Types Of Polyhedral Oligomeric Silsesquioxane Research Articles

Nanotailoring of polyurethane adhesive by polyhedral oligomeric silsesquioxane (POSS)

The development and commercialization of nanoparticles such as nanoclays (NCs), carbon nanotubes (CNTs) and polyhedral oligomeric silsesquioxanes (POSS) offers new possibilities to tailor adhesives at the nanoscale. Four types of POSS, with reactive mono-functional groups of isocyanatopropyl, glycidoxypropyl, aminoethyl and non-reactive octaphenyl, were incorporated in concentrations of 1, 3 and 5 wt% into a polyurethane (PU)-based adhesive. Thermo-mechanical bulk properties were studied using dynamic mechanical analysis (DMA). Adhesive properties were characterized in shear and peel modes. Atomic force microscopy (AFM) was used to study the nanoscale morphology. DMA measurements indicated that the neat PU possessed a glass transition temperature (T g) of ≈ 30°C. The T g of PU/POSS-glycidoxypropyl nanocomposite adhesive increased gradually with POSS concentration to 50°C for 5 wt%. PU/POSS-octaphenyl nanocomposite adhesive exhibited an increased T g by 10°C for 5 wt%. The incorporation of POSS-isocyanatopropyl in the PU had no effect on the T g. With respect to shear properties of POSS-octaphenyl-, POSS-isocyanatopropyl- and POSS-glycidoxypropyl-based PU nanocomposite adhesives, shear strength improved by 230, 178 and 137%, respectively, compared to neat PU. POSS-aminoethyl exhibited lower shear and peel strengths, while POSS-isocyanatopropyl provided the best balance of both higher shear and peel strengths compared to neat PU. It was concluded that the grafted functional group on the POSS and its reactivity with the PU network components were the decisive factors with respect to the thermo-mechanical, morphological and adhesive properties of the resulting nanocomposite adhesives. Consequently, the POSS/polyurethane based nanocomposite adhesives could be tailored for a large range of applications.

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

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.