Styrene-butadiene rubbers random solution

APPROACHES FOR PREPARATION OF RANDOM SOLUTION STYRENE-BUTADIENE RUBBERS... 

An increasing amount of styrene-butadiene rubber is being manufactured by solution processes using alkyllithium catalysts. Production techniques resemble those used for the polymerization of isoprene (section 20.3.3) and butadiene (section 20.4.3). There is a tendency for alkyllithium initiation to lead to block copolymers since the butadiene in the mixture polymerizes first to the virtual exclusion of the styrene. In order to obtain random copolymers it is necessary to add the butadiene incrementally so that the molar ratio of... 

Polybutadiene (BR rubber) and the random styrene/butadiene copolymer (SBR rubber) are the most widely used polymers. Their principal use is in tyres, which are typically blends of natural/synthetic rubber. BR rubber has good resilience, abrasion resistance and low heat build-up. SBR contains 10-25% styrene which is added chiefly to reduce cost but also to improve wearing and blending characteristics compared with BR alone. BR and SBR are polymerized by a free-radical mechanism as a water emulsion at 50-60 °C (hot rubber) or 0°C (cold rubber). Typical compositions are 70% trans-1,4, 15% cis-1,4 and 15% 1,2. Ziegler systems used in solution polymerization yield an SBR which has higher MW, narrower MWD and higher cis-1,4-content than the emulsion free-radical type. 

Random copolymers are commercially produced by both emulsion and solution polymerizations. It was discovered in the author s laboratory that the use of barium alkoxides in combination with organometalhc compounds is yet another method to prepare random styrene/butadiene solution rubbers. With Ba/Mg/Al catalyst systems, random SBRs are obtained with no more than 4% vinyl unsaturation. The principal effect of lower vinyl content is a lower glass transition temperature than that of a corresponding, conventional solution SBR. 

Latex adhesives consist of particles of polymers with diameters of the order of 1 pm suspended in an aqueous medium. Surfactant molecules such as anionic soaps, which are adsorbed on the surfaces of the particles, maintain the particles in solution and thereby stabilize the latex. Stabilization can also be gained by the presence of a soluble polymer in the aqueous phase. The volume fraction of the phases is about 50%. Current adhesives include the latices of natural rubber, styrene-butadiene random copolymer, polyvinyl acetate and its copolymers with ethylene and vinyl chloride. For any further information on polymer latices the reader is directed to the three volumes of Blackley (1997). 

Many random copolymers have found commercial use as elastomers and plastics. For example, SBR (62), poly(butadiene- (9-styrene) [9003-55-8] has become the largest volume synthetic mbber. It can be prepared ia emulsion by use of free-radical initiators, such as K2S20g or Fe /ROOH (eq. 18), or in solution by use of alkyl lithium initiators. Emulsion SBR copolymers are produced under trade names by such companies as American Synthetic Rubber (ASPC), Armtek, B. F. Goodrich (Ameripool), and Goodyear (PHoflex) solution SBR is manufactured by Firestone (Stereon). The total U.S. production of SBR in 1990 was 581,000 t (63). 

Weiss et al. [75] have synthesized Na and Zn salt of sulfonated styrene(ethylene-co-butylene)-styrene triblock ionomer. The starting material is a hydrogenated triblock copolymer of styrene and butadiene with a rubber mid-block and PS end-blocks. After hydrogenation, the mid-block is converted to a random copolymer of ethylene and butylene. Ethyl sulfonate is used to sulfonate the block copolymer in 1,2-dichloroethane solution at 50°C using the procedure developed by Makowski et al. [76]. The sulfonic acid form of the functionalized polymer is recovered by steam stripping. The neutralization reaction is carried out in toluene-methanol solution using the appropriate metal hydroxide or acetate. 

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