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Title: Synthesis, characterization and applications of amphiphilic core-shell particles with polyvinylamine-based shells
Authors: Li, Weiying
Degree: Ph.D.
Issue Date: 2008
Abstract: Novel routes have been developed to synthesize various amphiphilic core-shell particles that consist of well-defined hydrophobic polymer cores and polyvinylamine (PVAm)-based shells via direct graft copolymerization of vinyl monomer(s) from PVAm-based water soluble polymers, such as polyvinylamine, poly(vinylalcohol-co-vinylamine) and poly(N-vinylacetamide-co-vinylamine) using tert-butyl hydroperoxide as an initiator in aqueous system. The PVAm-based water soluble polymers were synthesized through a two-step reaction: 1) a free-radical polymerization of N-vinylacetamide or N-vinylformamide with/without vinyl acetate in water to generate a poly(N-vinylalkylamide)-based polymer; 2) the hydrolysis of the preformed poly(N-vinylalkylamide)-based polymer to a PVAm-based polymer under acidic conditions. The PVAm-based polymer was then treated with a small amount of tert-butyl hydroperoxide (TBHP) to generate free radicals that are able to subsequently initiate both graft- and homo-polymerization of vinyl monomer(s) such as n-butyl acrylate (BA), methyl methacrylate (MMA) and styrene to generate the amphiphilic core-shell particles. Stable and highly mono-dispersed particles were produced in high yield with diameters in the range between 100 and 300 nm. The formation of graft copolymers and homopolymers was confirmed by Fourier Transform Infrared spectroscopy (FT-IR). D-potential measurement suggested the formation of cationic PVAm-based shells. Transmission Electron Microscopy (TEM) micrographs of the particles revealed that they had well-defined core-shell nanostructures with thick and hairy PVAm shells. Surface morphology studies with Field Emission Scanning Electron Microscopy (FE-SEM) and particle size analysis with dynamic light scattering indicated that the structure of vinyl monomer and water-soluble polymer strongly influenced particle formation, size and morphology. The reaction conditions were optimized via systematic investigation on reaction pH, initiator concentration, weight ratio of PVAm to MMA, salt concentration and solid content, while tailoring the shell thickness and surface functionality of particles were carried out via the variation of the molecular weight and functionality of PVAm-based polymer as well as their polymeric architectures (crosslinking degree of PVAm) with respect to the particle stability, the monomer conversion, particle size and size distribution, surface charge density, grafting percentage and efficiency, and surface morphology. The formation of stable particles was strongly dependent on the reaction pH, weight ratio of PVAm to MMA, salt concentration and molecular weight of PVAm. The monomer conversion increased with the increase of the reaction pH, initiator concentration, weight ratio of PVAm to MMA and amination of poly (NVA-PVAm). The particle size and size distribution were able be controlled through the variation of the TBHP concentration and crosslinking degree of PVAm, while the surface functionality of the particles can be controlled by tailoring the functionality of the PVAm-based water soluble polymer. It was also found that the grafting efficiency of PMMA increased with the increase of reaction pH and decrease of TBHP concentration. The application of PMMA/PVAm core-shell particles in enzyme immobilization showed that they could immobilize cellulase with high capacity (up to 200 mg/g) and nearly full preservation of its activity (94%).
Subjects: Hong Kong Polytechnic University -- Dissertations.
Polymeric drug delivery systems.
Drugs -- Controlled release.
Pages: xix, 305 p. : ill. ; 31 cm.
Appears in Collections:Thesis

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