Physical aging in amorphous polymers causes a decrease in specific volume and thus in the gas transport properties of their membranes. In this work, the effect of simultaneous thermal decomposition of a thermolabile tert-butyl carbonate group, BOC, and cross-linking by a propargyl group (−CH2–CCH) on the gas selectivity–permeability properties of the resulting membranes is studied to learn how membranes with mitigated variations in the gas permeability coefficients with aging time may be produced. The model copolymer is a poly(oxyindole biphenylylene) that bears BOC and propargyl groups, [(PN-BOC) x -(PN-Pr) y ] n . Systematic studies on the structure/processing/property relationship assessed by TGA, DSC, and permeation measurement using pure gases reveal that a single thermal treatment for 1 h at 240 °C on a neat copolymer membrane, 12–20 μm thickness, is enough to produce chemically robust membranes (insoluble in NMP and DMSO) and that are physically more resistant to aging since the permeability reduction rate approaches zero. The cross-linked membranes possess lower gas permeability coefficients with higher ideal selectivity with respect to the corresponding neat copolymer membranes, i.e., the P(H2) decreases from 60 to 42 Barrers but H2/CH4 selectivity increases by a factor of 2 (21 to 40), and in general the selectivity–permeability properties for the gas pairs H2/CH4, O2/N2, and CO2/CH4 do not present drastic variations with aging time at least from 72 to 2000 h.
This work studies useful routes to produce cross-linked poly(oxyindole biphenylylene) bearing a crosslinkable propargyl group, PNPr. Thus, the effect of crosslinking temperature and time on gas permeability and ideal selectivity for a non-cross-linked PNPr membrane to produce a cross-linked PNPr membrane is studied in detail in order to learn how more productive membranes, in terms of permeability−selectivity combinations, and membranes resistant to solvent swelling and CO 2 plasticization may be produced. Systematic studies on structure/processing/property relationship assessed by Fourier transform infrared attenuated total reflectance (FTIR-ATR), gel content (GC [%]), swelling degree (SD [%]), specific volume, wide-angle X-ray diffraction (WAXD), and gas permeability measurements reveal that PNPr membranes cross-linked under vacuum (1 mmHg) at 190 °C for 24 h, and further vacuum-annealed for 1584 h, at 35 °C and 10 −3 mmHg, produce membranes that overcome the typical trade-off between permeability and selectivity. In effect, the thermally cross-linked membranes annealed under vacuum for 1584 h, as compared to the non-cross-linked membranes, possess P(H 2 ) and P(CO 2 ) that increase by 2.4 and 2.1 factors while selectivity increases from 25 to 45 for the H 2 / CH 4 pair and from 25 to 39 for the CO 2 /CH 4 pair, whereas P(O 2 ) increases by a 2.4 factor with an associated increase in selectivity from 4.4 to 9.6 for O 2 /N 2 which situates this membrane above Robeson's 2008 upper-bound limit, at least for this pair of gases. The cross-linked membranes are resistant to solvent selling, since their SD [%] in NMP is on the order of 1−3%, and also to CO 2 plasticization since the plasticization pressure was not observed at least up to the 18 bar upstream pressure studied here.
Design of polymer concrete involves extensive studies on their materials in order to get improved properties; specifically on the physicochemical properties of both polymer resin and mineral aggregates, including size and shape of the last one. Alternative studies are focusing on using different materials or methods to obtain such improvements. In this work, polymer concrete was elaborated with unsaturated polyester resin, marble particles and polypropylene fibres, after it was modified by using gamma radiation to achieve a complete polymerization. The results show improvements in the compressive strength and in the modulus of elasticity with 0.2 vol.% of polypropylene fibres and irradiation at a dose of 250 KGy. However, lower compressive strains were obtained when using gamma radiation.
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