Oxirane/carbon dioxide copolymerisation

Studies of the regioselectivity of oxirane/carbon dioxide copolymerisation showed the polar effect exerted by the ring substituent, but not the bulkiness, to be the factor determining the direction of ring opening [231,232]. In the case of propylene oxide/carbon dioxide copolymerisation, C g—O bond cleavage... 

A concerted mechanism of oxirane/carbon dioxide copolymerisation with catalysts formed in diethylzinc-dihydric phenol systems and related systems has been proposed [76,206,207], According to this mechanism, the oxirane coordination and enchainment occur as shown by the following scheme ... 

At the end of considerations dealing with oxirane/carbon dioxide copolymerisation, copolymerisation run under supercritical conditions in carbon dioxide as the reaction medium should be mentioned [239]. 

As regards oxirane/carbon dioxide copolymerisation with (dmca) A1C1, it yields low molecular weight propylene oxide/carbon dioxide copolymers with a prevailing content of ether linkages as well as cyclohexene oxide/carbon dioxide copolymers of predominantly carbonate linkages. 

Although propylene oxide has been the oxirane most widely studied in copolymerisation with carbon dioxide, there are a variety of other oxiranes capable of coordination copolymerisation with carbon dioxide (Table 9.4). 

Copolymerisation of propylene oxide as well as other oxiranes with carbon dioxide in the presence of zinc-based coordination catalysts is generally accompanied with the formation of a cyclic five-membered carbonate, propylene carbonate or another alkylene carbonate [147,206,207,210,212,230]. The alky-lene carbonate, however, is not the precursor for poly(alkylene carbonate), since it hardly undergoes a polymerisation under the given conditions [142-146],... 

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