Thermal stability of a ureidopyrimidinone model compound

A dimer of N-[(butylamino)carbonyl]-6-methylisocytosine was prepared as a model compound in order to study the thermal stability of ureidopyrimidinone supramolecular polymers during heat/cool cycles. The dimer did not self-heal (i.e. disintegrate and reform reversibly) as expected; it underwent thermal degradation in three stages once heated to its melting point of 225 degreesC. Infrared spectra and optical micrographs were taken before and after these cycles, and the gases evolved at each stage of the degradation process were identified by gas chromatography-mass spectroscopy. A degradation mechanism is proposed whereby the dimer's butane-1-isocyanate 'tail' cleaves first, followed by the isocytosine 'head' breaking down above 244 degreesC. The kinetics of the degradation process were also determined, from which the activation energy was calculated to be 71.5 kJ/mol. In conclusion, the implications for processing related supramolecular polymers are discussed. (C) 2001 Elsevier Science B.V. All rights reserved.