NMR Investigations of Interfaces in Tapered and Inverse-tapered Copolymers in the Solid State

Abstract

A review of recent literature reveals that magnetic resonance experiments can quantify interfacial chain content in tapered and inverse-tapered copolymers in their end-use, solid-state forms. Chemically dissimilar chain segments organize into nanoscale domains according to copolymer chain structure, sizes for which depend upon whether diblock or multiblock versions of discrete, tapered, or inverse-tapered chain designs are used. Broad calorimetric glass-transitions can be further resolved through variable-temperature solid-state MAS NMR methods, revealing that some high-Tg components in copolymers can exhibit dynamics usually associated with low-Tg polymers, while some low-Tg components can exhibit chain dynamics characteristic of high-Tg polymer segments. The amount, distribution, and temperature-dependence of this dynamic and compositional heterogeneity can be systematically varied for copolymers with the same chemical composition by tailoring the arrangement of monomers in the chain. In sequence-controlled copolymers of styrene and butadiene, comparison to microscopy data indicates that solid-state NMR methods can quickly and non-invasively yield reasonable estimates of interphase fractions by quantifying “rigid butadiene” and “mobile styrene” segments in their tapered and inverse-tapered copolymers. These developments in which solid-state NMR has been used to understand relationships between chain structure, overall morphology, and differential ordering and dynamics within and between interfaces resulting from sequence-controlled polymerizations are reviewed and described in a format suitable for non-NMR specialists.