Poly(trimethylsilylpropyne) copolymers with bromobutyl side chains were synthesized from 1-trimethylsilyl-1-propyne and 1-(4-bromobutyldimethylsilyl)-1-propyne using a TaCl5/Ph3Bi catalyst system in toluene. After polymerization, azide groups were introduced into the polymers by phase transfer catalysis to yield poly[(1-trimethylsilyl-1-propyne)-co-(1-(4-azidobutyldimethylsilyl)-1-propyne)] copolymers. Results from thermal analyses, elemental analyses; and IR spectroscopy confirm that the azide content in the copolymers matches the original comonomer feed ratios. Films of the copolymers were thermally cross-linked in vacuo, with the rate of azide decomposition monitored by the loss of the azide absorption band in the IR. For a copolymer with 15 mol % azide content, an activation energy of 130 kJ/mol was calculated from IR data collected over the azide- decomposition temperature range. For the copolymer with the highest azide content (20 mol %), DSC measurements give -1.2 kJ/g for the enthalpy of azide decomposition. Swelling experiments performed on the cross-linked films indicate that a relatively low cross-link density (similar to5%) is required to render membranes dimensionally stable in good solvents for the polymer.