Rheological properties of HyperMacs - Long chain branched analogues of hyperbranched polymers

HyperMacs are long chain branched analogues of hyperbranched polymers, differing only in the sense that they have polymer chains, rather than monomers between branch points. Although the building blocks for HyperMacs, AB(2) macromonomers, can be well-defined in terms of molecular weight and polydispersity, the nature of the coupling strategy adopted for the synthesis of the HyperMacs results in branched polymers with a distribution of molecular weights and architectures. Melt rheology showed polystyrene HyperMacs to be thermorheologically simple, obeying William-Landel-Ferry (WLF) behavior. Zero shear viscosities of the polymers were shown to increase with average molecular weight and the melts display shear thinning behavior. HyperMacs showed little evidence for relaxation by reptation and the rheological behavior agreed well with the Cayley tree model for hierarchical relaxation in tube models of branched polymers. This implies that HyperMacs exhibit architectures similar in nature to long chain branched polymers obtained commercially from metallocene catalysts.