Abstract
ABSTRACT We have introduced the concept of comb-coil supramolecule into linear (AB)n-type multiblock copolymer and investigated the self-assembly behavior of the copolymer as a function of the unit number n. Linear (polystyrene-block-poly(2-vinylpyridine))n (denoted as (PS-b-P2VP)n) (n =1, 2, 3) with symmetric compositors were complexed with dodecylbenzenesulfonic acid (DBSA) to yield the comb-coil multiblock copolymers in which DBSA bound stoichiometrically with P2VP block by ionic bonding. The phase behavior of the copolymers was studied by temperature-dependent small angle X-ray scattering (SAXS). All three comb-coil block copolymers, including diblock (n=1), tetrablock (n=2) and hexablock (n=3), self-organized to form cylinder-within-lamellae morphology at the lower temperature, where the cylindrical microdomains formed by the PS block embedded in the matrix composed of the lamellar mesophase organized by the P2VP(DBSA) comb block. The disordering of the smaller-scale lamellar mesophase formed by the comb block occurred upon heating. At the same time, the larger-scale cylindrical domains transformed to body-centered-cubic (BCC) packed spheres in the diblock complex and to another hexagonally-packed cylinder (HEX) structure with smaller domain spacing in tetrablock and hexablock complexes, indicating that the order-disorder transition (ODT) of the smaller-scale structure drove an order-order transition (OOT) of the larger-scale structure irrespective of n. The transition temperatures were found to increase with increasing n due to the increase of the enthalpy of transition arising from the larger interfacial energy contribution in the multiblock. Another aim of this study is to understand the relative orientation between the larger-scale copolymer domain and the smaller-scale lamellae in multiblock comb-coil copolymer. The two-dimensional (2-D) SAXS patterns of the samples treated by large amplitude oscillatory shear revealed that the relative orientation varied with the binding fraction (x) of DBSA to P2VP block, but is independent of n. At the lower binding fraction (x ≤ 0.5), the smaller-scale lamellae showed an edge-on arrangement around the PS cylinders. At the higher binding fraction (x > 0.5), the two type of structures exhibited the orthogonal orientation, where the smaller-scale lamellae stacked along the long axis of the PS cylinders.