Molecular weight distribution characterization of hydrophobe-modified hydroxyethyl cellulose by size-exclusion chromatography

• Successful SEC conditions for HmHEC are reported for the first time.
• β-CD was used to eliminate hydrophobic interactions to enable SEC elution.
• The developed SEC conditions were robust for HmHEC having MW up to 2000 kg/mol.
• Comparison of MW obtained by SEC-MALLS, PEO and HEC calibration is reported.

Size-exclusion chromatography (SEC) of hydrophobe-modified hydroxyethyl cellulose (HmHEC) is challenging because polymer chains are not isolated in solution due to association of hydrophobic groups and hydrophobic interaction with column packing materials. An approach to neutralize these hydrophobic interactions was developed by adding β-cyclodextrin (β-CD) to the aqueous eluent. SEC mass recovery, especially for the higher molecular weight chains, increased with increasing concentration of β-CD in the eluent. A β-CD concentration of 0.75 wt% in the eluent was determined to be optimal for the HmHEC polymers studied. These conditions enabled precise determinations of apparent molecular weight distributions exhibiting less than 2% relative standard deviation in the measured weight-average molecular weight (MW) for five injections on three studied samples and showed no significant differences in MW determined on two different days. The developed technology was shown to be very robust for characterizing HmHEC having MW from 500 kg/mol to 2000 kg/mol, and it can be potentially applied to other hydrophobe-modified polymers.