Synthesis and Polymerisation of Novel Monomers for Radical Ring-Opening Polymerisation
Creators: name: BINGHAM, NATHANIEL MARTIN
Publisher: name: University of Surrey
Year: 2021

description: "This thesis investigates two sets of novel radical ring-opening (RRO) monomers and the degradable polymers that they form. The first involves the well-documented cyclic allylic sulphide (CAS) lactones, whereby new synthetic methods were trialled to install different functional groups into the 2-position of the 7-membered ring: 6-methylene-1,4-oxathiepan-7-one (MOTPO). Initially it was thought that a library of monomers could be produced via a 2-step synthesis involving an intramolecular Passerini reaction. Unfortunately, this did not produce the desired monomers, either through non-reaction or through the competing intermolecular Passerini reaction. Instead a 3-step synthesis, utilising epoxides to add functionality was shown to produce the desired monomers. Synthesised MOTPO-(N-(2-hydroxypropyl)methacrylamide) (HPMA) copolymers were demonstrated to undergo degradation at different rates depending on the functional group included at the 2-position of the ring. Additionally it was shown that MOTPO-(N-isopropyl methacrylamide) (NIPMAm) copolymers could express lower critical solution temperatures (LCST), with the potential for future investigation for tunability of the cloud point.
description: In the second part of this study, thionolactones were discovered to be an entirely novel class of RRO monomer. Termed thiocarbonyl addition – ring-opening (TARO) polymerisation, this type of polymerisation takes advantage of C=S bond reactivity towards radicals, forming copolymers with degradable thioester groups as part of their backbone. The prototype monomer, dibenzo[c,e]oxepine-5(7H)-thione (DOT), was shown to be stable at room temperature, copolymerise with acrylates, acrylamides, acrylonitrile and maleimides as well as being compatible with both reversible addition-fragmentation chain transfer (RAFT) polymerisation and atom transfer radical polymerisation (ATRP). DOT was found not to homopolymerise readily, however a small amount of oligomer was synthesised and analysed, along with its small molecule degradation products. The kinetics of DOT-acrylamide copolymerisations were analysed allowing a greater understanding of the polymer makeup. This allowed for greater understanding of DOT compositional drift throughout copolymers, which was taken advantage of with regards to polymer solubility. Copolymers could be synthesised with the same total monomer ratios but different distributions of DOT which led to differences in LCST pre- and post-degradation. Additionally, several thioester selective degradation conditions were investigated to degrade DOT copolymers, such as oxone, cysteine and glutathione. Here, it was found that some water insoluble copolymers could be turned fully soluble upon degradation, due to the reduction in polymer size and end-group modifications. Lastly, DOT-PEGA copolymers were demonstrated not to show cytotoxicity, except in the degraded form when in high concentration (10 g/L). Although only one monomer, DOT, has been shown to undergo this type of polymerisation it is hoped that this field will grow with the discovery of other monomers."