Chain-End Lactonization of Polyacrylates Prepared by Photopolymerization

The structural change of the end groups of UV-cured acrylates with time has been investigated as well as photopolymerization behavior. 2-Ethylhexyl acrylate, n-lauryl acrylate, 2-(2-ethoxyethoxy)ethyl acrylate, and 2-ethylhexyl methacrylate were used as a monomer in the current study. In order to mimic industrial conditions, the photopolymerization was conducted with relatively high UV intensity (576 mW/cm(2)) using a common photoinitiator 1-hydroxycyclohexyl phenyl ketone. Conversion-time profile gave a linear first-order plot suggesting that the steady state was hold throughout the polymerization. Matrix-assisted laser desorption/ionization time-of-flight mass spectra of the resultant polymers indicated the number of the hydroxycyclohexyl chain-ends decreased with storage time at room temperature. Instead, a lactonic ring appeared to form at the chain-end by transesterification of the hydroxycyclohexyl group with the ester side chain of the adjacent acrylate according to the results of mass spectrometry and C-13 NMR. (c) 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014, 52, 1161-1171