Catalytic Synthesis and Characterization of Biodegradable ...

Chapter 1
hence, the CO2 content of the copolymer provided by this method was generally about 90%
even though the reactions were carried out at high CO2 pressures. 18 The copolymerization
processes were performed in the absence of an organic solvent at 55 bar CO2 pressure and 80
. Bulk polymerization reactions were run over a 24 h period, providing minimum values of
TOFs of about 10 h -1 with catalytic activity varying slightly as a function of the substituents
on the phenoxide ligands. Although the coupling reaction of propylene oxide and CO2
provided predominantly propylene carbonate at 80 , at 40 , the reaction selectivity
switched mainly to copolymer formation. This temperature dependence of product selectivity
is a general phenomenon observed for most catalyst systems investigated. Terpolymers with
up to 20% propylene oxide content were produced from reaction mixtures of propylene
oxide/cyclohexene oxide and carbon dioxide. More moisture-tolerant dimeric zinc derivatives
(Figure 1.2.4) containing the less sterically encumbering 2,6-difluorophenoxide were also
shown to be quite active for the copolymerization process. 19
Figure 1.2.3 Monomeric zinc-bis(phenoxide) complex for the copolymerization of cyclohexene
oxide and CO2. The phenoxide ligand is 2,6-diisopropylphenoxide.
Figure 1.2.4 Dimeric zinc-bis(phenoxide) complex for the copolymerization of cyclohexene
oxide and CO2. The phenoxide ligand is 2,6-difluorophenoxide.
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