Cationic UV curing behavior and thermal properties of oxetane‐modified polysiloxane prepared from tetraethyl orthosilicate

The oxetane‐modified polysiloxane (Oxe‐PSiO) was synthesized via the partial hydrolysis/condensation of tetraethyl orthosilicate (TEOS) and then transesterification reaction with 3‐ethyl‐3‐(hydroxymethyl)oxetane (EHO), and characterized by FT‐IR, ¹H NMR, ¹³C NMR, and ²⁹Si NMR spectroscopy. Using the water/TEOS molar ratios of 0.8–1.2, the number‐average molecular weights and polydispersity indices were obtained by GPC to range from 1.013 to 2.716 g mol^?1 and around 2.0, respectively. The viscosity of Oxe‐PSiO prepared from the water/TEOS molar ratio of 1.2 sharply increased to 177,545 cps from 438 cps of that from the molar ratio of 0.8. A series of cationic UV‐curable formulations were prepared by blending the Oxe‐PSiO synthesized with the water/TEOS molar ratio of 1.0 into an commercial oxetane‐based resin, 3,3′‐oxydi(methylene)]bis(3‐ethyloxetane), in different weight ratios. The photopolymerization kinetics studied by photo‐DSC in the presence of triphenylsulphonium hexafluoroantimonate as a cationic photoinitiator showed that both the maximum photopolymerization rate and final oxetane conversion in the cured film decreased with increasing Oxe‐PSiO loading mainly due to the sharp increase in viscosity. The DMTA and DSC results both indicated the improvement in thermal stability, showing 12 and 13.4°C, respectively, higher T_g for the cured film with 50 wt % Oxe‐PSiO loading compared with the pure polymer. Moreover, the temperatures (T_10% and T_50%) at the weight loss of 10 and 50% and final char yields measured by TGA increased with increasing Oxe‐PSiO content. After adding 50 wt % Oxe‐PSiO, compared with the pure polymer the T_10% increased from 349 to 361°C, while the T_50% increased from 409 to 424°C, and with a char yield increase of 8.2% at 800°C. In addition, its greatly increased crosslinking density due to the formation of silica network resulted in the enhancement in pencil hardness from B of the pure polymer to 2H grade. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011