Synthesis and characterization of fluorinated polybenzoxazoles via solution cyclization techniques

Abstract

High molecular weight film-forming flexible fluorinated poly(arylene ether benzoxazole)s, which are suitable as gas separation membranes, adhesives and matrix resins, were synthesized in aprotic dipolar solvents such as N-methyl pyrrolidinone via an intermediate poly(hydroxy amide). The cyclodehydration was subsequently achieved at moderate temperatures (e.g. 150–195°C) in solution via an acid-catalysed (p-toluene sulfonic acid or pyridine hydrochloride) process. The water of dehydration could be azeotropically removed in an analogous manner to the well known synthesis of polyimides via intermediate poly(amide acid)s. The fluorinated monomers were bis(arylamino phenol)s based upon either the 6F or a novel 3F connecting link. Oxybis(benzoylchloride) appears to be a particularly attractive comonomer which allows the synthesis of soluble high molecular weight products. The amorphous macromolecules produced highly transparent ductile cast films with glass transition temperature values of about 300°C or higher. Semicrystalline morphologies could also be produced by incorporating more rigid comonomers. The synthetic procedures described herein are considered to be attractive relative to several alternative methods described in the literature for the synthesis of amorphous polybenzoxazoles.