DRINKING WATER. INDUSTRIAL WATER AND/OR FOOD PRODUCTS

OBJECT OF THE INVENTION

The present invention is related to the preparation of new polymers which act as colorimetric sensors, in aqueous media and/or food products, of divalent metals such as mercury or copper, and in addition, of oxidising anions such as nitrites. The polymers are provided in the form of films or dense membranes, obtained by copolymerisation of three or more monomers, which include polyfunctional monomers, to provide materials having good mechanical properties, both in dry form and expanded form, which behave like solid colorimetric sensors.

BACKGROUND OF THE INVENTION

The need to use inorganic heavy metal salts in mining areas for extracting precious metals and/or minerals of interest has led in the last decades to the development of analytical methods for determining and quantifying said heavy metals. For example, controlling the concentration of mercury is of maximum interest for preventing poisoning in areas near gold mines, since mercury is used as an extractant in this type of industry.

The classical method for determining the amount of mercury in water is UV-visible spectroscopy. This method requires mercury complexing reagents which form coloured compounds, in addition to an expensive spectrophotometer for obtaining the corresponding absorbance values.

Also available are other colorimetric methods which also require chemical reagents. In practice, these procedures have a considerable error and require adding a solvatochromic compound, previously obtaining a calibration line of each sample with the molar extinction coefficient of the solvatochromic compound and other empirical parameters burdensome to calculate.

A third method, widely used mercury determination, is flame atomic absorption spectroscopy. This method is more accurate but also requires an expensive flamee atomic absorption equipment.

It should be noted that all these techniques can be extrapolated to copper detection. However, with regard to the detection of nitrites, the methods used are limited to reactive strips (inexpensive, but with errors due to interferences) and/or ICP-MS analysis (very accurate, but extremely expensive and without selectivity, since only the total nitrogen value of the sample is obtained).

Within this context, the development of molecules which act as chromogenic or fluorogenic sensors, with the objective of facilitating the detection of nitrites by simplifying the method and lowering costs, is a topic of great scientific and technological interest (R. Martinez-Mafiez, F. Sancenon, Chem. Rev. 2003, 4419-4476; J. Janata, Chem. Rev. 2008, 108, 327-328). The design, synthesis and setup thereof as a sensor system results in new analyte detection technologies characterised by being inexpensive, highly sensitive and user-friendly, enabling their use by non-specialist staff. Moreover, the preparation of dense hydrophilic membranes as sensor materials represents a step forward in the development of this field (S. Vallejos, A. Munoz, S. Ibeas, F. Serna, F. Garcia, J. M. Garcia, J. Mater. Chem. A. 2013, 1 , 15435-15441 , S. Vallejos, A. Munoz, S. Ibeas, F. Serna, F. Garcia, J. M. Garcia, J. Hazard. Mater. 2014, 276, 52-57, S. Vallejos, A. Munoz, S. Ibeas, F. Serna, F. Garcia, J. M. Garcia, ACS Appl. Mater. Interfaces. 2015, 7, 921- 928, J. L. Pablos, S. Vallejos, A. Munoz, M. J. Rojo, F. Serna, F. C. Garcia, J. M. Garcia, Chem. Eur. J. 2015, 21 , 8733-8736, S. Vallejos, A. Munoz, F. Garcia, R. Colleoni, R. Biesuz, G. Alberti, J. M. Garcia, Sens. Actuators B. 2016, 233, 120-126). Therefore, the availability of solid films that can be easily handled, both dry and wet, opens up new prospects for this technology. DESCRIPTION

The invention relates to new processes for preparing and modifying copolymers and, in particular, gel-like acrylic materials, for obtaining copolymers with dithizone-derived structures which act as cross-linking agents. Likewise, it relates to the applications obtained from these materials in different fields.

The invention relates to the preparation of new cross-linked copolymers, both in the form of a dense or porous membrane, or a gel. Said copolymers are copolymers cross-linked by dithizone-derived structures of formula (I):

The copolymers cross-linked by structures of formula (I) described herein have the form of films, also called solid membranes. Said solid membranes may be dense membranes or porous membranes. The invention relates to said dense membranes and also to the porous membranes obtained by means of chemical and/or physical foaming processes carried out in the previously described membranes.

Said copolymers cross-linked by structures of formula (I) are membranes which act as chromogenic sensors, i.e. they are materials that change colour in the presence of certain substances. Said change in colour occurs when divalent metal cations and/or oxidising anions are present in the medium.

For the purposes of this invention, non-limiting examples of divalent metals include mercury [Hg(ll)], copper [Cu(ll)], zinc [Zn(ll)], lead [Pb(ll)] or cadmium [Cd(ll)]. In a preferred embodiment, said change in colour occurs when mercury [Hg(ll)] and/or copper cations [Cu(ll)] are present in the medium.

For the purposes of the present invention, non-limiting examples of oxidising anions include nitrite (N0 ₂ ), periodate (IGv), permanganate (Mn0 ₄ ), hypchlorite (CIO ) and peroxides. In a preferred embodiment, said change in colour occurs when nitrites (N0 ₂ ^~ ) are present in the medium.

This specific behaviour enables the detection of metals, such as Hg(ll) or Cu(ll), and/or oxidising anions, such as nitrites (N0 ₂ ), via changes in the visible colour spectrum, such that said changes, in addition to be able to be measured using a spectrophotometer, they can also be measured with the naked eye, in addition to enabling quantifying said oxidising metals and/or anions through the digital definition of the colour (RGB) of a photograph taken of the material. The change in colour due to the presence of mercury cations, for example, can be observed with the immersion of the membranes or copolymers cross-linked by structures of formula (I) of the present invention in different media, without any type of prior treatment of the sample. Therefore, the cross-linked copolymers of the invention can be used as sensors for the qualitative or quantitative detection of the metals and/or oxidising anions in question.

For the purposes of present invention, the term copolymer is used equivalently to the term membrane, due to the membrane structure of the copolymers described herein. Likewise, the copolymers cross-linked by structures of formula (I) described herein are indistinctly referred to as sensor membrane or chromogenic sensors due to their properties, described herein.

The term polymer refers to a molecule comprising one or more successively repeated structural units. Said units are called monomers. The polymers are obtained from the repeated bonding of said monomers by reaction of reactive groups (or polymerisable groups) present in each of the monomers, in a process called polymerisation.

The term copolymer relates to a polymer comprising at least two different monomers.

The term cross-linked copolymer refers to a copolymer that gives rise to a network formed bythe link between different polymer chains. The formation of said network from different polymer chains is called cross-linking.

The structures of formula (I) of the cross-linked copolymers of the present invention, are synthesized by cross-link reaction of copolymers comprising R ₂ groups, wherein said R ₂ group comprises an aromatic ring substituted with at least one NH ₂ group.

For the purposes of the present description, said R ₂ group is called an anchor group R ₂ , since said group is responsible for the union or the cross-linking of different copolymer chains.

The cross-linking process can be schematised according to Scheme 1 below:

Scheme 1

Said Scheme 1 graphically represents the cross-linking process that occurs when two copolymer chains comprising anchor groups R ₂ are bonded to form a network of copolymers chains cross-linked by structures of formula (I) derived of dithizone .

In an embodiment of the present invention, the copolymers cross-linked by structures of formula (I) are obtained in a process comprising the following steps:

(a) obtaining a copolymer through polymerisation of at least two types of monomers, wherein at least one of the monomers type comprises an anchor group R ₂ and wherein said anchor group R ₂ comprises an aromatic ring substituted with at least one NH ₂ group, and wherein said polymerisation is carried out by direct reaction of polymerisable groups present in each of the monomers;

(b) carrying out an immersion of the copolymer obtained in step (a) in an acid solution with a pH between 1 and 3, comprising a nitrite salt and subsequently an immersion in a basic solution with a pH between 8 and 12 comprising nitromethane;

(c) carrying out an immersion of the copolymer obtained in step (b) in an aqueous solution comprising ammonium sulphide; and

(d) carrying out an immersion of the copolymer obtained in step (c) in an aqueous solution with a base and subsequently in an acid aqueous solution.

For the purposes of present invention, carrying out an immersion implies that the copolymer is completely immersed in the solution used. The copolymers obtained in step (a) comprise anchor groups R ₂ and, therefore, are referred indistinctly as anchor copolymers or as anchor membranes for the purposes of the present invention.

In a preferred embodiment, the copolymer obtained in step (a) is obtained in the presence of a thermal or a photochemical initiator.

In a preferred embodiment, the copolymer obtained in step (a) is obtained by polymerisation of three types of monomers, wherein

one of said three types of monomers comprises a group Ri and an anchor group R ₂ which comprises an aromatic ring substituted with at least one NH ₂ group, wherein Ri is H or CH ₃ ;

X, Y and Z represent the percentages of each of the monomers types from the total number of monomers; wherein the proportion of X with respect to Y is 1 :3 to 3:1 ; Z represents the percentage of the monomer type comprising a group Ri and an anchor group R ₂ , and wherein Z represents between 0.1 % and 10% of the total number of monomers; and

wherein the copolymer obtained in said step (a) is a copolyer of formula (II):

For the purposes of present invention, the image of formula (II) above herein included is for illustration purposes only and does not intend to represent a particular order in which the three types of monomers are present in the polymer chain.

The previously described process for obtaining the cross-linked copolymers of the invention can be represented by Scheme 2 below:

Scheme 2

wherein Ri is H or CH ₃ and wherein X, Y and Z represent the percentages of the three type of monomers used, wherein Z represents the percentage of the monomer type comprising an anchor group R2 and is between 0.1 % and 10% of the total number of monomers and wherein the proportion of X with respect to Y is 1 :3 to 3:1 .

Scheme II shows illustrations of copolymers described in present disclosure, but does not intend to represent a particular order in which the three types of monomers are present in the polymer chain.

In a preferred embodiment, the proportion of X with respect to Y is 1 :1. In a preferred embodiment, Z represents 0.25% of the total number of monomers. One embodiment of the invention relates to a copolymer cross-linked by structures of formula (I), as described above herein, obtained by polymerisation of three type of monomers, wherein one of the monomers types is a monomer type cross-linking copolymer chains by a structure of formula (I), and wherein said monomer comprises a group Ri, wherein Ri is a H or CH ₃ group; and wherein

X, Y and Z represent the percentage of each monomer type from the total number of monomers;

Z represents the percentage of the monomer type cross-linking copolymer chains by a structure of formula (I) and represents between 0.1 % and 10% of the total number of monomers;

the proportion of X with respect to Y is from 1 :3 to 3:1 , and

wherein the cross-linked copolymer is a copolymer of formula (X):

As described before, the image of the copolymer of formula (X) represented above herein is an illustration, but but does not intend to represent a particular order in which the three types of monomers are present in the polymer chain.

In a preferred embodiment, the proportion of X with respect to Y is 1 :1. In a preferred embodiment, Z represents 0.25% of the total number of monomers.

For the purposes of present invention, the polymers are obtained by the link of monomers wherein the monomers comprise polymerisable groups.

For the purposes of present invention, non-limiting examples of polymerisable groups are vinyl, methacrylate, acrylate, methacrylamide or acrylamide group.

vinyl group methacrylate group acrylate group

methacrylamide group acrylamide group

(wherein R is H or an aikyl, an alkenyl or an aryl group).

The monomers used in step (a) of the process to obtain the copolymers described herein may be both commercial monomers or synthesis monomers.

In a preferred embodiment of the invention, at least one of the types of monomers used in step (a) is selected independently from a group consisting of pyrrol idone vinyl, methyl methacrylate, butyl acrylate, butyl methacrylate, methyl acrylate, styrene, 2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate, 2-ethoxyethyl methacrylate, lauryl acrylate, lauryl methacrylate, vinyl acetate, methacrylic acid, methacrylic anhydride, acrylic acid and 2- N , N-d imethylaminoethyl methacrylate .

In a preferred embodiment of the invention, at least one of the types of monomers used in step (a) is vinyl pyrrolidone.

In a preferred embodiment of the present invention, at least one of the types of monomers used in step (a) is methyl methacrylate.

For the purposes of the present invention, anchor monomers refer to a type of monomers used in step (a) that comprises a R ₂ anchor group.

In a preferred embodiment of the present invention, the anchor monomers comprise a polymeri sable vinyl group, an anchor group R _2, as described above herein, and a group Ri, and are anchor monomers of formula (III):

(III) wherein Ri is H or CH ₃ and R ₂ comprises an aromatic ring substituted with at least one NH ₂ group.

In an embodiment of present invention, said R ₂ group is selected independently from

In a preferred embodiment of the invention, the polymerisation described in step (a) is carried out in solution or block.

For the purposes of the present invention, block polymerisation, or bulk polymerisation, refers to a polymerisation technique wherein only the monomers and the initiator are present in the reaction medium. In the event that the block polymerisation is carried out by thermal initiation and without need for an initiator, only the monomers are present in the reaction medium.

For the purposes of the present invention, solution polymerisation refers to a polymerisation technique where a solvent is used in addition to the monomers and an initiator.

The acid solutions, used in the process to obtain the copolymers described above herein, are prepared using inorganic acids including, but not limited to: hydrochloric acid, sulfuric acid, nitric acid or perchloric acid. In a preferred embodiment of the invention, the acid used is hydrochloric acid.

The basic solutions, used in the process to obtain the copolymers described above herein, are prepared using bases including, but not limited to: sodium acetate, alkali or alkaline- earth metal hydroxides, bicarbonates and carbonates. In a preferred embodiment of present invention, the base used is selected independently from sodium acetate, sodium hydroxide, potassium hydroxide, sodium carbonate, sodium bicarbonate, potassium carbonate and potassium bicarbonate.

In a preferred embodiment, step (b) of the process to obtain the copolymers described above herein comprises carrying out an immersion of the copolymer obtained in step (a) in an acid solution with a pH between 1 and 3, comprising between 0.4 g/L and 40 g/L, more preferably between 1 g/L and 10 g/L, of a nitrite salt; and subsequently an immersion in a basic solution with a pH between 8 and 12 comprising nitromethane.

In a more preferred embodiment of step (b) of the present invention, the acid solution has a pH between 1 and 3 and comprises 4 g/L of a nitrite salt.

In a preferred embodiment, the nitrite salt is an alkaline metal salt or an alkaline-earth metal salt. In one embodiment, the nitrite salt is sodium nitrite, potassium nitrite, lithium nitrate, calcium nitrite or iron nitrite (III). In a preferred embodiment of the invention, the nitrite salt is sodium nitrite.

In a preferred embodiment of step (b) of the present invention, the immersion in an acid solution is carried out for at least 30 minutes.

In a preferred embodiment of step (b) of the present invention, the nitrite salt is sodium nitrite.

In a preferred embodiment of step (b) of the process to obtain the copolymers described above herein, comprises carrying out the immersion of the copolymer obtained in step (a) in an acid solution with a pH between 1 and 3, comprising a nitrite salt and subsequently an immersion in a basic solution with a pH between 8 and 12 comprising nitromethane, wherein the base is sodium acetate.

In a preferred embodiment, step (b) of the process described herein comprises carrying out an immersion in a basic solution with a pH between 8 and 12, comprising between 0.4 ml/L and 40 ml/L, more preferably between 1 ml/L and 10 ml/L, of nitromethane.

In a more preferred embodiment, step (b) comprises an immersion in a basic solution with a pH between 8 and 12 which comprises 4 ml/L of nitromethane.

In a preferred embodiment, step (b) of the present invention, comprises an immersion in a basic solution carried out for at least 90 minutes.

In a preferred embodiment described herein, the concentration of ammonium sulphide in step (c) is between 1wt% and 20wt%. In another preferred embodiment, the concentration of ammonium sulphide is between 1wt% and 10wt%. In a more preferred embodiment, the concentration of ammonium sulphide is 2.15wt%.

In a preferred embodiment step (c) described herein, comprises carrying out an immersion in a aqueous ammonium sulphide solution for at least 90 minutes.

In a preferred embodiment of the present invention, the base used in step (d) is potassium hydroxide. In a preferred embodiment step (d) described herein, comprises carrying out an immersion in an aqueous solution for at least 30 minutes.

The synthesis of the cross-linked copolymers comprising a structure of formula (I), described herein, cannot be carried out by conventional routes in organic chemistry, i.e. (i) synthesising a dithizone-derived monomer, represented in bold in the last step of Scheme 2, and (ii) performing a subsequent copolymerisation with other commercial monomers, as described in the bibliography (S. Vallejos, A. Munoz, S. Ibeas, F. Serna, F. Garcia, J. M. Garcia, J. Mater. Chem. A. 2013, 1 , 15435-15441 ). Said conventional process is not possible due to the fact that the dithizone-derived monomer does not support such polymerisation process and, therefore, it would be impossible to obtain the cross-linked copolymers comprising a formula (I) structure of the invention by said conventional routes.

It is also not possible to obtain dithizone-containing materials, which behave like chromogenic sensors, through a dithizone-coating process of a first material acting as support, since, even if said dithizone-coated material can be obtained, it is not stable for long periods of time (S. Vallejos, A. Munoz, F. Garcia, R. Colleoni, R. Biesuz, G. Alberti, J. M. Garcia, Sens. Actuators B. 2016, 233, 120-126).

Furthermore, in the method described herein, since the synthesis of the dithizone-derived structure I is carried out within the copolymer itself, obtained in step (a) of the process describe herein, by direct modification of the copolymer chains according to steps (b), (c) and (d), as described above herein, the resulting copolymers cross-linked by structures of formula (I) are stable over the years without any type of special storage or treatment. To this end, it is essential to carry out polymerisation using an anchor monomer comprising a R ₂ group as described above herein.

In a preferred embodiment of step (a) described herein, the at least two type of monomers used are monomers of formula (IV),

monomers of formula (V)

(V)

and anchor monomers of formula (III),

wherein

- Ri is selected independently between H or CH ₃ and R ₂ comprises an aromatic ring substituted with at least one NH ₂ grou

X, Y and Z represent the percentage of monomers (IV), (V) and (III), respectively, from the total number of monomers;

Z represents between 0.1 % and 10% of the total number of monomers;

- the proportion of X with respect to Y is from 1 :3 to 3:1 ;

and wherein the copolymer obtained in said step (a) is a copolymer of formula (VI):

(IV) (V) (ill)

The image of the copolymer of formula (VI) represented above herein is an illustration, but does not intend to represent a particular order in which the three types of monomers are present in the polymer chain.

In a preferred embodiment, step (a) described herein is carried out through the polymerisation of vinyl pyrrolidone, methyl methacrylate and N-(4- aminophenyl)methacrylamide, wherein

X, Y and Z represent the percentage of vinyl pyrrolidone, methyl methacrylate and N-

(4-aminophenyl)methacrylamide, respectively, from the total number of monomers; Z represents between 0.1 % and 10% of the total number of monomers;

the proportion of X with respect to Y is from 1 :3 to 3:1 ;

and wherein the copolymer obtained in said step (a) is copolymer of formula (VII):

The image of the copolymer of formula (VII) represented above herein is an illustration, but does not intend to represent a particular order in which the three types of monomers are present in the polymer chain.

In a preferred embodiment, the proportion of X with respect to Y is 1 :1. In a preferred embodiment, Z represents 0.25% of the total number of monomers.

In said preferred embodiment of the invention, the anchor monomer of fomula (III) used is

N-(4-aminophenyl)methacrylamide (wherein Ri is CH ₃ and R ₂ is

and the commercial monomers vinyl pyrrolidone (monomer of formula IV wherein Ri is H) and methyl methacrylate (monomer of formula V wherein Ri is CH ₃ ) are also used.

In general, the copolymerisation of the monomers in step (a) as described herein, either comprising commercial vinyl monomers or not, can be carried out by any of the methods described in literature for the polymerisation of multiple bonds.

The anchor monomers comprising an anchor group R ₂ , as described herein, may be also obtained commercially.

In a preferred embodiment of the present invention, the anchor monomer used in step (a) is 4-aminostyrene, which can be obtained commercially.

In another embodiment of present invention, the anchor monomer used in step (a) is

an anchor monomer of formula (III) comprising an anchor group R ₂ and a group Ri selected independently between H and CH ₃ . Said monomers can be prepared according to Scheme 3 and in accordance with the terms and conditions described in Example 1 :

Scheme 3

In a preferred embodiment of the method for obtaining the anchor monomer according to Scheme 3 above, Ri is CH ₃ .

The synthesis of the anchor monomer can also be carried out by other conventional routes in organic chemistry.

A preferred embodiment of present invention is a copolymer cross-linked by structures of formula (I), as described above herein, obtained by polymerisation of three types of monomers, a first type being monomers of formula (IV),

a second type being monomers of formula (V);

and a third type being monomers comprising a group Ri, wherein Ri is a H or CH ₃ group, wherein said third type of monomer cross-links copolymer chains by structures of formula (I); wherein

X corresponds to the percentage monomers of formula (IV), Y corresponds to the percentage of monomers of formula (V), and the proportion of X with respect to Y is at least 1 :3 and up to 3:1 ,

Z is the percentage of monomers cross-linking copolymer chains by structures of formula (I) and represents between 0.1 % and 10% of the total number of monomers; and wherein the cross-linked copolymer is a copolymer of formula (VIII):

The image of the copolymer of formula (VIII) represented above herein is an illustration, but does not intend to represent a particular order in which the three types of monomers are present in the polymer chain

In a preferred embodiment of the present invention, the proportion of X with respect to Y is 1 :1. In a preferred embodiment of the present invention, Z represents 0.25% of the total number of monomers.

A preferred embodiment of the invention is a copolymer cross-linked by structures of formula (I), as described above herein, obtained by polymerisation of three types of monomers, a first type being monomers of vinyl pyrrolidone, a second type being monomers of methyl methacrylate and a third type of monomers comprising a group CH ₃ , wherein said third type of monomers cross-links copolymer chains by structures of formula (I); wherein

X corresponds to the percentage of vinyl pyrrolidone;

- Y corresponds to the percentage of methyl methacrylate; Z is the percentage of monomers cross-linking copolymer chains by structures of formula (I) and represents between 0.1 % and 10% of the total number of monomers; the proportion of X with respect to Y is from 1 :3 to 3:1 ; and

and wherein said copolymer cross-linked by structures of formula (I) is a copolymer of formula (IX):

The image of the copolymer of formula (IX) represented above herein is an illustration, but does not intend to represent a particular order in which the three types of monomers are present in the polymer chain

In a preferred embodiment of the present invention, the proportion of X with respect to Y is 1 :1. In a preferred embodiment of the invention, Z represents 0.25% of the total number of monomers.

The copolymers cross-linked by structures of formula (I) described herein, membranes, films, coatings and materials in solid state obtained therefrom, are characterised by an ideal combination of mechanical properties, both dry and expanded, i.e. with water within the polymer network. This makes the copolymers cross-linked by structures of formula (I) of present invention into suitable materials for preparing dense membranes that can be used, among other applications, in the detection of divalent metal cations, such as mercury (II) or copper (II), and/or of oxidising anions and nitrites, in water and/or in food products. That is, the cross-linked copolymers of the invention are colorimetric sensors of divalent metals and/or of oxidising anions, in water and/or in food products.

One embodiment relates to the use of the copolymers cross-linked by structures of formula (I) in accordance with the present invention in the detection and/or quantification of divalent metal cations in aqueous media or food products by means of at least one method selected independently between:

the use of the RGB parameters of a digital photograph; or the use of spectroscopic techniques.

A preferred embodiment relates to the use of the copolymers cross-linked by structures of formula (I) in accordance with present invention, wherein the divalent cation is mercury [Hg(ll)]. In another preferred embodiment, the metal is copper [Cu(ll)].

Another embodiment relates to the use of the copolymers cross-linked by structures of formula (I) in accordance with the present invention in the detection and/or quantification of oxidising anions in aqueous media or food products by means of at least one method selected independently between:

the use of the RGB parameters of a digital photograph; or the use of spectroscopic techniques.

A preferred embodiment relates to the use of the copolymers cross-linked by structures of formula (I) in accordance with the present invention, wherein the oxidising anion detected and/or quantified is the nitrite anion (N0 ₂ ).

One embodiment of the invention also relates to the porous membranes obtained by means of chemical and/or physical foaming processes carried out in the previously described solid membranes formed by the copolymers cross-linked by structures of formula (I). Examples of physical foaming processes include dissolved high-pressure gas (C0 ₂ and/or N ₂ ) and some non-limiting examples of chemical foaming processes include leaching from polymer salts or mixtures or the use of endo- or exothermal chemical foaming agents produced by the cell structure by heating and release of the gas and, in general, any foaming process that gives rise to a porous structure inside the solid membrane. DESCRIPTION OF THE FIGURES

Figure 1. Characterisation of N-(4-nitrophenyl)methacrylamide: (a) chemical structure; (b) infrared spectrum; (c) proton magnetic resonance (NMR ¹ H); (d) carbon magnetic resonance (NMR ¹³ C). Figure 2. Characterisation of N-(4-aminophenyt)methacrylamide: (a) chemical structure; (b) infrared spectrum; (c) proton magnetic resonance (NMR ¹ H); (d) carbon magnetic resonance (NMR ¹³ C).

Figure 3. Sensor membrane prepared according to Example 3 immersed in water buffered at pH=2: addition of between 0.002 and 10 mg/L of Hg(N0 ₃ ) ₂ H ₂ 0 to independent pieces of material. Figure 3A shows the effect on the disappearance of a band in the UV-visible spectrum. The graph of Figure 3B shows the relationship between the ppb of mercury added and the intensity of the green colour at 650 nm, and the graph of Figure 3C shows the relationship between the logarithm of the ppb of mercury added and the intensity of the green colour at 650 nm, in addition to the adjustment to a polynomial of order 3.

Figure 4. Sensor membranes prepared according to Example 3 after being immersed in solutions with varying concentrations of mercury (samples 1 to 6, where the grey scale corresponds to a colour scale where the darkest grey corresponds to the green colour and the lightest grey colours correspond to yellow colours), and the change in colour of said membranes translated into the principal components (PC) of the R and G parameters obtained using the digital camera of a mobile telephone. The graph represents the relationship between log[Hg, ppb] and PC, in addition to the adjustment to a polynomial of order 2.

Figure 5. Sensor membrane prepared according to Example 3 immersed in water buffered at pH=2: addition of 0.0635 to 63.5 mg/L of Cu(N0 ₃ )2-3H ₂ 0 to independent pieces of material and effect on the disappearance of a band on the UV-visible spectrum (Figure 5A). The graph of Figure 5B shows the relationship between the ppb of copper added and the intensity of the green colour at 650 nm, and the graph of Figure 5C shows the relationship between the logarithm of the ppb of copper added and the intensity of the green colour at 650 nm, in addition to the adjustment to a polynomial of order 2.

Figure 6. Sensor membranes prepared according to Example 3 after being immersed in solutions with varying concentrations of copper (samples 1 to 6, where the grey scale corresponds to a colour scale where the darkest grey corresponds to the green colour and the lightest grey colours correspond to yellow colours), and the change in colour of said membranes translated into the principal components (PC) of the R and G parameters obtained using the digital camera of a mobile telephone. The graph represents the relationship between log[Cu, ppb] and PC, in addition to the adjustment to a polynomial of order 2. Figure 7. Sensor membrane prepared according to Example 3 immersed in water buffered at pH=2: addition of 0.046 pg/L to 30.36 mg/L of NaN0 ₂ to independent pieces of material and the effect on the disappearance of a band on the UV-visible spectrum (Figure 7A). The graph of Figure 7B shows the relationship between the ppb of nitrite added and the intensity of the green colour at 650 nm, and the graph of Figure 7C shows the relationship between the logarithm of the ppb of nitrite added and the intensity of the green colour at 650 nm, in addition to the adjustment to a polynomial of order 2.

Figure 8. Sensor membranes prepared according to Example 3 after being immersed in solutions with varying concentrations of nitrite (samples 1 to 6, where the grey scale corresponds to a colour scale where the darkest grey corresponds to the green colour and the lightest grey colours correspond to yellow colours), and the change in colour of said membranes translated into the principal components (PC) of the R and G parameters obtained using the digital camera of a mobile telephone. The graph represents the relationship between log[N0 ₂ ^~ , ppb] and PC, in addition to the adjustment to a polynomial of order 2.

EXAMPLES

The following illustrative examples are not intended to be limiting and describe: a) the preparation of one e anchor monomer, N-(4-aminophenyl)methacrylamide (Example 1 ); b) the preparation of a copolymer of formula (VII), which comprises the previous anchor monomer as a comonomer (Example 2); c) the preparation of a copolymer cross-linked by structures of formula I (sensor membrane) using the previous copolymer of formula VII (Example 3), d) the colorimetric sensor-like behaviour of the sensor membrane in the presence of mercury in water (Example 4); e) the colorimetric sensor-like behaviour of the sensor membrane in the presence of copper in water (Example 5); and f) the colorimetric sensor-like behaviour of the sensor membrane in the presence of nitrites in water (Example 6).

Example 1. Synthesis of an anchor monomer.

This example illustrates the preparation and characterisation of the anchor monomer N-(4- aminophenyl)methacrylamide (2), which was carried out by the following synthetic route:

1 2

1.1. Synthesis of N-(4-nitrophenyl)methacrviamide (1 ).

1.98 ml (20.33 mmol) of methacryloyl chloride were dripped into a pressurised flask containing a solution of 20 ml of N-methylpyrrolidone (NMP), 2.16 g (15.64 mmol) of 4- nitroaniline and 3.27 ml (23.46 mmol) of triethylamine. The solution was agitated at 50°C for one night and precipitated in an aqueous solution of 4% HCI. The yellow solid was filtered and washed with water. A yield of 95% was obtained. The characterisation of the compound obtained is included in Figure 1. Figure 1A shows the chemical structure of the compound obtained, Figure 1 B is the infrared characteristic spectrum and Figures 1C and 1D show the ¹ HRMN and ¹³ C spectra, respectively.

1.2. Synthesis of N-(4-aminophenyl)methacrylamide (2):

10 g (48.5 mmol) of N-(4-nitrophenyl) methacrylamide (1 ), 100 ml of absolute ethanol, 140 ml of ethyl acetate and 46 g (242.6 mmol) of tin(ll) chloride were added to a pressurised flask. The solution was agitated for 2 hours at 120°C and the solvent mixture subsequently removed by evaporation. The brown oil was precipitated drop by drop onto a solution of 300 ml of water and 20 g of NaOH, to produce a suspension of a white solid with pH 10. The solid was filtered in a vacuum and the water removed at low pressure. Lastly, the compound was extracted in a Soxhlet extractor using acetone as a solvent. A yield of 60 % was obtained. The characterisation of the compound obtained is included in Figure 2. Figure 2A shows the chemical structure of the compound obtained, Figure 2B is the infrared characteristic spectrum and Figures 2C and 2D show the ¹ HRMN and ¹³ C spectra, respectively.

Example 2. Preparation of a copolymer of formula (VII) (membrane with the anchor monomer).

A membrane having the composition indicated below was prepared by means of block copolymerisation. Monomers: vinyl pyrrolidone, methyl methacrylate and N-(4- aminophenyl)methacrylamide (2), with a molar ratio of 49.875, 49.875 and 0.25, respectively. AIBN thermal initiator with a percentage by weight of 1 %. The resulting solution was injected in a 200 μιτι thick silanised crystal mould, in the absence of oxygen, and placed in a heater at 60°C for a whole night.

Example 3. Preparation of a copolymer cross-linked by structures of formula (I) (or sensor membrane).

The following steps were successively followed to prepare the sensor membrane: a) immersion of the membrane with the anchor monomer (copolymer of formula (VII)) in an acid sodium nitrite solution (250 ml of water + 25 ml of HCI (37%) + 1 g of sodium nitrite) for 30 minutes; b) immersion of the membrane in a basic nitromethane solution (250 ml of water + 10 g of sodium acetate + 1 ml of nitromethane) for one night; c) immersion of the membrane in an aqueous ammonium sulphide solution (250 ml of water + 30 ml of 20% ammonium sulphide) for one night; d) immersion in a aqueous potassium hydroxide solution (250 ml of water + 10 g of potassium hydroxide) at 50°C for 30 minutes; and e) immersion in an aqueous hydrochloric acid solution (250 ml of water + 25 ml of 37% HCI) for 10 seconds.

Example 4. Sensor-like behaviour of the sensor membrane in the presence of mercury in water.

This example illustrates the colori metric sensor-like behaviour of the copolymer material synthesized in Example 3, in the presence of mercury in an aqueous medium. The immersion of the membrane prepared in Example 3 in water buffered at pH=2 gave rise to a UV-visible spectrum band in the 550-750 nm range (Figure 3A). In said spectrum it can be observed that the increase in the concentration of mercury gives rise to a reduction in absorbance, i.e. the addition of increasing amounts of mercury (from 0.002 mg/L to 10 mg/L of Hg(N0 ₃ )2 H ₂ 0) gave rise to the disappearance of the colour band as observed in Figure 3A. Figure 3B shows the relationship between the ppb of mercury added and the intensity of the green colour at 650 nm, giving rise to a detection limit of 2.3 ppb, and a quantification of 11.9 ppb, as indicated in Figure 3C, showing the relationship between the logarithm of the mercury added and the intensity of the green colour at 650 nm. The adjustment to a polynomial of order 3 performed in Figure 3C is shown in Table 1 below*: Table 1

^• Detection limit 2.26 ppb/Quantifi cation limit 11.86 ppb

Similarly, various films were photographed after being immersed in solutions with different amounts of mercury (samples identified in the photograph of Figure 4 as samples 1 to 6). Once the RGB parameters of each sample had been obtained, the R and G components were grouped together in a single variable, performing a multivariant principal component analysis as shown in Table 2 for each of samples 1 to 6:

Table 2

The immersion of the films in solutions with different amounts of mercury gives rise to a variation in these principal components which is related to the increase in the amount of mercury, as can be graphically observed in Figure 4. The mercury detection limit reached was 1.3 ppb and the quantification limit was 2.2 ppb. The adjustment to a polynomial of order 2 of the relationship between log[Hg, ppb] and PC shown in the graph of Figure 4 is shown in Table 3*: Table 3

Example 5. Sensor-like behaviour of the sensor membrane in the presence of copper in water.

This example illustrates the colorimetric sensor-like behaviour of polymer material with structure (II), whose synthesis is illustrated in Example 3, in the presence of copper in an aqueous medium. The immersion of the membrane prepared in Example 3 in water buffered at pH=2 gave rise to a UV-visible spectrum band in the 550-750 nm range (Figure 5A). The addition of increasing amounts of copper (from 0.0635 mg/L to 63.5 mg/L) gave rise to the disappearance of this colour band as observed in Figure 5A. The graph of Figure 5B shows the relationship between the ppb of copper added and the intensity of the green colour at 650 nm, and the graph of Figure 5C shows the relationship between the logarithm of the ppb of copper added and the intensity of the green colour at 650 nm. The adjustment to a polynomial of order 2, giving rise to a detection limit of 1.4 ppb and a quantification limit of 3.0 ppb, as shown in Table 4*:

Table 4

'Detection limit 1.44 ppb/Quantifi cation limit 3.03 ppb

Similarly, various films were photographed after being immersed in solutions with different amounts of copper (samples identified in the photograph of Figure 6 as samples 1 to 8). Once the RGB parameters of each sample were obtained, the R and G components were grouped together in a single variable, performing a multivariant principal component analysis, as shown in Table 5 for each of samples 1 to 8: Table 5

The immersion of the films in solutions with different amounts of copper gives rise to a variation in these principal components which is related to the increase in the amount of copper, as can be graphically observed in Figure 6. The detection limit reached was 1.8 ppb and the quantification limit was 5.8 ppb. The adjustment to a polynomial of order 2 of the relationship between the logarithm of the ppb of copper added and the intensity of the green colour at 650 nm shown in the graph of Figure 6 is shown in Table 6*:

Table 6

Example 6. Sensor-like behaviour of the sensor membrane in the presence of nitrites in water.

This example illustrates the colorimetric sensor-like behaviour of polymer material synthesized in Example 3, in the presence of nitrites in an aqueous medium. The immersion of the membrane prepared in Example 3 in water buffered at pH=2 gave rise to a UV-visible spectrum band in the 550-750 nm range (Figure 7A). The addition of increasing amounts of copper (from 0.046 μg/L to 30.36 mg/L) gave rise to the disappearance of this colour band as observed in Figure 7A. The graph of Figure 7B shows the relationship between the ppb of nitrite added and the intensity of the green colour at 650 nm, and the graph of Figure 7C shows the relationship between the logarithm of the ppb of nitrite added and the intensity of the green colour at 650 nm. The adjustment to a polynomial of order 2, giving rise to a detection limit of 1.5 ppb and a quantification limit of 3.4 ppb, as shown in Tables 7(1 ) and 7(2) below: The adjustments were made separately for two different ranges of nitrite amount added marked in Figure 7C as (1 ), in Table 7(1 ) and (2) in Table 7(2):

Table 7(1 )

Table 7(2)

'Detection limit 1.49 ppb/Quantifi cation limit 3.38 ppb

Similarly, various films were photographed after being immersed in solutions with different amounts of nitrites (samples identified in the photograph of Figure 8 as samples 1 to 7). Once the RGB parameters of each sample were obtained, the R and G components were grouped together in a single variable, performing a multivariant principal component analysis, as shown in Table 8 for each of samples 1 to 7: Table 8

The immersion of the films in solutions with different amounts of nitrites gives rise to a variation in these principal components which is related to the increase in the amount of nitrites, as can be graphically observed in Figure 8. The detection limit reached was 2.8 ppb and the quantification limit was 23.2 ppb. The adjustment to a polynomial of order 2 of the relationship between log[N0 ₂ \ ppb] and PC shown in the graph of Figure 8 is shown in Table 9:

Table 9

^• Detection limit 2.82 ppb/Quantifi cation limit 23.18 ppb