Synthesis and characterisations of architecturally complex branched polymers

Abstract

Well-defined branched polymers are fundamental in the understanding and prediction of the relationship between structure and properties. This work focused on two different types of branched polymers which we described in terms of their synthesis and characterisation. In particular we carried out a study on Hyperblocks and asymmetric three-arm stars. The combination of living anionic polymerisation and “macromonomer” approach was successfully used for the production of both types of branched polymers demonstrating the great versatility of this synthetic methodology. HyperBlocks were constructed from well-defined AB2 macromonomers of polystyrene-polyisoprene-polystyrene while asymmetric three-arm stars involved the synthesis of well-defined polystyrene arms with different chain-end functionalities for the ‘long’ and the ‘short’ arm respectively. We have explored Williamson coupling reaction and copper (I)-catalysed azide-alkyne ‘click’ reaction for the final assembly of both HyperBlocks and three-arm stars. These materials were characterised by differential scanning calorimetry (DSC), transmission electron microscopy (TEM), mechanical tensile testing and temperature gradient interaction chromatography (TGIC). The characterisations in terms of morphology, thermal and mechanical properties carried out on HyperBlocks, macromonomers and the commercial thermoplastic elastomer (TPE) KratonTM D-1160 are here described and compared. Microphase separation with no long-range order was observed in the case of HyperBlocks and blends of the latter with the commercial TPE, suggesting that the highly branched structure frustrates and inhibit the formation of long-range order morphologies. Nevertheless the mechanical properties of HyperBlocks demonstrated to be superior to the properties of their well-defined linear precursors with long-range order morphologies. Analysis of the three-arm stars using the TGIC showed structural dispersity The ability of TGIC technique to separate polymers in terms of molecular weights allowed us to fully characterise the star polymers and quantify the impurities left after purification by fractionation.