Radical Grafting of Polar Monomers onto Polypropylene by Reactive Extrusion Tarik Sadik, 1,2,3 Val  erie Massardier, 4 Fr  ed  eric Becquart, 1,2,3 Mohamed Taha 1,2,3 1 Universit e de Lyon, F-42023, Saint Etienne, France 2 CNRS, UMR 5223, Saint Etienne, France 3 IMP@UJM, Universit e de Saint Etienne, Jean Monnet, F-42023, Saint Etienne, France 4 INSA-Lyon, IMP, UMR5223, Universit e de Lyon, F-69621 Villeurbanne, France Correspondence to: M. Taha (E-mail: mtaha@univ-st-etienne.fr) ABSTRACT: Polypropylene (PP) was functionalized in the melt by grafting polar monomers using an internal mixer and a corotating twin-screw extruder. 2,5-Bis(tertbutylperoxy)-2,5-dimethylhexane (Luperox 101) and dicumyl peroxide (DP) were the used radical ini- tiators. The polar monomers were itaconic acid (IAc), 2-octen-1-ylsuccinic anhydride (OY), 2-hydroxyethyl methacrylate (HEMA), and 3-allyloxy-1,2-propanediol (AP). Grafting was quantified by FTIR combined to Elemental Analysis. Grafting degree depends mainly on monomer and initiator natures and concentrations. Grafting degree maxima were 3.9, 2, 9.5, and 3.9 wt %, respectively, for IAc, OY, HEMA, and AP. Some properties of the modified PP were evaluated. Thermal analysis indicated that the polarity of PP increased by grafting reaction and size-exclusion chromatography showed that the grafting was not accompanied by a significant M w and viscosity decrease. VC 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 129: 2177–2188, 2013 KEYWORDS: functionalization of polymers; polyolefins; extrusion Received 5 September 2012; accepted 15 December 2012; published online 15 January 2013 DOI: 10.1002/app.38942 INTRODUCTION The modification of polymers, especially polyolefins through the grafting of functional monomers via free-radical reaction, has led to wide industrial applications and has continually gained scientific interest. Functionalized polyolefins 1–4 and more particularly functionalized PP were used to compatibilize a large number of polar polymers such as polyesters and polyamides thus improving the properties and stability of immiscible poly- mer blends. 5–19 Polypropylene (PP) has been one of the poly- mers that present great commercial interest, since some proper- ties of ordinary PP such as adhesion, dyeability, and compatibility can be improved thanks to its modifications. 20–28 PP compatibilization with polar polymers either can be due to specific interactions such as hydrogen bonding or to the forma- tion of graft copolymers by reactions between the functions grafted onto the PP and others existing in polar polymers. Reactive extrusion is a favorable process to obtain modified polymers continuously in molten state. Radical functionalization of PP by reactive extrusion is a very challenging industrial pro- cess. The occurrence of side reactions such as chain scission makes the grafting process quite critical for the production of grafted polymers with high graft contents while preserving the mechanical properties or processability of PP. 29,30 Besides, another challenge is to control the chemical structure of the grafts during processing, and the coexistence of several types of grafts is usually observed in commercial products. 31 Among re- active monomers, the most important ones for PP modification by free-radical mechanisms are unsaturated organic compounds having oxygen-containing functional groups. The best known modification is performed with maleic anhydride. It generally improves the adhesion of PP to metals, glass fibers, or other polymers such as polyamides. The grafting of maleic anhydride to PP is usually carried out in the presence of radical initiators in solution, 1,32–34 in the solid state 35,36 or directly in the melt. 20,22,25,26,37–43 Generally, the grafting reaction is accompa- nied by chain scissions then the grafting degree and efficiency are relatively low. In the case of acrylic acid, grafting is accom- panied by homopolymerization. 29 Other polar monomers such as unsaturated carboxylic acid derivatives and vinyl or acrylic substances containing more than one functional group have also been investigated. 25,39,43–59 Coagents like styrene were used to assist the PP radical functionalization and also to reduce molar mass decrease during grafting. 57,60–63 The literature clearly shows that maleic anhydride can be grafted onto PP leading to various grafting degrees going up to 5 wt %. A high grafting is VC 2013 Wiley Periodicals, Inc. WWW.MATERIALSVIEWS.COM WILEYONLINELIBRARY.COM/APP J. APPL. POLYM. SCI. 2013, DOI: 10.1002/APP.38942 2177