Monitoring of the Shrinkage during the Photopolymerization of Acrylates Using Hyphenated Photorheometry/Near-Infrared Spectroscopy

This article describes a new method for the quantitative determination and time-resolved monitoring of the polymerization shrinkage during ultraviolet (UV) photopolymerization. It is based on rheometry using a modified oscillating rheometer. Shrinkage is determined from the decrease of the gap between the rheometer plates. Moreover, near-infrared (NIR) spectra can be recorded directly in the rheometer, which allows continuous determination of the conversion at any time of a shrinkage measurement. As both shrinkage and conversion data come from the same experiment, shrinkage can be analyzed in dependence on the current conversion achieved during UV irradiation, which enables direct investigation of correlations between both parameters. Hyphenated photorheometry/FT-NIR spectroscopy was used for the determination of the polymerization shrinkage of pure acrylate monomers and oligomers as well as acrylate-based formulations. Quantitative shrinkage values were found to be in excellent correlation with data that were determined by an independent method (via buoyancy measurements) and data from literature. Furthermore, the effect of ambient and irradiation conditions or the content of nanoparticles on the degree of shrinkage was studied. (c) 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2015, 53, 729-739