STUDY ON SURFACE GRAFTING POLYMERIZATION OF CPP/AA SYSTEM WITH TWO-STEP METHOD

Surface grafting polymerization of cast polypropylene (CPP)/acrylic acid(AA) system was studied with two\|step method, which is a novel technique advantageous over traditional surface grafting polymerization initiated by UV.It consists of two steps.Firstly, dormant groups (semi benzopinacol) were introduced on the CPP film under UV irradiation in the presence of benzophenone (BP) solution; and then, AA was grafted on the substrate surface by thermoactivating polymerization.The principle is as following, after BP is excited with UV irradiation, it extracts the H atoms from CPP surface and is reduced into semipinacol free radicals, meanwhile macromolecular free radicals are produced on CPP film surface.Because of spatial hindrance originated from its aromatic group, it is difficult for semipinacol free radicals to perform coupling termination and so does the surface radical.If no monomer was available, these two kinds radicals will combine.When CPP film with dormant groups is heated in a monomer solution, the C—C bonds of surface semipinacol groups break into the surface free radicals and semipinacol free radicals.The surface radicals induced monomer to propagate, result in grafting chains; whileas the reactivity of semipinacole free radical is too low to initiate grafting polymerization.Consequently, this method has two advantages:high grafting efficiency and suited to more monomers which can not be used directly in traditional photografting polymerization.The results show that acetic anhydride is an ideal solvent for CPP/AA surface grafting system; grafting yield increases with the growth of photosensitizer and monomer concentration; and polymerization temperature has positive effect on grafting yield.The contact angle of grafted CPP film against water decreases with the increase of grafting yield.In addition, the grafted CPP g AA film was identified by FTIR spectra.