Polymerization of Lactides and Lactones, 8. Study on the Ring‐Opening Polymerization of 3‐Phenyl‐ε‐caprolactone and 5‐Phenyl‐ε‐caprolactone

Ring‐opening polymerization of 3‐phenyl‐ε‐caprolactone (3‐ph‐CL) and 5‐phenyl‐ε‐caprolactone (5‐ph‐CL) by tin(II) salt, Al(OⁱPr)₃ and CpNa has been studied; 3‐ph‐CL cannot be initiated by Al(OⁱPr)₃. Polymerization of 5‐ph‐CL initiated with Al(OⁱPr)₃ in toluene at 15°C yielded a polymer of a predictable molecular weight and a narrow molecular weight distribution. 3‐ph‐CL and 5‐ph‐CL can be polymerized by initiating with tin(II) salt, and CpNa. In CpNa‐based polymerization, high molecular weight P(3‐ph‐CL) and P(5‐ph‐CL) were obtained. DSC studies indicate that P(5‐ph‐CL) is an amorphous material, exhibiting a rubber state at room temperature. Compared with PCL, the glass transition temperature of P(3‐ph‐CL) and P(5‐ph‐CL) is higher (–60°C), in contrast to the melting temperature, which is higher for PCL. These new monomers give a route to novel aliphatic polyesters.