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 M-n = 42 and M-w = 252 kg/mol. The recorded T-g was 115 degreesC, which is in excellent agreement with the reported value of 116 degreesC. 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 gamma -transition around -110 degreesC, the presence of which has been related to toughness. The magnitude of this gamma -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 (M-e) of ca. 15,000 g/mole was estimated, which is in the same order of magnitude as the M-e of the brittle polystyrene. (C) 2001 Elsevier Science Ltd. All rights reserved.