The thermodynamics of polyolefins in reaction mixtures is of considerable interest because sorption and diffusion in growing polymer particles strongly affect polymerization rate, copolymer composition, and subsequent product degassing. The thermodynamics of polyethylene (PE)/hydrocarbon systems related to gas-phase polymerization was extensively studied and described in the literature. However, such data are not yet available for PE–liquid penetrant systems related to slurry polymerization. Hence, we developed a simple methodology for investigating the solubility of liquid penetrants in polymer samples. Common diluents (n-octane, n-hexane, n-pentane) were sorbed in PE samples of varying density from 902 to 967 kg m–3. Equilibrium solubilities were obtained by extrapolation from the drying data using the initial slope method. The dependence of liquid n-hexane solubility in PE on temperature (in the range 25–68 °C) is the principal outcome of our measurements. Comprehensive measurements provide a unique set of thermodynamic data useful especially for slurry olefin polymerizations.

The attempts to predict the swelling of semicrystalline polyolefins using equations of state have not been successful so far and the few conducted experimental investigations have been limited to a narrow range of samples and conditions. This article presents a systematic video‐microscopic study of the swelling induced in various grades of PE particles by the sorption of ethylene and co‐monomers (propylene, 1‐hexene) at condition relevant to gas‐phase polymerization. Based on experimental data for various PE densities, the swelling factor H was evaluated, which enables the prediction of PE swelling by ethylene. The swelling data were compared with the corresponding gravimetrically measured sorption isotherms. In the case of ethylene and propylene sorption, the swelling significantly influences the evaluation of sorption isotherms. Conversely, the effect of swelling was negligible for higher hydrocarbons. The observed impact of swelling on the sorption is discussed based on the evaluated partial molar volumes of penetrants. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017, 134, 45035.