Question

The monomer used in Novolac; a polymer used in paints is:
A. Butadiene and styrene
B. Phenol and formaldehyde
C. Butadiene and acrylo nitrile
D. Melamine and formaldehyde

Answer 1

Hint: There are different classes of polymers. Novolac is a phenolic resin type of polymer. It is extensively used in microelectronics.

Complete step by step answer: A polymer is a large molecule formed by continuous linking of many small subunits called Monomers. Basically, it is a repetition of monomers.
Another name for novolac is phenolic resin or phenol formaldehyde resin. As this suggests, the two monomers needed to form novolac are phenol and formaldehyde.
The reaction that occurs is –

The reaction stops when the formaldehyde reactant is exhausted, often leaving up to 10% of un-reacted phenol.

So, B is the correct option.

Additional information: There are two types of polymers, natural and artificial. Natural polymers are found in plants. Apart from natural and manmade, polymers are classified in various other ways.
Based on the type of monomer used and mechanism of polymerization, there are different types of polymers. Novolac is a cross linked polymer formed by condensation polymerisation. During preparation of novolac, as a general rule phenol gets substituted on both ortho and para positions. But we know that para position is almost twice as reactive as ortho. But there are twice as many ortho sites (two per phenol molecule) so the fractions of ortho-ortho, para-para and ortho-para bridges are approximately equal. In this reaction, a water molecule gets eliminated. Hence the type of polymerization mechanism is condensation. Distillation of the molten resin during manufacturing removes the excess phenol and water.

Note: To remember this easily, we can keep in mind that novolac is a phenolic resin type of polymer. It has a cross linked structure and is formed by condensation polymerization.