Aliphatic epoxy composites with multifunctional polyhedral oligomeric silsesquioxane (POSS) ((C 6H5CHCHO)4(Si8O12)(CHdCHC6H5)4) nanophases (epoxy/POSS 95/5 and 75/25) and epoxy blends with the prepolymer of ladderlike polyphenylsilsesquioxane (PPSQ) (95/5, 90/10, and 85/15) were prepared by solution casting and then curing. These composites and blends were studied by dynamic mechanical thermal analysis (DMTA) and mechanical testing. The POSS units incorporated into the epoxy network are well dispersed in the composite, probably on the molecular scale, even at high POSS content (25 wt %) based on TEM observations. However, the aliphatic epoxy/PPSQ blends exhibit good miscibility only at low PPSQ content (e10 wt %). Phase separation was clearly observed when the PPSQ content was 15%. Incorporation of the POSS macromer into this epoxy network by curing at upper temperatures of 120 and 150 °C broadened the temperature range of glass transition of the resulting composites but has almost no influence on their T g (the tan δ peak temperature). The Tg of epoxy/PPSQ blends containing e10 wt % PPSQ increased slightly with increasing PPSQ content. However, the Tg of epoxy/PPSQ 85/15 is lower than that of the neat epoxy resin because cross-linking density is reduced in the blend. Inclusion of PPSQ into the epoxy resin has no effect on the width of their glass transition range. The storage moduli E′ of both epoxy/POSS composites and epoxy/PPSQ blends at T > Tg are higher than those of neat epoxy resin and increase with the POSS or PPSQ content, improving their thermal dimensional stability. The flexural modulus of the epoxy resin is raised by POSS incorporation or PPSQ addition. Modification of the epoxy resin's flexural modulus is larger for composites with molecularly dispersed POSS than for those containing PPSQ. The magnitude of this increase goes up as more POSS or PPSQ was added. But, the flexural strengths of epoxy/POSS nanocomposites and epoxy/PPSQ blends are lower than that of neat epoxy.

Poly[isobutyl methacrylate‐co‐butanediol dimethacrylate‐co‐3‐methacrylylpropylheptaisobutyl‐T8‐polyhedral oligomeric silsesquioxane] [P(iBMA‐co‐BDMA‐co‐MA‐POSS)] nanocomposites with different crosslink densities and different polyhedral oligomeric silsesquioxane (MA‐POSS) percentages (5, 10, 15, 20, and 30 wt %) were synthesized by radical‐initiated terpolymerization. Linear [P(iBMA‐co‐MA‐POSS)] copolymers were also prepared. The viscoelastic properties and morphologies were studied by dynamic mechanical thermal analysis, confocal microscopy, and transmission electron microscopy (TEM). The viscoelastic properties depended on the crosslink density. The dependence of viscoelastic properties on MA‐POSS content at a low BDMA loading (1 wt %) was similar to that of linear P(iBMA‐co‐MA‐POSS) copolymers. P(iBMA‐co‐1 wt % BDMA‐co‐10 wt % MA‐POSS) exhibited the highest dynamic storage modulus (E′) values in the rubbery region of this series. The 30 wt % MA‐POSS nanocomposites with 1 wt % BDMA exhibited the lowest E′. However, the E′ values in the rubbery region for P(iBMA‐co‐3 wt % BDMA‐co‐MA‐POSS) nanocomposites with 15 and 30 wt % MA‐POSS were higher than those of the parent P(iBMA‐co‐3 wt % BDMA) resin. MA‐POSS raised the E′ values of all P(iBMA‐co‐ 5 wt % BDMA‐co‐MA‐POSS) nanocomposites in the rubbery region above those of P(iBMA‐co‐5 wt % BDMA), but MA‐POSS loadings < 15 wt % had little influence on glass‐transition temperatures (Tg's) and slightly reduced Tg values with 20 or 30 wt % POSS. Heating history had little influence on viscoelastic properties. No POSS aggregates were observed for the P(iBMA‐co‐1 wt % BDMA‐co‐MA‐POSS) nanocomposites by TEM. POSS‐rich particles with diameters of several micrometers were present in the nanocomposites with 3 or 5 wt % BDMA. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 355–372, 2005

SYNOPSISImpact strength and dynamic mechanical analysis of polystyrene/polyphenylsilsesquioxane (PS/PPSQ) in situ blend was studied. Toughness, thermal stability, and storage modulus of the brittle PS matrix could be improved by addition of some much more brittle PPSQ particles when the percentage of PPSQ in this blend was not more than 5%. The toughening mechanism about the deformation of the PPSQ particles, which is due to good adhesion between the dispersed PPSQ particles and the continuous PS matrix and some particle-induced crazes or yielding zones, was discussed. PPSQ has the better effect on the modification of PS than its prepolymer with low molecular weight.

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Polystyrene (PS) blends with rigid ladderlike polyphenylsilsesquioxane (PPSQ) were prepared by solution casting followed by hot pressing. The rheological properties of these blends were studied under dynamic shear and uniaxial elongation conditions. The loss modulus (GЉ) and dynamic shear viscosity (*) of the 95/5 PP/PPSQ blend were slightly lower than those of pure PS at low frequencies (Յ10 Ϫ2 rad/s). However, the storage modulus (GЈ), GЉ, and * of the other blends (90/10, 85/15, and 80/20) were higher than those of pure PS and increased with PPSQ content. The E data demonstrated that PS/PPSQ blends exhibited slightly weaker (5% PPSQ) or much weaker (10% PPSQ) strain hardening than PS. In contrast, the 85/15 and 80/20 PP/PPSQ blends showed strain softening, and the extent of strain softening increased with PPSQ content. PS entanglements might have been reduced by the specific interactions between PS and PPSQ, which locally ordered some PS molecules in the 95/5 blend sample, because most of the PPSQ might have been well dispersed in the PS continuous phase, and only a few small PPSQ particles (ϳ1.3 m) were formed because of good miscibility. However, at high PPSQ contents (Ն10%), many larger hard PPSQ particles were formed, which acted as fillers during the rheological measurements.

This paper reports the first observation on morphology of single crystals of ladder‐like polyphenylsilsesquioxane (PPSQ) by polarized optical microscopy. These crystals prepared from benzene solution are cubic or pyramidal, whose bases are parallelograms with acute angles of 70° and 60°, while those pyramidal shaped crystals formed from toluene solution have also parallelogram‐like basal planes with small acute angles of 39° and 26°. Most pyramidal crystals exhibit fringes, sectors, stripes or colorful stripes.

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