Ab initio evidence for slow fragmentation in RAFT polymerization

Area of Science:

• Polymer Chemistry
• Computational Chemistry

Background:

• Reversible Addition-Fragmentation Transfer (RAFT) polymerization is a widely used technique for controlled radical polymerization.
• A significant retardation effect is frequently observed during methyl acrylate polymerization using cumyl dithiobenzoate as a RAFT agent.
• The underlying mechanism for this retardation effect remains incompletely understood.

Purpose of the Study:

• To investigate the molecular-level mechanisms responsible for the retardation effect in methyl acrylate RAFT polymerization.
• To elucidate the role of the RAFT adduct radical in the observed polymerization kinetics.

Main Methods:

• High-level ab initio molecular orbital calculations were employed.
• Model systems simulating key steps of RAFT polymerization, specifically focusing on methyl acrylate and cumyl dithiobenzoate, were analyzed.

Main Results:

• The calculations indicate that the fragmentation of the RAFT adduct radical is a slow process.
• This slow fragmentation step is identified as the primary contributor to the retardation effect observed in methyl acrylate polymerization.
• The energy barriers for fragmentation were quantitatively assessed.

Conclusions:

• The study provides a mechanistic explanation for the retardation effect in methyl acrylate RAFT polymerization.
• The findings highlight the importance of the RAFT adduct radical's fragmentation rate in controlling polymerization.
• This research offers insights for optimizing RAFT polymerization conditions and designing new RAFT agents.