The Synthesis and Characterisation of Complex Branched Polymers via Living Anionic Polymerisation

Abstract

This work is focused on the synthesis and characterisation of a range of branched polybutadiene materials using a combination of anionic polymerisation and post-polymerisation coupling reactions. The branched polymer architectures targeted included stars, H-shaped polymers and long-chain randomly branched polymers. Both three and four-arm star polymers were synthesised. The stars were characterised using both size exclusion chromatography (SEC) and interaction chromatography (IC) – in particular temperature gradient interaction chromatography (TGIC). TGIC was able to confirm structural dispersity within the crude and purified star polymers, which was otherwise undetectable by SEC. H-shaped polymers were synthesised using the “macromonomer” approach, which involves the use of polymers with reactive chain-end functionalities introduced via a functionalised protected initiator or a functionalised protected end capping agent. The functional macromonomers were then coupled together in a post-polymerisation Williamson coupling reaction to give the final H-shaped polymers. All macromonomers were prepared using anionic polymerisation resulting in well-defined polymers with narrow molecular weight distributions. The telechelic “crossbar” polymers were prepared in copolymerisation reactions exploiting monomer reactivity ratios, whereas the arms were prepared using an end capping agent. Normal-phase isothermal IC was employed to analyse the macromonomers by their molecular weight as well as functionality and was able to quantitatively assess the degree of functionalization for the polymers. The H-shaped polymers were synthesised using the functionalized macromonomers and TGIC analysis allowed for very detailed compositional analysis, revealing structural heterogeneity which was unclear from SEC analysis alone. Randomly branched polybutadienes were synthesised by using a crosslinking agent, a chain transfer promoter and toluene as both a chain transfer agent and solvent. This resulted in the production of soluble, highly branched, high molecular weight polymers from a one-pot facile reaction. The materials synthesised are to be used in a separate study as model polymers for structure-property correlation rheological studies.