A. Chandramohan

Synthesis and characterization of epoxy modified cyanate ester POSS nanocomposites

Polyhedral oligomeric silsesquioxane (POSS) viz; namely, Octa functional silsesquioxanes [octa amino (OAPS) and octa glycidyl (OG)] reinforced epoxy modified cyanate ester nanocomposites were prepared through intercrosslinked network. The intercrosslinking formation between cyanate ester and POSS was confirmed by Fourier transform infrared spectroscopy. The morphology of nanocomposites was studied using X-ray diffraction, scanning electron microscopy, transmission electron microscopy and atomic force microscopy techniques. The electrical properties of the nanocomposites were evaluated by impedance analyzer. The influences of POSS macromer on the thermal and mechanical properties of epoxy modified cyanate ester nanocomposites were also addressed. The thermogravimetric analysis indicates that the thermal stability of the nanocomposites increases with increasing percentage of both types of POSS macromer. The dielectric constant and dielectric loss are decreased with increasing POSS concentration in the epoxy modified cyanate ester nanocomposites.

Synthesis and characterization of 1, 1-bis (3-methyl-4-epoxyphenyl) cyclohexane-toughened DGEBA and TGDDM organo clay hybrid nanocomposites

1,1-bis (3-methyl-4-epoxyphenyl) cyclohexane (BMEPC) was synthesized from 1,1-bis (3-methyl-4-hydroxyphenyl) cyclohexane and 2-(chloromethyl) oxirane, and its structure was confirmed by Fourier transform infrared (FT-IR), 1H-, 13C-NMR and electron impact-mass spectrometry. Both diglycidyl ether of bisphenol-A (DGEBA) and tetraglycidyl diamine diphenyl methane (TGDDM) epoxy resins were toughened with BMEPC using 4,4′-diaminodiphenylmethane (DDM) as a curing agent. Epoxy and BMEPC-toughened epoxy systems were further modified with organophilic MMT (OMMT) clay. The chemical reactions involved between epoxy and DDM with OMMT was confirmed by FT-IR. OMMT clay-filled hybrid BMEPC-epoxy resin castings were characterized for their mechanical, thermal, thermo-mechanical and morphological properties. The values of Tg and heat distortion temperature of hybrid epoxy decreased with increasing incorporation of OMMT. The data obtained from thermal studies indicated that the incorporation of nano clay into BMEPC-modified hybrid systems possess improved thermal stability. The mechanical properties were studied as per ASTM standards. The TGDDM-based hybrid epoxy system exhibited higher values of tensile and flexural properties than that of the DGEBA hybrid epoxy system, whereas the impact strength of the DGEBA system was higher when compared with that of the TGDDM system. The values of dielectric constant (ϵ′) and dielectric loss (ϵ′′) were increased with increased incorporation of OMMT clay in both systems. From the X-ray diffraction analysis it was observed that the absence of d001 reflections in OMMT-filled BMEPC-modified epoxy systems indicated the formation of exfoliated nano hybrids. The homogenous morphologies were ascertained from scanning electron microscope and transmission electron microscope.

Thermal and Morphological Properties of Octa(maleimido phenyl) Silsesquioxane (OMPS)-Reinforced Polybenzoxazine Hybrid Nanocomposites

We prepared an octa maleimido functionalized POSS, namely octa(maleimido phenyl) silsesquioxane (OMPS)-reinforced polybenzoxazine hybrid nanocomposites, by using four different types of benzoxazines (BZ-Cy-DDM, BZ-Cy-DDE, BZ-Cy-DDS, and BZ-Cy-Ani). They were synthesized from 1,1-bis(3-methyl-4-hydroxyphenyl) cyclohexane, paraformaldehyde, and aromatic amines (4,4′-diaminodiphenylmethane, 4,4′-diaminodiphenylether, 4,4′-diaminodiphenylsulphone, and aniline) by the Mannich reaction. We used 10 wt.% OMPS in all four polybenzoxazine matrices in order to compare the effect of OMPS on various benzoxazines. They were polymerized through thermal ring-opening polymerization at identical conditions. The thermal properties of the resulting OMPS-reinforced polybenzoxazine hybrid nanocomposites were studied using differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). The dispersion of OMPS in the polybenzoxazine and nanostructure of the composites were confirmed by X-ray diffraction analysis, transmission electron microscopy, and atomic force microscopy.

Preparation and Characterization of Cyclohexyl Moiety Toughened POSS-Reinforced Epoxy Nanocomposites

Polyhedral oligomeric silsesquioxane (POSS)-reinforced epoxy nanocomposites were prepared by reacting commercially available diglycidyl ether of bisphenol-A (DGEBA) and tetraglycidyl diamino diphenyl methane (TGDDM) epoxy resins with 1,1-bis(3-methyl-4-glycidyloxyphenyl)cyclohexane (Cy-Ep) separately and reinforced with POSS nanocluster. POSS (OAPS)-reinforced hybrid Cy-Ep-epoxy resin castings were characterized for their mechanical and morphological properties. The data obtained from mechanical studies indicated that the incorporation of nano OAPS into Cy-Ep modified hybrid systems results in improved stability. Among the epoxy systems studied, the TGDDM-based hybrid epoxy system exhibited higher values of tensile and flexural properties than that of the DGEBA hybrid epoxy system, whereas the impact strength of the DGEBA system was higher than that of the TGDDM system. The dispersion of POSS was confirmed by scanning electron microscopy and visual observation studies.

Polysilsesquioxane-reinforced phosphorous containing bis(4-maleimidophenyl)benzoxazine hybrid nanocomposites

In this study, octa(aminophenyl)silsesquioxane (OAPS), octakis(dimethylsiloxypropylglycidylether) silsesquioxane (OG) and phosphorous skeletal bis(4-maleimidophenyl)benzoxazine were synthesized and characterized. The polyhedral oligomeric silsesquioxane (POSS) derivative (OAPS and OG)-reinforced polybenzoxazine (PBZ) hybrid nanocomposites were prepared by thermal method. The chemical reactions between POSS and PBZ were confirmed by Fourier transform infrared spectroscopy. The effect of the incorporation of POSS derivatives on the properties including thermal, dielectric properties and water absorption behaviour of POSS/PBZ hybrids was analyzed and discussed systematically. The test results indicate that the addition of POSS into PBZ increased the thermal stability and decreased the values of dielectric constant and dielectric loss. The morphology of the POSS-PBZ hybrid nanocomposites was characterized using x-ray diffraction, confocal optical microscopy, scanning electron microscopy, transmission electron microscopy and atomic force microscopy.

Thermal, thermoechanical and morphological behavior of Octa (maleimido phenyl) silsesquioxane (OMPS)-cyanate ester nanocomposites

Polyhedral oligomeric silsesquioxane (POSS)-cyanate ester (CE) nanocomposites have been developed by the incorporation of octafunctional maleimide POSS (OMPS) into the bisphenol-A based CE network through in situ method by thermal curing with the use of diaminodiphenylmethane (DDM) as coupling agent. The formation of nanocomposite was confirmed by Fourier transform infrared analysis. X-ray diffraction, scanning electron microscopy and transmission electron microscopy images confirm the morphology of CE/OMPS nanocomposites. The thermal and morphological properties were studied by varying different weight percentages (1, 3, 5 and 10%) of OMPS. The 5 wt.% OMPS-incorporated nanocomposite possesses higher values of glass transition temperature than those of nanocomposites filled with a lower percentages of OMPS. Further thermal stability of nanocomposites increased with increase in percentage composition of OMPS.

Synthesis and characterization of linseed vinyl ester fatty amide-modified epoxy layered silicate nanocomposites

Bio-based epoxy/clay nanocomposites were prepared by swelling organoclay in an epoxy (DGEBA)/linseed vinyl ester fatty amide (LVEFA), followed by curing with an aromatic hardener, 4,4′-diaminodiphenylmethane (DDM). The X-ray diffraction showed the existence of intercalated clay in the polymer matrix. Differential scanning calorimetry (DSC) indicated a gradual increase in the glass transition temperature as the organoclay loading increased. The tensile strength, flexural strength and impact strength of 20 wt.% linseed vinyl ester-modified epoxy composites significantly increased by 23.65, 13.19 and 40.7%, respectively, with increasing organoclay concentration. The tensile modulus and flexural moduli were enhanced by 14 and 9.28%, respectively.

Organoclay-Filled Vinyl Ester Monomer Toughened Epoxy-Intercrosslinked Matrix Materials

A vinyl ester monomer (VEM), namely cyclohexyl-1,1′-bis[4-(γ-2-methylphenoxy)-α-hydroxypropylacrylate], was synthesized from 1, 1-bis (3-methyl-4-glycidyloxyphenyl) cyclohexane, and acrylic acid via nucleophilic addition. The structure of VEM was confirmed by FTIR, 1H, 13C NMR, and electron impact-mass spectroscopy. Diglycidyl ethers of bisphenol-A (DGEBA) epoxy resin were toughened with varying percentages of 5, 10, and 15% (by wt) VEM using 4, 4′-diaminodiphenylmethane (DDM). VEM-modified epoxy systems were further modified with organophilic montmorillonite (OMMT) clay. OMMT clay-filled hybrid VEM-epoxy resin systems, developed in the form of casting, were characterized for their mechanical, thermomechanical, dielectric, and morphological properties.

Studies on thermal, mechanical, electrical, and morphological behavior of organoclay-reinforced polybenzoxazine–epoxy nanocomposites

Organoclay-reinforced polybenzoxazine–epoxy nanocomposites were prepared via in situ polymerization and thermal, thermomechanical, mechanical, electrical, and morphological properties were characterized by standard methods. Two types of skeletal-modified benzoxazines namely 1,1-bis(3-methyl-4-hydroxyphenyl)cyclohexane benzoxazine and bis(4-maleimidophenyl) benzoxazine were synthesized by reacting paraformaldehyde and 4,4′-diaminodiphenylmethane with 1,1-bis(3-methyl-4-hydroxyphenyl)cyclohexane and N-(4-hydroxyphenyl)maleimide, respectively. Diglycidyl ether bisphenol A epoxy resin was modified with 5, 10, and 15 wt% of benzoxazines and were cured using 4,4′-diaminodiphenylmethane at appropriate conditions. The occurrence of chemical reaction between benzoxazines and epoxy resin was ascertained by Fourier transform infrared spectra. Epoxy and benzoxazines-modified epoxy systems were further reinforced with 1, 3 and 5 wt% of organically modified montmorillonite (OMMT). Thermal behavior of matrices was characterized by differential scanning calorimetry, thermogravimetric analysis, and dynamic mechanical analysis. Mechanical properties were studied as per ASTM standards. The organoclay (OMMT)-reinforced polybenzoxazine–epoxy nanocomposites exhibited lower values of glass transition temperature and dielectric constant/dielectric loss with enhanced values of thermal stability, char yield, impact strength, and storage modulus than those of neat matrix. The morphology of organoclay-reinforced benzoxazine-modified epoxy matrix was studied by scanning electron microscopy, x-ray diffraction, and transmission electron microscopy analyses.

Preparation and Characterization of Vinyl Ester Monomer–Toughened Epoxy-Clay Hybrid Nanocomposites: Thermal and Morphological Properties

An intercross-linked network of vinyl ester monomer (VEM)-toughened epoxy-clay hybrid nanocomposites was developed and characterized using analytical methods. Cyclohexyl-1,1′-bis[4-(γ-2-methylphenoxy)-α-hydroxypropylacrylate]-based VEM was synthesized from 1,1-bis(3-methyl-4-glycidyloxyphenyl) cyclohexane and acrylic acid. The VEM was subsequently blended with diglycidyl ether of bisphenol-A (DGEBA) resin cast and cured with 4,4′-diaminodiphenylmethane (DDM). VEM-toughened epoxy matrices were reinforced with organophilic montmorillonite (OMMT) clay yielding hybrid epoxy nanocomposites. Data obtained from thermal characterization indicate that the introduction of VEM into epoxy resin improves thermal properties. The morphological behavior of the nanocomposite was analyzed by X-ray diffraction (XRD) analysis and transmission electron microscopy (TEM).