Styrene-hydrogenated polybutadiene block copolymers

Commercially, anionic polymerization is limited to three monomers styrene, butadiene, and isoprene [78-79-5], therefore only two useful A—B—A block copolymers, S—B—S and S—I—S, can be produced direcdy. In both cases, the elastomer segments contain double bonds which are reactive and limit the stabhity of the product. To improve stabhity, the polybutadiene mid-segment can be polymerized as a random mixture of two stmctural forms, the 1,4 and 1,2 isomers, by addition of an inert polar material to the polymerization solvent ethers and amines have been suggested for this purpose (46). Upon hydrogenation, these isomers give a copolymer of ethylene and butylene. 

The product obtained by the partial hydrogenation of polybutadiene (Hydropol) has been used as a wire coating and a saturated ABA copolymer (Kraton) is produced by the hydrogenation of the ABA block copolymer of styrene and butadiene. 

The use of core-shell impact modifiers combined with styrene-hydrogenated poly butadiene block copolymers in sPS is described by Rohm and Haas [24]. The core of the former type is of polybutadiene or its copolymer, the shell consists predominately of polystyrene. Rohm and Haas found that a synergistic effect is present and that the Izod notched impact strength is higher when both rubber types are used instead of only one. 

The universal compatibilizers are multi-component copolymers, with parts that either are soluble in some components of the blend, chemically bond to chain ends, or have a tendency for hydrogen bonding. Because of the universality, these materials are rather expensive to use. A better chance offers the proprietary compatibilizers-cwm-impact modifiers, formulated for specific types of polymer mixtures, viz. Blendex (polybutadiene-type compatibilizer for styrenics, PVC, TPU, PET), EXL (an acrylic-based additive for PEST), Fusabond (maleated-PO compatibilizer for PO/PET blends), Vector (is SBS-type block copolymer with stabilizers, designed for PO/PS commingled mixtures), and many others. 

Orientations in elongated mbbers are sometimes regular to the extent that there is local crystallization of individual chain segments (e.g., in natural rubber). X-ray diffraction patterns of such samples are very similar to those obtained from stretched fibers. The following synthetic polymers are of technical relevance as mbbers poly(acrylic ester)s, polybutadienes, polyisoprenes, polychloroprenes, butadiene/styrene copolymers, styrene/butadiene/styrene tri-block-copolymers (also hydrogenated), butadiene/acrylonitrile copolymers (also hydrogenated), ethylene/propylene co- and terpolymers (with non-conjugated dienes (e.g., ethylidene norbomene)), ethylene/vinyl acetate copolymers, ethyl-ene/methacrylic acid copolymers (ionomers), polyisobutylene (and copolymers with isoprene), chlorinated polyethylenes, chlorosulfonated polyethylenes, polyurethanes, silicones, poly(fluoro alkylene)s, poly(alkylene sulfide)s. 

Studies of polymers dissolved in various oils indicate general agreement, with the volume fraction exponent reported to be 2 to 2.3 (5,6). In a recent study, W.W. Graessley and co-workers (7) reported exponents of 2.22 and 2.26 for polybutadiene and hydrogenated polybutadiene in various diluents. G. Kraus and K.W. Rollmann (8) reported on the only study of resins as the polymer diluent. Using a styrene-isoprene-styrene block copolymer, they found exponents of 2.28 for the glycerin ester of stabilized rosin and 2.62 for a C -stream resin. Plateau modulus was identified as G in the rubbery plateau where tan 6 was a minimum in a temperature scan of the systems. 

Styrenk Block Copolymers. Styrenic TPEs are copolymers whose molecules have the S-D-S structure, where S is a hard segment of polymerized styrene or styrene derivative, and D is a soft central segment of polymerized diene or hydrogenated diene units. Polybutadiene (B), polyisoprene (I), and polyethylenebutylene (EB) are the most commonly used rubbery segments (D). Structures for these triblock copolymers are represented as follows ... 

Hydrogen abstraction by alkoxy radicals at any of the allylic sites jdelds a site for styrene polymerization, resulting in a graft (282,283). Model studies based on styrene-butadiene block copolymers show a strong influence of graft structure on particle morphology (81,82). The double bonds in polybutadiene are much less... 

This paper is a discussion of the main results we have on the thermoreversible gelation of block copolymers of the MXM type in o-xylene, where M is syndiotactic poly(methyl methacrylate) (sPMMA) and X is either polybutadiene (PBD), hydrogenated PBD (PEB), poly(styrene-b-butadiene-b-styrene) (SBS) triblock or the hydrogenated version of this triblock (SEBS) (25-28). 

With the exception of a few commercial polymers such as polyisobutylene, polybutadiene and styrene-butadiene block copolymers, living polymers are prepared in small quantities under stringent conditions. Larger amounts can only be prepared by repeating the synthesis many times, and this is a costly and time-consuming process. In the case of hydrogenated polybutadiene, to prepare samples that resemble polyethylene, the need for a secondary reaction step renders the preparation even more costly. This has so far limited the extent to which it has been possible to use these materials to test models. Cell et al. [ 18] prepared asymmetric stars with structures similar to ethylene-propylene copolymers by hydrogenation of star-branched polyisoprene. The reactions to produce these materials took up to three weeks, and... 

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