Chinnaswamy Thangavel Vijayakumar

Structurally diverse benzoxazines: synthesis, polymerization, and thermal stability

Bisphenol-A is converted to indane bisphenol and spirobiindane bisphenol. The compounds bisphenol-A benzoxazine (BAB), indane bisphenol benzoxazine (IBPB), and spirobiindane bisphenol benzoxazine (SBIB) are prepared by condensing the respective bisphenols with paraformaldehyde and aniline. The structural characterization of the synthesized materials is done by using FTIR, 1H, and 13C NMR. Curing behavior of these benzoxazines and glass transition temperature for polybenzoxazines are studied using differential scanning calorimeter (DSC). The curing exotherm of these benzoxazines is much influenced by the nature of the aromatic unit present in the chosen bisphenol. Compared to the aromatic nucleus in BAB, the indane nucleus present in IBPB shifts the cure exotherm to lower temperatures, whereas the biindane moiety present in SBIB shifts the same to high temperatures. These benzoxazines are thermally cured both at the onset and at the peak maximum of the curing exotherm. The thermal stability of these cured materials is investigated using thermogravimetry. The nature of the aromatic nucleus present in the bisphenol and the temperature at which the curing is done decide the glass transition temperature and thermal stability of the polybenzoxazine.

High temperature matrix resins based on bispropargyl ethers – part 1: Effect of copper salts on the thermal polymerisation of bispropargylether of bisphenol-A and the thermal stability of these polymers

The compound bispropargyl ether of bisphenol-A (BPEBPA) is prepared using phase transfer catalyst. Different copper salts like cuprous chloride (CuCl), cupric chloride dihydrate (CuCl2.2H2O), copper sulphate pentahydrate (CuSO4.5H2O), basic copper carbonate (CuCO3.Cu(OH)2), cupric acetate monohydrate ((CH3COO)2Cu.H2O), and cupric oxide (CuO) are blended separately with BPEBPA (1%, w/w) and the curing characteristics of these materials are investigated using differential scanning calorimetry (DSC). The presence of copper salt in BPEBPA shifts the curing temperature to a lower temperature region. The materials are thermally cured and the structural characterisation and the thermal properties of these cross-linked materials are investigated using Fourier-transform infrared (FTIR) spectrophotometer and thermogravimetric analyzer (TGA). Of the different copper salts investigated, the presence of copper sulphate pentahydrate in BPEBPA increases the thermal stability of the cured BPEBPA. The thermal degradation products of thermally cured pure BPEBPA and copper salts containing BPEBPA are studied using TG-FTIR. The phenols, substituted phenols, carbon monoxide (CO), carbon dioxide (CO2), and alkenes are major volatiles evolved during the thermal degradation of these materials.

Synthesis and Polymerization of Bismaleimide Derived from 5(6)-amino-1(4′-aminophenyl)-1,3,3′-trimethyl indane

The acid-catalyzed dimerization of α-methyl styrene led to the formation of trimethyl phenyl indane, which on nitration followed by reduction using hydrazine hydrate gave 5(6)-amino-1(4′-aminophenyl)-1,3,3′-trimethyl indane. This aromatic diamine was used to synthesize bismaleamic acid and imidized to yield bismaleimide. The bismaleamic acid was converted to prepolymer directly by imidizing it in refluxing toluene. All the materials synthesized were characterized using FTIR, 1H and 13C NMR. The direct inlet mass spectral characterizations were carried out for bismaleamic acid, bismaleimide and bismaleimide prepolymer. The fragmentation pattern was discussed in detail and the structure proposed was confirmed. The thermogravimetric studies were done for all the materials and kinetic parameters (energy of activation and frequency factor) were calculated using Dharwadkar and Kharkhanavala method. The structural changes occurring in the thermally polymerized bismaleimide and bismaleimide prepolymer were discussed.

Synthesis, characterization and degradation behavior of thermoplastic polyurethane from hydroxylated hemp seed oil

Abstract Thermoplastic polyurethane based on renewable resource was synthesized from hydroxylated hemp seed oil. Before hydroxylation, the cold-pressed hemp seed oil was initially epoxidized and then hydroxylated in the presence of catalyst using water, ethanol and butanol. The hydroxylated hemp seed oil was used along with 1,1′-methanediylbis(4-isocyanatobenzene), linear polyester diol from caprolactone monomer (CAPA 2200), and chain extender from resorcinol-based aromatic diol (HER™) to prepare seven different polyurethane elastomers. The structural changes in the modified oils and in the newly synthesized TPUs were characterized using FTIR. Similarly, the structural changes during the TPU polymerization at isothermal temperature were monitored by real-time FTIR. The thermal stabilities and the degradation behavior of the synthesized TPUs were investigated using TG and TG-FTIR studies. The presence of hydroxylated hemp seed oil in the TPU structure has decreased the thermal stabilities and also altered the degradation mechanism.

A kinetic analysis of thermogravimetric data of radically polymerised N-phenylmaleimide

Abstract The thermal behaviour of the radically polymerised poly(N-phenylmaleimide) was studied, adopting the thermogravimetric method at heating rates of 1, 5, 10 and 50°C min−1 in a nitrogen atmosphere. The kinetic parameters, such as activation energy, reaction order, Arrhenius pre-exponential factor etc., have been calculated using different mathematical approximations available in the literature. It is observed that the energy of activation values and pre-exponential factors estimated for the degradation of poly(N-phenylmaleimide) from a single heating thermogram using different approximations decrease with increase in heating rate, whereas nearly constant values are observed in the Dharwadkar and Kharkhanavala approximation irrespective of the variation in sample size and heating rate. It is also observed that the different approximations, when applied to multiple heating data, give nearly constant values for the kinetic parameters. These values are broadly similar to that calculated using the Dharwadkar and Kharkhanavala approximation from a single heating thermogram.

An insight into the degradation aspects of 1,4,5,6,7,7-hexachlorobicyclo[2.2.1]hept-5-ene-2,3-dicarboxylic acid based two component polyesters

Abstract 1,4,5,6,7,7-Hexachlorobicyclo[2.2.1]hept-5-ene-2,3-dicarboxylic acid (HET-acid) was melt condensed with 1,2-ethanediol (EG) and 1,4-butanediol (BD). The prepared polyesters were pyrolysed under vacuum. The components of the volatile and cold ring fractions were separated using a gas chromatograph provided with a capillary column and were identified in a mass-selective detector. The occurrence of several secondary reactions during the degradation process due to the release of hydrogen chloride from the chlorinated part of the poly(ester) ester chain are evidenced by the identification of several chlorinated products. Although the presence of HET units in HETBD does not have any radical influence on the degradation of the diol component, it has a tremendous influence on the degradation of the diol component in HETEG polyester.

Studies on structurally different benzoxazines: Curing characteristics and thermal degradation aspects

Bisbenzoxazines were prepared by the condensation of the respective bisphenols bisphenol A (BA), indane bisphenol (IBP), and spirobiindane bisphenol (SBI) with paraformaldehyde and aniline. The apparent activation energies for the polymerization curing process (E a-C) and the degradation process (E a-D) were calculated using Flynn–Wall–Ozawa, Vyazovkin, and Friedman methods. The variation in E a-C noted for the thermal curing of different bisbenzoxazines is attributed to the operation of different mechanisms for the curing process. The variation of the E a-D for the degradation of spirobiindane benzoxazine polymerized at high temperature was different from the other materials investigated and is attributed to its complex structure. The volatile products obtained during the thermal degradation of the polymers were analyzed using thermogravimetric–Fourier transform infrared analyses. Aniline was found to be the major product and was released during the primary degradation. At higher temperatures, breakage of the isopropylidine, indane, and biindane structural entities were favored.

Pyrolysis studies on polyalkylene phthalates

Abstract The synthesis and identification of pyrolysis products of five polyalkylene phthalates are reported. The pyrolysis products are separated in a capillary gas chromatograph and the products are identified using a mass selective detector. The major degradation products for the polyesters now investigated are phthalic anhydride and the appropriate diol. In nearly all the polyesters studied, cyclic ether from the diol and the cyclic diester formed from phthalic anhydride and the diol are detected. A wide variety of low molecular weight compounds and considerable quantities of complex mono- and diesters of phthalic acid are identified among the pyrolysis products. The mode of formation of the products identified by GC/MS analysis are discussed with reference to the general polyester degradation mechanism.

Bismaleimide/rice husk silica reinforced composites Synthesis and thermal degradation studies

Silica derived from the renewable resource rice husk is modified using stearic acid and N-[4-(chlorocarbonyl)phenyl]maleimide. These materials are used as fillers in the bismaleimide, 4,4′-bismaleimidodiphenylmethane (BMIM), and thermally cured. The thermogravimetric (TG) curves for polyBMIM/silica composites showed no pronounced changes compared to the TG curve for the pure polyBMIM. Kissinger–Akahira–Sunose, Flynn–Wall–Ozawa, and Friedman methods are used to compute the activation energy (Ea) for degradation. Silica and surface-modified silica using stearic acid dispersed by ultrasonication increase the activation energy for degradation and show considerable influence on the thermal stability of cured BMIM. The long alkyl chain present in the stearic acid modified silica and the bulky spacer present in the chemically modified silica definitely alter the degradation process of cured BMIM. The SEM studies indicated uniform dispersion of the silica particles in the polyBMIM.

Thermal degradation aspects of model copolymers based on styrene, maleic anhydride, diethyl maleate and diethyl fumarate

Abstract Three copolymers, poly(styrene-maleic anhydride), poly(styrene-diethyl fumarate) and poly(styrene-diethyl maleate) were pyrolysed isothermally at 450 °C for 30 min in a nitrogen atmosphere. The pyrolysis products were separated and identified with a gas chromatograph coupled to a mass spectrometer. In the case of poly(styrene-maleic anhydride) and poly(styrene-diethyl fumarate) toluene, ethylbenzene and styrene were detected as the major pyrolysis products from the styrene moiety. In the case of poly(styrene-diethyl maleate), dimers and trimers of styrene were detected among the pyrolysis products. These results agree well with the conclusions from the IR studies and the reported copolymerisation parameters of the monomers. On-line pyrolysis experiments of poly(styrene-maleic anhydride) showed that the incorporated maleic anhydride units degrade at a temperature around 80 °C lower than the polymer backbone.