Vibrational Photopolymerization of Methyl Methacrylate and Quantitative Analysis of Polymerization Results

Radical photopolymerization of methyl methacrylate (MMA) with 2,2‘-azobis(isobutyronitrile) (AIBN) as an initiator was carried out by visible light excitation. Excitation of the fifth vibrational overtone of the CH stretch of AIBN at 628 nm initiates the reaction with subsequent monomer conversion of up to 86% after 24 h. The quantitative analysis of monomer conversion was accomplished by a partial least-squares (PLS) analysis of the second vibrational overtone spectra of methyl, methylenic, and vinyl CH stretch absorptions. The wavelength selectivity of the process was studied by irradiating samples at the fifth vibrational overtone of the methyl CH stretch of AIBN (628 nm), the fifth vibrational overtone of vinyl CH stretch of MMA (602 nm), and a wavelength where both monomer and initiator do not absorb light (595 nm). The mixtures irradiated at the monomer absorption peak exhibited about 4 times less polymer formation than mixtures irradiated at the initiator absorption peak after 24 h. The overall quantum yields (φ) for 24 h of polymerization were estimated to be φ628 = 9937 and φ602 = 1810 for the mixtures irradiated at 628 and 602 nm, respectively.