Lithium and potassium alcoholates of poly(ethylene glycol)s as initiators for the anionic polymerization of 2,2-dimethyltrimethylene carbonate. Synthesis of AB and ABA block copolymers

Abstract

Alkali metal salts of poly(ethylene glycol)s (PEG) and poly(ethylene glycol) monomethylethers (PEGMe) may be used as initiators for the anionic ring-opening polymerization of 2,2-dimethyltrimethylene carbonate (DTC). The potassium salts of PEG and PEGMe are highly cryptated and lead under the reaction conditions to low block copolymer yields and relatively high yields of cyclic DTC oligomers. The lithium salts, however, lead to high yields of block copolymers of the AB and ABA types, depending on the initiator used—PEGMe or PEG. The properties of the copolymers are strongly dependent on the molar ratio of the repeating units. In ABA triblock copolymers having large B blocks, two melting transitions corresponding to each block are observed, especially upon the second heating. The thermal properties as compared to the homopolycarbonate are not influenced by small PEG blocks; therefore, the dilithium salt of PEG 200 can be considered to be a good bifunctional initiator for the polymerization of DTC. PEG-PDTC block copolymers with equal size of the PDTC block show no difference in the GPC elution volume with THF as solvent when the PEG block increases in size.