Polybutadiene
2164907
219883468
2008-06-17T08:35:34Z
Arun Kumar Basu
7302379
/* Properties */
'''Polybutadiene''' is a [[synthetic rubber]] that is a [[polymer]] formed from the [[polymerization]] of the [[monomer]] [[1,3-butadiene]]. It has a high resistance to wear and is used especially in the [[Tire manufacturing|manufacture]] of [[tire]]s. It has also been used to coat or encapsulate electronic assemblies, offering extremely high electrical resistivity. It exhibits a recovery of 80% after stress is applied, a value only exceeded by [[elastin]] and [[resilin]].
==Polymerization of butadiene==
1,3-Butadiene is an [[organic compound]] which is a rather simple [[conjugated system|conjugated]] [[diene]] [[hydrocarbon]]; the [[chemical structure]] is shown as a [[reactant]] in the diagram below. A hydrocarbon diene [[molecule]] has two carbon-carbon [[double bond]]s (i. e. between two sets of [[carbon]] atoms). Polybutadiene can be formed from many 1,3-butadiene monomers undergoing [[Radical polymerization|free radical polymerization]] to make a much longer polymer chain molecule.
A chain propagating step in this [[chemical reaction]] involves a [[free radical]] near the end of a growing polymer chain forming a [[covalent bond]] with the #1 carbon in a 1,3-butadiene monomer molecule being added, resulting in a polymer chain intermediate with a substituted [[allyl]] free radical at the end of the chain. This allyl free radical, formed from the butadiene just added, can further bond to another monomer molecule at either the #2 or #4 carbons of the previous butadiene monomer. Most of the time, the new monomer bonds to the #4 or terminal carbon of the previous butadiene, resulting in a 1,4-addition of the previous butadiene unit. In a 1,4-addition, the two double bonds of the previous butadiene unit are turned into [[single bond]]s and a new double bond is formed between the #2 and #3 carbons. This new double bond may have either a ''[[cis]]'' or a ''[[trans]]'' configuration. A smaller fraction of the time (perhaps 20%), the new monomer bonds to the #2 carbon of the previous butadiene, resulting in a 1,2-addition of the previous butadiene unit. The double bond between the #1 and #2 carbons turns into a single bond in the previous butadiene unit, and the double bond between the #3 and #4 carbons remains intact in a short [[vinyl]] side group available for [[branching]] or [[cross-linking]]. ''Cis'' or ''trans'' configurations are not applicable in 1,2-additions of butadiene. See the following reaction diagram for examples of 1,2- and 1,4-addition in a polybutadiene chain.
[[Image:1,3-Butadiene Polymerization.PNG]]
The ''trans'' double bonds formed during polymerization allow the polymer chain to stay rather straight, allowing sections of polymer chains to line up against each other and effectively form microcrystalline regions in the material. The ''cis'' double bonds cause a bend in the polymer chain, preventing polymer chains from lining up and forming crystalline regions and resulting in larger regions of amorphous polymer. It has been found that a substantial percentage of ''cis'' double bond configurations in the polymer will result in a material with flexible [[elastomer]] (rubber-like) qualities. In free radical polymerization, both ''cis'' and ''trans'' double bonds will form in percentages which depend on temperature. There are different [[catalyst]]s available which can result in polymerization either in the ''cis'' or the ''trans'' configurations.
==Properties==
Polybutadiene rubber is a highly resilient synthetic rubber. Due to outstanding resilience, it can be used for the manufacturing of golf balls. Heat build up will be less in polybutadiene rubber based vulcanizate subjected to repeated flexing during service. This property leads to the use in the sidewall of the truck tires. Good abrasion resistance of this rubber leads to the use in tread portion of truck tires; however, skidding may be the problem in passenger car tires due to low rolling resistance. For high temperature curing, polybutadiene rubber may be blended with natural rubber and other rubbers, due to resistance in reversion of physical properties. Polybutadiene rubber can be used in water seals for dam due to its low water absorption properties. Rubber bullets and road binders can be also produced by polybutadiene rubber.
Processing of Poly Butadiene Rubber will come after Properties
==Copolymers==
1,3-butadiene is normally [[copolymer]]ized with other types of monomers such as [[styrene]] and [[acrylonitrile]] to form rubbers or [[plastic]]s with various qualities. The most common form is [[styrene-butadiene]] copolymer, which is a commodity material for car [[tires]]. It is also used in [[block copolymer]]s and tough [[thermoplastic]]s such as [[ABS plastic]]. This way a copolymer material can be made with good [[stiffness]], [[hardness]], and [[toughness]].
Because the chains have a double bond in each and every [[repeat unit]], the material is sensitive to [[ozone cracking]].
Processing of Poly Butadiene Rubber
Seldom PBR is used alone. It is used with other rubbers. Poly Butadiene Rubber is difficult to band in Two roll Mixing Mill. A thin shheet may be prepared and to be kept separate. After proper mastication of Natural Rubber, when it is banded in Two roll mill, Poly butadiene Rubber may be added. Similar practice may be adopted, if PBR has to be mixed with SBR. In Internal Mixer also, Natural Rubber and/or SBR may be put first folloed by Poly Butadiene Rubber.
Plasticity of Poly Butadiene Rubber may not be reduced due to over mastication.
==See also==
*[[Polymer degradation]]
*[[Ozone cracking]]
==References==
{{Unreferenced|date=May 2008}}
[[Category:Organic polymers]]
[[Category:Elastomers]]
[[Category:Thermoplastics]]
[[Category:Polymers]]
{{Link FA|es}}
[[de:Butadien-Kautschuk]]
[[es:Polibutadieno]]
[[it:Polibutadiene]]
[[pl:Polibutadien]]