Plasticizers styrene block copolymers

Styrene block copolymers have been used as compatihilizers for mixed plastics to permit their processing for appHcations such as those outlined earlier (52,61). 

Fig. 10. Viscosity vs shear rate for solutions of a styrene—butadiene—styrene block copolymer (42). A represents cyclohexanone, where c = 0.248 g/cm (9-xylene, where c = 0.246 g/cm C, toluene, where c = 0.248 g/cm. Courtesy of the Society of Plastics Engineers, Inc.

Adhesives, Coatings, and Sealants. Eor these appHcations, styrenic block copolymers must be compounded with resins and oils (Table 10) to obtain the desired properties (56—58). Materials compatible with the elastomer segments soften the final product and give tack, whereas materials compatible with the polystyrene segments impart hardness. The latter are usually styrenic resins with relatively high softening points. Materials with low softening points are to be avoided, as are aromatic oils, since they plasticize the polystyrene domains and reduce the upper service temperature of the final products. 

Multiblock Copolymers. Replacement of conventional vulcanized mbber is the main appHcation for the polar polyurethane, polyester, and polyamide block copolymers. Like styrenic block copolymers, they can be molded or extmded using equipment designed for processing thermoplastics. Melt temperatures during processing are between 175 and 225°C, and predrying is requited scrap is reusable. They are mostiy used as essentially pure materials, although some work on blends with various thermoplastics such as plasticized and unplasticized PVC and also ABS and polycarbonate (14,18,67—69) has been reported. Plasticizers intended for use with PVC have also been blended with polyester block copolymers (67). 

Styrene-based resins, extrusion of, 23 398 Styrene block copolymers, as mixed plastics compatibilizers, 21 454 Styrene-butadiene (SB) block copolymers, 20 324, 23 377, 393 Styrene-butadiene copolymer latex binders, 19 360... 

One simple idea is that styrenic block copolymers are almost never used as a stand-alone 100% neat polymer for any application or use. We tend to think about polymers in terms of this plastic soda bottle is polyester, or this carpet fiber is polyamide, or this house siding is PVC, or this garbage bag film is polyethylene , fully understanding and meaning that virtually 100% of the named object is that polymer. Our brains usefully process the named polymer properties set (as neat polymer) into the desired and required property set for its application. Life is simple in the 100% world. It is intuitive, and what we seem to know makes sense, looking either way properties wise, to why this polymer is used for this application. 

R.M. Suffield, J.E. Kiesser, and S.H. Dillman. Antioxidant performance of mixed tocopherols in styrenic block copolymers. In Proceedings ANTEC, Society of Plastic Engineers, Brookfield, CT, Boston, MA, May 1-5, 2005. 

HMPSA - TP elastomers such as styrene block copolymers, tackifier resin, plasticizers, fillers, stabilizers. 

As noted, TPEs are either block copolymers or combinations of a rubber-dispersed phase and a plastic continuous matrix. The attribute contributed by the rubbery phase - such as butadiene or ethylenebutylene in an S-E-S or SEB-S styrenic block copolymer, or the completely vulcanized EPDM rubber particles in a polypropylene (PP)/EPDM EA - is classical elastomeric performance. The elastic properties of a rubber result from long, flexible molecules that are coiled in a random manner. When the molecules are stretched, they uncoil and have a more specific geometry than the coiled molecules. The uncoiled molecules have lower entropy because of the more restricted geometry and, since the natural tendency is an increase in entropy, the entropic driving force is for the molecules to retract. 

The three major types of TPEs are block copolymers such as SEES (styrene-ethylene-butylene-styrene block copolymer) (Kraton by Kraton Polymer), polyether— polyester (Hytrel by DuPont), rubber/plasticblends (900 series Sumitomo Chemical), and dynamically vulcanized rubber/plastic alloys (Innoprene by Kumho Polychem, Santo prene by Exxon-Mobil, Sarlink by DSM, Unipene byTeknor Apex). Figure 3.28 shows the cost versus general performance comparison for different TPEs [31]. 

Silicone plastics Styrene acrylonitrile copolymer St ene-butadiene rubber Styrene butadiene styrene block copolymer Sheet molding compound St50 ene acrylonitrile copolymer Styrene butadiene block copolymer Styrene butadiene styrene block copolymer -a thermoplastic elastomer... 

Styrenic block copolymers and their compounds have been in widespread commercial use for many years, with many applications. With the latest technology, they have become particularly interesting as impact modifiers for plastics, both thermoplastics and thermosets. Most polymers are thermodynamically incompatible with others polymers and mixtures tend to separate into two phases, even when they are part of the same molecule, as in block copolymers. Poly(styrene-P-elastomer-P-styrene) copolymers, in which the elastomer is the main constituent, give a structure in which the polystyrene end-segments form separate spherical regions ( domains ) dispersed in a continuous phase. 

The functional uses of styrenic block copolymers are usually a result of the unique characteristics of these types of synthetic polymers, related to the nature of the block segments covalently linked in the polymer chain to the nature of the energetic interactions between the chain segments, or to the network stucture that is achieved in combinations where the block copolymer has multiple hard blocks in each chain. The functional utility of the block copolymer is to provide a specialized and vital function to the whole without imparting the "rubber identity to the whole. For example, the rubber seals in a power transmission device are vital to the operation of the transmission, yet there is no identity imparted to the transmission by the rubber gaskets and seals. A rubber which is added to a thermoplastic or thermoset to provide a mechanism of impact resistance has a functional use rather than a monolithic structural use even though that is the function of the plastic. 

Styrenic block copolymer (SBS) TPEs are multiphase compositions in which the phases are chemically bonded by block copolymerization (see chapter Introduction to Plastics and Polymers). At least one of the phases is a hard styrenic polymer. This styrenic phase may become fluid when the TPE composition is heated. Another phase is a softer elastomeric material that is rubber-like at room temperature. The polystyrene blocks act as cross-links, tying the elastomeric chains together in a three-dimensional network. SBS TPEs have no commercial applications when the product is just a pure polymer. They must be compounded with other polymers, oils, fillers, and additives to have any commercial value. 

---