Two-dimensional tools for analyzing polymer microstructure; coupling non-aqueous ion-exchange chromatography to size-exclusion chromatography

Traditional liquid-chromatographic techniques, such as size-exclusion chromatography, (critical) interac-tion chromatography, and hydrodynamic chromatography, can all reveal certain aspects of polymers and the underlying distributions. The distribution of incorporated acid groups present in polyacrylates can be determined by non-aqueous ion-exchange chromatography, independent of other distributions present. The microstructural details on how this number of acid groups is incorporated in the polymer remains unknown. A low-molar mass polymer molecule with high acid content and a high-molar mass polymer with a low acid content may have the exact same number of acid groups. To take a next step towards understanding the polymer microstructure of water-borne resins, the distribution of incorporated acid groups over the molar-mass distribution has been investigated.For this purpose, an on-line coupling of non-aqueous ion-exchange chromatography (NAIEX) to size -exclusion chromatography (SEC) was established. Practical considerations regarding the system setup with respect to chromatography modes and column-and valve switching dimensionality are discussed. The orthogonality of NAIEX and SEC is demonstrated. Both liquid chromatography modes may be calibrated using polymer standards, yielding a calibrated separation plane. Cross-sectional data on either the molar mass distribution or the acid group distribution at a certain point of the separation plane is obtained. The value of the designed setup was demonstrated by the detailed characterization of the combined acid -group and molar-mass distribution in polymers with a low acid content, in the order of a few mass-%. Several stages of the emulsion polymerization process could be identified using the combined power of NAIEX and SEC.(c) 2022 Elsevier B.V. All rights reserved.