Ring-Opening Polymerization Of 1-Methyltrimethylene Carbonate Initiated By Rare Earth Compounds

Biodegradable and biocompatible poly(ester-carbonate)s have received great attention for their medical and biological applications. Ring-opening polymerizations of 1-methyltrimetylene carbonate (MTMC) initiated by highly active single-component rare earth tris(2,6-di-tert-butyl-4-methylphenolate)s [Ln(OAr)3, Ln=La, Dy, Y] or yttrium isopropoxide [Y(OiC3H7)3] are reported for the first time. Poly(1-methytrimetylene carbonate) (PMTMC) (Mw=8.4×104 Da, MWD=1.5) initiated by La(OAr)3 at [MTMC]/[initiator]=1000 was obtained with the yield of 99% in toluene within 1 hr at 30℃. Random and block copolymers of MTMC with s-caprolactone (CL),2,2-dimethyltrimethylene carbonate (DTC) and polyethylene glycol (PEG) including poly(MTMC-r-CL), poly(MTMC-b-CL), poly(MTMC-r-DTC), poly(MTMC-b-DTC), poly(MTMC-b-PEG-b-MTMC) were synthesized. The DSC results show that thermal behaviors of the polymers sensitively depend on their compositions and chain structures. Further,1H-1H COSY measurements and density functional theory (DFT) calculations are applied to investigate the mechanism. The polymerization of MTMC takes place according to a coordination-insertion mechanism. The MTMC ring is opened via acyl-oxygen bond cleavage resulting in a Ln-0 active center. There exist two ring-opening modes of MTMC in which mode b, breaking the CH2O-CO bond, is the major pathway.