LOW SHRINKING AGENT, THERMOSETTING RESIN COMPOSITION CONTAINING THE SAME AND MOLDED ARTICLE FORMED THEREFROM

PROBLEM TO BE SOLVED: To provide a low shrinking agent that imparts good low shrinking properties combined with excellent coloring properties to a thermosetting resin composition, especially an unsaturated polyester resin composition, and also provide a resin composition containing the shrinking agent and a molded article formed from the resin composition. SOLUTION: A low shrinking agent for a thermosetting resin has a multi- phase structure comprising a rubbery polymer phase and a glassy polymer phase produced by the first stage of reaction in which a first polymerizable monomer (I) forming a rubbery polymer phase is subjected to suspension polymerization to produce a rubbery polymer particle having a glass transition temperature of not more than 20 deg.C and the subsequent second stage of reaction in which a second polymerizable monomer (II) forming a glassy polymer phase having a glass transition temperature of not less than 50 deg.C is subjected to radical polymerization in the presence of the rubbery polymer particle, and comprises a multi-phase structure polymer particle having a weight-average particle size in a range of 2-100 μm.