Shin-etsu Chemical Co., Ltd.

Yoshio Tomizawa

Masaharu Takahashi

Minoru Igarashi

Yutaka Hagiwara

Kenji Tawara

Susumu Ueno

Keiji Shibata

Masanobu Nishimine

Kiyoshi Shirasuna

Hidekazu Uehara

An organopolysiloxane gum is prepared by polymerizing a cyclic organopolysiloxane with a low molecular weight linear organopolysiloxane end-blocked with a triorganosilyl group in the presence of a thermally decomposable catalyst. After the polymerization reaction, the catalyst is deactivated by heating the reaction product under a subatmospheric pressure of typically up to 500 mmHg.

Preparation of organopolysiloxane gum

An organopolysiloxane gum is continuously prepared by (I) mixing at least one cyclopolysiloxane with an end capping agent, (II) feeding the mixture to a self-cleaning reactor along with a polymerization catalyst of thermal decomposition type, and effecting polymerization at a temperature of 80-130&deg; C., (III) heating the reaction mixture of step (II) at a temperature of 130-200&deg; C. under subatmospheric pressure for deactivating the catalyst, thereby terminating the polymerization reaction, and (IV) continuously removing the cyclopolysiloxane and volatile components from the reaction product.

Crude fumed silica resulting from pyrogenic hydrolysis is purified by continuously feeding particulate silica and steam or a mixture of steam and air in a steam/air volume ratio of at least 1/2 through an upright column from its bottom toward its top for forming a fluidized bed within the column at a gas linear velocity of 1 to 10 cm/sec. and a temperature of 250.degree. to 400.degree. C., whereby steam deprives the particulate silica of the halide borne thereon, and removing fine particulate silica from which the halide has been eliminated from the top of the column. Using a simple apparatus, pure fine particulate silica is collected at a low cost of energy consumption.

Method for porifying fine particulate silica

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Annaka, Japan

Yoshio Tomizawa