Styrene-butadiene rubber copolymer solution process

The family consists of, in order of market volume, polybutadiene (or butadiene rubber, BR), solution styrene butadiene rubber (SSBR) and styrenic block copolymers (SBC). A further subdivision may be made into those polymers that require vulcanisation (BR, SSBR) and those that do not (SBC). The latter are also known as thermoplastic rubbers as they have rubbery properties below a certain temperature when they soften and may be processed like thermoplastics. 

Some styrene-butadiene rubber is manufactured by solution processes using alkyllithium catalysts. Production techniques resemble those used for the polymerization of isoprene (Section 18.3.3) and butadiene (Section 18.4.3). Solution styrene-butadiene rubbers have microstructures similar to those of the emulsion copolymers but show narrower molecular weight distribution, less long chain branching and lower non-rubber content. The two types of materials have very similar bulk properties. 

Pressure sensitive and contact adhesives are made from a variety of polymers including acrylic acid esters, polyisobutylene, polyesters, polychloroprene, polyurethane, silicone, styrene-butadiene copolymer and natural rubber. With the exception of acrylic acid ester adhesives which can be processed as solutions, emulsions, UV curable 100% solids and silicones (which may contain only traces of solvents), all remaining rubbers are primarily formulated with substantial amounts of solvents such as hydrocarbon solvents (mainly heptane, hexane, naphtha), ketones (mainly acetone and methyl ethyl ketone), and aromatic solvents (mainly toluene and xylene). 

Solution polymerised rubbers are usually homopolymers of butadiene or copolymers of styrene and butadiene. They can have a variety of behaviours and properties depending on the molecular structure. However, they are classed as one family because of one common feature of the polymerisation process, i.e. the monomers, catalyst and other ingredients are all dissolved in an organic solvent... 

Produced by a solution polymerization process, this material exhibited an ordered molecular structure with the styrene monomer located at the ends of the butadiene monomer chain. In addition, other monomers such as isoprene, ethylene, butylene, and others, could be added to the polymer chain, which further modified basic properties. These materials possess a continuous rubber phase for resilience and toughness, and a discontinuous plastic phase for solubility and thermoplasticity. A variety of different grades are also available for this type of SBR, with differences in molecular weight, differences in the types of monomers used, differences in structural configuration, and differences in the ratio of endblock to midblock. Both emulsion and solution polymerized grades of SBR are available as solvent-based and water-based adhesives and sealants. Block copolymers are extensively used for hot melt formulations and both water-based and solvent-based pressure sensitive adhesive applications. Today, SBR elastomers are the most popular elastomers used for the manufacture of adhesives and sealants. 

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