Novel phosphine containing poly(arylene ether)s with trivalent phosphorus are prepared by reaction of bis(4-fluorophenyl) phenylphosphine with 2,2-bis(4-hydroxyphenyl)propane. The reaction conditions are adjusted to avoid partial oxidation of the phosphine derivative during polycondensation. Solution polycondensation results in copolymers with phosphine and phosphorus oxide containing repeating units with high molar contents of phosphine oxide (up to 45 mol% P = O repeating units), while solvent-free melt polycondensation of bis(4-fluorophenyl) phenylphosphine with bis(trimethylsilyl)-2,2-bis(4-oxyphenyl)propane and CsF as catalyst yields 85 mol% phosphine containing repeating units. The weight-averaged molar masses are in the range of 40,000 g/mol.The phosphine containing polymers are used, to illustrate an example, as polymeric reagent in the Mitsunobu reaction for the etherification of 5-hydroxyisophthalic acid dimethylester with henicosaperfluoroicosanol to yield a monomer for semifluorinated polyesters. The Mitsunobu reaction requires triaryl phosphine derivatives as reactants which are oxidized to phosphorus(V) compounds during the course of the reaction. The separation of the oxidized products in the reaction with triphenyl phosphine (TPP) is generally complicated and the application of the novel poly(aryl ether)s results in simplification of the work-up and increase of the yield of the desired product (33% with TPP vs. 55% with the phosphine containing poly(aryl ether) P13). Thus, the applicability of the polymers as polymer-supported phosphine derivatives replacing low molar mass phosphines is demonstrated.