Poly(diphenylacetylene) membranes having perfluoroalkyl groups were quantitatively synthesized via a three-step membrane reaction, that is, desilylation (the 1st step), Williamson reaction (the 2nd step), and Click reaction (the 3rd step). The conversions of the all reactions were confirmed by IR. spectra and elemental analysis. Even though the reactions were carried out in membrane state, the conversions were fairly high. These high conversions are attributed to high swelling property of poly(diphenylacetylenes), including the extremely large fractional free volume. The gas permeability and thermal property of the perfluoroalkylated poly(diphenylacetylene) membranes were investigated. Polymer reactions are a very useful and powerful