The initiation of the polymer chain growth is brought about by free-radicals produced by the decomposition of compounds called initiators. Initiators are thermally unstable compounds and decompose into free-radicals. The decomposition can be induced by heat energy, light energy or catalysts. Mainly peroxides, hydroperoxides, peracids and peresters are useful as initiators. Commonly used catalysts are Methyl Ethyle ketone Peroxide, Benzoyl Peroxide, Hydrogen Peroxide etc.