The effect of melting conditions on the iPB-1 structure and the II → I phase transformation rate

The melting conditions, mainly the temperature and time, influence a polymer samples characteristics. Changes in normal or repeated melting procedures can influence the crystallinity, phase, structure, phase transformation rate and type of polymorphous polymers as was demonstrated here on a sample of isotactic polybutene-1. In the treatment temperature range 120-130 °C and 5 min treatment time the phase II → I transformation type after crystallization was neutral (N), which was faster than the type M (slow transformation type), which took place when the treatment temperature was 160 °C or higher. The change from N to M transformation type involved the formation of an induction period. During this period some configuration or crystal changes can take place in the sample, and the newly formed structures block the phase transformation nuclei until all of the newly formed blocking structures have reacted with the transformation nuclei and then the formation of phase I nuclei and their growth can start again. Based on the results here, as an initial standard thermal history for molded iPB-1 samples, avoiding the M transformation type, holding 5 min at 120-130 °C, followed by free cooling to room temperature and pressure is recommended.