Well-Defined Synthesis of Poly(dimethylsiloxane) Homopolymers

MARIO D. NINAGO; ANGEL J. SATTI; JORGE A. RESSIA; ANDRÉS E. CIOLINO; ENRIQUE M. VALLÉS; MARCELO A. VILLAR

Roma, Italia

Congreso; 9th International Conference on Chemical and Process Engineering; 2009

AIDIC

Poly(dimethylsiloxane) (PDMS) is a silicon-based homopolymer that can be regarded as derivative of inorganic silicates by partial substitution with methyl groups. This fact offers a wide spectrum of properties that cannot be offered by common organic polymers, which result from the combination of the polar Si-O backbone with the contribution of the organic groups. Among these properties, we can mention a low glass transition temperature; high gas permeability; usability over a wide range of temperatures; low chemical reactivity; and essentially a non-toxic nature. Therefore, PDMS are used as rubbers, resins, dielectric multimedia, hydraulic or heat transfer fluids, lubricants, medical materials and surfactants among other application. The synthesis of PDMS usually starts with dichlorosilanes by hydrolysis and condensation, giving cyclic and linear polymers. This method of synthesis results in a poor molecular weight control of the resulting polymers which provides polymers that cannot be used as model material for special purposes. Therefore, in order to have a better control of the molecular parameters, the above mentioned method of synthesis was gradually replaced by ring opening polymerization (ROP) of cyclic siloxanes. Kinetically controlled polymerization of PDMS is based on anionic polymerization of hexamethyl(cyclotrisiloxane) (D3), and is quite similar to living polymerization. This method of synthesis allows the preparation of nearly monodisperse PDMS with tailored structures, and is based on a chain extension reaction in which a particular catalyst reacts with D3 to yield short silanolate-ended chains that are able to attack other D3 molecules to yield the desired polymer. Since the ring opening polymerization of D3 is affected by several parameters (solvent, temperature, reaction time, etc.), in this work we wish to present a method that allows preparing model PDMS polymers with a precise control of molecular weight and molecular weight distributions ranging from 10,00 - 100,000 g/mol and polydispersity indexes lower than 1.09