Cage octasilsesquioxane-pendant polynorbornenes connected with short spacers exhibiting optical transparency

Heptaisobutyl-norbornenylethyl-substituted cage octasilsesquioxane (POSS) (1a) and heptaphenyl-norbornenylethyl-substituted POSS (1b) were subjected to ring-opening metathesis polymerizations (ROMP) at room temperature with the Grubbs 2nd generation catalyst. The metathesis polymerizations of 1a and 1b were performed at room temperature for 3 h with initial monomer molar concentrations of [1a, 1b] = 10 mM, and the number average molecular weights (M_n) of 2a and 2b were 82,000 g/mol and 87,000 g/mol, respectively. Dynamic light scattering (DLS) and static light scattering (SLS) measurements showed that the R_g/R_h value for 2a was 4.91, suggesting the formation of polydisperse rod-shaped particles. Chloroform solutions of 2a and 2b were cast onto glass substrates and dried at room temperature to obtain optically transparent free-standing films. X-ray diffraction (XRD) analyses of the casted films revealed their amorphous natures. Thermogravimetric analyses (TGA) of 2a and 2b under N₂ atmospheres showed 5 wt% losses (T_d5) at 416 °C and 451 °C, respectively. The POSS-pendant polynorbornenenes connected with short spacers exhibited showed high optical transparencies owing to the prevention of POSS crystallization and the excellent thermal stability.