Temperature Effects in Conventional and RAFT Photopolymerization.

Area of Science:

• Polymer Chemistry
• Photochemistry
• Chemical Kinetics

Background:

• Photochemical processes are often assumed to be temperature-independent.
• Photochemical polymerization combines light-driven radical generation with thermal-driven propagation reactions.

Purpose of the Study:

• To investigate the temperature dependence of photochemical polymerization.
• To determine the apparent activation energy of propagation (E_A(Rp)) for methyl acrylate (MA), methyl methacrylate (MMA), and styrene (STY).
• To compare these values with benchmark data derived from pulse laser polymerizations coupled with size exclusion chromatography (PLP-SEC).

Main Methods:

• Arrhenius analysis of conventional and RAFT photopolymerization across a range of temperatures.
• Comparison of photopolymerization-derived E_A(Rp) with PLP-SEC derived E_A(kp).

Main Results:

• For conventional photopolymerization, small discrepancies between E_A(Rp) and E_A(kp) were attributed to temperature-induced termination changes.
• RAFT photopolymerization showed deviations dependent on retardation strength.
• MMA and STY exhibited minimal retardation and good agreement between RAFT-derived E_p and PLP-SEC E_A(kp).
• MA, with strong retardation in RAFT photopolymerization, showed a significantly larger E_A(Rp) than E_A(kp).
• The high apparent E_A(Rp) in MA RAFT polymerization is likely due to temperature effects on the RAFT equilibrium.

Conclusions:

• Photochemical polymerization exhibits significant temperature dependence.
• Retardation strength in RAFT polymerization influences the observed activation energy.
• Temperature-induced changes in RAFT equilibrium contribute to the apparent activation energy in systems like MA polymerization.