Thermal properties and rheological behavior of biodegradable aliphatic polycarbonate derived from carbon dioxide and propylene oxide

Alternating poly(propylene carbonate)s (PPCs) were synthesized from carbon dioxide and propylene oxide on a relatively larger scale. The thermal properties of the alternating PPC copolymers, with various molecular weights, were investigated with modulated differential scanning calorimetry (MDSC) and thermogravimetric analysis (TGA). The melt-flow indices of the as-made PPCs were determined in a melt-flow indexer, and the rheological properties of the PPCs were studied with a capillary rheometer. The MDSC and TGA results showed that the glass-transition temperatures of the PPCs increased with increasing molecular weight. The rheological measurements revealed that the PPCs exhibited pseudoplastic flow behavior in the melt. The molecular weight played a key role in the rheological behavior of the PPCs. Moreover, the PPCs with high molecular weights were more sensitive to the temperature and shear rate than those with low molecular weights. The melt viscosity of the PPCs with low molecular weights decreased dramatically with increasing temperature. The flow activation energy of such PPCs diminished with an increase in the shear rate, whereas the flow activation energy of the PPCs with high molecular weights remained nearly unchanged. © 2004 Wiley Periodicals, Inc.