Nano-Reactors for Controlling the Selectivity of the Free Radical Grafting of Maleic Anhydride Onto Polypropylene in the Melt Dean Shi, R.K.Y. Li Department of Physics and Materials Science, City University of Hong Kong, Kowloon, Hong Kong, People’s Republic of China Faculty of Chemistry and Material Science, Hubei University, Wuhan 430062, People’s Republic of China Yutian Zhu, Zhuo Ke, Jinghua Yin, and Wei Jiang State Key Laboratory of Polymer Physics and Chemistry, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, Changchun 130022, People’s Republic of China Guo-Hua Hu Laboratory of Chemical Engineering Sciences, CNRS-ENSIC-INPL, 54001 Nancy, France Institut Universitaire de France, Maison des Universite ´ s, 103 Boulevard Saint-Michel, 75005 Paris, France This paper reports on a successful application of the concept of nanoreactors to effectively controlling the selectivity of the free radical grafting of maleic anhydride (MAH) onto polypropylene (PP) in the melt, an industrially relevant process. More specifically, a free radical initia- tor of type ROOR was first confined into (or encapsu- lated by) the galleries of an organically modified mont- morillonite (o-MMT) whose interdistance was 2.4 nm. Primary free radicals (RO  ) formed inside the o-MMT galleries had to diffuse out before they could react with the PP backbone. The controlled release of the primary free radicals significantly increased the grafting degree of MAH onto PP and greatly reduced the level of the chain scission of the latter. Those results were better understood by electron spin resonance studies on model systems and by Monte Carlo simulations. POLYM. ENG. SCI., 46:1443–1454, 2006. © 2006 Society of Plastics En- gineers INTRODUCTION Functionalization of polypropylene (PP), through the grafting of unsaturated monomers such as maleic anhydride (MAH) in the presence of organic peroxide as a free radical initiator, has already received much attention. The function- alized PP can have many applications [1, 2]. Solution [3], melt [4 – 6] and solid-state processes [7, 8] have been suc- cessfully used for the preparation of functionalized PP. Among them, the melt process has widely been used in the industry owing to its economic and operational advantages. However, a major problem this process faces is the PP chain scission. Recently, new efforts have been made toward reducing PP chain scission during the grafting reaction. Among the examples is the use of supercritical carbon dioxide [9, 10]. However, operating conditions are rela- tively complicated. During the past few decades, to find a way of controlling PP chain scission, many studies have focused on the grafting mechanism [3, 6, 7, 11–16]. Nev- ertheless, the grafting process at the molecular level is still not fully understood, and controversies still remain over the precise grafting mechanisms for the PP and MAH system. Russell and Kelusky [11] found that there existed a ceiling temperature, above which MAH could not homopolymer- ize. De Roover et al. [12] suggested that -scission should take place prior to the MAH grafting reaction. As a result, MAH should be grafted onto PP chain ends. At the same time, they reported evidence that MAH oligomers existed in Correspondence to: G.-H. Hu; e-mail: hu@ensic.inpl-nancy.fr; D. Shi; e-mail: dshi@citgu.edu.hk Contract grant sponsor: Research Grants Council; contract grant number: CityU 1202/02E; Contract grant sponsor: National Science Foundation of China; contract grant numbers: 50373011 and 50390090; Contract grant sponsor: Wuhan Youth Scheme of Science and Technology; contract grant number: 20025001012; Contract grant sponsor: French National Research Agency (ANR). DOI 10.1002/pen.20610 Published online in Wiley InterScience (www.interscience. wiley.com). © 2006 Society of Plastics Engineers POLYMER ENGINEERING AND SCIENCE—2006