STEREOCOMPLEX FORMATION OF ISOTACTIC POLY(METHYL METHACRYLATE) WITH A WIDE VARIETY OF SYNDIOTACTIC POLYMETHACRYLATES

Syndiotactic (st-) polymers of mcthacrylates with primary and secondary ester groups, prepared by the syndiotactic-specific living polymerization with t-C4H9Li/R3Al, were found to form stereocomplexes with isotactic (it-) poly(methyl methacrylate) (PMMA) by annealing in the solid state or by mixing in certain solvents such as acetone and toluene. Melting points of the complexes depend on the structure of the ester group and can be changed in a wide range of temperature. st-Polymers of tertiary esters did not form the complex. Effects of anneal conditions, molecular weight, and tacticity on the melting point of the complex were studied in some detail for the combination of st-poly(benzyl methacrylate) and it-PMMA. st-Random copolymers of MMA with several alkyl methacrylates also formed stercocomplexes with it-PMMA, whose melting point could be changed continuously by changing the composition in a certain range of temperature. st-Block copolymers of PMMA and poly(benzyl methacrylate) formad stereocomplexes with it-PMMA which showed two melting points, provided the block lengths arc long enough for the two types of the complexes to form independently. Stercoblock PMMA, it-PMMA-block-st-PMMA, and stercoblock copolymer, it-PMMA-block-st-poly(butyl methacrylate), were found to form stereocomplexes more easily than the corresponding mixtures. The stercoregular uniform PMMAs were used for elucidating the process of stereocomplex formation and its stoichiometry by means of gel-permeation chromatography (GPC). The preliminary results clearly indicated that the complexation occurs mainly in 1:1 stoichiometry in the beginning, while a small fraction of 1:2 (it-:st-) complex was also formed concomitantly. By similar GPC experiments using a series of uniform PMMAs, the minimum length of PMMA chains for the complex formation was found to bc in the range of degrees of polymerization from 42 to 46.