Measurement Of Photopolymerization Kinetics Using A Thin-Film Calorimeter

Todd M Roper; C Allan Guymon; Charles E Hoyle

Photopolymerization is a field experiencing rapid growth due to its versatility, low environmental impact, and the performance of the final materials. Efforts to increase polymerization efficiency has driven recent research as evident by both discovery of monomers which display rapid polymerization rates and identification of the structural characteristics responsible for the increased rate of reaction. With these developments come new applications which are often difficult to quantitatively characterize using traditional instrumentation. The construction of versatile tools which are efficient, simple to use, inexpensive, and capable of accurately evaluating the polymerization kinetics of such highly reactive systems would significantly promote future technological advances. Measurement of polymerization kinetics has been achieved in the past using a variety of different methods such as changes in physical parameters (volume, modulus), real-time spectroscopy (IR and Raman), and calorimetry. Calorimetry is advantageous because it is not affected by crosslinking reactions and offers direct measurement of the polymerization rate. Photocalorimetry involves the measurement of heat evolved during a chemical reaction initiated by a photon of light. The polymerization rate is calculated assuming the amount of heat released is directly proportional to the number monomer units converted to polymer. Photo differential scanning calorimetry (photo-DSC) is one of the most commonly used calorimetric methods for examining bulk polymerization kinetics of unfilled systems. Despite its widespread use, photo DSC is plagued by poor time resolution (on the order of seconds), large sample volumes (not applicable to thin films), and is limited to the analysis of nonvolatile monomers. In addition, accuracy and reproducibility are problems because the exotherm curve is dependent on the distribution of sample in an aluminum sample pan. Also, instrument cost prevents its usage in many industrial settings. A photocalorimeter based upon a single thin-film heat flux senor was first developed by Wisnosky and Fantazier.4 Minor modifications and basic applications of this technology have since been documented. Based on this literature, a thin-film calorimeter (TFC) with significantly improved performance characteristics was assembled in an attempt to offer solutions to the short comings associated with photo-DSC. The superior time response and increased sensitivity of the thin-film sensor suggests many exciting new applications. The following report details the construction and application of a TFC.

Measurement Of Photopolymerization Kinetics Using A Thin-Film Calorimeter

View Online

Abstract

Details

Metrics