Effective Interaction between Homo- and Heteropolymer Block of Poly(-butyl acrylate)--poly(methyl methacrylate--styrene) Diblock Copolymers.

We investigated the segregation behavior of a molten diblock copolymer, poly(-butyl acrylate)--poly(methyl methacrylate--styrene) (PBA--P(MMA--S)), wherein styrene (S) is incorporated as a comonomer in the second block to modulate the effective interaction between homopolymer and a random copolymer block. The temperature dependence of the effective interaction parameter χeff between -butyl acrylate (BA) and the average monomer of the MMA--S random block was evaluated from small-angle X-ray scattering (SAXS) analysis using the random phase approximation (RPA) approach. The calculated χeff, as a function of the styrene fraction in the random copolymer block, shows a good agreement with the mean-field binary interaction model. This consistency indicates that the effective interaction between component BA and the average monomer of the random copolymer block is smaller than the interactions between pure components (χBA,MMA,χBA,S). The present study suggests that the introduction of a random copolymer block to a block copolymer can effectively reduce the degree of incompatibility of the block copolymer system without altering the constituent species, which may serve as a viable methodology in designing novel thermoplastic elastomers based on triblock or multiblock copolymers.