Kraton thermoplastic elastomer

KRATON Thermoplastic Elastomers bulletins. Shell Chemical Co., Houston, Tex. 

I, vinylruthenocene, 66, vinylosmocene, and the T)5-(vinylcyclopentadienyl)metal carbonyl monomers in radical-initiated polymerizations summarized in Scheme 1.1 no longer exists for anionically initiated addition polymerizations. Styrene is readily initiated by such anionic species as BuLi and Na1 Naphth. Living anionic styrene homopolymerizations and block copolymerizations have been extensively commercialized for many years (e.g., Kraton thermoplastic elastomers). However, the exceptionally electron-rich vinyl metal-containing monomers 1, 8-18, 24-30, and 66 were never successfully initiated by anionic systems in our laboratory despite many attempts. In these systems, the a-carbocations are very stable, but the a-carbanions are quite unstable. Thus, the addition of an anion to tbe vinyl function of these monomers is unfavorable. 

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. 

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). 

An interesting observation arose with the thermoplastic elastomer styrene/ butadiene (S/B) tri-block copolymer (Kraton ). These are made by anionic... 

The ABA block copolymer of styrene (12.5%)-butadiene (75%)-styrene (12.5%) (Kraton), is a thermoplastic elastomer CTPE) with the multiple repeating units shown below ... 

The development of anionic chemistry over the past 30 years has led to the emergence of new processes and products of Industrial Importance, the most significant being a family of thermoplastic elastomers. These unique elastomers are presently commercialized by Shell Chemical Company as Kratons and by Phillips Chemical Company as Solprenes. Their uniqueness is the result of deliberate design of the polymeric structure and composition. 

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... 

HMX HMX HMX HMX HMX HMX HMX HMX HMX HMX HMX HMX HNS NTO NTO/HMX NTO/HMX NTO/HMX PETN PETN PETN PETN PETN PETN PETN PETN PETN PETN RDX RDX RDX RDX RDX RDX RDX RDX RDX RDX RDX RDX RDX TATB/HMX Cariflex (thermoplastic elastomer) Hydroxy-terminated polybutadiene (polyurethane) Hydroxy-terminated polyester Kraton (block copolymer of styrene and ethylene-butylene) Nylon (polyamide) Polyester resin-styrene Polyethylene Polyurethane Poly(vinyl) alcohol Poly(vinyl) butyral resin Teflon (polytetrafluoroethylene) Viton (fluoroelastomer) Teflon (polytetrafluoroethylene) Cariflex (block copolymer of butadiene-styrene) Cariflex (block copolymer of butadiene-styrene) Estane (polyester polyurethane copolymer) Hytemp (thermoplastic elastomer) Butyl rubber with acetyl tributylcitrate Epoxy resin-diethylenetriamine Kraton (block copolymer of styrene and ethylene-butylene) Latex with bis-(2-ethylhexyl adipate) Nylon (polyamide) Polyester and styrene copolymer Poly(ethyl acrylate) with dibutyl phthalate Silicone rubber Viton (fluoroelastomer) Teflon (polytetrafluoroethylene) Epoxy ether Exon (polychlorotrifluoroethylene/vinylidine chloride) Hydroxy-terminated polybutadiene (polyurethane) Kel-F (polychlorotrifluoroethylene) Nylon (polyamide) Nylon and aluminium Nitro-fluoroalkyl epoxides Polyacrylate and paraffin Polyamide resin Polyisobutylene/Teflon (polytetrafluoroethylene) Polyester Polystyrene Teflon (polytetrafluoroethylene) Kraton (block copolymer of styrene and ethylene-butylene)... 

The above thermal analysis studies demonstrated the enhanced thermal stability of POSS materials, and suggested that there is potential to improve the flammability properties of polymers when compounded with these macromers. In a typical example of their application as flame retardants, a U.S. patent39 described the use of preceramic materials, namely, polycarbosilanes (PCS), polysilanes (PS), polysilsesquioxane (PSS) resins, and POSS (structures are shown in Figure 8.6) to improve the flammability properties of thermoplastic polymers such as, polypropylene and thermoplastic elastomers such as Kraton (polystyrene-polybutadiene-polystyrene, SBS) and Pebax (polyether block-polyamide copolymer). 

It is important to appreciate that polymer produced by an anionic chain-growth mechanism can have drastically different properties from one made by a normal free radical reaction. Block copolymers can be synthesized in which each block has different properties. We mentioned in Chapter 4 that Michael Szwdrc of Syracuse University developed this chemistry in the 1950s. Since that time, block copolymers produced by anionic polymerization have been commercialized, such as styrene-isoprene-styrene and styrene-butadiene-styrene triblock copolymers (e.g., Kraton from Shell Chemical Company). They find use as thermoplastic elastomers (TPE), polymers that act as elastomers at normal temperatures but which can be molded like thermoplastics when heated. We will discuss TPEs further in Chapter 7. 

Obviously, the resistance of these products towards light, oxygen and other chemicals will be much better, and close to that of the corresponding polyolefins. Moreover, the hydrogenation can be stopped at different conversions opening a much broader range of applications conditions. Industrial developments already include successful materials like Kraton G 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). 

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. 

In the studies at Lehigh the thermoplastic elastomer Kraton G served as polymer I (see Fig, 1). Styrene and methacrylic acid were dissolved into the Kraton G, and polymerized in situ. 

PROPERTIES OF SPECIAL INTEREST In general, thermoplastic elastomers (TPE) provide the mechanical properties of rubber in combination with the processing characteristics of plastics recyclable Kraton D s are the lowest cost TPE (> 0.85 Ib ). 

Important commercial uses of block copolymers depend on phase separation in the solid state. For example, triblock copolymers PS-b-PB-b-PS (PB = polybutadiene) that contain a long PB block form glassy domains of PS (Tg=100°C) within a matrix of low Tg PB (Tg -100°C). The glassy PS domains function as physical crosslinks, which prevent the PB chains from slipping past one another under deformation. This generates elastomeric properties but, unlike normal elastomers which are permanently chemically crosslinked, heating above the Tg of the PS block allows the material to be reprocessed. This reversibility has led to the term thermoplastic elastomer for these materials, which are known as Kratons and are sold commercially [39]. 

Multi-Flex TPE G 7680 [Multibase http //www.multibase.com], Multi-Flex TPE G 7890 [Multibase http //www.multibase.com], Multi-Flex TPE G 7940 t[Multibase http //www.multibase.com], Multi-Flex TPE RP-6568 B2 [Multibase http //www.multibase.com], Multi-Flex TPE RP-6568 C [Multibase http //www.multibase. com] Styrene-ethylene-propylene block copolymer Uses Thermoplastic elastomer used as a modifier in solv.-based weatherable sealants Trade Name Synonyms Kraton G 1701 t[Kraton Polymers http //www.kraton.com], Kraton G 1701X [Kraton Polymers http //www.kraton.com]-, Kraton G 1702X [Kraton Polymers http //www.kraton.com]... 

The tear strength of a representative thermoplastic elastomer, Kraton 1101 (Shell Chemical Company), is quite comparable to that of a well-... 

Kraton DllOl SBS three block thermoplastic elastomer Shell Chem. Co. 

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