The purpose of the present invention is to provide: a copolymer for cosmetics, which has excellent water repellency and oil repellency even though a polyfluoroalkyl group therein has 6 or less carbon atoms a surface treatment agent which contains the copolymer for cosmetics a powder for cosmetics, which is treated with the surface treatment agent and has excellent water repellency and oil repellency and a cosmetic preparation which contains the powder for cosmetics. A copolymer for cosmetics of the present invention contains: 70-90% by mass of a constituent unit (A) that is derived from a compound represented by formula (a) 2-25% by mass of a constituent unit (B) that is derived from a compound represented by formula (b) 2-25% by mass of a constituent unit (C) that is derived from a compound represented by formula (c) 0.1-10% by mass of a constituent unit (D) that is derived from a compound represented by formula (d) and a residue (E) of a chain-transfer agent (e) that contains an OH group or a COOH group. CH2=CR1-COO-Q1-Rf (a) CH2=CR2-Q2-COOH (b) CH2=CR3-COO-(R4O)n-R5 (c) CH2=CR7-COO-Q3-P(O)(OH)-R8 (d).本發明提供不拘於聚氟烷基的碳數為6以下而具有優異撥水撥油性之化妝品用共聚物以及含其之表面處理劑,進一步,以提供經該表面處理劑處理的撥水撥油性優異的化妝用粉體以及含該化妝用粉體的化妝料為目的,本發明的化妝品用共聚物,含有下述式(a)所表示的化合物所衍生之構成單元(A)70~90質量%、下述式(b)所表示的化合物所衍生之構成單元(B)2~25質量%、下述式(c)所表示的化合物所衍生之構成單元(C)2~25質量%、下述式(d)所表示的化合物所衍生之構成單元(D)0.1~10質量%以及含有OH基或COOH基之鏈轉移劑(e)的殘基(E)之化妝品用共聚物。CH2=CR1-COO-Q1-Rf (a)CH2=CR2-Q2-COOH (b)CH2=CR3-COO-(R4O)n-R5 (c)CH2=CR7-COO-Q3-P(O)(OH)-R8 (d)
