Self-assembled structures in polystyrene-blodc-polyisoprene-blend-polystyrene and polystyrene-block-poly(methyl methacrylate)-blend-polystyrene or -blend-poly(methyl methacrylate) in the strong segregation regime

摘要

This study deals with the investigation of microphase-separated morphology and phase behaviour in blends of polystyrene-block-polyisoprene with homopolystyrene and blends of polystyrene-block-poly(methyl methacrylate) with homopoly(methyl methacrylate) or homopolystyrene in the strong segregation regime using small-angle X-ray scattering and transmission electron microscopy as a function of composition, molecular weight of homopolymers, r_M and temperature. Parameter r_M = M_H/M_C (where M_H is the molecular weight of homopolymer and M_C that of the corresponding block copolymer) was selected to encompass behaviour of the chains denoted as a 'wet brush' (i.e. r_M < 1). The relative domain spacing D/D_o increases in the regime 0 < r_M ≤ 1 with increasing concentration of homopolymer w_P and increasing r_M but depends on the specific implemented morphology. We tested a new approximate D/D_o versus w_P relation in the strong segregation regime using block copolymers of high molecular weights. It is shown that the parameters r_M and χ ~(3/2)N determine the slope of the D/D_o versus w_P relation in the strong segregation regime and the new approximation generally matches the experimental data better than the approximations used so far.