AbstractA method for determining polymer melting temperatures,Tm, based on a simple modification of thermo‐optical analysis is described. The method makes use of a small, highly conducting substrate and a preselectedTm, procedure which results in rapid heating rates (∼1500°C/min) without temperature overshoot or superheating. Accuracies to within ±0.15°C are readily obtained. Application of the method to isothermally crystallized polyoxymethylene (Delrin 100 and 500) shows thatTm, increases with both time and temperature of crystallization as well as with increasing molecular weight. The potential of the method for characterizing polymer thermal history and molecular weight is dis