INFLUENCE OF THE STRETCHING RATE ON THE TRANSITION FRONT STRUCTURE OFUNIAXIALLY DEFORMED ISOTACTIC POLY(PROPYLENE)

Recent models on the melting process of polymer crystals allow the stu dy of semicrystalline polymer structures by calorimetric (DSC) measure ments. In particular, this work is devoted to the study of those chang es occurring during the deformation process of isotactic poly(propylen e) samples along the transition front. By observing the evolution of t he parameter of intrachain melting cooperativity in comparison with, l amellar thickness, it has been possible to characterise the birth and further evolution of double fold molecules, totally extended polymer c hains connecting two adjacent crystallites in the fibrillar structure, ''taut tie molecules''. Furthermore, those structural changes depend on the stretching conditions. In general, low rate promotes high lamel lar fragmentation and the presence of a small number of taut tie molec ules. On the contrary, at higher rates crystallites coming from the or iginal lamella show bigger size and a higher number of tie molecules a re achieved.