A series of polynorbornene homo- and copolymers containing aryl- and/or hetaryl-azo dyes were prepared through ring-opening metathesis polymerization (ROMP). Thermal studies indicated that the polymers were thermally stable up to 250 °C, and possessed glass transition temperatures ranging from 93 to 133 °C. In THF solutions, the aryl-azo dye containing homopolymers, displayed λ max = 417 nm while the hetaryl-azo dye containing homopolymers displayed λ max = 495 nm. The copolymers displayed a λ max that encompassed both the aryl-and hetaryl-azo dye range. The monomers and polymers showed bathochromic shifts in solution when acidified. The polymers were cast into films that changed colour in the presence of both aqueous 1.2 M HCl or HCl (g) . The colour change reverses when exposed to aqueous 1.2 M NaOH or NH 3(g) . This process was repeated several times without disintegration of the polymer film, indicating that these polymers may be useful as reusable acid sensors.