PP was invented in early 1950s by independent groups in the United States and Europe. The commercial production of PP began in 1957 in the USA and in 1958 in Europe. Commercially available PP contains predominently isotactic isomer which has the highest strength than the other two syndiotactic and atactic somers. Now-a-days PP copolymer are available which are less crystalline and more impact resistant than PP homopolymers. PP is manufactured by number of methods. In one of the commercially important processes, Himont's Spheripol process, Polymerisation takes place in a loop rector filled with liquid propylene. The liquid monomer, catalyst system, comonomer in the case of copolymer and hydrogen for molecular weight control are continuously fed into a loop reactor in which polymerisation takes place at 60-80ºc and 3.5 to 4 Mpa pressure. The polymer is continuously discharged from the reactor and the unreacted monomer is pumped back into the reactor for polymerisation.