The appearance of double melting endotherms in dynamic d.s.c, runs of polypropylene fractions was studied with the aim of relating their appearance to the structure of the polymer. Fractions obtained by fractionation either according to stereoregularity or to molecular weight were investigated. Double peaks were detected for low molecular weight, non-isotactic fractions, as well as for low molecular weight fractions with isotacticities around 90%. Fractions consisted of pure ~ crystal form and those showing double melting endotherms had low average isotactic sequence lengths, generally below 80 propylene units. The occurrence of double-peak shapes was attributed to two different processes, one characteristic of highly stereoirregular material, and probably constituted by melting of two different crystalline species, and the other consisting of reorganization or recrystallization of less-ordered domains of crystalline material taking place during the melting scan.
Посилання на статтю:
Thermal behaviour of polypropylene fractions: 2. The multiple melting peaks / Ritva Paukkeri and Arja Lehtinen // Polymer. – 1993. – Vol 34. – P. 4083-4088.