Process for production of cyclic polyorganosiloxane, curing agent, curable composition, and cured product of the curable composition

Abstract

An object of the invention is to provide a curing agent and a curable composition capable of forming a cured product, which is applicable for optical material and which has excellent heat and light transparency and crack resistance, and a cured product obtained by curing the same. Moreover, an object of the invention is to provide a method for producing with use of the components of the curing agent a cyclic polyorganosiloxane having a specific structure, in a selective manner and in high yield. In order to attain the objects, a curable composition including, as essential components, (A) an organic compound including at least two carbon-carbon double bonds that are reactive with a SiH group, (B) a compound having at least two SiH groups per molecule, and (C) a hydrosilylation catalyst, uses a modified polyorganosiloxane compound having at least two SiH groups per molecule as the compound having at least two SiH groups, which modified polyorganosiloxane compound is a reaction product of a specific cyclic polyorganosiloxane.