Bis-4-(1’,4’-phenylene)-5-phenyl-1,2,3,5-thiaoxadiazole-1-oxide 1, a blocked bifunctional carbodiimide, has been used as a crosslinker for carboxyl functional poly(meth)acrylates. The thermolysis ("deblocking") reaction of 1 has been analyzed by FTIR spectroscopy. The crosslinking reaction has been simulated by using monofunctional model compounds. Intermediate compounds detected were thermally instable N-acylurea’s decomposing into isocyanates and amides. Also some anhydride formation occurred. The final structure of the crosslinked product and the rates of crosslinking have been analyzed by FTIR and NMR spectroscopy. Modulus-M(c) relations of networks based on carbodiimide compared with those based on bisketeneimine indicate thermolysis of crosslinks in the former case.