Which one of the following polymers is prepared by addition polymerisation?

               Polymers formed by addition of monomers:

• monomers must be unsaturated
•  emperical formula of monomer and addition polymer are always same
• can be formed by free radical or ionic mechanism small molecules like CO₂, H₂O
  are not released
  Example: Polythene, polypropene, PVC, teflon, polyvinyl cyanide, polystyrene.

• (1) Dacron or terylene or polyester:
      it is a condensation polymer or step growth polymer.
  (3) Nylon-6,6:
• It is a polyamide
•  It is a condensation polymer
  (4) Novalac:
• Condensation polymer Reaction of phenol with formaldehyde gives o-hydroxymethyl phenol.
  Further reaction with phenol gives a linear product novolac. On heating with formaldehyde, novolac undergoes further polymerisation to give crosslinked polymer bakelite.