A monofunctional phosphine oxide containing endcapping reagent, 4-carboxyphenyl biphenyl phosphine oxide, was synthesized for the preparation of telechelic polyester oligomers. The chemical structure of the endcapping reagent was verified using NMR spectroscopy, mass spectroscopy, and elemental analysis. Phosphine oxide telechelic polyesters were prepared for the first time via copolymerization of a low molar mass polyester oligomer precursor and the phosphine oxide endcapping reagent in the melt state. The quantitative incorporation of telechelic phosphine oxide functionality was confirmed using H-1 NMR spectroscopy and elemental analysis. The corresponding complexes of phosphine oxide terminated polyesters and cobalt(II) chloride were prepared via charging the cobalt salt at the onset of melt polymerization. P-31{H-1} NMR spectroscopy, FT-IR spectroscopy, and UV-vis spectroscopy indicated that the cobalt(II) ion preferentially coordinated with the phosphine oxide end groups. The complexes exhibited higher melt viscosity than their salt-free analogues due to the formation of coordinated polymers. The presence of the telechelic phosphine oxide end groups also aided in the homogeneous dispersion of the cobalt salt in a poly(ethylene terephthalate) (PET) matrix. (c) 2006 Elsevier Ltd. All rights reserved.