Synthesis and physical characterization of poly(cyclohexane carbonate), synthesized from CO2 and cyclohexene oxide
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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 Mw = 252 kg/mol. The recorded Tg was 115C, which is in excellent agreement with the reported value of 116C. 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 -transition around - 110C, the presence of which has been related to toughness. The magnitude of this -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. 2001 Elsevier Science Ltd.