Block copolymers from styrene and butadiene

Elastomeric polyetherester [((CH2)4-0)n-C0-cp C0-0-]m Thermoplastic, elastomeric block copolymer from styrene and butadiene... 

Block copolymer from styrene and butadiene containing carboxylic groups... 

S. 2 Polyetherurethanes from methylene Block copolymers from styrene and butadiene... 

Ceresa drew attention to the fact that out of 1400 copolymers only 5% of the products had been isolated with a reasonable degree of purity and only 20 species had been properly characterized. Exploitation of anionic polymerization, however, soon improved the situation markedly. The use of alkyllithium initiators, which were initially evaluated by Stavely and co-workers at Firestone for the synthesis of high-cis polyisoprene, in the preparation of block copolymers from styrene and butadiene, and styrene and isoprene, is particularly noteworthy. 

The heat of fusion AHf (obtained from the area under the DSC melting curve) and percentage crystallinity calculated from AHf is found to be linearly dependent on butadiene content, and independent of the polymer architecture. This is shown in Figure 3. Also, the density of the block copolymers was found to be linearly dependent on butadiene content (see Figure 4). The linear additivity of density (specific volume) has been observed by other workers for incompatible block copolymers of styrene and butadiene indicating that very little change in density from that of pure components has occurred on forming the block copolymers.(32) While the above statement is somewhat plausible, these workers have utilized the small positive deviation from the linear additivity law to estimate the thickness of the boundary in SB block copolymers.(32)... 

The preparations by anionic mechanism of A——A type block copolymers of styrene and butadiene can be carried out with the styrene being polymerized first. Use of alkyl lithium initiators in hydrocarbon solvents is usually a good choice, if one seeks to form the greatest amount of c/s-1,4 microstructure [346]. This is discussed in Chap. 4. It is more difficult, however, to form block copolymers from methyl methacrylate and styrene, because living methyl methacrylate polymers fail to initiate polymerizations of styrene [347]. The poly(methyl methacrylate) anions may not be sufficiently basic to initiate styrene polymerizations [345]. 

Block copolymers of styrene and butadiene are extensively used in blends as well as neat products. Most of the blends are made with polystyrene resins, where addition of block copolymer improves the toughness of otherwise brittle polystyrene. Such materials find widespread use in food packaging, from yogurt cups to polystyrene film used for food packaging. Some volume of copolymer is also used as an impact modifier in the manufacture of specialty grades HIPS. 

Pathway 2 is generally chosen in the academic literature. In addition to sodium naphthalene, dilithium compounds are often used [146-150]. The following terminators are described for the third pathway silicon tetrachloride and tintetrachloride dicarbonic acid ester [151], divinylbenzene [152], and polymers formed from divinylbenzene [153] containing numerous vinyl groups yielding star-shaped polymers. Block copolymers of styrene and butadiene or isoprene are synthesized commercially in large ranges. 

In a block copolymer, a long segment made from one monomer is followed by a segment formed from the other monomer. One example is the block copolymer formed from styrene and butadiene. Pure polystyrene is a transparent, brittle material that is easily broken polybutadiene is a synthetic rubber that is very resilient, but soft and opaque. A block copolymer of the two monomers produces high-impact polystyrene, a material that is a durable, strong, yet transparent plastic. A different formulation of the two polymers produces styrene-butadiene rubber (SBR), which is used mainly for automobile tires and running shoes, but also in chewing gum. 

SBS block copolymers differ structurally from the random copolymer of styrene and butadiene (SBR). Because styrene and butadiene blocks are incompatible, they form separate phases joined at the junctions where the various blocks are connected. This gives an elastomeric material where the butadiene blocks form the soft segments and the styrene blocks form hard blocks. 

FIG. 13.6 The mechanical spectra (log G and A, i.e. n tan <5, at 1 Hz vs. temperature) for copolymers of styrene and butadiene (random, block and graft) and their homopolymers. From McCrum, Buckley and Bucknall, 1988. Courtesy Oxford University Press. 

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. 

Polymer characterization is an important use of NIR spectrometry. Polymers can be made either from a single monomer, as is polyethylene, or from mixtures of monomers, as are styrene-butadiene rubber from styrene and butadiene and nylon 6-6, made from hexamethylenediamine and adipic acid. An important parameter of such copolymers is the relative amount of each present. This can be determined by NIR for polymers with the appropriate functional groups. Styrene content in a styrene-butadiene copolymer can be measured using the aromatic and aliphatic C—H bands. Nylon can be characterized by the NH band from the amine monomer and the C=0 band from the carboxylic acid monomer. Nitrogen-containing polymers such as nylons, polyurethanes, and urea formaldehyde resins can be measured by using the NH bands. Block copolymers, which are typically made of a soft block of polyester and a hard block containing aromatics, for example, polystyrene, have been analyzed by NIR. These analyses have utilized the... 

Figure 9-19. A universal gel-permeation chromatography calibration curve obtained from measurements on linear poly(styrene) (O), comb-branched poly(styrene) (O ), star-branched poly(styrene) ( ), poly(methyl methacrylate) ( ), poly(vinyl chloride) (a) c -l,4-poly-(butadiene) (A), poly(styrene)-poly(methyl methacrylate) block copolymer (Qj ), random copolymer from styrene and methyl methacrylate O), and ladder polymers of poly(phenyl siloxanes) ( ) (according to Z. Grubisic, P. Rempp, and H. Benoit).

Styrene-Butadiene Copolymers. Styrene-butadiene polymers are block copolymers prepared from styrene and butadiene monomers. The polymerization is performed using sequential anionic polymerization. The copolymers are better known as thermoplastic elastomers, but copolymers with high styrene contents can be treated as thermo-... 

Styrene butadiene copolymers. Styrene butadiene polymers are block copolymers prepared from styrene and butadiene monomers. The... 

The most important copolymers are those from styrene and butadiene, either as statistical copolymers or block copolymers. From a kinetic point of view the association behavior discussed above becomes even more complex because of the possible cross-association between the different growing chain ends. This issue has seldom been addressed [35, 120]. 

Standard contact adhesives and pressure-sensitive adhesives are made from SBR in solution. Styrene-butadiene rubber latices, in some cases containing carboxyl groups, are used for special emulsion-based adhesives. Thermoplastic elastomeric block copolymers of styrene with butadiene or isoprene are of increasing significance in contact adhesives and hot-melt adhesives. 

Electron Microscopy. Figure 3 shows electron micrographs of ultra-thin sections of film specimens of the three kinds of block copolymers. As can be seen in the figure, TR-41-1647 and TR-41-1648 specimens have a heterogeneous structure in which the polystyrene domains are dispersed within a polybutadiene matrix and are connected to each other to form a swirl-like structure. On the other hand, TR-41-1649 specimen is seen to consist of alternating lamellar domains of the two components. Changes of the domain structure with fractional compositions of styrene and butadiene components are consistent with predictions of the current theories of micro-phase separation (12,13,14,15) for block copolymers cast from such a nearly nonselective solvent as the mixture of THF and methylethylketon (90/10 in volume ratio). 

Poly(l,4-butadiene) segments prepared by the ruthenium-mediated ROMP of 1,5-cyclooctadiene can be incorporated into the ABA-type block copolymers with styrene (B-106) and MMA (B-107).397 The synthetic method is based on the copper-catalyzed radical polymerizations of styrene and MMA from the telechelic poly(butadiene) obtained by a bifunctional chain-transfer agent such as bis(allyl chloride) or bis-(2-bromopropionate) during the ROMP process. A more direct route to similar block copolymers is based on the use of a ruthenium carbene complex with a C—Br bond such as Ru-13 as described above.67 The complex induced simultaneous or tandem block copolymerizations of MMA and 1,5-cyclooctadiene to give B-108, which can be hydrogenated into B-109, in one pot, catalyzed by the ruthenium residue from Ru-13. 

Despite the drawbacks of this method, it has been used to prepare a tremendous number of polypeptide hybrid block copolymers (Table 1), and when carefully executed provides reasonably well-defined samples. Synthetic polymer domains have been prepared by addition polymerization of conventional vinyl monomers, such as styrene and butadiene, as well as by ringopening polymerization in the cases of ethylene oxide and e-caprolactone. The generality of this approach allows NCA polymerization off of virtually any primary amine functionality, which was exploited in the preparation of star block copolymers by polymerization of sarcosine NCA from an amine-terminated trimethyleneimine dendritic core [37]. In most examples, the polypeptide domain was based on derivatives of either lysine or glutamate, since these form a-helical polypeptides with good solubility characteristics. These residues are also desirable since, when deprotected, they give polypep-... 

In looking at surface energies vs styrene content, (Figure 4) it can be seen from this data that as ozone exposure is Increased, the deviation of (25-30%) styrene block copolymers from the other samples becomes more pronounced. This implies that butadiene and styrene are both involved in some reaction with ozone (or each other) and this reaction is enhanced at these concentrations of block copolymer. Figures 2 and 4 would tend to imply that this phenomenon does not occur with the random copolymer or homopolymers nor with block copolymers with more than 30% styrene content. 

During the middle sixties a series of butadiene-styrene and isoprene-styrene block copolymer elastomers were developed. These materials possess typical rubber-like properties at ambient temperatures, but act like thermoplastic resins at elevated temperatures. The copolymers vary from diblock structures of styrene and butadiene ... 

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