A mixture of mono- or polynuclear melamine compounds, which have at least one 2,4,6-triamino-1,3,5-triazine ring, wherein at least one amino group of at least one of the 2,4,6-triamino-1,3,5-triazine rings is of the formula A: NR 1 R 2 where R 1 is H, CH(R 3)OR 4 or R 2, R 2 is CH(R 3)O(A-O) x -R 5, where R 3 is H, C 1 -C 10 -alkyl or aryl, R 4 is H, C 1 -C 4 -alkyl or C 1 -C 4 -alkoxy-C 1 -C 4 -alkyl, R 5 is a hydrocarbon radical having from 1 to 40 carbon atoms, which is selected from C 1 -C 22 -alkyl, aryl-C 1 -C 4 -alkyl or aryl, where aryl in the last two mentioned radicals is phenyl or naphthyl, which is unsubstituted or carries 1 or 2 C 1 -C 10 -alkyl groups; x is an integer from 2 to 500, having a number average value in the range from 3 to 200; A is an C 2 -C 4 -alkan-1,2-diyl radical; where the mono- or polynuclear melamine compounds are selected from mononuclear melamine compounds of the formula, binuclear polynuclear melamine compounds of the formula and polynuclear melamine compounds of the formulae, where in formula M1 at least one of the radicals A 1, A 2 and A 3 is a radical of the formula, while the remaining radicals are of the formulae NHR x or NR x R y, respectively where in formula M2 at least one of the radicals A 1, A 2, A 4 and A 5 is a radical of the formula, while the remaining radicals A 1, A 2, A 4 and/or A 5 are of the formulae NHR x or NR x R y, respectively, L is a bivalent linker CH(R 3) or CH(R 3)[O-CH(R 3)] k, where k is an integer, which is in the range from 1 to 5, and A 33 and A 34 are radicals NR z, and where in formula M3 at least one of the radicals A 6, A 7 and A 8 is a radical of the formula Ma wherein p is 0 or an integer from 1 to 20, provided that in at least one of the groups Ma the variable p is different from 0, # indicates the point of attachment to the triazine ring of M3, L and L' are identical or different bivalent linkers as defined for L in formula M2, A 33, A 34, A 35 and A 36 are radicals NR z, provided at least one of the radicals A 2, A 4, A 5, A 6, A 7 and A 8 is a radical of the formula, while the remaining radicals A 2, A 4 and A 5, are of the formulae NHR x or NR x R y, respectively, and the remaining radicals A 6 and A 7, are of the formulae Ma, NHR x or NR x R y, respectively, and where R x is CH(R 3)OR 4 or CH(R 3)O-R 8, R y is CH(R 3)OR 4 or CH(R 3)O-R 8, R z is hydrogen, CH(R 3)OR 4 or CH(R 3)O-R 8, and R 8 is a hydrocarbon radical having from 5 to 40 carbon atoms. R 1 is H, CH(R 3)OR 4 or R 2, R 2 is CH(R 3)O(A-O) x -R 5, where R 3 is H, C 1 -C 10 -alkyl or aryl, R 4 is H, C 1 -C 4 -alkyl or C 1 -C 4 -alkoxy-C 1 -C 4 -alkyl, R 5 is a hydrocarbon radical having from 1 to 40 carbon atoms, which is selected from C 1 -C 22 -alkyl, aryl-C 1 -C 4 -alkyl or aryl, where aryl in the last two mentioned radicals is phenyl or naphthyl, which is unsubstituted or carries 1 or 2 C 1 -C 10 -alkyl groups; x is an integer from 2 to 500, having a number average value in the range from 3 to 200; A is an C 2 -C 4 -alkan-1,2-diyl radical; R 3 is H, C 1 -C 10 -alkyl or aryl, R 4 is H, C 1 -C 4 -alkyl or C 1 -C 4 -alkoxy-C 1 -C 4 -alkyl, R 5 is a hydrocarbon radical having from 1 to 40 carbon atoms, which is selected from C 1 -C 22 -alkyl, aryl-C 1 -C 4 -alkyl or aryl, where aryl in the last two mentioned radicals is phenyl or naphthyl, which is unsubstituted or carries 1 or 2 C 1 -C 10 -alkyl groups; x is an integer from 2 to 500, having a number average value in the range from 3 to 200; A is an C 2 -C 4 -alkan-1,2-diyl radical; wherein p is 0 or an integer from 1 to 20, provided that in at least one of the groups Ma the variable p is different from 0, # indicates the point of attachment to the triazine ring of M3, L and L' are identical or different bivalent linkers as defined for L in formula M2, A 33, A 34, A 35 and A 36 are radicals NR z, provided at least one of the radicals A 2, A 4, A 5, A 6, A 7 and A 8 is a radical of the formula, while the remaining radicals A 2, A 4 and A 5, are of the formulae NHR x or NR x R y, respectively, and the remaining radicals A 6 and A 7, are of the formulae Ma, NHR x or NR x R y, respectively, R x is CH(R 3)OR 4 or CH(R 3)O-R 8, R y is CH(R 3)OR 4 or CH(R 3)O-R 8, R z is hydrogen, CH(R 3)OR 4 or CH(R 3)O-R 8, and R 8 is a hydrocarbon radical having from 5 to 40 carbon atoms.