Analytical Sciences

Characterization of Cross-linking Structures in UV-cured Acrylic Ester Resin by MALDI-MS Combined with Supercritical Methanolysis

Hideki MATSUBARA,*¹ Shun-ichiro HATA,*² Yosuke KONDO,*² Yasuyuki ISHIDA,*³ Hiroshi TAKIGAWA,*⁴ and Hajime OHTANI*⁵

*1 Aichi Industrial Technology Institute, Kariya 448-0003, Japan
*2 Department of Materials Applied Chemistry, Graduate School of Engineering, Nagoya University, Nagoya 464-8603, Japan
*3 EcoTopia Science Institute, Nagoya University, Nagoya 464-8603, Japan
*4 Sumitomo Chemical Co., Ltd., Tsukuba 300-3266, Japan
*5 Department of Materials Science and Engineering, Graduate School of Engineering, Nagoya Institute of Technology, Nagoya 466-8555, Japan

The cross-linking structure of the ultra violet (UV)-cured resin prepared from dipentaerithritol hexacrylate (DPHA) was characterized by matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS) combined with supercritical methanolysis. The MALDI-mass spectrum of the decomposition products obtained by supercritical methanolysis contained a series of peaks of sodium-cationized methyl acrylate (MA) oligomers up to around m/z = 4000 formed through selective cleavage and methylation occurred at ester linkages in UV-cured DPHA. Furthermore, in order to observe widely distributed sequence lengths in the cross-linking junctions, the decomposed products of the cured resin were then fractionated using size exclusion chromatography followed by the MALDI-MS measurements of the individual fractions. The MALDI-mass spectra of the lower molar mass fractions mainly consisted of a series of peaks of MA oligomers around m/z values of several thousands, whereas those of higher molecular weight showed a broad peak up to m/z ca. 180000. The observed distributions of the supercritical methanolysis products suggested that the network junctions in the given UV-cured resin were composed of up to around 2000 acrylate units.

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