Studying the Curing Kinetics of a Diacrylate by Using Infrared Spectroscopy

Abstract

Fourier transform infrared (FT-IR) spectroscopy was used to study the photopolymerization of 4,4'-bis(acryloyl)biphenyl (BAB), dispersed in the liquid crystal (E7). The infrared absorbance of the carbon–carbon double bond of the acrylate group was monitored to follow the course of the polymerization and to determine the extent of cure. It was also observed that a major change in the character of the infrared absorbance band shape and position of the acrylate carbonyl group accompanied the reduction of the carbon–carbon double-bond absorbance. Curing was found to be rapid, on the order of minutes. It was found that the reaction did not proceed appreciably after a brief initial exposure to ultraviolet (UV) radiation. This result implies that this type of system may be time-stable with programmable degrees of cure. It was also discovered that single continuous doses of UV exposure produced a higher degree of cure than equivalent UV exposure times administered in multiple shorter doses. This observation indicates the existence of a relatively long induction period in this system. The long induction period may be caused by a UV screening effect due to the other components of this system.