(256a) Sulfonated Block Copolymer Technology for Water Treatment

Selectively middle-segment sulfonated pentablock copolymers¹, Nexar^TM polymers, exhibit strong phase segregation in the solid phase as well as in the presence of many solvents.  The phase separated structure of these polymers in solvent has been correlated with the morphology of the polymer in a cast membrane. 

Two distinct micelle structures have been observed in solutions of these polymers².  In aliphatic hydrocarbon solvents like cyclohexane, a micellar structure having the sulfonated styrene segment in the core of the micelle is observed.  On the other hand, polar solvents like N,N-dimethylacetamide, DMAc, afford micelles having the sulfonated styrene segment in the corona of the micelle.

 In the cast membrane, the transport properties of the material are regulated by an ion microphase (sulfonated polystyrene segment) while the hydrophobic thermoplastic microphase (poly-t-butylstyrene and hydrogenated isoprene segments) accounts, in large part, for the mechanical properties of the product.  The co-continuous nature of these two phases allows the generation of a material having simultaneously good transport characteristics and good mechanical properties.  As the mechanical performance of the cast membrane is derived from the physical (not chemical) crosslinking of the poly-t-butylstyrene end segments of the block copolymer, thin membranes are strong under both wet and dry conditions.  Water does not erode the strength mechanism that is holding these membranes intact.

The properties derived from this microphase separated structure of the cast membrane have been found to be useful in various applications where water and ion transport (reduced area resistance, elevated permselectivity) are valued in a membrane having strength whether wet or dry³. It is to be emphasized that the transport characteristics of these thin membranes are enhanced as the thickness of the membrane is reduced.  Thin, strong membranes, in turn, have been achieved as a consequence of the structure of the phase separated block copolymer.

The relationship between Nexar polymer structure in solvent and performance of the cast Nexar membrane in various water treatment applications will be discussed in this presentation.

References

(1)  Willis, C.L.; Handlin, D.L.; Trenor, S.R.; Mather, B.D.; US Patent 7,737,224 B2, 2010; ibid.; US Patent 7,919,565 B2, 2011; ibid.; US Patent 7,981,970 B2, 2011; ibid.; US Patent 8,003,733 B2, 2011; ibid.; US Patent 8,058,353 B2, 2011.

 (2) Choi, J.-H.; Kota, A.; Winey, K.I.; Industrial and Engineering Chemistry, 49, 12093-12097, 2010; Choi, J.-H.; Willis, C.L.; Winey, K.I.; Journal of Membrane Science, 394-395, 169-174, 2012.

(3) Willis, C.L.; Handlin, D.L.; Trenor, S.R.; Mather, B.D.; US Patent 8,084,546 B2.

(4) Geise, G.M.; Freeman, B. D.; Paul, D. R; Polymer, 51, 5815-5822, 2010; Geise, G. M; Lee, H.-S.; Miller, D. J.; Freeman, B. D.;  McGrath, J. E.; Paul, D. R.; Journal of Polymer Science Part B: Polymer Physics, 48, 1685-1718, 2010.