Synthesis and Properties of Poly(isobutyl methacrylate- co-butanediol dimethacrylate-co-methacryl polyhedral oligomeric silsesquioxane) Nanocomposites GUI ZHI LI, 1 HOSOUK CHO, 1 LICHANG WANG, 1 HOSSEIN TOGHIANI, 2 CHARLES U. PITTMAN, JR. 1 1 Department of Chemistry, Mississippi State University, Mississippi 39762 2 Department of Chemical Engineering, Mississippi State University, Mississippi 39762 Received 12 August 2004; accepted 7 September 2004 DOI: 10.1002/pola.20503 Published online in Wiley InterScience (www.interscience.wiley.com). ABSTRACT: Poly[isobutyl methacrylate-co-butanediol dimethacrylate-co-3-methacrylyl- propylheptaisobutyl-T8-polyhedral oligomeric silsesquioxane] [P(iBMA-co-BDMA-co-MA- POSS)] nanocomposites with different crosslink densities and different polyhedral oligo- meric silsesquioxane (MA-POSS) percentages (5, 10, 15, 20, and 30 wt %) were synthesized by radical-initiated terpolymerization. Linear [P(iBMA-co-MA-POSS)] copolymers were also prepared. The viscoelastic properties and morphologies were studied by dynamic mechanical thermal analysis, confocal microscopy, and transmission electron microscopy (TEM). The viscoelastic properties depended on the crosslink density. The dependence of viscoelastic properties on MA-POSS content at a low BDMA loading (1 wt %) was similar to that of linear P(iBMA-co-MA-POSS) copolymers. P(iBMA-co-1 wt % BDMA-co-10 wt % MA-POSS) exhibited the highest dynamic storage modulus (E') values in the rubbery region of this series. The 30 wt % MA-POSS nanocomposites with 1 wt % BDMA exhibited the lowest E'. However, the E' values in the rubbery region for P(iBMA-co-3 wt % BDMA- co-MA-POSS) nanocomposites with 15 and 30 wt % MA-POSS were higher than those of the parent P(iBMA-co-3 wt % BDMA) resin. MA-POSS raised the E' values of all P(iBMA- co- 5 wt % BDMA-co-MA-POSS) nanocomposites in the rubbery region above those of P(iBMA-co-5 wt % BDMA), but MA-POSS loadings  15 wt % had little influence on glass-transition temperatures (T g ’s) and slightly reduced T g values with 20 or 30 wt % POSS. Heating history had little influence on viscoelastic properties. No POSS aggregates were observed for the P(iBMA-co-1 wt % BDMA-co-MA-POSS) nanocomposites by TEM. POSS-rich particles with diameters of several micrometers were present in the nanocom- posites with 3 or 5 wt % BDMA. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 355–372, 2005 Keywords: morphology; nanocomposites; poly(isobutyl methacrylate-co-butanediol dimethacrylate-co-methacryl polyhedral oligomeric silsesquioxane) [P(iBMA-co-BDMA-co- MA-POSS)]; synthesis; viscoelastic properties INTRODUCTION Nanocomposites containing one or more phases with ultrafine (1–100 nm) dimensions have at- tracted considerable interest as researchers strive to enhance material properties via nano- scale reinforcement in contrast to conventional particulate-filled microcomposites. 1,2 Polyhedral oligomeric silsesquioxane (POSS) modified nano- composites have attracted special attention. 3–18 POSS compounds are 1–3 nm in diameter and are unique inorganic– organic hybrid reagents. Their inorganic cage framework is made up of silicon and oxygen (SiO 1.5 ) n (n = 8, 10, or 12). This inor- ganic cage is externally covered by organic sub- stituents, which can enhance their solubility in organic media. One or more of these substituents Correspondence to: C. U. Pittman, Jr. (E-mail: cpittman@ ra.msstate.edu) Journal of Polymer Science: Part A: Polymer Chemistry, Vol. 43, 355–372 (2005) © 2004 Wiley Periodicals, Inc. 355