Process for producing amido-methylated vinyl-aromatic polymerizates

A process for preparing amidomethylated vinylaromatic polymers, wherein at least one vinylaromatic polymer is reacted with at least one compound of formula (I) or salts thereof

• where R1=—C(H(C1-C6-alkyl)- or —CH2— and R2=—C(H(C1-C6-alkyl)- or —CH2— or R1 and R2 are two carbon atoms of an aromatic Ce ring optionally substituted by one or two C1-C6-alkyl radicals, or R1 and R2 are each —CH═, and
• at least one condensed formaldehyde
• in the presence of at least one protic acid and
• in the presence of sulfur dioxide.