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.

Thesis (MSc (Chemistry and Polymer Science))--University of Stellenbosch, 2005. / Synthesis of two surfmers (cationic and anionic) was carried out and the surfmers were used to stabilize particles in miniemulsion polymerization. Surfmers were used to eliminate adverse effects associated with free surfactant in the final product e.g. films and coatings. The Reversible Addition Fragmentation chain Transfer (RAFT) polymerization process was used in miniemulsion polymerization reactions to control the molecular weight distribution. RAFT offers a number of advantages that include its compatibility with a wide range of monomers and solvents. Moreover block copolymer synthesis is possible via chain extension. A comparative study between classical surfactants and surfmers was conducted in regard to reaction rates and molar mass distribution. The rates of reactions of surfmer stabilized RAFT miniemulsion polymerization of Styrene and MMA were similar (in most cases) to classical surfactant stabilized RAFT miniemulsion polymerization reactions. The final particle sizes were also similar for polystyrene latexes stabilized by surfmers and classical surfactants. However PMMA latexes stabilized by surfmers had larger particle sizes compared to latexes stabilized by classical surfactants. The surfmers were also oligomerized in homogeneous media using the RAFT process and their Mn values were estimated using UV-VIS spectroscopy. The oligosurfmers were then used as emulsifiers in RAFT miniemulsion polymerization. The rates of reaction were slower than rates obtain when the surfmers (monomer or oligosurfmers) were used directly as emulsifiers in RAFT miniemulsion polymerization of styrene and MMA. The final latex particle sizes obtained with oligosurfmers were also larger than that of latex stabilized by their parent monomers. The RAFT process was successfully applied in miniemulsion polymerization in both classical surfactant and surfmer stabilized miniemulsions. The molecular weight increased with conversion showing that the molecular weights of the polymers were controlled.

Thesis (MSc (Chemistry and Polymer Science))--University of Stellenbosch, 2007. / Two series of poly(methyl methacrylate)-graft-poly(dimethylsiloxane) copolymers were synthesized via conventional free radical copolymerization of methylmethacrylate and monomethacryloxypropyl terminated PDMS macromonomers of different lengths. It is shown how these copolymers can be electrospun to produce the copolymer nanofibers. The affects of copolymer compositions, the electrospinning tip-to-collector (TCD) distance and the concentration of the polymer solution on the fiber morphology are discussed. Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM) were used to establish the surface topography as well as the fiber morphology of the electrospun copolymer nanofibers. It is also shown that these nanofibers produce superhydrophobic surfaces where the preferential surface segregation of the PDMS component is combined with the roughness of the nanofiber surface. It is shown that after exposure of these nanofiber surfaces to corona discharge, the initial superhydrophobic surfaces become easily wettable. The samples show the phenomena of hydrophobicity recovery after corona exposure. The rate and extent of this recovery depends on the PDMS content of the nanofibers as well as the time of corona treatment. The hybrid copolymer nanofibers were evaluated as potential reinforcing fillers for cross linked polydimethylsiloxane compounds. The fibers show a remarkably good distribution in the PDMS matrix and show a dramatic improvement in the mechanical properties of the composites.

Thesis (MSc (Chemistry and Polymer Science))--University of Stellenbosch, 2006. / Isotactic polypropylene (iPP) exists in four different crystalline phases: α-, β-, γ- and the mesomorphic (smectic) form. The α-phase is probably the most predominant form of iPP with a monoclinic unit cell, whereas the unit cell of the γ-phase is orthorhombic. The aim of this study was to examine the ability of AFM to identify the α and γ crystalline forms of polypropylene and polypropylene copolymers that were not especially treated. Spherulites imaged on propylene-ethylene random copolymer surfaces had diameters ranging from 10-30μm and predominantly radial lamellae. The cross-hatching phenomenon of isotactic polypropylene was observed for samples containing both the α- and γ-phase. Two types of γ-phase spherulites were observed, namely a featherlike form for samples with a high content of the γ-phase and a bundle-like form with varying sizes, which is typical for the mixed structure of both α- and γ-forms. In some images of polypropylene-ethylene copolymer sample lozenge-shaped structures could be observed between the γ-spherulites, which might be single polyethylene crystals. Both the α- and γ-phase of iPP were successfully imaged and identified with AFM without prior treatment of the surface. The degree of crystallinity obtained from AFM images was calculated as a percentage of the surface area exhibiting regular structures. The results compared well to X-ray results.

Thesis (MSc (Chemistry and Polymer Science))--University of Stellenbosch, 2005. / This study involves the fractionation and characterisation of three propyleneethylene random copolymers. The fractionation technique used in the study was temperature rising elution fractionation (TREF). The TREF fractions were subsequently analysed offline by crystallisation analysis fractionation (CRYSTAF), differential scanning calorimetry (DSC), 13C NMR, high-temperature gel-permeation chromatography (HT-GPC), and wide-angle x-ray diffraction (WAXD). The effect of the ethylene comonomer on the crystallisability of the propylene was investigated, along with the effect of the comonomer on the type of crystal phase formed during the crystallisation. The results show that the comonomer inhibits the crystallisation of the copolymer and that as the ethylene content increases, the crystallisation and melting points decrease. It was also shown that the higher the ethylene content, the more of the γ-phase crystal type is formed. The distribution of the comonomer throughout the copolymers was also investigated. The results show that there is an uneven distribution of the comonomer with most of the comonomer accumulating in the amorphous areas, and very little actually being incorporated in the crystalline regions. It was also observed that the fractions eluting at the highest temperatures had considerably higher polydispersities and lower molecular weights than the fractions eluting just before them. The highest temperature fractions also have lower melting and crystallisation temperatures than the preceding fractions. This has been attributed to a nucleation effect by the sand support used during the TREF fractionation.

119 leaves single sided printed, preliminary pages and numbered pages 1-101. Includes bibliography and a list of tables, figures, schemes and abbreviations. Digitized at 300 dpi (OCR), used Bizhub 250. / Thesis (MSc (Polymer Science))--University of Stellenbosch, 2006. / ENGLISH ABSTRACT: The properties and interactions of cellulose surfaces are of a great technical interest during papermaking and recycling. Sizing, the modification of fiber surfaces, e.g. with the purpose to reduce water penetration into the paper structure, plays an important role in obtaining paper with good printability and water resistance. Water resistance is the key end-property of paper being investigated in this study. Firstly a comparison was made between the degree of surface modification of cellulose by means of anionic, nonionic and reactive surfactants. The amount of surfactant adsorbed by the paperboard was determined and the paper surface evaluated via scanning electron microscopy (SEM). The sizing efficiency of the three industrial surfactants was evaluated in order to establish the surfactant structure best suited for sizing recycled paperboard. This was done via the Cobb test, an industrial method to measure water uptake by paper, and contact angle measurements. The reactive surfactant was found to have the best sizing efficiency and focus shifted to synthesizing selected copolymer surfactants via free radical copolymerization. Two copolymers were synthesized, with maleic anhydride as the polar part in both. Butyl methacrylate and lauryl methacrylate were selected as the hydrophobic parts in the respective copolymer systems. The unavailability of reactivity ratios for the respective copolymer systems led to the use of in situ proton nuclear magnetic resonance spectroscopy CH NMR) for the determination of the co-monomer incorporation in both copolymer systems. Quantitative 13C NMR spectroscopy was also employed in order to establish the co-monomer content of the isolated copolymers obtained during bench-scale (laboratory) experiments. Lastly, a comparison of the degree of surface modification of cellulose was made between that which was achieved with the industrial reactive surfactant and that with the two synthesized polymeric reactive surfactants. The two synthesized polymeric surfactants were found to have a better sizing efficiency than the industrial reactive surfactant, and the maleic anhydride-lauryl methacrylate copolymer system gave the best results. / AFRIKAANSE OPSOMMING: Die eienskappe en interaksies van sellulose-oppervlaktes is van groot tegniese belang gedurende die vervaardiging en hergebruik van papier. Oppervlakte behandeling, die modifikasie van vesel-oppervlaktes bv. met die doel om water indringing in die papierstruktuur te verminder, speel 'n belangrike rol in die daarstel van papier met goeie drukkwaliteit en waterweerstand. Waterweerstand is die sleuteleienskap van papier wat in hierdie werkstuk ondersoek word. Eerstens is daar 'n vergelyking getref tussen die verandering van sellulose-oppervlaktes deur middel van anioniese, nie-ioniese en reaktiewe sepe. Die hoeveelheid seep geabsorbeer deur die papierbord is bepaal en die papier-oppervlak ondersoek deur middel van skandeer-elektronmikroskopie (SEM). Die behandelingsdoeltreffendheid van die drie industriele sepe is ondersoek om vas te stel watter seep die beste struktuur het om hergebruikte papierbord effektief te behandel. Dit is gedoen deur middel van die Cobbtoets, 'n industriele metode om wateropname van papier te meet, asook kontakhoekmetings. Daar is gevind dat die reaktiewe seep die beste behandelingsdoeltreffendheid het en daar is vervolgens gekonsentreer op die bereiding van geselekteerde reaktiewe kopolimeersepe deur middel van vryeradikaalkopolimerisasie. Twee kopolimere is berei, met maleienanhidried as die polere gedeeite van albei. Butielmetakrilaat en laurielmetakrilaat is gekies vir die nie-polere gedeeltes van die onderskeie kopolimeersisteme. Die onbeskikbaarheid van reaktiwiteitsverhoudings vir die onderskeie kopolimeersisteme het gelei tot die gebruik van in situ proton kern magnetiese resonansie spektroskopie eH KMR) vir die bepaling van die ko-monomeer insluiting in beide kopolimeersisteme. Kwantitatiewe koolstofdertienkemmagnetieseresonansie spektroskopie (13C KMR) is ook gebruik om die ko-monomeerinhoud van die geisoleerde kopolimere, verkry tydens laboratoriumeksperimente, te bepaal. Laastens is 'n vergelyking getref tussen die graad van modifikasie van selluloseoppervlaktes deur middel van die industriele reaktiewe seep in vergelyking met die twee bereide polimeriese reaktiewe sepe. Daar is gevind dat die twee gesintetiseerde polimeriese sepe beter behandelingsdoeltreffendheid as die industriele reaktiewe seep het, met die maleienanhidried-laurielmetakrilaat-kopolimeersisteem wat die beste resultaat lewer.

Thesis (MSc)--Stellenbosch University, 2004. / ENGLISH ABSTRACT: Polydimethylsiloxane (PDMS) compounds are utilized in outdoor high voltage insulation due to their low weight, vandalism resistance, better anti-contamination performance and their superior hydrophobic nature. Under severe environmental conditions and over prolonged service time, however, the hydrophobic surface can gradually become hydrophilic and then recover with adequate resting period. In this study, room temperature vulcanized (RTV) PDMS samples were prepared with different formulations and then exposed to corona discharge to evaluate its effect. The influence of different additives, such as different types and amount of fillers and additionally added low molar mass silicone oils, on the hydrophobicity recovery of the material was investigated. The effects of two types of corona treatment were also evaluated. Hydrophobicity recovery of corona and UV-C aged PDMS samples was evaluated by means of static contact angle measurements. Positron annihilation spectroscopy (PAS) gave important information on the micro structural change after corona treatment of RTV PDMS as well as naturally aged high temperature vulcanized (HTV) PDMS samples. The different formulations of the RTV PDMS samples and the effect of the additives were studied with this technique. The formation of a thin, highly crosslinked inorganic silica-like (SiOx) layer was confirmed even at the early stage of degradation. It was also possible to estimate the thickness of the silica-like layer formed during corona exposure that is responsible for the loss and recovery of hydrophobicity. The surface hardness and hydrophilicity change of PDMS samples due to corona treatment were studied simultaneously with force distance measurements by atomic force microscopy (AFM). The adhesive force calculated from the pull-off force-distance curves showed that the adhesive force between the probe and the sample decreased with increasing corona treatment time, indicating hydrophobicity recovery. In addition to this, the increase in hardness after corona exposure provides indirect evidence of the formation of a silica-like layer. In all cases the hydrophilicity and the surface hardness of the PDMS samples increased directly after corona treatment and recovered with time. Two types of FTIR spectroscopy were used to analyse the surface of the polymer. / AFRIKAANSE OPSOMMINGS: Polidimetielsiloksaan (PDMS) word in buitelug hoogspanninginsulasie gebruik as gevolg van sy lae massa, weerstand teen vandalisme, verbeterde anti-kontaminasie werkverrigting en superieure hidrofobiese karakter. Die hidrofobiese oppervlakte kan egter gelydelik hidrofillies word onder uiterste omgewingsomstandighede en oor langdurige dienstyd. PDMS materiaal herstel egter nadat dit genoeg rustyd toegelaat is. Kamertemperatuur-gevulkaniseerde (KTV) PDMS met verskillende formulasies is in hierdie studie voorberei, aan korona ontlading blootgestel, geëvalueer en vergelyk. Die invloed van bymiddels soos verskillende tipes en hoeveelhede vuiler, asook addisionele lae molekulêre massa silikoonolie, op die herstel van hidrofobisiteit van die materiaal is ondersoek. Twee verskillende metodes van korona behandeling is ook geëvalueer. Die herstel van hidrofobisiteit van korona en UV-C verouderde PDMS monsters is met statiese kontakhoekmeting geëvalueer. Positronvernietigingspektroskopie (PVS) is 'n kragtige tegniek wat belangrike inligting oor die mikrostrukturele verandering van korona behandelde van KTV PDMS sowel as natuurlik-verouderde hoë temperatuur gevulkaniseerde (HTV) PDMS monsters gee. Die verskillende formulasies van die KTV PDMS monsters, sowel as die effek van die vullers, is met behulp van hierdie tegniek ondersoek. Die vorming van 'n dun, hoogskruisgebinde, anorganiese silika-agtige (SiOx) laag op die PDMS oppervlak, selfs tydens die vroeë stadium van degradasie, is bevestig. Dit was ook moontlik om die dikte van die silika-agtige laag wat gedurende die korona blootstelling gevorm het, en wat verantwoordelik is vir die verlies aan hidrofobisiteit, te bepaal. Die oppervlakhardheid en hidrofilisiteit verandering van PDMS monsters as gevolg van korona behandeling, was gelyktydig met krag-afstand metings deur middel van atoomkragmikroskopie (AKM) bestudeer. Die kleefkrag, soos bereken van aftrek kragafstandkurwes, dui daarop dat kleefkragte tussen die taster en die monster afneem met toenemende korona behandelingstyd, wat beduidend is op die herstel van hidrofobisiteit. Daarbenewens is die toename van oppervlakhardheid na korona blootstelling "n indirekte bewys van die formasie van 'n silika-agtige laag. In alle gevalle het die hidrofilisiteit en die oppervlakhardheid van die PDMS monsters toegeneem direk na afloop van korona behandeling en gevolglik herstel met tyd. Twee tipes IR spektroskopie metodes is gebruik vir die chemiese-oppervlak analises

Thesis (MSc (Chemistry and Polymer Science))--University of Stellenbosch, 2010. / ENGLISH ABSTRACT: Unsaturated polyesters resins (UPRs) of maleic anhydride (MA), phthalic anhydride (PA) and propylene glycol (PG) were synthesized using the fusion polycondensation process for use in Multi-vesiculated Particles (MVPs). The UPRs were synthesized using different MA:PA mole ratios and process parameters, including heating rates, agitation speed, exotherm rate and maximum processing temperature. Design of Experiments (DoE) software (Design Expert 7) was employed to find the optimum experimental space, i.e. least amount of experiments, but covering all the factors. The variations in the formulation and process parameters had a significant effect on the molecular structure and physical properties of the UPRs. The molecular structure and physical properties of the UPRs was successfully determined using various techniques including viscometry, acid-base titration, Proton Nuclear Magnetic Resonance (1H NMR) spectroscopy, Size-Exclusion Chromatography (SEC), Fourier Transform Infrared (FTIR) spectroscopy and Differential Scanning Calorimetry (DSC). Furthermore, the carboxyl and hydroxyl end-group concentrations of the UPRs were determined by derivatization of the groups with trichloroacetyl isocyanate (TAI) and analysis by 1H NMR. As a second part of the study, the effect of the above-mentioned monomer ratio and process factors of the UPRs, on the properties of the MVPs (produced from the UPRs), was investigated. Results showed that these factors had a significant effect on the particle size and degree of vesiculation of the MVPs. The degree of vesiculation of the MVPs was determined by Scanning Electron Microscopy (SEM). Attempts were also made to determine the relative hardness of the MVPs by AFM and microhardness testing to determine a relationship with UPRs properties (e.g. molecular weight, degree of unsaturation and chain branching). These techniques were however found to be unsuitable due to the physical nature of the MVPs. / AFRIKAANSE OPSOMMING: Onversadigde poliësters (OPs) van maleïensuuranhidried (MA), fataalsuuranhidried (PA) en propileen glikol (PD) is berei deur die fusie polikondensasie-proses vir gebruik in multi-vesikulerende partikels (MVPs). Die OPs is berei deur gebruik te maak van verskillende MA:PA molverhoudings en reaksie faktore wat verhittingstempo‟s, roerspoed, eksoterm tempo en maksimum reaksie temperatuur, insluit. As gevolg van die groot hoeveelheid faktore is eksperimentontwerp sagteware (Design Expert 7) gebruik om die aantal eksperimente te verminder, maar ook waardevolle afleidings van die data te maak. Die verskille in die formulasie en reaksie faktore het „n merkwaardige effek op die molekulêre struktuur en fisiese eienskappe van die OPs gehad. Hierdie eienskappe is bepaal m.b.v. verskeie tegnieke, naamlik viskometrie, suur-basis titrasie, Proton Kern-Magnetiese Resonansie (1H KMR) spektroskopie, Grootte-Uitsluitings-Chromatografie (SEC), Fourier Transform Infrarooi (FTIR) spektroskopie en Differensiële Skandeerings Kalorimetrie (DSC). Die hidroksiel en karboksielgroep konsentrasies van die OPs is bepaal deur hul reaksie met trichloroasetiel-isosianaat (TAI) gevolg deur 1H KMR analise. In die tweede deel van hierdie studie is die invloed van bogenoemde faktore op die eienskappe van die MVPs ondersoek. Die resultate het getoon dat hierdie faktore „n merkwaardige effek op die partikel grootte en graad van “vesiculation” van die MVPs gehad het. Die graad van “vesiculation” van die MVPs is bepaal met behulp van Skandeer Elektron Mikroskopie (SEM). Pogings is ook gemaak om die relatiewe hardheid van die MVPs te bepaal deur middel van AFM en Mikro-hardheid toetsing. Dit is gedoen om die verhouding van die OPs eienskappe (molekulêre gewig, graad van onversadigheid en sy-kettings) vas te stel. Hierdie tegnieke is egter ongeskik bevind as gevolg van die inherente fisiese aard van die OPs.