Enzymatic Polymerization of Vinyl Polymers

Probably the first example reporting enzymatic polymerization of vinyl monomers was reported in 1951 by Parravano [1] on the oxidase-initiated polymerization of methyl methacrylate. However, it was only in the 1990s that this reaction type was further investigated. Ever since then, enzymatic polymerizations of vinyl monomers have been experiencing a steadily growing popularity [2-5]. Inspired by the very mild reaction conditions combined with the usually high selectivity, significant benefits of biocatalysis have also been assumed for polymer synthesis. 

It has been demonstrated that enzyme-catalyzed vinyl polymerizations enable significant control over polymer properties such as molecular weight, polydisper-sity and yield. Even though a convincing demonstration of enzyme-derived stereoselectivity is missing so far, this approach exhibits an enormous potential for environmentally benign and economically feasible production of tailored polymers. 

This chapter introduces the most predominant enzyme classes used for vinyl polymerization so far. An overview the current mechanistic understanding as well as selected practical examples are given. Complementary to the content of this chapter, detailed enumerations of polymer characteristics can be obtained from some excellent reviews [2-5]. 

Biocatalysis in Polymer Chemistry. Edited by Katja Loos 

Copyright 2011 WILEY-VCH Verlag GmbH Co. KGaA, Weinheim 

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In Chapter 6 the enzymatic polymerization of vinyl monomers is presented. Polymers, such as polystyrene and poly(meth)acrylates can be readily polymerized under catalysis of oxidoreductases like peroxidases, oxidases, etc. In addition oxidoreductases can be used to polymerize phenolic monomers (Chapter 7) and even to synthesize conducting polymers such as polyaniline (Chapter 8). 

Enzymes may be classified generally into six groups the details of typical polymers produced via catalysis with respective enzymes are listed in Table 23.1. In the past, the target macromolecules for enzymatic polymerization have included polysaccharides, poly(amino acid)s, polyesters, polycarbonates, phenolic polymers, poly(aniline)s, and vinyl polymers. In this chapter, attention is focused on the enzymatic synthesis of phenohc polymers and polyesters, based on the increasing industrial application of these materials. Notably, most such polymers can be obtained from commercially available, inexpensive monomers by using industrially produced enzymes. Another important point is that the enzymatic process must be regarded as an environmentally benign synthetic pathway. Details of the enzymatic synthesis of other polymers are provided in recent pertinent reviews [3-10]. 

Abstract The in vitro enzyme-mediated polymerization of vinyl monomers is reviewed with a scope covering enzymatic polymerization of vitamin C functionalized vinyl monomers, styrene, derivatives of styrene, acrylates, and acrylamide in water and water-miscible cosolvents. Vitamin C functionalized polymers were synthesized via a two-step biocatalytic approach where vitamin C was first regioselectively coupled to vinyl monomers and then subsequently polymerized. The analysis of this enzymatic cascade approach to functionalized vinyl polymers showed that the vitamin C in polymeric form retained its antioxidant property. Kinetic and mechanistic studies revealed that a ternary system (horseradish peroxidase, H2O2, initiator fS-diketone) was required for efficient polymerization and that the initiator controls the characteristics of the polymer. The main attributes of enzymatic approaches to vinyl polymerization when compared with more traditional synthetic approaches include facile ambient reaction environments of temperature and pressure, aqueous conditions, and direct control of selectivity to generate functionalized materials as described for the ascorbic acid modified polymers. 

Enzymes are generally classified into six groups. Table 1 shows typical polymers produced with catalysis by respective enzymes. The target macromolecules for the enzymatic polymerization have been polysaccharides, poly(amino acid)s, polyesters, polycarbonates, phenolic polymers, poly(aniline)s, vinyl polymers, etc. In the standpoint of potential industrial applications, this chapter deals with recent topics on enzymatic synthesis of polyesters and phenolic polymers by using enzymes as catalyst. 

Morphology of the enzymatically synthesized phenolic polymers was controlled under the selected reaction conditions. Monodisperse polymer particles in the sub-micron range were produced by HRP-catalyzed dispersion polymerization of phenol in 1,4-dioxane-phosphate buffer (3 2 v/v) using poly(vinyl methyl ether) as stabihzer. °° ° The particle size could be controlled by the stabilizer concentration and solvent composition. Thermal treatment of these particles afforded uniform carbon particles. The particles could be obtained from various phenol monomers such as m-cresol and p-phenylphenol. 

In the case of polyester synthesis from divinyl esters, hydrolysis of the vinyl end group partly took place, resulting in the limitation of the polymer growth.201 A mathematical model showing the kinetics of the polymerization predicts the product composition. On the basis of these data, a batch-stirred reactor was designed to minimize temperature and mass-transfer effects.202 The efficient enzymatic production of polyesters was achieved using this reactor poly(l,4-butylene adipate) with Mn 2 x 104 was synthesized in 1 h at 60 °C. 

PPL catalyzed the polymerization of methyl esters of 5-hydroxypentanoic and 6-hydroxyhexanoic acids.149 In the polymerization of the latter in hexane at 69 °C for more than 50 days, the polymer with DP up to 100 was formed. Relationships between solvent type and polymerization behaviors were systematically investigated hydrophobic solvents such as hydrocarbons and diisopropyl ether were suitable for the enzymatic production of high molecular weight polymer. Pseudomonas sp. lipase catalyzed the polymerization of ethyl esters of 3- and 4-hydroxybu-tyric acids, 5- and 6-hydroxyhexanoic acids, 5-hy-droxydodecanoic acid, and 15-hydroxypentadecanoic acid.157 Oxyacid vinyl esters were demonstrated as new monomers for polyester production under mild reaction conditions, yielding the corresponding polyesters with A/n of several thousands.276... 

N,N-dimethyl-p-phenylenediamine by the method of Bernthsen33 to give poly( -vinyl Methylene Blue), This polymer acts as a hydrogen acceptor in the enzymatic dehydrogenation of ethanol. The carbinol form (XVIl) of polymeric Malachite Green may be prepared by the. nucleophilic attack of poly(p-lithium styrene) on Michler s ketone 3 acidification gives the colored dye (XVIIl). 

During the lipase-catalyzed polymerization of divinyl esters and glycols, there was a competition between the enzymatic transesterification and hydrolysis of the vinyl end group, resulting in the limitation of polymer... 

In this chapter, the focus is on in vitro enzyme catalysis for vinyl polymerization. To the best of our knowledge, prior to the work of Derango et al. (1992) there is a single short report showing the formation of low molecular weight vinyl polymers when studied in a suspension of Escherichia coli in the presence of methyl methacrylate [15,16]. Unhke polyaromatics, vinyl polymerization offers better control of polymer characteristics, as has been demonstrated with ternary systems (enzyme, oxidant, and initiator such as b-diketone). The number of different vinyl monomer chemistries investigated for susceptibility toward enzymatic polymerization (1-12) is fewer than reported aromatics, as is the extent of literature covering these types of syntheses. In addition, the discovery of multienzymatic approaches for the synthesis of antioxidant-functionalized vinyl polymers provides new impetus for the use of enzymatic methods related to vinyl polymers. 

Enzymatic polymerization has emerged in the last few decades as a field of considerable interest and commercial promises. It proceeds with high regio-, enantio-, and chemos-electivity under relatively mild conditions. So far, enzymes have been used to synthesize polyesters, polysaccharides, polycarbonates, polyphenols, polyanilines, vinyl polymers, and poly(amino acid)s. Namely, the lipase B of Candida antarctica (Cal-B, a serine hydrolase) immobilized on polyacrylic resin (Novozyme 435) has proven to be a very versatile catalyst in terms of reaction conditions and acceptance of various substrates. For example, this enzyme has been successfully used to synthesize polyesters. ° However, little has been reported so far on the synthesis of polyamides catalyzed by enzymes. " ... 

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