Buna-S is a copolymer of butadiene and styrene. It is prepared by copolymerisation of 1,3 butadiene and styrene along with sodium. It is used for making tyres, and conveyor belts. This rubber is slightly inferior to natural rubber in its physical properties. Polymer – is a large molecule composed of repeating structural units connected by covalent bonds. Copolymer – a polymer made from more than one kind of monomer.