Styrene system, polybutadiene-polystyrene

The correct explanation of the peculiar behaviour of the butadiene-styrene system was provided by O Driscoll and Kuntz 144). As stated previously, under conditions of these experiments butadiene is indeed more reactive than styrene, whether towards lithium polystyrene or polybutadiene, contrary to a naive expectation. This was verified by Ells and Morton 1451 and by Worsfold 146,147) who determined the respective cross-propagation rate constants. It is germane to stress here that the coordination of the monomers with Li4, assumed to be the cause for this gradation of reactivities, takes place in the transition state of the addition and should be distinguished from the formation of an intermediate complex. The formation of a complex ... 

In a system of significant interest to the present works, Graillard, et al. [62] studied the ternary phase diagrams of the systems polybutadiene-styrene-polystyrene and polybutadiene-block-polystrene-styrene-polystyrene. They showed that the presence of block copolymer increased the miscibility of the two poljrmers, as the styrene component polymerized. Similar effects are probable in the IPN s, as compared with the corresponding blends. 

While studying polymer distribution between the emulsion phases it was found that in the systems mentioned above obtained both by copolymerization of styrene with polybutadiene rubber and mixing styrene solutions of polymers when the composition is far enough from the critical mixing point, thermodynamic equilibrium is reached.At this thermodynamic equilibrium the ratio of polymer concentration (Cp) in rubber (index ) as well as in polystyrene (index ) phases is practically constant (table II),... 

The polystyrene/styrene/polybutadiene (PS/S/PBD) system occurs in the production of high impact polystyrene. The process for making toughened polystyrene as described by Moulau and Keskkula (1) starts with a rubber in styrene solution. As S is polymerized to PS, phase separation results in immediate formation of droplets of a PS phase. With further polymerization, the PS phase increases in volume until phase volumes are equal. At this point, phase inversion occurs—the dispersed PS phase becomes the continuous phase and the PBD phase becomes the disperse droplets. Complete conversion of S to PS yields the commercially important high impact polystyrene. 

Technically important examples of block copolymers are the thermoplastic rubbers, such as the styrene-butadiene-styrene system. These molecules are essentially polybutadiene tipped with polystyrene end-blocks. Butadiene (CH2=CH—CH=CH2), on polymerization, yields a polymer consisting of three structures ... 

Figure 9.17 Plot of log [i ]M versus retention volume for various polymers, showing how different systems are represented by a single calibration curve when data are represented in this manner. The polymers used include linear and branched polystyrene, poly(methyl methacrylate), poly(vinyl chloride), poly(phenyl siloxane), polybutadiene, and branched, block, and graft copolymers of styrene and methyl methacrylate. [From Z. Grubisec, P. Rempp, and H. Benoit, Polym. Lett. 5 753 (1967), used with permission of Wiley.]...

In these mbber-modified polystyrene polymers, the mbbers should have low T, large particle sizes (0.5—5 J.m), graftable and cross-linkable sites, and should be compatible with styrene monomer (93). Polybutadiene, with a T of —SS C, meets all of these requirements and is used most frequently. These mbber-modified systems exhibit excellent low temperature impact strength, a required attribute for use in refrigerators. 

Addition of poly(styrene-block-butadiene) block copolymer to the polystyrene-polybutadiene-styrene ternary system first showed a characteristic decrease in interfacial tension followed by a leveling off. The leveling off is indicative of saturation of the interface by the solubilizing agent. 

Butadiene is used primarily in the production of synthetic rubbers, including styrene-butadiene rubber (SBR), polybutadiene nibber (BR), styrene-butadiene latex (SBL), chloroprene rubber (CR) and nitrile rubber (NR). Important plastics containing butadiene as a monomeric component are shock-resistant polystyrene, a two-phase system consisting of polystyrene and polybutadiene ABS polymers consisting of acrylonitrile, butadiene and styrene and a copolymer of methyl methacrylate, butadiene and styrene (MBS), which is used as a modifier for poly(vinyl chloride). It is also used as an intermediate in the production of chloroprene, adiponitrile and other basic petrochemicals. The worldwide use pattern for butadiene in 1981 was as follows (%) SBR + SBL, 56 BR, 22 CR, 6 NR, 4 ABS, 4 hexamethylenediamine, 4 other, 4. The use pattern for butadiene in the United States in 1995 was (%) SBR, 31 BR, 24 SBL, 13 CR, 4 ABS, 5 NR, 2 adiponitrile, 12 and other, 9 (Anon., 1996b). 

The system with which we have begun our investigations is the styrene-dimethylsiloxane system. The dimethylsiloxane blocks should be considerably less compatible with polystyrene blocks than either polybutadiene or polyisoprene since the solubility parameter of dimethylsiloxane is much farther from that of polystyrene than are the solubility parameters of polybutadienes or of polyisoprenes (17), no matter what their microstructure. Furthermore, even hexamers of polystyrene and of polydimethylsiloxane are immiscible at room temperature and have an upper critical-solution temperature above 35°C (18). In addition, the microphases in this system can be observed without staining and with no ambiguity about the identity of the phases in the transmission electron microscope (TEM) silicon has a much higher atomic number than carbon or oxygen, making the polydimethylsiloxane microphases the dark phases in TEM (19,20). 

Since this work of adhesion has been correlated (41, 44) with the adhesive strength, we can presumably use Wad to estimate the theoretical maximum adhesive strength between a rubber and a resin for all four systems discussed in this paper. For example, the work of adhesion between polystyrene and polybutadiene is 67 dyne/cm., and that between polystyrene and styrene-butadiene copolymer is 69 dyne/cm. 

A preliminary screening indicated that excellent impact could be obtained using 15-20 wt % butadiene based on the total polymer blend. At 20 wt % butadiene, several block polymers were screened for optimum impact and overall balance of properties. Two-component systems (block polymer-polystyrene) and three-component systems (block poly-mer-polybutadiene-polystyrene) were tried. The impact varied with the styrene content of the block polymer in both two- and three-component systems as shown in Figure 1. Subsequent work showed that the best overall balance of impact, flexural modulus, and heat distortion was obtained at 15% butadiene. 

Figure 3.4 Ternary phase diagram for the system styrene-polystyrene-polybutadiene rubber. Reproduced with permission from Encyclopedia of Polymer Science and Engineering, Mark (Ed.), John Wiley Sons, NY. Copyright John Wiley Sons...

In HIPS a wide variety of rubber particle morphology is possible. Echte et al. summarized this in an excellent review (see Figure 14.5) [41]. The key to these different structures is the composition of the styrene-butadiene block rubber, which is an emulsifier for the polystyrene-polybutadiene system. Additional grafting can generate a shift from one structure to another. 

The system Cp2TiCl2/MAO is suggested to be less active than CpTiCl3/MAO and Cp2TiCl/MAO in the polymerization of 1,3-butadiene, 4-methyl-l,3-pentadiene, and styrene to give predominantly cis-, 4-polybutadiene, 1,2-syndiotactic poly(4-methyl-l,3-pentadiene), and syndiotactic polystyrene.1214... 

Polystyrene and polybutadiene homopolymers as well as random and block copolymers of these mers have been studied via dielectric relaxation spectroscopy and tensile stress-strain measurements. The results suggest that some block copolymer systems studied have styrene rich surfaces which appear to partially crosslink upon initial exposure to ozone even though surface oxygen concentrations are not significantly affected. After continued exposure these samples appear to then undergo chain scission. Complex plane analysis implies that after degradation... 

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