Elastomers styrene-based

In the absence of impurities there is frequently no termination step in anionic polymerisations. Hence the monomer will continue to grow until all the monomer is consumed. Under certain conditions addition of further monomer, even after an interval of several weeks, will eause the dormant polymerisation process to proceed. The process is known as living polymerisation and the products as living polymers. Of particular interest is the fact that the follow-up monomer may be of a different species and this enables block copolymers to be produced. This technique is important with certain types of thermoplastic elastomer and some rather specialised styrene-based plastics. 

The network of the Styrene-Butadiene Elastomers is based on a second principle which, again, differs from the covalent cross-links of typical theromsets. The three-dimensional structure in this case is... 

TNPP is used as a phospite antioxidant and a stabilizer for elastomers such as SBR, NBR, and SIS. Used as a stabilizer and a chelator/complexing agent in PC, PE, PP, PVC, copolymers such as ABS (Acrylonitrile-Styrenic based), SBR, and EVA (Ethylene-vinyl acetate) and in polymer latex and other aqueous systems. TNPP also prevents gel formation during polymerization finishing, storage, and factory processing. 

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. 

Commercial IPNs have been developed to combine useful properties of two or more polymer systems. For example, high levels of silicone have been combined with the thermoplastic elastomer (TPE) based on Shells Kraton styrene-ethylene/butadiene-styrene TPE and Monsantos Santoprene olefin TPE. These IPN TPEs are said to provide the biocompatibility and release properties of silicone with tear and tensile strength up to five times greater than medical-grade silicone. Thermal and electronic properties and elastic recovery are also improved. 

TPVs combine the rapid molding of thermoplastics with the elastomeric properties of thermoset rubber. They are useful in a broad range of applications. TPVs comprise the second largest group of soft, mbbery thermoplastic elastomers, after styrenic-based block copolymers. 

Table 4.7 Typical Properties of Styrene-based Thermoplastic Elastomers...

Examples of vulcanizable elastomers include natural rubber (NR), styrene butadiene rubber (SBR), butadiene rubber (BR), ethylene-propylene-diene monomer-rubber (EPDM), butyl rubber (HR), polychloroprene or neoprene (CR), epichlorohydrin rubber (ECO), polyacrylate rubber (ACM), millable polyurethane rubber, silicone rubber, and flu-oroelastomers. Examples of thermoplastic elastomers include thermoplastic polyurethane elastomers, styrenic thermoplastic elastomers, polyolefin-based thermoplastic elastomers, thermoplastic polyether-ester (copolyester) elastomers, and thermoplastic elastomers based on polyamides. 

The next two decades saw the development of new polymers such as thermoplastic PU (1961), aromatic polyamides, polyimides (1962) polyaminimides (1965), thermoplastic elastomers (styrene-butadiene block copolymers in 1965), ethylene-vinyl acetate copolymer, ionomers (1964), polysulfone (1965), phenoxy resins, polyphenylene oxide, thermoplastic elastomers based on copolyesters, poly butyl terephthalate (1971) and polyarylates (1974). 

Besides the thermoplastic elastomers based on poly(styrene-6-elastomer- -styrene) block copolymers, five others are of commercial importance polyurethane/elastomer block copolymers, polyester/elastomer block copolymers, polyamide/elastomer block copolymers, polyolefin block copolymers, and polyetherimide/polysiloxane block copolymers. All five have the multiblock A-B-A-B. structure. The morphology of the polyurethane, polyester,... 

Diene Types The diene elastomers are based on polymers prepared from butadiene, isoprene, their derivatives and copolymers. The oldest elastomer, natural rubber (polyisoprene), is in this class (see Section 9.2). Polybutadiene, polychloroprene, styrene-butadiene rubber (SBR), and acrylonitrile-butadiene rubber (NBR) are also in this class. 

Saengsuwan S, Saikrasim S (2012) Thermal stability of styrene-(ethylene butylene)-styrene-based elastomer composites modified by liquid crystalline polymer, clay and carbon nanotube. J Therm Anal Calorim 110 1395-1406... 

Among thermoplastic elastomers, the styrene-based block copolymers constitute the largest quantity of TPEs. Their chemical structure makes those polymers with unsaturated center blocks (polybutadienes (SBS) or polyisoprene (SIS)) much more oxidation prone than those with saturated elastomer components (ethylene/butyl-ene (SEES) or ethylene/propylene (SEPS)) [86]. 

Styrene-based polymers (SAN) Polyester (saturated linear PET) Polyvinylidene fluoride (PVDF) Thermoplastic elastomers (TPE)... 

Weng et al measured the adhesion resistance of a Styrenic based Thermoplastic Elastomer (TPE) overmolded on Polypropylene, Polycarbonate, Polymethyl methacrylate and Polyamide 6. They observed good adhesion with PP since they have similar 5, but with the other materials, since the compatibility was limited, they had to modify the TPE generating specific interactions with the substrate, to obtain good adhesion. 

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