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No description available.

The aim of the work described in this thesis was to prepare polymers of structure I (SiMe2(CH2)yC(CN)2(CH2)ySiMe2O)n (y &'61 1, 2 or 3). Chapters 1 provides an introduction to the work. Methods for producing diadducts of malononitrile, which were central to the synthesis of I (y &'61 1, 2 or 3), are reported in Chapter 2. For the nucleophilic attack of allyl chloride by sodium, calcium and ammonium salts of malononitrile, polar aprotic solvents such as DMSO, sulpholane and liquid ammonia provided the best yields. During this work a GLC technique was developed for following the progress of the reaction. The results obtained revealed that both the mono- and diadducts of malononitrile were formed in the early stages of the reaction. This technique also demonstrated that calcium hydride gave better yields of diadduct than sodium hydride. The synthesis of I (y &61 3) is reported in Chapter 3. The stages were; i) synthesis of diallyl malononitrile, ii) hydrosilylation of the diadduct with dimethylchlorosilane, iii) hydrolysis of the resultant product to give (HOSiMe2CH2CH2CH2)2C(CN)2, and iv) the polymerization of the disilanol with various catalysts. Chapter 4 covers the attempt at the synthesis of I (y &'61 2). The diadduct (CH2&'61 CH)2C(CN)2 was synthesized by a variation on the Michael addition reaction. However, the both the yield and purity of the product were low. This led to poisoning of the platinum catalyst in the hydrosilylation reaction that followed. The attempts at the synthesis of polymer I (y &'61 1) are described in Chapter 5. Attempts to produce (HSiMe2CH2)2C(CN)2 were hindered by the low reactivity of HSiMe2CH2Cl. Further attempts were made to produce I (y &'61 1) by the ring-opening polymerization of a nitrile containing cyclic disiloxane.

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After reviewing the literature relating to the synthesis and properties of hydrophobic materials, and then considering potential methods for their synthesis, a route for the preparation of novel materials was chosen. A reaction scheme involving the condensation of an excess of 1,4-bis (chloromethyl) benzene with bisphenolic compounds, and conversion of the resultant chloromethyl products to their vinyl analogues is described. A variety of methods were used to accomplish the initial etherification. The use of dimethyl acetamide and potassium carbonate was found to reduce the incidence of side reactions. The vinylation stage, using the Wittig reaction was also studied. The products were characterised by NMR and IR spectroscopy and by gel permeation and high perfonnance liquid chromatography. The curing reaction of the vinyl terminated material was studied using differential scanning calorimetry. The reaction product derived from bisphenol A was cured into various specimens, and the physical properties of the material examined. The polymer combines reasonable mechanical properties with one of the lowest water absorption maximov reported in the literature for non-fluorinated thennosets. On immersion in water at 700 C. the absorption maximov was 0.28% by weight. The thermooxidative degradation of the base material was also examined.

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Fluoropolymers are a versatile and attractive group of compounds having an interesting mix of properties that make them highly useful for various applications. Because of strong bonding between the carbon and fluorine atom, they exhibit unique physical and chemical properties such as high thermal stability, increased chemical resistance, low refractive index, enhanced inertness towards many solvents and hydro-compounds. These characteristics have led them to be widely used in aerospace, aeronautics, optics, microelectronics, paints and coatings, and engineering structures and as biomaterials. Amphiphilic copolymers possess unique solution and solid-state properties due to their well-defined molecular architecture. These properties arise as the result of covalently combining two thermodynamically different polymer blocks that phase separate on the nanoscale. Amphiphilic copolymers based on a fluoro-monomer will combine the favourable physiochemical properties of the desired fluorine segment in combination with complementary hydrophilic segments. Such fluorinated amphiphilic copolymers are potentially useful for drug delivery vehicles and membrane applications. This project is aimed at making fluorinated amphiphilic block copolymers of hydrophobic 2, 3, 4, 5, 6 –pentafluorostyrene (PFS) and hydrophilic methacrylic acid (MAA). A controlled radical polymerization mechanism, nitroxide mediated polymerization (NMP) using NHS-BlocBuilder as the initiator was employed. The advantage of using NMP is that it facilitates the synthesis of copolymers with well-controlled narrow molecular weight distribution. However, methacrylate homopolymerization by NMP is challenging due to the high dissociation equilibrium constant therefore, the use of PFS as a controlling comonomer was explored. We established that to obtain a controlled copolymerization, a minimum of 70 mol% PFS was required, which is significantly greater than other copolymerization systems such as using as little as 4.5-8 mol% styrene to control the copolymerization of MAA. We surmise that this lack of control is due to the unfavourable reactivity ratios (Appendix I) which favour the addition of MAA rather than PFS (rPFS = 0.012, rMAA = 8.12). However, these unique reactivity ratios suggest that a semi-batch approach can be utilized to synthesize almost pure block copolymers in one pot. Therefore, poly(PFS)–b-(PFS-ran-MAA) block copolymers were synthesized and characterized by a semi batch addition of MAA. While successful, the concentration of irreversibly terminated chains was evident and greater care in reducing these unwanted reactions needs to be addressed.

abstract: Zwitterionic polymers, due to their supurior capability of electrostatically induced hydration, have been considered as effective functionalities to alleviate bio-fouling of reverse osmosis (RO) membranes. Bulk modification of polysulfone-based matrices to improve hydrophilicity, on the other hand, is favored due to the high membrane performance, processibility, and intrinsic chlorine resistance. Here a novel synthetic method was demonstrated to prepare zwitterionic poly(arylene ether sulfone) (PAES) copolymers, which was blended with native polysulfone (PSf) to fabricate free-standing asymmetric membranes via non-solvent induced phase separation process. Both the porosity of the support layer and surface hydrophilicity increased drastically due to the incorporation of zwitterion functionalities in the rigid polysulfone matrix. The water permeance and antifouling ability of the blend membranes were both remarkably improved to 2.5 Lm−2 h−1 bar−1 and 94% of flux recovery ratio, respectively, while salt rejection remained at a high level (98%) even under the high exposure to chlorine (8,000 ppm•h). Besides the preliminary blended membrane design, for the future membrane property enhancement, this dissertation also focused on polymer structure optimizations via elucidating the fundamentals from two perspectives: 1). Synthetic reaction kinetics and mechanisms on polycondensation of PAES. Interestingly, in combination of experiments and the computational calculations by density functional theory (DFT) methods in this work, only the aryl chlorides (ArCl) monomer follows the classical second-order reaction kinetics of aromatic nucleophilic substitution (SNAr) mechanism, while the kinetics of the aryl fluorides (ArF) reaction fit a third-order rate law. The third order reaction behavior of the ArF monomer is attributed to the activation of the carbon-fluorine bond by two potassium cations (at least one bounded to phenolate), which associate as a strong three-body complex. This complex acts as the predominant reactant during the attack by the nucleophile. 2). Optimized copolymer structures were developed for controlled high molecular weight (Mw ~ 65 kDa) and zwitterionic charge content (0~100 mol%), via off-set stoichiometry during polycondensations, following with thiol-ene click reaction and ring-opening of sultone to introduce the sulfobetaine functional groups. The structure-property-morphology relationships were elucidated for better understanding atomic-level features in the charged polymers for future high-performance desalination applications. / Dissertation/Thesis / Doctoral Dissertation Chemical Engineering 2019

<p> Trimethylsilylstyrenes undergo protiodesilylation (Scheme 1, path A), via the β-silyl carbonium ion under acidic conditions. In contrast, the corresponding trichlorosilyl substituted compound was found to undergo an oligomerization reaction (Scheme 1, path B) with triflic acid as the catalyst. (See Diagram in Thesis)</p> <p> The β-effect [(σ-p)π overlap] may play a significant role in the weakening of the silicon-carbon bond and thus promote the cleavage process, as is observed in scheme 1, path A. Introduction of electronegative chloro groups on silicon weakens the β-effect and hence the silyl leaving group ability, resulting in oligomerization of the styrene (Scheme 1, path B).</p> <p> In this oligomerization reaction, chain termination by an internal Friedel-Crafts reaction competes with the chain propagation. As a result, indane terminated low moldecular weight oligomers are formed. The case is similar to β-methyldichlorosilylstyrene, with the only difference that here ca. 20% desilylation has occured, again reflecting the fact that subtle changes in the β-effect acan influence the course of electrophilic reactions.</p> / Thesis / Master of Science (MSc)