Kinetics of heterogeneous polymerization of glycidol with B(C6F5)3 in toluene in the absence and presence of water
The synthesis of polyglycidol (or polyglycerol) using tris-(pentafluorophenyl)borane [B(C6F5)3] as a catalyst produces a branched structure with a cyclic core by a mechanism of zwitterionic ring expansion polymerization. The solvent choice is limited since the polymerization does not occur in good s...
| Autores: | , , , , , , |
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| Tipo de recurso: | artículo |
| Estado: | Versión publicada |
| Fecha de publicación: | 2024 |
| País: | España |
| Institución: | Consejo Superior de Investigaciones Científicas (CSIC) |
| Repositorio: | DIGITAL.CSIC. Repositorio Institucional del CSIC |
| OAI Identifier: | oai:digital.csic.es:10261/387659 |
| Acceso en línea: | http://hdl.handle.net/10261/387659 |
| Access Level: | acceso abierto |
| Palabra clave: | Polyglycidol Polyglycerol Cyclic polymer Ring polymer Polymerization mechanisms DFT calculations |
| Sumario: | The synthesis of polyglycidol (or polyglycerol) using tris-(pentafluorophenyl)borane [B(C6F5)3] as a catalyst produces a branched structure with a cyclic core by a mechanism of zwitterionic ring expansion polymerization. The solvent choice is limited since the polymerization does not occur in good solvents for polyglycidol (e.g. DMF, DMSO). In poor solvents for polyglycidol but good solvent for glycidol (e.g. toluene), the polymerization does occur but in a heterogeneous manner. The polymer precipitates during reaction forming two phases, the solution and precipitated phase. In the presence of water a competitive initiation mechanism consisting in the formation of hydronium ions by reaction between B(C6F5)3 and two water molecules, followed by the protonation of glycidol (Gly) epoxide is the responsible for the formation of analogous linear-core structures. In present study we evaluated the kinetic parameters of the initial stage of polymerization of Gly with B(C6F5)3 in the presence and absence of water by in situ 1H NMR monitoring in toluene-d8 phase. The results indicated first order kinetics with respect to Gly and B(C6F5)3, zero order with respect to water, similar initial rate constants for the polymerization initiated by B(C6F5)3 and H3O+ and similar activation energies for the polymerization in the absence and presence of water. The decrease in intensity of the 19F NMR signal relative to the initial value indicated that B(C6F5)3 goes to a precipitated phase just after the polymerization started due to a change in the solubility of the formed oligomeric active chains that carry the catalyst. In the precipitate, the reaction continued due to chain fusion events that take place increasing the molecular weight and producing a product with identical mass distribution as that of a polyglycidol produced under dry and solvent-free conditions. Density functional theory calculations supported the kinetic data by obtaining similar energy barriers and thermodynamic enthalpies for the reaction of Gly with B(C6F5)3 and H3O+. |
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