Maleic anhydride grafted grafting reaction mechanisms

Polypropylene is functionalized to improve or enhance one or more properties. Carboxylation of polypropylene adds an acid group to the polymer that improves adhesion to many substrates and imparts compatibility with many other polymers. Polypropylene is commonly carboxylated by grafting onto the backbone either acrylic acid or maleic anhydride. The grafting reaction mechanisms are quite different for AA and MA. Glicidyl methacrylate (GMA) is another monomer that can be grafted onto the polypropylene backbone. 

Solution or bulk functionalization of PO by unsaturated functional molecules is largely studied. In particular, maleic anhydride (MAH)-grafted polymers are widely used commercial products [4-7]. As in the case of halogenation, the mechanism is not clearly understood. Overall, MAH-grafting reactions are complicated. Reactions in an extruder are particularly difficult to predict. Several schemes of reactions and structures of the grafted polymers have been proposed [7-10]. The insertion of a MAH group into the backbone of PO has also been reported. A commercial product from BP Chemicals, Polybond , has been reported to be maleated selectively at the chain ends. Ionic crosslinked rubber-like polymers were obtained from the reaction of maleic anhydride-grafted PO with some alkali metal compounds [11]. 

Mechanism of free radical initiated grafting reaction of maleic anhydride onto PE (from ref 11). 

Propose the reaction mechanism of grafting of maleic anhydride onto the polyethylene. 

There have been many studies conducted on the grafting of maleic anhydride onto polypropylene. These studies have produced many different theories on the grafting mechanism. One important aspect to consider in comparing the results from these studies are the methods used to conduct the grafting reactions. Different compounding methods, different initiator types, and monomer and peroxide... 

Figure 3.2 Possible reaction mechanism for grafting maleic anhydride onto polypropylene according to De Roover et al. (From Ref. 15, Reprinted with permission of John Wiley Sons.)...

Yuan et al. [120] has reported the research on PLA/PBAT blend foam. Maleic anhydride is used to enhance compatibility between PLA and PBAT. The compatibilization mechanism of maleic anhydride (MAH) is that MAH enhances intermolecular force by forming hydrogen bond between grafted MAH and polymer backbone. Grafting MAH onto PLA and PBAT is performed by reactive extrusion, which can improve the interfacial adhesion between PBAT and PLA matrix. In order to increase the maleicing reaction activity, a free radical initiator, 2, 5-dimethyl-2, 5-di-(/er/-butylperoxy) hexane (LlOl), can be used. 

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