Magister Scientiae - MSc (Chemistry) / Reactions of furan, thiophene and alkyl carbonyl chlorides with Unsubstituted and substituted pyrazoles produced the desired pyrazolyl ligands, [R2pyrazole-CO-R/] (R= H, Me, tBu, Ph, R/ = furan, thiophene, Me or tBu) in good yields. The reaction of these synthons with Pd(NCMe)2Cl2 as the metal precursor afforded the respective palladium(II) complexes in moderate to high yields. All compounds synthesised were characterised by a combination of 1H NMR, 13C NMR and IR spectroscopic techniques for structure elucidation. Microanalyses were performed to confirm the purity of the compounds. Single crystal X-ray crystallography of complexes bis{2-(3,5-dimethylpyraz olyl-1-carbonyl)furan}PdCl2 ,1, and bis{2-(3,5-dimethylpyrazolyl-1-carbonyl)thiophene} PdCl2, 2, was performed to determine the molecular structures of the compounds. The two structures show that the complexes formed are mononuclear. The ligands exhibit monodentate coordination with trans-geometry being favoured in the square planar complexes. Activation of some of the complexes, 1-4, with the methylaluminoxane (MAO) produced active catalysts for ethylene polymerisation at elevated temperatures giving high-density linear polyethylene. The optimum Al:Pd ratio was found to be 5000:1. The nature of the substituent on the pyrazolyl moiety affects the activity of these catalysts in ethylene polymerisation. In general, increase in steric bulk resulted in decreased catalytic activity and low molecular weight polyethylene. The use of the Lewis acid, B(C6F5)3, with catalyst 2 resulted in enhanced catalytic activity towards ethylene polymerisation. When ethylaluminium dichloride, EtAlCl2, was used as the co-catalyst, these catalyst systems were found to be active towards ethylene oligomerisation producing mostly C10 and C12 oligomers. An optimum Al:Pd ratio of 1000: in the catalytic activity of catalyst 2 was observed. The nature of the alkyl substituent on the pyrazolyl system also shows significant influence in the oligomerisation process. The activity of the catalysts as well as the nature of the oligomers produced greatly depends on the oligomerisation conditions. For example, increase in both temperature and pressure resulted on significant increase in turnover number of catalyst 1 and 2. Longer reaction times resulted in drastic drop in the catalytic activity of the complexes. When acetic acid was reacted with the appropriate pyrazole in the presence of a phase transfer catalyst, the bidentate bis-pyrazolyl acetic acid ligands, {(pyrazole)2CHCO2H}, L14, {(Me2pyrazole)2CHCO2H, L15, and {(tBu2pyrazole)2CHCO2H} L16 were obtained in good yields. The reaction of these ligands with Pd(NCMe)2Cl2 in a 1:1 ratio afforded the corresponding yellow complexes, Pd(L14)Cl2, 9, Pd(L15)Cl2, 10, and Pd(L16)Cl2, 11, in moderate yields. 1H NMR, 13C NMR and IR spectroscopy have been used to characterise these compounds. Microanalysis confirmed the purity and empirical formulae of the complexes. Reaction of L14 with ethanol under acidic conditions produced the respective ester, bis(pyrazol-1-yl)ethyl acetate, (L17) in good yield. The acid dissociation constants of the ligands and their palladium(II) complexes have been determined by titration using dilute NaOH. Ka values within the range of 1.8 × 10-4 to 1.75 × 10-2 were obtained. Acidity was found to decrease with increase in the electron donor ability of the alkyl pyrazolyl substituents. In general, the palladium(II) complexes were more acidic than their corresponding ligands. / South Africa

In this study, fluorescent polymers with pendant quinoline groups were synthesized by reversible addition-fragmentation chain transfer polymerization (RAFT) from a fluorescent quinoline-based vinyl monomer, synthesized in multiple steps from p-nitroaniline and crotonaldehyde. The structures of the synthesized vinyl monomer and polymers were confirmed by NMR and FT-IR spectroscopy, X-ray studies and modeling stdies. The photophysical properties of the synthesized quinoline compounds and resulting polymers were investigated. In order to evaluate the binding potential of our quinoline-based polymer in the presence of transition metal ions, preliminary studies on a complexation of quinoline-based polymers with Zn, Cd, Hg, Fe, and Ni were carried out. The investigation of fluorescence properties of the complexes showed fluorescence quenching for Fe(II), and fluorescence enhancement for the remaining ions [Zn(II), Cd(II), Hg(II), and Ni(II)].

Click chemistry is one of the growing areas of research which is applied in the design and synthesis of a wide range of polymeric architectures. This investigation focuses on the synthesis of fluorescent coumarin based polymers by “click” A-B step growth polymerization process and evaluation of their photophysical properties. Non-fluorescent azide-alkyne functionalized coumarin-based monomers were synthesized in multiple steps from 2,4-dihydroxybenzaldehyde in reasonable yields. Polymers with coumarin backbone were synthesized from azide-alkyne functionalized coumarin monomers via the Cu(I) catalyzed 1,3-dipolar cycloaddition reaction between azides and alkynes, a typical click reaction, to form polymers whose repeating units are connected by a 1,2,3-triazole ring. The structures of the synthesized polymers were confirmed by NMR and FT-IR spectroscopy. Finally, the photophysical properties of the synthesized monomers and polymers were evaluated in DMF. All coumarin based monomers showed reduced fluorescent properties due to the quenching effect from the azido group. Although all polymers absorbed at maximum wavelength of 340 nm, a characteristic for coumarin chromophore, the homo-polymers emitted at a shorter wavelength of 413 nm as compared to the co-polymers which emitted at 421 nm.

Stress relaxation experiments have been carried out on single filaments of nylon, viscose rayon and acetate rayon over the temperature range 0°C. to -80°C. Similar experiments were also performed on viscose rayon yarns immersed in water at 35°C. In these latter experiments, a marked change in the shape of the stress relaxation curve was noted as the strain was decreased. At strains of the order of 0.05% the relaxation curve had the shape characteristic of a single Newtonian Maxwell element, while the curve obtained at higher elongations could not be explained in terms of a single such element. It was concluded that the flow process involved was non-Newtonian in character. The low temperature results, as well as those obtained previously by Price (20) are discussed In terms of Eyring's hyperbolic tangent equation for describing stress relaxation. / Science, Faculty of / Chemistry, Department of / Graduate

The effect of increment addition of monomer, during the emulsion polymerization of styrene, upon the molecular homogeneity of polystyrene has been investigated. This procedure results in a polymer containing large amounts (greater than 60%) of benzene insoluble material indicating that there is a considerable degree of cross-linking during the process. A small amount of the product (less than 20%) exhibits a fair degree of homogeneity with respect to the molecular weight. Low molecular weight polystyrene can be obtained by the use of mercaptan modifiers. The mercaptan appears to be carried into the reaction loci by the styrene during the early stages of the polymerization. Later, the effectiveness of the modifier is governed by diffusion through the aqueous phase. / Science, Faculty of / Chemistry, Department of / Graduate

Cellulose nanocrystals (CNCs) are rod-shaped nanoparticles derived from cellulose, the most abundant polymer in the world. CNCs are as strong as Kevlar™, have a high aspect ratio (traditional nanoparticles are spherical) and thus, a higher surface area, which makes them ideal for use in nanocomposites. In addition, CNCs are considered the only safe nanomaterial according to Health Canada. In this thesis, CNCs were used to produce nanocomposites via in situ semi-batch emulsion polymerization. The target application for these nanocomposites was as pressure sensitive adhesives (PSAs). In the past, CNCs have been blended with polymers rather than added in situ. Emulsion polymerization is considered a more sustainable method to synthesize polymers compared to say, solution polymerization. However, adhesives synthesized using this method tend to have a lower shear strength due to poor gel network formation. As a result, conventional emulsion-based PSAs suffer from the inability to increase certain adhesive properties (e.g., tack and peel strength) while simultaneously increasing shear strength. In this thesis, we demonstrate how the use of CNCs via in situ emulsion polymerization overcomes this classic problem. Two polymer systems were tested: isobutyl acrylate (IBA)/n-butyl acrylate (BA)/methyl methacrylate (MMA) and 2-ethylhexyl acrylate (EHA)/BA/MMA. The use of CNC with IBA, a relatively hydrophilic monomer, rather than with EHA, a highly hydrophobic monomer, resulted in the simultaneous improvement of tack, peel strength and shear strength of the PSA films. Dynamic mechanical analysis (DMA) also indicated improved storage and loss moduli with increasing CNC content, further supporting the reinforcing effect of the CNCs within the PSA. EHA followed similar trends as IBA for conversion, particle size, viscosity, pH, glass transition temperature and gel content. On the other hand, the use of CNC with EHA yielded less improvement in adhesive properties due to poor dispersion of the CNCs because of the hydrophobic repulsion by the EHA.

Fractional stress relaxation ( S(t)/S(0.04 ) ) was used to compare time-dependent properties of papers, plastics and paper plastic composites ( PPC ). No similar observations appear in the literature. Laboratory handsheets were prepared from commercial western hemlock ( Tsuga heterophylla (Raf.) Sarg. ) unbrightened and brightened groundwoods, as well as unbleached and bleached kraft pulps. Adjustments were made to provide equivalent basis weights ( 150 ± 30 g/m² ) for materials of the study. Handsheets were impregnated with methyl methacrylate ( MMA ) and tetraethylene glycol dimethacrylate ( TEGDMA ) (co)monomer systems. Saturated handsheets and plastic films were cured by ⁶⁰Co gamma irradiation ( 1.4 ± 0.9 Mrad ). It was found that the standard log-time equation, S(t)/S(0.04) = a + b ln t, applied to data collected between 0.04 and 35 min following completion of simulated step-loading ( r ² mostly 0.97 or higher ). A second quantity, energy dissipation ( ΔS), ΔS = 1 - S(35)/S(0.04), was used to compare between treatments. Some plastics gave the highest ΔS values, while groundwoods gave lowest values and kraft papers were intermediate. Pulp delignification level appeared to relate directly to ΔS. Within limits of the study it seems that PPC stress relaxation curves were influenced by both polymer ( matrix ) and fibre ( substrate ) employed. The former contributed in minor ways, while the latter operated in major ways. / Forestry, Faculty of / Graduate

Ph.D. (Chemistry) / Please refer to full text to view abstract

The bulk polymerization of vinyl chloride is still at the present time far from being well understood. In spite of the economic importance of the process, the detailed quantitative behavior of the reactor has not been elucidated. Immediate reasons for this, are given by the physical complexities of particle formation (arising from oligomer precipitation in solution), and heterogeneous polymerization kinetics, recalling that the process starts with one liquid monomer phase and finishes with three phases: liquid and gaseous monomer, and solid polymer.

This study examined the mechanical and durable press properties of cotton 3/1 twill-woven fabrics finished with various concentrations of reactants in the BTCA/IA/AA combinations. The regression analysis was used to determine the relationship among each finishing variable, BTCA, IA, and AA concentrations, mole ratio of acid monomers to the sodium hypophosphite monohydrate catalyst, and curing times at 180°C, and the finished fabric's property variable, breaking strength, tear strength, wrinkle recovery angle whiteness index, and durable press rating. Based on the results of the reduced regression equations and range dispersion of mean values of finished fabric properties. The results of the study indicated the some BTCA/IA/AA combinations applied to cotton fabric provided good results in wrinkle recovery angle, breaking strength, and tear strength, comparable to those of the fabric finished with either BTCA only or DMDHEU reactant. The combinations of BTCA/IA/AA reactants did not provide as good whiteness index and durable press rating as the BTCA or DMDHEU reactant. / Ph. D.