What is the primary structural feature necessary for a molecule to make it useful in a condensation polymerisation reaction ?

Polymers are high molecular mass substances consisting of large number of repeating structural units derived from simple molecules. The polymers formed from one type of monomers are called homopolymers and those formed from two or more different monomers are called copolymers. Depending upon the molecular forces between monomers, polymers may be classified as elastomers, fibers, thermoplastic and thermosetting polymers. The polymers may be formed simply by addition of monomers called addition polymers or by combination of two or more monomers by elimination of simple molecules, called condensation polymers. What is the primary structural feature necessary for a monomer to form condensation polymer?

The monomers used in the condensation polymerisation have__________.

The primary structure of a protein molecule has