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Brominated isobutylene-co-p-methylstyrene (BIMS) rubber has been blended with hydrocarbon resin tackifier and alkyl phenol formaldehyde resin tackifier, and the compatibility between the blend components has been systematically evaluated. Dynamic mechanical analysis (DMA) and differential scanning calorimetry (DSC) studies show that BIMS rubber and hydrocarbon resin tackifier blends are compatible at all blend proportions studied. However, BIMS rubber and phenol formaldehyde resin blends exhibit very limited compatibility with each other and phase separation even at very low phenolic tackifier concentration. Morphological studies of the rubber-resin blends by scanning electron microscopy (SEM) corroborate well with the DMA and DSC results. From the DMA frequency sweep and temperature sweep studies, it is shown that the hydrocarbon resin tackifier acts as a diluent and causes a decrease in the storage modulus values (by reducing the entanglement and network density) in the rubbery plateau region. On the other hand, phenol formaldehyde resin behaves in the way similar to that of the reinforcing filler by increasing the storage modulus values (by increasing the entanglement and network density) in the rubbery plateau zone. The relaxation time estimated from the different zones of frequency sweep master curves provides information about the influence of the two tackifiers on the viscoelastic properties of the BIMS rubber in the respective zones.

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Barium titanate (BT) has attained research focus in recent past owing to considering its high dielectric constant and stealth capabilities in microwave region. Shape effects of BT viz. powder, micron size flakes, nano particles and nanotubes have been studied vastly for its stealth capabilities. Present study aims at the preparation of millimetric size barium titanate flakes (BTFs) via controlled sol-gel process followed by tape casting. BTFs were mixed in varied weight ratio (50-90 wt.%) with polyurethane resin to fabricate composite laminates. Electromagnetic properties measurement in X and Ku band revealed high values of real and imaginary permittivity. Reflection loss measurements demonstrated more than 20 dB loss in wide frequency range (11.4-13.6 GHz). For single layer microwave absorber, reflection loss values have been calculated and it is observed that calculated and measured reflection loss values are in good agreement to each other. Developed material can find applications in broadband radar signature reduction.

The viscoelastic behavior of brominated isobutylene‐co‐p‐methylstyrene (BIMS) rubber/hydrocarbon resin blends and BIMS/phenol formaldehyde resin blends was studied with the use of a rubber process analyzer. Dynamic mechanical analysis and scanning electron microscopy were used to evaluate the compatibility between the BIMS/tackifier blends. Strain sweep tests at temperature below the softening point of the tackifiers showed the formation of resin–resin networks in the incompatible BIMS/phenolic resin blends. However, resin–resin network was not prominent in the case of the compatible BIMS/hydrocarbon resin blends. Frequency sweep tests were performed at the strain amplitude within the linear region at several temperatures and the variations of shear storage modulus, G′ and complex viscosity, η* against frequency were recorded. The tackifying resins modified the viscoelastic properties of the BIMS rubber by reducing the storage modulus at lower frequency and by increasing the storage modulus at higher frequencies. However, this action was found to be highly dependent on (a) rubber‐tackifier compatibility, (b) blend proportions, and (c) test temperature. Furthermore, stress relaxation measurements of the BIMS/tackifier blends at temperature below the softening point of the tackifiers showed longer period of relaxation for the incompatible BIMS/phenolic resin blends. POLYM. ENG. SCI., 2008. © 2008 Society of Plastics Engineers