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  • Author or Editor: I. Varma x
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Abstract  

A series of ethynyl and ethenyl end-capped imide resins were synthesised by the reaction of 9,9-bis(4-aminophenyl) fluorene (BAF) with pyromellitic dianhydride (PMDA)3/3′, 4,4′-benzophenone tetracarboxylic acid dianhydride (BTDA)/2,2-bis(3,4-dicarboxy phenyl) hexafluoropropane dianhydride (6F) and 3-ethynyl aniline/maleic anhydride. Structural characterisation was done by infra red and elemental analysis. Thermal characterisation was done by differential scanning calorimetry and thermogravimetric analysis. The decomposition temperatures of cured resins were above 200°C in nitrogen atmosphere. Char yield at 800°C ranged from 59–65.5%.

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4,4′-bismaleimidophenyl methane (BM) and 3,3′-bismaleimidophenyl sulfone (BS) were blended in solution using weight ratios 3∶1 (MS31), 2∶1 (MS21), 1∶1 (MS11), 1∶2 (MS12) and 1∶3 (MS13). Chain extended bismaleimide resins were also prepared by treating BS/BM with 4,4′-diaminodiphenyl ether in molar ratios of 1∶0.3 (BM-E and BS-E resins). These resins were also blended with bismaleimides and the curing characteristics were evaluated by differential scanning calorimetry. Increase in BM content in BM∶BS blends or increase in chain extended bismaleimide content in BM-E∶BS or BS-E ∶ BM blends resulted in a reduction of melting and curing temperatures. Indication about the extent of cross-linking was obtained from solubility measurements (in DMF) of isothermally cured resins (180 °C, lh and 220 °C, lh in an air oven). Thermogravimetric analysis of samples isothermally cured at 180 °C and 220 °C (lh each) was carried out in nitrogen atmosphere. Improvement in thermal stability of chain extended bismaleimides was observed on blending.

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The curing behaviour of bismethacryloxy derivative of diglycidyl ether of bisphenol A (vinyl ester resin) containing styrene as the reactive diluent (40% w/w) was studied using gel point determination method and DSC. Seven samples of styrene/α-methylstyrene in the ratio 40∶0, 35∶5, 30∶10, 25∶15, 20∶20, 15∶25 and 0∶40 were studied. Delayed curing was observed in samples containing increasing proportions of α-methylstyrene. The energy of activation decreased from 869 kJ mol−1 to 333 kJ mol−1 as the concentration of α-methylstyrene increased in the formulations. However, no difference in thermal stability was observed by replacement of styrene by α-methylstyrene. It was concluded that in vinyl ester resin samples 10–15% α-methylstyrene and 30-25% styrene can be used as reactive diluent.

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The crystallisation behaviour of binary blends of high density polyethylene (HDPE) and ethylene-propylene-diene tercopolymer (EPDM) was investigated using differential scanning calorimetry (DSC) and wide angle X-ray diffraction studies (WAXS). The rate of crystallization and nucleation of HDPE was influenced by the addition of EPDM. The% crystallinity (WAXS) increased up to 25% (w/w) addition of EPDM to HDPE. A significant improvement in tensile and impact properties was observed upon addition of EPDM to HDPE.

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Abstract  

Thermal behaviour of blends based on N,N'-bis(4-itaconimidophenyl) ether (IE) and 4,4'-bis(4-allyl-2-methoxyphenoxy) benzophenone (R1) or 4,4'-bis(2-allylphenoxy) benzophenone (R2) are described in this paper. The reactive diluent content was varied from 5-50% (mass/mass) in these blends. A decrease in the melting point and exothermic peak temperature was observed with increasing mass percent of reactive diluent. Thermal stability of blends was affected at high mass percentage of reactive diluents.

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Abstract  

Structurally different poly(arylene ether sulphone) (PES) copolymers were synthesized by reacting stoichiometric amount of dichlorodiphenyl sulphone (DCDPS) with bisphenols. The molar ratio of bisphenol-A and phenolphthalein (ESP)/hydroquinone (ESH)/resorcinol (ESR) was varied to prepare nine copolymer samples. Structural characterization was done by FT-IR and 1H-NMR studies. The initial decomposition temperature as well as temperature of maximum rate of mass loss in ESR and ESH copolymers were similar and a marginal decrease in these decomposition temperatures were observed by increasing the isopropylidine units in the backbone. High char residue at 800C was observed in polymers having high content of phthalein units.

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Abstract  

Carbocationic polymerization of N-ortho/meta/para tolyl-exo-norbornene dicarboximide (nadimide) was carried out using Pd(II) catalyst. Under similar conditions of polymerization, poly(N-m-tolyl nadimide) showed higher molecular mass compared to poly(N-p-tolyl nadimide) and poly(N-o-tolyl nadimide). Thermal stability of these polymers was evaluated by dynamic thermogravimetry in nitrogen atmosphere. The polymers were stable up to 460°C and lost mass above this temperature in a single step. The characteristic decomposition temperature and char yield of these polymers were higher than the polymers prepared by using ring opening metathesis polymerization. The difference has been attributed to the presence of rigid bicyclic ring structure in these polymers.

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