Size and chemistry selective membranes from block polymer templates
The use of block polymers continues to gain attention with their myriad applications in industry for advanced applications in biology, medicine, electronics, and separations. The ability of block polymers to self assemble into ordered states on the nanometer level makes these materials suitable for applications that mandate structural order on this scale. By tuning the chemistry of these block domains, we may explore their utilization for advanced separations. In this dossier, we detail the efforts into the controlled radical polymerization of polyisoprene-b-polystyrene-b-poly( N,N-dimethylacrylamide) (PI-PS-PDMA) via. a facile reversible addition-fragmentation chain transfer (RAFT) mechanism. For this high molecular weight block polymer synthesis, it was experimentally established that rate retardation occurred during the addition of the PS and PDMA domains. Utilizing ab initio methods, it was determined that this rate retardation may be attributed to slow intermediate radical termination. Utilizing a scalable self-assembly and non-solvent induced phase separation (SNIPS) technique, casting a solution of PI-PS-PDMA as a convectively drying thin film before quenching in water affords an anisotropic, size-selective membrane template. Scanning electron microscopy imaging of these films yielded a pore density on the order of 1013 pores m-2 with pore sizes down to less than 1 nm, pushing the observed limits of size separation observed using block polymer membranes. Upon fashioning PI-PS-PDMA into membrane devices, the PDMA interior may be deprotected to a polyacrylic acid (PAA) functionality. Facile amidation chemistry of these deprotected PI-PS-P(Acrylate) templates to PI-PS-PAA membranes demonstrates these devices are versatile in their tunable capacity for size and chemistry separation of target analytes (e.g., small molecules and heavy metal salts). By incorporation of acrylate block chemistries into a PI-PS support, the potential for low pore sizes for separation of salts and small molecules using block polymers are possible. By integrating the tunable block polymer chemistry to enable chemical tuning of pores, precise chemo-selective control may be made for targeted elution of analytes and fouling resistant membranes for advanced reverse osmosis (RO) and small molecule purification for application in industry.
Boudouris, Purdue University.
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