(486e) Kinetics and Thermodynamics of the Ring Opening Reaction of Hexamethyl Cyclotrisiloxane (D3)

The ring opening polymerization (ROP) of hexamethyl cyclotrisiloxane is a promising method for the synthesis of oligo- and polysiloxanes with narrow molecular weight distributions and therefore reproducible properties.[1,2] However, side product formation, e.g. other cyclic oligosiloxanes, was observed in batch syntheses.[1]

Implementation of the ROP of D3 requires profound knowledge of its kinetics and thermodynamic properties. This project systematically characterizes all three reaction steps: the initiation, propagation and termination reaction.

Target of this project is the process transfer from batch to continuously fed reactors in order to synthesize polysiloxanes with limited chain length and well specified physical properties.

In the first step, the reaction rate of D3 with one equivalent tert-butyl lithium was investigated. The reaction is highly exothermic and obeys second order kinetics law. Arrhenius parameters were calculated for a temperature range of 30 K. The reaction is irreversible and no side products were detected during D3 consumption.

Due to the fast rate of the reaction, mixing and the design of the mixer is the critical step of this initiation reaction.

References:

[1] M. Brandstätter, Diploma Thesis 2007, Institute of Inorganic Chemistry, Graz University of Technology

[2] T. Akimoto, K. Kawahara, Y. Nagase, T. Aoyagi, Macromol. Chem. Phys. 2000, 201, 2729-2734