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This research focused on the development of two different classes of gels: physically crosslinked hydrogel and covalently crosslinked organogel. Amphiphilic copolymers, composed of hydrophilic and hydrophobic monomers, have the potential to form physically crosslinked hydrogels depending on the hydrophobic monomer content in the backbone. The hydrophobic units form aggregates which act as physical crosslinking sites. The effect of methylene spacer and branched structure on the physical and viscoelastic properties of physically crosslinked hydrogels were investigated.Accurate values of the comonomer reactivity ratios are required to fully understand the properties of the amphiphilic copolymer hydrogels and to design new comonomer systems leading to advanced properties. A novel methodology was demonstrated to determine the reactivity ratios of chain copolymerizations that follow the terminal model with high precision. The St-MMA model system showed the validity of the novel technique. The methodology was applied to determine the reactivity ratios of two separate systems: N,N'-dimethylacrylamide (DMA) and 2-(N-ethylperfluorooctanesulfonamido)ethyl acrylate (FOSA) and N,N'-dimethylacrylamide (DMA) and 2-(N-ethylperfluorooctanesulfonamido)ethyl methacrylate (FOSM), which are very difficult to measure precisely using conventional technique due to the aggregating nature of FOSA and FOSM. During copolymerization DMA-FOSA should form slightly blocky morphology (rDMA, rFOSA > 1) if the copolymerization is living. On the other hand DMA-FOSM copolymer produced slightly gradient type chain morphology (rDMA < 1, rFOSM > 1) during living radical copolymerization.7,7,8,8,9,9,10,10,11,11,12,12,13,13,14,14,14-Heptadecafluorotetradecyl acrylate (PFA) and 2-bromo-3-((7,7,8,8,9,9,10,10,11,11,12,12,13,13,14,14,14-heptadecafluorotetradecyl)oxy)-3-oxopropyl acrylate (PFI) were synthesized in high purity. PFA was copolymerized with DMA in three different ratio to obtain three amphiphilic linear copolymers (DFA). The density of the DFA copolymer increased, while the Tg and equilibrium water content decreased, with increasing PFA content. Thermal stability of the DFA copolymer decreased with increasing PFA content. SAXS study confirmed that the resulting hydrogels exhibited nanophase separation in dry and swollen forms. The nanodomains in DFA hydrogels are more phase separated in water swollen form than dry form. SAOS experiment exhibited that the DFA hydrogels are viscoelastic solids in nature. The viscoelasticity of the DFA hydrogels is subject to strain, at low strain it’s solid-like and at high strain it’s liquid-like. None of DFA copolymers showed any relaxation in the terminal regime at elevated temperature due to introduction of hydrophobic methylene spacer, which eventually increased the nanodomain relaxation time and produced thermally more stable physical hydrogels.PFI and PFA were copolymerized with DMA using Me4Cyclam as ligand in three different ratio to obtain three amphiphilic branched copolymers (DFI). The branched structure was confirmed by GPCPSt and GPCLS study. The density of the DFI copolymer increased, while the Tg and equilibrium water content decreased with increasing PFA content. As speculated the SAXS results confirmed that the inter-domain spacing, d significantly reduced in branched DFI copolymer hydrogels. However, the branched structure showed improvement in the stiffness of DFI hydrogels at low fluorine content (< 10%). Tensile properties of DFI hydrogels are similar to that of DFA hydrogels.(2-Bromo-n-nonan-1-oxycarbonyl)ethyl acrylate was synthesized as an inimer for self-condensing vinyl polymerization (SCVP) to produce hyperbranched poly(n-nonyl acrylate) with many halogen atoms in the backbone. The resulting hyperbranched polymers were crosslinked by atom transfer radical coupling (ATRC) in both one-pot and two-step procedures. The radical-radical crosslinking reaction is extremely efficient, resulting in hard plastic particles from the homopolymer of (2-bromo-n-nonan-1-oxycarbonyl)ethyl acrylate synthesized in bulk. Crosslinked organogels that swell in THF were formed when the rate of crosslinking decreased using acetonitrile solutions. Dynamic shear and stress relaxation experiments demonstrated that the dry network behaves as a covalently crosslinked soft gel, with a glass transition at -50 °C according to differential scanning calorimetry. |
