Toughened poly(methyl methacrylate) nanocomposites by incorporating polyhedral oligomeric silsesquioxanes

Edward T. Kopeskya, Gareth H. McKinleyb and Robert E. Cohena, Corresponding Author Contact Information, E-mail The Corresponding Author

aDepartment of Chemical Engineering, Massachusetts Institute of Technology, Cambridge, MA 2139, USA
bDepartment of Mechanical Engineering, Massachusetts Institute of Technology, Cambridge, MA 2139, USA

Received 23 September 2005;  revised 28 October 2005;  accepted 31 October 2005.  Available online 21 November 2005.


We have investigated the toughenability of poly(methyl methacrylate) (PMMA) using polyhedral oligomeric silsesquioxane (POSS) nanocages at loadings between 0 and 15 wt%. Three distinct POSS species were used: a crystallizable type that did not disperse on a molecular scale within the PMMA matrix (cyclohexyl-POSS), and two types of POSS that formed homogeneous mixtures over the loadings we have investigated (methacryl-POSS and trisilanol-phenyl-POSS). Each of the three types of POSS was able to toughen PMMA in slow-speed tension tests at loadings ≤5 wt%; however, the reproducibility was poor due to the high flaw sensitivity of these binary blends. Ternary blends containing both cyclohexyl-POSS and methacryl-POSS showed the greatest increase in tensile toughness and also excellent reproducibility of toughening. A blend containing 2.5 wt% of both cyclohexyl-POSS and methacryl-POSS maintained the same modulus as the unfilled PMMA while increasing the toughness by a factor of 4. Electron micrographs showed extensive particle–matrix debonding of the PMMA from the cyclohexyl-POSS crystallites and some evidence of plastic deformation on the fracture surface. In high rate (1000 s−1) split-Hopkinson pressure bar (SHPB) tests, binary blends of POSS and PMMA were able to improve the impact toughness of PMMA; however, once again the combined addition of both cyclohexyl-POSS and methacryl-POSS led to the greatest reproducibility of toughening. Comparison with previous results suggests that in order to toughen PMMA with rigid fillers, weakly-adhering particles with sizes on the order of 100 nm are required.

Keywords: Nanocomposies; Mechanical properies; POSS