Figure 10. Chemo-Selective Polymerizations Using Mixtures of Epoxide, Lactone, Anhydride and CO2. Figure 13.

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.

在开环聚合（ring-opening polymerization）与开环共聚（ring-opening copolymerization）反应（尤其是单体混合投料的场景下）实现的反应调控与选择性控制，是一项极具研究价值的课题：该策略可通过一锅法便捷制备多嵌段共聚酯/碳酸酯。本研究通过原位红外光谱（in situ infra-red spectroscopy）与密度泛函理论（Density Functional Theory, DFT）相结合的实验与理论手段，针对以环氧环己烷（cyclohexene oxide）、邻苯二甲酸酐（phthalic anhydride）、二氧化碳与ε-己内酯（ε-caprolactone）中任意三种单体按不同组合混合投料的聚合反应展开系统探究。所选用的催化剂为均相二锌配合物（homogeneous di-zinc complex），其合成方法此前已由Kember等人报道（Angew. Chem. Int. Ed. 2009, 931-933）。针对不同的单体组合，该催化剂均表现出优异的选择性，可精准制备嵌段共聚物。单体的反应活性顺序为：酸酐＞二氧化碳＞ε-己内酯。由此，环氧单体、酸酐与二氧化碳的混合体系可生成嵌段聚(酯-碳酸酯)；内酯、环氧单体与二氧化碳的混合体系可得到嵌段聚(碳酸酯-酯)；而内酯、环氧单体与酸酐的混合体系则仅生成嵌段共聚酯。所有聚合体系均通过实验与密度泛函理论两种手段进行表征分析；理论研究表明，观测到的选择性可由多项热力学参数解释，包括单体插入锌-烷氧键的相对能垒，以及插入反应所形成键合结构的相对稳定性。