Porous Polypropylene Membranes with Different Carboxyl Polymer Brush Layers for Reversible Protein Binding via Surface-Initiated Graft Copolymerization

Abstract

Photoinitiated surface-selective graft copolymerization onto polypropylene (PP) microfiltration membranes was performed using two different methods for coating the photoinitiator, benzophenone (BP), on the membrane surface. An already established adsorption method and a novel method based on preswelling of the PP in heptane, subsequent solvent exchange, and thus entrapping of the BP in the surface layer of the PP had been evaluated. With acrylic acid (AA) as the monomer, functional polymer brush structures on the entire membrane pore surface were obtained. Further variations of the grafted layer had been achieved by copolymerization of AA with acryl amide (AAm) and methylene bisacrylamide (MBAA). Characterization had been done mainly by detailed measurements of membrane permeability including pH dependency as well as the reversible binding of a protein (lysozyme, Lys) under membrane chromatography conditions. Compared with BP adsorption, the BP entrapping method yielded a less dense grafted layer with longer PAA chains at the same degree of functionalization (DG). This was due to somewhat lower immobilized BP amounts, but also less side reactions via nonselective photoinitiated cross-linking by dissolved BP. Unexpected properties of the PAA-co-AAm brush layers were their even larger swelling/deswelling as a function of a pH change (above and below the pK a of PAA) as compared with the PAA brushes. Both PAA-co-AAm and cross-linked PAA-co-MBAA layers showed Lys binding capacitiessmore than 10 times higher than monolayer adsorption onto the unmodified PP membrane surfacesand quantitative recoveries similar to PAA of the same DG; and the highest efficiencies of protein binding (Lys amount relative to amount graft copolymer) were achieved with the membranes prepared by the entrapping method. In general, the more controlled BP entrapping method had distinct advantages in terms of the control of grafted layer structure leading to an improved membrane adsorber performance.

Surface functionalization of PHBV by HEMA grafting via UV treatment: Comparison with thermal free radical polymerization

“…It is well known that excited BP can abstract hydrogen in the absence of monomer to form surface with semipinacol groups. 23,32,33 In presence of H 2 O 2 , hydroperoxide functions were generated directly on the PHBHV film via UV treatment in the presence of oxygen. Several authors have reported that hydroxyl radicals formed under UV irradiation have the ability to abstract hydrogens from the backbone of polymer producing macroradicals, which can react with the monomer to initiate grafting during the second step.…”

“…23,32,33 This process in two separate steps should take over better control of surface modification in comparison with free radical method developed previously because it can be considered as a ''quasi-living'' polymerization via recombination and photocleavage of semipinacol radical. 32,33 We have chosen to apply this procedure to PHBHV for grafting PHEMA either with BP as photoinitiator or H 2 O 2 to create photolabile functions on the polymer surface. Then in a second step, the functionalized films were put in contact with the monomer solution to achieve UV-initiated graft copolymerization.…”

Self‐Supporting, Double Stimuli‐Responsive Porous Membranes From Polystyrene‐block‐poly(N,N‐dimethylaminoethyl methacrylate) Diblock Copolymers

“…A very important issue is also the additional functionalization of membrane materials. [6] Often, membrane surfaces are post-functionalized through ''grafting-to,'' [7] ''grafting-from,'' [8] or reactive coating with polymers. [9] An alternative are additives to the membrane polymer, and special graft or block copolymers have already been found to be rather efficient in rendering the surface of porous membranes from standard engineering polymers such as poly (vinylidene fluoride) or polyethersulfone more hydrophilic and less susceptible to fouling.…”

Tailored “Grafting‐From” Functionalization of Microfiltration Membrane Surface Photo‐Initiated by Immobilized Iniferter

“…[5][6][7][8][9][10] Thus, the functionalized membranes have been explored for many applications according to base membrane structure and newly endowed functions. [1,11] For example, via tailored grafted functional polymeric layers on their entire surface, porous polymer base membranes are rendered waterwettable and low-fouling for filtration and fractionation processes, can been turned into highly efficient membrane adsorbers or are developed toward stimuli-responsive materials where the pores open or close upon changes of, e.g., pH value or temperature.…”