Facile preparation of a soluble polymer containing polyhedral oligomeric silsesquioxane units in its main chain

Abstract

A soluble polymer containing polyhedral oligomeric silsesquioxane (POSS) units in its main chain was successfully prepared in one-step by hydrolytic condensation of a mixture of two types of amino group-containing organotrialkoxysilanes using the aqueous trifluoromethanesulfonic acid (CF₃SO₃H) as a catalyst. In this CF₃SO₃H-catalysed synthesis, 3-(2-aminoethylamino)propyltrimethoxysilane and bis[3-(trimethoxysilyl)propyl]amine acted as a starting material of POSS and a cross-linker, respectively. The ²⁹Si NMR spectrum of the resulting POSS polymer only showed signals in the T³ region. The IR spectrum of the hydrophobised POSS polymer indicated a single absorption peak at 1119 cm⁻¹, attributed to the Si–O–Si stretching absorption band, but no absorption peak at ca. 3500 cm⁻¹ for silanol groups. In addition, its weight-average molecular weight was 3.24 × 10⁴. Overall, these results suggested the formation of a polymer composed of POSS units. The POSS polymer provided optically transparent films. This may result from the coexistence of POSS components bearing two different randomly distributed side-chain groups in the polymer, which suppresses crystallization. The POSS polymer exhibited 5% and 10% weight losses at 351 °C and 368 °C, respectively, indicative of its relatively high thermal stability.