Effects of swelling and annealing on the viscoelastic behavior of solution‐crystallized and melt‐crystallized samples of fractionated polypropylene

Dynamic viscoelastic measurements, E′ and E″, were carried out on solution-crystallized and melt-crystallized samples of fractionated isotactic polypropylene over the temperature range of −100°C to 150°C. The molecular weight ranged from 1.26 × 104 to 1.77 × 105. The effects of swelling and annealing on the α and β peaks were more pronounced for the lower molecular weight fraction than for the higher one. It was found that both the untreated solution-crystallized and quenched melt-crystallized samples contain a fair amounts of a constrained amorphous phase in which the molecular motions were so depressed that the corresponding peak could be observed as the low-temperature component of the α peak. These constraints on the molecular motions are considered to originate from the spatial restrictions imposed by the presence of the surrounding crystallities.