Larder, Ryan
(2021)
Synthesis and application of P4VP based block copolymers from supercritical CO2.
PhD thesis, University of Nottingham.
Abstract
In recent years, supercritical carbon dioxide (scCO2) has proven to be an efficient and green medium to produce block copolymer microparticles with internal nanostructures. When conducting controlled radical dispersion polymerisations, the unique physical properties of scCO2 allow for spontaneous self-assembly of the block copolymers within the confines of the stabilised microparticles. This has successfully yielded highly pure hierarchically structured polymers in a single reaction procedure, without the need for any non-renewable or toxic solvents. Moreover, preliminary tests show that when a poly(4-vinylpyridine) (P4VP) block is incorporated into the polymer, the resulting microparticles can be capable of directing the formation of inorganic materials. Selective association of inorganic components to the pyridinyl nitrogen moieties of the P4VP can allow the polymer materials to act as structural templates to fabricate nanoscale functional materials.
However, utilisation of these P4VP based block copolymers in nanofabrication has thus far been underexplored. The main aim of this thesis is to demonstrate the versatility of these block copolymers in templating various functional materials with good control over the end nanoscale morphology. New synthetic strategies were explored to alter both the size and shape of the P4VP templates, allowing the end product to be intricately tailored for its final application. The nanofabrication of several inorganic materials was also studied to prove the breath of possible end applications that these polymeric templates are suitable for.
Specifically, Chapter 3 demonstrates that simple modifications to the synthesis of P4VP block copolymers in scCO2 allows the size of the templates to be altered. Size modification on both the microscale and nanoscale dimensions were investigated by controlling the size of the microparticles formed in the dispersion polymerisation, and by adjusting the size of the phase separated P4VP domains. In addition, this chapter also studies the nanofabrication of LiFePO4, a common cathode material for rechargeable batteries, by applying the polymer templates in a sol-gel synthetic procedure. The effect of the template microparticle size was investigated by examining the morphology, surface area and electrochemical properties of the fabricated battery materials.
Chapter 4 highlights a new approach to change the shape of the P4VP morphology in scCO2, without needing to alter the ratio of P4VP in the copolymer. Complex P4VP morphologies were obtained by synthesising ABC triblock copolymers in scCO2, allowing the self-assembly dynamics to be controlled by changing the ratio of the other two constituent blocks. These three-phase morphologies were studied through microscopy and X-ray scattering techniques. The new P4VP morphology was then used to template TiO2, an already well-studied inorganic material that has potential application as a photocatalyst. The nanostructure and photocatalytic activity of the triblock templated TiO2 was then studied and compared to an equivalent material templated using the spherical morphology of a simple diblock P4VP copolymer.
Finally, Chapter 5 details a method to combine both the polymer synthesis and inorganic templating into a single green process in scCO2. Polymerisation of the P4VP block of the copolymer was performed while simultaneously synthesising silver nanoparticles (AgNPs) by thermal degradation of a precursor complex. Chemical association of the silver to the 4VP monomers led to the synthesis of homogeneous composites materials with AgNPs distributed throughout the block copolymer particles. Furthermore, a CO2 extraction procedure was performed on the materials post-synthesis, removing the residual unreacted monomer and precursor to yield clean and non-toxic composites. The cleaned materials were assessed for their potential use in biomedical applications by evaluating their biocompatibility and antimicrobial activity. The composites were also exploited for use as an antimicrobial ‘ink’ in selective laser sintering (SLS) 3D printing, yielding small solid objects containing an even distribution of AgNPs.
Overall, a number of new strategies are presented to modify the microparticle size, nanoscale dimensions and morphology of P4VP based block copolymers in scCO2. This also includes a method to combine the template synthesis and inorganic structure-directing into one environmentally benign process. The P4VP templates are applied to the fabrication of several functional inorganic materials with multiple end applications investigated. Potential use for the templated materials in both the energy and healthcare sectors proves the value and versatility of these P4VP polymers, with even further applications still to be investigated.
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