engleski

Softening of Octyl-modified Phenyl-silsesquioxanes

Polysilsesquioxane particles prepared from phenyl-silane exhibit glass transition and softening when heated, which can be useful in preparation of transparent thick films or a matrix for conductive materials. In order to tune the properties of phenyl silsesquioxanes, hybrid phenyl-octyl polysilsesquioxanes have been prepared by a two-step acid-base catalysed process. Molar ratio of octyl- to phenyl-silanes used in preparation was 0.2, 0.3 and 0.4. Influence of solvent quantity was also studied, varying molar ratio of ethanol to silanes in 0-50 range. Polysilsesquioxanes were investigated by differential scanning calorimetry (DSC), scanning electron microscopy (SEM) and gel permeation chromatography (GPC). Well-defined spherical particles were formed only for the octyl-phenyl ratio 0.2, while higher ratios produced a solid phase which was either completely amorphous (ratio 0.4) or a mixture of particles and the amorphous phase (ratio 0.3). Increased content of octyl chains also adversely influenced level of condensation of the hybrid particles, as determined by GPC. For hybrid particles prepared with the ratio of 0.2, increased solvent quantity decreased the level of condensation as determined by GPC, but also produced particles with more homogeneous size distribution. DSC investigation of hybrid polysilsesquioxane particles showed a glass transition superimposed with endothermic effect at 50-60 °C. The endothermic effect is possibly due to evaporation of ethanol and water produced by further condensation of silanol and residual ethoxy groups in hybrid particles at temperatures above the glass transition. The amorphous hybrid polysilsesquioxanes did not exhibit a glass transition. Softening behaviour of hybrid polysilsesquioxane particles was confirmed by SEM.

sol-gel; organic-inorganic hybrids; softening

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