Phase Behavior of Pentablock Terpolymers Differing in Molecular Architecture and Modified with a Block-Selective Oil

Abstract

Thermoplastic elastomer gels constitute a valuable class of composition-tunable materials that are typically fabricated from styrenic ABA triblock copolymers (i) possessing a morphology with A-dispersions in a B-matrix and (ii) physically modified with a B-selective, low-volatility oil to controllably alter mechanical properties such as modulus and extensibility. In this work, we extend these earlier studies by investigating the phase behavior of two chemically-identical pentablock terpolymers differing primarily in molecular architecture—ABCBA vs ACBCA—in the presence of a B-selective oil at different loading levels. Our reason for studying these polymers is that they constitute the precursors to anionic block polymers (with a sulfonated C-block) that have emerged as amphiphilic block polymers with remarkably versatile bulk and surface properties. Morphological characteristics are experimentally interrogated here by transmission electron microscopy (TEM) and small-angle X-ray scattering (SAXS), and are complemented by dissipative particle dynamics (DPD) simulations. By changing the block sequence, the morphologies of the neat polymers are observed and predicted to be considerably different. Addition of oil is found to promote vastly dissimilar blend morphologies, along with macrophase separation at moderate oil concentrations. The experimental and simulation results reported here are in generally favorable agreement and clearly demonstrate that the molecular architecture of multicomponent block polymers plays a critical role in the morphological development of these blends.