Copolymer butadien-styrene diblock

Example 3.47 Preparation of a Butadiene/Styrene Diblock Copolymer... 

Through hydrogenation of butadiene-styrene diblock copolymers in which the butadiene block had either mixed 1,4/1,2 addition or only 1,4 addition, these workers obtained LDPE/PS and HDPE/PS block copolymers. They have demonstrated the... 

ADMET depolymerization has been explored in a variety of ways [174]. In its simplest form, an unsaturated polymer subjected to metathesis conditions in the presence of ethylene will undergo a retro-ADMET reaction, resulting from CM with ethylene. This concept had been explored with classical catalyst systems [le]. Schrock s catalyst was used to depolymerize PBD, poly-tr s-isoprene, polynor-bornene, andKraton (a butadiene/styrene diblock copolymer) [175] in the presence of ethylene (ethenolysis), and a mixture of products comprising the monomer and some oligomers were produced. 

Fig. 2.9. Thin film of butadien-styrene diblock copolymer cast from petrol ether solution and annealed 1 h at 100 °C. At 17% by weight the styrene aggregates in the form of spheres and of cylinders (Courtesy G. Kampf, Uerdingen).

Annis B K, Noid D W, Sumpter B G, Reffner J R and Wunderlich B 1992 Application of atomic force microscopy (AFM) to a block copolymer and an extended chain polyethylene Makromol. Chem., Rapid. Commun. 13 169 Annis B K, Schwark D W, Reffner J R, Thomas E L and Wunderlich B 1992 Determination of surface morphology of diblock copolymers of styrene and butadiene by atomic force microscopy Makromol. Chem. 193 2589... 

Butadiene copolymers are mainly prepared to yield mbbers (see Styrene-butadiene rubber). Many commercially significant latex paints are based on styrene—butadiene copolymers (see Coatings Paint). In latex paint the weight ratio S B is usually 60 40 with high conversion. Most of the block copolymers prepared by anionic catalysts, eg, butyUithium, are also elastomers. However, some of these block copolymers are thermoplastic mbbers, which behave like cross-linked mbbers at room temperature but show regular thermoplastic flow at elevated temperatures (45,46). Diblock (styrene—butadiene (SB)) and triblock (styrene—butadiene—styrene (SBS)) copolymers are commercially available. Typically, they are blended with PS to achieve a desirable property, eg, improved clarity/flexibiHty (see Polymerblends) (46). These block copolymers represent a class of new and interesting polymeric materials (47,48). Of particular interest are their morphologies (49—52), solution properties (53,54), and mechanical behavior (55,56). 

Another important class of copolymers synthesized by chain polymerisation are block (or sequenced) copolymers diblock and triblock copolymers being the most important ones. They are very useful as compatibilisers (emulsifiers) in immiscible polymer blends. Another major use is as thermoplastic elastomers. Both uses are best explained through the example of butadiene-styrene block copolymers. 

Table 19.3 Typical reaction conditions for the hydrogenation of polybutadiene (PB), styrene-butadiene diblock copolymer (SB), styrene-butadiene-styrene triblock copolymer (SBS) and nitrile butadiene rubber (NBR).

Commercial methods for preparing block copolymers of styrene-hutadiene-styrene utilize cyclohexane or toluene as a solvent since the polystyryl lithium is insoluble in straight chain alphatic solvents.Usually the 1,3-butadiene is added to the polystyryl lithium to produce the diblock styrene-butadienyl lithium. At this point in the reaction two processes are employed. 

Recently, cyclic diblock copolymers of styrene and butadiene were synthesized (Fig. 12). The synthetic approach of the cycles involved the reaction of (l,3-phenylene)bis(3-methyl-l-phenyl-pentylidene)diUthium initiator... 

Figure 6. Electron micrograph of diblock copolymer of styrene and butadiene cast from xylene (courtesy of M. Hoffman)...

Since A and B are constants for a given copolymer and the possible temperature interval is relatively limited, a transition is predicted at an approximately constant shear stress. Melt transitions have in fact been reported at approximately constant shear stresses for styrene-butadiene-styrene triblock copolymers (4). However, this behavior was certainly not observed for the styrene methylmethacrylate diblock copolymer,... 

Using the same method Storey et al. prepared ionic star—block copolymers.55-58 Styrene was oligomerized followed by the polymerization of butadiene. The living diblock copolymer was subsequently linked with methyltrichlorosilane to provide a three-arm star—block copolymer of styrene and butadiene. Hydrogenation of the diene blocks and sulfonation of the styrene blocks produced the desired ionic star-block structure having ionic outer blocks and hydro-phobic inner blocks, as depicted in Scheme 13. 

The catalyst composed of [( -allyl)Ni(OCOCF3)]2 and hexafluoroacetone or hexachloroacetone polymerizes various monomers such as 1,3-butadiene, vinyl ethers, norbornene, isocyanide, styrene, and isoprene [91]. [(zr-Allyl) Ni(OCOCF3)]2 is used to synthesize butadiene-isocyanide diblock [92] and triblock copolymers (Scheme 8) [93]. 

Linear low-density polyethylene (LLDPE) and PS resins were the same as described previously (Chapter 21). The various block copolymers that were used as compatibilizers have also been described (I). A series of crystalline copolymers (Q series) was prepared by hydrogenation of diblock and triblock copolymers of styrene and butadiene [styrene-hydrogenated butadiene (SEB) and styrene-hydrogenated butadiene—styrene (SEBS)J (1). Triblock copolymers of styrene and butadiene [styrene-butadiene-styrene (SBS)] and a noncrystalline hydrogenated block copolymer (SEBS) (Kraton) were supplied by Shell Chemical Co. Diblock copolymers of styrene and butadiene [styrene-butadiene (SB) (Vector)] were obtained from Dexco Polymers. The characteristics of the resins are given in Table I. 

It is claimed that styrene/butadiene diblock polymers bring about an improvement in the hardness, strength, and processability of polybutadiene elastomers (27), as well as an improvement in the ozone resistance of neoprene rubber (28). Styrene diblock polymers have also been made with isoprene, a-methyIstyrene, methyl methacrylate, vinylpyridine, and a-olefins. Block copolymers of ethylene, propylene, and other a-olefins with each other have been made as well. Heteroatom block copolymers based on styrene or other hydrocarbons and alkylene oxides, phenylene oxides, lactones, amides, imides, sulfides, or slloxanes have been prepared. 

LDPE/PS LLDPE/PS HDPE/PS hydrogenated butadiene-b-styrene diblock copolymer (HPB-b-PS) Eayt et al., 1981, 1982, 1986... 

One way to achieve compatibilization involves physical processes such as shear mixing and thermal history, which modify domain size and shape. The second way is the use of physical additives to increase attraction between molecules and phases. The third method is reactive processing, which is used to change the chemical structure of one or more of the components in the blend and thus increase their attraction to each other. Table 1.5 contains a list of compatibilizers used in the formulation of polyolefin blends. As can be seen from Table 1.5, most of the compatibilizers used in the formulation of polyolefin blends contain compounds such as maleic anhydride, acrylic and methacrylic acid, glycidyl methacrylate, and diblock and triblock copolymers involving styrene, ethylene, and butadiene. 

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