Previous Year Papers

Download Solved Question Papers Free for Offline Practice and view Solutions Online.

Test Series

Take Zigya Full and Sectional Test Series. Time it out for real assessment and get your results instantly.

Test Yourself

Practice and master your preparation for a specific topic or chapter. Check you scores at the end of the test.

141.
Elaborate the structure of natural rubber.

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.

251 Views