Soluble, semi-crystalline PEEK analogs based on 3,5-difluorobenzophenone: Synthesis and characterization

The solubility and thermal properties of poly(ether ether ketone) (PEEK) have been modified by utilizing various ratios of the traditional electrophilic component, 4,4′-difluorobenzophenone, 1, utilized to synthesize PEEK and a comonomer, 3,5-difluorobenzophenone, 2, which is simply a geometric isomer of 1. The resulting polymers (“m-PEEK”) have the same chemical composition as PEEK, allowing for accurate structure–property relationships to be determined. The thermal properties were investigated by thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). The ratio of monomer 1 to monomer 2 had a dramatic influence on the thermal properties and solubility characteristics of PEEK. At higher ratios, 90:10, 85:15, and 80:20, the materials were semi-crystalline and their solubility was very limited in solvents such as N-methyl-pyrrolidinone (NMP) while at lower ratios, 75:25 and 50:50, the PEEK derivatives were completely amorphous and soluble in NMP. TGA analysis indicated excellent thermal stability as most of the materials displayed 5% weight loss temperatures (Td-5%) greater than 450 °C.