Synthesis and characterisation of novel polymeric materials via living romp

Abstract

A new series of dendronised monomers of different generations possessing different chemical structures has been designed, synthesised and characterised. Dendrons were initially synthesised in a stepwise manner from t-butanol, CDI and 1- [N, N-bis(2-hydroxyethyl)amino]-2-propanol (HEAP) and were then coupled to norbomene derivatives for the provision of dendronised monomers, in particular, mono- and di-substituted first generation and di-substituted second generation polycarbonate dendronised monomers containing t-butyl terminal groups have been synthesised. Two di-substituted second generation polyurethane dendronised monomers containing t-butyl and 4-heptyl terminal groups were also successfully synthesised. Dendronised polymers have been synthesised from the NMR scale ring opening metathesis polymerisations of mono- and di-substituted first generation polycarbonate dendronised monomers along with a di-substituted second generation polycarbonate dendronised monomer, using varying ratios of monomer to initiator. It was found that the polymerisations were well-defined and that di-block copolymer products could be obtained due to the living nature of the systems. Molecular modelling studies have been performed using the CAChe® 3.2 program on the di-substituted second generation polycarbonate dendronised monomer and on a dendronised polymer up to a degree of polymerisation of 16. It was found that low DP oligomers of the second generation polycarbonate dendronised monomer had an approximately spherical shape, which tended towards cylindrical as the DP increased. The polymer at a DP of 16 had dimensions of approximately 10 nm diameter by 4 nm thickness. AFM images were also obtained using a scanning probe microscope MultiMode™ Nanoscope IV. The structures were found to be pancake shaped with dimensions of between 30-50 nm diameter and 3-6 nm thickness, which was approximately a factor of 3 greater than the dimensions calculated by molecular modelling. This discrepancy in size between the modelling studies and the AFM results is thought to arise from the effect that structure-solvent and structure-substrate interactions have on the overall conformation of the dendronised polymer when imaging by AFM.