Polymer with elastomeric properties

Polymers with elastomeric properties have been obtained since the 1960s by copolymerization of tetrafluoroethylene vith trifluorovinyl ethers such as heptafluoropropyl trifluorovinyl ether (PPVE). These so-called second-generation fluoropolymers combine high thermal and chemical resistance with elasticity and are used for coatings, seals, and other parts which can be produced by conventional extrusion and molding processes. 

SYNTHETIC TECHNIQUES AND TYPES OF SYNTHESIS (a) Thermal two-stage polymerization (ring-opening of hexachlorocyclotriphosphazene followed by nucleophilic substitution).(b) Mixed nucleophiles have also produced useful elastomers using the same two-step procedure, (c) Now better defined block and random polymers with elastomeric properties have been developed and characterized. ... 

Collins et al. reported in 1995 that catalysts based on hafnium are desirable for the production of elastomeric polypropylene in that they polymerize propylene to a high molecular weight polymer and are indefinitely stable under typical polymerization conditions [8], Based on the theory that hafnium as a catalytic center leads to a significant increase of molecular weight in propene polymerization compared with the zirconium-based catalyst, Rieger et al. searched for hafnocene systems to obtain polymers with new properties. 

A number of synthetic rubbers and elastomeric materials have been developed with special characteristics that extend the overall usefulness of the elastomers for corrosion-resistant equipment. In addition, polymers of ethylene and propylene have been developed with elastomeric properties. Like natural rubber, each of these may be compounded in several ways for maximum resistance to specific chemical exposures. Natural rubber and other elastomers are frequently used in combination with brick linings for temperature conditions that are above those allowed for elastomer material alone. They have proved to be excellent membrane linings for such construction. 

Figures (a) Liquid-like poly(ethylene butylene) precursor, and (b) supramolecular polymer material 12 with elastomeric properties resulting from functionalization with UPy groups. (Reproduced with permission from Folmer, B.J.B. et al., Adv. Mater., 12 874-878, 2000. Copyright John Wiley Sons, Inc.)... 

Although many polymers have some of these characteristics there are only relatively few which display true elastomeric behaviour. For example, polyethylene is above its Tg at room temperature but it is also highly crystalline and so it is not an elastomer. The copolymerization of ethylene with propylene destroys the crystallinity of the polymer and can lead to materials commonly known as ethylene/propylene rubbers. On crosslinking such polymers display elastomeric properties. The elastomeric properties of natural rubber, which is a naturally-occurring form of c -l,4-polyisoprene, have been known for many years. Although it is rather tacky and also tends to flow in iis natural state, on crosslinking it exhibits useful elastomeric behaviour. 

Fluoiocaibon elastomeis aie synthetic, noncrystaUine polymers that exhibit elastomeric properties when cross-linked. They are designed for demanding service appHcations in hostile environments characterized by broad temperature ranges and/or contact with chemicals, oils, or fuels. 

Applications of NBR adhesives are based on the excellent elastomeric properties of the polymer coupled with its polarity, which provides good solvent resistance... 

As previously discussed, solvents that dissolve cellulose by derivatization may be employed for further functionahzation, e.g., esterification. Thus, cellulose has been dissolved in paraformaldehyde/DMSO and esterified, e.g., by acetic, butyric, and phthalic anhydride, as well as by unsaturated methacrylic and maleic anhydride, in the presence of pyridine, or an acetate catalyst. DS values from 0.2 to 2.0 were obtained, being higher, 2.5 for cellulose acetate. H and NMR spectroscopy have indicated that the hydroxyl group of the methy-lol chains are preferably esterified with the anhydrides. Treatment of celliflose with this solvent system, at 90 °C, with methylene diacetate or ethylene diacetate, in the presence of potassium acetate, led to cellulose acetate with a DS of 1.5. Interestingly, the reaction with acetyl chloride or activated acid is less convenient DMAc or DMF can be substituted for DMSO [215-219]. In another set of experiments, polymer with high o -celliflose content was esterified with trimethylacetic anhydride, 1,2,4-benzenetricarboylic anhydride, trimellitic anhydride, phthalic anhydride, and a pyridine catalyst. The esters were isolated after 8h of reaction at 80-100°C, or Ih at room temperature (trimellitic anhydride). These are versatile compounds with interesting elastomeric and thermoplastic properties, and can be cast as films and membranes [220]. 

Most polystyrene products are not homopolystyrene since the latter is relatively brittle with low impact and solvent resistance (Secs. 3-14b, 6-la). Various combinations of copolymerization and blending are used to improve the properties of polystyrene [Moore, 1989]. Copolymerization of styrene with 1,3-butadiene imparts sufficient flexibility to yield elastomeric products [styrene-1,3-butadiene rubbers (SBR)]. Most SBR rubbers (trade names Buna, GR-S, Philprene) are about 25% styrene-75% 1,3-butadiene copolymer produced by emulsion polymerization some are produced by anionic polymerization. About 2 billion pounds per year are produced in the United States. SBR is similar to natural rubber in tensile strength, has somewhat better ozone resistance and weatherability but has poorer resilience and greater heat buildup. SBR can be blended with oil (referred to as oil-extended SBR) to lower raw material costs without excessive loss of physical properties. SBR is also blended with other polymers to combine properties. The major use for SBR is in tires. Other uses include belting, hose, molded and extruded goods, flooring, shoe soles, coated fabrics, and electrical insulation. 

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