Vinylimidazole-acrylic acid

So far, many kinds of nucleophiles active for hydrolysis such as imidazolyl-, amino-, pyridino-, carboxyl- and thiol-groups, have been used for preparation of hydrolase models. Overberger et al.108,1091 prepared copolymers of vinylimidazole and acrylic acid 60 (PVIm AA), by which the cationic substrate, 61 (ANTI), was hydrolyzed. This kind of copolymer is considered to be a model of acetylcholinesterase. With ANTI, the rate of the copolymer catalysis was higher than that of imidazole itself in the higher values of pH, as is seen in Table 9. In this work, important contributions of the electrostatic interactions are clear. The activity of the copolymer was not as high with the negatively charged and neutral substrates. 

A large number of macromolecules possess a pronounced amphiphilicity in every repeat unit. Typical examples are synthetic polymers like poly(l-vinylimidazole), poly(JV-isopropylacrylamide), poly(2-ethyl acrylic acid), poly(styrene sulfonate), poly(4-vinylpyridine), methylcellulose, etc. Some of them are shown in Fig. 23. In each repeat unit of such polymers there are hydrophilic (polar) and hydrophobic (nonpolar) atomic groups, which have different affinity to water or other polar solvents. Also, many of the important biopolymers (proteins, polysaccharides, phospholipids) are typical amphiphiles. Moreover, among the synthetic polymers, polyamphiphiles are very close to biological macromolecules in nature and behavior. In principle, they may provide useful analogs of proteins and are important for modeling some fundamental properties and sophisticated functions of biopolymers such as protein folding and enzymatic activity. 

Fig. 23 Examples of amphiphilic polymers a poly(l-vinylimidazole), b poly(AT-isopropyl acrylamide), and c poly(2-ethyl acrylic acid)...

IM-COOH-OH cooperation. Polymers such as poly(4(5)-vinylimidazole-co-7-vinyl-7-butyrolactone), poly(IM-la), and poly(4(5)-vinylimidazole-co-acrylic acid-covinyl alcohol) derived from poly(4(5)-vinylimidazole-co-methyl acrylate-co-vinyl acetate), both of which contain imidazole, carboxylic acid and hydroxyl moieties are synthesized and studied as a model of a-chymotrypsin (29). The former has a relatively ordered sequence and the latter has a random one. Results are tabulated in Table 11. The polymers cited in the Tabel contain a similarly low quantity of imidazole moiety, so that the cooperation of two subsequent imidazole moieties need not be discussed. Polymers such as L-84, L-68, M-83 and A-84 have higher catalytic activities than the polymer V-82. This suggests that the catalytic activity of the imidazole moiety in the polymers is much promoted by the carboxylate moiety in the polymers. The catalytic activities of L-84 and L-68 which have an ordered sequence are more than twice as high as that of M-83, having a random sequence. From these results it is concluded that the introduction of the hydroxyl moiety which has little cooperative effect on the imidazole moiety in V-82 in this reaction conrfition into imidazole and carboxylate — containing polymer, increases... 

A clear-cut molecular relay system is materialized with the combination of two nucleophile moieties such as hydroxamic acid and imidazole introduced in a polymer (38, 40, 82). Hydroxamate anion has a high nucleophilicity but deacylation of the acylhydroxamate is very slow. The significance of the deacylation step in the hydrolysis in polymer catalyst is pointed out in several works, for example, the deacylation of acetylated poly(4(5)-vinylimidazole) (83,84) and the aminolysis of nitrophenyl ester of poly(styrene-co-acrylic acid) (85—87). To promote the deacylation velosity of the acylated hydroxamic acid imidazole moiety is introduced in the hydroxamic acid-containing polymer. The polymers are shown in tire following page. 

The significance of the coulombic field is observed (79). Figure 9 shows the catalytic activities of poly(4(5)-vinylimidazole-co-acrylic acid), poly(IM-ac), and low molecular weight imidazole derivatives in hydrolyses of various substituted phenyl acetates of which leaving groups have different activities. 

The copolymerization of different functional monomers during precipitation polymerization can be used for design of amphoteric aqueous microgels [76-82], Amphoteric microgels were prepared by copolymerization of NIPAAm with acrylic acid and vinylimidazole (Vim) [76-80], Alternatively, Tan and coworkers prepared amphoteric colloids by copolymerization of acrylic acid, 2-(diethylamino)ethyl... 

The electrostatic attraction would be used more effectively by employing carboxylic acid groups whidi completely dissociate under most solvolytic conditions. Cr olymers of vinylimidazole and acrylic acid (VIm-AAc, 34) were first prepared by the Overberger group (80,81). This polymer catalyst diows a substrate... 

It has been attempted to perform template polymer syntheses without using biological sources. Concepts focus on the formation of a complex between monomer molecules and a present macromolecule [4,480], This way the monomer will get preorganized and the polymerization is supposed to follow a zip mechanism controlled by the length and the configuration of the template polymer, offering replication of the molecular weight and control of the stereo structure. Polymerization of acrylic acid in the presence of poly(ethyleneimine), N-vinylimidazole/ poly(methacrylic acid) or acrylonitrile with poly(vinylacetate) have been described [469,470,471,472,473]. Recently the preparation of solid polyelectrolyte complexes from chitosan and sodium-styrenesulfonate has been reported [481]. 

The same technique can be used to dye a material that is otherwise difficult to dye. An ethylene-propylene copolymer rubber was reacted first with maleic anhydride, then with an aromatic amine dye in an extruder to produce a dyed rubber.81 Dye sites can also be inserted into polyolefins by grafting them with dimethylaminoethyl methacrylate, using azo or peroxide catalysts in an extruder.82 jV-Vinylimidazole has been grafted to polyethylene in an extruder with the help of dicumylperoxide.83 The product was mixed with an acrylic acid-modified polypropylene and used to compatibilize polyethylene and polypropylene. This could be helpful in the recycling of mixed polyolefins from municipal solid waste. Recycling of cross-linked (thermoset) polymers is more of a problem because they cannot be remelted in an extruder. However, they can be if... 

The nature of the interaction between the monomer and the template is more obvious in cases where specific ionic or hydrogen bonding is possible. For example, A-vinylimidazole has been polymerized along a PMAA template" " " and acrylic acid has been polymerized on a A -vinylpyrrolidone template." The daughter PAA had a similar degree of polymerization to the template and had a greater fraction of isotaclic triads than PAA formed in the absence of the template. 

Letsinger and Klaus investigated the solvolysis of poly(acrylic acid-co-2,4-dinitro-phenyl p-vinylbenzoate) 9 catalyzed by partly protonated poly(N-vinylimidazole) 4 (57). The poly(N-vinylinudazole) showed a sufficient activity at the imidazole unit concentration much lower than that of N-methylimidazole 11 (Table 4—1), and the rate attained a limiting value at high catalyst concentrations. The rate saturation was... 

SSlimidzu et al. 83) also studied the c ytic solvolysis by copolymers of vinylimidazole and acrylic acid. The Michaelis-Menten type behavior was observed for the solvolysis of ANTI 32 but not for that of PNPA 3 in 100% aqueous systems, in contrast to the second-order kinetic behavior in 28.5% ethanol-water as reported by Overberger et al. 80). Substrate binding as given by 1/Am fias maximal at 25 to 30 mol% imidazole content, and the intracomplex rate for the neutral imidazole unit was minimal at 20 to 30 mol% imidazole contents. The resulting overall efficiency simply decreased with increasing imidazole contents. 

Note PAC, poly(acrylic acid) PVAI, poly(vinyl alcohol) PMAAc, poly(methacrylic acid) PVIA, poly(A-vinylimidazol) PVPy, poly(4-vinylpyridine). coordination number (CN) = 4. 

Compatibilized blends of ethylene-methacrylic acid copolymer and PS were prepared by Kim et al. (1998) through addition of S-co-4-vinylpyridine. Similarly, blends of poly(isobutyl methacrylate) were compatibilized with poly(styrene-co-methacrylic acid) using poly(isobutyl methacrylate-co-2-(A, A -dimethylamino) ethyl methacrylate) or poly(isobutyl methacrylate-co-4-vinylpyridine) (Habi and Djadoun 1999). Turcsayii (1995) has reported compatibilized blends of PE-g-(N-vinylimidazole) with acrylic acid-modified PP. 

The copolymer of A -vinylimidazole and acrylic acid has been found to be an effective esterolytic catalyst for the hydrolysis of p-nitrophenyl acetate (Letsinger and Klaus, 1964 Shimidzu et al., 1974). The carboxyl groups in this polymer can bind a positively charged substrate, e.g. (3). Thus, the catalytic esterolytic activity of such a polymer for the positively charged 3, the neutral 4 and the negatively charged 5 is in the order ... 

Perhaps a more dramatic indication of a bifunctional participation is in the solvolysis of a positively charged substrate, 3-acetoxy-N-trimethyl-anilinium iodide (ANTI), by poly(vinylimidazole)-co-poly(acrylic acid). 

The cooperative interaction between imidazole and carboxylic groups was also investigated by Overberger and his collaborators. They looked at the solvolysis of 3-acetoxy-A -trimethylanilinium iodide (ANTI) catalyzed by a polymer of 4(5)-vinylimidazole and acrylic acid (see Figure 3). More recently, Overberger et al [16] have investigated the effect of copolymers containing imidazole and mercaptan functions upon ester hydrolysis. 

Shimidzu etal.111 studied the catalytic activity of poly (4(5)-vinylimidazole-co-acrylic add) 60 (PVIm AA) in hydrolyses of 3-acetoxy-N-trimethylanilinium iodide 61 (ANTI) and p-nitrophenylacetate 44 (PNPA). The hydrolyses of ANTI followed the Michaelis-Menten-type kinetics, and that of PNPA followed the second-order kinetics. Substrate-binding with the copolymer was strongest at an imidazole content of 30 mol%. The authors concluded that the carboxylic acid moiety not... 

In these equations I is the initiator and I- is the radical intermediate, M is a vinyl monomer, I—M- is an initial monomer radical, I—MnM- is a propagating polymer radical, and and M7 are polymer end groups that result from termination by disproportionation. Common vinyl monomers that can be homo-or copolymerized by radical initiation include ethylene, butadiene, styrene, vinyl chloride, vinyl acetate, acrylic and methacrylic acid esters, acrylonitrile, IV-vinylimidazole, IV-vinyl-2-pyrrolidinone, and others (2). 

Among the most frequently used monomers we can mention carboxylic acids (e.g. acrylic, methacrylic and vinyl benzoic acids), sulfonic acids and heterocyclic bases (e.g. vinylpyridines, vinylimidazoles). 

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