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Critical Assessment of RAFT Equilibrium Constants: Theory Meets Experiment
Macromolecular Theory and Simulations ( IF 1.8 ) Pub Date : 2020-06-09 , DOI: 10.1002/mats.202000022 Martin Werner 1 , João C. A. Oliveira 2 , Wibke Meiser 3 , Michael Buback 3 , Ricardo A. Mata 1
Macromolecular Theory and Simulations ( IF 1.8 ) Pub Date : 2020-06-09 , DOI: 10.1002/mats.202000022 Martin Werner 1 , João C. A. Oliveira 2 , Wibke Meiser 3 , Michael Buback 3 , Ricardo A. Mata 1
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Equilibrium constants, Keq, for the reversible addition–fragmentation chain transfer (RAFT) polymerization of butyl acrylate mediated by trithiocarbonate and dithiobenzoate RAFT agents have been estimated by quantum chemical calculations, namely by a combination of density functional structure optimizations, corrections for solvent effects plus the double harmonic approximation as well as high‐level ab‐initio local correlation methods. Individual contributions to Keq are analyzed. The results are compared to experimental Keq measured by microsecond time‐resolved electron paramagnetic resonance (EPR) spectroscopy. Dithiobenzoate (DTB) RAFT agents are of particular interest, as earlier quantum chemical calculations resulted in Keq values differing by several orders of magnitude from the numbers deduced via EPR measurements. This mismatch between theory and experiment is overcome by new quantum chemical estimates. The major factors behind the improved agreement are the application of dispersion‐corrected density functional theory (DFT) functionals for the equilibrium structures and full‐system coupled cluster calculations. The so‐obtained ab initio Keq data provide clear evidence for rate retardation with DTB‐mediated acrylate polymerizations being due to cross‐termination rather than to slow fragmentation of the RAFT intermediate radical.
中文翻译：
RAFT平衡常数的严格评估：理论与实验
由三硫代碳酸酯和二硫代苯甲酸酯RAFT试剂介导的丙烯酸丁酯的可逆加成-断裂链转移（RAFT）聚合反应的平衡常数K eq已通过量子化学计算进行估算，即结合密度泛函结构优化和溶剂效应校正加上双谐波近似以及高级从头算起的局部相关方法。以个人缴费ķ EQ进行了分析。将结果与实验K eq进行比较通过微秒时间分辨电子顺磁共振（EPR）光谱测量。二硫代苯甲酸酯（DTB）RAFT试剂特别受关注，因为较早的量子化学计算导致K eq值与通过EPR测量得出的数量相差几个数量级。新的量子化学估计克服了理论与实验之间的不匹配。改进协议背后的主要因素是色散校正密度泛函理论（DFT）泛函用于平衡结构和全系统耦合聚类计算。这样获得的从头算起K eq 数据提供了DTB介导的丙烯酸酯聚合速率延迟的清晰证据，这是由于交叉终止而不是由于RAFT中间基团的缓慢裂解所致。
更新日期：2020-06-09
中文翻译：
RAFT平衡常数的严格评估：理论与实验
由三硫代碳酸酯和二硫代苯甲酸酯RAFT试剂介导的丙烯酸丁酯的可逆加成-断裂链转移（RAFT）聚合反应的平衡常数K eq已通过量子化学计算进行估算，即结合密度泛函结构优化和溶剂效应校正加上双谐波近似以及高级从头算起的局部相关方法。以个人缴费ķ EQ进行了分析。将结果与实验K eq进行比较通过微秒时间分辨电子顺磁共振（EPR）光谱测量。二硫代苯甲酸酯（DTB）RAFT试剂特别受关注，因为较早的量子化学计算导致K eq值与通过EPR测量得出的数量相差几个数量级。新的量子化学估计克服了理论与实验之间的不匹配。改进协议背后的主要因素是色散校正密度泛函理论（DFT）泛函用于平衡结构和全系统耦合聚类计算。这样获得的从头算起K eq 数据提供了DTB介导的丙烯酸酯聚合速率延迟的清晰证据，这是由于交叉终止而不是由于RAFT中间基团的缓慢裂解所致。
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