HCN polymers are of great interest in research on the origin of life and, currently, in materials science because they have shown potential for the design of electrical devices, (photo)catalysts and biomedicine. Herein, calorimetric measurements have successfully described the bulk polymerization of HCN tetramer, diaminomaleonitrile (DAMN). Two series of nonisothermal experiments were carried out by differential scanning calorimetry (DSC), and low-heating rate (β) the thermograms (β ≤ 5 °C/min) indicated that the polymerization is initiated at temperatures lower than the DAMN melting point, ~180 °C; while higher heating rates results in a rapid polymerization reaction, which occurs entirely in the liquid phase. The DSC data were analysed using model-free linear iso-conversional methods to estimate kinetic parameters, such as activation energy, and a suitable kinetic model was proposed for these thermal polymerizations in the melt. A preliminary structural and morphological characterization by means of Fourier transform infrared (FTIR) spectroscopy and scanning electron microscopy (SEM) was also completed. This study demonstrated the autocatalytic, highly efficient and straightforward character of this stimulated thermal polymerization of DAMN and, to the best of our knowledge, describes for the first time a systematic and extended kinetic analysis to gain mechanistic insights into this process. The latter was done through the help of simultaneous thermogravimetry (TG)-DSC and in situ mass spectrometry (MS) technique to investigate the gas products generated during these melt polymerizations. These analyses revealed that deamination and dehydrocyanation processes are two relevant reactions involved in DAMN polymerization mechanism.

The authors used the research facilities of the Centro de Astrobiologia (CAB) and were supported by the Instituto Nacional de Tecnica Aeroespacial Esteban Terradas (INTA), by the projects ESP2017-89053-C2-2-P, PID2019-104205GB-C21 and PID2019-107442RB-C32 from the Spanish Ministerio de Ciencia, Innovacion y Universidades and by the Spanish State Research Agency (AEI) project MDM-2017-0737 Centro de Astrobiologia (CSIC-INTA), Unidad de Excelencia Maria de Maeztu. C. Hortelano wants to express his gratitude to INTA for this training scholarship. Additionally, the authors are grateful to Ma Teresa Fernandez from CAB for performing the FTIR spectra and to Pilar Valles from INTA for recording the SEM images.

Kinetic, structural characteristics and the mechanism for the formation of DAMN polymers was studied. Šesták-Berggren model can successfully describe these melt polymerizations. TG-DSC-MS analysis of DAMN revealed thermal processes during its bulk polymerization. Prebiotic chemistry inspires polymeric materials with advanced performances. These DAMN polymers may be potentially applied as multi-functional materials.

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