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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.

A novel series of multi-walled carbon nanotube (MWCNT) reinforced siloxane dianhydride based polyimide (PI) nanocomposites were designed and developed using in situ polymerization approach via thermal imidization. The polyamic acid obtained from the reaction of siloxane dianhydride and pyridine diamine/ p-phenylenediamine was then incorporated with varying percentages of MWCNTs, which then undergoes thermal imidization to form MWCNT-PI nanocomposites. The synthesized PIs were then characterized using analytical methods. From thermal analysis, it can be seen that the glass transition temperature increased significantly by incorporating acid functionalized MWCNTs into the PI matrix than that of neat PI. This is due to the constraint effect of MWCNTs as well as the reduction in the movement of polymer chains. It exhibits an increased dielectric constant with the increase in weight percentage of MWCNTs to PI matrix. No aggregation and homogeneous dispersion of MWCNTs throughout the PI matrix have been achieved as evidenced by scanning electron microscopy and transmission electron microscopy. The newly designed PI system is responsible for the significant improvement of dispersion, thus enhancing attractive flame retardancy and dielectric properties.

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.

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.

Bio-based neat unsaturated polyester (UPE) containing linseed vinyl ester fatty amide (LVEFA) modified with N, N′-bismaleimido-4,4′-diphenyl methane (BMI) composite were prepared with dicumyl peroxide as initiator. Up to 20% of the UPE was replaced by LVEFA to prepare biobased UPE. The combination of UPE and LVEFA resulted in an excellent new biobased thermoset polymer with high toughness at the expense of thermal properties. The loss of thermal properties by the addition of LVEFA to the UPE was compensated through (BMI) reinforcement. Biocomposite were made using BMI (5, 10, 15 wt.%) as thermal modifier, and blends of unsaturated polyester (UPE) and linseed vinyl ester fatty amide as the polymer matrix. The mechanical, thermal, hardness and dielectric properties of the biocomposite increased as a result of the incorporation of BMI. The fractured surface of the composites was analyzed using scanning electron microscopy to understand the morphology.

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 ( Tg), 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.

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.

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 ( Tg), 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.

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.