POLYASPARTIC ACID DERIVATIVE SOLUBLE OR DISPERSIBLE IN WATER, ITS PRODUCTION, BEAUTY TREATMENT ASSISTANT COMPOSED OF THE COMPOUND AND HAIR-TREATMENT COMPOSITION CONTAINING THE COMPOUND

PROBLEM TO BE SOLVED: To obtain the subject new polymer useful as a hair-conditioning agent having good biodegradability, conditioning properties, etc., by reacting a polysuccinimide or a polyaspartic acid with a specific amine mixture. SOLUTION: This water-soluble and/or dispersible polyaspartic acid derivative, its salt or its quaternarized product is composed of a unit of the formula I [x1 +x2 +y1 +y2 +z=100; x1 +x2 is 30-99.9; y1 +y2 is 0.1-70; (z) is 0-20; A is a primary to tertiary alkylamine having a 2-6C alkyl and/or a cyclic diamine of the formula II ((n) and (o) are each 1-5; X is NR ; R is H or an alkyl), etc.; B is an amine of the formula III (R is H or a hydrocarbon group of a saturated or an unsaturated fatty acid; Y is CH2 , NH, etc.; (p) is 1-23; R and R are each H, a hydroxyalkyl, etc.); C is a residue obtained by eliminating amine hydrogen from the amine A having primary or secondary amino group; D is a residue obtained by eliminating amino hydrogen from the amine B having primary or secondary amino group].