] The different linear side chains can result in different solubility properties and different volume expanding properties.

[0061] In one aspect of the present disclosure, an inventive curable composition includes a comb polymer additive comprising a main chain with two or more three-way branch points, and linear side chains extending from each branch point added to a curable resin functionalized with groups selected from maleimide, epoxy, (meth)acrylate, vinyl ether, vinyl acetate, nadimide, itaconimide or any two or more thereof, and a curing agent.

[0062] In still yet another aspect, a repetitively branched dendrimer additive is disclosed. A dendrimer is typically symmetric around the core, and often adopts a spherical three-dimensional morphology. An example of a dendrimer is illustrated below.

[0063] In embodiments, the dendrimer additive of the present disclosure has a molecular weight between about 10 and about 250 kDa.

[0064] A combination of the various additives so described herein may be used in the inventive curable compositions. That is, two or more additives of polyamide, the star polymer, the comb polymer, the dendrimer may be used.

[0065] Among others, the curable resin may be chosen from those selected from a maleimide- functionalized resin, a nadimide-functionalized resin, an itaconimide-functionalized resin or mixtures of any two or more thereof having the structure: , respectively, where:

m is 1-15;

p is 0-15;

each R ² is independently selected from hydrogen or lower alkyl (such as C1-5); and

J is a monovalent or a polyvalent radical comprising organic or organosiloxane radicals.

[0066] In embodiments, J is a monovalent or polyvalent radical selected from:

- hydrocarbyl or substituted hydrocarbyl species typically having in the range of about 6 up to about 500 carbon atoms, where the hydrocarbyl species is selected from alkyl, alkenyl, alkynyl, cycloalkyl, cycloalkenyl, aryl, alkylaryl, arylalkyl, aryalkenyl, alkenylaryl, arylalkynyl or alkynylaryl, provided, however, that X can be aryl only when X comprises a combination of two or more different species;

- hydrocarbylene or substituted hydrocarbylene species typically having in the range of about 6 up to about 500 carbon atoms, where the hydrocarbylene species are selected from alkylene, alkenylene, alkynylene, cycloalkylene, cycloalkenylene, arylene, alkylarylene, arylalkylene, arylalkenylene, alkenylarylene, arylalkynylene or alkynylarylene;

- heterocyclic or substituted heterocyclic species typically having in the range of about 6 up to about 500 carbon atoms;

- polysiloxane; or

- polysiloxane-polyurethane block copolymers; as well as

combinations of one or more, with a linker selected from covalent bond, -0-, -S-, -NR-, -NR-C(O)- , -NR-C(0)-0-, -NR-C(0)-NR-, -S-C(O)-, -S-C(0)-0-, -S~C(0)-NR-, -0-S(0) ₂ -, -0-S(0) ₂ -0-, -0-S(0) ₂ -NR- , -O-S(O)-, -O-S(O)-0-, -0-S(0)-NR-, -O-NR-C(O)-, -0-NR-C(0)-0-, -0-NR-C(0)-NR-

, -NR-O-C(O)-, -NR-0-C(0)-0-, -NR-0-C(0)-NR-, -O-NR-C(S)-, -0-NR-C(S)-0-, -0-NR-C(S)- R-, -NR-O-C(S)-, - NR-0-C(S)-0-, -NR-0-C(S)-NR-, -O-C(S)-, -0-C(S)-0-, -0-C(S)-NR-, -NR-C(S)-, -NR-C(S)-0-, -NR-C(S)-NR-, -S- S(0) ₂ -, -S-S(0) _2- 0-, -S-S(0) ₂ -NR-, -NR-O-S(O)-, -NR-0-S(0)-0-, -NR-0-S(0)-NR-, -NR-0-S(0)r, -NR-0-S(0) ₂ - O-, -NR-0-S(0) ₂ -NR-, -O-NR-S(O)-, -0-NR-S(0)-0-, -0-NR-S(0)-NR-, -0-NR-S(0) ₂ -0-, -0-NR-S(0) ₂ -NR- , -0-NR-S(0) ₂ -, -0-P(0)R _2-; -S-P(0)R _2-; or -NR-P(0)R ₂ -; where each R is independently hydrogen, alkyl or substituted alkyl.

[0067] In embodiments, J is oxyalkyl, thioalkyl, aminoalkyl, carboxylalkyl, oxyalkenyl, thioalkenyl, aminoalkenyl, carboxyalkenyl, oxyalkynyl, thioalkynyl, aminoalkynyl, carboxyalkynyl, oxycycloalkyl, thiocycloalkyl, aminocycloalkyl, carboxycycloalkyl, oxycloalkenyl, thiocycloalkenyl, aminocycloalkenyl, carboxycycloalkenyl, heterocyclic, oxyheterocyclic, thioheterocyclic, aminoheterocyclic,

carboxyheterocyclic, oxyaryl, thioaryl, aminoaryl, carboxyaryl, heteroaryl, oxyheteroaryl, thioheteroaryl, aminoheteroaryl, carboxyheteroaryl, oxyalkylaryl, thioalkylaryl, aminoalkylaryl, carboxyalkylaryl, oxyarylalkyl, thioarylalkyl, aminoarylalkyl, carboxyarylalkyl, oxyarylalkenyl, thioarylalkenyl,

aminoarylalkenyl, carboxyarylalkenyl, oxyalkenylaryl, thioalkenylaryl, aminoalkenylaryl,

carboxyalkenylaryl, oxyarylalkynyl, thioarylalkynyl, aminoarylalkynyl, carboxyarylalkynyl, oxyalkynylaryl, thioalkynylaryl, aminoalkynylaryl or carboxyalkynylaryl. oxyalkylene, thioalkylene, aminoalkylene, carboxyalkylene, oxyalkenylene, thioalkenylene, aminoalkenylene, carboxyalkenylene, oxyalkynylene, thioalkynylene, aminoalkynylene, carboxyalkynylene, oxycycloalkylene, thiocycloalkylene,

aminocycloalkylene, carboxycycloalkylene, oxycycloalkenylene, thiocycloalkenylene,

aminocycloalkenylene, carboxycycloalkenylene, oxyarylene, thioarylene, aminoarylene, carboxyarylene, oxyalkylarylene, thioalkylarylene, aminoalkylarylene, carboxyalkylarylene, oxyarylalkylene,

thioarylalkylene, aminoarylalkylene, carboxyarylalkylene, oxyarylalkenylene, thioarylalkenylene, aminoarylalkenylene, carboxyarylalkenylene, oxyalkenylarylene, thioalkenylarylene,

aminoalkenylarylene, carboxyalkenylarylene, oxyarylalkynylene, thioarylalkynylene,

aminoarylalkynylene, carboxy arylalkynylene, oxyalkynylarylene, thioalkynylarylene,

aminoalkynylarylene, carboxyalkynylarylene, heteroarylene, oxyheteroarylene, thioheteroarylene, aminoheteroarylene, carboxyheteroarylene, heteroatom-containing di- or polyvalent cyclic moiety, oxyheteroatom-containing di- or polyvalent cyclic moiety, thioheteroatom-containing di- or polyvalent cyclic moiety, aminoheteroatom-containing di- or polyvalent cyclic moiety, or a carboxyheteroatom- containing di- or polyvalent cyclic moiety.

[0068] In addition to the curable resins, the curable compositions may also include a free radical initiator (thermal or UV generated) and a curing agent. Curing may be by thermal or UV mechanisms or both. In embodiments where an epoxide ring is present, a latent epoxy-curing agent may also be employed. [0069] Useful thermal free radical initiators include, for example, organic peroxides and azo compounds that are known in the art. Examples include: azo free radical initiators such as AIBN

(azodiisobutyronitrile), 2, 2'-azobis(4-methoxy-2, 4-dimethyl valeronitrile), 2, 2'-azobis(2, 4-dimethyl valeronitrile), dimethyl 2,2'-azobis(2-ethylpropionate), 2,2'-azobis(2-methylbutyronitrile), 1,11- azobis(cyclohexane-l-carbonitrile), 2,2'-azobis[N-(2-propenyl)-2-methylpropionamide]; dialkyl peroxide free radical initiators such as l,l-di-(butylperoxy-3, 3, 5-trimethyl cyclohexane); alkyl perester free radical initiators such as TBPEH (t-butyl per-2-ethylhexanoate); diacyl peroxide free radical initiators such as benzoyl peroxide; peroxy dicarbonate radical initiators such as ethyl hexyl percarbonate; ketone peroxide initiators such as methyl ethyl ketone peroxide, bis(t-butyl peroxide) diisopropylbenzene, t- butylperbenzoate, t-butyl peroxy neodecanoate, and combinations thereof.

[0070] Further examples of organic peroxide free radical initiators include: dilauroyl peroxide, 2,2- di(4,4-di(tert-butylperoxy)cyclohexyl)propane, di(tert-butylperoxyisopropyl) benzene, di(4-tert- butylcyclohexyl) peroxydicarbonate, dicetyl peroxydicarbonate, dimyristyl peroxydicarbonate, 2,3- dimethyl-2,3-diphenylbutane, dicumyl peroxide, dibenzoyl peroxide, diisopropyl peroxydicarbonate, tert-butyl monoperoxymaleate, 2,5-dimethyl-2,5-di(tert-butylperoxy)hexane, tert-buty I peroxy 2- ethylhexyl carbonate, tert-amyl peroxy-2-ethylhexanoate, tert-amyl peroxypivalate, tert-amylperoxy 2- ethylhexyl carbonate, 2,5-dimethyl-2,5-di(2-ethylhexanoylperoxy) hexane 2,5-dimethyl-2,5-di(tert- butylperoxy) hexpe-3, di(3-methoxybutyl)peroxydicarbonate, diisobutyryl peroxide, tert-butyl peroxy-2- ethylhexanoate (Trigonox 21 S), 1,1 -di(tert-butylperoxy)cyclohexane, tert-butyl peroxyneodecanoate, tert-butyl peroxypivalate, tert-butyl peroxyneoheptanoate, tert-butyl peroxydiethylacetate, l,l-di(tert- butylperoxy)-3,3,5-trimethylcyclohexane, 3,6,9-triethyl-3,6,9-trimethyl-l,4,7-triperoxonane, di(3,5,5- trimethylhexanoyl) peroxide, tert-butyl peroxy-3, 5, 5-trimethyl hexanoate, 1,1,3,3-tetramethylbutyl peroxy-2-ethylhexanoate, 1,1,3,3-tetramethylbutyl peroxyneodecanoate, tert-butyl peroxy-3, 5,5- trimethyl hexanoate, cumyl peroxyneodecanoate, di-tert-butyl peroxide, tert-butylperoxy isopropyl carbonate, tert-butyl peroxybenzoate, di(2-ethylhexyl) peroxydicarbonate, tert-butyl peroxyacetate, isopropylcumyl hydroperoxide, and tert-butyl cumyl peroxide.

[0071] Examples of useful epoxy curing agent include but are not limited to the Ajicure series of hardeners available from Ajinomoto Fine-Techno Co., Inc.; the Amicure series of curing agents available from Air products and the JERCURE™ products available from Mitsubushi Chemical. These curing agents or hardeners or hardeners are oftentimes used in an amount of about 1% to about 50 % by weight of the total composition, such as from about 5% to about 20% by weight of the total composition. [0072] The curable composition may optionally contain, as desired, a further component capable of a photopolymerization reaction such as a vinyl ether compound. In addition, the curable composition may further comprise additives, resin components and the like to improve or modify properties such as flowability, dispensing or printing property, storage property, curing property and physical property after curing.

[0073] Various other compounds may be contained in the composition as desired, for example, organic or inorganic fillers, thixotropic agents, silane coupling agents, diluents, modifiers, coloring agents such as pigments and dyes, surfactants, preservatives, stabilizers, plasticizers, lubricants, defoamers, leveling agents and the like; however it is not limited to these. In particular, the composition may comprises an additive selected from an organic or inorganic filler, a thixotropic agent, and a silane coupling agent. These compounds may be present in amounts of about 0.1% to about 50% by weight of the total composition, more preferably from about 2% to about 10% by weight of the total composition.

[0074] The filler may include, but is not limited to, inorganic fillers such as silica, diatomaceous earth, alumina, zinc oxide, iron oxide, magnesium oxide, tin oxide, titanium oxide, magnesium hydroxide, aluminium hydroxide, magnesium carbonate, barium sulphate, gypsum, calcium silicate, talc, glass bead, sericite activated white earth, bentonite, aluminum nitride, silicon nitride, and the like; meanwhile, organic fillers such as poly(methyl) methacrylate, poly(ethyl) methacrylate, poly(propyl) methacrylate, poly(butyl) methacrylate, butylacrylate-methacrylic acid-(methyl) methacrylate copolymer,

polyacrylonitrile, polystyrene, polybutadiene, polypentadiene, polyisoprene, polyisopropylene, and the like. These may be used alone or in combination. These fillers may be present in amounts of about 1% to about 80%, more preferably from about 5% to about 30% by weight of the total composition.

[0075] The thixotropic agent may include, but is not limited to, talc, fume silica, superfine surface- treated calcium carbonate, fine particle alumina, plate-like alumina; layered compounds such as montmorillonite, spicular compounds such as aluminium borate whisker, and the like. Among them, talc, fume silica and fine alumina are particularly desired. These agents may be present in amounts of about 1% to about 50%, such as from about 1% to about 30% by weight of the total composition.

[0076] The silane coupling agent may include, but is not limited to, g-minopropyltriethoxysilane, g - mercaptopropyltrimethoxysilane, g-methacryloxypropyltrimethoxysilane, y- glycidoxypropyltrimethoxylsilane, and the like.

[0077] The curable composition may be obtained by mixing the various constituents by means of, for example, a mixer such as a stirrer having stirring blades and a three roll mill. When the composition is liquid at ambient temperature, with a viscosity of say 200-400 Pa-s (at 25°C) at 1.5s-l shear rate, easy dispensing may be achieved.

[0078] According to the present disclosure, a method of synthesizing a so-disclosed star polymer additive includes providing (meth)acrylate such as t-butyl acrylate, injecting an initiator such as tert- butyl a-bromoisobutyrate, injecting a ligand such as tris[2-(dimethlyamino)ethyl]amine, adding (meth)acrylate such as n-butyl acrylate dissolved in acetonitrile, adding 1,6-hexanediol diacrylate and additional ligand, and isolating a resulting star polymer.

[0079] One aspect of the present disclosure includes a method of imparting improved viscosity slump resistance to a curable composition. The method includes the steps of providing a curable resin selected from an epoxy-functionalized resin, a (meth)acrylate-functionalized resin, a vinyl ether-functionalized resin, a vinyl ester-functionalized resin, an oxetane-functionalized resin, a cyanate ester-functionalized resin, a maleimide-functionalized resin, a nadimide-functionalized resin, a itaconimide-functionalized resin, or mixtures of any two or more thereof, providing a curing agent, adding an expandable viscosity modifier additive which provides at least about 2 times improved viscosity slump resistance from a first, lower temperature condition to a second, higher temperature condition compared to the curable composition without the additive and expands its volume with an increase in temperature. The expandable viscosity modifier additive provides a greater viscosity index compared to the curable composition without the additive, in some cases an order of magnitude or two greater. The improved viscosity slump resistance may be observed within the temperature range of about 25°C to Tonset, which will depend on the nature and identity of the reactive constituents in the composition. In many cases, the Tonset may be about 65°C.

EXAMPLES

[0080] The examples provided below present more detail of objects, features and advantages of the present disclosure, but are not intended to be limiting.

[0081] In Table 1, various formulations were evaluated to test the viscosity modifying properties of certain exemplary additives. The formulations are listed, including a source and description.

Table 1

[0082] In Table 1, Formulation A is a curable maleimide-functionalized resin system used as a control. Formulation A consists of two parts (about 66%) epoxy-functionalized and maleimide-functionalized resin and one part (about 33%) hardener FIXA5923 from Asahi Kasei (Chiyoda, Tokyo, Japan). The maleimide-functionalized resin used in Formulation A has the general structure of:

where: R is a multivalent hydrocarbyl linker selected from linear or branched alkyls, linear or branched cycloalkyls, alkylenes, cycloalkylenes, bicycloalkylenes, tricycloalkylenes, linear or branched alkylenes, linear or branched cycloalkylenes, linear or branched alkenylenes, arylenes, aralkylenes,

arylbicycloalkylenes, aryltricycloalkylenes, bicycloalkylarylenes, tricycloalkylarylenes, bisphenylenes, cycloalkylarylenes, heterocycloalkylene or heterocycloarylenes; the alkyls, cycloalkyls, alkylenes, cycloalkylenes, alkenylenes, arylenes, aralkylenes, arylbicycloalkylenes, aryltricycloalkylenes, bicycloalkylarylenes, tricycloalkylarylenes, bisphenylenes, cycloalkylarylenes, heterocycloalkylene and heterocycloarylenes that can optionally contain O or S or hydroxyl group; and

n and are each independently about 1 to about 10.

[0083] Formulation B is the curable maleimide-functionalized resin system of Formulation A with 5% F351 (also known as ZEON F351) available from Zeon Corporation, Japan. F351 is a core-shell polymer that has a core phase polymer that is a rubbery polymer and a shell phase polymer that is a non-rubbery and that has carboxylic acid functional groups on the shell phase non-rubbery polymer. Formulation C is the curable maleimide-functionalized resin system of Formulation A with 3% E00075. Formulation D is the curable maleimide-functionalized resin system of Formulation A with 3% E00075 and 4% Crayvallac ^® SF. As discussed above, E00075 3% and Crayvallac ^® SF 4% are available from Arkema (King of Prussia, PA).

[0084] As illustrated in FIG. 1 and Table 2 below, the viscosity slump resistance of a curable maleimide- functionalized resin system was improved with additives of the present disclosure, as compared to a control curable maleimide-functionalized resin system without the additives. Viscosity at 25°C and 65°C was measured using photo-rheometers from Anton Paar GmbH, Germany. In particular, MCR 301 and MCR 302 type rheometers provided the viscosity measurements via controlled compression of the formulations.

Table 2

[0085] The viscosity index of Table 2 is a ratio calculated by dividing the pascal-second ("Pa-s") value at 65°C by the Pa-s value at 25°C. [0086] As FIG. 1 and Table 2 depict, each of the tested formulations (B, C and D) had a higher viscosity index than the control (A) without the additives.

[0087] As illustrated in Table 3 below, the percentage viscosity index increase of each of the tested formulations, as compared to the control, resulted in a 1 times, 10 times, and 150 times increase, respectively.

Table 3

[0088] Other formulations were also evaluated. In Table 4, the formulations are listed, including a source and description.

Table 4

[0089] In Table 4, Formulation E is another curable maleimide-functionalized resin system used as a control. Formulation E consists of two parts (about 66%) epoxy-functionalized and maleimide- functionalized resin and one part (about 33%) hardener HXA5923 from Asahi Kasei (Chiyoda, Tokyo, Japan). The maleimide-functionalized resin used in Formulation E has the general structure of:

where:

R is a multivalent hydrocarbyl linker selected from linear or branched alkyls, linear or branched cycloalkyls, alkylenes, cycloalkylenes, bicycloalkylenes, tricycloalkylenes, linear or branched alkylenes, linear or branched cycloalkylenes, linear or branched alkenylenes, arylenes, aralkylenes,

arylbicycloalkylenes, aryltricycloalkylenes, bicycloalkylarylenes, tricycloalkylarylenes, bisphenylenes, cycloalkylarylenes, heterocycloalkylene or heterocycloarylenes; the alkyls, cycloalkyls, alkylenes, cycloalkylenes, alkenylenes, arylenes, aralkylenes, arylbicycloalkylenes, aryltricycloalkylenes, bicycloalkylarylenes, tricycloalkylarylenes, bisphenylenes, cycloalkylarylenes, heterocycloalkylene and heterocycloarylenes that can optionally contain 0 or S or hydroxyl group; and

n and ni are each independently about 1 to about 10.

[0090] Formulation F is the curable maleimide-functionalized resin system of Formulation A with 2% E00075. Formulation G is the curable maleimide-functionalized resin system of Formulation A with 3% E00075. E00075 is available from Arkema (King of Prussia, PA). Formulation H is the curable maleimide- functionalized resin system of Formulation A with 5% F351s. F351s (also known as ZEON F351s) is available from Zeon Corporation, Japan and is a two acrylic rubber core-shell structure consisting of acrylic rubber. F351s has a core layer of n- butyl acrylate and a shell layer of methyl methacrylate.

[0091] As illustrated in FIG. 2 and Table 5 below, the viscosity slump resistance of curable maleimide- functionalized resins was improved with additives of the present disclosure, as compared to a control curable maleimide-functionalized resin system without the additives.

Table 5

[0092] In Table 5, Formulation F had a viscosity index of 1.768. This is particularly notable because the additive in Formulation F resulted in a greater viscosity at 65°C compared to 25°C, which is the reverse of the other three formulations in Table 5.

[0093] As FIG. 2 and Table 5 depict, each of the tested formulations (F, G and FI) had a higher viscosity index than the control without the additives.

[0094] As illustrated in Table 6 below, the percentage viscosity index increase of each of the tested formulations as compared to the control resulted in a 90 to 400 times increase.

Table 6

[0095] For Formulations F, G and FI the viscosity increased with an increase in temperature. This behavior is very different from the control system and typical cure systems where, upon the application of heat, the resin viscosity drops initially, and continues to drop through a region of maximum flow.

EXAMPLE— Star Polymer and Synthesis

[0096] The star polymer may be synthesized in a receptacle, such as a 250 ml four neck round bottom flask, optionally containing a copper mesh, a mechanical stirrer, a condenser, an additional funnel, and a rubber septum. A procedure for synthesizing the star polymer includes some or all of the following steps.

[0097] Pre-treating the copper mesh with 0.1 N hydrochloric acid aqueous solution and rinsing the copper mesh with acetone. Adding acetonitrile (13 g) and t-butyl acrylate (12.80 g; 100 mmol). Adding copper (II) bromide (0.013 g; 0.05 mmol). Purging the mixture with nitrogen for a period of time of 30 minutes. Heating the mixture to approximately 45 °C. Injecting initiator tert- Butyl a-bromoisobutyrate (1.115 g; 5 mmol) and ligand Me ₆ TREN (0.12 g; 0.50 mmol) to the mixture via airtight syringes.

[0098] The reaction may be monitored with NMR until t-butyl acrylate conversion is greater than 85%. In embodiments, the t-butyl acrylate conversion takes approximately two hours.

[0100] Referring to FIG. 3, the molecular weight and polydispersity index ("PDI") may be determined using size exclusion chromatography, in particular, GPC. After testing, in embodiments, the molecular weight of the star polymer was about 7.5 Kda and the PDI was just 1.02.

[0101] The procedure for synthesizing the star polymer may further include the steps of: adding n-butyl acrylate (51.2 g; 400 mmol) in acetonitrile (52 g) in a 200 ml additional funnel purged with nitrogen. The reaction can be monitored with ^X H NMR until t-butyl acrylate conversion is greater than 85%, which may take approximately three hours. Again, the molecular weight and PDI may be determined by GPC.

[0102] The procedure for synthesizing the star polymer may further include the steps of: adding 1,6- hexanediol diacrylate ("HDDA") (7.49 grams; 35 mmol in acetonitrile (13 g)) in a 60 ml additional funnel purged with nitrogen. Additional ligand Me ₆ TREN (0.12 g; 0.50 mmol was injected. The ensuing reaction may be monitored with NMR until t-butyl acrylate conversion is greater than 95%, which may take approximately three hours.

[0103] Referring to FIG. 4, the molecular weight and PDI can be determined by GPC. In embodiments, the molecular weight was found to be about 31 kDa and the PDI was about 1.15.

[0104] The procedure for synthesizing the star polymer may further include the steps of removing the Cu (0) mesh from the receptacle, and adding p-toluenesulfonic acid monohydrate ("p-TSA H2O") (2 g) to the mixture. In embodiments, the mixture can be refluxed for approximately six hours. After the refluxing, poly t-butyl acrylate in the star copolymer is converted to poly acrylic acid, which may be monitored by ¹³ C NMR with the disappearance of t-butyl group.

[0105] The procedure for synthesizing the star polymer may further include the step of precipitating a resulting star polymer from acetonitrile solution by methanol and water ("MQOH/HSO") in a ratio, for example, of 10 : 1. In embodiments, additionally or alternatively, the star polymer can be fractionally precipitated with tetrahydrofuran and methanol ("THF/MeOH"), washed with MeOH, and dried in vacuum.

[0106] Most arm copolymer could be removed after two passes through the fractional precipitation method. In preferred embodiments, nearly 99% of the star polymer was obtained.

[0107] Referring to FIG. 5, from the ¹³ C NMR spectrum, it was found that the tert-butyl group was removed by the acid treatment. EXAMPLE— Hyper-Branched Polymers

[0108] Referring to FIG. 6, in one aspect of the present disclosure, hyper-branched polymers, which include the comb polymer additives of the present disclosure, were synthesized based on a polyamide structure. In embodiments, different amines and acids were introduced into the system to check viscosity slump resistance effect. An example of a possible synthesis route of hyper-branched polymers is further described below.

[0109] Adding a trimer acid (Autrex 1006, three functional group, from Autrex Industrial (Pty) Ltd., Western Cape, South Africa) (2.10 g; 10 mol), p-phenylene diamine (1.08 g; 10 mmol), pyridine (7.5 mL), triphenyl phosphite (7.82 ml; 130 mmol) and 80 mL N-methyl-2-pyrrolidone ("NMP") to a 250 mL three necked bottle, with the protection of nitrogen. Then, with an oil bath, heating the reaction to 180°C for approximately two hours.

[0110] The resulting product was precipitated in methanol. The product was washed with more methanol and dried in vacuum. The product was confirmed by GPC.

[0111] Different amide polymers were synthesized by this method and the reactants are set forth in Table 7. Most of these amide polymers showed a molecular weight from about 13kDa to about 30kDa.

Table 7

[0112] While the present disclosure has been illustrated and described more specifically in the preceding examples, it should be appreciated by those of ordinary skill in the art that various modifications to this disclosure may be made without departing from the spirit and scope thereof.