Browsing by Author "Van Zyl, Andries Jakobus Petrus"
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- ItemThe synthesis and characterization of styrene-grafted epoxidized natural rubber (ENR50-PS) by gradient HPLC analysis(Stellenbosch : Stellenbosch University, 1999-12) Van Zyl, Andries Jakobus Petrus; Sanderson, R. D.; Pasch, H.; Stellenbosch University. Faculty of Science. Dept. of Chemistry & Polymer Science.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.