Polymers of carbonic acid. XIV. High molecular weight poly(trimethylene carbonate) by ring-opening polymerization with butyltin chlorides as initiators

Numerous BuSnCl, Bu₂SnCl, and Bu₃SnCl-initiated polymerizations of cyclo(tri-methylene carbonate) (TMC) were conducted in bulk. In addition to the initiator, reaction time, temperature, and monomer/initiator (M/I) ratio were varied. Yields above 90% were obtained with all three initiators, but their reactivities decrease in the order BuSnCl₃ > Bu₂SnCl₂ > Bu₃SnCl. The maximum molecular weights decrease in the same order. With BuSnCl₃ M_ws up to 250,000 were obtained. These molecular weights were determined by GPC on the basis of the universal calibration method. In this connection Mark-Houwink equations for two solvents, tetrahydrofuran (THF) and CH₂Cl₂ were determined and compared with literature data. Furthermore, mechanistic aspects were studied. ¹H- and ¹³C- NMR spectra revealed that BuSnCl₃ forms complexes with the CO-group of TMC, whereas Bu₂SnCl₃ do not cause NMR spectroscopic effects. Kinetic studies in chloroform and nitrobenzene and a comparison with Bu₃SnOMe suggest that at least BuSnCl₃ initiates a cationic mechanism. However, in contrast to SnCl₄ (or SnBr₄), BuSnCl₃ does not cause decarboxylation. Regardless of the initiator ¹H-NMR spectroscopy revealed CH₂OH and CH₂CI endgroups in all cases. © 1995 John Wiley & Sons, Inc.