Connection of polymer chains using diepoxide in CO2/propylene oxide copolymerizations

When a small amount of vinylcyclohexene dioxide ([diepoxide]/[cat] = 60, 0.14 w% propylene oxide) is additionally added in CO2/propylene oxide copolymerization catalyzed by a highly active catalyst, cobalt(III) complex of a Salen-type ligand tethered by four quaternary ammonium salts (2), some polymer chains are connected consequently resulting in an increased molecular weight of up to Mw = 606000 and broadened molecular weight distribution. The same chain-connecting process is also applicable in the presence of chain transfer agent, tricarballylic acid (C3H5(CO2H)3), 1,2,3,4-butanetetracarboxylic acid (C4H6(CO2H)4), or adipic acid (C4H8(CO2H)2), although a higher amount of diepoxide is needed. Gel permeation chromatography reveals multi-modal distributions along with a tail at a high molecular weight portion due to formation of the connected chains. The shape of the chain transfer agent varies the chain topology, but the rheological properties are not influenced by the topology change. The poly(propylene carbonate)-block-poly(ethylene glycol) copolymer, which is obtained by feeding poly(ethylene glycol)-OH as a chain transfer agent, becomes tough in the tensile properties and shows a high shear sensitivity in the rheological properties when some chains are connected using diepoxide.