Component-Specific Heterogeneity and Differential Phase Partitioning in Gradient Copolymers Revealed by Solids NMR

Abstract

Gradient copolymers can exhibit physical properties that are different than their block polymer analogues. Property variations should depend upon differences in the molecular arrangement of individual comonomers in the polymer chain and in the gradient zone of each chain as well as the morphological arrangement of those chains in space. Here we describe experimental approaches based on fast and slow magic-angle spinning (MAS) NMR, which reveal the amount of rigid and soft phases in styrene–butadiene gradient copolymers with component specific resolution. In addition, we introduce a spin-counting strategy that quantitatively and directly determines the amount of the low-Tg, or “soft”, butadiene component that is incorporated into the rigid domains and also the amount of high-Tg, or “hard”, styrene component that is incorporated into the mobile domains. In total, the experiments provide bulk rigidity, amount of polybutadiene partitioned in both soft and hard phases and the amount of polystyrene partitioned in each phase. We show that the synthesis conditions can be changed to vary the partitioning of each gradient copolymer component in a systematic way and propose that the interphase between the hard and soft domains is responsible for differential partitioning.