Morphology and Thermomechanical Properties of Organic−Inorganic Hybrid Composites Involving Epoxy Resin and an Incompletely Condensed Polyhedral Oligomeric Silsesquioxane

Abstract

Epoxy was modified by an incompletely condensed polyhedral oligomeric silsesquioxane (POSS), and the phenyltrisilanol POSS [Ph7Si7O9(OH)3, POSS-triol] was incorporated into the epoxy networks with the content of POSS up to 30 wt %. The organic−inorganic hybrid composites were prepared via in situ polymerization of epoxy monomers in the presence of POSS-triol, which started from the homogeneous solutions of POSS-triol and epoxy monomers. The nanocomposites of epoxy with POSS-triol can be prepared with the metal complex, aluminum triacetylacetonate ([Al]) being used as the catalyst for the reaction between POSS-triol and diglycidyl ether of bisphenol A (DGEBA). Otherwise, the phase separation induced by polymerization occurred, and the fine phase-separated structures were obtained, in which the spherical POSS-triol particles (0.3−0.5 μm in diameter) were dispersed in the continuous epoxy matrices. The hybrid composites with the different morphological structures displayed quite different thermomechanical properties. The phase-separated composites possessed the higher glass transition temperatures (T g's) than the nanocomposites while the nanocomposites displayed the higher storage modulus of glassy state in light of dynamic mechanical analysis (DMA). In terms of thermogravimetric analysis, the nanocomposites displayed the higher initial thermal decomposition temperatures (T d's). The improvement in thermomechanical properties has been ascribed to the nanodispersion of POSS moieties.

Viscoelastic properties and residual stresses in polyhedral oligomeric silsesquioxane‐reinforced epoxy matrices

“…39 In another study, the brelaxation of epoxy matrices for a DGEBA/DDM/ octa(propylglycidyl ether) POSS (OpePOSS) system split into two peaks, with the b-relaxation shifting to lower temperatures presumably because of the increased mobility due to the plasticization effect of the R group on the POSS and the b 0 -relaxation shifting to higher temperatures due to the rigidity of the POSS cage which restricts the polymer chain motions. 32 In three of these studies, the glass transition temperature T g decreased with POSS content; 31,39,40 whereas the T g of DGEBA/DDM/OpePOSS is invariant with POSS content below 30 wt % and it decreases above 30 wt % up to 40 wt %. 32 The DGEBA/BDMA/ hydroxyl group-functionalized POSS system showed a depressed b-relaxation peak intensity with increasing POSS content, 40 whereas the other three systems did not exhibit any trend.…”

“…37 The moduli of the POSS-filled nanocomposites similarly depend on the POSS structures. The glassy modulus of the nanocomposites is found to either increase due to the nanoreinforcement of the nanoparticles 27,31,39 or decrease; 37 furthermore, the rubbery modulus also either increases presumably due to the increased crosslink density or the reinforcement of the nanoparticles 28,30,43 or decreases due to the decreased crosslink density associated with the flexible structure of the POSS. 27 One study also showed that the instantaneous modulus of the nanocomposites is not affected by the incorporation of POSS, although the physical aging process of the composites in the glassy state was found to be retarded.…”

“…It has been found that the glass transition temperature of POSSreinforced epoxy nanocomposites either increases, 24,28,29,35,38 decreases, 27,31,[38][39][40] stays unchanged, 30,32,37,39 , or even disappears 37 with the addition of POSS depending on the chemical structure of the functional group (R group) on the POSS and the POSS loading. In general, the glass transition temperature of the nanocomposites decreases when the R group on the POSS is long and flexible and a ''soft'' interface can be formed between the nanoparticle and matrix; 27,32,40,45 on the other hand, T g increases if the interface is rigid and the polymer chain motions are hindered by their covalent bonding to POSS clusters.…”

“…58 The effect of POSS nanoparticles on the b-relaxation of DGEBA-type epoxy matrices has been investigated by a few authors using DMA and different phenomena have been observed for various systems. 31,32,39,40 A shift of the peak temperature of the b-relaxation was attributed to an increased free volume introduced by the POSS cage for DGEBA/benzyldimethylamine (BDMA)/hydroxyl group-functionalized POSS with bulky and flexible organic substituents, 40 DGEBA/DDM/phenyltrisilanol-POSS, 31 and DGEBA/DDM/aminophenyl-POSS systems. 39 In another study, the brelaxation of epoxy matrices for a DGEBA/DDM/ octa(propylglycidyl ether) POSS (OpePOSS) system split into two peaks, with the b-relaxation shifting to lower temperatures presumably because of the increased mobility due to the plasticization effect of the R group on the POSS and the b 0 -relaxation shifting to higher temperatures due to the rigidity of the POSS cage which restricts the polymer chain motions.…”

“…32 The DGEBA/BDMA/ hydroxyl group-functionalized POSS system showed a depressed b-relaxation peak intensity with increasing POSS content, 40 whereas the other three systems did not exhibit any trend. 31,32,39 In the current study, we investigate the effects of POSS content on the shear viscoelastic properties, the coefficient of thermal expansion (CTE), the glass transition temperature, and the b-relaxation of an epoxy resin. These properties are chosen because they impact the residual stresses that would occur in fiber-reinforced composites using an epoxy/POSS nanocomposite as matrix.…”