Differentiate the following pairs of polymers based on the properties mentioned against each.

(i) Novolac & Bakelite (structure)

(ii) Buna-S & Terylene (Intermolecular force of attraction)

When phenol and formaldehyde are heated in the excess of phenol (P/F > 1) with an acid catalyst, such as HCl, H2SO4 or oxalic acid, a linear polymer is formed which is thermoplastic in nature and is known as Novolac.

On further heating, in the presence of hexamethylene tetramine, Novolac produces 3D cross-linked networked thermosetting polymer which is known as bakelite. The hexamethylene tetramine decomposes into formaldehyde and ammonia, which is used as catalyst and HCHO decreases the P/F ratio as 0.8.

Buna-S is a addition polymerization. When 1,3 butadiene react with styrene it forms Buna-S rubber.

Terylene is a condensation polymerization. When dimethyl glycol and dimethyl terephthalate  react, it forms Terylene polymer.