Thermoresponsive Nanoparticles Synthesized By RAFT Dispersion Polymerization

In the past few decades, great progress has been obtained on reversible addition-fragmentation chain transfer(RAFT) polymerization due to their ability to synthesize polymers with well-controlled molecular weights and well-defined structures under relatively simple and convenient experimental conditions.In this thesis, thermoresponsive nanoparticles(nanogel and star polymer) synthesized by RAFT. Firstly, Poly(N-isopropylacrylamide)(PNIPAM) was found to exhibit cononsolvency in water mixtures with various other polar solvents. Cononsolvency is a rare phenomenon that refers to a polymer becoming less soluble in a mixture of two good solvents. RAFT dispersion polymerization in cononsolvents of PNIPAM was developed as a versatile strategy for the synthesis of thermoresponsive nanogels with controlled composition, functionality and architecture. Besides, we have synthesized a new type of thermoresponsive heteroarm CCS by RAFT co-cross-linking of hydrophilic poly(N,N-dimethylacryl-mide)(PDMA) and thermoresponsive PNIPAM in water solution. furthermore, we systematically studied their thermoresponsive behavior and their use as emulsifiers.The main contents are listed as follows:1. RAFT dispersion polymerization of NIPAM in water-ethanol(75 : 25, v : v)solution using PDMA as the macromolecular chain transfer agent(Macro-CTA)showed good control over the molecular weight, polydispersity and pseudo linear polymerization kinetics, as characterized by gel permeation chromatography(GPC)and 1H NMR. The effect of the molecular weight of Macro-CTA, the degree of polymerization of PNIPAM, the molar ratio of [crosslinker]:[Macro-CTA] and the solid content on the formation and size of nanogels was investigated. We can see that,in general, higher DPs of the PNIPAM block, higher molar ratios of [BIS] :[Macro CTA], and higher solid contents can be used to synthesize defined nanogels.This cononsolvency strategy for dispersion polymerization was shown to be compatible with the incorporation of hydrophilic comonomers of N-(2-hydroxyethyl)acrylamide(HEAM), diacetone acrylamide(DAAM) and the hydrophobic components of butyl acrylate(BA), fluorescein O-acrylate(FLA), 1,6-hexanediol diacrylate(HDDA), to be reliably copolymerized with NIPAM. An amphiphilic block copolymer PDMA-b-PBA was used as a Macro-CTA to produce the triple-layered nanogel. RAFT dispersion polymerization employing the cononsolvency effect of PNIPAM in water–ethanol solution significantly expands the composition,functionality and architecture of nanogels. The thermal profiles of nanogels were characterized by dynamic light scattering(DLS) both in cononsolvents and water.2. We have successfully synthesized a type of heteroarm CCS by RAFT co-cross-linking of PDMA and PNIPAM in water solution using 1,6-hexanediol diacrylate(HDDA) as the corsslinker and ascorbic acid/Tert-butyl hydroperoxide(ASA/t-Bu OOH) as the initiator. A series of homoarm and heteroarm CCS polymers with adjustable polarity was easily prepared by controling the feeding ratio. We systematically studied their thermoresponsive behavior and investigated their use as emulsiers. We found the heteroarm CCS was able to respond to temperature and as effective emulsifiers in the stabilization of emulsions of dodecane.