Poly(4-methyl-1-pentene) as a semicrystalline polymeric matrix for gas separating membranes

Abstract The appearance of gas (vapor) membrane separation technologies stimulates the expansion of the boundaries of the existing membrane material applications. One of these materials is commercially available poly(4-methyl-1-pentene) (PMP). This paper presents results of a theoretical and experimental study of selective gas transfer in PMP with varying degrees of crystallinity. In this study, the experimental measurements of selective gas transfer were carried out in the range of temperatures covering the glassy and high-elasticity state of the amorphous PMP phase. Pierotti's theory was used to estimate the solubility coefficients of ethane in the crystalline and amorphous PMP phases. The diffusion (D), solubility (S), and permeability (P) coefficients of the amorphous and crystalline PMP phase with respect to lower alkanes were determined for the first time. It was shown that the PMP crystalline phase is selectively permeable to gases with the properties, that are close to those of the amorphous phase below the Tg. It can be concluded that the crystalline phase “works” according to the solution–diffusion model and makes a significant contribution to the gas permeability of PMP. It is noted that the PMP crystalline phase has high selectivity for C1–C4 alkane separation.