Theoretical and Experimental Study of Light-assisted Polymerization by Multimechanism Action

A novel bicomponent alkyd system was designed to decrease the usage of Cobalt-based drier due to its latent carcinogensis. The system was polymerized using a Cobalt-salt complex as an air-sensitive drier and an isopropylthioxanthone photoinitiator as a light-sensitive accelerator, as well as using irradiation in the form of visible light. The combined influence of the two additives on autoxidation was analyzed using real-time infrared spectroscopy. The results show that isopropylthioxanthone can increase the efficiency of hydrogen abstraction at the beginning of the curing reaction. A linear free energy relationship was used to theoretically predict the hydrogen abstraction ability of photoinitiators. Nanosecond laser flash photolysis was used to obtain the quenching rate constants between alkyd monomers and isopropylthioxanthone according to the Stern-Volmer equation. The thermodynamic data of transition state theory, such as the activation energy, were calculated by using quantum chemistry program. The reaction rate constant and the Wigner tunneling factor were predicted from the result of quantum chemistry. The vertical excitation energy obtained from the time-dependent density functional theory was used to explain the anomalous behavior of the photoinitiators. These theoretical results fit well with the experimental result of linear free energy relationship. On the basis of these observed results, an accelerated mechanism of the photoassisted autoxidation of alkyd resins was proposed.