Four powd. samples of syndiotactic polypropylene with mol. wts. 27,000 to 826,000 and fraction of syndiotactic pentads 88% to 91% quenched from the melt in an ice-water bath were extd. at room temp. and aged for 1 mo. Changes in the structural organization during the aging time at room temp. were followed by x-ray, transport property, and IR anal. The x-ray diffractograms showed that all the fresh samples crystd. in the disordered helical form I, contg. also a fraction of chains in trans-planar conformation. The helical crystallinity was found very similar for all the samples, and a small increase of this parameter, not higher than 4-6%, was obsd. during the aging time. At variance, a study of sorption of CH2Cl2 vapor at low activity indicated the presence of an intermediate phase not cryst., yet impermeable to the vapors, increasing during the aging at room temp. The fraction of the intermediate phase was very high in the lowest mol. wt. sample, and decreased on increasing the mol. wt., reaching a const. value for mol. wts. higher than 80,000. Anal. of the IR spectra showed that the helical bands increase during the aging, indicating that the intermediate phase is composed by very small and disordered helical crystals. The elastic modulus of each sample was measured soon after quenching and during the aging. WE found a consistent increase of this parameter, not ascribable only to the small increase of crystallinity. An increase of the elastic modulus of all the samples was correlated to the increase of the intermediate phase derived by sorption, and a good dependence on this parameter was found.
Influence of molecular weight on the structure and ageing behavior of quenched syndiotactic poly(propylene)
GUADAGNO, Liberata;GORRASI, Giuliana;LONGO, Pasquale;PRAGLIOLA, Stefania
2002-01-01
Abstract
Four powd. samples of syndiotactic polypropylene with mol. wts. 27,000 to 826,000 and fraction of syndiotactic pentads 88% to 91% quenched from the melt in an ice-water bath were extd. at room temp. and aged for 1 mo. Changes in the structural organization during the aging time at room temp. were followed by x-ray, transport property, and IR anal. The x-ray diffractograms showed that all the fresh samples crystd. in the disordered helical form I, contg. also a fraction of chains in trans-planar conformation. The helical crystallinity was found very similar for all the samples, and a small increase of this parameter, not higher than 4-6%, was obsd. during the aging time. At variance, a study of sorption of CH2Cl2 vapor at low activity indicated the presence of an intermediate phase not cryst., yet impermeable to the vapors, increasing during the aging at room temp. The fraction of the intermediate phase was very high in the lowest mol. wt. sample, and decreased on increasing the mol. wt., reaching a const. value for mol. wts. higher than 80,000. Anal. of the IR spectra showed that the helical bands increase during the aging, indicating that the intermediate phase is composed by very small and disordered helical crystals. The elastic modulus of each sample was measured soon after quenching and during the aging. WE found a consistent increase of this parameter, not ascribable only to the small increase of crystallinity. An increase of the elastic modulus of all the samples was correlated to the increase of the intermediate phase derived by sorption, and a good dependence on this parameter was found.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
