Synthesis and physical characterization of poly(cyclohexane carbonate), synthesized from CO2 and cyclohexene oxide

Using [Zn(2,6-difluorophenoxide)2]2 (THF)2 as the catalyst, poly(cyclohexane carbonate) (PCHC) was synthesized from CO2 and cyclohexene oxide. The ether content of the polymer was limited to a few mol%. The molecular weight distribution of the linear polycarbonate was broad, with Mn=42 and M w =252 kg/mol. The recorded Tg was 115°C, which is in excellent agreement with the reported value of 116°C. In spite of its high molar mass, PCHC behaves like a brittle polymer, with an elongation at break of 1–2%. On the other hand, the tensile modulus of PCHC (3600 MPa) is much higher than the corresponding value for bisphenol-A polycarbonate (BP-A PC) (2400 MPa). Like the extremely tough BP-A PC, the PCHC exhibits a γ-transition around −110°C, the presence of which has been related to toughness. The magnitude of this γ-transition is lower than the corresponding value for BP-A PC, which indicates that the main chain of PCHC is less flexible than that of BP-A PC. Moreover, the low temperature relaxation of PCHC is probably related to chair–chair transitions of the cyclohexane side group. The brittle behavior of PCHC is expected from the relatively low plateau modulus of PCHC in the melt, from which a relatively high average molecular weight between entanglements (Me) of ca. 15,000 g/mole was estimated, which is in the same order of magnitude as the Me of the brittle polystyrene.