Computational determination of ring opening polymerization reaction mechanism of alpha-angelica lactone

WOS: 000447572000001In the present study, we investigated the ring opening polymerization of alpha-angelica lactone (AL) catalyzed by the tin (II) 2-ethylhexanoate, Sn(Oct)(2) through the coordination insertion mechanism by employing the semi empirical PM6, PM6-D3H4, PM7, and the DFT-B3LYP, B3LYP-D2 and omega B97X-D methods in both gas and solvent (toluene, THE, DMF and DMSO) media. The DFT calculations revealed that the initiation stage consists of three steps; a stable complex formation, a low energy conformational transformation and the ring opening. NBO analysis was conducted to explain the interactions between the electrophilic and nucleophilic centers. The omega B97X-D method gives the closest result (30.2 kcal/mol) to the experimentally found activation barrier (26.3 kcal/mol) for this system. Therefore, omega B97X-D has the best performance among all the methods studied here. The mechanism of the addition of a new monomer to the active chain, which constitutes the propagation stage of the polymerization, was further investigated and, as expected, a lower barrier compared to that of the initiation stage was obtained (14.5 kcal/mol). The PCM calculations revealed that the solvent did not affect the activation barrier. In addition, the enthalpy of ring opening polymerization of alpha-angelica lactone was calculated based on the initiation and propagation stages and the thermodynamics of the system was discussed.research foundation of Ege University-TurkeyEge University [2016 FEN 041]This work was supported by the research foundation of Ege University-Turkey (No: 2016 FEN 041). The DFT calculations reported in this study were performed at TUBITAK ULAKBIM, High Performance and Grid Computing Center (TRUBA resources)