Study Of Crosslinking And Grafting Of EPDM And In Situ Compatibilization Of PS/EPDM Blends In The Presence Of Lewis Acids

In this paper, ethylene propylene diene rubber (EPDM) was used as a reactive substance, which have unsaturated bonds at side chains. The properties and mechanisms of cross-linking and grafting with PS of EPDM in the presence of Lewis Acids were investigated. Using the Friedel-Crafts alkylation reaction for in situ compatibilization of PS and EPDM blends, the influences of all conditions to the cross-linking-grafting reaction and the properties of PS/EPDM blends were mainly discussed. The study provided a theory basis for the further application of the technic.To reduce the influence of viscosity, the reaction was carried out in solution system firstly. The influence of temperature, amounts of catalyst, kinds of solvent on properties of crosslinking and grafting of EPDM were investigated. The results showed:Anhydrous AlCl3 could initiate carbonium ion polymerization between the double bonds in EPDM backbone, resulting EPDM gel. At low temperature, the crosslinking reaction was difficult, but small amount of the grafting reaction between EPDM and PS occurred. It was difficult to initiate EPDM macro-carbocation in benzene or xylene solution. The amount of gel and the crosslinking density increased with the amount of catalyst. Being part of gel networks, the heat stability and the glass temperature of the PS were improved. In melt system, the cross-linking and grafting with PS of EPDM in the presence of Lewis Acids was investigated also. The results showed:anhydrous AlCl3 was an efficient catalyst for the initial carbocation formation. The initial carbocation initiated carbonium ion polymerization between the unsaturated bonds among EPDM backbone, and substituted for a proton from the phenyl ring in the presence of PS forming EPDM-g-PS copolymer. There was a competition reaction between the cross-linking-grafting reaction and the degradation of blending components. On the basis of detailed analysis on the characteristics of Friedel-Crafts alkylation reaction and molecule structure of EPDM, the experimental phenomena and the mechanism of reaction could be explained well.The influences of the temperatures and the amounts of AlCl3 content to the mechanical properties, PS grafting ratios, content of gel, molecule weight of PS, rheological behaviours, and morphology of PS/EPDM (80/20 wt%) blends were investigated, and a comprehensive study of in situ compatibilization of PS/EPDM blends by the Friedel-Crafts alkylation reaction was taken. The results showed:the PS-g-EPDM copolymer played a role of compatibilizer at the interface of PS/EPDM blends, resulting in reducing the interfacial tension between polymer phases and the size of the domains, setting the ultimate morphology, which then leaded to an improvement in mechanical properties of the PS/EPDM blends. The optimum reaction conditions were 140℃mixing temperature and 0.4% catalyst concentration, the condition were favorable for the formation of PS-g-EPDM copolymer and the improvement of the properties of the blends, further increasing of the mixing temperature or the dosages of the catalyst, would decrease the PS grafting ratios and the properties of the blends, due to the degradation of blend component (especially PS).In this paper, the direct compatibilization technic and pre-blending compatibilization technic were compared. The results showed:using pre-blending compatibilization technic, dispersing EPDM domains in PS matrix to some extent before grafting reaction, were in favor of reducing the amount of gel, increasing the amount of PS-g-EPDM copolymer, then leaded to an improvement in mechanical properties of the PS/EPDM blends.In order to reduce the degradation, increase the efficiency of grafting, decrease the amount of gel, the influence of the styrene (St) monomers and "two-step" compatibilization technique to the properties of PS/EPDM blends were investigated. The results showed:the St/AlCl3 composite catalyst could initiate more PS-g-EPDM copolymer than the single AlCl3 catalyst and produced low amount of gel. Using "two-step" compatibilization technique to prepare PS/EPDM (80/20 wt%) blends, could reduce the influence of the degradation of PS effectively. The same result was obtained for the in situ compatibilized PS/LLDPE (80/20 wt%) blends, so the technique had a potential value of application.