The results of an infrared spectroscopic characterization of poly(vinyl cinnamate) (PVCIN) and its blends with poly(4-vinyl phenol) (PVPh) are reported before and after photo-crosslinking the PVCIN by exposure to UV radiation. The purpose of this article is to demonstrate methodology, and it is shown that quantitative analysis of the fraction of unsaturated (-C=C-) double bonds, "free" (non-hydrogen bonded) and hydrogen bonded unsaturated (-CO-C=C-) and saturated (-CO-C-C-) acetoxy carbonyl groups is feasible in these blends as a function of UV exposure time.