Synthesis and Characterization of Multicomponent Polyesters via Step-growth Polymerization
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Poly(ethylene terephthalate) (PET) is an important commercial polyester and widely used as fibers, packagings, containers and engineering materials. It is believed that the incorporation of a low level of ionic groups into PETs dramatically improves the mechanical performance and compatibility with other substrates. However, polymers containing ionic groups always exhibit complicated behavior due to the presence of ionic aggregates in the organic matrix, and this thesis investigates the effect of backbone architectures on the properties of PET ionomers in detail. Three series of random and telechelic PET ionomers with equivalent molecular weights and ionic contents were synthesized using conventional melt polymerization. Solid state sodium NMR spectroscopy and melt rheological analysis demonstrated that the stability of ionic aggregates of telechelic ionomers decreased dramatically with an increase in temperature. A slightly branched structure resulted in high molecular weight ionomers bearing more than two ionic end groups. However, when the level of the branching reagent was lower than 3 mol%, the ionomers with flexible backbone (poly (ethylene terephthalate-co-ethylene isophthalate)) tended to form a high fraction of intramolecular aggregates at high temperatures. When the level of branching agent was higher than 3 mol%, the compact structures led to strong intermolecular aggregates. PEG endcapped PET and PET random ionomers were synthesized to investigate the effect of PEG end groups on the morphology and rheology of PET and PET ionomers. A small fraction of incorporated PEG end groups increased PET crystallization rate dramatically. Moreover, the PEG endgroups tended to aggregate on the surface of PET to result in a PEG rich layer, which improved the biocompatibility and decreased protein adhesion. The PEG end groups also plasticed the ionic clusters of PET ionomers to decrease melt viscosity, and resulted in a water soluble polyester. Hyperbranched polymers contain a well-defined plurality of peripheral functionalities. These functionalities subsequently serve as sites for further chemical modification or as templates for noncovalent intermolecular association. In most cases, hyperbranched polymers are prepared using a one-step polymerization process involving ABn monomers. A novel AB2 monomer, 4-(fluorophenyl)-4',4"-(bishydroxyphenyl) phosphine oxide, was synthesized. The monomer was successfully polymerized to a modest molecular weight with various catalysts, including K2CO3 and Cs2CO3/Mg(OH)2. Moreover, an efficient approach to hyperbranched polyarylates via the polymerization of A2 and B3 monomers without gelation was also developed. A dilute bisphenol A (A2) solution was added slowly to a dilute 1,3,5-benzenetricarbonyl trichloride (B3) solution at 25 Â°C to prepare hyperbranched polyarylates in the absence of gelation.
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