HIGHLY HETEROTACTIC POLYMERIZATION OF METHACRYLATES - HIGHER-ORDER STEREOREGULATION AND STEREOCHEMICAL SIGNIFICANCE

A combination of tert-butyllithium (t-BuLi) and bis(2,6-di-t-butylphen oxy)methylaluminium (MeAl(ODBP)(2)) was found to be an efficient initi ator for heterotactic living polymerization of certain alkyl methacryl ates in toluene at low temperatures. The polymerization of methyl meth acrylate (MMA) with t-BuLi/MeAl(ODBP)(2) (Al/Li=5mol/mol) in toluene a t -78 degrees C gave heterotactic-rich poly(methyl methacrylate) (PMMA ) with narrow molecular weight distributions (MWDs) (heterotactic tria d fraction mr = 68%, ratio of weight- to number-average molecular weig hts (M) over bar Mw/(M) over bar n = 1.06-1.17). Other alkyl methacryl ates also gave heterotactic polymers under the same conditions; in par ticular, ethyl and butyl methacrylates gave polymers with heterotactic triad fractions of 87%. The highest triad heterotacticity of 91.6% wa s obtained for the polymerization of ethyl methacrylate at -95 degrees C. Some characteristic features of this stereospecific polymerization were discussed based on the polymerization results combined with othe r structural information of the polymer such as chain-end stereostruct ure and stereosequence distribution in the main chain.