Q.Write structure of natural rubber and neoprene rubber along with the name and structure of thier monomers.

Elastomers are popularly called rubbers, used in balloons, shoe soles, tyres, surgeon's gloves and garden hoses. Natural rubber's monomer is isoprene (2-methyl-1,3-butadiene, CH2=C(CH3)-CH=CH2); natural rubber is a high molecular mass linear addition polymer of isoprene (polyisoprene), with molecular mass ranging from about 130,000 to 340,000 u (roughly 2000-5000 monomer units per chain). Its double bonds are locked in the cis configuration, and the resulting chains are held together only by weak van der Waals forces, giving a loosely coiled structure that lets the material stretch like a spring and spring back -- the hallmark of elasticity. Natural rubber first reached the market in the early 19th century, recovered entirely from wild Hevea brasiliensis trees of the Amazon basin (about 35% hydrocarbon in the bark latex); today roughly 1.5 million tonnes reach the market yearly, tapped as a milky latex that is coagulated into amorphous solid rubber with a coagulant such as acetic acid. Synthetic rubbers built to similar elastomeric principles include Buna-S (SBR, from butadiene + styrene) and neoprene (from chloroprene), both of which are addition polymers vulcanized to improve their properties, and both of which can outperform natural rubber in specific respects such as abrasion resistance (Buna-S) or resistance to oils, heat and light (neoprene).