Pulsed laser polymerization of alkyl acrylates : potential effects of the oxygen presence and high laser power

Unexpected difficulties are encountered in the determination of propagation rate coefficients (kp) in free radical polymerization of alkyl acrylates by pulsed laser polymerization (PLP), mainly due to intramolecular transfer to polymer. This article is focused on the role played by the high laser power in these difficulties and the possible reactions of mid-chain radical with residual oxygen. Removing the oxygen by simple bubbling of nitrogen is sufficient to avoid alteration of the polymerization kinetics of acrylates by residual oxygen under PLP conditions. Moreover, no degradation of polymer (or solvent) has been detected after irradiation with the high laser power typically used in PLP experiments. However, it has been shown that this high laser power completely prevents from having a temporally and spatially homogeneous radical concentration in the PLP cell. A model is proposed here to simulate the pulsed laser polymerization taking initiator consumption and laser energy absorption into account. According to our simulation results, this non-negligible initiator consumption and laser power absorption can indeed have a positive influence, i.e., it favors the obtainment of a bimodal molar mass distribution fulfilling the IUPAC consistency criteria. This observation may contradict the idea that PLP-SEC is not suitable to determine accurate kp values for acrylates above 20–30 8C.