Polyesters with functional groups on side chains are attractive in biomedical applications since they can be conjugated with functional molecules. Many researches have been conducted aiming to synthesize functional polyesters, but linear polyesters containing a high number of amino groups have not been much reported. In this study, poly(propane adipate–co-2-aminopropane adipate) was synthesized by enzymatic polymerization of divinyl adipate, 1,3-propanediol, and N-protected 2-amino-1,3-propanediol, with subsequent hydrogenolysis deprotection (Fig). The mild reaction conditions and the specificity of the enzymatic polymerization could reduce side reactions, and the protecting groups of monomers prevented the polymer branching from the amino groups. The feed ratio of N-protected monomers ranged from 0 to 75 mol%, and the composition of the N-protected copolymers was calculated through 1H NMR analysis. The incorporation rate of the N-protected monomer to the copolymers was only a few percent lower than the feed ratio. From the GPC analysis, it was found that the molecular weight of the N-protected copolymers gradually decreased from 7.2 to 3.8 kg/mol as the N-protected monomer content increased. The results indicated the reactivity of N-protected monomers was lower than that of plain monomers. After the deprotection, thermal analyses of poly(propane adipate-co-2-aminopropane adipate) were conducted by DSC. All copolymers were found to be amorphous, and the glass transition temperature gradually increased with the increase in the 2-aminopropane adipate content, reaching -12.4°C at the 2-aminopropane adipate content of 75 mol%. These results indicated that the enzyme-catalyzed polymerization of protected monomers could become a prospective candidate for liner polyesters with abounding amino groups.

Enzyme-catalyzed polymerization of linear polyesters bearing amino groups from protected monomers

ACS Spring 2022

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