PREPARATION OF HETEROTACTIC-RICH POLY(METHYL METHACRYLATE) WITH NARROW MOLECULAR-WEIGHT DISTRIBUTION BY TERT-BUTYLLITHIUM/BIS(2,6-DI-TERT-BUTYLPHENOXY)METHYLALUMINUM

Polymerization of methyl methacrylate (MMA) with tert-butyllithium (t-C4H9Li) in toluene in the presence of aluminum alkoxides such as ethoxide, tert-butoxide and 2,6-di-tert-butylphenoxide, were examined at various Al/Li ratios. In the cases of ethoxide and tert-butoxide, predominantly isotactic polymers with broad molecular weight distribution were obtained. CombinationS Of t-C4H9Li and bis(2,6-di-tert-butylphenoxy)methylaluminum [MeAl(ODBP)2] were found to be an efficient initiating system for heterotactic polymerization of MMA, which gives PMMA rich in heterotactic triads up to 68% with narrow molecular weight distribution (MwBAR/MnBAR =1.09-1.17). End group analysis by H-1 NMR indicated that t-C4H9Li initiates the polymerization and MeAl(ODBP)2 works as a stereospecific modifier. From stereosequence analysis of the heterotactic PMMA by C-13 NMR, it was found that the calculated pentad fractions from the first-order Markovian statistics (Pm/r=0.742, Pr/m=0.627) fitted the observed ones better than those from Bernoullian statistics. The glass transition temperature of the heterotactic PMMA was 13-degrees-C lower than that of syndiotactic PMMA, and the intrinsic viscosity in tetrahydrofuran was close to that of isotactic PMMA with a similar molecular weight but higher than that of syndiotactic PMMA.