Determining Free-Radical Propagation Rate Coefficients with High-Frequency Lasers: Current Status and Future Perspectives

Detailed knowledge of the polymerization mechanisms and kinetics of academically and industrially relevant monomers is mandatory for the precision synthesis of tailor-made polymers. The IUPAC-recommended pulsed-laser polymerization-size exclusion chromatography (PLP-SEC) approach is the method of choice for the determination of propagation rate coefficients and the associated Arrhenius parameters for free radical polymerization processes. With regard to specific monomer classes - such as acrylate-type monomers, which are very important from a materials point of view - high laser frequencies of up to 500 Hz are mandatory to prevent the formation of mid-chain radicals and the occurrence of chain-breaking events by chain transfer, if industrially relevant temperatures are to be reached and wide temperature ranges are to be explored (up to 70 C). Herein the progress and state-of-the-art of high-frequency PLP-SEC with pulse repetition rates of 500 Hz is reported, with a critical collection of to-date investigated 500 Hz data as well as future perspectives for the field. The pulsed laser polymerization-size exclusion chromatography (PLP-SEC) approach is the method of choice for the investigation of propagation rate coefficients and Arrhenius parameters in free radical polymerization. An overview of the state-of-the-art of high-frequency PLP and monomers studied via 500 Hz PLP is provided and observed trends and family-type behavior are critically described, jointly with a future perspective for the field.