22 in the trans configuration the main polymer chain is on opposite sides of the
internal carbon-carbon double bond. Trans BR has a melting point of about 80C. It is made with transition metal catalysts similar to the high cis process
La, Nd, and Ni. These catalysts can make polymers with 90 trans again using the solution process. Kline, 1974
Figure 2.7: High Trans Polybutadiene
2.8 Styrene Butadiene Rubber SBR
SBR stands for Styrene – Butadiene Rubber that is a random copolymer from the aforesaid monomers. SBR is a synthetic rubber copolymer consisting of styrene and
butadiene Mallick, 1993 It has good abrasion resistance and good aging stability when protected by additives, and is widely used in car tires, where it is blended with
natural rubber. It was originally developed prior to World War II in Germany, http:www.wisegeek.comwhat-is-styrene-butadiene-rubber.htm - online on 1
September 2010 There are two major types of SBR, Emulsion SBR E-SBR and Solution SBR S-SBR, based on the different manufacturing process. The peculiar
nature of the insertion of butadiene on the growing chain, ie the 1,4 and 1,2 additions, together with the two possible 1,4 addition isomers, cis and trans, suggests
that it would be more appropriate to refer to SBR as a four-monomer copolymer. This remark acquires a particular meaning if we consider the physical and
rheological characteristics of the finished polymer. The balance between the structural unit content of styrene, 1,4 and 1,2 butadiene along the chain is the most
important parameter affecting the Tg of the material. Most interestingly, the
23 concentration of 1,4 trans units has a strong influence on the strain induced
crystallization of the rubber, which means a reinforcing effect on the tensile ultimate properties: in this sense, natural rubber shows a strain induced crystallization
behavior. Moreover, the relative concentration of 1,4 and 1,2 units may influence the thermal stability of the polymer. The oxidative degradation of the rubber starts from
the addition of oxygen on a double bond: if the double bond id part of the main chain, as in the case of 1,4 units, the reaction will lead to a chain scission.
2.9
Polymer
Nowadays, the polymer industry has grown to be larger than the metals industries, as polymers have already had a range of applications in nowadays
industry. These included adhesive, coatings, foams and even to packaging materials to textile and industrial fibers industry. Polymer is a large molecule
macromolecule composed of repeating structural units typically connected by covalent chemical bonds. Plastic is the most synonyms with this term and this term
actually refers to a large class of natural and synthetic materials with a variety of properties. Polymers have become an essential and ubiquitous role in everyday
life due to the extraordinary range of properties accessible in polymeric materials, from plastics and elastomers on the one hand to natural biopolymers such as DNA
and proteins that are essential for life on the other. A simple example is polyethylene, whose repeating unit is based on ethylene IUPAC name ethene
monomer. Most commonly, as in this example, the continuously linked backbone of a polymer used for the preparation of plastics consists mainly of carbon atoms.
However, other structures do exist; for example, elements such as silicon form familiar materials such as silicones, examples being silly putty and waterproof
plumbing sealant. The backbone of DNA is in fact based on a phosphodiester bond, and repeating units of polysaccharides e.g. cellulose are joined together by
glycosidic bonds via oxygen atoms. Natural polymeric materials such as shellac, amber, and natural rubber have been in use for centuries. The list of
syntheticpolymers includes synthetic rubber, Bakelite, neoprene, nylon, PVC,
