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Issue 17, 2014
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Studying the polymerization initiation efficiency of acetophenone-type initiators via PLP-ESI-MS and femtosecond spectroscopy

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Abstract

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.

Graphical abstract: Studying the polymerization initiation efficiency of acetophenone-type initiators via PLP-ESI-MS and femtosecond spectroscopy

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Publication details

The article was received on 24 Mar 2014, accepted on 28 Apr 2014 and first published on 29 Apr 2014


Article type: Paper
DOI: 10.1039/C4PY00418C
Citation: Polym. Chem., 2014,5, 5053-5068
  • Open access: Creative Commons BY license
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    Studying the polymerization initiation efficiency of acetophenone-type initiators via PLP-ESI-MS and femtosecond spectroscopy

    E. Frick, H. A. Ernst, D. Voll, T. J. A. Wolf, A. Unterreiner and C. Barner-Kowollik, Polym. Chem., 2014, 5, 5053
    DOI: 10.1039/C4PY00418C

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