Kinetic modelling and optimization of the trifluoropropylmethylsiloxane polymerization

Publisher Website
Google Scholar
Abstract
Use of promoter dimethylsulfoxide (DMSO) in conjunction with initiator normal butyllithium has resulted in rapid and controllable ring‐opening polymerization of 1,3,5‐tris‐(3′,3′,3′‐trifluoro‐propyl)1,3,5‐trimethylcyclotrisiloxane at 40°C; monomer consumption rate can be varied by at least four orders of magnitude depending on the ratio of promoter‐to‐initiator concentrations. Compared to the sodium counterion also studied here, the lithium initiator slows the backbiting alkyl‐reactions which cause degradation of polymer to cyclics containing four or more fluoroal‐kylsiloxy units. This previously uninvestigated polymerization methodology offers greater opportunity for capturing high, nonequilibrium polymer yield of this fluoroalkylsiloxane through appropriately timed termination of the reaction. To facilitate this optimization, a kinetic model of the polymerization was developed by solving the isothermal, constant density rate expressions for a two‐step, series mechanism. The solution to the coupled system of nonhomogeneous ordinary differential equations is obtained by matrix variation of parameters. The rate constants were determined by appropriate kinetic analysis of the experimental data obtained for polymer and cyclics concentrations as a function of time under various conditions. This results in a quantitative model capable of predicting optimum polymerization time to maximize the yield of poly(3,3,3‐trifluoropropylmethylsiloxane) at ca. 85–90%.
Keywords