Polyolefins melt-phase grafting

Radical induced grafting may be carried out in solution, in the melt phase,292 29 or as a solid state process.296 This section will focus on melt phase grafting to polyolefin substrates but many of the considerations are generic. The direct grafting of monomers onto polymers, in particular polyolefins, in the melt phase by reactive extrusion has been widely studied. Most recently, the subject has been reviewed by Moad1 9 and by Russell.292 More details on reactive extrusion as a technique can be found in volumes edited by Xanthos," A1 Malaika and Baker et a 21 7 The process most often involves combining a frcc-radical initiator (most commonly a peroxide) and a monomer or macromonomer with the polyolefin as they are conveyed through the extruder. Monomers commonly used in this context include MAII (Section 7.6.4.1), maleimidc derivatives and malcate esters (Section 7.6.4.2), (meth)acrylic acid and (meth)acrylate esters (Section 7.6.43), S, AMS and derivatives (Section 7.6.4.4), vinylsilancs (Section 7.6.4.5) and vinyl oxazolines (Section 7.6.4.6). 

Many studies on the melt phase grafting of GMA onto polyolefins... 

Many studies on the melt phase grafting of GMA onto polyolefins PP 298.3[Pg.397]

With a history of more than 25 years, the free radical-induced grafting of MAH onto polyolefin substrates is one of the most studied polyolefin modification processes.29 "29, 302 The process has been carried out in the melt phase, in various forms of extruders and batch mixers, and there are numerous patents covering various aspects of the process. It has also been carried out successfully in solution and in the solid state. The materials have a range of applications including their use as precursors to graft copolymers, either directly, or during the preparation of blends.297... 

As we have indicated above the presence of these block and graft copolymers at the interface between two polymer melts has a substantial influence on the interfacial tension between the two melt phases (see Section 5.7). This effect has been investigated by various researchers [26, 44 to 47]. Typical results are shown in Table 6.1 for the polyethylene-poly(ethylene terephthalate) system [47]. This indicates that block copolymers where the two segments dissolve in different melt phases cause substantial reductions in interfacial tension. This also is the case when the block/graft copolymer are added they are chemically react with the molecules of one of the phases as in the case of the maleated polyethylene and maleated ethylene copolymers with polyamides or polyesters in blends with polyolefins. 

State with the coexistence of isotropic and anisotropic phases. In some cases, the occurrence of miscibility phenomena in the melt has been observed, due to the presence of chemical and/or specific interactions between the polymer components [135], For blends of LCP with polyolefins, such as PE or PP, due to the different chemical nature of these polymers, compatibilization with modified polymers is required to improve the adhesion and mechanical properties. Several functionalized polyolefins and copolymers (PP-g-MA, PP-AA, E-GMA) [136], as well as polyolefin-LCP graft copolymers (PE-g-SBH, PP-g-SBH) synthesized by melt polycondensation, have been used [137,138]. 

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