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 °C. 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-l-isocyanate 'tail' cleaves first, followed by the isocytosine 'head' breaking down above 244 °C. 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.