SnOct<sub>2</sub>‐Catalyzed and Alcohol‐Initiated ROPS of <scp>l</scp>‐Lactide—Control of the Molecular Weight and the Role of Cyclization
Hans R. Kricheldorf, Steffen M. Weidner, Felix Scheliga
Abstract
Abstract Ring‐opening polymerizations (ROP) of l ‐lactide (LA) are conducted in bulk at 130, 160, or 180 °C and are initiated with two different alcohols at 160 °C. The lactide/initiator ratio (LA/In) is varied from 50/1 (20/1 at 180 °C) to 900/1 and the lactide/catalyst ratio (LA/Cat) between 2000/1 and 8000/1. At all temperatures a nearly perfect control of number average molecular weight ( M n ) via the LA/In ratio is feasible up to LA/In = 200/1, but at higher ratios the M n value lags behind the theoretical values and the discrepancy increases with higher LA/Cat ratios. Variation of the LA/Cat ratio influences the formation of cycles but does not significantly influence M n , when the LA/In ratio is kept constant. The formation of cycles is favored by lower In/Cat ratios and is the main reason for the unsatisfactory control of M n at high LA/In ratios. The results also suggest that the cycles are mainly or exclusively formed by end‐to‐end cyclization and not, as believed previously, by back‐biting.