Thesis (MSc (Chemistry and Polymer Science))--University of Stellenbosch, 2010. / ENGLISH ABSTRACT: Impact polypropylene copolymers (IPPC) are important commercial materials, but their morphology and molecular architecture are not yet fully understood. In this study the focus was on selectively removing specific fractions from the original IPPC, recombining the remaining fractions, and studying the properties of these recombined polymers. It was found that some properties of the samples changed remarkably, depending on the fraction of material that was removed before recombination. For example, the degree of phase separation and the crystalline morphology of the recombined materials varied noticeably. During the study an effective way of staining samples for transmission electron microscopy (TEM) was developed. Furthermore, a comparison of fourier transform infrared spectroscopy (FTIR), with TEM and scanning electron microscopy (SEM) results, revealed a hitherto unreported relationship between phase separation. Absorption bands appeared at 1100 cm-1 and 1080 cm-1 in the FTIR spectra and appear to be an indication of phase separation. It was further established that specific copolymer fractions present in the original polymer affect not only the morphology of the final polymer, but also the hardness and impact resistance. / AFRIKAANSE OPSOMMING: Impak polipropileen kopolimere (IPPK) is belangrike kommersïele materiale, maar die kennis met betrekking tot die morfologie en molekulere argitektuur van die materiale is nog gebrekkig. Tydens hierdie studie was die fokus op die selektiewe verwydering van spesifieke fraksies van die oorspronklike IPPK, herkombinering van die oorblywende fraksies, en die studie van die eienskappe van hierdie herkombineerde polimeriese materiale. Daar is gevind dat sommige van die eienskappe van die herkombineerde materiale daadwerklik verskil van die oorspronklike materiaal, en dat die verskille direk verband hou met die spesifieke fraksie wat uit die oorspronklike materiaal verwyder is. Die mate van fase-skeiding asook die kristal-morfologie van die herkombineerde materiaal het opmerklik verskil van die oorspronklike. Tydens die studie is n effektiewe manier ontwikkel om die materiale te vlek vir transmissie elektron-mikroskopie (TEM). Verder is daar ‘n verband tussen die resultate verkry deur Fourier Transform infrarooi spektroskopie (FTIS) en die verkry met TEM en skandeer elektron mikroskopie (SEM) vasgestel. Die verwantskap tussen FTIS en fase-skeiding is tot dusver nie in die wetenskaplike literatuur vermeld nie. Meer spesifiek is daar gevind dat absorbsie-bande sigbaar by 1100 cm-1 en 1080 cm-1 in die FTIS spektra ‘n aanduiding van fase skeiding kan wees. Dit was verder vasgestel dat spesifieke kopolimeer fraksies wat teenwoordig is in die oorspronklike IPPK, nie alleen die morfologie van die materiaal beinvloed nie, maar ook die hardheid en impak-weerstand van die materiaal.

Thesis (MSc (Chemistry and Polymer Science))--University of Stellenbosch, 2007. / This study comprises the synthesis, functionalization, and characterization of 1-butene oligomers, as well as the synthesis of oligobutene-based macro-RAFT agent. The directed oligomerization of 1-butene was carried out with a Cp2ZrCl2 as a catalyst, activated with MAO as a co-catalyst (10% in toluene), in the ratio Al/Zr =1000/1. Oligomers possessing vinylidene double bonds, with low molecular weight (Mw), ranging between 800 and 2000 g.mol-1 as confirmed by gel permeation chromatography, were obtained. The oligomers were successfully functionalized by adding hydroxyl functionality to the vinylidene double bond using oxymercuration-demercuration reaction, and as a result hydroxy-terminated oligobutenes were obtained. Characterization techniques such as 1H NMR, 13C NMR, GC-MS and FTIR confirmed the successful synthesis and functionalization of 1-butene oligomers. The hydroxy-terminated oligobutenes were used to prepare an oligobutene-based macro-RAFT agent. The synthesis of the macro-RAFT agent was carried out with an esterification reaction between the hydroxy-terminated oligobutenes and an acid functionalized RAFT agent. The successful synthesis of the macro-RAFT agent was confirmed by 1H NMR, 13C NMR, FTIR, and UV spectroscopy. The chain transfer ability of the macro-RAFT agent to induce living characteristics in free radical styrene polymerization was investigated with respect to molecular weight control and kinetic behaviour. The macro-RAFT agent was identified as suitable RAFT agent, yielding polystyrene-b-oligobutnes with low polydispersities and molecular weight ranging from 3000 to 40000 g/mol.

Thesis (MSc (Chemistry and Polymer Science))--University of Stellenbosch, 2006. / Cellulose, one of the most abundant organic substances on earth, is a linear polymer of D-glucose units joined through 1,4-β-linkages. Cellulose is however not easily processed without chemical modification. A number of techniques exist for the modification of cellulose, of which the viscose process is one of the most widely applied. Grafting of synthetic polymeric chains onto or from cellulosic materials is an useful technique that can be used to combine the strengths of synthetic and natural polymers dramatically, so changing the properties of cellulosic materials (pulp, regenerated cellulose, cellulose derivatives). In this study five model xanthate (Reversible Addition-Fragmentation chain Transfer (RAFT)/Macromolecular Design through Interchange of Xanthates (MADIX)) agents, namely, monofunctional, difunctional, trifunctional and tetrafunctional species of the form S=C(O-Z)-S-R, with different leaving groups and different activating moieties, were prepared and then studied to determine the feasibility of cellulose modification via addition fragmentation processes. These agents were characterized by Nuclear Magnetic Resonance spectroscopy (NMR), Fourier Transform Infrared spectroscopy (FT-IR) and Ultraviolet spectroscopy (UV). Polyvinyl acetates (PVAc) in the form of linear, three armed and four armed star shaped polymers were then successfully synthesized in reactions mediated by these xanthate RAFT/MADIX agents Xanthates were applied to polysaccharide materials using the viscose process (xanthate esters were formed directly on a cellulosic substrate, with subsequent alkylation) Grafting reactions were then conducted with the polysaccharides; cellulose was modified with vinyl acetate, [this is an example of a surface modification of natural polymers that is of interest in various industries, such as textiles and paper manufacture]. Analysis of the graft copolymers was conducted via Size Exclusion Chromatography (SEC), Liquid Adsorption Chromatography (LAC), Thermogravimetric Analysis (TGA), and FT-IR. Polyvinyl acetate was successfully grafted onto three polysaccharides (cellulosic materials), namely Hydroxyl Propyl Cellulose (HPC), Methyl Cellulose (MC) and cellulose. The study showed that the modification of cellulosic substrates with defined grafts of vinyl acetate can be easily achieved through minor modifications to existing industrial techniques.

Thesis (MSc (Chemistry and Polymer Science))--University of Stellenbosch, 2006. / Hydrophobic core/shell latex particles were synthesized for use in barrier coatings using the miniemulsion polymerization process. Particles with liquid or with hard cores were successfully synthesized using miniemulsion as a one-step nanoencapsulation technique. Different materials, including an oil (hexadecane, HD) and two different waxes (paraffin and microcrystalline wax), were used as the core of the particles. The shell of the particles was mainly made from a copolymer containing three relatively hydrophobic monomers, namely methyl methacrylate (MMA), butyl acrylate (BA) and vinyl neodecanoate (Veova-10). Before any further investigations could be carried out, it was important to determine the morphology of the synthesized core/shell particles at the nanometer level. Particle morphology was mainly determined by two different techniques: transmission electron microscopy (TEM) and atomic force microscopy (AFM). TEM was used to directly visualize the morphology of the investigated core/shell particles at the nanometer level, while AFM was used to confirm the formation of these core/shell particles. AFM was a powerful technique with which to study the particle morphology of the core/shell latices during the film formation process. As a second part of the study, the effect of various factors on the hydrophobicity and barrier properties of the resulting films produced from the synthesized core/shell latices to water and water vapour was investigated. This included the effect of: (i) the surfactant concentration, (ii) the wax/polymer ratio for both waxes, (iii) the molecular weight of the polymeric shell, (iv) the amount of the most hydrophobic monomer used (Veova-10), and (v) the degree of crosslinking in the polymeric shell. Results showed that all the above-mentioned factors had a significant impact on the water sensitivity of the resultant films prepared from the synthesized core/shell latices. It was found that the presence of wax materials as the cosurfactant, instead of HD, in the miniemulsion formulation could significantly improve the hydrophobicity and barrier properties of the final films to water and water vapour. In addition, increasing the amount of wax, Veova-10, and the molecular weight of the resultant polymeric shell, led to a significant increase in the hydrophobicity and barrier properties of the resultant latex films. In contrast, hydrophobicity and water barrier properties decreased drastically as the quantity of surfactant and degree of crosslinking increased in the final latex films.

Thesis (MSc (Chemistry and Polymer Science))--University of Stellenbosch, 2006. / Co-crystallization is the phenomenon by which chains of different crystallizabilities crystallize at the same temperature. Co-crystallization is frequently observed in the blends of different types of polyethylene. It is believed that co-crystallization can occur due to the thermodynamically miscible parts of two components in the blends having similar crystallization rate. The study focused on the phenomenon of co-crystallization in polyethylene blends and how by varying the crystallization conditions the co-crystallization region will change. Three techniques have been used in this study. TREF was used to fractionate the polymers and blends. Each of the TREF fractions was studied using both DSC and CRYSTAF to determine whether the fraction contained both types of materials. It is shown that the difference in the crystallization fractionation mechanisms between TREF, CRYSTAF and DSC can be utilize to study co-crystallization effects in polyethylene blends. Results also shows that by varying the heating and cooling rate profiles in DSC and CRYSTAF the co-crystallization fractions will appeared as a single fraction or as two separate fractions. Further, it was demonstrated how the co-crystallization area could be illustrated using a unique 3-dimensional plot where the data from the prep-TREF fractionation, and the DSC and CRYSTAF, were combined to give the “crystallization map” of the blend. These plots give a quiche visual illustration of any co-crystallization regions in the blends as well as how much the crystallization conditions effect the blend crystallization.

Thesis (MSc (Chemistry and Polymer Science))--University of Stellenbosch, 2007. / The synthesis of complex architectures, namely block copolymers with tailored enduse properties, is currently an important research area in academia and industry. The challenge is finding a versatile polymerization technique capable of controlling the molecular properties of the formed copolymers, which in turn determines their macroscopic properties. Reversible addition-fragmentation chain transfer (RAFT)- mediated living polymerization is a robust technique capable of producing controlled polymer products. With the great advances in living polymerization techniques and the environmental awareness of society there is an increasing demand to produce these polymer products via the RAFT living technique in heterogeneous media. Conventional emulsion and miniemulsion polymerization present various problems when used to produce polymers mediated by the RAFT process. There is an inherent need to find cost effective and flexible operating conditions to conduct RAFT polymerization in heterogeneous media with the ability to produce well-defined block copolymers. In this study the use of three novel trithiocarbonate RAFT agents to produce welldefined AB-type, ABA-type and star block copolymers via the RAFT process was investigated. Optimal operating conditions for the production of living block copolymers in homogenous and heterogeneous media were determined. The main focus was on the development of the RAFT process in heterogeneous media to efficiently produce block copolymer latex products. The RAFT-mediated miniemulsion polymerization system stabilized with non-ionic surfactants was thoroughly investigated. The ability of the ab initio and in situ RAFT-mediated emulsion polymerization systems to produce controlled latexes was demonstrated. Controlled block copolymer products were successfully synthesized in homogenous and heterogeneous media via the RAFT process when the optimum reaction conditions were chosen.

Thesis (MSc (Chemistry and Polymer Science))--University of Stellenbosch, 2006. / This study concerns the investigation of the isomerization of different metallocene catalysts in solution, and the effects thereof on the microstructure of polypropylenes prepared with these catalysts. Two C2 symmetric ansa metallocenes, ethylene-bis(indenyl) zirconium dichloride (EI) and dimethylsilyl-bis(2-methyl benzoindenyl) zirconium dichloride (MBI) were exposed, in solution, to both sunlight and UV radiation. The rac-meso isomerization of these catalysts were followed by 1H NMR spectroscopy. The reaching of a photostationary state is described, as well as the effect of isomerization of these catalysts in solution on the polymerization of propylene. Results show that metallocene structure has an effect on the isomerization rate and photostationary state. Results also show that the wavelength of light plays a role in the isomerization process. Effects on stereochemistry and molecular weight of the formed polymer as well as the catalyst activity is described and discussed. In addition the effect of activating the catalysts with MAO before exposure to light is discussed.

Thesis (MSc (Chemistry and Polymer Science))--University of Stellenbosch, 2007. / Hybrid A-B type block copolymers of polydimethylsiloxane (PDMS) and polystyrene (PS) were synthesised. Three different synthetic routes, which allowed control over polymer structure, were chosen to synthesise these block copolymers. The first technique, coupling of functional prepolymers, involved using anionic polymerisation to produce PDMS and PS functional prepolymers of controlled structure. These prepolymers were functionalised with either silane or allyl functionality and then coupled using a hydrosilylation reaction with Karstetds platinum catalyst. This technique was the least efficient in block synthesis due to the incompatibility of the disparate prepolymers. The second technique under study, sequential anionic polymerisation, gave excellent block copolymer formation with good control over the chain architecture. The final technique employed atom transfer radical polymerisation (ATRP) of styrene using a bromoisobutyrate functionalised PDMS macroinitiator. Silane functional PDMS molecules underwent a hydrosilylation reaction with allyl-2-bromo-2-methyl-propionate to produce the bromoisobutyrate functionalised polymer in excellent yields. Subsequent ATRP with styrene allowed the successful synthesis of block copolymers of controlled structure. Chromatographic systems that allowed liquid chromatography at the critical conditions (LC-CC) of PS and gradient elution chromatography (GEC) of the products were developed. GEC was used successfully in the monitoring of the presence and removal of PDMS homopolymer present in the block copolymer products. LCCC at the critical point of PS allowed successful chromatographic separation of PS homopolymer from the block material, as well as, the molecular weight distribution of the block material according to the segmental length of the PDMS component. LC-CC coupled to FT-IR using a LC-transform device allowed successful characterisation of the block copolymer chemical composition. Corona treatment was used to modify the surface structure of the block copolymer films. Optical microscopy and slow positron beam studies highlighted the formation of a thin silica like layer on the surface of the films after corona. The positron studies enabled determination of the silica like layer’s thickness. Contact angle studies provided the first evidence of hydrophobic loss and recovery for these PDMS containing hybrid polymer materials after corona treatment. A novel offline coupling technique was developed between LC-CC separation and transmission electron microscopy (TEM) analysis. This allowed easy sample preparation without the difficult bulk extraction procedures needed to remove homo-PS contaminants from the block copolymer. This technique also provided morphological information as a function of PDMS segmental length.

Thesis (MSc (Chemistry and Polymer Science))--University of Stellenbosch, 2008. / This study involved (a) the development and testing of a solution turbidity fractionation analyser (TFA) and (b) the investigation of possible molecular weight effects on solution crystallisation. To investigate the latter highly isotactic polypropylene was polymerised with a C2 symmetric metallocene catalyst. Blends were made of these homopolymers. The homopolymers as well as the blends were fractionated by means of temperature rising elution fractionation (TREF). The fractionated and unfractionated homopolymers as well as the fractionated blends were characterised by 13C NMR, differential scanning calorimetry (DSC) and gel permeation chromatography (GPC). The TFA was successfully developed and helped in explaining the shifting of solution crystallisation temperature that was seen when blending of the homopolymers occurred. This was done performing analyses on the machine of blends of the homopolymers. Fractions, of the homopolymers and blends, obtained from TREF were also done. Subsequent runs of blends made from the fractions obtained from TREF were also done. In the end it was shown that the shift of the solution crystallisation temperature is either due to the tacticity or the molecular weight depending on the sample.

Thesis (MSc (Chemistry and Polymer Science))--University of Stellenbosch, 2006. / Graft and block copolymers were synthesized using multifunctional and monofunctional macroinitiators to produce the copolymers. The process involved hydroboration of commercially available unsaturated rubbers and chain-end unsaturated macromonomers with 9-borabicyclo [3.3.1] nonane (9-BBN). The resulting secondary alkyl 9-BBN moieties in the starting materials were subsequently exposed to oxygen in the presence of free radical polymerizable monomers to facilitate the formation of graft and block copolymers. This research was initiated by first studying the hydroboration of a model compound, 2-hexene, in order to determine the optimal conditions for the graft reactions. The model compound was subsequently used as a macroinitiator to initiate the polymerization of methylmethacrylate (MMA). The same borane chemistry was extended to the synthesis of polystyrene (PS) block copolymers. Chain-end unsaturated PS macromonomers, synthesized by anionic polymerization, were effectively hydroborated and then polymerized to produce PS-b-PMMA block copolymers. The synthesis of polyolefin graft copolymers was subsequently achieved by hydroboration. Several commercial rubbers with different levels of unsaturated segments were efficiently grafted with vinyl monomers MMA and styrene (St) following the “graft from” approach. The grafted reactions were carried out under various reaction conditions to determine the effect of the following factors: concentration of oxygen, amount of borane and monomer concentration. By controlling these factors, different graft densities were achieved with high graft efficiencies. All reactions produced mixed products including unreacted (non-functional) macroinitiator, homopolymer, graft copolymer and in case of the highly unsaturated polymer a crosslinked gel. Finally, the chemical compositions as well as the molar mass distribution of the graft copolymers were fully characterized by different chromatographic techniques. 1H-NMR and FTIR were also used to confirm the structure of these copolymers. Gradient HPLC was developed and extensively used to characterize the graft copolymers.