Thermoplastic elastomers Kraton-type

The hydrogenation of the centre block of SBS copolymer produced oxidation stable thermoplastic elastomer. This product was commercialized by the Shell Development Company under the trade name of Kraton G. The field of thermoplastic elastomers based on styrene, 1-3-butadiene or isoprene has expanded so much in the last 10 years that the synthetic rubber chemist produced more of these polymers than the market could handle. However, the anionically prepared thermoplastic system is still the leader in this field, since it produced the best TPR s with the best physical properties. These TPR s can accommodate more filler, which reduces the cost. For example, the SBS Kraton type copolymer varies the monomer of the middle block to produce polyisoprene at various combinations, then, followed... 

Thermoplastic Elastomers. These represent a whole class of synthetic elastomers, developed siace the 1960s, that ate permanently and reversibly thermoplastic, but behave as cross-linked networks at ambient temperature. One of the first was the triblock copolymer of the polystyrene—polybutadiene—polystyrene type (SheU s Kraton) prepared by anionic polymerization with organoHthium initiator. The stmcture and morphology is shown schematically in Figure 3. The incompatibiHty of the polystyrene and polybutadiene blocks leads to a dispersion of the spherical polystyrene domains (ca 20—30 nm) in the mbbery matrix of polybutadiene. Since each polybutadiene chain is anchored at both ends to a polystyrene domain, a network results. However, at elevated temperatures where the polystyrene softens, the elastomer can be molded like any thermoplastic, yet behaves much like a vulcanized mbber on cooling (see Elastomers, synthetic-thermoplastic elastomers). 

SB block copolymers are made anionically. These copolymers can be dlblocks, triblocks, and radial block copolymers with different degrees of tapering. Kraton was introduced in the mid-1960s by Shell. Another major manufacturer is Phillips with Solprene and K-Resins. These products can be used as thermoplastic elastomers or as impact modifiers. One of the most interesting aspects of these resins is the different types of morphologies that can be obtained as shown in Figure 6 (12-15). 

The most extensively studied block copolymers prepared by anionic polymerization are the styrene-butadiene or styrene-isoprene rubbers. Shell Chemical Company s Kraton thermoplastic elastomers are ABA block copolymers of this type. Their elastomeric properties are excellent, yet they differ from other rubbers in that vulcanization is not required. These elastomers consist of a rubbery polybutadiene matrix with the styrene segments serving as anchors in thermoplastic microdomains. 

The thermoplastic elastomers shown in Table 2.3 come in two types. One is the triblock copolymer type manufactured by the Shell Chemical Co. under the name of Kraton . Star block copolymers, which contain a number of radial arms of elastomer emanating from a central source, each tipped with a plastic block, are made by the Phillips Petroleum Co. under the name of Solprene . 

There are several types including polyester (Hytrel by Du Pont Co.), polystyrene-butadiene—polystyrene block copolymers (Kra-ton —KRATON Polymers U.S LLC., www.kraton. com), polystyrene—isoprene—polystyrene block copolymers (Solprene —Dynasol Elastomers, http // dynasolelastomers.com/), polyolefin (TPR thermoplastics rubber by Uniroyal, Inc.), and polyurethane. 

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