Synthesis and characterization of highly random copolymer of ε-caprolactone andD,L-lactide using rare earth catalyst

Abstract

Highly random copolymers of ϵ‐caprolactone (CL) and D,L‐lactide (LA) were synthesized by a new catalyst system, rare earth chloride–propylene oxide (PO) system. In the presence of propylene oxide, all rare earth chlorides tested are highly effective for the copolymerization. The influences of reaction conditions on the copolymerization catalyzed by the NdCl3‐5PO system have been investigated in detail. The reactivity ratios of ϵ‐caprolactone and D,L‐lactide were determined and show that the copolymerization with this new rare earth catalyst is closer to ideal copolymerization than reported for other catalysts. The microstructure of copolymer analyzed by 13C‐NMR shows that the monomer units in the copolymer is near to completely random distribution with a short average monomer sequence length. The DSC measurement confirms the high randomness of the chain structure. The mechanism studied by NMR indicates that the rare earth alkoxide generated by the reaction of rare earth chloride with propylene oxide initiates the copolymerization, and then proceeds via a “coordination‐insertion” mechanism with acyl‐oxygen bond cleavage of CL and LA. © 1996 John Wiley & Sons, Inc.

Controlled random copolymerization of rac‐lactide and ɛ‐caprolactone by well‐designed phenoxyimine Al complexes

“…These results suggest that the rac ‐LA monomer is polymerized in a faster rate than is the ɛ ‐CL monomer. This phenomenon is common and consistent with previous reports . The reactivity ratios ( r LA and r CL ) are determined by the nonlinear least‐squares (NLLS) method (Table ) .…”

“…Furthermore, 13 C NMR spectra of the copolymers (Figs. S9–S11) reveal that the average sequence lengths of the lactidyl unit ( L LA ) and the caproyl unit ( L CL ) are in the range of 2.7–3.8 and 1.3–1.5 at low conversions and both reach around 2 at high conversions (Table , runs 1–9) . Again, these results indicate that gradient copolymers were produced by complexes 1–3 .…”

Phosphido‐diphosphine pincer aluminum complexes as catalysts for ring opening polymerization of cyclic esters

“…A single signal was observed in the region between 173.02 and 173.74 ppm characteristic of the caproyl units. This resonance was attributed, according to literature data, to the carbonyl carbon of the LA‐CL‐LA triad. The signals relative to the CL‐CL‐CL homosequence and to the triads LA‐CL‐CL or CL‐CL‐LA were not detected coherently with a structure in which prevailingly isolated CL units are present.…”

Ring‐opening copolymerization of L‐lactide with ε‐caprolactone initiated by diphenylzinc

“…It can be seen that with higher monomer ratio the lower is the conversion in polymerization. This is in contrast to the results of homopolymerization of pure monomers, where ε‐caprolactone polymerization is faster than that of L ‐lactide, due to less nucleophilicity and self‐coordination for the active lactide sites 11, 12, 14. The M n of the copolymers shows a tendency to increase with the content of ε‐caprolactone in the feed composition ( f ε‐CL ).…”