Selective synthesis of structurally isomeric poly‐β‐ester and poly‐δ‐ester from β‐(2‐acetoxy‐ethyl)‐β‐propiolactone with Al and Zn catalysts

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Abstract
It was found that structurally isomeric polymers were formed by the ring‐opening polymerization of β‐(2‐acetoxy ethyl)‐β‐propiolactone with (EtAlO)n and Et(ZnO)2ZnEt catalysts; that is, the Al catalyst catalyzed normal polymerization which led to poly‐β‐ester and the Zn catalyst formed isomerized poly‐β‐ester as the main product. The polymer structure was determined by nuclear magnetic resonance (NMR), T1‐value, thermal decomposition product, and (Tg). The NMR studies for the monomer–catalyst systems indicated that the Al catalyst interacted predominately with the lactone group, whereas the Zn catalyst interacted with the side‐chain ester group. These site‐selective interactions could be related to the difference in the stereoregulation by the two catalysts during the poly(β‐ester)‐forming polymerization process.