Abstract
A method for the synthesis of 3,4-dihydro-3-pentafluorophenyl-2H-1,3-benzoxazine in a high yield derived from pentafluoroaniline is described. This fluorinated benzoxazine monomer has been developed as a potential precursor for a polybenzoxazine in electronic applications as well as others taking advantage of the low dielectric constant, low flammability, low refractive index, low coefficient of friction, and high glass transition temperature of fluorinated compounds. The traditional benzoxazine synthesis conditions are inappropriate for the synthesis of fluorinated benzoxazines when the fluorination is on the primary amine component. It is found that the pH value of the reaction medium is the controlling factor in the yield of the compound from weak amines. A strongly acidic condition is necessary for the synthesis of similar compounds from other very weak amines having a pKa lower than 3. A dramatic increase in the yield of benzoxazine ring has been observed when benzoxazines with very weak amines are synthesized in an acidic medium. The effects of solvent and pKa of phenol are also discussed. The synthesized compounds have been characterized by 1H NMR, FTIR, GPC and HPLC.