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Positron studies of the temperature-dependence of free volumes in Polydimethyls...
Marques, M. F. Ferreira; Gordo, P. M.; Kajcsos, Zs.; Gil, C. Lopes; Lima, A. P. de; Queiroz, D. P.; Pinho, M .N. deFree-volume parameters in polyurethane/urea membranes have been studied by positron annihilation lifetime and Doppler broadening measurements. The bi-soft segment membranes were obtained by varying the ratio of the structural constituents, polypropylene oxide and polydimethylsiloxane (PU/PDMS), with PDMS content from 25 to 75 wt%. The free-volume holes determined by PALS are correlated with gas permeation featu...
Free-volume studies in polyurethane membranes by positron annihilation spectros...
Marques, M. F. Ferreira; Gil, C. Lopes; Gordo, P. M.; Kajcsos, Zs.; Lima, A. P. de; Queiroz, D. P.; Pinho, M. N. deThe free-volume parameters in various urethane/urea membranes obtained by varying the ratio of the structural constituents, polypropylene oxide and polybutadiene, were studied by positron lifetime and Doppler broadening measurements. On bi-soft segment membranes, a correlation was found between the composition of membranes, the normalized free volume, the radii of the holes and gas permeability. However, the co...
Structural characteristics and gas permeation properties of polynorbornenes wit...
Zhao, Chun-tian; Ribeiro, M. do Rosário; Pinho, M. N. de; Subrahmanyam, V. S.; Gil, C. L.; Lima, A. P. dePolynorbornenes of different molecular weights were synthesised by addition polymerisation, using a nickel based catalyst. This polymerisation route leads to amorphous polymers that were shown to display unique properties: high glass transition temperature, rigid random coil conformation, and dense packing in the amorphous state. Gas permeation membranes were prepared from these addition type non-substituted po...
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