Copolymerization of γ‐butyrolactone and β‐propiolactone

Copolymerization of β‐propiolactone (BPL) with γ‐butyrolactone (GBL) was carried out by using triethylaluminum‐water system as catalyst. The formation of copolymer was confirmed by infra‐red spectrum, X‐ray diffraction pattern and analysis of the alcoholysis product of the copolymerization product. The compositions of copolymers were analyzed, from the amounts of ethyl β‐hydroxypropionate in the alcoholysis products, from which the copolymerization parameters were determined; r1 (BPL) = 18 ± 2 and r2 (GBL) = 0.36 ± 0.10. The viscosity of the copolymer was usually higher than that of poly‐β‐propiolactone prepared under a similar condition. Some other catalyst systems, diethylzine‐water system, aluminum isopropoxide, potassium hydroxide and potassium carbonate gave only the homopolymer of β‐propiolactone from the BPL‐GBL mixture.