| 摘要 |
Disclosed herein are novel linear copolymers having weight average molecular weight of 500-30,000 and comprising structural units represented by the following formulae (I), (II), (III) and (IV): <IMAGE> (I) <IMAGE> (II) <IMAGE> (III) <IMAGE> (IV) wherein R1, R2 and R3 mean individually an alkyl group having 4 or fewer carbon atoms and R4 denotes an alkyl, cycloalkyl, aralkyl or phenyl group, and multivalent metal salts thereof in each of which the multivalent metal forms the multivalent metal salt between carboxyl groups within the same molecule of the copolymer or between different molecules of the copolymer; color-developing agents comprising multivalent metal-modified resins of the copolymers; and color-developing sheets obtained by coating the color-developing agents on their surfaces. |
