ABC terpolymers : micelles, polymersomes and stabilisation of water in water emulsions

Ghasdian, Negar

Chemistry
December 2013

Thesis or dissertation


Rights
© 2013 Negar Ghasdian. All rights reserved. No part of this publication may be reproduced without the written permission of the copyright holder.
Abstract

Polymersomes are vesicles formed from block copolymers. Their large internal volumes and thick walls make them very attractive for the encapsulation of different species. However, a major issue which prevents the use of polymersomes in most of the applications is that the encapsulation efficiency of payload molecules using current encapsulation methods is too low. This problem is thought to be related to the formation mechanism of polymersomes through self-assembly of the constituent block copolymer molecules.

This project is concern with employing a fundamentally different strategy for polymersomes formation and encapsulation based on coupling the separation properties of aqueous two phase systems (ATPSs), which are able to provide w/w emulsions, with templated self-assembly of polymersomes. This novel method provides high encapsulation efficiencies of payload species which is effective, scalable and biocompatible.

This work started by design and synthesis of a series of amphiphilic ABC terpolymers consisting of hydrophilic poly[poly(ethylene glycol) methyl ether methacrylate] (PEGMA), hydrophobic poly(n-butyl methacrylate) (BuMA) and hydrophilic poly[2-(dimethylamino) ethyl methacrylate] (DMAEMA) blocks of general structure Px-By-Dz and varied compositional parameters using group transfer polymerisation. The synthesised terpolymers were well-characterised and their ability to self-assemble into polymer structures in aqueous solution was assessed.

In addition, we show how these terpolymers can be used as effective stabilisers to stabilise ATPS consisting of dextran and poly(ethylene glycol) in order to form stable water-in-water emulsion or templated polymersomes-like structures, based on the affinity of each block towards the ATPS. The influence of terpolymers compositional parameters on the stability of w/w emulsions or templated polymersome-like structures was investigated. In favourable cases, the emulsion drop (or templated polymersome) sizes were a few μm and were stable for periods in excess of 8 months. The emulsions can be inverted from dextran-in-PEG to PEG-in-dextran by increasing the volume fraction of dextran-rich aqueous phase. We demonstrate that both high and low molecular weight fluorescent solutes “self-load” into either the dextran- or PEG-rich regions and that solute can mass transfer across the water-water interface based on its affinity towards each phase.

This work was further extended using modified silica nanoparticles (hydrophobised or PEGylated) for stabilisation of dextran-PEG ATPS. We show how the hydrophobicity and PEGphilicity of such particles can lead to relative stabilisation of dextran-PEG ATPS and formation of particle-stabilised w/w emulsions.

Publisher
Department of Chemistry, The University of Hull
Supervisor
Georgiou, Theonitsa K.; Fletcher, Paul D. I.; Buzza, D. M. A.
Sponsor (Organisation)
University of Hull; Funds for Women Graduates
Qualification level
Doctoral
Qualification name
PhD
Language
English
Extent
8 MB
Identifier
hull:8621
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