Abstract
The aim of this work was to develop integral asymmetric membranes via self-assembly and non-solvent induced phase inversion process from novel diblock and triblock copolymers. Diblock copolymers of polystyrene-block-poly(solketal methacrylate) (PS-b-PSMA) of different composition were successfully synthesized by sequential living anionic polymerization whereas polystyrene-b-poly(glyceryl methacrylate) (PS-b-PGMA) were obtained by acid hydrolysis of the acetonide groups of the poly(solketal methacrylate) (PSMA) blocks into poly(glyceryl methacrylate) (PGMA). By utilizing the binary THF/DMF and ternary THF/DMF/DOX solvent system, integral asymmetric membranes of PS-b-PGMA via self-assembly and non-solvent-induced phase separation process could be achieved. Later, a comparative study of amphiphilic PS-b-PGMA and hydrophobic PS-b-PSMA diblock copolymers for the development of isoporous integral asymmetric membranes was presented. Within this study, no suitable solvents were found to prepare isoporous membranes from the PS-b-PSMA diblock copolymer. This will require a more subtle choice of solvents, as the level of selectivity of a solvent and non-solvent is much less pronounced in a block copolymer composed of similar polar (or nonpolar) blocks.
Further, static protein adsorption measurements were performed to analyze the increase in hydrophilic behavior of isoporous membranes of PS-b-PGMA and were compared with a PS-b-P4VP system of similar molecular weight and block ratio. Different nanofillers were added to the PS-b-PGMA diblock copolymer system and the hybrid membranes fabricated via SNIPS.
For the first time, PS-b-P4VP-b-PSMA triblock terpolymers with varying compositions were successfully synthesized by sequential living anionic polymerization. Composite membranes of PS-b-P4VP-b-PSMA and PS-b-P4VP-b-PGMA triblock terpolymers with ordered hexagonally packed cylindrical pores were developed. The morphology of the membranes was studied with scanning electron microscopy (SEM) and atomic force microscopy (AFM). PS-b-P4VP-b-PSMA triblock terpolymer membranes were further treated with acid to get polystyrene-b-poly(4-vinylpyridine)-block-poly(glyceryl methacrylate) (PS-b-P4VP-b-PGMA). An increase in the hydrophilicity was observed after treatment of isoporous membranes from PS-b-P4VP-b-PSMA, through acidic hydrolysis of the hydrophobic poly(solketal methacrylate) PSMA block into a hydrophilic poly(glyceryl methacrylate) PGMA block, which contains two neighbored hydroxyl (–OH) groups per repeating unit. Notably, the pristine porous membrane structure could be maintained even after acidic hydrolysis. The membrane properties were analyzed further by contact angle, protein retention, and adsorption measurements. It was found that membranes containing hydroxyl groups (PS-b-P4VP-b-PGMA) show a stable and higher water permeance than membranes without hydroxyl groups (PS-b-P4VP-b-PSMA), what is due to the increase in hydrophilicity.
The new functional triblock terpolymer PS-b-P4VP-b-PGMA showed significantly lower (cut off) retention and fouling compared to the more hydrophobic PS-b-P4VP-b-PSMA precursor membrane and also compared to a PS-b-P4VP membrane, indicating a strong and positive influence of the third hydrophilic block on the membrane properties. Thus, the introduction of a highly functional and hydrophilic block containing repeating units with two hydroxyl groups could be carried out, which allows for a large variety of further post-modification reactions.
