Synthesis of 4-chloro-2,5-diphenyloxazole derivatives and their copolymers

Abstract

Two types of monomers containing 4-chloro-2,5-diphenyloxazole moiety were designed and successfully been synthesized with reasonable yield via a cyclization of the corresponding benzoyl cyanides and benzaldehydes. A plausible mechanism of this reaction is proposed based on an experimental results and observation. Having established an efficient synthetic route to monomers, the construction of polymer containing functionalized 4-chloro-2,5-diphenyloxazole scintillant moiety in both main chain and side chain by condensation and free radical polymerization, respectively, have been proceeded. To obtain free radical polymers, acrylate monomers with various substituents including H, F, OCH₃, NO₂ and NH₂ were copolymerized with methyl methacrylate in two different feed ratios, 1% and 5%. These polymers showed a high thermal stability in the range of 247-280℃. The glass transition temperature (Tg) valued in the range of 114-128℃. 4-Chloro-2,5-bis-(4- fluorophenyl) oxazole monomer was synthesized and condensed with bisphenol A to construct a poly (aryl ether) containing 4-chloro-2,5-diphenyloxazole. The optimum polymerization time to obtain a high molecular weight was around 9 h. These poly (aryl ether) exhibited an excellent thermal stability ranging from 334-364℃ and Tg valued in the range of 192-205℃. All polymers show the distinct and well-defined fluorescence of the characteristic 2,5-diphenyloxazole chromophore. These materials are possess the ability to scintillate efficiently in the presence of β-ionizing radiation.