Enzymatic synthesis, thermal and crystalline properties of a poly(β–amino ester) and poly(lactone-co-β–amino ester) copolymers

Ethyl 3-(4-(hydroxymethyl)piperidin-1-yl)propanoate (EHMPP) was prepared in quantitative yield under mild conditions via Michael addition reaction of 4-piperidinemethanol with ethyl acrylate. EHMPP underwent condensation polymerization in the presence of a lipase catalyst (CALB) to form poly[3-(4-(methylene)piperidin-1-yl)propanoate] (poly(MPP) or PMPP). Ring-opening and condensation copolymerization of EHMPP with ω-pentadecalactone (PDL) led to the synthesis of novel poly(PDL-co-MPP) copolymers, whose compositions were readily controlled by varying the monomer feed ratio. NMR analyses, including statistical analysis on repeating unit sequence distribution, indicate that the copolymers are totally random polymers. TGA analysis revealed that the degradation temperature of PMPP is approximately 160 °C lower than that of PPDL and that all poly(PDL-co-MPP) copolymers degrade in two well defined weight loss steps attributable to thermal degradation of MPP and PDL unit fractions in the polymers. The crystallinity of the polymers was studied by DSC analysis. Although PMPP and the copolymers rich in MPP units do not easily crystallize upon cooling from melt, the homopolymer and all copolymers obtained via precipitation from solution are semi-crystalline materials. WAXS analysis showed that the copolymers rich in PDL (≥51 mol%) crystallize in PPDL lattice and those with ≤21 mol% PDL content develop PMPP-type crystals while in the copolymer with 36 mol% PDL, PMPP-type and PPDL-type crystals co-exist. PMPP and poly(PDL-co-MPP) represent a new type of biodegradable poly(β–amino esters) that are potentially useful biomaterials for specific biomedical applications (e.g., gene delivery).