Surface Modification of Gold Nanoparticles with Polyhedral Oligomeric Silsesquioxane and Incorporation within Polymer Matrices SHIAO-WEI KUO, 1 YUNG-CHIEN WU, 2 CHU-HUA LU, 2 FENG-CHIH CHANG 2 1 Department of Materials and Optoelectronic Science, Center for Nanoscience and Nanotechnology, National Sun Yat-Sen University, Kaohsiung, Taiwan 2 Department of Applied Chemistry, National Chiao Tung University, Hsinchu, Taiwan Received 20 October 2008; revised 2 February 2009; accepted 2 February 2009 DOI: 10.1002/polb.21686 Published online in Wiley InterScience (www.interscience.wiley.com). ABSTRACT: A new approach to achieve polymer-mediated gold ferromagnetic nano- composites in a polyhedral oligomeric silsesquioxane (POSS)-containing random co- polymer matrix has been developed. Stable and narrow distributed gold nanopar- ticles modified by 3-mercaptopropylisobutyl POSS to form Au-POSS nanoparticles are prepared by two-phase liquid-liquid method. These Au-POSS nanoparticles form partial particle aggregation by blending with poly(n-butyl methacrylate) (PnBMA) homopolymer because of poor miscibility between Au-POSS and PnBMA polymer ma- trix. The incorporation the POSS moiety into the PnBMA main chain as a random copolymer matrix displays well-dispersed gold nanoparticles because the POSS-POSS interaction enhances miscibility between gold nanoparticles and the PnBMA-POSS copolymer matrix. This gold-containing nanocomposite exhibits ferromagnetic phe- nomenon at room temperature. V V C 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 811–819, 2009 Keywords: nanocomposites; nanoparticles; POSS; self-assembly INTRODUCTION Metal and semiconductor nanoparticles possess unique electronic and chemical properties because of their high-surface areas and confinement of electronic states. 1–4 The versatility of physical and chemical properties of these metal and semi- conductor nanoparticles provides potential appli- cations in fields ranging from optoelectronics, 5 sensing, 6 magnetism, 7 catalysis, and medicine. 8 Despite the diamagnetic character of bulk gold, well-dispersed gold nanoparticles capped with thi- ols exhibit ferromagnetic behavior at room tem- perature. 7 When gold nanoparticles are capped with thiols, the interaction between Au and the S atoms at the end of the alkyl chain modifies the electronic structure of the nanoparticle surface and results in 5d localized holes. 9 These holes pro- duce the localized magnetic moments strongly aligned along the bond direction and thus create magnetic properties independent of temperature in the range 5–300 K. 10 Incorporation of nanoparticles into polymer matrices through nanoparticle-polymer matrix interaction is an important subject for materials engineering, therefore, various attempts have been attempted to achieve polymer-mediated nanocomposites. In general, three different Journal of Polymer Science: Part B: Polymer Physics, Vol. 47, 811–819 (2009) V V C 2009 Wiley Periodicals, Inc. Correspondence to: S.-W. Kuo (E-mail: kuosw@faculty. nsysu.edu.tw) 811