Polylactones. 41. Polymerizations of β-d,l-Butyrolactone with Dialkyltinoxides as Initiators

The usefulness of dimethyl-, diethyl-, dibutyl- and dioctyltin oxide for the preparation of syndiotactic poly(β- d, l -butyrolactone) was studied. Most polymerizations were conducted in bulk and a few polymerizations in toluene or chlorobenzene. The reaction temperature was varied between 50 and 100 °C. Below 50 °C the initiatiors were not reactive enough. Me 2 SnO proved to be the least reactive initiator. High yields and the highest molecular weights ( M n 's up to 80 000 and M w up to 130 000) were achieved with Bu 2 SnO. These high molecular weights were obtained at low monomer/initiator ratios (M/I = 50−400). In contrast to literature data, no conversion was observed at M/I ratios >600 regardless of the reaction conditions. The highest percentage of syndiotactic diads (72%) resulted either from polymerizations with Bu 2 SnO at 50 °C or with Et 2 SnO at 100 °C. Transparent films with high expansibility were cast from the 63 and 70% syndiotactic polybutyrolactone samples, which may be useful as biodegradable packaging materials.