Self-assembly of block copolymer-based ionic supramolecules based upon multi-tail amphiphiles

Abstract

Utilising simple acid–base titration chemistry, a new family of Linear-b-Amphiphilic Comb (L-b-AC) ionic supramolecules [Soft Matter 2013, 9, 1540–1555] featuring multi-tail side-chains have been synthesized and examined by synchrotron SAXS. To three different parent diblock copolymers of poly(styrene)-b-poly(methacrylic acid) PS-b-PMAA multi-tail ammonium side-chains of (C8)₂-, (C8)₄- or (C12)₂-type were attached at various side-chain grafting densities (X), making it possible to separate effects of the details of the AC-block architecture from effects of the overall volume fraction of the AC block. The micro-segregated morphologies of these systems include AC-block filled spherical microdomains in a liquid-like state (SPH_LL), AC-block filled hexagonally-packed cylinders (CYL), alternating lamellar microlayers of AC- and L-blocks (LAM) and L-block filled hexagonally-packed cylinders (CYL*). For systems with the same parent diblock copolymer that also carry a constant volume fraction of AC-blocks, an increase in the side-chain length (l_sc) and/or in the number of alkyl tails at a side-chain branch point (m) result in a microdomain morphology that is either unchanged or changed into one with a less curved interface. For lamellae-forming L-b-AC ionic supramolecules made up of the same parent diblock copolymer, a body of experimental data showing small variations in the repeat distance of the LAM micro-segregated structure (d_LAM) could be obtained by making appropriate combinations of X, l_sc and m. For such lamellae-forming L-b-AC ionic supramolecules, the average of d_LAM values decreases when l_sc and/or m increase. For systems with (C12)₂-type side-chains, the effective Flory–Huggins interaction parameter between L- and AC-blocks χ′_(C12)2/X was determined at various side-chain grafting densities and it was observed that χ′_(C12)2/X increases when X is increased.