Preparation of SBS-g-VP copolymer membrane by UV radiation without degassing

The solvent-cast film of styrene-butadiene-styrene triblock copolymer (SBS) was prepared, and the grafting of 4-vinyl pyridine (VP) to the SBS membrane was induced by ultraviolet radiation without degassing to obtain the SBS-g-VP copolymer membrane. The chemical composition of the graft copolymer membrane was studied by infrared spectroscopy. In addition to those absorption peaks associated with pure SBS, the SBS-g-VP graft copolymer also showed a peak of absorption at 820 cm^-1, which appeared in the spectra of homopolyvinylpyridine. The degree of grafting and the mechanical properties of SBS and SBS-g-VP were measured. Contact angle, water content, and protein absorption of fibrinogen and albumin experiments were also performed to evaluate the blood biocompatibility of the SBS-g-VP membrane. It was found that the degree of grafting exhibited an approximate linear increase with VP concentration at 0°C. The degree of grafting increased sharply with VP concentration above 30% v/v at 10°C. The degree of grafting increased with VP concentration and then leveled off when the temperature was at 30°C. The rate of grafting followed Arrhenius law. The activation energy obtained was 3.25 kcal/mol. PolyVP has a glass transition temperature (T_g) at about 240°C, and hence, it performes as a hard rigid plastic at room temperature. Therefore, the SBS-g-VP graft copolymer showed the plastic performance with increasing degree of grafting. The surface tension of SBS-g-VP was determined by using Kaelble's equation and the contact angle data. It was found that the surface tension and water content of SBS-g-VP membrane increased, whereas the contact angle decreased with grafting degree. Albumin and fibrinogen adsorption increased with time and reached a steady-state level after 20 and 40 min, respectively. The maximum desorption appeared in 30 min for albumin, but it took more time to reach maximum desorption for fibrinogen. The amount of protein adsorption decreased with the increasing of grafting degree, and the amount of protein adsorption eventually leveled off.