Enhancement of the physical properties of poly((2-terthiophenyl)norbornene) through cross-linking pendant terthiophenes

The synthesis of norbornene polymers containing 2-terthiophenyl side chains, poly((2-terthiophenyl)norbornene), by ring-opening metathesis polymerization (ROMP) and the cross-linking of pendant terthiophene units to form conductive polymers is reported. Physical characteristics including conductivity, thermal stability, electrochromic activity, fluorescence, and surface topography are evaluated for the resulting cross-linked ROMP polymers and compared to those of poly(terthiophene). The in-situ conductivity of cross-linked ROMP polymer films doped with PF ₆ ^- was approximately half that of poly-(terthiophene) films. However, thermal stability was substantially higher for powders formed from chemically cross-linked ROMP polymers, which retained 60% of their total mass at 800°C compared to a total decomposition of non-cross-linked ROMP polymers at 500°C. Electrochemically deposited films of cross-linked ROMP polymers proved to have considerably higher thermal stability and smoother, more uniform surfaces than films of poly(terthiophene). The root-mean-square value of electrochemically cross-linked ROMP polymer films, derived from atomic force microscopy images (AFM), was approximately 6 nm while that of poly(terthiophene) films prepared in the same manner was 118 nm. These cross-linked films display a reversible electrochromic color change when oxidatively doped.