Thesis (MSc)--Stellenbosch University, 2011. / ENGLISH ABSTRACT: Block copolymers are very interesting materials but they are quite complex. During polymer synthesis only a certain amount of control can be enforced. As copolymers are made up of two or more different homopolymer segments, and therefore have different end group possibilities, varying block lengths and block sequences, they have complex structures and are therefore difficult to analyse. Different techniques exist by which polymers can be analysed to determine the aforementioned distributions. In order to achieve a complete characterisation of a polymer structure, it is best to first use a separation technique to fractionate the polymer into more homogeneous fractions, and then use identification techniques to analyse these fractions. Polystyrene-block-poly(ethylene oxide) (PS-b-PEO) copolymers were investigated using liquid chromatography at the critical conditions (LCCC) of the copolymers' corresponding homopolymers, two-dimensional liquid chromatography (2D-LC) and FTIR. The block copolymers were analysed using the established LCCC of PS but it was found that even though separation of PS homopolymer and copolymer was obtained, PS blocks of the copolymers contributed to some extent to the retention of the PEO blocks. Some of the block copolymer samples were fractionated at the established critical conditions of PS. These fractions were qualitatively and quantitatively analysed using FTIR spectroscopy. The settings for the 2D-LC analysis were established, using LCCC of PS as the first dimension and as the second dimension SEC, using DMF as eluent. DMF was a suitable solvent to be used for the second dimension because PS, PEO and PS-b-PEO exhibited good solubility in this solvent. THF did not dissolve the block copolymers completely. The same solvent system as used for LCCC of PS was used for LCCC of PEO, but the critical conditions correspond to a different solvent composition. The block copolymers were analysed using the established LCCC of PEO but it was found that even though separation of PEO homopolymer and copolymer was obtained, the PEO blocks of the copolymers contributed to some extent to the retention of the PS blocks. Some of the block copolymer samples were fractionated at the established critical conditions of PEO. These fractions were qualitatively and quantitatively analysed using FTIR spectroscopy. The settings for the 2D-LC analysis were established, using LCCC of PEO as the first dimension and as the second dimension SEC using DMF as eluent was used. Lastly, qualitative and quantitative analyses of the block copolymers were carried out using FTIR spectroscopy. / AFRIKAANSE OPSOMMING: Alhoewel blokkopolimere baie interessante verbindings is, is hulle redelik ingewikkeld. Gedurende die kopolimerisasiereaksie kan daar net 'n sekere mate van kontrole behaal word. Aangesien kopolimere uit twee of meer homopolimeersegmente, met verskillende end-groep moontlikhede, bloklengtes en blokvolgordes bestaan, is dit baie moeilik om hierdie verbindings te analiseer. Verskillende tegnieke kan gebruik word vir die analise van polimere en die bepaling van bogenoemde verspreidings. Ten einde 'n polimeerstruktuur volledig te karakteriseer is die beste manier om eers 'n skeidingstegniek te gebruik om die polimeer in meer homogene fraksies te fraksioneer en dan daarna hierdie fraksies te analiseer. Polistireen-blok-poli(etileenoksied) (PS-b-PEO) kopolimere is ondersoek deur gebruik te maak van vloeistofchromatografie by kritiese kondisies (LCCC) van die kopolimeer se ooreenkomstige homopolimere; twee-dimensionele vloeistofchromatografie (2D-LC) en FTIR. Die blokkopolimere is gekarakteriseer deur gebuik te maak van bevestigde LCCC van PS. Daar is egter gevind dat alhoewel skeiding van die PS homopolimeer en die kopolimeer behaal is, PS blokke van die kopolimere in 'n mate bygedra het tot die retensie van die PEO blokke. Sommige van die blok-kopolimeermonsters is gefraksioneer by die bepaalde kritiese kondisies van PS. Hierdie fraksies is kwalitatief en kwantitatief geanaliseer deur gebruik te maak van FTIR spektroskopie. Die stellings vir die 2D-LC analise is bepaal deur gebruik te maak van LCCC van PS as die eerste dimensie en SEC as die tweede dimensie, met DMF as elueermiddel. DMF was 'n geskikte oplosmiddel vir die tweede dimensie aangesien PS, PEO en PS-b-PEO goed oplosbaar is daarin. Die blokkopolimere was nie volledig oplosbaar in THF nie. Dieselfde oplosmiddelsisteem soos gebruik vir die LCCC van PS is gebruik vir die LCCC van PEO, maar die kritiese kondisies stem ooreen met 'n ander oplosmiddelsamestelling. Die blokkopolimere is geanaliseer deur gebruik te maak van die bevestigde LCCC van PEO, maar daar is bevind dat alhoewel skeiding van die PEO homopolimeer en kopolimeer behaal is, die PEO blokke van die kopolimere in 'n mate bygedra het tot die retensie van die PS blokke. Sommige van die blokkopolimeermonsters is gefraksioneer by die bevestigde kritiese kondisies van PEO. Hierdie fraksies is kwalitatief en kwantitatief geanaliseer deur gebruik te maak van FTIR spektroskopie. Die stellings vir die 2D-LC analise is bepaal deur gebruik te maak van LCCC van PEO as die eerste dimensie en SEC as die tweede dimensie, met DMF as elueermiddel. Laastens is kwalitatiewe en kwanitatiewe analises van die blokkopolimere m.b.v. FTIR spektroskopie uitgevoer.

Thesis (MSc)--Stellenbosch University, 2011. / ENGLISH ABSTRACT: Polymeric nanofibrous membranes that act as surfaces offer two compelling properties; they have extremely large surface areas that can be modified and they can offer multiple reactive sites depending on which polymer they were electrospun from. Combining nanofibrous surfaces such as these with photochromic dyes can give remarkable, light responsive materials. In this study, a terpolymer was electrospun and crosslinked (to impart insolubility to the material) to produce a nanofibrous mat that contained surface secondary-hydroxyl units and benzyl chloride units, from which monomers could grow using surface-initiated atom transfer polymerization (SI-ATRP). The surface was further fluorinated though the secondary-hydroxyl moieties to produce a hydrophobic crosslinked nanofibrous surface. n-Butyl acrylate and a photochromic spiropyran dye were copolymerized from the surface using SIATRP, in order to produce a surface that exhibited reversible adhesion towards a water droplet using ultraviolet and visible light as a stimulus to change between the two states. This in principle would allow the droplet to roll off and stick to the surface respectively. Although the surface displayed a colour change when switched, proving that the SI-ATRP had taken place, the droplet of water remained attached to the surface in both states. / AFRIKAANSE OPSOMMING: Polimeriese nanovesel membrane wat dien as oppervlaktes bied twee aantreklike eienskappe; hulle het baie groot oppervlakareas wat gemodifiseer kan word en hulle bied veelvuldige reaktiewe punte, afhangende van die polimeer waarvan hulle ge-elektrospin is. Deur sulke nanovesel oppervlaktes met fotochromiese kleurstowwe te kombineer, kan uitstekende lig reagerende materiale verkry word. In hierdie studie is ‘n terpolimeer ge-elektrospin en daarna gekruisbind (om die materiaal onoplosbaar te maak) om ‘n nanovesel web te kry wat oppervlak sekondêre-hidroksiel en benzielchloried eenhede bevat. Monomere kan dan vanaf hierdie eenhede groei deur middel van oppervlak-geïnisieerde atoomoordrag polimerisasie (OI-AOPR). Die oppervlak was verder gefluorineer via die sekondêre-hidroksiel eenhede om ‘n hidrofobiese, gekruisbinde nanovesel oppervlak te vorm. n-Butielakrilaat en ‘n fotochromiese spiropiraan kleurstof is gekopolimeriseer vanaf die oppervlak deur middel van OI-AORP om sodoende ‘n oppervlak te skep wat omkeerbare adhesie van ‘n water druppel gee as ultraviolet en sigbare lig as stimulus gebruik word om tussen die twee toestande te wissel. In beginsel sal die water druppel vanaf die oppervlak kan afrol én daaraan vassit, afhangende van die toestand van die oppervlak. Alhoewel die oppervlak van kleur verander het met die wisseling tussen die twee toestande, wat as bewys dien dat OI-AORP wel plaasgevind het, het die druppel water bly vassit aan die oppervlak in beide toestande.

Thesis (MSc)--Stellenbosch University, 2011. / ENGLISH ABSTRACT: In reverse iodine transfer polymerisation (RITP), chain transfer agents (CTAs) are generated in situ from the reaction between 2,2’-azobis(isobutyronitrile) (AIBN) and molecular iodine. This stage of RITP is the inhibition period, which ends when all iodine has been consumed. The evolution of CTAs was studied for the polymerisation reactions of n-butyl acrylate and styrene respectively. RITP of n-butyl acrylate was performed at 70 °C. In situ 1H nuclear magnetic resonance (NMR) experiments were carried out to study the evolution of CTAs during the inhibition period of n-butyl acrylate polymerisation and the structures A-I and A-Mn-I (where A represents the moiety originating from AIBN, M represents the monomer unit and n is the mean number degree of polymerisation) were observed. A polymer with the general structure A-Mm-I is formed. The molecular weight of poly(n-butyl acrylate) (PnBA) was evaluated with size exclusion chromatography (SEC) and NMR. Structural analysis of PnBA was done using NMR spectroscopy and matrix-assisted laser desorption/ionisation time-of-flight (MALDI-ToF) mass spectrometry. Similar conditions to those used for n-butyl acrylate polymerisation were used for RITP of styrene. The evolution of CTAs during the inhibition period of styrene polymerisation was studied using in situ 1H NMR. The inhibition period of styrene polymerised by RITP was much shorter than expected. This is due the consumption of iodine in the reaction between styrene and iodine which reversibly forms 1,2-diiodo-ethyl benzene. The CTAs A-I and A-Mn-I are formed, as well as 1-phenylethyl iodide (1-PEI). The molecular weight of polystyrene (PS) was determined using SEC and NMR and the functionality was evaluated using 1H NMR. The structure of PS was confirmed with 1H NMR and MALDI-ToF mass spectrometry. By increasing the temperature of the reaction, the inhibition period can be shortened. Both polymerisation systems retain control over molecular weight with an increase in temperature, however, n-butyl acrylate is limited due to the possible formation of mid-chain radicals. The formation of an A–Mm–A population (direct combination of the initiator and styrene) in RITP of styrene results in more initiator being consumed than for n-butyl acrylate, despite limited conversion of styrene to polymer. / AFRIKAANSE OPSOMMING: In omgekeerde-jodium-oordrag polimerisasie, is die kettingoordragagente gegenereer in situ van die reaksie tussen 2,2’-azobis(isobutironitriel) (AIBN) en molekulêre jodium. Hierdie fase van RITP is die inhibisie tydperk wat eindig wanneer alle jodium verbruik is. Die evolusie van kettingoordragagente is vir die polimerisasiereaksies van butielakrilaat en stireen onderskeidelik bestudeer. Omgekeerde-jodium-oordrag polimerisasie van butielakrilaat was uitgevoer by 70 °C. In situ 1H kernmagnetieseresonans (KMR) eksperimente is uitgevoer om die evolusie van die kettingoordragagente te bestudeer tydens die inhibisie van butielakrilaat polymerisasie en die strukture A-I en A-Mn-I (waar A die gedeelte voorstel wat afkomstig is van AIBN, M die monomeer-eenheid en n die gemiddelde aantal polymerisasiegraad verteenwoordig) is ge-identifiseer. 'n Polimeer met die algemene struktuur A-Mm-I is gevorm. Die molekulêre gewig van poli(butielakrilaat) (PnBA) was geëvalueer deur grootte-uitsluitings chromatografie en KMR spektroskopie. Strukturele ontleding van PnBA is gedoen deur die KMR spektroskopie en matriks ge-assisteerde laser desorpsie/ionisasie tyd-van-vlug massaspektroskopie. Soortgelyke kondisies as dié wat gebruik word vir butielakrilaat polymerisasie, is gebruik vir omgekeerde-jodium-oordrag polimerisasie van stireen. Die evolusie van die ketting oordrag agente gedurende die inhibisie periode van stireen polymerisasie is deur in situ 1H KMR bestudeer en die inhibisie periode is baie korter as verwag. Dit is as gevolg van die opname van jodium in die reaksie tussen stireen en jodium wat omkeerbare stireen-di-jodied tot gevolg hê. Die ketting oordrag agente A-I en A-Mn-I is gevorm, sowel as 1-feniel-etiel jodied. Die molekulêre massa van polistireen (PS) is bepaal met behulp van grootte-uitsluitings chromatografie en KMR spektroskopie en die funksioneering is geëvalueer met behulp van 1H KMR. Die struktuur van PS is bevestig deur 1H KMR en matriks ge-assisteerde laser desorpsie/ionisasie tyd-vanvlug massaspektroskopie. Deur die verhoging van die temperatuur van die reaksie, kan die inhibisie periode verkort word. Beide polimerisasie sisteme behou beheer oor die molekulêre massa met 'n toename in temperatuur, alhoewel butielakrilaat beperk word as gevolg van die moontlike vorming van middel kettingradikale. Die vorming van die A-Mm-A spesie (direkte kombinering van AIBN en stireen) in omgekeerdejodium- oordrag polimerisasie van stireen veroorsaak dat meer AIBN verbruik word as butielakrilaat, ten spyte van die beperkte omskakeling van stireen tot polimeer.

Thesis (MSc)--Stellenbosch University, 2011. / ENGLISH ABSTRACT: Needle-electrospinning is an uncomplicated and highly versatile nanofiber (fiber diameter of 50 to 500 nm) production technique. Nevertheless the process can only produce 0.01 to 1.0 g/h/m2 of nanofibers, unpractical for large-scale productions. Bubble-electrospinning, in the presence of surfactants, is a novel nanofiber mass-production technique developed at Stellenbosch University.[1] The technique is similar to needle-electrospinning only that the surface area of a bubble surpasses that of a solution droplet, making it possible for multiple jets to form on the bubble surface at high field strengths. Thus far little research has been done on the influence of solution properties on the bubble-electrospinning technique. During electrospinning the solution experiences three competing forces, namely, surface tension (contracting force), charge repulsion (expanding force), and viscosity (resistance to flow). The first aim of this study was to obtain better understanding on the influence of three significant solution properties (viscosity, conductivity and surface tension) on bubble-electrospinning in terms of bubble lifetime, bubble size, average number of jets and the resultant fibers. The solution properties were varied using a range of polymer and surfactant concentrations. A second aim was to obtain better understanding on the comparison of the bubble-electrospinning process between two polymer solutions, namely Polyvinyl alcohol (PVOH) solutions containing sodium lauryl ether sulphate (SLES) surfactant, and Polyacrylonitrile (PAN) solutions containing silicone surfactant. Results indicated that the solution viscosity and conductivity increased with increasing polymer concentrations for both polymer solutions. In addition, both the solution surface tensions were not influenced by polymer concentration. With regards to bubble-electrospinning of PVOH solutions, results indicated that the average number of jets per bubble was influenced by the polymer concentration. Regarding PAN solutions, bubble lifetime and the average number of jets was influenced by polymer concentration. Results indicated that the solution viscosity increased and surface tension decreased with increasing surfactant concentration for both polymer solutions. PVOH solution conductivity increased whilst PAN solution conductivity decreased with increasing surfactant concentrations. With regards to bubble-electrospinning of PVOH solutions, the bubble lifetime and bubble size was significantly influenced by the SLES concentration. Regarding PAN solutions, the silicone surfactant concentration had no significant effect on the bubble-electrospinning process. Overall, PVOH fiber diameters decreased with increasing surfactant concentration. There was no common trend between the bubble-electrospinning of PVOH and PAN solutions in relation to their solution properties. It was concluded that solution viscosity, conductivity and surface tension are not the only significant contributing parameters to the bubble-electrospinning process. / AFRIKAANSE OPSOMMING: Die naald-elektrospinproses is 'n eenvoudige, hoogsaanpasbare tegniek wat gebruik word vir die maak van nanovesels. Nanovesels het tipies 'n deursnee van 50nm tot 500nm. Ongelukkig is dit onprakties vir grootskaalse produksie omdat die uitset daarvan beperk is tot 0.01 tot 1.0 g/h/m2. Die borrel-elektrospinproses, waar elektrospinstrale gespin word vanaf die oppervlak van borrels op die oppervlak van die spinoplossing en waar die borrels gestabiliseer is m.b.v. sepe, is 'n nuwe tegniek wat ontwikkel is by die Universiteit van Stellenbosch. [1]. Die tegniek is soortgelyk aan die naald-elektrospinproses in dié sin dat die elektrospinstraal vorm vanaf 'n gelaaide halfsfeervormige oppervlak in die spinoplossing, maar die aansienlik groter oppervlakarea van die borrel in die borrel-elektrospinproses maak dit moontlik om verskeie elektrospinstrale gelyktydig op die oppervlak van die borrel te onderhou. Dit lei tot baie hoër doeltreffendheid in die saamgroeppering van die strale en gevolglik tot hoër nanoveseluitsette. Tot dusver is daar weinig navorsing aangaande die invloed van oplossingseienskappe op die borrel- elektrospintegniek gedoen. Tydens die elektrospinproses ervaar die oplossing drie kompeterende kragte, naamlik: oppervlakspanning (sametrekkende krag), elektrostatiese afstoting (afstotende krag) en viskositeit (vertragende effek op vloei van die oplossing). Die hoofdoelwit van hierdie navorsing was om 'n beter begrip te kry van die invloed van drie gemete oplossingswaardes, d.w.s. viskositeit, elektriese geleidingsvermoë en oppervlakspanning op die borrel-elektrospinproses. Die impak van hierde waardes is spesifiek geëvalueer in terme van borrellewensduur, borrelgrootte, gemiddelde hoeveelheid elektrospinstrale per borrel en die morfologie van die vesels wat in die proses gevorm is. Die tweede doelwit van die studie was om 'n vergelyking te tref tussen die mees optimale oplossingswaardes in die borrel-elektrospinproses van twee baie uiteenlopende polimeerspinoplossings, naamlik polivinielalkohol (PVOH), met natrium dodesieletersulfaat (SLES) as die borrelstabiliserende seep en poliakrilonitriel (PAN) oplossing, met 'n silikoonseep as die borrelstabiliserende seep. Resultate het getoon dat die viskositeit en elektriese geleidingsvermoë toeneem met toename in polimeerkonsentrasie vir beide PVOH- en PAN-oplossings. Verder is oppervlakspanning in beide gevalle nie beduidend beïnvloed deur die polimeerkonsentrasie nie. In die geval van die borrel-elektrospin van die PVOH-oplossings het resultate daarop gedui dat die gemiddelde aantal elektrospinstrale per borrel moontlik beïnvloed kon word deur die polimeerkonsentrasie. In die geval van borrel-elektrospin van PAN-oplossing is bevind dat polimeerkonsentrasie die borrelleeftyd en die gemiddelde aantal elektrospinstrale per borrel beïnvloed. Resultate het ook getoon dat die viskositeit vermeerder en die oppervlakspanning afneem met toename in die konsentrasie van die sepe in beide die polimeeroplossings. Die PVOH-oplossing se elektriese geleidingsvermoë het vermeerder terwyl dit verminder in die geval van die PAN-oplossings met 'n toename in die seepkonsentrasie. Tydens borrel-elektrospin van die PVOH-oplossings is beide borrelleeftyd en borrelgrootte beduidend beïnvloed deur die SLES konsentrasie. By die borrel-elektrospin van PAN-oplossings het die silikoonseepkonsentrasie nie 'n beduidende invloed gehad op die borrelleeftyd en borrelgrootte nie. Oor die algemeen het die gemiddelde PVOH veseldeursnee afgeneem met toename in seepkonsentrasie. Geen algemene tendens kon waargeneem word tussen die optimale oplossingswaardes vir borrel-elektrospin van die PVOH- en die PAN-oplossings onderskeidelik nie. Die gevolgtrekking is dat die viskositeit, elektriese geleidingsvermoë en oppervlakspanning nie die enigste beduidende waardes is wat bepaal of die borrel-elektrospinproses sal werk vir 'n spesifieke polimeeroplossing nie.

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))--Stellenbosch University, 2008. / Reversible addition fragmentation chain transfer (RAFT)-mediated polymerization has emerged as a versatile method for preparing polymers with control over molecular weight and polydispersity. Inherent in its mechanism is the retention of the chain transfer agent, the RAFT agent, at the polymer chain ends. Typically RAFT agents are made up of two parts, the so called R (leaving) and Z (thiocarbonyl thio, stabilizing) groups. These are retained as the a-and the w-end groups of the final polymer, respectively. RAFT polymerization offers a ready method for preparing polymers with well defined end functionalities. The a-end functionality can easily be built into the R group. The Z group, however, is thermally unstable and can impart color and smell to the polymer. Hence, two new methods for Z end group removal were introduced. Both methods take advantage of the facile reaction between thiocarbonyl thio compounds and radicals. By matching the functionalities of the R group (a-end group) with that of the end modified w-chain end, both methods offer an easy route to accessing telechelic functional polymers. End functional polymers have many important uses in industry and in the biomedical field. An alcohol functional xanthate RAFT agent was synthesized and successfully used to conduct the RAFT-mediated polymerization of N-vinylpyrrolidone (NVP). Characterization by NMR and MALDI ToF MS confirmed that a-hydroxyl-w-xanthate-functional PVP was easily produced. In the first end group modification method radicals were generated as in atom transfer radical addition (ATRA). A hydroxyl functional a-haloester was used as the ATRA initiator with a Cu catalyst system. The alkyl radical produced by this ATRA initiator then replaced the Z group giving a telechelic hydroxyl functional polymer. NMR analysis showed that the thiocarbonyl thio end group was completely removed. The hydroxyl functionality was quantified by derivatizing with trichloro acetyl isocyanate and subsequent analysis by NMR. MALDI ToF MS analysis, however, was inconclusive. In the second method the thiocarbonyl thio end group was removed by simply heating the polymer with hydrogen peroxide, thereby replacing the Z group with a hydroxyl end group at the w-chain end, giving a telechelic functional polymer. The telechelic hydroxyl functional polymer was subsequently crosslinked with a trifunctional isocyanate to make a PVP hydrogel. This confirmed that the end-modified polymer was indeed telechelic. The swelling kinetics of this hydrogel were determined in water at 37 oC.

Thesis (MSc)-- Stellenbosch University, 2012. / ENGLISH ABSTRACT: Over the past two decades, field flow fractionation (FFF), as a polymer characterization technique, has become cutting edge technology. The demand for molar mass and size characterisation of complex polymer systems has increased, especially in cases where classical calibration techniques such as size exclusion chromatography (SEC) has shown several shortcomings. FFF is a technique resembling chromatography. It has several significant advantages over SEC, especially for the characterisation of ultrahigh molar mass (UHMM), branched and gel-containing polymers. In this study, polybutadienes, which often contain the abovementioned species, were analysed by SEC and asymmetric flow field flow fractionation (AF4). Both separation techniques were coupled to refractive index and multi-angle laser light scattering detection. Similarly, polyrotaxanes, which are polymers with complex and unique molecular architectures, were also investigated. Results showed that AF4 can explicitly be used as a superior tool over SEC. In the case of UHMM polybutadienes, much higher molar masses could be detected by AF4, due to the absence of shear degradation which is often encountered in SEC. Gel-containing species could be detected by AF4 as no filtering is required prior to injection. Abnormal retention behaviour, a phenomenon often encountered in UHMM branched polymers, was observed in SEC analysis of the polyrotaxanes materials. AF4 provided sufficient separation from low to high molar masses, without out any irregularities. / AFRIKAANSE OPSOMMING: Gedurende die afgelope twee dekades het veldvloeifraksionering (FFF) as ‘n polimeerkarakteriseringstegniek groot veld gewen. Die aanvraag na molekulêre massa en groottekarakterisering van komplekse polimeersisteme het toegeneem, veral in die gevalle waar klassieke kalibrasietegnieke soos grootte-uitsluitingschromatografie (SEC) etlike tekortkominge getoon het. FFF is ‘n tegniek soortgelyk aan chromatografie, en het voorheen bewys dat dit oor ‘n redelike aantal voordele bo SEC beskik, veral in die geval van ultrahoë molekulêre massa- (UHMM-), vertakte- en jelbevattende spesies. In die huidige studie is polibutadieenpolimere, wat dikwels bogenoemde spesies bevat, geanaliseer met behulp van SEC en onsimmetriese vloei-veldvloeifraksionering (AF4). Beide skeidingstegnieke is gekoppel aan ‘n brekingsindeks en multihoek-laserligverstrooiingsdetektors. Op dieselfde wyse is polirotaksane (polyrotaxanes) met komplekse molekulêre argitektuur bestudeer. Daar is bewys dat AF4 uitsluitlik gebruik kan word as ‘n meer geskikte tegniek bo SEC. Baie hoër molekulêre massas kon deur middel van AF4 vir UHMM polibutadieenpolimere raakgesien word as gevolg van die verminderde afbrekende degradasie wat dikwels voorkom met SEC. Jel-bevattende spesies is suksesvol geïdentifiseer met behulp van AF4 waartydens geen filtrering vir analise nodig was nie. Abnormale retensie was sigbaar tydens SEC analise van monsters van polirotaksane, wat dikwels voorkom in vertakte polimere. In teenstelling het AF4 bewys dat ‘n bevredigende skeiding van klein na groot molekulêre massas, sonder enige tekortkominge, moontlik is.

Thesis (MSc)--Stellenbosch University, 2012. / ENGLISH ABSTRACT: In the modern, fast moving society of today, there is a strong focus in research placed on the elimination of lengthy invasive medical procedures. Target specific, and chemo selective treatments are of great interest. Various advantages of this include patient comfort and over and above all cost reduction of invasive procedures. This project focused on the development of an injectable gel system with the use of biocompatible polymers. A system is regarded as injectable if the functional polymers are in solution before administration, but gels when added together. In order to design this system, one has to make use of polymers with complimentary functional groups. Telechelic amino-functionalized PVP with narrow molecular weight distribution was synthesized via RAFT-mediated polymerization. The polymer was thoroughly characterized and cross-linked with Poly(styrene-alt-maleic anhydride) to form a three dimensional polymeric network capable of absorbing and retaining large amounts of water and or biological fluid. Unfortunately the cross-linking needed to be performed in non-aqueous solution due to hydrolysis of maleic anhydride as a competing reaction in water. The gel was used in two model studies. The first model study focused on the attachment of a synthetic polypeptide onto the gel. The second model study evaluated the cytotoxicity effects of these gels when placed in direct contact with rodent cardiac myoblast and myocyte cells. These studies rendered promising results for future biological applications. / AFRIKAANSE OPSOMMING: In die moderne, vinnig bewegende samelewing van vandag, word daar in navorsing, 'n sterk fokus geplaas op die uitskakeling van lang indringende mediese prosedures. Doel spesifieke, en chemo selektiewe behandelings is van groot belang. Verskeie voordele van hierdie is die toename in gemak van die pasiënt en die verlaging van kostes verbonde aan hierdie indringende prosedures. Hierdie projek het gefokus op die ontwikkeling van 'n inspuitbare gel stelsel deur gebruik te maak van biologiese aanvaarbare polimere. ‘n Stelsel word beskou as inspuitbaar, indien die funksionele polimere in oplossing is voor toediening, maar wel kan gel wanneer bymekaar gevoeg word. Om hierdie tipe stelsel te kan ontwerp moet daar gebruik gemaak word van polimere met beskikbare funksionele groepe. Telecheliese amino-funksionele Poly(N-vinielpirollideen) met 'n smal molekulêre gewig verspreiding is gesintetiseer deur middel van RAFT-bemiddelde polimerisasie. Die polimeer is deeglik gekarakteriseer en daarna gekruis-koppel met P(STY-alt-MAnh) om 'n driedimensionele polimeriese netwerk te vorm. Hierdie netwerk is dan ook in staat om groot hoeveelhede water en/of biologiese vloeistof te absorbeer en te behou. Ongelukkig was hierdie reaksie uitgevoer in ʼn nie-waterige oplossing as gevolg van die hidrolise van Maleïne anhydride as 'n mededingende reaksie in water. Die gel is in twee model studies gebruik. Die eerste model-studie het gefokus op die beslaglegging van 'n sintetiese polipeptied op die gel. Die tweede model studie het die sitotoksiese uitwerking van hierdie gels in direkte kontak met knaagdier hart myoblast en lymfocyten selle geëvalueer. Hierdie studies het dan ook belowende resultate vir toekomstige biologiese toepassings gelewer.

Thesis (MSc (Chemistry and Polymer Science))--University of Stellenbosch, 2009. / In papermaking, the addition of filler can be detrimental to the properties of the resulting paper hence the use of additives that enhance paper properties are of paramount importance. Syndiotacticity rich poly(vinyl alcohol) (PVA) microfibrils were prepared for use as filler retention aids. They were prepared via in situ fibrillation during the saponification of high molecular weight poly(vinyl pivalate). The resulting fibers had high thermal stability and crystalline melting temperature. They were not fully soluble in water even at 100 oC. In order to make them less water resistant the syndiotacticity of the PVA microfibrils was varied by copolymerizing vinyl pivalate with vinyl acetate and saponifying the resultant copolymer. It was observed that changes in syndiotacticity had a significant effect on the crystallinity, morphology and thermal properties of the resultant PVA. The surfaces of the fibers were modified by first crosslinking using glyoxal (a dialdehyde), and then attaching cationic and anionic groups by grafting and by carboxymethylation. Crosslinking prior to modification was beneficial in minimizing the solubility of the fibers in the aqueous media in which they were modified. Heterogeneous modification techniques were employed so that fiber properties could be preserved. Carboxymethylation was carried out using the two step Williamson’s ether synthesis. The first step involves the formation of a highly reactive alkoxide by the reaction of PVA with a strong base and the second its etherification using a functional alkyl halide. Poly(methacryloyloxy ethyl trimethyl ammonium chloride) and poly(acrylic acid) were grafted from the PVA microfibrils using the KPS/Na2S2O3 redox initiation system. Grafting was confirmed by FTIR and NMR spectroscopy. Differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) were carried out on both modified and unmodified PVA microfibrils. The results showed that crosslinking resulted in an enhancement of the thermal properties of the microfibrils. A decline in the onset temperature for thermal degradation and crystalline melting temperature were observed, and were attributed to the modification of the PVA microfibrils.

Thesis (MSc (Chemistry and Polymer Science))--University of Stellenbosch, 2006. / Dyeing has an influence on the characteristic properties of wool fibres. This can result in changes in the final properties of the fibre including fibre elasticity, fibre strength and breaking elongation of the wool fibres, especially in the case of dark colours. Damage that occurs to the fibre surface due to the action of acid, alkali, dyestuff, water, heat, and mechanical stress during the dyeing process can thus have an affect on the fibre breaking elongation and the fibre strength. The aim of this project was to assess the effect of dyeing with different colours (ranging from light to dark) on the surface of wool fibres using atomic force microscopy (AFM). The results indicated that four different types of surface damage can be discerned: scale raising, scale chipping, fluting and pitting. The findings also indicate that the surface damage to the fibres was greater and more noticeable (especially the scale raising) on fibres dyed with dark colours than to fibres dyed with light colours. The same applied to the fibre strength and elongation, where generally the fibre breaking extension and the breaking load was smaller in the case of darker colours. The effect of dyeing with different colour shades on the fibre surface was observed with AFM. Several characteristic scale parameters of a statistical significant number of dyed and undyed fibres were measured in order to determine the surface damage caused by dyeing. The correlation between the surface damage, observed by AFM, and the loss in tensile strength and fibre elongation, determined by tensile tests, were investigated. This was done in order to determine the effect of the cuticle damage on the tensile stress/strain behaviour. The results show that AFM is a viable tool to study the effects of different dyes on the fibre surface and for detecting surface modifications with great accuracy. It was found that dyeing with dark colours caused greater damage to the surface than light colours, and it was possible to distinguish different lightness areas, which could be regarded as light and dark colours.