Miscibility and viscoelastic properties of acrylic polyhedral oligomeric silsesquioxane–poly(methyl methacrylate) blends

By E. Kopesky, T. Haddad, G. H. McKinley, R. Cohen. 2005

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Abstract We investigate the miscibility of acrylic polyhedral oligomeric silsesquioxanes (POSS) [characteristic size d ≈2 nm] and poly(methyl methacrylate)(PMMA) in order to determine the effect of well-dispersed POSS nanoparticles on the thermomechanical properties of PMMA. Two different acrylic POSS species (unmodified and hydrogenated) were blended separately with PMMA at volume fractions up to ϕ =0.30. Both POSS species have a plasticizing effect on PMMA by lowering the glass transition temperature T g and decreasing the melt-state linear viscoelastic moduli measured in small amplitude oscillatory shear flow. The unmodified acrylic-POSS has better miscibility with PMMA than the hydrogenated form, approaching complete miscibility for loadings ϕ ϕ =0.05, the unmodified acrylic POSS induces a 4.9 °C decrease in the T g of PMMA, far less than the 17.4 °C decrease in the glass transition temperature observed in a blend of 5 vol% dioctyl phthalate (DOP) in PMMA; however, the decrease in the glass transition temperature per added plasticizer molecule is nearly the same in the unmodified acrylic-POSS–PMMA blend compared with the DOP–PMMA blend. Time-temperature superposition (TTS) was applied successfully to the storage and loss moduli data and the resulting shift factors were correlated with a significant increase in free volume of the blends. The fractional free volume f 0 =0.046 for PMMA at T 0 =170 °C while for a blend of 5 vol% unmodified acrylic-POSS in PMMA f 0 =0.057, which corresponds to an addition of 0.47 nm 3 per added POSS molecule at ϕ =0.05. The degree of dispersion was characterized using both wide-angle X-ray diffraction (WAXD) and dynamic mechanical analysis (DMA). Diffraction patterns for both blend systems show clear evidence of phase separation at ϕ =0.20 and higher, but no significant phase separation is evident at ϕ =0.10 and lower. The storage modulus measured in DMA indicates appreciable phase separation for unmodified acrylic POSS loadings ϕ ≥0.10, while no evidence of phase separation is present in the ϕ =0.05 blend in DMA.

Subfields: Materials Chemistry, Polymers and Plastics

View Paper: https://www.semanticscholar.org/paper/827618e588b7487ab073a9820a77f4b0c19aebc9

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In Materials Chemistry

  1. S. Kuo
  2. Feng-Chih Chang
  3. Jian Wu
  4. P. Mather

In Polymers and Plastics

  1. S. Kuo
  2. Feng-Chih Chang
  3. Jian Wu
  4. P. Mather
  5. Tao Xie
  6. Jinlian Hu
  7. H. Meng

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