What is lipofectamine 2000? i know from its site that it contains some cationic lipid and polymers. I want to know which cationic lipid and what polymers they have used. do anyone know about its chemical composition.

"Lipofectamine™ 2000 Transfection Reagent is a proprietary formulation......"

....the important term being "proprietary". It would be interesting to check whether they have a patent for the compound - if so you'll see more details on the composition. However, it could be being held as a corporate secret, in which case there will be no patent info - just a trade mark registration on the name.