Films of highly syndiotactic polypropylene (sPP) were quenched at different temperatures between 0 degrees C and 100 degrees C and analyzed as soon as prepared and after 1 month of aging at room temperature. Wide-angle X-ray diffractograms (WAXDs) showed that all the samples crystallized in the disordered helical form I, with the crystallinity increasing both on increasing the quenching temperature and on aging, although to a lower extent. The analysis of sorption and diffusion of dichloromethane vapor at low activity shows that, in some samples, the fraction of impermeable phase is consistently higher than the crystalline fraction. This induced us to hypothesize the presence of an intermediate phase, or mesophase, not crystalline, yet impermeable to the vapors. The fraction of mesophase decreases on increasing the quenching temperature, and it is a very small quantity at 100 degrees C. The dynamic-mechanical analysis showed two transitions in the aged samples, which could correspond to the lower and upper glass transitions, already suggested for aged films of isotactic polypropylene (IPP).
Structural organization of syndiotactic polypropylene films quenched at different temperatures
GUADAGNO, Liberata;VITTORIA, Vittoria;LONGO, Pasquale;
2000-01-01
Abstract
Films of highly syndiotactic polypropylene (sPP) were quenched at different temperatures between 0 degrees C and 100 degrees C and analyzed as soon as prepared and after 1 month of aging at room temperature. Wide-angle X-ray diffractograms (WAXDs) showed that all the samples crystallized in the disordered helical form I, with the crystallinity increasing both on increasing the quenching temperature and on aging, although to a lower extent. The analysis of sorption and diffusion of dichloromethane vapor at low activity shows that, in some samples, the fraction of impermeable phase is consistently higher than the crystalline fraction. This induced us to hypothesize the presence of an intermediate phase, or mesophase, not crystalline, yet impermeable to the vapors. The fraction of mesophase decreases on increasing the quenching temperature, and it is a very small quantity at 100 degrees C. The dynamic-mechanical analysis showed two transitions in the aged samples, which could correspond to the lower and upper glass transitions, already suggested for aged films of isotactic polypropylene (IPP).I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
