Thesis (MSc)--Stellenbosch University, 2001. / ENGLISH ABSTRACT: A novel approach to conducting controlled free radical polymerization in aqueous systems using Reversible Addition-Fragmentation Chain Transfer (RAFT) has been studied. When conducting RAFT in aqueous systems, reaction conditions must be chosen such that monomer transport across the aqueous-phase is either eliminated or facilitated. This is to prevent the formation of the red layer associated with RAFT in emulsions. The formation of the red layer is ascribed to the inability of waterinsoluble, dithiobenzoate-endcapped oligomers to be sufficiently transported across the aqueous phase. The novel approach in this study focussed on eliminating monomer transport and comprises two fundamental steps: the synthesis of dithiobenzoate-encapped oligomers in bulk followed by miniemulsification of these oligomers to yield a polymerizable miniemulsion. Dithioesters that act as chain transfer agents in the RAFT -process were synthesized in situ, thereby eliminating laborious and time-consuming organic purification procedures of dithioesters. In situ formation of the RAFT-agents involved conducting the reaction between di(thiobenzoyl) disulfide and conventional azo-initiators of differing structures in the presence of monomer. The structure of the chosen azo-initiator played a role in the efficiency of the RAFT process when the reaction was conducted in the presence of monomer to control the free radical polymerization process. Synthesis of the oligomers was performed by heating di(thiobenzoyl) disulfide and a selected azo-initiator, in the presence of monomer for a specific reaction duration in bulk. After the reaction was stopped, these oligomers were then miniemulsified by adding water, surfactant and cosurfactant, followed by the application of shear to form the resulting mini emulsion. The free radical polymerization of the dithiobenzoate-endcapped oligomers in the miniemulsion proceeded in a controlled manner with molecular weight increasing in a linear fashion with increasing conversion, while polydispersities remained low. The familiar red layer formation associated with RAFT polymerization in conventional emulsions was not observed under these conditions. The effects of changing the cosurfactant (hydrophobe) as well as changing the degree of polymerization of the emulsified oligomers were also investigated and described. / AFRIKAANSE OPSOMMING: Hierdie studie is geloods om 'n nuwe benadering tot die beheerde vry-radikaal polimerisasie in water gebaseerde sisteme te ondersoek. Daar is spesifiek gekyk na die uitvoer van die RAFT (Reversible Addition-Fragmentation Chain Transfer) proses in emulsies. Wanneer RAFT in emulsies toegepas word, moet die toestande waaronder die reaksie uitgevoer word, versigtig opgestel word. Die toestande moet so gekies word dat die vervoer van monomere deur die waterfase óf geëlimineer word óf gefasiliteer word. Dit word gedoen om die faseskeiding in die vorm van 'n rooi laag, wat so kenmerkend van RAFT -polimerisasie in emulsies is, te voorkom. Hierdie faseskeiding vind plaas omdat die vervoer van ditiobensoaat endgroep-bevattende oligomere deur die waterfase tydens interval II, moeilik is a.g.v. hulle oplosbaarheid in water. Die nuwe benadering wat hier bestudeer is, het twee basiese stappe. Eerstens word die ditiobensoaat endgroep-bevattende oligomere in bulk gesintetiseer. Dit word gevolg deur die emulsifisering van die oligomere. Hierna vind verdere polimerisasie van die oligomere plaas deur die dormante oligomere te heraktiveer. Die ditio-esters wat as kettingoordrag agente optree in die RAFT proses, word in situ gesintetiseer. Hierdie modifikasie sny tydrowende organiese suiweringsmetodes uit. Die in situ RAFT agente word gesintetiseer deur di(tiobensoïel) disulfied met verskillende konvensionele azo-inisieerders te laat reageer. Die struktuur van die spesifieke azoinisieerder het wel 'n rol gespeel in die effektiwiteit van die RAFT proses om molekulêre massa te beheer as bg. reaksie in die teenwoordigheid van monomere uitgevoer is. Die sintese van die oligomere is gedoen deur di(tiobensoïel) en 'n azo-inisieerder te verhit in die teenwoordigheid van monomere. Die reaksie is gedoen in bulk en die graad van polimerisasie van die oligomere is beheer deur die reaksie te stop by verskillende tydstippe. Nadat die bulk reaksie gestop is, is hierdie oligomere ge-emulsifiseer deur die oligomere te meng met 'n seep, hidrofoob en water. Hierdie mengsel word dan onderwerp aan 'n vermengingskrag om 'n polimeriseerbare mini-emulsie te vorm. Die voortsetting van die polimerisasie van die oligomere in die mini-emulsie het op 'n beheerde wyse verloop, m.a.w. molekulêre massa wat linieêr toeneem met stygende omsetting. Polidispersiteit indekse van die polimere het deurentyd laag gebly in die stabielste sisteme. Onder hierdie toestande was daar geen kenmerkende rooi laagvorming te bespeur nie. Die effekte wat die verandering van die hidrofoob, asook die verandering van die graad van polimerisasie van die oligomere op die sisteem gehad het, is onder andere ook ondersoek en beskryf.

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Thesis (M.S.)--Ohio University, March, 2006. / Title from PDF t.p. Includes bibliographical references (p. 113-116)

Thesis (MSc (Chemistry and Polymer Science))--University of Stellenbosch, 2005. / Polymerization using the reversible addition-fragmentation chain transfer (RAFT) process affords a researcher control over the molecular weight and polydispersity of the final polymer. Research is being carried out globally, using heterogeneous RAFT systems, as these systems offer superior industrial possibilities. Many emulsion systems fail when incorporating RAFT agents due to phase separation and colloidal instability. Exchanging conventional emulsion polymerizations with predispersed polymerization systems (i.e. miniemulsions) has shown many improvements. Evidence of uncontrolled aqueous phase polymerization (i.e. not mediated by the RAFT process) has however been found. This behaviour is similar to polymerization in a conventional emulsion polymerization system, but is not expected in miniemulsion polymerization.

Thesis (MSc (Chemistry and Polymer Science))--University of Stellenbosch, 2006. / Synthesis of a series of poly (methylmethacrylate)-graft-poly (styrene) polymer was carried out via free radical polymerization of methylmethacrylate and polystyrene macromonomers. The macromonomers were synthesized via living anionic polymerization techniques. Two series of macromonomers where synthesized with different polymerizable end group functionalities, by termination with p-vinyl benzyl chloride and 3-(dimethyl chloro silyl) propyl methacrylate. The branch density was varied by controlling the composition feed ratio of the macromonomers to comonomer. Liquid chromatographic techniques were used to fully characterize the chemical composition and branch distributions of the graft polymer. Liquid chromatography under critical conditions of adsorption of styrene coupling with Fourier Transform Infrared Spectra was used to investigate the chemical composition and distribution of the branches in the graft. Physical properties of the graft copolymers such as Tg and free volume were determined using differential scanning calorimetry and positron lifetime spectrometry respectively. The relationship between the chemical composition and the graft copolymer properties such as Tg and free volume were investigated. The results show that for long chain macromonomers phase segregation occurs in the graft copolymers. In the case of shorter chain macromonomers at low content no phase segregation is observed and the macromonomers have an antiplasticization effect on the graft polymers.

Thesis (MSc (Chemistry and Polymer Science))--University of Stellenbosch, 2005. / The primary focus of the research was the use of adamantane-containing molecules in polymer science. The research is divided into 2 parts, the first involving the syntheses of a new ligand for use in a metallocene catalyst system. The second part involved the synthesis of new monomers for the use in free radical polymerization systems, In the first part of the research, the synthesis of the ligand, 2-dimethyladamantylethylcyclopentadiene was attempted. This was done via the starting materials adamantylethylbromide and dimethylfulvene. In the first step the adamantylethylbromide was prepared via the tosylation reaction of admantaneethanol. Further, the use of either a Grignard or Barbier reaction to insert the 6,6 dimethylfulvene to yield the final product was attempted. The isolation of the final product could not successfully be completed, even though spectroscopic evidence suggested that the synthesis had been partially succssful. In the second part of the reasearch, the monomers 4-(1-adamantyl)phenolmethacrylate, adamantylmethylacrylate and admantylethylacrylate were synthesized. These monomers were homo-and copolymerized using a controlled radical reaction mechanism (RAFT).

Thesis (MSc)--University of Stellenbosch, 2007. / ENGLISH ABSTRACT: The main objective of this project was the controlled synthesis of graft copolymers via a thiol-ene addition mechanism. The Reversible Addition-Fragmentation chain Transfer (RAFT) process was used in all polymerization reactions with the aim to achieve a certain degree of control over the molecular weight. Several synthetic steps were required in order to obtain the final graft copolymer and each step was investigated in detail. Firstly, two RAFT agents (cyanovaleric acid dithiobenzoate and dodecyl isobutyric acid trithiocarbonate) were synthesized to be used in the various polymerization reactions of styrene and butyl acrylate. This was done successfully and the RAFT agents were used to synthesize low molecular weight polystyrene branches of the graft copolymer. Different molecular weights were targeted. It was found that some retardation phenomena were present especially at high RAFT agent concentrations. The polystyrene branches that were synthesized contained RAFT end-groups. Various pathways were explored to modify these RAFT end-groups to form thiol end-groups to be used in the thiol-ene addition reaction during the grafting process. The use of sodium methoxide for this purpose proved most successful and no evidence of the formation of disulfide bridges due to the initially formed thiols was detected. Allyl methacrylate (AMA) was chosen as monomer to be used for the synthesis of the polymer backbone because it has two double bonds with different reactivities. For the first time, RAFT was used to polymerize AMA via the more reactive double bond to obtain linear poly(allyl methacrylate) (PAMA) chains with pendant double bonds. However, at higher conversions, gelation occurred and the molecular weight distributions were uncontrolled. NMR was successfully used to study the tacticity parameters of the final polymer. Finally, the synthesis of the graft copolymer, PAMA-g-polystyrene, was carried out by means of the “grafting onto” approach. The thiol-functionalized polystyrene branches were covalently attached to the pendant double bonds of the PAMA polymer backbone via a thiol-ene addition mechanism in the presence of a free radical initiator. A Multi- Angle Laser Light Scattering (MALLS) detector was utilized in conjunction with Size- Exclusion Chromatography (SEC) to obtain molecular weight data of the graft copolymer. The percentage grafting, as determined by 1H-NMR, was low. / AFRIKAANSE OPSOMMING: Die hoofdoel van hierdie projek is die beheerde sintese van ‘n entkopolimeer via ‘n merkaptaan-een addisiereaksie. Die sogenaamde “Reversible Addition-Fragmentation chain Transfer” (RAFT) proses is in al die polimerisasiereaksies gebruik met die doel om ‘n mate van beheer oor die molekulêre massa van die polimere te verkry. Verskeie stappe (waarvan elkeen ten volle ondersoek is) was nodig om die finale entkopolimeer te verkry. Eerstens is twee RAFT-agente (sianovaleriaansuur ditiobensoaat en dodekielisobottersuur tritiokarbonaat) gesintetiseer vir gebruik in verskeie polimerisasiereaksies van stireen en butielakrilaat. Hierdie stap was suksesvol en die RAFT-agente is toe gebruik vir die sintese van lae molekulêre massa polistireensytakke vir die entkopolimeer. Die molekulêre massas van die sytakke is gevarieer en daar is gevind dat vertragings in die polimerisasiereaksies voorgekom het, veral by hoë konsentrasies van die RAFT-agente. Die polistireensytakke wat gemaak is, besit almal ‘n RAFT-eindgroep. Verskeie roetes is bestudeer ten einde die RAFT-eindgroepe tot merkaptaan-eindgroepe te modifiseer om sodoende tydens ‘n merkaptaan-een addisiereaksie gebruik te word. Die gebruik van natriummetoksied was hier die suksesvolste en daar was geen teken van die vorming van disulfiedbrûe as gevolg van die oorspronklik gevormde merkaptane nie. Allielmetakrilaat (AMA) is gekies as die monomeer wat gebruik sou word vir die sintese van die polimeerruggraat omdat die monomeer twee dubbelbindings met verskillende reaktiwiteite besit het. Vir die eerste keer is RAFT gebruik vir die polimerisasie van AMA via die meer reaktiewe dubbelbinding om lineêre poli(allielmetakrilaat) (PAMA) kettings met dubbelbindings in die sygroepe te verkry. Gelvorming en onbeheerde molekulêre massaverspreiding het egter by hoër monomeeromsettings voorgekom. KMR is susksekvol gebruik om die taktisiteitsparameters van die finale polimeer te bestudeer. Ten slotte is die sintese van die entkopolimeer, PAMA-g-polistireen, uitgevoer deur die aanhegting van voorafgevormde sytakke. Die polistireensytakke met die merkaptaaneindgroepe is kovalent geheg aan die dubbelbindings in die sygroepe van die PAMA-polimeerruggraat via ‘n merkaptaan-een addisiemeganisme in die teenwoordigheid van ‘n vrye radikaalinisieerder. ‘n Kombinasie van gelpermeasiechromatografie en multi-hoeklaserligverstrooiing is gebruik om die molekulêre massa van die entkopolimeer te bepaal. Die persentasie sytakke soos bepaal deur 1H-KMR was laag.

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.