The infrared spectra of blends of various ortho-phthalate esters with poly(vinyl chloride) and vinylidene chloride/(20%)acrylonitrile copolymer were recorded. The data indicate that the lowering of the ester carbonyl absorption frequency is due to a dipole-dipole/complex type interaction between the carbonyl of the ester and the chlorine of the polymer in addition to hydrogen bonding with acidic hydrogens. The lowering of the absorption frequence increases with an increase in the amount of chlorine in the polymer chain.
Edison C. Dessain and Dennis Anderson, "A Study of the Interaction of Phthalate Esters with Chlorine-Containing Polymers," Appl. Spectrosc. 46, 152-155 (1992)