In this paper the dynamic mechanical preperties of POY spun at 1500-5000 m/min have been studied. Three peaks of a loss tangent have been shown: α1

α2 and the superposition of α1

α2. It reflects that as the spinning speed increases the amorphous regions of POY change from liberal to double and finally to a network.In order to correlate the molecular motion

the fibre formation and structure with the mechanical properties of POY

we introduce a molecular motion parameter which can be defined as. Experimental results show that there is a good relationship among ψ

structure parameter and mechanical properties.