In Situ Compatibilization Of PS/POE Blends By Friedel-Crafts Alkylation Reactions

In situ compatibilization by Friedel-Crafts alkylation reaction has an important advantage that the materials used as the catalyst are common and inexpensive, so that it has the commercial potential in the recycling of mixed post-consumer polymers containing polystyrene (PS) and polyolefin. To increase the compatibility of polystyrene (PS) and new polyolefin elastomer (POE) blends, a Lewis acid catalyst, aluminum chloride (AlCl₃), was adopted to initiate the Friedel-Crafts alkylation reaction for the formation of PS-graft-POE copolymer. In this paper, the structure and properties of PS/POE blends was mainly discussed, contributing to the deeply understanding on the mechanism of in situ compatibilization for PS/POE blends.Ethylene-octene copolymer (POE), as a new thermoplastic elastomer, is mostly applied to toughening polypropylene (PP) because of its good mechnical and thermal properties. Comparing with the traditional elastomers, POE can increase the toughness of PP, at the same time, the PP/POE blends also had nice yield strength and processing property. So POE was applied to toughening PS in this paper. Percolation model was applied on the brittle to ductile transition for PS/POE blends. And on the basis of creep tests, a new method to quantify the craze deformation of PS/POE blends by tensile test was developped.AlCl₃ was adopted to initiate in situ grafting reaction of immiscible PS/POE blends, and the PS-graft-POE copolymer acted as the compatibilizer, resulting in increasing the adhesion between PS and POE and reducing the size of the domains. The study on the changes of structure and properties for PS/POE blends after in situ compatibilization reflected the effects of Friedel-Crafts alkylation reaction on the morphology, mechnical propoties, rheological behaviors, and thermal propoties. Results showed that in situ compatibilization was an effective technique for increasing the compatibility of blends containing PS.The catalysts of Friedel-Crafts alkylation reaction are usually a strong Lewis acid, which can not only initiate the in situ grafting reaction, but also initiate the side reactions, such as crosslinking, degradation and gelation. The results of GPC, SEMand DMA showed that the mechnical properties, morphology, rheological behaviors and thermal properties of PS/POE/AlCl₃ blends were the results of the competition between in situ compatibilization and the degradation of the component polymers. At low AlCl₃ contents, the in situ graft reaction played a significant role, resulting in the improvement of the compatibility. At high AlCl₃ contents, however, the degredation of the component polymers was the dominating effect, which was not in favor of the miscibility.The Friedel-Crafts alkylation reaction is common in organic synthesis. However, only a few articles on the Friedel-Crafts alkylation reaction for in situ compatibilization of PS and polyolefin blends have been published so far. The mechanism of Friedel-Crafts alkylation reaction adopted in PS/polyolefin blends kept unclear, and the concerned study was not sufficient. On the basis of detailed analysis on the characteristics of Friedel-Crafts alkylation reaction, this paper provided the clear analysis of the mechanism, which could explain the experimental phenomena well.In order to increase the efficiency of grafting, the styrene (St) monomers were added in in situ compatibilized PS/POE blends, which were found good at the acceleration of Friedel-Crafts alkylation reaction. Therefore, the St/AlCl₃ catalyst system initiated more PS-graft-POE copolymer than the single AlCl₃ catalyst. The two-step extrusion procedure gave better mechanical properties of PS/POE blends, which were the results of a limitation of degradation of blending components when the master batch product and virgin polymers were extruded in the second extrusion step.