Emulsion polymerizations ESBR

Emulsion polymerization (ESBR)—via free radical polymerization. Makes a random copolymer. The material has some long chain branching. This is an economical way of making this type of rubber. Viscosity is not a problem, since the emulsion does not change viscosity. 

The quahty of the water used in emulsion polymerization has long been known to affect the manufacture of ESBR. Water hardness and other ionic content can direcdy affect the chemical and mechanical stabiUty of the polymer emulsion (latex). Poor latex stabiUty results in the formation of coagulum in the polymerization stage as well as other parts of the latex handling system. 

In the late 1920s Bayer Company began studies of the emulsion polymerization process of polybutadiene for producing synthetic rubber. Incorporation of styrene as a comonomer produced a supenor polymer compared to polybutadiene. The product, Buna S, was the precursor of the single largest-volume polymer produced in the 1990s, emulsion styrcne-buladieiie rubber (ESBR). 

Snap. A critical ingredient for emulsion polymerization is the soap, which performs a number of key roles, including production of oil (monomer) m water emulsion, provision of the loci for polymerization (micelle), stabilization of the latex particle, and imputation of characteristics to the finished polymer. Both fatty acid and rosin acid soaps, mamly derived from tall oil, are used in ESBR,... 

A less expensive version of BR is manufactured by the emulsion polymerization process (very similar to the emulsion polymerization of ESBR except for the absence of the styrene). These emulsion BR polymers are usually called EBR. They do not have the same microstructure as the solution-polymerized ds-BRs. Therefore the EBRs may not impart as good wear resistance or rolling resistance. 

In the 1960s, anionic polymerized solutron SBR (SSBR) began to challenge emulsion SBR in the automotive tire market. Organolithium compounds allow control of the butadiene microstructure, not possible with ESBR. Because this type of chain polymerization takes place without a termination step, an easy synthesis of block polymers is available, whereby glassy (polystyrene) and rubbery (polybutadicnc) segments can be combined in the same molecule. These thermoplastic elastomers (TPE) have found use ill nontire applications. 

Free-radical initiation of emulsion copolymers produces a random polymerization m which the trans/ds ratio cannot be controlled. The nature of ESBR free-radical polymerization results in the polymer being heterogeneous, with a broad molecular weight distribution and random copolymer composition. The microstructurc is not amenable to manipulation, although the temperature of the polymerization affects the ratio of trans to cis somewhat... 

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