Synthesis of All-Aromatic Phthalazinone-Containing Polymers by a Novel N−C Coupling Reaction

Abstract

High molecular weight poly(phthalazinone)s with high glass transition temperatures were prepared by a novel N−C coupling reaction. New bis(phthalazinone) monomers ( 5a − f ), such as 7,7‘-oxobis[4-phenylphthalazin-1(2 H )-one] ( 5c ), were synthesized from the corresponding bis(phthalic anhydride)s ( 3a − f ) in two steps. Other types of bis(phthalazinone) monomers ( 8, 9 ) were synthesized from phthalic anhydride and diphenyl sulfide or diphenyl ether. AB-type phthalazinone monomers ( 11a, 12 − 14 ) were also synthesized from phthalic anhydride. Poly(phthalazinone)s, having inherent viscosities of 0.3−0.4 dL/g, were prepared by the reaction of the bis(phthalazinone) monomers with an activated aryl halide such as bis(4-fluorophenyl) sulfone ( 22 ) in a dipolar aprotic solvent in the presence of potassium carbonate. AB-type phthalazinone monomers do not form high molecular weight polymers because of premature precipitation during the polymerization reaction. One of the AB-type phthalazinone monomers, 4-[4-((4-fluorophenyl)sulfonyl)phenyl]phthalazin-1(2 H )-one, was successfully copolymerized with 4,4‘-biphenol and bis(4-fluorophenyl) sulfone to form high molecular weight polymers. The copolymers showed higher glass transition temperatures ( T g s) as the phthalazinone ratio increased. All phthalazinone homopolymers except the Bisphenol A phthalazinone polymers show T g s around 300 °C by differential scanning calorimetry. The decomposition temperatures for 5% weight losses in air and in nitrogen measured by thermogravimetric analysis are in the range of 480−530 °C. Polymers from the Bisphenol A phthalazinone monomer are soluble in chlorinated solvents such as chloroform. Other polymers are soluble in dipolar aprotic solvents such as N -methyl-2-pyrrolidinone. The soluble polymers can be cast into flexible films from solution.