Material Properties of Poly(Propylene Carbonates)

Abstract

Abstract The material properties of poly(propylene carbonate) (PPC) are discussed with respect to thermal features, viscoelastic and mechanical properties, processability, characteristics in solution, biodegradability, and biocompatibility. Thermal decomposition proceeds in two steps: (1) backbiting at temperatures as low as 150°C in the presence of catalyst residues, giving cyclic propylene carbonate; and (2) chain scission at temperatures over 200°C with possible involvement of initial hydrolysis. PPC shows one thermal transition at a glass temperature of around 40°C. PPC is a pseudoplastic material, and a master curve constructed for frequency-dependent viscosity shows no real plateau for material of number-average molecular weight (Mn) < 50 kDa. At temperatures in the range of the glass transition, the apparent activation energy for flow changes rapidly from 500 kJ/mol to about 40 kJ/mol. The viscosity of PPC has an activation energy in the range of 5–25 kJ/mol (Mn < 50 kDa). The modulus of elasticity (around 800 MPa) and yield strength (10–20 MPa) are reminiscent of low-density polyethylene. PPC has a large elongation at break, and may be useful for the preparation of composites and blends. Biodegradation of PPC is dominated by hydrolysis, which can be accelerated by Lewis acid catalyst residues. Biocompatibility is excellent in the sense that it does not induce an inflammatory reaction in tissue.