Poly(ethylene terephthalate) was degraded by transestrification with oligoesters made by conversion of azelaic or adipic acid, glycerol, diethylene or dipropylene glycol and 2-ethylhexanol at 190-210 degrees C to resp. oligoterephthalates used then as plasticizers of poly(vinyl chloride) (PVC). Use of the plasticizers resulted in an improvement of mech. properties of PVC.