MORPHOLOGY AND RHEOLOGICAL BEHAVIOR OF MIXTURES OF POLY(STYRENE-B-ETHYLENE-CO-BUTYLENE-STYRENE) BLOCK-COPOLYMER AND POLY(2,6-DIMETHYL-1,4-PHENYLENE ETHER)

The morphology and rheological behaviour of binary mixtures of poly(styrene-b-ethylene-co-butylene-styrene) (SEBS) block copolymer (Kraton G1651) and poly(2,6-dimethyl-1,4-phenylene ether) (PPE), prepared by melt blending using a twin-screw extruder, were investigated. It was found that the cylindrical microdomains of the PS phase in Kraton G1651 were changed into lamellar microdomains in a mixture containing 14.3 wt% PPE. However, when the amount of PPE in a mixture was greater than 28 wt%, we found that part of the PPE was solubilized into the PS block of the copolymer, and the rest underwent macrophase separation. For a Kraton G1651/PPE mixture containing 28.6 wt% PPE, the microdomain structure in a melt blended sample was different from that found in a sample prepared by solution casting followed by annealing, although macrophase-separated PPE regions were observed in both samples. This observation led us to conclude that the morphology of mixtures of block copolymers and homopolymers depended upon the sample preparation method. In addition, it was found that plots of the dynamic shear modulus versus the loss modulus for these mixtures was a very useful method of monitoring the morphological change in mixtures of block copolymers and homopolymers as a function of composition or temperature.