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Title: Functionalisable cyclopolymers by ring-closing metathesis
Author: Alkattan, Mohammed
ISNI:       0000 0004 8509 3313
Awarding Body: University of Edinburgh
Current Institution: University of Edinburgh
Date of Award: 2020
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Post‐polymerisation modification of polymers is extremely beneficial in terms of designing brand new synthetic pathways toward functional complex polymers. While many chemical groups could provide a platform for chemical functionalisation, arguably one of the most versatile groups is the olefin functionality. This could be significant as the olefins do not readily interfere with common polymerisation techniques such as ring-opening polymerisation (ROP) but can be transformed into a broad range of functional groups. Ring-Closing Metathesis (RCM) is a powerful method for the preparation of cyclic compounds by the formation of new carbon-carbon double bonds. The aim of this project is utilising RCM as a post-polymerisation modification tool for preparing novel functionalisable cyclopolymers. This work includes monomer synthesis, ring-opening polymerisation and post-polymerisation modification. Whereas aliphatic polyethers are highly established polymers and used for an immense variety of applications, stereoregular cyclic architectures of polyethers mimic natural polymers remain rare in synthetic polymer chemistry. Herein we disclosed the formation of a stereocontrolled 1,4-linked six-membered functionalisable cyclopolyether (FCPE) prepared by RCM. Further post-polymerisation modification by diastereoselective dihydroxylation (DH) afforded a novel polymer family encompassing a poly(ethylene glycol) backbone and sugar-like functionalities "PEGose". The high stereoregularity of FCPE and PEGose produced helical conformation structures. In particular, (R,R) cis PEGose structure has an extended pseudohelical structure similar to amylose. Different ring sizes of cyclopolyethers were sought from two other different starting polymers; poly(epoxy-hexene) (PEH) and poly(divinyl-oxirane) (PDVO). While divinyl oxirane (DVO) and epoxy hexene (EH) were successfully polymerised by ROP, the RCM of PEH gave mainly a cross-linked polymer. The project also attempted to expand the principle to polyesters to afford 1,4-linked six-membered functionalisable cyclopolyesters. To have the desired structure, a novel polymer of poly(vinyl glycolic acid) (PVGA) was made by ROP of a new monomer, 5-vinyl-1,3-dioxolan-4-ones (vinyl-Dox), using an aluminium salen catalyst system. However, the RCM of the last polymer was not completed even after two days of the reaction and gave mainly a cross-linked polymer. Finally, in a collaborative project, ROP of L-thionolactide was reported for the first time using aluminium salen catalysts. The polymerisation was controlled, regioselective and completed within a few hours.
Supervisor: Nudelman, Fabio ; Lloyd-Jones, Guy Sponsor: Engineering and Physical Sciences Research Council (EPSRC)
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
Keywords: synthetic polymer chemistry ; polymers ; Ring-closing metathesis ; RCM ; stereocontrolled cyclopolyethers ; helical conformation ; dihydroxylation ; L-thionolactide ; aluminium salen catalysts