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 08D0C9EA79F9BACE118C8200AA004BA90B02000000080000000E0000005F005200650066003200320037003400370031003600370030000000 . 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