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Cyanate ester (PT-15, Lonza Corp.) composites containing the blended polyhedral oligomeric silsesquioxane (POSS), TriSilanolPhenyl-POSS (C 42 H 38 O 12 Si 7 ), were prepared containing PT-15/POSS 99/1, 97/3, 95/5, 90/10, and 85/15 w/w ratios. The composites were characterized by FT-TR, X-ray diffraction (XRD), small-angle neutron scattering (SANS), scanning electron microscopy (SEM), X-ray energy dispersive spectroscopy (X-EDS), transmission electron microscopy (TEM), dynamic mechanical thermal analysis (DMTA), and three-point bending flexural tests. TriSilanolPhenyl-POSS was throughly dispersed into uncured liquid PT-15 resin. After curing, XRD, SANS, and X-EDS measurements were consistent with partial molecular dispersion of a portion of the POSS units in the continuous matrix phase while the remainder forms POSS aggregates. Larger aggregates are formed at higher loadings. SANS, SEM, and TEM show that POSS-enriched nanoparticles are present in the PT-15/POSS composites. The storage bending moduli, E′, and the glass transition temperatures, T g , of PT-15/POSS 99/1, 97/3, and 95/5 composites are higher than those of the pure PT-15 over the temperature range from 35 to 350 °C. The E′ values for all these composites (except for the 15 wt % POSS sample) are significantly greater than that of the pure resin at T > T g . Therefore, small amounts (e5 wt %) of TriSilanolPhenyl-POSS incorporated into cyanate ester resin PT-15 can improve the storage modulus and the hightemperature properties of these cyanate ester composites versus the pure PT-15 resin. The flexural strength and flexural modulus are also raised by POSS incorporation.

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Cyanate ester (PT‐15, Lonza Corp) composites containing the inorganic–organic hybrid polyhedral oligomeric silsesquioxane (POSS) octaaminophenyl(T8)POSS [1; (C6H4NH2)8(SiO1.5)8] were synthesized. These PT‐15/POSS‐1 composites (99/1, 97/3, and 95/5 w/w) were characterized by X‐ray diffraction (XRD), transmission election microscopy (TEM), dynamic mechanical thermal analysis, solvent extraction, and Fourier transform infrared. The glass‐transition temperatures (Tg's) of the composite with 1 wt % 1 increased sharply versus the neat PT‐15, but 3 and 5 wt % 1 in these cyanate ester composites depressed Tg. All the PT‐15/POSS composites exhibited higher storage modulus (E′) values (temperature > Tg) than the parent resin, but these values decreased from 1 to 5 wt % POSS. The loss factor peak intensities decreased and their widths broadened upon the incorporation of POSS. XRD, TEM, and IR data were all consistent with the molecular dispersion of 1 due to the chemical bonding of the octaamino POSS‐1 macromer into the continuous cyanate ester network phase. The amino groups of 1 reacted with cyanate ester functions at lower temperatures than those at which cyanate ester curing by cyclotrimerization occurred. In contrast to 1, 3‐cyanopropylheptacyclopentyl(T8)POSS [2; (C5H9)7(SiO1.5)8CH2CH2CH2CN] had low solubility in PT‐15 and did not react with the resin below or at the cure temperature. Thus, phase‐separated aggregates of 2 were found in samples containing 1–10 wt % 2. Nevertheless, the Tg and E′ values (temperature > 285 °C) of these composites increased regularly with an increase in 2. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 3887–3898, 2005