Surface-selective photo-grafting on porous polymer membranes via a synergist immobilization method

A novel synergist immobilization photo-graft polymerization method has been developed to functionalize polymer materials in polar organic solutions. This two-step method, based on the immobilization of tertiary amine groups as synergists for the photoinitiator benzophenone (BP), had been evaluated for commercial hydrophilized polypropylene (PP) microfiltration membranes. It was shown that the hydrophilization of the PP membrane was due to a thin layer of a polyacrylate, and reaction conditions for the introduction of tertiary amino groups via an aminolysis reaction with N,N-diethylethylenediamine had been optimized. Compared with the original membrane, aminolysed membranes demonstrated high surface-selectivity for photo-grafting of polyacrylamide from methanol solution. Grafting density and polymer chain length can be well controlled by adjusting the main functionalization parameters (synergist surface concentration, BP concentration, UV irradiation time and monomer concentration). The mechanism had been analysed based on the effects of the main functionalization parameters mentioned above. The membrane pore structure was verified to be well maintained based on SEM analyses, the pore size distribution and water permeability of the membranes. The primary functionalization via aminolysis should be applicable to all polymers with ester groups on their surfaces. Via the synergist immobilization method numerous monomers which are soluble in organic solvents can be effectively grafted onto polymer surfaces for various tailored functionalizations.