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 nearinfrared 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 R p) when considering the rate of development of mechanical properties (cure speed).

Real‐Time NMR. How Fast Can We Do It?

“…Nano-gel is already formed on initial stages of UVcuring where hardly any change in viscosity is observed, as was shown by real-time rheological studies of UV-curing of acrylates. [6] The component with long decay time (T 2 1 ) corresponds to the relaxation of non-network fraction and unreacted oligomers. The distinction between a non-network ('sol' and network defects) fraction and network chains is made in this study on the basis of the distinct differences in molecular mobility, as reflected by the T 2 relaxation behaviour.…”

“…[6] The fraction of gel increases at the expense of the sol fraction with increasing curing time. The rate of increase in gel content slows down with the reaction time ( Figure 3).…”

“…[4][5][6] This method relies on interpretation of volume average macroscopic properties with a number of assumptions and, therefore, does not provide information about network topology at intermediate conversion of reaction groups. [7] Network structure development during photocuring has received little attention mainly because of a lack of techniques that allow to zoom on nano-scale topology on polymer networks.…”

Rheological Investigation of the Gel Time and Shrinkage in Hybrid Organic/inorganic UV Curable Films

“…After a short time, the complex viscosity starts to grow up rapidly which is an evidence of the polymerization process [28]. The initial plateau part of the curve at the very beginning stage of polymerization has also been observed in other studies [19,29,30]. At the initial stage of the curing, the modulus of the formulation is too low and cannot be measured accurately.…”

“…At the initial stage of the curing, the modulus of the formulation is too low and cannot be measured accurately. After a few seconds, the modulus increases enough for the system to be measured accurately [30].…”