• I K Varma

      Articles written in Bulletin of Materials Science

    • Effect of structure on properties of vinyl ester resins

      P Siva I K Varma D M Patel T J M Sinha

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      The paper describes the synthesis of vinyl ester resins based on diglycidyl ether of bisphenol-A (epoxy equivalent = 450–465 g/eq) (VR resin) and tetrabromobisphenol-A (epoxy equivalent = 380–420 g/eq) (VR-1 resin). The viscosity of styrenated VR resin was higher than VR-1 resin. The effect of styrene andα-methyl styrene on curing of VR resins was studied. An increase in styrene from 30 to 50 wt% resulted in an increase in gel time and a decrease in exothermic peak. Addition ofα-methyl styrene delayed and depressed the exotherm. The mechanical properties of VR resin sheets and glass fabric reinforced laminates were better than VR-1 resins; whereas LOI of VR-1 was higher. A resin formulation containing 20–30 wt% of VR: VR-1 showed optimum mechanical properties and LOI.

    • Phosphorous-containing nadicimide resins: synthesis and characterization

      Sarfaraz Alam V G Jayakumari Amar Singh L D Kandpal I K Varma

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      A series of phosphorous-containing nadicimide end-capped resins, having different backbone, were prepared by reacting endo-5-norbornene- 2,3-dicarboxylic anhydride (nadic anhydride), pyromellitic dianhydride (PMDA)/3,3′,4,4′-benzophenone tetracarboxylic acid dianhydride (BTDA) andtris [3-azo(4-aminophenyl)] phosphine oxide (TAZP) in dimethyl acetamide. Yields were essentially quantitative. Structural characterization of resins was done by elemental analysis, IR and1H-NMR. Thermal behaviour of the resins was investigated by differential scanning calorimetry and thermogravimetric analysis, which revealed good high temperature performance. Isothermal ageing studies done at 340°C for various time periods showed good thermo-oxidative stability.

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