Functional polymers conjugated with functional molecules through the side chains have been widely expected to be used as biomedical materials. Biodegradability is also very important when the polymers are used for temporary implants, since removal surgeries can be avoided. As for the development of a biodegradable functional polymer, we attempted to produce a new polyester bearing amino groups on its side chains. First, N-protected copolymers were synthesized by transesterification of divinyl adipate, 1,3-propanediol, and N-protected 2-amino-1,3-propanediol using a lipase catalyst. The protecting groups of monomers efficiently prevented the formation of polyamide, while the specificity of the enzymatic polymerization reduced the side reactions. The feed ratio of N-protected monomers ranged from 0 to 75 mol%. The chemical characterization of the N-protected copolymers was conducted by 1H NMR. The initial feeds of 25, 50, 75 mol% of N-protected monomers led to the actual incorporation rates of 24.5, 49.5, 74.7 mol%, respectively in the synthesized copolymers, calculated from the phenyl-ring protons at 7.20-7.44 ppm and the methylene protons at 2.24 ppm (Fig.(A)). Next, the deprotection of the protected copolymers was conducted. The deprotection was experimentally confirmed by the disappearance of the peak from the phenyl-ring protons and the appearance of the peak at 8.25-8.74 ppm, corresponding to the amino groups (Fig.(B)). Thermal analysis was carried out by DSC. It was revealed that the synthesized copolymers bearing amino groups were amorphous with only one glass transition temperature (Tg) in each sample. In addition, Tg of the copolymer gradually increased with the increase in the content ratio of the amino group. These results indicated that the resulting copolymers are randomly copolymerized and that the molecular mobility was suppressed due to the amino groups.

Synthesis of poly(propane adipate–co-2-aminopropane adipate) via enzyme-catalyzed polymerization of N-protected monomers

ACS Spring 2022

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