Enzymatic Template Polymerization of Phenol in the Presence of Water-soluble Polymers in an Aqueous Medium

Abstract

ABSTRACT:The enzymatic polymerization of phenol was investigated by using water-soluble polymers (WSPs) as template in an aqueous medium. The addition of PEG, one of WSPs, produced a miscible complex of polyphenol and PEG as precipitates in high yields. CD measurement verified the formation of a phenol-PEG complex by hydrogen bonding interaction. The presence of PEG in an aqueous medium greatly improved the regioselectivity of the polymerization, yielding a polyphenol with the phenylene unit content higher than 90%. The amount of PEG strongly affected the polyphenol yield. The unit molar ratio of polyphenol and PEG was ca. 1:1. The FT IR, DSC, and XRD analyses exhibited the formation of the miscible complex of polyphenol and PEG by hydrogen bonding interaction. [DOI 10.1295/polymj.36.992] KEY WORDS Enzymatic Polymerization / Poly(ethylene glycol) / Polyphenol / Regioselectivity / Template Polymerization / Water-soluble Polymer / Polymerization of a monomer in the presence of a preformed macromolecule is usually defined as template polymerization.1 The presence of the template can influence the polymerization rate of the monomer with respect to the blank polymerization and also properties of the final product such as molecular weight and stereoregularity. Template polymerization leads to formation of polymer-polymer complexes stabilized via noncovalent binding forces like electrostatic interactions, hydrogen bonds, hydrophobic interactions, and stereocomplexation.2 It is accepted that template polymerization proceeds according to two different mechanisms, zip and pick-up mechanisms. 1 Usually, when the monomers are connected with the template by strong forces such as hydrogen and electrostatic bonds, the polymerization starts through a zip mechanism.1,2 However, strict control of the free radical polymerization by using the template has not successfully been achieved even in the case of a linear template polymer with a narrow molecular weight distribution. This is probably because the free radical polymerization is randomly initiated in the template.Recently, enzymatic syntheses of phenolic polymers have received much attention as an alternative process for preparing conventional phenolic resins without the use of toxic formaldehyde, a monomer for production of conventional phenolic resins (phenol-formaldehyde resins).3 So far, a new class of useful and high-performance polyphenols have been prepared by utilizing characteristic catalysis of enzymes, most of which can not be obtained by conventional chemical methods. 4 In the enzymatic oxidative polymerization of phenol derivatives, however, control of the coupling selectivity (regioselectivity) is often very difficult, since the reaction proceeds via coupling of free radical intermediates. From phenol, the simplest and most important phenolic compound in industrial fields, a soluble polyphenol consisting of a mixture of phenylene and oxyphenylene units was synthesized in a mixture of methanol and phosphate buffer (Scheme 1). 5 The regioselectivity depended on ...

Enzyme Initiated Radical Polymerizations

“…Templated polymerization of phenols can be achieved also using uncharged templates such as poly(ethylene glycol) and others [88][89][90][91][92]. Probably due to H-bond-mediated phenol-template interactions, a certain degree of regioselectivity favoring phenylene connections over oxyphenylenes was observed [89][90][91] Interestingly, using carbon nanotubes as polymerization templates, Liu and coworkers observed oxyphenylene selectivity in the polymerization of phenol [93].…”

Enzyme-catalyzed chemical structure-controlling template polymerization

“…It was observed by NMR measurements that increased amounts of phenylene units as compared to oxyphenylene units formed in the polyphenol product if the reaction was carried out under optimal reaction conditions in the presence of the templates, indicating template-induced regioselectivity. 97,98,101 In the case of PEG and PEGMDE, it was proposed that interactions of phenol with the template (possibly via H-bonds) led to the observed regioselectivity in the polymerization reaction, see Fig. 11.…”

Hydrophobic Polymers from Food Waste: Resources and Synthesis

“…Several studies are based on the enzymatic oxidative polymerization of phenol using horseradish peroxide [227][228][229][230] as catalyst. One example is Oguchi's work 227 which focuses on the study of the polyphenol solubility, composition, and molecular weight and the effects of modifying the reaction conditions.…”