INITIATING SYSTEMS FOR NITROXIDE-MEDIATED LIVING FREE-RADICAL POLYMERIZATIONS - SYNTHESIS AND EVALUATION

A variety of initiating systems for the preparation of macromolecules by nitroxide-mediated ''living'' free radical procedures have been pre pared and evaluated. The systems can be divided into two classes, unim olecular initiators in which alkylated TEMPO (2,2,6,6-tetramethylpiper idinyloxy) derivatives dissociate to provide both the initiating radic al and the stable radical, and bimolecular systems in which a traditio nal free radical initiator, such as BPO or AIBN, is used in conjunctio n with TEMPO. For the unimolecular initiators it was found that an alp ha-methyl group is essential for ''living'' character, while a variety of substituents could be placed on the phenyl ring or the beta-carbon atom without affecting the efficiency of the unimolecular initiator. It was also found that the rate of polymerization is approximately the same for both the unimolecular and corresponding bimolecular systems; however, the unimolecular initiators afforded better control over mol ecular weight and polydispersity.