Question

Isotactic polypropylene polymer is one, in which:
(A) All the methyl groups are on one side of the extended chain. It is highly crystalline, has a high melting point and forms strong fibres.
(B) the methyl groups present alternates regularly from one side to the other
(C) the methyl groups are distributed at random. It is a soft, elastic and rubbery material
(D) None of these

Answer 1

Tacticity is actually observed in macromolecules and it is related to the relative stereochemistry of chiral centres which are adjacent to each other in the macromolecules. The isotactic polymer is a polymer in which the repeating units have the same stereochemical configuration.

Complete step by step solution:
-Tacticity is the stereochemistry of adjacent chiral centres in a macromolecule. It has significance in polymers. In vinyl polymers, tacticity is seen as-the repeating unit has a substituent R on one side of the polymer backbone which is followed by the next repeating unit which has a substituent on the same side as the previous one or the other side of the previous one or is positioned randomly from the previous one.
In polymers, it is of three types- Isotactic polymers, syntactic and atactic.
-In syntactic polymers, the substituents are in the alternate positions along the chain and in atactic substituents are placed randomly along the chain.
-In isotactic, all the substituent are on one side of the chain backbone. In polypropylene, the substituent R is a methyl group. So, in isotactic polypropylene, the entire methyl group will be on the same side of the chain backbone. Isotactic propylene can be denoted as iPP. It can be produced at low temperatures and pressure using the Ziegler-Natta catalyst.

Therefore, the correct answer is option (A) all the methyl groups are on one side of the extended chain. It is highly crystalline.

Note: Due to the arrangement of the substituent on the same side, isotactic polypropylene is very stiff with a high melting point and is oxidation sensitive. It is used in fabrics for home furnishing and polypropylene fibres are used in numerous industries such as rope and cordage, diapers and etc.