SPECTROSCOPIC AND PHOTOREDUCTION STUDY OF 2-ACRYLOXY THIOXANTHONE - PHOTOINITIATION ACTIVITY OF METHYL-METHACRYLATE POLYMERIZATION

The spectroscopic properties in terms of absorption, fluorescence and phosphorescence, of 2-acryloxy thioxanthone (TXA) were examined in various solvents. A photoreduction study was also carried out in benzene and acetonitrile solution using 2-diethylaminoethanol as hydrogen donor. A lower photoreduction quantum yield was found for TXA in benzene, phi(r)=0.12, compared with that of the model compound 2-acetoxy thioxanthone (AcOTX), phi(r)=0.60. A notable decrease in the photoreduction quantum yield of AcOTX was found with increasing concentration of methyl acrylate, confirming the involvement of a strong intermolecular interaction between the triplet state of the thioxanthone carbonyl and the acrylic double bond. All the data are related to the ability of the TXA to photoinduce methyl methacrylate (MMA) polymerization as followed by photodilatometry. Moreover, the effect of the TXA, amine and monomer concentration was examined together with the rate of polymerization R(p), and quantum yields of initiation phi(i) and polymerization phi(m). All the polymers obtained by photodilatometry were characterized by size exclusion chromatography (SEC) and with the molar mass values the ratio k(p)/k(t)1/2 for MMA was determined.