Formation of Tetragonally-Packed Rectangular Cylinders from ABC Block Terpolymer Blends

Effect of composition distribution of ABC linear terpolymers on the formation of periodic structures was investigated. Five poly(isoprene-b-styrene-b-2-vinylpyridine) (ISP) triblock terpolymers with almost constant molecular weights of ca. 130k and with similar center-block fraction at around 0.55, were blended variously. It has been found that tricontinuous gyroid structures gradually transform into a cylindrical structure whose rectangular cylinders are packed tetragonally if composition distribution increases. Further experiments by 3D-TEM observation on binary equimolar mixtures of two molecules with similar molecular weights of 122k and 124k, giving the average composition of phi(1)/phi(S)/phi(P) = 0.23/0.59/0.18, has verified to show more evident rectangular-shaped cylinders with 4-fold symmetry. This new structure, having periodic surfaces with nonconstant mean-curvature, could be formed due to the systematic localization of component polymer chains along the domain interfaces.