Experimental work was performed to elucidate the role of acids, including HCl, H₂SO₄, H₃PO₄ and CH₃COOH, to adjust the pH value of n-BTMS solutions, in the preparation of hydrophobic TiO₂. The main findings are as follows :
1. Preparation of hydrophobic TiO₂, using an n-BTMS solution consisting of n-BTMS-EtOH-H₂O(pH3.3), by the dry coupling treatment method was achieved most quickly with HCl, followed by H₂SO₄ and CH₃COOH. With H₃PO₄, it was impossible to reach the maximum M value, which is a parameter of hydrophobic degree, under the experimental conditions employed.
2. The resulting time required to achieve the same average molecular weight and average polymerization degree of n-BTMS oligomer of solution system consisting of n-BTMS-EtOH-H₂O(pH3.3), was in the sequence of HCl>H₂SO₄>H₃PO₄>CH₃COOH.
3. No matter which acid was used, an increase of drying temperature resulted in a quick increase of the M value, followed by a stagnation period.
4. When wet treatment methods were used to apply n-BTMS to TiO₂, an increasing rate of M value was found in the sequence of HCl>H₂SO₄>H₃PO₄>CH₃COOH. On the contrary, with a fixed amount of n-BTMS polymer on TiO₂, less than 30% of the theoretical amount was needed to produce the maximum M value with CH₃COOH. With other acids, approximately twice as much fixed polymer was required. This fact indicates that the fixed polymer amount does not correspond directly to maximum M values.

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