Improved syntheses of poly(oxy-1,3-phenylenecarbonyl-1,4-phenylene) and related poly(ether–ketones) using polyphosphoric acid/P2O5 as polymerization medium

Based on the model-compound studies, the composition of polyphosphoric acid (PPA)/P2O5 mixture as an effective catalytic/dehydrative medium for the preparation of poly(ether–ketones) was optimized. Thus, with the optimal weight ratio of 4:1 (PPA:P2O5), the electrophilic substitution polycondensation of 3-phenoxybenzoic acid and related AB monomers was substantially promoted at 130 °C to yield the subject polymer abbreviated as mPEK and related poly(ether–ketones) with significantly higher molecular weights. In the cases where the polymerization systems were completely homogeneous, the ensuing polycondensation was rapid and yielded high molecular weight polymers (e.g. mPEK [η]=2.10 dl/g) at 130 °C within 30 min., as compared to PPMA (phosphorus pentoxide/methanesulfonic acid) method which gave only moderate molecular weight polymers, e.g. mPEK ([η]=0.64 dl/g). In some cases, where the monomers and PPA/P2O5 were not fully compatible, polycondensation did proceed and reasonable molecular weight range ([η]=0.69–0.76 dl/g) could be achieved. However, the complete incompatibility between the poly(ether–sulfone) and PPA/P2O5 medium precluded the successful polymerization of 4-phenoxybenzenesulfonic acid.