Molecular packing and diffusion in polyisobutylene

Abstract

Polyisobutylene (PIB) is an elastomer that is notable for low rates of diffusion of small molecules. This has been suggested to be due to efficient intermolecular packing as evidenced by relatively low specific volume. In the present work these questions were studied via simulations. Polyethylene (PE), which is chemically isomeric with PIB, was studied as a comparison material. Monte Carlo simulations of bulk PIB were carried out at constant temperature and pressure, and molecular dynamics simulations of methane diffusion in both polymers were made. The MC simulations result in lower specific volumes for PIB compared to PE, as observed experimentally. The more efficient packing in PIB is attributed to the unoccupied volume in the systems being largely at the intermolecular interfaces and thus a molecular surface phenomenon. The thicker cross-sectioned PIB molecules have less surface area per carbon atom. The MD simulations show a slower diffusion rate in PIB. Further simulations at different densities show the diffusion to be very sensitive to small volume changes. For example, diffusion in PIB at the experimental density of polyethylene is calculated to be faster than for PE at this density.

Molecular Modeling Simulations to Predict Density and Solubility Parameters of Ionic Liquids

“…This difference is more noticeable for MD simulations. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 (a) Reference [13] (b) Reference [7] (c) Reference [10] 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 …”

Design of functional macromonomer derivatives of poly(isobutylene‐co‐isoprene)

“…Methacrylic acid (0.322 g, 3.7 mmol) was treated with a 1 mol/L solution of Bu 4 NOH in methanol (3.7 mL, 3.7 mmol Bu 4 NOH) to yield the desired Bu 4 Ncarboxylate salt, which was isolated by removing methanol under vacuum. BIIR (11 g) and Bu 4 NBr (0.53 g, 1.65 mmol) were dissolved in toluene (100 g) and heated to 85 8C for 180 min.…”

“…[4] Much of the kilotonne quantities prepared in Canada and worldwide are halogenated to give bromobutyl rubber (BIIR) and chlorobutyl rubber (CIIR), whose sulphur cure reactivity is sufficient for tire inner liner formulations. Unfortunately, residual activating reagents and halogenated cure byproducts make these vulcanizates problematic for a wide range of packaging and health-related consumer applications due to the presence of significant quantities of leachables and extractables.…”

Evaluation of encapsulating coatings on the performance of polypyrrole actuators

“…At room temperature, PS remains below its glass transition temperature and forms glassy spherical domains within an elastomeric PIB matrix. PIB itself is an elastomer notable for low diffusion of small molecules [22]. Spray coating was chosen since it is a fast and simple technique to apply gel coatings with various thicknesses, and unlike dip coating there is no direct contact taking place between the substrate and the coating solution.…”