Lesson 5　Styrene Butadiene
Rubber (SBR)

New Words

Notes

[1] Emulsion polymerization is carried out either hot, at about 50℃， or cold, at about 5℃， depending upon the initiating system used. 乳液聚合可以在高温(约50℃)下进行，也可以在低温(约5℃)下进行，这取决于所使用的引发体系。

[2] SBR was originally produced by the hot emulsion method, and was characterized as more difficult to mill，mix, or calender than natural rubber, deficient in building tack, and having relatively poor inherent physical properties. 最初SBR是用高温乳液聚合的方法进行生产的，但是它比天然橡胶更难混炼和压延，而且加工黏性差、力学强度低。

[3] Since higher molecular weight can make cold SBR more difficult to process, it is commonly offered in oil-extended form. 因为较高的分子量使得低温SBR难以加工，所以通常低温SBR需要充油以改善其加工性能。

Exercises

1. Translate the first and second paragraphs of the text into Chinese.

2. Put the following words and phrases into English.

丁苯橡胶　　充油丁苯橡胶　　乳液聚合　　　　模量　　　　　　泡沫制品

无规共聚物　补强　　　　　　乳聚丁苯橡胶　　溶聚丁苯橡胶

Emulsion-SBR and Solution-SBR

SBR is derived from two monomers, styrene and butadiene. The mixture of these two monomers is polymerized by two processes: from solution or as an emulsion. Emulsion SBR (E SBR) produced by emulsion polymerization is initiated by free radicals. Reaction vessels are typically charged with the two monomers, a free radical generator, and a chain transfer agent such as an alkyl mercaptan. Radical initiators include potassium persulfate and hydroperoxides in combination with ferrous salts. Emulsifying agents include various soaps. By capping the growing organic radicals, mercaptans, control the molecular weight, and hence the viscosity, of the product. Typically, polymerizations are allowed to proceed only to ca. 70%, a method called “short stopping”. In this way, various additives can be emoved from the polymer.

Solution SBR(S SBR) is produced by an anionic polymerization process. Polymerization is initiated by alkyl lithium compounds. Water is strictly excluded. The process is homogeneous, which provides greater control over the process, allowing tailoring of the polymer. The alkyl lithium compound adds to one of the monomers, generating a carbanion that then adds to another monomer, and so on. Relative to E SBR, S SBR is increasingly favored because it offers improved wet grip and rolling resistance, which translate to greater safety and better fuel economy, respectively.

Words and Expressions