New polysilalkylenes: synthesis and gas-separation properties

A series of polysiltrimethylenes with different substituents at the silicon atom, as well as new polydimethylsilmethylene, were synthesized by the ring-opening polymerization of the corresponding sila- and disilacyclobutanes. For the first time, the copolymerization of dimethylsila- and tetramethyldisilacyclobutanes was carried out with formation of permethylsilalkylene elastomers containing a controlled number of silmethylene and siltrimethylene units in the main chain. Permeability coefficients of n-alkanes C1-C4 were measured for the prepared silalkylene homopolymers and copolymers by mass spectrometric and barometric techniques. An analysis of the permeability, solubility, and diffusion coefficients indicated that the separation of hydrocarbons proceeded according to a solubility-controlled mechanism. Polysilalkylenes with various structures of radicals at the Si atom were applied onto the surface of porous hollow fibers. The study of gas-separation parameters of the obtained composite membranes showed that they dramatically depended on the type of substituents at the Si atom. The series of polypermethylsilalkylenes are promising as membrane materials for the separation of hydrocarbon gases.