SBS/VP homograft membrane for oxygen enrichment

The grafting of 4‐vinyl pyridine (VP) onto styrene‐butadiene‐styrene triblock copolymers (SBS) by homografting irradiation with dissolved oxygen was studied. Homograft membranes of various degree of grafting were prepared from a casting solution of grafted copolymer in benzene. The mechanical properties of membranes, gas permeability, and the effect of operating temperature on gas permeation were investigated. The degree of grafting of 8.4% was the largest at an irradiation time of about 15.5 h. It was smaller at both shorter and longer duration because of the interference of dissolved oxygen. It was found that the tensile strength and elongation of SBS‐g‐VP were similar to those of SBS. The stress relaxation of SBS‐g‐VP was slower than that of SBS, and this might be due to the formation of rigid microphase separation domain of poly(4‐vinyl pyridine), which acted as permanent crosslinking points to reduce the stress relaxation. Using the properties of high flux of SBS and high O₂/N₂ selectivity of poly(4‐vinyl pyridine), the performance of gas permeation of 4‐vinyl pyridine homografted SBS membrane was studied. The selectivity of SBS‐g‐VP membrane increased with increasing degree of grafting. However, it was done at the expense of a decrease in the gas permeability. When the operating temperature of gas permeation increased, the permeability of oxygen and nitrogen increased, and the O₂/N₂ permeability ratio decreased. The activation energy (Ep) for gas permeation through different degree of grafting of SBS‐g‐VP membrane (obtained by the Arrhenius law) increased with increasing degree of grafting. For ungrafted SBS membrane, Ep was 5.5 kcal/mol for oxygen and 7.2 kcal/mol for nitrogen. For 8.4% grafting degree SBS‐g‐VP membrane, Ep for oxygen and nitrogen, were 6.5 and 8.1 kcal/mol, respectively.