Synthesis and oxygen permeation of novel well-defined homopoly(phenylacetylene)s with different sizes and shapes of oligosiloxanyl side groups

Six new silicon-containing phenylacetylenes having short oligosiloxane substituents with different sizes and shapes have been synthesized. Homopolymerization of the monomers yielded the corresponding homopoly(substituted phenylacetylene)s with high molecular weights and good solubility. These comb-shaped homopolymers gave self-standing membranes whose P O 2 and P O 2 / P N 2 could be measured. We discuss the effect of the chemical structures on their membrane performances together with the other seven related polymers we synthesized before and commercially available cross-linked polydimethylsiloxane (PDMS). While the homopolymers with linear oligodimethylsiloxanes (ODMS) show very high P O 2 values which are higher than PDMS, the homopolymers with branched ODMS show high P O 2 / P N 2 values which are close to that of poly(phenylacetylene) (poly(PA)) and, in addition, had ten times higher P O 2 than poly(PA). Introduction of the branched spherical ODMS substituents increases P O 2 without any drop of P O 2 / P N 2 and introduction of the linear ODMS substituents increases P O 2 largely which is higher than that of PDMS. It was found that the chemical structures, i.e., the shapes of the ODMS substituents were more important than that of composition for determining their performance as oxygen permselective membrane materials. In conclusion, oxygen permeation could be tuned by changing sizes and shapes of the ODMS side groups.