Critical Conditions for Liquid Chromatography of Statistical Copolymers: Functionality Type and Composition Distribution Characterization by UP-LCCC/ESI-MS

Abstract

Statistical ethylene oxide (EO) and propylene oxide (PO) copolymers of different monomer compositions and different average molar masses additionally containing two kinds of end groups (FTD) were investigated by ultra high pressure liquid chromatography under critical conditions (UP-LCCC) combined with electrospray ionization time-of flight mass spectrometry (ESI-TOF-MS). Theoretical predictions of the existence of a critical adsorption point (CPA) for statistical copolymers with a given chemical and sequence distribution1 could be studied and confirmed. A fundamentally new approach to determine these critical conditions in a copolymer, alongside the inevitable chemical composition distribution (CCD), with mass spectrometric detection, is described. The shift of the critical eluent composition with the monomer composition of the polymers was determined. Due to the broad molar mass distribution (MMD) and the presumed existence of different end group functionalities as well as monomer sequence distribution (MSD), gradient separation only by CCD was not possible. Therefore, isocratic separation conditions at the CPA of definite CCD fractions were developed. Although the various present distributions partly superimposed the separation process, the goal of separation by end group functionality was still achieved on the basis of the additional dimension of ESI-TOF-MS. The existence of HO-H besides the desired allylO-H end group functionalities was confirmed and their amount estimated. Furthermore, indications for a MSD were found by UPLC/MS/MS measurements. This approach offers for the first time the possibility to obtain a fingerprint of a broad distributed statistical copolymer including MMD, FTD, CCD, and MSD.

Reverse-phase high performance liquid chromatography (RP-HPLC) as a powerful tool to characterise complex water-soluble copolymer architectures

“…While these techniques have made possible the separation of copolymers according to the number and structure of their functional groups, the characterisation of monomer distribution within copolymers remains a major challenge. 50 In this study, we demonstrate the potential of RP-HPLC as a tool for the characterisation of monomer distribution in charged water-soluble copolymers. We demonstrate the influence of monomer distribution (block, multiblock and statistical) on the elution time of charged acrylamide copolymeric systems prepared via RAFT polymerisation (Scheme 1).…”

Cyclic polymers: Advances in their synthesis, properties, and biomedical applications

“…[124,125] The LCCC is also used for the characterization of block copolymers, functionalized polymers, polymer blends, and so on. [126][127][128][129] Even though this technique allows a highly efficient separation of the cyclic polymer from the linear impurities, the determination of the experimental conditions is a very tedious task and each different polymer backbone requires the different parameters to be readjusted, hence why, to date, the few examples that have been reported in the literature only concern PS samples. This is even more true for the smaller cyclic samples (e.g., those prepared by RC techniques), for which the resolution of the LCCC becomes too poor.…”

Detection challenges in quantitative polymer analysis by liquid chromatography

“…recently explored the use of LC‐ESI‐MS in the microstructure determination of copolymers; by combining retention time, chromatographic peak width, and MS information, it was possible to elucidate in depth microstructure and topology information on various glycol and ethoxylate oligomers [90]. Furthermore, by using separation at LCCC conditions coupled to ESI‐MS insight into the MWD, end‐group distribution, CCD, as well as the sequence of ethylene oxide‐propylene oxide copolymers could be obtained [91]. Cramer et al.…”