Nitrogen → Acrylic acid methyl acrylate

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Into a 200 ml flask equipped with a stirrer, dropping funnel, thermometer, condenser and N2 gas-introducing tube was placed 80 g of isopropyl alcohol (IPA). While introducing an N2 gas into the flask and stirring the contents of the flask, the inside temperature of the flask was raised to 80° C. Next, a solution (which was beforehand prepared by mixing 56 g of acrylic acid, 24 g of methyl acrylate and 0.4 g of 2,2'-azobisisobutyronitrile with each other) was dropwise added into the flask from the dropping funnel over a period of 1 hour. After completion of the adding, the stirring was further continued at 80° C. for 2 hours to carry out a copolymerization reaction; whereby there was obtained an IPA solution of an acrylic acid/methyl acrylate copolymer having a number-average molecular weight of 8,000. Next, into a 500 ml flask equipped with a stirrer were placed 133 g of a dispersion (in which colloidal silica (average diameter 35 nm; variation coefficient 58%) was dispersed in ethylene glycol (containing 30% of SiO2)), 267 g of ethylene glycol, 0.4 g of γ-glycidoxypropyltrimethoxysilane and 0.4 g of water. The contents of the flask was stirred at room temperature for 2 hours, whereby a colloidal silica slurry (A) (which had been treated with a coupling agent) was obtained. To this slurry (A) was added 1 g of the above-obtained IPA solution of the acrylic acid/methyl acrylate copolymer. The resulting mixture was stirred at room temperature for 1 hour to obtain a slurry (B). Hexane was added to this slurry (B) to carry out reprecipitation, and then the formed precipitate was examined by elemental analysis. However, no ash content of the precipitate was detected. In addition, the slurry (B) was analyzed by GPC. As a result, only a polymer having a number-average molecular weight of 8,000 was detected, and so it was confirmed that the acrylic acid/methyl acrylate copolymer does not bond with colloidal silica by the above-mentioned process. Although the slurry (B) was dried at 150° C. under a vacuum of 100 mmHg and then the obtained compound fine particles were mixed with ethylene glycol or IPA; the particles hardly re-dispersed and so there was obtained only a dispersion in which most of the particles were cohered or precipitated. In addition, no alkoxy group was found in the particles.

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