Synthesis and characterisation of branched polymers

Abstract

HyperMacs and HyperBlocks are polymers with highly branched architectures. The building blocks for these materials, AB(_2) macromonomers, are synthesized by living anionic polymerization and are well-defined in terms of molecular weight and polydispersity. The nature of the coupling reaction used to generate the highly branched HyperMacs results in branched polymers with a distribution of molecular weights and architectures. Previously a strategy for the synthesis of polystyrene HyperMacs has been reported in which the extent of reaction was limited by an unknown factor. In this thesis the modifications made to the synthetic strategy are reported for the production of more highly branched polystyrene HyperMacs or 'super' HyperMacs. Other variations along this theme include the addition of a B3 core creating core HyperMacs. Modifications to the improved HyperMac synthesis enabled the construction of polybutadiene AB(_2) macromonomers, resulting in polybutadiene HyperMacs; as well as triblock copolymer AB(_2) macromonomers constructed from polystyrene and polyisoprene forming block copolymer HyperMacs termed HyperBlocks. Characterisation of the materials above involved techniques including rheology, thermal analysis including differential scanning caliorimetry, (DSC), and dynamic mechanical analysis, (DMA), x-ray scattering (small angle x-ray scattering, SAXS) and transition electron microscopy, (TEM).Melt rheology showed polystyrene HyperMacs to be thermorheologically simple and HyperMacs showed little evidence for relaxation by reptation. Their rheological behaviour agreed well with the Cayley tree model for hierarchical relaxation in tube models of branched polymers. HyperBlocks showed phase separated morphologies with two distinct glass transition temperatures for their constituents. However the highly branched architecture of HyperBlocks disrupts long-range order seen in the macromonomers, as observed by SAXS and TEM