Graft polymerization of p-dioxanone onto polyhydroxyethylaspartamide through ring-opening polymerization using organometallic and enzyme catalysts

Abstract

The grafting of poly(p-dioxanaone) (PPDO) onto β-poly(N-2-hydroxyethyl)-DL-aspartamide (PHEA) was achieved, first, by synthesis of polysuccinimide (PSI) from DL-aspartic acid through thermal condensation polymerization, and then, followed by aminolysis of PSI to form PHEA with hydroxyl end groups, and finally the PPDO was grafted onto PHEA through these hydroxyl end groups by ring-opening polymerization (ROP) of PDO in the presence of tin octoate [Sn(Oct)2] and Candida Antarctica Lipase B (Novozyme 435) catalysts. Evidence of grafting was obtained by comparing Fourier transform infrared spectroscopy (FT-IR), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), X-ray diffraction (XRD) analysis, polarized optical microscopy (POM), proton nuclear magnetic resonance (1H–NMR) spectroscopy, and solubility characteristics of PHEA with PPDO-grafted copolymers (PHEA-g-PPDO). The FT-IR spectroscopic analysis reveals the formation of ester linkage between PPDO and hydroxyl end groups of PHEA. TGA analysis shows a quite different thermal profile for grafted polymers. DSC and XRD results reveal the existence of graft copolymer in two different crystalline forms. POM shows banded spherulitic morphology for the graft copolymers. The grafting of PPDO was further confirmed by 1H–NMR. Eventhough, graft copolymer was obtained by both these methods, the graft copolymer obtained by enzyme catalyzed ROP shows higher crystalline order, better spherulitic morphology, and solubility characteristics than that of the graft polymer obtained by organometal catalyzed ROP.