Thermally and photochemically reversible functional groups, such as photodimers of anthracene derivatives, offer interesting stimuli-responsive behaviour. To evaluate their potential for application in reversible polymer networks, accurate kinetic parameters and knowledge of their thermophysical behaviour are required. Accurate kinetic studies of the thermal dissociation of the photodimers in the condensed state, thus without the influence of solvents on their reactivity, is still lacking. A methodology was set up to accurately evaluate the chemical reaction kinetics and complex phase behaviour during the thermal dissociation of photodimers into their corresponding monomers. Temperature-controlled time-resolved FTIR spectroscopy was used to determine the reaction progress, while non-isothermal DSC measurements were used to study the thermophysical changes, resulting from the thermal dissociation reaction. The thermal dissociation behaviour in the condensed state is more challenging than in the solution state due to the crystallinity of the dimers, stabilizing the dimers and thus slowing down the initial dissociation rates. Distinctly different sets of kinetic parameters were found for the dissociation from the molten and the crystalline state. For experiments performed below the melting temperature of the photodimer, the reaction rate changes abruptly as the dimer is partly dissociated and partly dissolved into the formed monomer. This methodology provides an accurate assessment of the reaction kinetics with detailed knowledge about the complex phase behaviour of the mixture of the anthracene photodimer and monomer during thermal dissociation.

中文翻译：

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凝聚态蒽光二聚体的热解离：动力学评估和复杂相行为。

热和光化学可逆的官能团，例如蒽衍生物的光二聚体，提供有趣的刺激响应行为。为了评估其在可逆聚合物网络中应用的潜力，需要准确的动力学参数和其热物理行为的知识。仍然缺乏对在冷凝状态下光二聚体的热解离的精确动力学研究，因此没有溶剂对其反应性的影响。建立了一种方法来准确评估光二聚体热解离成相应单体时的化学反应动力学和复杂相行为。使用温度控制的时间分辨FTIR光谱确定反应进程，非等温DSC测量用于研究热解离反应引起的热物理变化。由于二聚体的结晶性，稳定二聚体并因此减慢了初始离解速率，因此在冷凝状态下的热解离行为比在溶液状态下更具挑战性。发现从熔融状态和结晶状态解离的截然不同的动力学参数集。对于在光二聚体的熔融温度以下进行的实验，由于二聚体部分解离并部分溶解在形成的单体中，因此反应速率急剧变化。