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The synthesis and characterization of styrene-grafted epoxidized natural rubber (ENR50-PS) by gradient HPLC analysis

Van Zyl, Andries Jakobus Petrus (1999-12)

Thesis (M.Sc.) -- University of Stellenbosch, 1999.

Thesis

ENGLISH ABSTRACT: In order to enhance the properties of polymers, it is first necessary to have a clear understanding of their chemical microstructure. Materials resulting from a grafting reaction have a very complex chemical microstructure due to the fact that grafting is random and emulsion polymerization is a heterogeneous process. In a grafting reaction between two polymers it is possible that grafted (either crosslinked or noncrosslinked) and non-grafted material will be formed. These products can be determined by gradient HPLC techniques which are based on the differences in the solubility/adsorption of the polymers present after the grafting reaction has taken place. Gradient HPLC allows separation by means of chemical composition distribution (CCD) as well as molar mass. Separation is determined by chromatographic conditions e.g. solvent/non-solvent pairs, columns, gradients etc. Styrene was grafted onto epoxidized natural rubber (ENR50) in an emulsion reaction. The initiator and monomer concentrations were chosen to represent five distinct reaction conditions, to be able to compare the gradient HPLC analyses of the different products. Solubility tests were performed on the ENR50 and solubility parameters evaluated for the rubber as well as for solvents. Cloudpoint determinations were performed both titrimetrically and chromatographically to determine which solvent/non-solvent pair was best suited for the separation process, as well as to investigate certain theoretical aspects of gradient HPLC. Other preliminary experiments performed on the styrene-grafted ENR50 included GPC, FTIR and LC-transform analyses. The results of these experiments were to be used to ease the explanation of gradient HPLC analysis results and to investigate the influence of the reaction conditions on the epoxidized natural rubber. The study was concluded with the optimization of the gradient HPLC method and consequent analysis of the grafted samples by gradient HPLC analysis. Results of these analyses confirmed that separation of the graft copolymerization mixture into the desired graft copolymer, non-grafted precursors and monomer was indeed possible. The presence of the graft peaks in the gradient chromatograms not only proved that grafting had taken place, but the very low intensity of the peaks also confirmed the low transfer coefficient of styrene. Unfortunately much of the grafted product crosslinked (polystyrene radicals terminate by coupling) arid was therefore not soluble.

AFRIKAANSE OPSOMMING: Om die eienskappe van polimere te bevorder, is dit noodsaaklik om 'n duidelike begrip van die chemiese struktuur van 'n polimeriese materiaal te he. Materiale wat voortvloei uit entkopolimerisasie reaksies het 'n baie komplekse chemiese mikrostruktuur as gevolg van die feit dat enting willekeurig is en emulsie polimerisasie 'n heterogene proses is. As gevolg van die entingsreaksie tussen twee polimere is dit dus moontlik dat geente sowel as ongeente materiaal aan die einde van die reaksie teenwoordig kan wees. Die moontlikheid bestaan ook dat sommige van die geente materiaal 'n gekruisbinde netwerk tydens die emulsie reaksie kan vorm. Deur gebruik te maak van gradient hoe-druk vloeistofchromatografie, wat gebaseer is op die oplosbaarheid/adsorpsie van die polimere wat teenwoordig is na afloop van die entingsreaksie, is dit dus moontlik om bostaande verskynsel te ondersoek en te analiseer. Gradient hoe-druk vloeistofchromatografie laat skeiding op die basis van chemiese komposisie distribusie sowel as molekulere massa toe en die skeiding is afhanklik van verskeie chromatografiese veranderlikes, byvoorbeeld oplosmiddel/presipiteermiddel pare, kolomme, gradiente ensovoorts. Vir hierdie studie is ge-epoksideerde natuurlike rubber (ENR50) met stireen geent deur middel van 'n emulsie reaksie. Die inisieerder- en monomeer-konsentrasies is spesifiek gekies om vyf duidelike reaksie kondisies voor te stel om sodoende die vergelyking van die resultate van die gradientchromatografie analise te vergemaklik. Oplosbaarheidstoetse van ENR50 is uitgevoer en oplosbaarheids-parameters geevalueer vir die rubber asook vir die oplosmiddels. Presipitasiepuntevaluerings is gedoen deur middel van titrasies en chromatografiese analises en resultate gevolglik aangewend om die oplosmiddel/presipiteermiddel te kies wat die beste skeiding sou verteenwoordig. Hierdie evaluasies is egter ook gebruik om sekere teoretiese aspekte te ontleed en te verklaar. Sekere preliminere eksperimente is ook uitgevoer met die oog op vereenvoudiging van die verduideliking van die gradienteksperimente, sowel as om die invloed van die reaksie kondisies op die ge-epokside'erde natuurlike rubber te bestudeer. Eksperimente het permeasiechromatografie, infrarooi spektroskopie en permeasiechromatografie gekoppel aan infrarooi spektroskopie ingesluit. Die studie is gevolglik afgesluit deur die optimisering en gevolglike analise van die geente monsters deur gradient hoe-druk vloeistofchromatografie. Hierdie analises het bevestig dat skeiding moontlik is tussen die verlangde entkopolimeer en homopolimere. Die teenwoordigheid van die entpieke het bewys dat enting wel plaasgevind het, maar die lae intensiteit van die pieke het ook die lae oordragkoeffisient van stireen, wat enting moes bewerkstellig, bevestig, asook die feit dat baie van die geente polimeer 'n gekruisbinde netwerk gevorm het (polistireenradikale termineer deur middel van koppeling) en dus nie oplosbaar was nie.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/51520
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