Surface modification of carbon black

A process for modifying the surface of a carbon black comprising contacting said carbon black with a conjugated diimine compound, wherein the conjugated diimine compound is obtained by oxidizing a p-phenylenediamine to form a quinonediimine compound with an oxidant which comprises an alkali- or alkaline earth-hypochlorite, -persulfate, -ferricyanide, -percarbonate, -perborate, -peroxymonosulfate or -permanganate;

• hydrogen peroxide or a salt thereof;
• or an aliphatic or aromatic organic peracid or a salt thereof and wherein the p-phenylenediamine is represented by the following structure:
• wherein R1 may be H, substituted or unsubstituted alkyl, substituted or unsubstituted aryl, substituted or unsubstituted cycloalkyl, hetaryl or polyoxyalkylene;
• R2 may be substituted or unsubstituted alkyl, substituted or unsubstituted aryl, substituted or unsubstituted cycloalkyl, hetaryl or polyoxyalkylene;
• each of R3 may independently be H, halogen, alkoxy, aryloxy, alkyl, aryl, hetaryl, hydroxyl, amino, alkyl- or dialkyl-amino, aryl- or diaryl-amino, arylalkylamino, alkylamido, arylamido, carbamoyl, alkylcarbamoyl, arylcarbamoyl, N,N-dialkylcarbamoyl, N,N-diarylcarbamoyl, N-alkyl, N-arylcarbamoyl, carboxy, sulfo, phospho, alkylsulfonamido, arylsulfonamido, alkoxycarbonyl, arylcarbonyl, acyl, ureido, alkyl- or aryl-ureido, thioalkyl, cyano or nitro;
• n represents an integer from 1 to 4;
• R1 and R2 or two adjacent R3 may be combined together to form a 5- to 7-membered carbo- or heterocyclic ring;
• and
• one of R3 may be combined together with R1 or R2 to form a 5- to 7-membered carbo- or heterocyclic ring.