Polylactones, 50. The reactivity of cyclic and noncyclic dibutyltin bisalkoxides as initiators in the polymerization of lactones

Abstract

Dibutyltin bisethoxide and bis(2,2,2-trifluoroethoxide), the cyclic alkoxidcs derived from cis-1,4-butenediol, 1,4-butanediol, 1,8-octanediol and triethylene glycol as well as bis(4-nitrophenoxide), bis(4-methoxyphenoxide) and tetrabutylstannoxane bisacetate were used as initiators in the polymerization of ε-caprolactone (ε-CL) and β-D,L-butyrolactone (β-BL). Most polymerizations were conducted at 60°C with 2 M solutions in chlorobcnzene, and time-conversion curves were recorded. The less reactive initiators yielded sigmoidal time-conversion curves with autoacceleration during the first stage of polymerization. Dibutyltin bisethoxide and the cyclic 1,8-octane dioxide showed the highest reactivities. The less reactive initiators yielded degrees of polymerization (DPs) exceeding the monomer/initiator (M/I) ratios after short reaction times, but at longer reaction times, an equilibration between unreacted initiator and the poly(ε-CL) chain took place. The slower polymerizing β-BL yielded DPs paralleling the M/I ratio even with less reactive initiators. The stannoxane and the dibutyltin bisphenoxides were considerably less reactive than the bisalkoxides, and only traces of phenylester endgroups were detectable by 1H NMR spectroscopy. MALDI-TOF mass spectrometry proved the formation of cyclic oligolactones with masses greater than 600 Da for reaction temperatures ≥60°C. © Wiley-VCH Verlag GmbH, 2001.