New organosoluble poly(arylene ether nitrile) copolymers based on 9,9-bis(3,5-dimethyl-4-hydroxyphenyl)xanthene

Several poly(arylene ether nitrile) (PAEN) copolymers containing multi-methyl and cardo xanthene groups were synthesized by nucleophilic substitution reaction of 2,6-difluorobenzonitrile with varying molar ratios of 9,9-bis(3,5-dimethyl-4-hydroxyphenyl)xanthene (BDMHPX) and hydroquinone (HQ) (80/20–40/60) in N-methyl-2-pyrrolidone (NMP) in the presence of anhydrous potassium carbonate. These new PAENs had inherent viscosities between 0.56 and 0.68 dL g^–1, and their weight-average molecular weights and number-average molecular weights were in the range of 33,300–36,500 g mol⁻¹ and 17,300–18,400 g mol⁻¹, respectively. All polymers were amorphous and soluble in dipolar aprotic solvents such as NMP and N,N-dimethylacetamide and even in THF and chloroform at room temperature. These PAENs showed glass transition temperatures (T_gs) between 248°C and 289°C, and the T_g values were found to increase with increase of the BDMHPX content in the polymeric main. Thermogravimetric analysis showed that all PAENs were stable up to 400°C, with 5% weight loss temperatures ranging from 427°C to 448°C and char yields of 57–61% at 700°C under nitrogen atmosphere. All new PAENs could be cast into strong and flexible films with a tensile strength of 93–115 MPa, elongation at break of 10–12%, and tensile modulus of 3.3–3.5 GPa.