In situ graft copolymer

In another approach, a small amount of maleic anhydride was copolymerized with styrene and acrylonitrile during the preparation of ABS by emulsion polymerization. The anhydride modified ABS was then melt blended with polyamide to form a compatibilized ABS/PA blend [Laven-good et al., 1986, 1987 Howe and Wolkowicz, 1987]. Obviously, a reaction between the anhydride functionality of ABS and the amine end group of polyamide leads to an in situ graft copolymer responsible for compatibilizing this blend. Monsanto s ABS/PA blends (Triax 1000... 

An alternative approach is to incorporate reactive functional groups Into the elastomer, producing an in-situ graft copolymer. This reduces interfacial tension, improving dispersion in processing, and improves the adhesion of the rubber to the thermoplastic In the solid state. A maleated polystyrene/poly(ethylene-co-butylene)/polystyrene triblock copolymer (SEES) has been used successfully to toughen polyamides and polyesters. 

Smeets and co-workers reported the synthesis of amphiphilic HBP from the copolymerisation of a vinyl and divinyl monomers [11]. Grafting of HBP has also been reported by other researchers [12]. Hou and Yan reported the synthesis of a star-shaped copolymer using in situ grafting, which contained a hyperbranched poly(3-methyl-3-oxetanemethanol) core and tetrahydrofuran arms [13]. 

The addition of a block copolymer of 10 phr epoxidized NR into NR/ chlorosulfonated polyethylene blends increased the tensile properties and tear strength of the blended system. The miscibility of the epoxidized NR was enhanced by an in situ grafting reaction of epoxidized NR onto the surface of the chlorosulfonated polyethylene particles. This graft copolymer reduced the interfacial tension between the chlorosulfonated polyethylene particles and the NR matrix, and the epoxidized NR acted as the load transferring agent between the NR and the chlorosulfonated polyethylene."... 

PS was grafted. Addition of DCP does not change this amount significantly (Fig. 6). Also addition of BA to PP/PS blends was found to generate copolymers in-situ. These copolymers contributed to the blend compatibilization. 

Finally, we would like to emphasize that, in most applications, in-situ formed copolymers are utilized, which are formed by the reaction of appropriately functionalized homopolymer additives at the polymer-polymer interface. A review article [106] cites not a single case where a premade copolymer had been used in a real application. Therefore, the interfacial behavior in such systems should be investigated fundamentally in greater detail in order to probe the effects of the characteristics of the reactive species on the kinetics of interfacial partitioning and the subsequent reaction, as well as on the effect of the resultant (diblock or graft or comb) copolymer on the interfacial tension and, thus, on the morphology of the macrophase-separated polymer blend. 

The use of reactive precursors of the compatibilizer offers a series of advantages. Indeed, the reactive polymers can be formed by easily implemented techniques, such as free radical copolymerization and melt grafting of reactive groups onto existing polymers. The compatibilizer is formed where it has to be localized, i.e. at the interface of the polyblend. Moreover, when the interface is saturated, the compatibilizer is no longer formed, so that the chance that the critical micelle concentration is exceeded is low compared to the use of pre-made compatibilizer, even though the in situ formed copolymer can be repelled from the interface after formation. Finally, the melt viscosity of the reactive precursors is lower than that of the parent pre-made compatibilizer, which is beneficial to the blend processing. 

The reactive compatibilization of a binary A7B immiscible polymer blend is usually ensured via the use of a chemical reaction during the melt-blending operation. The reaction leads to the formation of block or graft copolymers miscible, or at least sufficiently compatible, with both polymers A and B. Depending on its chemical composition and molecular architecture, the in situ formed copolymer is able to locate at the interface, improves the adhesion between the two phases, and constitutes a stabilizing barrier against coalescence (Fig. 22.8). 

Moreover, commercially available triblock copolymers designed to be thermoplastic elastomers, not compatihilizers, are often used in Heu of the more appealing diblock materials. Since the mid-1980s, the generation of block or graft copolymers in situ during blend preparation (158,168—176), called reactive compatibilization, has emerged as an alternative approach and has received considerable commercial attention. 

Compatibilization along with dynamic vulcanization techniques have been used in thermoplastic elastomer blends of poly(butylene terephthalate) and ethylene propylene diene rubber by Moffett and Dekkers [28]. In situ formation of graft copolymer can be obtained by the use of suitably functionalized rubbers. By the usage of conventional vulcanizing agents for EPDM, the dynamic vulcanization of the blend can be achieved. The optimum effect of compatibilization along with dynamic vulcanization can be obtained only when the compatibilization is done before the rubber phase is dispersed. 

Els and McGill [48] reported the action of maleic anhydride on polypropylene-polyisoprene blends. A graft copolymer was found in situ through the modifier, which later enhanced the overall performance of the blend. Scott and Macosko [49] studied the reactive and nonreactive compatibilization of nylon-ethylene-propylene rubber blends. The nonreactive polyamide-ethylene propylene blends showed poor interfacial adhesion between the phases. The reactive polyamide-ethylene propylene-maleic anhydride modified blends showed excellent adhesion and much smaller dispersed phase domain size. 

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