Polymerization and Network Formation of UV-Curable Systems Monitored by Hyphenated Real-Time Dynamic Mechanical Analysis and Near-Infrared Spectroscopy

Abstract

Hyphenated rapid real-time dynamic mechanical analysis (RT-DMA) and time-resolved near-infrared spectroscopy (RT-NIRS) have allowed simultaneous monitoring of acrylate photopolymerizations with regard to both their chemical conversion and mechanical properties. Up to 374 NIR spectra and up to 50 DMA data points can be accumulated within a second. We observe that modulus buildup does not linearly follow chemical conversion of acrylate bonds. The gel point is detected after passing a certain critical acrylate conversion. Beyond the gel point (determined when the phase angle drops below 45°) network formation proceeds exponentially with acrylate conversion. Experimental data reveal a critical dependence of the mechanical property development during the later stage of acrylate conversion. The experimental results across the modulus−conversion plot reveal the importance of final acrylate bond conversion as opposed to the early part of the conversion vs time (maximum rate of polymerization Rp) when considering the rate of development of mechanical properties (cure speed).