PP stands for polypropylene while PET stands for polyethylene terephthalate. The key difference between PP and PET is that PP is a saturated polymer, whereas PET is an unsaturated polymer. Also, PP is produced via addition polymerization of propylene while PET is produced via condensation polymerization of ethylene glycol and dimethyl terephthalate.
Moreover, applications of PP include the production of films for food packaging, textile industry (for the production of carpets, etc.), production consumer goods, etc. Meanwhile, PET is important for the production of soft drink bottles, production of fibers for clothing in the textile industry, production of containers for food and beverage storage, as a substrate in thin-film solar cells, as a waterproofing barrier in undersea cables, etc.