Synthesis of four- and six-armed star-shaped polycarbonates by immortal alternating copolymerization of CO2 and propylene oxide

Abstract

A series of four- and six-armed star-shaped poly(propylene carbonate)s (PPCs) have successfully been synthesized by carbon dioxide (CO₂)–propylene oxide (PO) immortal alternating copolymerization initiated either from tetra- or hexa-functional carboxylic acids. The copolymerization afforded star PPCs with a controlled molecular weight and molecular weight distribution irrespective of the chemical structure and the number of initiating points in carboxylic acids. The synthesized star PPCs showed apparent molecular weight (M_w(RI)) lower than the absolute molecular weight (M_w(RALLS)), indicating a highly shrunk form of the whole polymer chain compared to those of linear analogues. A comparison of the thermal properties of these star PPCs revealed a lower glass transition temperature (T_g) of a six-armed star PPC than those of four-armed star or linear PPCs.