Heterophase triblock copolymer networks

Abstract

The investigation of morphological properties of linear triblock copolymers in the strong segregation limit has received much experimental and theoretical interest. Butadiene - Styrene - Butadiene (B-S-B) triblock copolymers have been compared to analogous cross-linked varieties using the techniques of small angle x-ray scattering (SAXS), solid state (^1)H NMR and stress-strain analysis. The properties being sought are; the dimensions of domains, the type of packing within copolymer systems, polystyrene : polybutadiene composition, and the mechanical properties of network systems. The evaluation of structural changes in the networks whilst the copolymer is continuously stretched is an important section of the project. A comparison of annealed and unannealed samples has been studied in each case. A comprehensive description of network mechanical properties has been accomplished by performing numerous force-elongation experiments on the materials. Parameters for the chemical cross-link density, physical entanglements, and network looseness have been extracted from force-elongation data using the Ball-Edwards slip-link model. The Mooney-Rivlin model and swelling data from the network systems have served as comparisons to the Ball-Edwards model. Details of the structural organisation in these systems have been determined using SAXS. The uncross-linked materials have been compared to the analogous networks and show that structural differences are present due to the effect of cross-linking altering the equilibrium structure. It has been demonstrated that stretching the network systems at room temperature induces variations in the domain distances from affine deformation. Domain distances have been determined for a set of lamellar morphology uncross- linked copolymers using solid-state (^1)H NMR experiments. The results obtained show a good agreement to SAXS data and theoretical predictions.