Grafting of Polystyrene Chains on Surfaces of Nanosilica Particles via Peroxide Bulk Polymerization R.Y. Suckeveriene, 1 A. Tzur, 1 M. Narkis, 1 A. Siegmann 2 1 Department of Chemical Engineering, Technion-IIT, Haifa 32000, Israel 2 Department of Materials Engineering, Technion-IIT, Haifa 32000, Israel This article describes an in situ bulk polymerization process of styrene in the presence of silica nanopar- ticles. In this peroxide bulk polymerization process, two polystyrene fractions are formed: A polystyrene (PS) fraction attached to the particle’s surface, which cannot be detached by hot xylene extraction, and an unattached PS fraction which dissolves in xylene. Sol- vent extraction and TGA measurements have con- firmed the existence of grafted PS chains to the silica surfaces. FTIR measurements have indicated the exis- tence of SiOC bonds connecting the PS grafts to the silica surface. Polypropylene (PP) was blended with the extracted PS-g-silica particles to produce concen- trations of 1–3% nanoparticles in the PP composites. A remarkably improved dispersability of the nanopar- ticles was achieved, thus grafting reduces re-agglom- eration and increases the affinity of the grafted surface to the polymer matrix. POLYM. COMPOS., 30:422–428, 2009. ª 2008 Society of Plastics Engineers INTRODUCTION Polymeric nanocomposites consisting of inorganic nanoparticles and organic polymers comprise a new class of materials in which nanoscale particulates (e.g., clay, silica, alumina) are finely dispersed within polymer matri- ces [1–3]. Nanocomposites may show improved pro- perties including modulus, strength, barrier performance, solvent and heat resistance, and optical transparency. However, homogeneous dispersion of nanoparticles in polymers using conventional processing techniques is very difficult because nanoparticles tend to agglomerate. However, such processing techniques are still the most convenient ones for surface-treated particles to overcome agglomeration. Efficient methods for agglomerate breakdown have been sought in recent years. Researchers have focused on methods of in situ polymerization of monomers in the presence of nanoparticles such as sol–gel, or intercalation polymerization processes. To overcome agglomeration, various pretreatments of particulate nanoparticles have been suggested. For exam- ple, SiO 2 nanoparticles were mixed with a monomer solu- tion, and the mixture irradiated by Co 60 c-ray source. The irradiated product was extracted, leaving grafted nanopar- ticles which were subsequently compounded with poly- propylene (PP) as a matrix. The grafted polymer pre- vented agglomeration of the nanoparticles [4–6]. Other approaches have been introduced, including the use of suitable coupling agents to create grafting of polymer chains upon nanoparticle surfaces [7–9]. Ruan et al. [10] have suggested that pretreatment approaches are useful because they lower the nanoparticle surface energy and thus prevent agglomeration and improve dispersion. In another method [11, 12], nanoparticles were sus- pended in a low viscosity fluid (ethanol) through sonica- tion and then centrifuged to achieve narrow particle size dispersion. The nanoparticles were then coated with silane and dried. The treated nanoparticles were mixed with MMA monomer and dispersed using sonication. Initiator and chain transfer agent were added and bulk polymeriza- tion was conducted. The composites obtained exhibit good particle dispersion as shown by TEM observation. In our previous paper [13], a new in situ polymeriza- tion method without the use of coupling agents was described, where grafting takes place via peroxide bulk polymerization upon the surfaces of inorganic nanopar- ticles. The polymerization reaction was conducted in the presence of the nanoparticles without the use of preceding pretreatment steps. Small monomer molecules could eas- ily penetrate into the nanoparticle agglomerates, and thus cause weakening of inter-particle forces to prevent reag- glomeration. In the present work, further characterization of the par- ticles is taking place and also the extracted particles are hot blended with PP and the resulting nanocomposites are characterized. Correspondence to: M. Narkis; e-mail: narkis@tx.technion.ac.il DOI 10.1002/pc.20572 Published online in Wiley InterScience (www.interscience.wiley.com). V V C 2008 Society of Plastics Engineers POLYMERCOMPOSITES—-2009