Gas Selective Properties of Poly(4-Methyl-1-Pentene) Modifed by Gas Phase Fluorination

Fluorine-containing polymers have a number of valuable physical and chemical properties, such as high chemical and heat resistance, high mechanical strength and highly selective gas separation characteristics. One of the ways to produce fluoropolymer membranes is through surface fluorination. The modifcation of commercial polymers with membrane properties, poly(4-methyl-1-pentene) (PMP) in particular, is of special interest. PMP is widely used in the creation of protective coatings in microelectronics and it is used in membrane oxygenation. This paper presents new results for the gas-phase fluorination of PMP flms with improved gas separation characteristics. The fluorination is confrmed by infrared (IR) spectroscopy. It is shown that such modifcation of PMP under “soft” conditions leads to an increase in the ideal selectivity of He/CH4 and CO2/CH4 by up to 2.0 and 4.3 times, respectively, which is in contrast to data described in the available literature. Gas separation properties of PMP flms were monitored for 22 months. It is shown that the permeability coefcients of CO2 and CH4 after 5 months decrease by 2.7 and 6.0 times, respectively, and then return to values below those for virgin PMP flms. The permeability coefcients of He pass through a minimum as well and then return at values higher than the initial ones. The permeability of C1-C4 alkanes in fluorinated PMP was estimated by using the correlation approach. It is shown that modifed PMP has a practical application in the separation of the He from natural gas and for the separation of lower hydrocarbons as its components.