Synthesis of Structurally Well‐Defined Telechelic Polymers by Organostibine‐Mediated Living Radical Polymerization: In Situ Generation of Functionalized Chain‐Transfer Agents and Selective ω‐End‐Group Transformations

Abstract

Several organostibine chain-transfer agents possessing polar functional groups have been prepared by the reactions of azo initiators and tetramethyldistibine (1). Carbon-centered radicals thermally generated from the azo initiators were trapped by 1 to yield the corresponding organostibine chain-transfer agents. The high yields observed in the synthesis of the chain-transfer agents strongly suggest that distibines have excellent radicophilic reactivity. As the reactions proceeded under neutral conditions, functional groups that are incompatible with ionic conditions were incorporated into the chain-transfer agents. The chain-transfer agents were used in living radical polymerization to synthesize the corresponding alpha-functionalized polymers. As the functional groups in the chain-transfer agents did not interfere with the polymerization reaction, well-controlled polymers possessing number-average molecular weights (M(n)s) predetermined by the monomer/transfer agent ratios were synthesized with low polydispersity indices (PDIs). The organostibanyl omega-polymer ends were transformed into a number of different functional groups by radical-coupling, radical-addition, and oxidation reactions. Therefore, it was possible to synthesize well-controlled telechelic polymers with the same and also with different functional groups at their alpha- and omega-polymer ends. Distibine 1 was also found to increase PDI control in the living radical polymerization of styrene and methyl methacrylate (MMA) using a purified organostibine chain-transfer agent. Well-controlled poly(methyl methacrylate)s with M(n) values ranging from 10 000 to 120 000 with low PDIs (1.05-1.15) were synthesized by the addition of a catalytic amount of 1. The results have been attributed to the high reactivity of distibine 1 towards polymer-end radicals, which are spontaneously deactivated to yield organostibine dormant species.