Synthesis of dispersants to generate fillers for composites designed to have an enhanced echogenic response

Stimpson, Amy (2020) Synthesis of dispersants to generate fillers for composites designed to have an enhanced echogenic response. PhD thesis, University of Nottingham.

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Abstract

Ultrasound (US) imaging was identified as an advantageous imaging modality over the typically used X-ray. Thus, composites comprising of dispersed US-visible contrast agents embedded in a thermoplastic polyurethane matrix were made. To form the composite device, a commercially available material was used as a dispersant for microparticles. These coated phosphate-based glass microspheres were used as ultrasound visible contrast agents, in a medical grade polymer matrix. Ultrasound images of hollow tubes were obtained by Children’s National Medical Center (Washington DC, USA), which proved to show promising initial results. Imaging artefacts attributed to poor dispersion were observed, thus optimisation of device focussed on dispersant design. To optimise the dispersion of contrast agent throughout medical devices, bespoke dispersants were designed and synthesised to be more compatible with the matrix polymer. The first technique was to employ a thiol chain transfer agent (CTA) which was a one-pot, high yielding reaction to produce oligomers. The other method was catalytic chain transfer polymerisation (CCTP) followed by post-functionalisation of the vinyl-terminated oligomeric product via thiolene click chemistry. It was found that carboxylic acid containing thiols were excellent CTAs for monomers detailed.

The synthesis of various iron-a-diimine complexes as potential alternatives to commercially available cobalt-based complexes that are typically used as control agents in catalytic chain transfer polymerisation (CCTP) was carried out. Their efficiency as chain transfer agents was investigated and related to the catalyst generation method, concentration and heating type. Although they did not exhibit high efficiencies as catalytic chain transfer agents under the conditions described, chain transfer behaviour was observed for these complexes. It was noted that molecular weight and dispersity of polymer products were lower than products obtained from uncontrolled free radical polymerisations. The differential effects of utilising microwave heating (MWH) on the rate and molecular composition of final products obtained compared to when conventionally heating (CH) was applied was also investigated. The differences were found to be related to an increase in the rate of propagation in the case of MWH conditions, which was attributed to the selective heating of particular radical species. Higher molecular weight polymers were obtained from MWH reactions, with the dispersity remaining relatively equivalent to those of the products obtained from analogous CH reactions. This suggests the selective heating of the propagating polymer radical dominated in this CCTP system rather than additional heating of the iron complex. The latter having been proposed as a potential route that electromagnetic waves may have increased the efficiencies of the iron-based catalysts due to their ferromagnetic centre in comparison to the paramagnetic cobalt complexes.

Item Type: Thesis (University of Nottingham only) (PhD)
Supervisors: Irvine, Derek
Howdle, Steve
Ahmed, Ifty
Lester, Edward
Keywords: dispersants, chain transfer agent, catalytic chain transfer polymerisation
Subjects: T Technology > TP Chemical technology
Faculties/Schools: UK Campuses > Faculty of Engineering > Department of Chemical and Environmental Engineering
Item ID: 60983
Depositing User: Stimpson, Amy
Date Deposited: 27 Aug 2020 12:37
Last Modified: 27 Aug 2020 12:37
URI: http://eprints.nottingham.ac.uk/id/eprint/60983

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