Microdomain size of styrene-lsoprene block copolymers and unperturbed chain dimension of polyisoprene having high 1,2-and 3,4-linkages

Sizes of the microdomain structures for a series of styrene-isoprene A-B type block copolymer having approximately equal weight fractions of A and B blocks (and thus having alternating lamellar microdomains) were measured by the small-angle x-ray technique as a function of molecular weight. The unperturbed chain dimension of a polyisoprene homopolymer having the same microstructure as the poly-isoprene sequence of the block copolymer was measured by viscometry. For a polyisoprene microstructure of 38 wt % 1, 2-addition, 59 wt % 3, 4-addition, and 3 wt % 1, 4-addition, it was found that nm or nm at the temperature of 57.1°C. The observed domain size was shown to be predictable by the equilibrium theories of Meier and Helfand based upon random-flight chain statistics in the domain space.