The invention comprises an acid-catalysed reaction product of 2-chloroaniline (a), 2,5-dichloroaniline (b) and formaldehyde (c), in mol. ratios (a): (b):: 9:1 to 1:2 and [(a) + (b)]: (c) being at least 2:1. Said product is a mixture of bis(4 - amino - 3 - chlorophenyl)methane, bis(4-amino-2,5-dichlorophenyl)methane and 4,41-diamino - 2,5,31 - trichlorodiphenylmethane; the latter component, which is claimed per se, is separated from the mixture by extracting a benzene solution with 20% dichloroacetic acid.ALSO:A liquid isocyanate-terminated polyurethane prepolymer is cured by heating with a curing agent providing 0.5-1.1 equivalents of amine per equivalent of isocyanate, the agent being an acid catalysed 2-chloroaniline/2,5-dichloro-aniline/formaldehyd product comprising bis-(4 - amino - 3 - chlorophenyl)methane, bis-(4 - amino - 2,5 - dichlorophenyl)methane and 4,41 - diamino - 2,5,31 - trichlorodiphenyl-methane; alternatively, the latter compound alone may be utilized. Suitable prepolymers are listed, but in an example a hydroxy-terminated polyethylene adipate polyester (M.W. 1220)/2,4-toluenediisocyanate product is specified.