Films of syndiotactic polypropylene (sPP) elongated at room temperature up to a draw ratio λ = 6 showed the trans-planar form III with some trans-planar mesophase. Upon releasing tension, we obtained fibers with a high content of trans-planar mesophase and a small fraction of helical form II crystals. Released fibers were annealed at increasing temperatures up to 130°C, and the polymorphic behavior was investigated by X-ray and FTIR. Between 60 and 80°C, an increase of the helical forms I and II, both of them highly oriented, occurs, while the trans-planar mesophase practically disappears. Successive annealing at higher temperature brings further increase of both helical modifications until, around 130°C, significant percentages of form II melt and recrystallize in form I. The unrelaxed λ = 6 fiber was also annealed at 100°C, developing significant form II fractions along with form III and some form I. Two more sets of fibers were obtained under conditions in which the trans-planar mesophase was not present. In both cases, upon annealing at constant strain, no formation of the helical form II was observed and only a mixture of the trans-planar form III and the helical form I developed. The described observations suggest that, in oriented sPP samples, upon relaxing or annealing at temperatures below 100°C, the pseudohexagonal trans-planar mesophase plays a mayor role as precursor for crystallization of the chiral form II. This appears consistent with recently proposed analyses of chiral crystallization of helical polymers.

Development of form II crystallinity in oriented syndiotactic polypropylene: Role of the trans-planar mesophase

GUADAGNO, Liberata;D'ANIELLO, Concetta;NADDEO, Carlo;VITTORIA, Vittoria;MEILLE, STEFANO VALDO
2003

Abstract

Films of syndiotactic polypropylene (sPP) elongated at room temperature up to a draw ratio λ = 6 showed the trans-planar form III with some trans-planar mesophase. Upon releasing tension, we obtained fibers with a high content of trans-planar mesophase and a small fraction of helical form II crystals. Released fibers were annealed at increasing temperatures up to 130°C, and the polymorphic behavior was investigated by X-ray and FTIR. Between 60 and 80°C, an increase of the helical forms I and II, both of them highly oriented, occurs, while the trans-planar mesophase practically disappears. Successive annealing at higher temperature brings further increase of both helical modifications until, around 130°C, significant percentages of form II melt and recrystallize in form I. The unrelaxed λ = 6 fiber was also annealed at 100°C, developing significant form II fractions along with form III and some form I. Two more sets of fibers were obtained under conditions in which the trans-planar mesophase was not present. In both cases, upon annealing at constant strain, no formation of the helical form II was observed and only a mixture of the trans-planar form III and the helical form I developed. The described observations suggest that, in oriented sPP samples, upon relaxing or annealing at temperatures below 100°C, the pseudohexagonal trans-planar mesophase plays a mayor role as precursor for crystallization of the chiral form II. This appears consistent with recently proposed analyses of chiral crystallization of helical polymers.
File in questo prodotto:
Non ci sono file associati a questo prodotto.

I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.

Utilizza questo identificativo per citare o creare un link a questo documento: http://hdl.handle.net/11386/1064166
 Attenzione

Attenzione! I dati visualizzati non sono stati sottoposti a validazione da parte dell'ateneo

Citazioni
  • ???jsp.display-item.citation.pmc??? ND
  • Scopus 27
  • ???jsp.display-item.citation.isi??? ND
social impact