Ring-opening polymerization by lithium catalysts: an overview

Abstract

This critical review summarizes recent developments in the preparation and application of lithium catalysts/initiators such as, alkyl lithium, alkoxy lithium and bimetallic lithium compounds for ring-opening polymerization (ROP). The ROP of cyclic esters, cyclic carbonates, cyclo-silazanes, cyclo-silanes, cyclo-siloxanes, cyclo-carboxylate, cyclic phosphirene and quinodimethanes are covered in this review. The present paper emphasizes the polymerization kinetics and the control exhibited by the different types of lithium initiators/catalysts. For the cases where useful properties, such as high molecular weight, narrow PDI, or stereocontrol, have been observed, a more detailed examination of the mechanistic studies of the catalysts/initiators are provided. Furthermore, this review also focuses on the synthesis of block copolymers and graft copolymers by ROP principle. The topics covered in this review regarding lithium compounds toward ROP will be of interest to inorganic, organic and organometallic chemists, material, polymer and catalytic scientists due to its unique mode of activation as compared to transition and inner transition-metals. In addition, use of these compounds in catalysis is steadily growing, because of the complementary reactivity toward ROP as compared to other metals. Finally, some aspects and opportunities which may be of interest in the future are suggested (143 references).