Miscibility and Viscoelastic Properties of Acrylic Polyhedral Oligomeric Silsesquioxane-Poly(methyl methacrylate) Blends
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05-P-02.pdf
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Author(s)
Kopesky, Edward T.
Haddad, Timothy S.
McKinley, Gareth H.
Cohen, Robert E.
Date Issued
April 19, 2005
Series/Report no.
05-P-02;
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 Tg 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 < 0.10. At a loading φ = 0.05, the unmodified acrylic POSS induces a 4.9°C decrease in the Tg 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 f0 = 0.046 for PMMA at T0 = 170°C while for a blend of 5 vol% unmodified acrylic-POSS in PMMA f0 = 0.057, which corresponds to an addition of 0.47 nm3 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.
[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 Tg 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 < 0.10. At a loading φ = 0.05, the unmodified acrylic POSS induces a 4.9°C decrease in the Tg 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 f0 = 0.046 for PMMA at T0 = 170°C while for a blend of 5 vol% unmodified acrylic-POSS in PMMA f0 = 0.057, which corresponds to an addition of 0.47 nm3 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.
Description
Submitted to POLYMER, January 2005
Subjects
POSS
plasticization
nanocomposites
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