Chlorinated PVC :

Chlorination efficiently can modify PVC, which can increase chlorine content to 67%.
The new material has a great heat resistance so can mainly use for hot water pipe and fittings, but it is very expensive and it is found only in niche applications, for example certain water heaters and certain specialized clothing.
An extensive market for chlorinated PVC is in pipe for use in office building, apartment and condominium fire protection.
CPVC, as it is called, is produced by chlorination of aqueous solution of suspension PVC particles followed by exposure to UV light which initiates the free-radical chlorination.