The crystallization of cis-l,4-polyisoprene (PIP) in miscible blends with atactic poly (vinylethylene) (PVE) was investigated. Normalized to the PIP content, the extent of crystallization and the crystallization rate were suppressed in the mixtures. A reduction in the degree of crystallinity is contrary to the behaviour usually exhibited by blends in the absence of crosslinking. More anomalous was the observation that the magnitude of the crystallization suppression in the uncrosslinked PIP was independent of PVE concentration over a range from 5 to 50% PVE. Furthermore, whereas ~-lamellae predominate for pure PIP crystallization, blending with high-molecular-weight PVE caused preferential development of the/~-lamellar form. This bias may be a reflection of the known ability of the /~-lamellae to incorporate non-crystallizing entities more readily into the fold plane at the crystal surface. Changes in heat capacity at T~ measured before and after melting were consistent with the notion that PVE chains are trapped between the lamellae of the crystallizing PIP, with the extent of entrapment substantially greater for higher-molecular-weight PVE. The degree of crystallinity in the blends also varied with the molecular weight of the PVE, suggesting that suppression of the crystallization was a consequence of the entrapment of the PVE. In networks the suppression of crystallization significantly exceeded that observed in uncrosslinked blends and pure PIP networks. For free-radical crosslinking the presence of PVE increases the crosslink density of the PIP segments, contributing to the lower crystallinity in the crosslinked mixtures
Посилання на статтю:
Anomalies in the crystallization of cis-l,4-polyisoprene in blends with poly ( vi nylethylene ) / I. S. Zemel and C. M. Roland* // Polymer. – 1992. – Vol 33. – P. 3427-3432.