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

[摘要] ENGLISH ABSTRACT: In order to enhance the properties of polymers, it is first necessary to have a clearunderstanding of their chemical microstructure. Materials resulting from a graftingreaction have a very complex chemical microstructure due to the fact that grafting israndom and emulsion polymerization is a heterogeneous process. In a graftingreaction between two polymers it is possible that grafted (either crosslinked or noncrosslinked)and non-grafted material will be formed. These products can bedetermined by gradient HPLC techniques which are based on the differences in thesolubility/adsorption of the polymers present after the grafting reaction has takenplace. Gradient HPLC allows separation by means of chemical compositiondistribution (CCD) as well as molar mass. Separation is determined bychromatographic 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 distinctreaction conditions, to be able to compare the gradient HPLC analyses of the differentproducts. Solubility tests were performed on the ENR50 and solubility parametersevaluated for the rubber as well as for solvents. Cloudpoint determinations wereperformed both titrimetrically and chromatographically to determine whichsolvent/non-solvent pair was best suited for the separation process, as well as toinvestigate certain theoretical aspects of gradient HPLC. Other preliminaryexperiments performed on the styrene-grafted ENR50 included GPC, FTIR and LC-transformanalyses. The results of these experiments were to be used to ease theexplanation of gradient HPLC analysis results and to investigate the influence of thereaction conditions on the epoxidized natural rubber. The study was concluded withthe optimization of the gradient HPLC method and consequent analysis of the graftedsamples by gradient HPLC analysis. Results of these analyses confirmed thatseparation 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 thatgrafting had taken place, but the very low intensity of the peaks also confirmed thelow transfer coefficient of styrene. Unfortunately much of the grafted productcrosslinked (polystyrene radicals terminate by coupling) arid was therefore notsoluble.

[发布机构] Stellenbosch University