Studying the polymerization initiation efficiency of acetophenone-type initiators via PLP-ESI-MS and femtosecond spectroscopy
Studying the polymerization initiation efficiency of acetophenone-type initiators via PLP-ESI-MS and femtosecond spectroscopy
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DOI：
10.1039/c4py00418c
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发表时间：
2014-09-07
影响因子：
4.6
通讯作者：
Barner-Kowollik, Christopher
中科院分区：
文献类型：
--
作者：
Frick, Elena;Ernst, Hanna A.;Barner-Kowollik, Christopher
三种三重态自由基光引发剂MMMP的引发效率和激发态动力学（2-甲基-4 '-（甲硫基）-2-吗啉基苯丙酮），安息香（2-羟基-1，2-二苯基乙酮，Bz）和4-甲基苯偶姻（2-羟基-2-苯基-1-（对甲苯基）乙酮，4 MB）通过脉冲激光聚合和随后的电喷雾电离质谱的三重组合进行研究质谱（PLP-ESI-MS）、飞秒瞬态吸收（TA）光谱和密度泛函理论（DFT）方法。提出了一个定量阐明的基本机制，导致不平等的引发效率的三种光引发剂的建议更高的自由基形成能力的MMMP和4 MB相比，BZ的基础上的固有的物理化学性质的三个引发剂。MMMP显示出显着更高的复杂性的弛豫途径，由于部分激发到更高的单重态以及延长的三重态寿命。然而，与MMMP（Bz：MMMP对应于1：0.63）和4 MB（Bz：4 MB对应于1：0.86）两者相比，Bz在351 nm的波长下显示出MMA聚合的最高引发效率。因此，目前的研究证明，PLP-ESI-MS和TA实验的组合允许到达来自不同来源分子的相同自由基片段的定量引发能力。然而，源自不同来源分子的不同片段的定量引发评价需要关于片段对乙烯基键的反应性的额外信息。
The initiation efficiency and the excited state dynamics of the three triplet radical photoinitiators MMMP (2-methyl-4'-(methylthio)-2-morpholinopropiophenone), benzoin (2-hydroxy-1,2-diphenylethanone, Bz), and 4-methyl benzoin (2-hydroxy-2-phenyl-1-(p-tolyl) ethanone, 4MB) are investigated via a trifold combination of pulsed laser polymerization and subsequent electrospray ionization mass spectrometry (PLP-ESI-MS), femtosecond transient absorption (TA) spectroscopy, and density functional theory (DFT) methods. A quantitative elucidation of the underlying mechanisms that cause unequal initiation efficiencies of the three photoinitiators is proposed suggesting higher radical formation capabilities for MMMP and 4MB compared to Bz based on the inherent photophysical properties of the three initiators. MMMP shows significantly higher complexity of the relaxation pathways due to partial excitation into higher singlet states as well as extended triplet lifetimes. However, Bz shows the highest initiation efficiency for polymerization of MMA at a wavelength of 351 nm compared to both MMMP (Bz : MMMP corresponds to 1 : 0.63) and 4MB (Bz : 4MB corresponds to 1 : 0.86). The current study thus evidences that the combination of PLP-ESI-MS and TA experiments allows for arriving at quantitative initiation abilities of identical radical fragments originating from disparate source molecules. However, the quantitative initiation evaluation of different fragments originating from disparate source molecules requires additional information regarding the fragments' reactivity towards vinyl bonds.