Figure 11. Chemo-Selective Polymerizations Using Mixtures of Epoxide, Lactone, Anhydride and CO2

<p>The control and selectivity exerted during ring-opening and ring-opening copolymerizations polymerizations, particularly using mixtures of monomers, is an important topic as it allows multi-block copolyesters/carbonates to be easily prepared in one-pot. Experimental and theoretical studies, using in situ infra-red spectroscopy and DFT, are presented for polymerizations conducted using mixtures of three different monomers selected in different combinations from cyclohexene oxide, phthalic anhydride, carbon dioxide and e-caprolactone. The catalyst selected is a homogeneous di-zinc complex, the synthesis of which was previously reported by Kember et al. (Angew. Chem. Int. Ed. 2009, 931-933). Using various combinations of monomers, the catalyst exerts a high selectivity to produce block copolymers. The monomers react in the order: anhydride>carbon dioxide>e-caprolactone. Thus, mixtures of epoxide, anhydride and carbon dioxide result in the formation of block copoly(ester carbonates); mixtures of lactone, epoxide and carbon dioxide result in block copoly(carbonate esters), whilst lactone, epoxide and anhydride mixtures result in block copolyester formation. Each system is examined both experimentally and via DFT; the theoretical study suggests that there are thermodynamic parameters which may contribute to the observed selectivities, including the relative barriers to monomer insertions into zinc-alkoxide bonds and the relative stabilities of the linkages formed from insertion.</p>