Synthesis of cyclic macromolecular architectures

Abstract

Design and synthesis of complex polymer architectures is a promising field in polymer chemistry to produce new materials with unprecedented macroscopic properties. Recent advances in 'living' radical polymerization and polymer coupling chemistries has facilitated the fabrication of new polymer topologies. The main goal of this thesis is to develop novel methods to fabricate cyclic polymers with pendent functional groups, and use them as building blocks in the synthesis of complex polymer topologies. The 'click' reaction used to couple the cyclic polymers was by copper-catalyzed azide/alkyne cycloaddition reaction (CuAAC). The thermal properties of the resultant complex structures were investigate by Differential Scanning Calorimetry to determine the effect of topology on the glass transition temperature (T g ).First, the combination of RAFT polymerization and CuAAC reaction were used for the synthesis of cyclic polymer with pendent hydroxyl group. An alkyne functional RAFT agent was used for the synthesis of linear polystyrene (PSTY), in which the RAFT moiety was then converted to an azide moiety and a free OH group via a two step synthetic reaction.This linear polymer was cyclized in high yield and considered as a highly efficient method, and has the potential to be applied to a wide range of polymers made by RAFT. Although the monocyclic polymer was synthesized in high yield, we observed ester cleavage during the synthesis of more complex topologies from the monocyclic precursor building blocks. A detail degradation study was conducted using different catalyst/ligand complexes, and finally the methodology for the synthesis of different topologies of cyclics was amended to reduce this degradative side reaction. However, for the fabrication of more complex topologies, the synthetic methodology was redirected towards a more stable synthetic approach.A modular approach was followed for the synthesis of multifunctional linear polymer precursors through modulating the Cu(I) activity towards the click reaction over radical formation. The post-modification approach allowed for the synthesis of α, ω-heterotelechelic linear polymer precursors which was cyclised by using a modified CuAAC cyclization reaction in which the hydroxyl functional groups were equally spaced. The hydroxyl groups were converted to azides or alkynes and then further coupled together through the CuAAC reaction to produce complex structures, including a spiro tricyclic and 1 st generation dendritic structures. All these structures were produced in high yields with good 'click' efficiencies. The purity and 'click' efficiencies were calculated by fitting the experimental SEC traces with a log-normal distribution (LND) model based on fitting iii multiple Gaussiun functions for each polymer species. The crude polymer was purified by preparative SEC that essentially removes all the unreacted species and by-products.In the follow up work, a range of different topologies of cyclic homo and copolymers were synthesized by combining of ATRP, SET-LRP a...

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