In Situ X‐Ray and Infrared Measurements of Alkane Absorption and Desorption Processes of Isotactic Poly(4‐Methyl‐1‐Pentene) Film

Abstract

AbstractSmall molecules are absorbed selectively in the amorphous regions in semicrystalline polymers, except for some specific polymeric systems forming host‐guest cocrystals such as syndiotactic polystyrene. The crystalline density of isotactic poly(4‐methyl‐1‐pentene) (P4MP1) is substantially lower than those of analogs, and it is even slightly lower than the amorphous density. This study is investigated the absorption/desorption behaviors of short alkanes in P4MP1 in situ, and found that the alkanes are mainly absorbed in its amorphous region. Infrared spectroscopy measurements reveal that the P4MP1 film with low crystallinity absorbs higher amount of decane than the high crystallinity film does. Also it is found by small‐angle X‐ray scattering (SAXS) that, when hexane is dropped onto the P4MP1 as‐cast film, a lamellar long‐spacing peak appears at 0.16 nm−1 which disappears with the spontaneous desorption of hexane. Because the pristine P4MP1 films give no obvious SAXS peak due to the close density of crystalline and amorphous regions, the appearance of the SAXS peak indicates that an X‐ray contrast is obtained by the preferential absorption to amorphous region. The disappearance of the peak is thus reasonably understood by the loss of the contrast due to desorption.