Among the following polymers, how many are formed by condensation polymerisation: nylon-6,6, Dacron, Bakelite, PVC, Teflon, Buna-S, neoprene, PHBV…

Condensation polymers form by step-growth reaction of bifunctional (or polyfunctional) monomers with elimination of a small molecule such as $\mathrm{H_2O}$. Nylon-6,6 (hexamethylenediamine plus adipic acid, loses water), Dacron (ethylene glycol plus terephthalic acid, loses water), Bakelite (phenol plus formaldehyde, loses water), PHBV (3-hydroxybutanoic acid plus 3-hydroxypentanoic acid, loses water) and melamine-formaldehyde (melamine plus methanal, loses water) are condensation polymers. PVC (vinyl chloride), Teflon (tetrafluoroethene), Buna-S (buta-1,3-diene and styrene), neoprene (chloroprene), Orlon (acrylonitrile) and Buna-N (butadiene and acrylonitrile) are all addition polymers formed by chain-growth of unsaturated monomers without loss of any small molecule. The number of condensation polymers is therefore 5.