Unsaturated thermoplastic elastomer

CLASS Chemical copolymers unsaturated thermoplastic elastomers... 

Unsaturated thermoplastic elastomers Vinyl polymers Vinylidene polymers... 

Poly r 1 -(trimethylsilyl)-1 -propynel Unsaturated thermoplastic elastomer Urea resins Vespel Vestamid Vestenamer Vestolite... 

However, PIB is mostly manufactured as a block copolymer. Unsaturations in the backbone are common. Thermoplastic elastomers are composed of glassy outer blocks and rubbery inner blocks. Because of the phase separation of the glassy blocks into discrete domains, these materials behave like crosslinked rubbers at low temperatures. However, at elevated temperatures they can be processed in the same way as thermoplastics (4). 

Hybrid versions of silicone-thermoplastic semi-IPNs have been developed (19). A hybrid interpenetrating network is one in which the cross-linked network is formed by the reaction of two polymers with structurally distinct backbones. Hydride-functionalized siloxanes can be reacted with organic polymers with pendant unsaturated groups such as polybutadienes (5) in the presence of platinum catalysts. Compared with the polysiloxane semi-IPNs discussed earlier, the hydride IPNs tend to maintain mechanical and morphologically derived properties, whereas properties associated with siloxanes are diminished. The probable importance of this technology is in cost-effective ways to induce thermoset characteristics in thermoplastic elastomers. 

Styrene-based thermoplastic elastomers (see Chapter 4) are sensitive to oxidation since they contain unsaturated soft segments. These elastomers are manufactured by solution polymerization process in aliphatic hydrocarbons. In order to prevent autoxidation during the finishing steps (stripping, drying), which manifests itself by a rise in melt flow index and discoloration of the raw polymer, antioxidant is added to the polymer solution before finishing. Hence the antioxidant has to be soluble in the polymerization solvent. 

TPEE thermoplastic elastomer-polyester UA urea, unsaturated... 

Similar procedures have been used by several workers (Halasa et al., 1982) to hydrogenate poly(l,4-butadiene-co-1,2-butadiene) diblocks (Halasa, 1985) and poly(l,4-butadiene-co-l,4-isoprene-co-1,4-butadiene) triblocks. Hydrogenation of these diblock and triblock copolymers forms thermoplastic elastomers with crystalline and amorphous segments. All these materials exhibit crystallinity, glass transition, solubility, and dynamic mechanical loss spectra different from those of their unsaturated counterparts. 

Today ATH is a well established flame-retardant additive, especially for unsaturated polyesters, elastomers and some thermoplastics. 

Thermoplastic elastomers that are formulated into hot-melt adhesives include polyurethane and block terpolymers, such as styrene-butadiene-styrene styrene-iso-prene-styrene and styrene-olefin-styrene, in which the olefin component is typically ethylene, propylene, and/or butylene. The saturation in the mid-segment of these terpolymers results in better UV and thermooxidative resistance than that of unsaturated butadiene and isoprene midsegments. 

Thermoplastic elastomers with unsaturated center blocks, such as polybutadiene (SBS) or polyisoprene (SIS), are much more oxidation-prone than those with saturated elastomer segments such as ethylene/butylene (SEES) or ethylene/propylene (SEPS), because the elastomer component is more oxidation-prone than the thermoplastic component. UV stabilization thus has to be adapted to the elastomer component. Eor outdoor use, stabilization is recommended either with UV stabilizers or with carbon black filler. 

The most widely used elastomers are natural rubber [17], synthetic polyisoprene and butadiene rubbers, styrene-butadiene copolymers, ethylene-propylene rubber (specifically EPDM), butyl and halobutyl elastomers, polyurethanes, polysiloxanes, polychloroprenes, nitrile rubber, polyacrylic rubbers, fluorocarbon elastomers, and thermoplastic elastomers [18-20]. The examples which have unsaturation present in the repeat units (such as, the diene elastomers) have the advantage of easy cross-linkability, but the disadvantage of increased vulnerability to attack by reactants, such as oxygen and ozone. 

Olefinic thermoplastic elastomer (TPO) materials are defined as compounds (mixfures) of various polyolefin polymers, semicrysfalline thermoplastics, and amorphous elastomers. Most TPOs are composed of polypropylene and a copolymer of ethylene and propylene called ethylene-propylene rubber (EPR) [10]. A common rubber of this type is called ethylene-propylene diene monomer (EPDM) rubber, which has a small amount of a third monomer, a diene (two carbon-carbon double bonds in it). The diene monomer leaves a small amount of unsaturation in the polymer chain that can be used for sulfur cross-linking. Like most TPEs, TPO products are composed of hard and soft segments. TPO compounds include fillers, reinforcements. 

---