EFFECT OF BLOCK-COPOLYMER ARCHITECTURE ON COMPATIBILITY .3. EPOXIDIZED STYRENE-BUTADIENE BLOCK-COPOLYMERS WITH POLYSTYRENE CHLORINATED POLYMER BLENDS

The compatibilizing efficiency of epoxidized styrene-butadiene block c opolymers [E(S-b-B)] of varying architecture for the immiscible polyst yrene (PS)/chlorinated polymer (CP) blends [poly(vinyl chloride), chlo rinated polyethene] was examined. The copolymers were a diblock (ESB), a three-arm star (ESB), and a random ESBR. The techniques applied wer e dynamic mechanical analysis and tensile testing of specimens prepare d from solvent casting. Compatibilizing efficiency was found to depend on the degree of epoxidation of the butadiene unit in the copolymer, which in turn relates to the degree of chlorination of the CP, and als o on the CP/PS ratio in the ternary blend and the molecular architectu re of the E(S-b-B) compatibilizer. Other things being equal, this effi ciency varies as: ESB>(ESB)3>ESBR; thus it parallels the behaviour of the E(S-b-B) towards the CP in the binary blends. The same holds true for the degree of epoxidation of the E(S-b-B). This is in agreement wi th recent theoretical compatibilizing efficiency predictions and relat es to the relative strength of the interaction parameters among blend constituents. Use of appropriate values for these parameters allowed t he determination of the spinodal, approximating successfully the immis cibility gap of the ternary. This procedure could only be applied to t he PS/ESBR/CP system, since ESBR, unlike the other E(S-b-B) copolymers , is not microphase separated.