Synthesis and properties of poly(arylene-ether-ketone)s containing a dimethylnaphthalene skeleton in the main chain

Abstract

The synthesis of novel dihaloarenes (1,5-bis(4-halophenyl)-2,6-dimethylnaphthalenes, 1), polycondensation of 1 with biphenols, and properties of the obtained polymers were described. Selectively Friedel-Crafts acylation of 2,6-dimethylnaphthalene with 4-halobenzoyl chlorides in nitrobenzene afforded 1 in high yields. X-Ray single-crystal structural analysis of 1 supported that the dibenzoylation proceeded regioselectively at the 1- and 5-positions and the two methyl groups sterically inhibited the coplanarity of the aromatic planes. The polycondensation of 1a with Bisphenol A in toluene/ N-methyl-2-pyrrolidone (NMP) mixed solvent in the presence of excess potassium carbonate as a condensation reagent was carried out at 180°C for several hours to quantitatively afford the corresponding poly(arylene-ether-ketone) (PEK) 3 with a high molecular weight ( M n −30,000) as a slightly yellow powder. To evaluate the effect of the methyl groups of 3, polycondensation of 2,6-bis(4-fluorobenzoyl)naphthalene 2 with Bisphenol A was carried out for comparison and the corresponding PEK 4 was obtained quantitatively. Whereas 3 was soluble in ordinary organic solvents such as tetrahydrofuran (THF) and chloroform at room temperature, 4 was insoluble in common solvents except for strong acids such as conc. sulfonic acid. 3 showed a high glass-transition temperature (238°C) and a 5% weight loss temperature of 457°C. The polycondensations of 1a with various biphenols such as dihydroxybenzophenone were carried out to examine the properties of the obtained polymers. The obtained PEKs showed high glass transition temperatures and 5% weight loss temperatures as well as good solubilities in ordinary organic solvents at room temperature. Casting of the polymers from THF solution gave transparent, tough, flexible, and amorphous films. 1,5-Bis(4-chlorobenzoyl)-2,6-dimethylnaphthalene 1b similarly underwent a polycondensation reaction with Bisphenol A to give the corresponding polymer quantitatively.