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 φI/φS/φP = 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.

Self-assembled structures from poly(isoprene-b-styrene-b-2-vinylpyridine)(ISP)/styrene homopolymer blend were investigated. Five terpolymers whose total molecular weight, M, is in the narrow range of 121k < M < 214k, and volume fractions of the center block polystyrenes, / S , are similar at around 0.55, were prepared as parent block terpolymers. Their / P // I ratios, used as an indicator of asymmetry, are varied in the range 0.32 < / P // I < 2.46. Three low-molecular weight styrene homopolymers with molecular weights of 3k, 9k, and 12k, respectively, were mixed with those block terpolymers to produce blends with almost constant styrene content within the range 0.65 < / S < 0.68. Both ISP/S(3k) and ISP/S(12k) blend series show a morphological transition from tetragonally packed cylinders (TPC) to double hexagonal structure (DHS) with hexagonally arrayed polyisoprene cylinders, each sur-rounded by six thin cylinders as satellites. If one focuses on ISP-III(150k)/S blends whose / P // I is 0.88, TPC for ISP-III/S(3k) was transformed to DHS for ISP-III/S(12k), evidently due to the molecular weight effect of the added homopolymer. Finally a new periodic pattern, having P cylinders surrounded by five I cylinders each, has been discovered from ISP-III/S(9k) at overall composition of / I // S // P 5 0.17/0.68/0.15 and polystyrene block/ styrene homopolymer ratio of w S (b)/w S (h) 5 1.4. This structure was confirmed to possess hexagonal symmetry with larger unit cell than regular patterns ever known by X-ray diffraction experiment. V C 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2015, 53, 907-911