No abstract

Organic-inorganic hybrids involving cyanate ester and hydroxyl-terminated polydimethylsiloxane (HTPDMS) modified diglycidyl ether of bisphenol A (DGEBA; epoxy resin) filled with organomodified clay [montmorillonite (MMT)] nanocomposites were prepared via in situ polymerization and compared with unfilled-clay macrocomposites. The epoxy-organomodified MMT clay nanocomposites were prepared by the homogeneous dispersion of various percentages (1-5%), and the resulting homogeneous epoxy/clay hybrids were modified with 10% HTPDMS and g-aminopropyltriethoxysilane as a coupling agent in the presence of a tin catalyst. The siliconized epoxy/clay prepolymer was further modified separately with 10% of three different types of cyanate esters, namely, 4,4 0 -dicyanato-2,2 0 -diphenylpropane, 1,1 0 -bis(3-methyl-4-cyanatophenyl) cyclohexane, and 1,3-dicyanato benzene, and cured with diaminodiphenylmethane as a curing agent. The reactions during the curing process between the epoxy, siloxane, and cyanate were confirmed by Fourier transform infrared analysis. The results of dynamic mechanical analysis showed that the glass-transition temperatures of the clayfilled hybrid epoxy systems were lower than that of neat epoxy. The data obtained from mechanical studies implied that there was a significant improvement in the strength and modulus by the nanoscale reinforcement of organomodified MMT clay with the matrix resin. The morphologies of the siloxane-containing, hybrid epoxy/clay systems showed heterogeneous character due to the partial incompatibility of HTPDMS. The exfoliation of the organoclay was ascertained from X-ray diffraction patterns. The increase in the percentage of organomodified MMT clay up to 5 wt % led to a significant improvement in the mechanical properties and an insignificant decrease in the glass-transition temperature versus the unfilled-clay systems.

Epoxy-POSS based hybrid nanocomposites are prepared by in situ polymerization of a homogeneous blend of the diglycidylether of bisphenol-A (DGEBA) and 4,4'-diaminodiphenylmethane (DDM) in the presence of octa(maleimidophenyl)silsesquioxane (OMPS). The reaction of a maleimido-functionalised POSS cube with the epoxy resin is studied by Fourier transform infrared (FTIR) analysis and the formation of nanocomposites is confirmed by wide-angle X-ray diffraction (WAXD) and scanning electron microscopy (SEM). Dynamic mechanical analysis (DMA) studies indicate that the crosslinking structures of the nanocomposite networks are predominantly formed 2 between the terminal maleimide double bonds and the amino groups of DDM through a Michael addition reaction to form an aspartimide. The values of the glass transition temperatures (T g ) decrease with increasing POSS-maleimide content and this is likely to be due to the inclusion of POSS cages into the system and consequent increase in free volume. The dynamic thermal stability of the cured polymers is increased by increasing the POSS content in the hybrid epoxy matrices as evidenced from thermogravimetric analysis (TGA) data.

An intercrosslinked network of hybrid bismaleimide (BMI) modified vinyl ester oligomer-unsaturated polyester matrix systems have been developed. Vinyl ester oligomer (VEO) was used as a toughening agent for unsaturated polyester resin and was added in 2, 4, and 6% (by wt). Benzoyl peroxide was used as curing agent. The VEO-toughened unsaturated polyester matrix systems were further modified with 5, 10, and 15% (by wt) of bismaleimide. Bismaleimides modified vinyl ester-unsaturated polyester matrices were characterized by mechanical (tensile strength, flexural strength, tensile modulus, flexural modulus, and impact strength), thermal [differential scanning calorimetry (DSC), thermogravimetic analysis (TGA), heat deflection temperature analysis (HDT)] and morphological studies [scanning electron microscope (SEM)] and water absorption. Data obtained from mechanical studies indicated that the introduction of VEO into unsaturated polyester resin improves the fracture toughness. The introduction of BMI into VEO incorporated unsaturated polyester resin enhanced both thermal and mechanical behavior. The scanning electron micrographs of fractured surfaces of VEO-modified unsaturated polyester systems and BMI modified vinyl ester-unsaturated polyester matrices illustrate the presence of homogeneous morphology.