Cure type solid rubber

The reason why I take up these polymers in this review is that (1) CB-BR is a cure type solid rubber carrying OH groups and Cl atoms as active species besides double bonds, (2) viologen elastomers are thermoplastic elastomers (TPE) derived from liquid rubber, indicating some characteristic behaviors, i.e., high tensile properties and special functions, and (3) ABA type liquid crystalline elastomers are also new TPE at room temperature, but behave as liquid rubber at high temperature. 

The rubber samples were examined by FTIR for microstructural changes on curing, and solid state carbon-13 FT-NMR for identification of the cross-link types and mlcrostructural changes of the polymeric chain. 

The mechanism of the accelerated sulfur vulcanisation of EPDM is probably similar to that of the highly unsaturated polydiene rubbers. The vulcanisation of EPDM has been studied with emphasis on the cure behaviour and mechanical and elastic properties of the crosslinked EPDM. Hardly any spectroscopic studies on the crosslinking chemistry of EPDM have been published, not only because of the problems discussed in Section 6.1.3 but also because of the low amount of unsaturation of EPDM relative to the sensitivity of the analytical techniques. For instance, high-temperature magic-angle spinning solid-state 13C NMR spectroscopy of crosslinked EPDM just allows the identification of the rubber type, but spectroscopic evidence for the presence of crosslinks is not found [72]. 

In this type of sealant, the sealant consists of two parts, one containing polymer (also called the base) and a separate component containing the curing agent. These are combined by a mechanical mixer prior to application. Proper mixing is attained in approximately five minutes. Incomplete mixing is indicated by the appearance of streaks in the mix (if the two components are of different colour). At ambient temperatures the pot-life is about three hours. The pot-life decreases with increase in temperature. It is possible to increase or decrease the pot-life by incorporation of an accelerator or a retarder, respectively. At ambient temperatures the sealant cures to form a rubber-like solid. 

Lewis and co-workers (42) developed improved powder coatings with nitrile rubber-modification of an appropriate epoxy base (solid resin admixture) cured with an imidazoline-accelerated modified phenolic type hardener. Model coatings ground to 55 pm particle size, electrostatically applied to metals, cured 10 170°C, gave excellent therraocycling results as well as retained resistance to solvent attack. Elastomer-modified epoxy powder coatings have been covered extensively by Gelbel, Romanchick and Sohn in Chapter 5 of this volume. 

Reasonably early however in the development of telechelic polybutadiene/acrylonitrile, Brenner and Drake (22) showed that mercaptan- and carboxyl-terminated liquid polybutadiene/acrylonitrile did respond to electron-beam (1-5 megarads) and cure (2-3 seconds/pass) from the liquid to the solid state. The mercaptan polymer (3.1% RSH, 23% bound acrylonitrile, Mn 1700) cured more readily. CTBN as expected required 50-100% higher irradiation dosage levels. With both MTBN and CTBN-type products of higher acid content (6% vs 3%), gum rubber properties of 13.8-34.5 mPa were obtained with 60-100% elongation. The E-beam cures were carried out in air at ambient temperature. Thus, unformulated telechelic polybutadienes were shown to be substantive to cure in the presence of ionizing radiation. 

Dow Corning Corp. offers an improved silicone adhesive/sealant for high-temperature use. This is a one-part, non-slumping paste that cures to a tough, rubber solid at room temperature on exposure to water vapor in the air. This material is said to perform at temperatures ranging from —65 °C to 260 °C for continuous operation and to 316 °C for intermittent exposure. This material wiU meet the requirements of MIL-A-46106A (2), Type 1 (see http //mil-spec-industries.com). The adhesive/sealant is acid cured and acetic acid is evolved during cure. Table 8.1 summarizes some of the characteristics of silicone adhesives. 

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