title: Size-exclusion chromatography of ultrahigh molecular weight methylcellulose ethers and hydroxypropyl methylcellulose ethers for reliable molecular weight distribution characterization.
abstract: Size-exclusion chromatography (SEC) coupled with multi-angle laser light scattering (MALLS) and differential refractive index (DRI) detectors was employed for determination of the molecular weight distributions (MWD) of methylcellulose ethers (MC) and hydroxypropyl methylcellulose ethers (HPMC) having weight-average molecular weights (Mw) ranging from 20 to more than 1,000kg/mol. In comparison to previous work involving right-angle light scattering (RALS) and a viscometer for MWD characterization of MC and HPMC, MALLS yields more reliable molecular weight for materials having weight-average molecular weights (Mw) exceeding about 300kg/mol. A non-ideal SEC separation was observed for cellulose ethers with Mw>800kg/mol, and was manifested by upward divergence of logM vs. elution volume (EV) at larger elution volume at typical SEC flow rate such as 1.0mL/min. As such, the number-average molecular weight (Mn) determined for the sample was erroneously large and polydispersity (Mw/Mn) was erroneously small. This non-ideality resulting in the late elution of high molecular weight chains could be due to the elongation of polymer chains when experimental conditions yield Deborah numbers (De) exceeding 0.5. Non-idealities were eliminated when sufficiently low flow rates were used. Thus, using carefully selected experimental conditions, SEC coupled with MALLS and DRI can provide reliable MWD characterization of MC and HPMC covering the entire ranges of compositions and molecular weights of commercial interest.
authors.affiliation: Core R&D Analytical Sciences, The Dow Chemical Company, Midland, MI 48674, United States. Electronic address: ylli@dow.com.
authors.forename: Yongfu
authors.initials: Y
authors.lastname: Li
authors.affiliation: Core R&D Formulation Sciences, The Dow Chemical Company, Collegeville, PA 19426, United States.
authors.forename: Hongwei
authors.initials: H
authors.lastname: Shen
authors.affiliation: Core R&D Analytical Sciences, The Dow Chemical Company, Midland, MI 48674, United States.
authors.forename: John W
authors.initials: JW
authors.lastname: Lyons
authors.affiliation: Core R&D Materials Science and Engineering Laboratory, The Dow Chemical Company, Midland, MI 48674, United States.
authors.forename: Robert L
authors.initials: RL
authors.lastname: Sammler
authors.affiliation: Dow Pharma and Food Solutions, The Dow Chemical Company, Bomlitz, ND 29699, Germany.
authors.forename: Meinolf
authors.initials: M
authors.lastname: Brackhagen
authors.affiliation: Core R&D Analytical Sciences, The Dow Chemical Company, Midland, MI 48674, United States. Electronic address: dmmeunier@dow.com.
authors.forename: David M
authors.initials: DM
authors.lastname: Meunier
keywords: Hydroxypropyl methylcellulose ethers; Methylcellulose ethers; Size-exclusion chromatography; Ultrahigh molecular weight materials