Free-radical grafting of maleic anhydride

Huneault and Li described compatible blends of TPS-PLA made by free-radical grafting of maleic anhydride (MA) on the PLA backbone and then by reacting the modified PLA with the starch macromolecules in a twin-screw extruder provided with a degassing zone to eliminate water and free unreacted MA at both the PLA grafting and TPS-PLA blending steps. MA-grafted PLA showed a much finer dispersed phase, in the 1- 3 pm range, and exhibited a dramatic improvement in mechanical properties [69]. 

Elastomeric ionomers have also been developed from ethylene-propylene-diene ternary copolymers known as EPDM rubbers. The diene is commonly ethylidene norbomene. Du Pont made carboxylated ionomers by free-radical grafting of maleic anhydride (0.5—5%) onto the diene moiety of the polymer and neutralized the product with rosin salt. The ethylidene norbomene can also be sulfonated, thus ... 

Dorscht, B. M. and Tzoganakis, C. 2003. Reactive extrusion of polypropylene with supercritical carbon dioxide Free radical grafting of maleic anhydride. Journal of Applied Polymer Science 87 1116-1122. 

Li, X., Xie, X. M., and Guo, B. H. 2001. Study on styrene-assisted melt free-radical grafting of maleic anhydride onto polypropylene. Polymer 42 3419-3425. 

Shi, D., Hu, G. H., and Li, R. K. Y. 2006. Concept of nano-reactor for the control of the selectivity of the free radical grafting of maleic anhydride onto polypropylene in the melt. Chemical Engineering and Science 61 3780-3784. 

Free radical grafting of maleic anhydride (MA) onto polyolefins has gained wide industrial use. MA modified polyolefins are an essential part of many plastics formulations. They are used as chemical coupling agents, impact modifiers, and compatibilisers for blends and filler reinforced systems [65-67]. 

Free-radical initiated reactions can also be used, besides crosslinking, for otha- modifications. The thermal decomposition of benzoyl peroxide was successfully used to initiate the grafting of maleic anhydride on PHB which was reported to produce a material with increased thermal stability and biodegradability, the latter attributed to the appended maleic moieties [ 168,169]. 

GH Hu, JJ Flat, M Lambla. Free Radical Grafting of Chemically Activated Maleic Anhydride onto Polypropylene by Reactive Extrusion. ANTEC, 1994, pp. 2775-2778. 

Functionalization of PLA by grafting of maleic anhydride (MAn) by reaction extrusion in the presence of free radical initiators tert-h xiy peroxide) has also been carried out. The presence of high succinic anhydride units in the grafts was confirmed by FTIR and NMR studies. Low percentage grafting was observed in PLA due to presence of limited free radical sites [69, 70]. 

One of the most popular processes in reactive compa-tibilization is the grafting of maleic anhydride (MAH) onto polyolefins, to make them more reactive in the blending process [81-83]. For example, heating LDPE, PP, or EPR with peroxide produced free radicals which added easily across the double bond of MAH, thus making the polyolefins easily reactive with nylons, polyesters, and other second polymers in polyblends. 

Stenstad et al. [27] grafted both succinic and maleic anhydride to the surface of microfibrillated wood pulp under water-free conditions. This method introduced negative charge onto the fibril surfaces. Grafting of maleic anhydride to the MFC surface introduced vinyl groups that may serve as starting point for further radical-induced polymerization reactions. Grafting was confirmed qualitatively by FT-IR. The DS was 0.8 and 0.3 for succinic and maleic acid, respectively, as evaluated by XPS. 

Razavi Aghjeh, M.K., Nazockdast, H., Assempour, H. Parameters Affecting the Free-radical Melt Grafting of Maleic Anhydride onto Linear Low-density Polyethylene in an Internal Mixer. Journal of Applied Polymer Science, 99,141-149 (2006). 

Free-radical grafting is a preferred way to add functionality to polyolefins, e.g. reaction with maleic anhy de. Amine functionalized polymers can be obtained by further derivatization of carboxylic anhydride functionalized polyolefin with amines. Polymeric materials containing amino groups are important because of the chemical versatility of the amino function. Although such procedures are useful, they lack control over molecular weight and functional-group distribution in the polymer. 

Esen, H., Kusefoglu, S. and Wool, R. (2007) Photolytic and free-radical polymerization of monomethyl maleate esters of epoxidized plant oil triglycerides. Journal cf Applied Polymer Science, 103(1), 626-633. Ozturk, C. and Kusefoglu, S.H. (2010) Polymerization of epoxidized soybean oil with maleinized soybean oil and maleic anhydride grafted polypropylene mixtures. Journal cf Applied Polymer Science, 118(6), 3311-3317. 

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

Dong, Q. and Liu, Y. 2003. Styrene-assisted free-radical graft copolymerization of maleic anhydride onto polypropylene in supercritical carbon dioxide. 

Gaylord evaluated various clays in polyethylene using peroxide/maleic anhydride treatments [18]. He found very variable results, largely influenced by the nature of the clay surface, and concluded that some filler surfaces could actually inhibit the free radical grafting processes. 

Addition of maleic anhydride (MA) by simple physical mixing is also beneficial to the adhesion properties of PP. The threshold concentration in this case is rather high, being around 5 wt.%. It is more straightforward, however, to graft MA onto the PP chain via free radical initiation, e.g. either by thermal decomposition of peroxides or photo-chemically. The amount of grafted maleic anhydride is usually below... 

Maleic anhydride has been grafted onto the backbone of a non-polar NR structure by the Diels Alder and free radical reactions. " The free radicals generated at the C=C bond of maleic anhydride and the allylic carbon atoms of the NR backbone by heating and shearing then become one of the reactive sites for the grafting reaction. These grafting reactions with maleic anhydride into the polymer blends have been commercially popular and relatively inexpensive. 

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. 

A Monsanto patent by Lavengood [38] reported on the free radical copolymerization of styrene (S), acrylonitrile (AN) and maleic anhydride (MA) and the use of these terpolymers in the reactive compatibilization of PA6/ABS blends. Indeed, the amine end groups of nylon react with the MA groups of the terpolymer with formation of a graft copolymer at the interface. 

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