Copolymers of telechelic poly(2,6-dimethyl-1,4-phenylene ether) segments with terephthalic methyl ester endgroups (PPE-2T, 3700 g/mol) and different diols were made via a polycondensation reaction. The terephthalic endgroups of PPE-2T are stable during this reaction. The T-g of these polyether-ester copolymers decreases with increasing diol length and diol flexibility. The T-g can be set between 100 and 200 degreesC by changing the type of diol. However at increasing diol length the T-g becomes broader and the test bars are less transparent because the extent of phase separation increases with increasing diol length. Only polymers with a diol length up to C12 are homogeneous. Phase separation is probably enhanced by the bimodal molecular weight distribution of PPE-2T. Phase separation can be suppressed by using shorter PPE-2T segments with a short diol. It is even better to use fractionated, monomodal PPE-2T. Copolymerisation is much more effective in decreasing the T-g of PPE and therefore its processability than blending with polystyrene. It is expected that the processability of these copolymers is much better than that of PPE. (C) 2003 Published by Elsevier Ltd.