Detailed Kinetic and Mechanistic Insight into Radical Polymerization by Spectroscopic Techniques

Abstract

The in-depth understanding of the kinetics and mechanism of conventional and reversible deactivation radical polymerization (RDRP) strategies requires efficient techniques to attain accurate rate coefficients of the individual reaction steps. Within the recently developed SP-PLP-EPR technique, pulsed-laser polymerization (PLP) induced by a laser single pulse (SP) is carried out in conjunction with highly time-resolved EPR detection of the type and the concentration of radicals. The method provides an unrivaled direct access to the measurement of chain-length-dependent termination and also of propagation rate. Even for systems where as a consequence of transfer reactions different types of radical species with distinctly different properties occur, a full kinetic analysis is within reach. The SP-PLP-EPR technique is also applicable toward the measurement of RDRP-related rate coefficients for reversible addition–fragmentation transfer (RAFT) polymerization, atom transfer radical polymerization (ATRP), and organometallic-mediated radical polymerization (OMRP). Investigations into the latter two polymerization strategies benefit from additionally applying UV/vis/NIR in conjunction with Mössbauer spectroscopy to monitor reactions of the metal catalyst.

Online Monitoring of Polymerizations: Current Status

“…Spectroscopic techniques are employed extensively for the monitoring and control of chemical processes. The understanding of the kinetics and mechanism of conventional and reversible deactivation radical polymerization (RDRP) strategies by offline spectroscopic techniques was recently reviewed by Buback et al [7] This review focusses on the continuous in/online monitoring of polymerization processes based on spectroscopic techniques in the polymer production stage.…”

3D Printing Amorphous Polysiloxane Terpolymers via Vat Photopolymerization

“…This “click” reaction proceeds with rapid rates and high yields, insensitivity to water and oxygen (which both remain highly soluble in silicones), mild conditions, and without the formation of by‐products . Furthermore, the step‐growth polymerization kinetics of thiol–ene reactions allows for higher overall conversions prior to vitrification as compared to typical addition polymerization (e.g., acrylates), which results in reduced polymerization shrinkage and improved network homogeneity . Consequently, the thiol–ene reaction offers attractive advantages for covalently crosslinked polysiloxane elastomers …”

“…[24] Furthermore, the step-growth polymerization kinetics of thiolene reactions allows for higher overall conversions prior to vitrification as compared to typical addition polymerization (e.g., acrylates), which results in reduced polymerization shrinkage and improved network homogeneity. [25] Consequently, the thiol-ene reaction offers attractive advantages for covalently crosslinked polysiloxane elastomers. [26][27][28][29][30][31][32] The thiol-ene reaction has received wide attention in vat photopolymerization (VP) which is a class of layer-wise additive manufacturing (AM) that produces solid objects from liquid photopolymers upon irradiation with electromagnetic radiation (e.g., UV light).…”

Modeling of Semibatch Solution Radical Copolymerization of Butyl Methacrylate and 2‐Hydroxyethyl Acrylate

“…Propagation kinetics, for example, of styrene, alkyl and functional methacrylates, and alkyl acrylates are now well understood after application of the IUPAC recommended pulsed laser polymerization‐ size exclusion chromatography (PLP‐SEC) technique. Understanding of radical termination kinetics has also been generalized, with knowledge gained from PLP techniques coupled with electron paramagnetic resonance (EPR) spectroscopy to monitor radical concentrations, as summarized in a recent update from Buback et al…”