Styrenic thermoplastic elastomer

L. Brodrecht, P. Mortensen, and M. Tachiro, Styrenic Thermoplastic Elastomers, Stanford Research Institute, Menlo Park, Calif., 1990, p. 525.8600A. 

The particular type of thermoplastic elastomer (TPE) shown in Figure 3 exhibits excellent tensile strength of 20 MPa (2900 psi) and elongation at break of 800—900%, but high compression set because of distortion of the polystyrene domains under stress. These TPEs are generally transparent because of the small size of the polystyrene domains, but can be colored or pigmented with various fillers. As expected, this type of thermoplastic elastomer is not suitable for use at elevated temperatures (>60° C) or in a solvent environment. Since the advent of these styrenic thermoplastic elastomers, there has been a rapid development of TPEs based on other molecular stmctures, with a view to extending their use to more severe temperature and solvent environments. 

Ban H.T., Kase T., Kawabe M., Miyazawa A., Ishihara T., Hagihara H., Tsunogae Y., Murata M. and Shiono T.A. New approach to styrenic thermoplastic elastomers S3Tithesis and characterization of crystalline styrene-butadiene-styrene triblock copolymers. Macromolecules, 39, 171, 2006. 

The styrenic thermoplastic elastomers are the only type which are fully compounded in the manner of conventional elastomers. In this case, however, the addition of carbon black, or other fillers, does not give reinforcement. Additions of polystyrene, or high impact polystyrene, and oil are used to vary hardness and tear strength, and fillers can be used to cheapen the material. Other added polymers, e g., EVA, can be used to increase ozone resistance. These materials also require antioxidants for protection during processing and service life, and the poor UV stability restricts their use in outdoor applications. 

Styrene-Diene. These ( styrenic ) thermoplastic elastomers are block copolymers of styrene with butadiene (SBS) or isoprene (SIS) in about 30/70 monomer ratio. 

In addition to the relative ratio of the monomers, the arrangement of the units in the chain is important. This arrangement is referred to as the copolymer sequence distribution. In the previous discussion, the assumption was made that the comonomer units were well mixed in the polymer chain. If this is not the case, parts of the chain can reflect properties of the corresponding homopolymer. It is thus possible to produce polymers that have significantly different properties in different parts of the polymer chain. A most dramatic example of this can be found in styrene-butadiene-styrene or styrene-isoprene-styrene thermoplastic elastomers. The properties of these unique materials will be discussed in the section Thermoplastic Elastomers. ... 

Semifluorinated block copolymers, (I), were previously prepared by the author [1] and then blended with styrene-ethylene/butylene-styrene thermoplastic elastomers to provide surface-active block copolymers. 

ASTM D4474-00 Standard Classification System for Styrenic Thermoplastic Elastomer Injection Molding and Extrusion Materials (TES)... 

Erdogan and co-workers [11] report a MS analysis of the gases evolved during the pyrolysis of NR, butadiene rubber (BR), SBR, styrene-butadiene-styrene (SBS) and styrene-isoprene-styrene thermoplastic elastomers and PS in the low (0-150 amu) mass range, using a quadrupole mass spectrometer. The results are interpreted using the variations in ion ratio as a function of temperature. 

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. 

EPDM/PP elastomers compete directly with styreneic thermoplastic elastomers (TPEs) as low-cost, low-speciiic-gravity materials with fair to good mechanical performance and environmental resistance. They range in hardness from Shore A 60 up to Shore D 65. The harder products are more commonly found in commercial applications. The harder TPOs are essentially impact-modified thermoplastics and not true rubbers. The softer TPOs are rubbery at room temperature, but mechanical properties are radically lower at tanperatures above 70-80°C. 

The Swiss company, WW Fischer, offers PTFE (Teflon PTFE or Hostaflon), PBT (Celanex, Crastin, Ultradur or Valox) or PEEK (Victrex) insulator material options in its 405 series of cylindrical connectors according to the requirements of working temperature and other criteria. PEEK is an expensive polymer which tends to be employed when other materials fail to meet the specification requirements of the application. Other Fischer connector types use polyamide-imide (Torlon) or POM (Celcon, Delrin or Hostaform). Elastomeric seals used by Fischer in conjunction with their connectors are made from acrylonitrile-butadiene rubber (NBR N BUNA) or to MIL-P-25732, fluoroelastomer (FPM VITON), polychloroprene elastomer (CR Neoprene), ethylene-propylene diene elastomer (EPDM) and styrene-ethylene-butadiene-styrene thermoplastic elastomer (TPE-S or TPE-O) where each compound is followed by its trade name. Fischer s Swiss competitor, Lemo, manufactures a similar range of connectors including the Redel types which have a plastic body. 

Kishore K. Indukuri and Alan J. Lesser, Comparative deformational characteristics of poly(styrene-b-ethylene-co-butylene-b-styrene) thermoplastic elastomers and vulcanized natural mbber". Polymer, 46 (18) 2005,7218-7229. 

In all these multiblock (A-B)n polymers, both the number of segments and their individual molecular weights have a very broad distribution, in contrast to the simple A-B-A triblocks in the styrenic thermoplastic elastomers. 

The choice of polymer in the hard phase strongly influences the oil and solvent resistance of the thermoplastic elastomers. Even if the elastomer phase is resistant to a particular oil or solvent, if this oil or solvent swells the hard phase, all the useful physical properties of the thermoplastic elastomer will be lost. In many commercial thermoplastic elastomers, this hard phase is crystalline and so resistant to oils and solvents. Styrenic thermoplastic elastomers are an exception. As pure polymers they have poor oil and solvent resistance (although this can be improved by compounding—see Section 5.5.1. However, this gives them the advantage that they can be appUed from solution. 

In the styrenic thermoplastic elastomers, analogous S-B-S, S-I-S, S-EB-S, S-EP-S, and S-iB-S block copolymers have somewhat different properties. S-B-S... 

The hardness of these materials depends on the ratio of the volume of the hard phase to that of the softer elastomer phase. In the styrenic thermoplastic elastomers, this ratio can be varied within quite wide limits. Thus, in an S-B-S block copolymer, as the ratio of the S to B segments is increased, the phase morphology changes from a dispersion of spheres of S in a continuous phase of B to a dispersion of rods of S in a continuous phase of B and then to a lamellar or sandwich structure in which both S and B are continuous [1,43]. If the proportion of S is increased still further, the effect is reversed in that S now becomes disperse and B continuous. As the polystyrene phase predominates, the block copolymer gets harder and stiffer until eventually it... 

Compounding significantly changes many properties (e.g., solubility). Thus although the pure styrenic thermoplastic elastomers are completely soluble in solvents such as toluene, compounded products containing insoluble polymers (e.g., polypropylene) are not. The properties of compounded products produced from styrenic thermoplastic elastomers cover an exceptionally wide range and so their applications are more varied than those of the other thermoplastic elastomers. 

The plant opened in 1961 and is reportedly the largest styrenic thermoplastic elastomer production facility in the world. 

Pressure sensitive adhesives based on a variety of elastomers and applied from either latex, solvent, or hot melt systems have shown rapid growth in recent years. In addition, the development of hot melt assembly adhesives based on the styrenic thermoplastic elastomers is a key factor in the production of disposable diapers and other sanitary products. Even though the current emphasis of elastomer-based adhesive development is on pressure sensitive adhesives, large volumes of solvent cements, latex cements, and mastics are still produced. 

The influence of some pol5mier surface properties on bacterial attachment to the surface of the elastomeric and thermoplastic samples was shown. As promising materials in this field, butadiene-styrene thermoplastic elastomers (BSTPE) showed average characteristics of bacterial adhesion in comparison with other materials. All materials have passed cytotoxicity test. 

The materials we propose, such as block copolymer butadiene styrene thermoplastic elastomers, are producible, modifiable, and relatively inexpensive, and altogether have wide prospects for the production of reliable products. 

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