Anthony J Ryan OBE Department of Chemistry, University of Sheffield, Sheffield, UK

From the Pacific RIM to PISA: reaction induced phase transitions revealed by small angle scattering

Small angle scattering is a key tool in understanding polymer structure and phase behaviour. We are used to seeing polymer phase diagrams with axes in terms of, say, temperature and composition (concentration, mole or volume fraction) for a polymer blend or solution, degree of polymerisation versus composition (mole or volume fraction) for block copolymer, and in theoretical terms the product of the Flory-Huggins interaction parameter and the degree of polymerisation versus composition.

Recognising that the zoo of different phase diagrams are all essentially the same, and the theorists have it conceptually right, means that the phase diagram can be used as a tool to interpret the scattering from phase transitions initiated by polymerisation.

This will be illustrated with examples where the polymerisation is either a chain polymerisation, polymethacrylates, or a step-growth polymerisation, polyurethane or epoxy resin. Narrow molecular weight distributions in the former lead to well defined nanostructures in solutions of block polymers whereas most-probable molecular weight distributions lead to continuous morphologies in polyurethane multi-block copolymers and toughened epoxy resins.

All three systems show some generic features that are amenable to study by small angle scattering. A polymerisation in an initially homogeneous mixture crosses a phase boundary to yield a two phase system, there is a local concentration increase of reactive species leading to an acceleration in the reaction rate, the final structure is kinetically trapped.

The lecture is part of the symposium Recent progress in small-angle scattering from soft matter and biological systems on the occasion of Professor Jan Skov Pedersen's 60th birthday.