摘要：

Four samples of syndiotactic poly(propylene) were synthesized by changing either the polymerization temperature or the catalytic system. Samples with different molecular weights were obtained, ranging between 27000 and 826000, whereas the fraction of syndiotactic pentads was found very near in the different samples, ranging between 88 and 91%. The polymer powders were quenched from the melt in an ice-water bath, extracted at room temperature and aged for 1 month. Changes in the structural organization during the ageing time at room temperature were followed by X-rays, transport properties and infrared analysis. The X-ray diffractograms showed that all the fresh samples crystallized in the disordered helical form I, containing 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 observed during the ageing time. At variance, the study of sorption of a vapor at low activity indicated the presence of an intermediate phase not crystalline, yet impermeable to the vapors, increasing during the ageing at room temperature. The fraction of the intermediate phase was very high in the lowest molecular weight sample, and decreased on increasing the molecular weight, reaching a constant value for molecular weights higher than 80000. The analysis of the infrared spectra showed that the helical bands increase during the ageing, 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 ageing. It was found a consistent increase of this parameter, not ascribable only to the small increase of crystallinity. The 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. The absorbance of the helical bands at 810, 868, and 977 cm 1 , as a function of the ageing time.

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