PROBLEM TO BE SOLVED: To provide a surface treatment agent which is hydrophobic in dry conditions but gradually becomes hydrophilic when coming in contact with water and thereby makes long lasting of make-up compatible with ease of wash-off of make-up.SOLUTION: A surface treatment agent contains a first block copolymer of formula (1). In formula (1), R1 and R2 are independently an alkyl group, a polyoxyalkylene group, an acyl group, a phenyl group or an aralkyl group X is a 1-18C alkyl chain, with not adjacent carbons optionally substituted with an oxygen to form an ether Y is a single bond or a divalent connection group Z1 is H or a methyl group and n and m are polymerization degrees.COPYRIGHT: (C)2016,JPO&INPIT【課題】乾燥時には疎水性であるが、水に接触すると徐々に親水性となることで、化粧もちと洗い流し性とを両立した表面処理剤を提供する。【解決手段】式(1)で表される第1のブロック共重合体を含有する表面処理剤。(R1及びR2は各々独立にアルキル基、ポリオキシアルキレン基、アシル基、フェニル基、アラルキル基;Xは隣接しない炭素が酸素に置換されてエーテルを形成してもよいC1~18のアルキル鎖;Yは単結合又は2価の連結基;Z1はH又はメチル基;n、mは重合度)【選択図】なし
