PROPERTIES OF POLYSTYRENE-POLY(METHYLMETHACRYLATE) RANDOM AND DIBLOCKCOPOLYMERS IN DILUTE AND SEMIDILUTE SOLUTIONS

Solution properties for random and diblock copolymers of polystyrene ( PS) and poly (methyl methacrylate) (PMMA) have been measured by dynami c and total intensity light scattering in solvents of differing qualit y. The results are compared with the corresponding properties for PS a nd PMMA homopolymers of similar molecular weight, in order to determin e if interactions between unlike monomers are significant. The hydrody namic radius (R(h)) and diffusion second virial coefficient (k(d)) for the random copolymer are found to be larger than the corresponding va lues for the homopolymers in a solvent which is near-theta for the two homopolymers, whereas no such effect is observed for the block copoly mer. This suggests that most intrachain interactions occur a relativel y short distance along the chain backbone. In a mutual good solvent R( h) and k(d) of the random copolymer are comparable to the average of t he values for the homopolymers, indicating that in a good solvent mono mer/solvent interactions dominate over monomer/monomer interactions. F or an isolated diblock copolymer in a mutual good solvent, there is no evidence that interactions between unlike monomers lead to additional expansion of the entire molecule, as measured by R(h), nor expansion of the individual blocks as probed by light scattering with one block optically masked. However, at low but finite concentration there is ev idence (the coefficients of the binary interaction terms in the viscos ity and the mutual diffusion coefficient, and the second and third vir ial coefficients) that a weak ordering effect may exist in block copol ymer solutions, far from the conditions where microphase separation oc curs. Finally, measurements of ternary polymer-polymer-solvent solutio ns show no dependence on monomer composition or monomer distribution f or the tracer diffusion of probe PS-PMMA copolymers in a PMMA/toluene matrix. This indicates that the frictional interaction is largely unaf fected by interactions between unlike monomers. However, there is evid ence that the thermodynamic interaction is more unfavorable between a random copolymer and the homopolymer matrix than between a diblock and the matrix. (C) 1994 John Wiley & Sons, Inc.