Question
Elaborate the structure of natural rubber.
Solution
Natural rubber is a linear 1, 4 polymers of isoprene (2–methy1–1, 3-butadiene). In natural rubber, the original double bonds present in isoprene (between C1, = C2 and C3 = C4) are shifted between C2 and C3 and C1, of one unit gets attached to C4 of another unit and so on. All these double bonds in rubber have cis configuration and hence it is treated as 1, 4 poly-isoprene.
It is clear from the structure of rubber that no polar substituent is present, hence mainly Van der Waals forces are present in the molecules. Further, due to the cis configuration, the polymer chains are not close enough, hence the intermolecular attractive forces are very weak. Because of this reason cis-poly-isoprene chain i.e., rubber polymer is not a straight chain but forms a coiled structure which can be stretched like a spring. Rubber polymer becomes partially aligned with respect to each other, on stretching while the polymer chain reverts back to its original coiled shape on releasing the force.
It is clear from the structure of rubber that no polar substituent is present, hence mainly Van der Waals forces are present in the molecules. Further, due to the cis configuration, the polymer chains are not close enough, hence the intermolecular attractive forces are very weak. Because of this reason cis-poly-isoprene chain i.e., rubber polymer is not a straight chain but forms a coiled structure which can be stretched like a spring. Rubber polymer becomes partially aligned with respect to each other, on stretching while the polymer chain reverts back to its original coiled shape on releasing the force.
