The effect of cross-linking on the dynamics of amorphous poly(vinyl cinnamate) (PVCN) below and above the glass transition temperature (T-g) was studied by means of mechanical spectroscopy. The polymer is cross-linked by irradiating it with ultraviolet light, and it is controlled by the irradiation time, where the kinetics is observed by means of Fourier transform infrared spectroscopy. The evolving links between molecules hinder molecular mobility and thus influence the mechanical loss in the material, leading to (i) a shift of T-g to higher temperatures, (ii) a substantial decrease of the strength of the corresponding a-relaxation, (iii) an increase of Young's modulus, and (iv) an increased damping of PVCN below the alass transition.