STEREOCOMPLEX FORMATION IN BLENDS OF BLOCK-COPOLYMERS OF SYNDIOTACTICPOLY(METHYL METHACRYLATE) (PMMA)-POLY(DIMETHYLSILOXANE) (PDMS) AND ISOTACTIC PMMA - DIFFERENTIAL SCANNING CALORIMETRY (DSC) AND DYNAMIC-MECHANICAL THERMAL-ANALYSIS (DMTA)

PMMA stereocomplex formation was demonstrated in domains of PMMA-PDMS- PMMA block copolymers having syndiotactic (S) PMMA blocks by mixing a THF solution of the block copolymer and that of isotactic (I) PMMA in the S/I PMMA ratio of 2 followed by precipitation fi om THF or by form ing the same blend by precipitation from chloroform followed by anneal ing at temperatures in the 100-140 degrees C range. The various blends and the block copolymer itself were analyzed by DSC and DMTA. The dis sociation-melting temperature of the stereocomplexes present in the PM MA domains was shown to increase with increasing annealing temperature . The rate of formation of stereocomplexes in bulk was found to be muc h slower than that in blends of PMMA homopolymers. Crystallization of PDMS was shown to be hindered by stereocomplex formation. The modulus at temperatures above 100 degrees C of the blends in which stereocompl ex formation occurred was found to be higher than in the same blends i n which such a stereocomplex was absent. These results are interpreted by the formation of networks formed by fringed micellar crystallites of PMMA stereocomplexes acting as physical cross-links.