M. Alagar

Design of lamellar structured POSS/BPZ polybenzoxazine nanocomposites as a novel class of ultra low-k dielectric materials

A novel class of lamellar structured polyhedral oligomeric silsesquioxane/bisphenol Z (POSS/BPZ) polybenzoxazine (PBz) nanocomposites was successfully designed by a facile one-step copolymerization technique. The chemical structures of the monomer and resulting polymer were characterized by Fourier transform infrared (FTIR) spectroscopy, 1H, 13C, DEPT-135, 29Si NMR (nuclear magnetic resonance) spectroscopy, X-ray diffraction (XRD), differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). The desired cross-linked lamellae structural arrangement of POSS/BPZ polybenzoxazine (PBz) nanocomposites was confirmed by transmission electron microscopy (TEM). The BPZ-PBz and POSS-PBz layers were self-assembled by intermolecular hydrogen bonding in such a way as to form the lamellar structure during ring opening polymerization. An advantage of this lamellar structure is that 30% POSS/BPZ polybenzoxazine composite exhibits an ultra low-k value of 1.7 at 1 MHz as well as high thermal stability.

Thermal and Morphological Properties of Silicone‐Polyurethane‐Epoxy Intercrosslinked Matrix Materials

Three different types of epoxy resins based on an unmodified epoxy (diglycidyl ether of bisphenol‐A), polyurethane (PU) modified epoxy and silicone modified polyurethane‐epoxy matrices were developed. Epoxy resin was modified with PU prepolymer and hydroxyl terminated poly (dimethyl siloxane), also referred to as ‘silicones’ using a silane crosslinking agent and tin catalyst. Aromatic polyamine adduct (A), diethylenetriamine (B) and polyamidoamine (C) were used as epoxy curatives. The formation of intercrosslinked network was confirmed using Fourier transform‐infrared (FT‐IR) spectra and viscosity data. Thermo gravimetric analysis revealed reduced thermal stability for PU (10 wt%) modified epoxy, whereas the incorporation of silicone (10 wt%) into PU modified epoxy matrix improved their thermal properties. The morphology of silicone modified PU‐epoxy was also studied by scanning electron microscopy (SEM).

Thermo-mechanical and dielectric properties of graphene reinforced caprolactam cardanol based benzoxazine–epoxy nanocomposites

In the present work a new type of benzoxazine was synthesized using caproamine with cardanol and the molecular structure was characterized by FTIR and NMR spectroscopy. The graphene reinforced epoxy–polybenzoxazine nanocomposites were prepared by incorporating varying weight percentages of graphene and benzoxazine to an epoxy resin. Data obtained from the mechanical study infer the significant improvement in the values of tensile strength, impact strength and flexural strength of the composites reinforced with different weight percentages of benzoxazine and graphene. The values of the dielectric constant of the composite samples are appreciably enhanced and are higher than that of the neat epoxy matrix. Data from SEM, TEM and XRD ascertain the existence of homogeneous distribution of graphene in the composites. Data obtained from thermal, mechanical, dielectric and surface free energy studies infer that 20 wt% Bz–g reinforced composites possess better properties than those of the neat epoxy matrix and other weight percentages of composites.

Dielectric and thermal behaviors of POSS reinforced polyurethane based polybenzoxazine nanocomposites

POSS (polyhedral oligomeric silsesquioxane) reinforced polyurethane (PU) based polybenzoxazine (PBz) nanocomposites were prepared as an interlayer low k dielectric material for microelectronics applications based on the concept of polarization and porosity of the composite. The hydroxyl terminated benzoxazine (OH–Bz) materials containing a less polar long aliphatic chain and hydroxyl terminated nanoporous POSS (OH–POSS) material were synthesized and copolymerized with hexamethylenediisocyante (HMDI) to obtain POSS–Bz–PU nanocomposites. Dielectric analysis of different concentrations of POSS reinforced PU–PBz nanocomposites indicates that the incorporation of POSS into the polymer matrix significantly reduced the value of the dielectric constant. Despite this, the reduction of dielectric constant by reinforcement is limited up to 30% POSS–PU–PBz (k = 1.94) and beyond this concentration the reverse trend was observed which might be due to the increasing density of the resulting composites by agglomeration of POSS nanoparticles. The SEM images of 40% POSS–PU–PBz composites evidently support the agglomerate formation of POSS particles. Besides, the thermal stability of the resulting POSS reinforced PU–PBz nanocomposites also increased to an appreciable extent.

Mechanical properties of bismaleimides modified polysulfone epoxy matrices

Epoxy resin has been chemically modified using 4, 8, and 12% of bisphenol-A based polysulphone along with three types of bismaleimides, namely [N, N′-bismaleimido-4,4′-diphenylmethane (BMI-1), 1,3-bis (maleimido) benzene (BMI-2) and 1,1′-bis (4-maleimidophenyl) cyclohexane (BMI-3)]. The epoxy hybrid matrices developed, in the form of castings, were used to characterize their mechanical properties like tensile strength, tensile modulus, flexural strength, flexural modulus, impact strength, hardness, and dynamic mechanical analysis as per ASTM standards. Data obtained from mechanical studies indicate that the introduction of hydroxyl terminated polysulfone into epoxy resin enhanced the value of impact strength to the extent of 48% due to the formation of flexible graft structures. Similarly, the incorporation of bismaleimides into epoxy resin also improved both tensile and flexural behavior of epoxy resin. Further, the introduction of combination of both polysulfone and bismaleimides into epoxy resin improved the mechanical properties according to their percentage content. Among the bismaleimides-modified polysulfone epoxy matrices, the epoxy matrix modified with 8% polysulfone and 8% BMI-2 exhibited better mechanical properties than other modified epoxy matrices.

MODIFICATION OF SILICONIZED EPOXY RESIN USING MULTIFUNCTIONAL SILANES

Silane coupling agents, namely 3-[(2–aminoethyl)amino]propyltrimethoxysilane (AETMS), 3-[(2–maleicmonoamido)maleicmonoamido]propyltrimethoxysilane (MMTMS) and 3-[(2–maleicdiamido)maleicdiamido]propyltrimethoxysilane (MDTMS), were synthesized and characterized using FT–IR and viscosity studies. The silane coupling agents developed in the present investigation were utilized for coupling hydroxyl terminated polydimethylsiloxane with epoxy matrix and cured with hexamethylenediamine and diaminodiphenylmethane. The siliconized epoxy system developed using MDTMS and cured with diaminodiphenylmethane yielded higher glass transition temperature, better thermal stability and imparts higher crosslinking density due to its higher functionality (pentafunctional) than AETMS and MMTMS (trifunctional). Diamine–cured siliconized epoxy resins coupled with AETMS, MMTMS and MDTMS can be used for the development of high–performance advanced composites.

Vinyl silane-functionalized rice husk ash-reinforced unsaturated polyester nanocomposites

Organic–inorganic hybrid nanocomposites based on vinyl silane-functionalized rice husk ash-reinforced unsaturated polyester resin were developed and characterized. Rice husk ash (RHA) is an agro product resulting from the incineration of rice husk and is used as a silica source. The present work involves the functionalization of rice husk ash using vinyl triethoxy silane reinforced with UP resin to enhance the thermomechanical properties of the UP resin. The physio-chemical, thermal, mechanical and morphological properties of the composite samples were analysed using FT-IR, differential scanning calorimetry, electron microscopy, thermogravimetric analysis, XRD and goniometry. The mechanical properties i.e., tensile strength, modulus, flexural strength, impact strength and hardness were studied and reported. The values of dielectric constant and contact angle were also studied and discussed. The vinyl silane-functionalized rice husk ash-reinforced UP resin composites possess better thermomechanical, dielectric and surface properties than those of neat UP matrix.

Thermo-mechanical and surface properties of POSS reinforced structurally different diamine cured epoxy nanocomposites

In the present study three structurally different diamines namely bisphenol-A based ether diamine, octane diol based ether diamine, and capron based diamine were synthesized and characterized using FT-IR, 1H-NMR and 13C-NMR spectra. These diamines were used to cure DGEBA epoxy resin and were reinforced with NH2–POSS in different weight percentages (1%, 3% and 5% wt) to obtain epoxy matrices and composites. Data obtained from thermo-mechanical, dielectric and surface studies were compared with those of neat epoxy matrix cured with diamino diphenyl methane (DDM). The surface morphology was ascertained from the XRD and SEM analysis and the presence of POSS in the composites was ascertained from the TEM images. The capron based diamine cured epoxy matrix shows better improvement in tensile strength and impact strength of 39.8% and 137.0% respectively than those of neat epoxy cured with diamino diphenyl methane (DDM). The value of contact angle (91.3°) of the capron based diamine cured epoxy composites infers that the epoxy matrix becomes hydrophobic nature. Data obtained from different studies suggest that the capron diamine cured epoxy matrix can be used in the form of a coating, encapsulant, or a sealant for different industrial and engineering applications for better performance and improved longevity.

Development of hexa (aminophenyl)cyclotriphosphazene-modified cyanate ester composites for high-temperature applications

The organic–inorganic hybrid of hexa(aminophenyl)cyclotriphosphazene (CPA) was synthesized by reacting hexachlorocyclotriphosphazene with 4-acetamidophenol followed by hydrolysis. The resulting product CPA was then allowed to react with 2,2-bis(4-cyanatophenyl)propane (cyanate ester) in different ratios (5, 10, and 15%) to form six-membered oxygen-linked triazine ring with formation of highly cross-linked network structure. Thermal curing behavior was confirmed using Fourier transform infrared spectroscopy analysis and thermal properties were studied using thermogravimetric analysis and differential scanning calorimetry analyses. Dielectric constant and dielectric loss were measured using impedance analyzer. Data resulted from different studies indicate that these hybrid composites can be used for high-performance thermal applications in the place of conventional cyanate esters for better performance.

Studies on dielectric properties of GO reinforced bisphenol-Z polybenzoxazine hybrids

In the present work, an attempt has been made to reduce the value of the dielectric constant of bisphenol-Z (BPZ) polybenzoxazine (PBz) material by the reinforcement of graphene oxide (GO) into BPZ-PBz matrix by exploiting the concept of polarization to enable them to be utilized as dielectrics in microelectronics applications. GO-BPZ-PBz hybrid materials have been developed using BPZ-Bz and benzoxazine functionalized graphene oxide (GO-Bz) via a facile one step copolymerization technique. The GO-Bz is expected to function as a versatile precursor for polymer grafting through the formation of chemical linkages with the base polymer. The molecular structure of benzoxazine monomers and hybrid polybenzoxazines were confirmed using 1H and 13C NMR, FTIR spectroscopy and XRD patterns. The chemical composition of GO-Bz was characterized by X-ray photoelectron spectroscopy (XPS). Raman spectra were used to ascertain the graphitic nature of the carbon present in the hybrid matrix. The morphological properties of GO-BPZ-PBz have been explained using scanning electron microscope (SEM) and transmission electron microscope (TEM) images. Data obtained from dielectric studies infer that the value of the dielectric constant decreased with increasing the weight percentage of GO-Bz and the lowest value of the dielectric constant (k) of 1.95 was obtained for the 10 wt% GO-BPZ-PBz hybrid composite.