Temperature Effects in Conventional and RAFT Photopolymerization

• Published in: Macromolecules Vol. 58; no. 1; pp. 488 - 494
• Main Authors: Nwoko, Tochukwu, Zhang, Bo, Vargo, Taylor, Junkers, Tanja, Konkolewicz, Dominik
• Format: Journal Article
• Language: English
• Published: United States American Chemical Society 14.01.2025
• Subjects: activation energy; gel chromatography; photochemistry; polymerization; styrene; temperature
• ISSN: 0024-9297; 1520-5835; 1520-5835
• DOI: 10.1021/acs.macromol.4c02001

Photochemical processes are often thought to be temperature-independent. However, photochemical polymerization involves photochemical processes such as light-driven radical generation coupled with thermal-driven reactions such as monomer propagation. The apparent activation energy of propagation, E A(R p), of a series of three monomers, methyl acrylate (MA), methyl methacrylate (MMA), and styrene (STY), are deduced from Arrhenius analysis of conventional and RAFT photopolymerization of these monomers across a range of corresponding temperatures. The deduced E A(R p) was compared with the benchmarked E A(k p) derived from pulse laser polymerizations coupled with size exclusion chromatography (PLP-SEC). For conventional photopolymerization of MA, MMA and STY, the relatively small discrepancy between the photopolymerization-derived E A(R p) and the E A(k p) from PLP-SEC was rationalized due to temperature-induced changes in termination. The deviation between the E A(R p) measured in RAFT photopolymerization and E A(k p) from PLP-SEC depends on the retardation strength in RAFT polymerizations. MMA and STY monomers are characterized with minimal retardation and recorded excellent agreement in PLP-SEC and RAFT-derived E p values. However, the RAFT photopolymerization of MA, which is subject to strong retardation, had a much larger E A(R p) than the E A(k p) from PLP-SEC. The high apparent E A(R p) in RAFT polymerization of MA is likely due to the added influence of temperature-induced changes in the RAFT equilibrium. Overall, these results rationalize temperature-dependent effects in photochemical reactions.