GR-S rubber

Copolymerization of butadiene with styrene by free-radical mechanism has been explored very thoroughly [146]. The original efforts started during World War I in Germany. Subsequent work 

A redox initiator is used in the cold process, but not in the hot one. Also, the hot process is carried out at about 50°C for 12 h to approximately 72% conversion. The cold process is also carried for 12 h, but at about 5°C to a 60% conversion. The two recipes for preparation of GR-S rubbers are shown in Table 6.10 for comparison of the hot and cold processes. 

In both polymerizations, the unreacted monomer has to be removed. In the hot one the reaction is often quenched by addition of hydroquinone, and in the cold one by addition of N, A-diethyldithiocarbamate. After the monomers are steam stripped in both processes, an antioxidant like A-phenyl-2-naphthylamine is added. The latex is usually coagulated by addition of a sodium chloride-sulfuric acid solution. The cold process yields polymers with less branching than the hot one, slightly higher trans to cis ratios. 

During the middle 1960s 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 ones. The copolymers vary from diblock structures of styrene and butadiene 

A typical triblock copolymer may consist of about 150 styrene units at each end of the macromolecule and some 1,000 butadiene units in the center. The special physical properties of these block copolymers are due to inherent incompatibility of polystyrene with polybutadiene or polyisoprene blocks. Within the bulk material, there are separations and aggregations of the domains. The polystyrene domains are dispersed in continuous matrixes of the polydienes that are the major components. At ambient temperature, below the Tg of the polystyrene, these domains are rigid and immobilize the ends of the polydiene segments. In effect they serve both as filler particles and as cross-links. Above Tg of polystyrene, however, the domains are easily disrupted and the material can be processed as a thermoplastic polymer. The separation into domains is illustrated in Fig. 6.4. 

The cold process yields polymers with less branching than the hot one, slightly higher trans-io-cis ratios, and narrower molecular weight distributions. 

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Grove s synthesis org chem Production of alkyl chlorides by passing hydrochloric acid into an alcohol In the presence of anhydrous zinc chloride. grovz sin-th3S3s ) GR-S rubber org chem Former designation for general-purpose synthetic rubbers formed by copolymerization of emulsions of styrene and butadiene used in tires and other rubber products previously also known as Buna-S, currently known as SBR (styrene-butadiene rubber). je ar es. rab ar)... 

Elastic-gel comp proplnt is prepd by milling oil-extended GR-S rubber (contg 100 parts rubber 30 ps oil) with 5 ps RPA No 3 (A 36.5% soln of xylyl mercaptan in a hydrocarbon solvent), 5 ps ZnO 1 part stearic acid. Then 300 ps oil is added, in small increments, followed by Captax 12, Tuads 6, diphenylguanidine 18, C black 20, sulfur 6 and finally AN (50-100 mesh) 1892 parts. The batch is mixed 60 mins, deaerated, cast and cured for 24 hrs at 220°F] DD)C.C.Rice W.B.Reynolds, USP 2993769 (1961) CA 55, 27891 (1961) [Comp proplnt prepd by mixing petroleum pitch with a polymer, a phase -stabilized Amm nitrate Amm dichromate. 

By 1931 the first commercially successful rubber substitute, neoprene, was manufactured by DuPont. Among other rubber substitutes later developed in this country were butyl, Buna-N, and GR-S rubber made both from alcohol and from petroleum. Soon after the entry of the United States into World War II, our manufacture of synthetic rubber was stepped up to almost a millions tons a year. 

During World War II chemists contributed to the Allied effort by developing and producing antibacterials (sulfa drugs, penicillin), antimalarials, and synthetic buna-S (GR-S) rubber. They contributed to the purification of uranium 235 and plutonium 239 as well as the development of conventional explosives needed for the Manhattan Project. 

An analysis of their results indicated, that in the case of the 50% butadiene-50% styrene polymer used in the investigation, 40% of the styrene molecules were linked adjacently. Similar studies by Rabjohn et al. (1947) were carried out on various types of GR-S rubber then available but the results are not easy to analyze. 

Figure 13.43 Variation of tensiie strength (a) and uitimate strain (b) of a rubber with reduced strain rate ear- Vaiues were measured at various temperatures and rates and reduced to a temperature of 263 K. (Reproduced from Smith, T.L (1958) Dependence of the uitimate properties of a GR-S rubber on strain rate and temperature. /. Poiym. ScL, 32, 99. Copyright (1958) lohn Wiiey Sons, inc.)...

There exists periodically in the chain a double bond. In the process of vulcanization crosslinks are formed between sulphur and the highly reactive double bonds in the polyisoprene chain. As a result the mechanical behavior of the network material system can be calculated using the present formulation. For simplicity neglecting the effort of the side chains only the principal rubber chain and the crosslink need be considered in the analysis. For comparison the one-dimensional stress-strain relation in tension is calculated as this type of force-extension relationships is widely reported in the literature. For example, the shape of the force extension curve (conventional or nominal stress-strain relationship) for pure-gum GR-S rubber at 2 C is somewhat like a reversed "S" as reported inC 5 J. 

The dehydrogenation processes used for the production of butadiene from n-butane and -butenes dirring the development of GR-S rubber were modified in the 1990s for the dehydrogenation of propane to propylene. This compensated for the short supply of steam cracked propylene used to produce polypropylene. The new processes can also be used for the dehydrogenation of other paraflins. 

A wide variety of redox reactions between metals or metal compounds and organic matter may be employed in this context. Because most of them are ionic in nature, they may be conveniently carried out in aqueous solution and occur rather rapidly even at relatively low temperatures. As a consequence, redox systems with many different compositions have been developed into initiators that are very efficient and useful, particularly for suspension and emulsion polymerization in aqueous media [2], which is dealt with in detail in Chapter 6. The low-temperature (at 5°C) copolymerization of styrene and butadiene for the production of GR-S rubber was made possible with the success of these catalytic systems. 

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