A silicone-based copolymer resin powder is prepared by reacting a siloxane oligomer obtained from ring-opening of (a1) a cyclic organosiloxane in the presence of (a3) an acid catalyst and (a4) an anionic surfactant with (a2) a silane coupling agent having an alkoxy group and a polymerizable double bond to obtain (A) a linear or branched organopolysiloxane containing at least 2 silicon-bonded hydroxyl groups per molecule, copolymerizing (A) the linear or branched organopolysiloxane with (B) an ethylenically unsaturated monomer to form a copolymer as a core, and further polymerizing to the copolymer another ethylenically unsaturated monomer as a shell, the powder containing up to 0.3% by weight of the cyclic organosiloxane and up to 1% by weight of the anionic surfactant.本發明之聚矽氧系共聚樹脂粉體,其係對於1分子中含有至少2個鍵結於矽原子之羥基之有機聚矽氧烷共聚合含有乙烯性不飽和基之單體,並將所得之共聚物作為核骨架,作為殼成分,藉由聚合含有乙烯性不飽和基之單體而得到;其中,前述1分子中含有至少2個鍵結於矽原子之羥基之有機聚矽氧烷,係將環狀有機矽氧烷在酸觸媒及陰離子系界面活性劑之存在下予以開環,並將具有烷氧基且具有聚合性雙鍵之矽烷偶合劑、與前述開環後所得之矽氧烷低聚物反應而得到,環狀有機矽氧烷之含有量為0.3質量%以下,上述陰離子系界面活性劑之含有量為1質量%以下。將本發明之粉體調配於頭髮化妝品、美妝化妝品、防曬等中,可賦予順滑性、柔軟觸感、撥水性。
