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

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.

开环聚合与开环共聚（尤其是单体混合体系下）过程中的可控性与选择性是极具研究价值的课题，该过程可实现多嵌段共聚酯/碳酸酯的便捷一锅法制备。本研究采用原位红外光谱与密度泛函理论（DFT）相结合的方法，针对以环氧环己烷、邻苯二甲酸酐、二氧化碳与ε-己内酯中三种单体按不同组合配成的混合体系进行聚合的实验与理论研究展开报道。本研究选用的催化剂为均相二锌配合物，其合成方法此前已由Kember等人报道（Angew. Chem. Int. Ed. 2009, 931-933）。通过调整单体的不同组合，该催化剂可展现出优异的选择性以制备嵌段共聚物。单体的反应活性顺序为：酸酐＞二氧化碳＞ε-己内酯。据此，环氧烷烃、酸酐与二氧化碳的混合体系可生成嵌段聚（酯碳酸酯）；内酯、环氧烷烃与二氧化碳的混合体系则得到嵌段聚（碳酸酯酯），而内酯、环氧烷烃与酸酐的混合体系可生成嵌段共聚酯。各聚合体系均通过实验与DFT理论两种方式进行了表征；理论研究表明，热力学参数可能是观测到的选择性的成因之一，包括单体插入锌-烷氧键的相对能垒，以及插入后形成的连接键的相对稳定性。