Ordered structure in blends of block copolymers. 5. Blends of lamella-forming block copolymers showing both microphase separation involving unique morphological transitions and macrophase separation

It is pointed out theoretically that the ordered morphology in the binary m ixtures of A-B type diblock copolymers, ((A-B)(1)/(A-B)(2)), depends not on ly on the compositions of block copolymers (i.e., the volume fraction of th e A block, f(A1),f(A2)) but also on the relative chain-length differences o f the constituent copolymers (alpha (j) for jth (j = A or B) block where al pha (j) is defined by alpha (j) = (N-j(2) - N-j(1))N-j(1) and N-j(i) (i = 1 or 2) denotes the polymerization index of the jth block chain in the ith b lock copolymer (A-B)(i)) and blend composition (i.e., the mole fraction of( A-B)(2) having a larger molecular weight, q(2)), whereas the morphology in the single component A-B diblock copolymer system in a strong segregation l imit solely depends on the composition (f(A)) We explored ordered morpholog y of binary mixtures of lamella-forming polystyrene (PS)-block-polyisoprene (PI), (PS-PI), with given block compositions (f(PS1) = 0.44, f(PS2) = 0.46 ) and given relative chain-length differences (alpha (PS) = 6.18, alpha (PI ) = 5.68) as a function of q(2). Our results revealed both the regime where only microphase separation occurred (q(2) = 0 and 0.179 less than or equal to q(2) less than or equal to 1) and the regime where macrophase separatio n occurred as well (0.003 less than or equal to q(2) less than or equal to 0.127). In the microphase separation regime, we found a unique morphologica l transition between lamellar and cylindrical morphology with q(2) whose tr end is consistent with the theoretical prediction by Lyatskaya et al. (Poly mer 1992, 33, 343). In the macrophase separation regime we found the two co existing macrophases with cylindrical and lamellar morphology. The miscibil ity gap of the two PS-PIs, with respect to q(2) for the macrophase separati on, was found to be consistent with a theoretical prediction by Matsen.