SEC of Cationic Polymers – Aqueous (GFC) vs Organic (GPC) Options

Record: 728

Category: Column Selection
Product: SB-806M and KD-806M
Sample: cationic polymers

Question
A cationic acrylic copolymer (~600 kDa) appears to stick on OHpak SB-802.5 and SB-804 in DMF. The polymer is soluble in DMF, methanol, ethanol, IPA, acetone, and chloroform, but not in THF or hexane. What Shodex columns and conditions are recommended for reliable SEC/GPC characterization?

Answer
Cationic and amphiphilic polymers often adsorb onto column packing under low-ionic-strength organic conditions. For accurate SEC behavior, use an eluent that suppresses electrostatic and hydrophobic interactions.

Shodex offers two effective approaches, depending on sample solubility:

1. Use OHpak SB-806M HQ (often two in series) with an eluent containing both acid and supporting electrolyte to neutralize charge interactions.

Example application:
Measurement of Molecular Weight Distribution of Poly(Allylamine) Hydrochloride – SB-806M HQ

This method effectively prevents adsorption and provides size-based elution for cationic polymers such as poly(allylamine) and polyethyleneimine.

2. If water-based eluent is unsuitable, use the Shodex KD-series, which are designed for organic SEC. Add LiBr (0.05–0.10 M) to DMF or DMAc to reduce ionic adsorption and stabilize elution.
Recommended column: KD-806M

Example application (illustrating DMF + LiBr GPC setup):
Vinyl Chloride–Vinyl Acetate Copolymer (1) – KD-806M

Although this example uses a neutral polymer, it demonstrates optimal DMF/LiBr SEC conditions applicable to charged or polar polymers.

Summary

• If water-tolerant: Use SB-806M HQ + 0.5 M AcOH + 0.1–0.2 M NaNO₃ (GFC).

• If strictly organic: Use KD-806M + DMF + 0.05–0.10 M LiBr (GPC).

• Both suppress adsorption and improve molecular-weight accuracy.

 
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