PURPOSE: To provide a polymer compound obtained by polymerizing 1- diallylamino-2,3-epoxypropane with a quaternary ammonium salt reacted with alkylsulfonate and enhancing the wet fastness of a cellulosic fiber dyed with a reactive dye.

CONSTITUTION: Alkylsulfonate (e.g.; dimethyl sulfate, etc.), represented by formula Z-SO2-OR (wherein R is a 1-3C alkyl; and Z is an aryl residue or OR) is added to 1-diallylamino-2,3-epoxypropane under stirring while the reaction temp. is held to 60°C by cooling to be reacted therewith to obtain a quaternary ammonium compd. represented by formula (wherein Q- is 1-3C alkylsulfate ions or a aromatic sulfonic acid anion). Next, this compd. is diluted with water and a radical polymn. initiator composed of 2,2'-azobis(2-amidinopropane) hydrochloride is added to the diluted compd. and the resulting mixture is held at 75°C for 1.5 hr to polymerize the compd. to obtain the objective polymer.