ORDER-DISORDER TRANSITION, MICRODOMAIN STRUCTURE, AND PHASE-BEHAVIOR IN BINARY-MIXTURES OF LOW-MOLECULAR-WEIGHT POLYSTYRENE-BLOCK-POLYISOPRENE COPOLYMERS

Order-disorder transition, microdomain structure, and phase behavior i n binary mixtures of low molecular weight polystyrene-block-polyisopre ne (SI diblock) copolymers were investigated. For the study, four SI d iblock copolymers were synthesized, namely (i) SI-Q having a weight-av erage molecular weight (M-w) of 2.8 x 10(4) and polystyrene volume fra ction (f) of 0.186, (ii) SI-R having M-w = 1.5 x 10(4) and f= 0.508, ( iii) SI-S having M-w = 1.76 x 10(4) and f = 0.372, and (iv) SI-M havin g M-w = 1.55 x 10(4) and f = 0.626. Then binary mixtures of SI-Q and S I-R and binary mixtures of SI-M and SI-S, with various compositions, w ere prepared via solvent casting. The order-disorder transition of the binary mixtures was investigated using rheology and small-angle X-ray scattering (SAXS), respectively. Also investigated was the microdomai n structure of the binary mixtures using SAXS and transmission electro n microscopy (TEM). Experimentally determined phase diagrams are compa red with predictions based on a self consistent mean-field theory.