S. Devaraju

SBA-15 filled polybenzoxazine nanocomposites for low-k dielectric applications

Low dielectric polybenzoxazine nanocomposites (SBA-15/PBZ) containing mesoporous silica (SBA-15) were successfully synthesized, using benzoxazine functionalized SBA-15 (BZ/SBA-15) and benzoxazine monomer, through thermal ring opening polymerization. SBA-15 was functionalized with benzoxazine functional silane via grafting method. The benzoxazine functionality in BZ/SBA-15 was confirmed by FT-IR, 13C CPMAS, 29Si CPMAS NMR, XPS, TGA and nitrogen porosimetry analysis. By increasing the amount of BZ/SBA-15, the SBA-15/PBZ nanocomposites possess higher Tg and good thermal stability. 7.5 Wt % of BZ/SBA-15 reinforced polybenzoxazine nanocomposite possesses an ultra-low dielectric constant of 1.75 at 1 MHz.

Studies on thermal and dielectric properties of ether linked cyclohexyl diamine (ELCD)-based polyimide POSS nanocomposites (POSS-PI)

Polyhedral oligomeric silsesquioxane (POSS)-polyimide (PI) hybrid nanocomposites were prepared from ether linked cyclohexyl diamine (ELCD)-modified polyamic acid with POSS derivative of octaaminophenylsilsesquioxane (OAPS). Polyamic acid (PAA) was prepared by reacting ELCD with pryomelletic dianhydride (PMDA) in 1-methyl-2-pyrrolidone (NMP) medium. The PAA reacted with varying weight percentages of OAPS and undergoes thermal imidization to form POSS-PI nanocomposites upon heating. The formation of hybrid nanocomposites was confirmed with Fourier transform infrared spectra. The thermal and dielectric properties of POSS-PI nanocomposites were characterized by using differential scanning calorimetry, thermogravimetric analysis and an impedance analyzer. Morphology of the nanocomposites was studied by using scanning electron microscopy. Data from thermal studies indicated that the incorporation of POSS in to PI substantially enhanced the glass transition temperature (T g), thermal stability and char yield of hybrid nanocomposites in comparison with those of neat PI. From the dielectric studies it was inferred that the increasing percentage concentration of OAPS into the PI network exhibits a decreasing trend in the values of dielectric constant when compared with those of neat PI.

Studies on thermal and dielectric properties of Octa (maleimido phenyl) silsesquioxane (OMPS) – polybenzoxazine (PBZ) hybrid nanocomposites

Polybenzoxazine (PBZ) hybrid nanocomposites were prepared from new type of allyl-terminated benzoxazine monomer and various weight percentage of Octa (maleimido phenyl) silsesquioxane (OMPS). The allyl terminal benzoxazine monomer was synthesized from 1,1-bis (3-methyl-4-hydroxy phenyl) cyclohexane with allyl amine and formaldehyde through Mannich condensation and it was characterized by using Fourier transform infrared, 1H-NMR and 13C-NMR spectroscopy. Data from differential scanning calorimetry (DSC) analysis shows that the newly synthesized benzoxazine monomer (BZ-Cy-al) begins to show ring opening polymerization at lower temperature than that of conventional allyl terminal benzoxazine (BZ-al).Thermal properties of hybrid nanocomposites were analysed by using DSC and thermogravimetric analyser. The POSS-PBZ nanocomposites possess higher glass transition temperature and thermal stability than that of neat PBZ. Dielectric properties of hybrid polybenzoxazine nanocomposites were found decreasing with an increase in the OMPS content. The water absorption properties of hybrid polybenzoxazine nanocomposites decrease with increase in OMPS content. A homogeneous morphological behavior of the hybrid nanocomposites were studied by X-ray diffraction, scanning electron microscopy and transmission electron microscopy analysis.

Low surface free energy cyanate ester–silica hybrid (CE–SiO2) nanomaterials for low k dielectric applications

The present work addresses the synthesis of 1,4-bis(2-(4-hydroxyphenyl)-2-propyl)benzene based cyanate ester–silica hybrid (CE-SiO2) nanomaterials by an in situ sol–gel method. The nanomaterials are synthesized using a 1,4-bis(2-(4-cyanotophenyl)-2-propyl)benzene [CE] (organic phase) monomer and tetraethoxysilane (TEOS) (inorganic phase) in the presence of various molar ratios of coupling agents [γ-aminopropyltriethoxysilane (APTES) or 3-glycidoxypropyltrimethoxysilane (GPTMS)] through covalent bond interaction. The formation of a covalent bond between the organic and inorganic phases is confirmed by FT-IR. Thermal studies indicate that nanomaterials (CE–SiO2) show a higher Tg and thermal degradation temperature when compared with neat CE. Morphological studies confirm the molecular level dispersion of silica and CE resin. From the contact angle measurement, the hybrid materials are seen to possess better hydrophobicity i.e. the contact angle value increases from 89° and 57° to 108° and 78° for water and diiodomethane as a probe liquid respectively, also surface free energy reduced from 32.8 to 19.00 mJ m−2. These materials are expected to find wide application in the field of microelectronics and optoelectronics.

Synthesis and characterization of bisphenol-A ether diamine-based polyimide POSS nanocomposites for low K dielectric and flame-retardant applications

Polyhedral oligomeric silsesquioxane (POSS) – polyimide (PI) hybrid nanocomposites were prepared by a two-step approach, bisphenol-A ether diamine (BAED) and pyromelletic dianhydride (PMDA) in 1-methyl-2-pyrrolidone (NMP) were used to prepare polyamic acid (PAA) to which varying weight percentages of OAPS in NMP were added. During the second step, the polycondensation was effected by thermal imidization. The formation of hybrid nanocomposites was confirmed by using FTIR spectra. The thermal properties of POSS-PI nanocomposites were studied using differential scanning calorimetry and thermogravimetric analysis. The lowest dielectric constant 2.68 was achieved for 15 wt.% POSS-PI material when compared with the value of 3.34 for the neat PI. Data from thermal studies indicate that the incorporation of POSS into polyimide significantly enhanced the glass transition temperature (T g), thermal stability, char yield and flame-retardant properties of hybrid nanocomposites than that of neat PI. The excellent combination of both dielectric and thermal properties of the material developed in the present study will find application in microelectronics.

Studies on synthesis and characterization of surface-modified mullite fibre-reinforced epoxy nanocomposites:

The present work describes the development of epoxy composites using varying weight percentages (0.5, 1.0 and 1.5 wt%) of glycidyl-functionalized mullite (GM) fibre and diglycidyl ethers of bisphenol-A epoxy resin cured with diamino diphenyl methane. The mullite fibre was synthesized via the sol–gel method and its surface was modified with 3-glycidoxypropyltrimethoxysilane. The glycidyl functionality in the mullite fibre has been confirmed by Fourier transform infrared and thermogravimetric analyses. The data obtained from the thermal, mechanical, dielectric water absorption studies and contact angle showed that the GM fibre had a significant impact in the resultant epoxy nanocomposites compared to neat epoxy matrix. The molecular level dispersion of mullite fibres into the epoxy matrix was confirmed by the scanning electron microscopy and x-ray diffraction analyses.

The effect of UV radiation on polybenzoxazine/epoxy/OG-POSS nanocomposites

Degradation against atomic oxygen (AO), ultra-violet (UV) and vacuum ultra-violet (VUV) radiation has to be controlled in order to maintain the longevity and performance of light weight and high strength nanocomposites used in space and nuclear applications. With this in mind, a new synthetic route has been used to develop a semi-organic precursor, [polyhedral oligomeric silsesquioxane (POSS)] reinforced polybenzoxazine/epoxy (PBZ/EP) nanocomposites. PBZ/EP/POSS nanocomposites have been developed by reinforcing varying weight percentages of (0, 1.0, 3.0, and 5.0 wt%) POSS into 1 : 1 (w/w) ratio of BZ and DGEBA epoxy (EP) matrix via thermal curing. The developed nanocomposites were tested under UV irradiation at the wavelength of 365 nm for a period of one week. The values of tensile strength and morphological behaviour before and after exposure to UV irradiation have been determined in order to assess their radiation resistant behaviour. It was ascertained that the data obtained from the value of tensile strength for 5 wt% POSS reinforced PBZ/EP has changed only to an insignificant extent when compared to that of before UV irradiation. From SEM and XPS analysis, it was observed that a passive inert silica protective layer has been formed after radiation, which protects the composite materials from further deterioration due to radiation. Data from thermal and dielectric studies indicate that the POSS incorporated system possesses better thermal and low dielectric properties than those of the neat PBZ/EP matrix.

Synthesis of soluble polyimides based on ether-linked cyclohexyldiamine and their ultraviolet shielding behavior

A series of polyimides (PIs) based on ether-linked cyclohexyldiamine were prepared using pyromellitic dianhydride (PI-1), benzophenone dianhydride (PI-2), naphthalene dianhydride (PI-3), and perylene dianhydride (PI-4) in 1-methyl-2-pyrrolidone (NMP) medium to obtain respective polyamic acids and are subsequently converted into PIs through thermal imidization. The resulting PIs were characterized by Fourier transform infrared, X-ray diffraction, thermogravimetric analysis, differential scanning calorimetry, and impedance analyses. In addition, the ultraviolet (UV) shielding ability of PIs was also studied and discussed. The vibrational analysis confirms the imidization, and the XRD profile indicates the amorphous nature of the resulting PIs. The PIs synthesized in the present work exhibit good solubility in organic solvents such as NMP, dimethylformamide (DMF), and dimethyl sulfoxide (DMSO). The PI-4-based imide possesses very good solubility with the highest glass transition temperature value of 256°C, highest char yield of 50.16%, highest dielectric constant of 3.9 and higher UV shielding performance of 89% than those of other PIs. Further, the good solubility also makes them useful for coating applications in aerospace and liquid crystal displays.

Studies on thermal, mechanical and morphological properties of organoclay filled azomethine modified epoxy nanocomposites:

Inter cross-linked networks of organoclay-filled, azomethine-modified epoxy nanocomposites have been developed. Two types of azomethine epoxies (AE1 and AE2) incorporated into diglycidyl ether of bisphenol A (DGEBA) epoxy resin with varying percentages (5, 10 and 15%) were cured with diamine diphenyl methane (DDM). The azomethine epoxies were synthesized and characterized by Fourier transform infrared and 1H-NMR spectroscopy. The incorporation of azomethine epoxies into DGEBA epoxy resin improved both thermal and mechanical properties to an appreciable extent. The introduction of organoclay into DGEBA epoxy resin exhibited almost similar characteristics to that of the azomethine-modified DGEBA epoxy resin. Both azomethine epoxy and organoclay have been incorporated into DGEBA epoxy resin in order to improve the thermal and mechanical properties in comparing other modified epoxies. The glass transition temperature and thermal degradation temperature of azomethine-modified epoxies, organoclay-filled epoxy and organoclay-filled azomethine-modified DGEBA epoxies were determined by using differential scanning calorimeter and thermogravimetric analysis. The mechanical properties, namely the tensile strength, flexural strength and impact strength of the resultant nanocomposites were studied as per ASTM standards. X-ray diffraction studies of the cured nanocomposites indicate that the organophillic montmorillonite clay was exfoliated into the cured product. The homogeneous morphology of azomethine-modified DGEBA epoxy and organoclay-filled azomethine-modified epoxy were ascertained by scanning electron microscopy.

Low dielectric and low surface free energy flexible linear aliphatic alkoxy core bridged bisphenol cyanate ester based POSS nanocomposites

The aim of the present work is to develop a new type of flexible linear aliphatic alkoxy core bridged bisphenol cyanate ester (AECE) based POSS nanocomposites for low k applications. The POSS-AECE nanocomposites were developed by incorporating varying weight percentages (0, 5, and 10 wt %) of octakis (dimethylsiloxypropylglycidylether) silsesquioxane (OG-POSS) into cyanate esters. Data from thermal and dielectric studies imply that the POSS reinforced nanocomposite exhibits higher thermal stability and low dielectric value of k = 2.4 (10 wt% POSS-AECE4) compared than those of neat AECE. From the contact angle measurement, it is inferred that, the increase in the percentage incorporation of POSS in to AECE, the values of water contact angle was enhanced. Further, the value of surface free energy was lower when compared to that of neat AECE. The molecular level dispersion of POSS into AECE was ascertained from SEM and TEM analyses.