(628f) Scale-up of the Production of Monofunctional Polysiloxanes

Linear polydimethylsiloxanes (PDMS) have high industrial importance, however, the production of monofunctional PDMS is limited. These substances are starting materials for various inorganic-organic block copolymers¹.

Target of this project is the development of a continuously operated reactor system for the production of monohydrido-substituted polysiloxanes with 15 to 60 monomer units, a narrow molecular weight distribution and highly reproducible physical and chemical properties. The feedstock for the process is a multicomponent mixture containing various cyclic oligosiloxanes such as hexamethylcyclotrisiloxane (D3), octamethylcyclotetrasiloxane (D4) and higher analogs.

The ring opening polymerization (ROP) of D3 with tert-butyllithium (t-BuLi) is a promising route for this process. The first part of our investigation covers the kinetics and thermodynamic properties of the individual reactions shown in Figure 1. D3 is selectively polymerized from the oligosiloxane mixture. Furthermore, no side product formation was detected in the kinetically controlled regime.

Figure 1: Ring Opening Polymerization (ROP) of Hexamethylcyclotrisiloxane (D3): (a) Initiation reaction; (b) Propagation reaction; (c) Termination reaction

The second part focuses on the validation of polymerization in a laboratory scale plug flow reactor (PFR) and the investigation of the reproducibility of product properties.

¹ P. J. Miller, and K. Matyjaszewski, Macromolecules, 1999, 32(26), 8760-8767