polymers reactive towards free amino groups , such as polyamides , polyureas , polyurethanes or polyesters , are provided with durable modified properties by being brought into contact with an additive polymeric material which is compatible with the polymer being treated , contains a plurality of oxyalkylene groups effective to impart to the modified polymer improved properties such as reduced static propensity , modified dyeability , or greater water absorbency ; and has one or more reactive sites , in the form of a pendant free primary amino group or potential primary amino group , blocked by the dehydration of an aldehyde or a ketone with the amine , which in either case affords the capability in proper circumstances of attaching the modifying polymeric material to the polymer being treated by a covalent chemical bond . suitable modifying polymers are made by reacting a diamino or higher amino compound with a proportion of an aldehyde or ketone sufficient to block at least some of the amino groups present , oxyalkylating the blocked starting material through a surviving amino group to an extent capable of affording the desired properties , and if desired , cross - linking or chain - extending the resulting material to obtain a substance of increased molecular weight . modifying polymers so made may be used as such for treatment of the reactable polymer to be modified , either by blending into a melt or by surface treatment of freshly produced fiber or sheet material . the formation of free amino groups in the modifying polymer can occur in situ when the modified polymer is exposed to water under suitable conditions . the modifying polymer may also be used in a free amino form generated by hydrolyzing before bringing it into contact with the polymer to be modified . novel treated polymers are thus produced which display modified properties which are retained despite repeated washings and / or long - continued use .