ALUMINUM THIOLATE COMPLEXES OF PORPHYRIN AS EXCELLENT INITIATORS FOR LEWIS ACID-ASSISTED HIGH-SPEED LIVING POLYMERIZATION OF METHYL-METHACRYLATE

Thiolatealuminum porphyrins ((propylthio)- and (phenylthio) aluminum 5,10,15,20-tetraphenylporphyrins ((TPP)AlSPr (1c) and (TPP) AISPh (1d))) as nucleophiles in conjunction with a bulky Lewis acid such as methylaluminum bis(2,6-di-tert-butyl-4-methylphenolate) (2) served as excellent initiating systems for the high-speed synthesis of poly(methyl methacrylate) (PMMA) with controlled molecular weight. The living character of polymerization was demonstrated by the two-stage polymerization of MMA. In contrast with the method using methylaluminum porphyrin ((TPP)AlMe (1a)) as initiator, the new system features initiation of polymerization with no need for irradiation owing to the high nucleophilicity of the initiator, thereby allowing ''one-shot'' high-speed polymerization by simple mixing of MMA, Lewis acid (2), and initiator (1c or 1d). Other aluminum porphyrins such as (TPP)AlX (1, X = Cl, O2CMe, OC6H3(2,4-tBu2), OMe) did not bring about the polymerization at all even in the presence of 2. Use of lithium thiolate as initiator in combination with 2 resulted in a rather slow polymerization of MMA to give a polymer with a broad MWD and much higher M(n) than expected.