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This work reports poly(allylamine) of 900 kDa (PAA-L) as a polymeric ligand for protein ion-exchange chromatography. PAA-L-modified Sepharose FF with 9 ionic capacities (ICs) from 80 to 880 mmol/L were prepared and bovine serum albumin adsorption and chromatography were investigated. With increasing IC, protein adsorption capacity increased somewhat in the IC range of 80–420 mmol/L, and then increased twice in the IC range of 420–740 mmol/L, and finally kept unchanged till 880 mmol/L; the uptake rate (De/D0) increased about 14 times (from 0.029 to 0.42) in the IC range of 420–700 mmol/L, and finally kept almost unchanged till 880 mmol/L. The maximum adsorption capacity and uptake rate of the resins reached 336 mg/mL and 0.42, which were 24% and 2.5 times respectively larger than those of 17.5 kDa PAA-grafted resins. The selected PAA-L resin of IC = 740 mmol/L was salt-tolerant up to 750 mmol/L NaCl. The dynamic binding capacity (DBC) of this resin showed a maximum of 142 mg/mL at 350 mmol/L NaCl, and kept over 90 mg/mL in the range of 150–500 mmol/L NaCl. Linear gradient elution on the column of this resin proved high protein recovery (>97%) and stability of the column. Taken together, the results indicate that the PAA-L resin was a promising anion exchanger for high-performance protein chromatography for use at extended ionic strengths.

Poly(ethylenimine) (PEI)-grafted Sepharose FF with an ionic capacity (IC) of 740 mmol/L (FF-PEI-L740) was modified with succinic anhydride, and six mix-charged resins of different ionic capacities (ICs) were synthesized [denoted as “Am-Cn” according to their anion exchange groups (amino groups) and cation exchange groups (carboxyl groups)]. Protein adsorption behaviors were investigated using bovine serum albumin (BSA) and lysozyme (LZM) as model proteins. The modification led to the net positive charge decrease to approximately zero (A320-C270), and then reversed the net charge to negative till the maximum negatively charge resin A20-C970. Adsorption capacity for BSA decreased from 205 ± 5 mg/mL (FF-PEI-L740) to 65 ± 3 mg/mL (A320-C270), but increased, for LZM, from 31 ± 1 mg/mL (A320-C270) to 281 ± 13 mg/mL (A20-C970) with increasing net negative charge. The uptake rate of BSA or LZM decreased with decreasing net positive charge or increasing net negative charge due to the decreased flexibility of the PEI chains brought from the increased electrostatic attraction or repulsion and/or tight binding due to the high net charge density. Effect of ionic strength (IS) showed that the resins with high net charge densities exhibited high adsorption capacities at high IS. Besides, dynamic binding capacity values achieved as high as 55 mg/mL for BSA and 143 mg/mL for LZM. Chromatographic experiments demonstrated favorable elution of bound proteins at NaCl lower than 370 mmol/L.