Surface photografting of polymer fibers, films and sheets

Abstract

In our recent work on surface photografting, we have studied the molecular mechanism of the grafting reaction and found that the far UV irradiation at 250 nm is the main activation wavelength for the benzophenone to singlet state (S 2 about 110 kcal/mol). When the BPS 2 is transformed to BPS 1 and the triplet states T 1 and T 2 (about 70 kcal/mol), the excess energy is transferred to the substrate where the BPT 1 and T 2 are reacting with the activated substrate groups by hydrogen transfer and form substrate radicals which add monomer leading to grafted chains. We have further studied the rate of penetration of the grafting reaction into the substrate fibers and films. In the continuous process for surface photografting, the reactions are fast and give a very thin layer of grafted polymer (<10 nm) in a few seconds with no or very small effects on the bulk of the substrate. In the batch process carried out between two substrate films, the reaction is slow and requires a few minutes. Both initiator and monomer diffuse into and through the substrate films. Grafting occurs on both sides of the substrate films.