Coupling of NMR and Liquid Chromatography at Critical Conditions: A New Tool for the Block Length and Microstructure Analysis of Block Copolymers

Abstract

The online coupling of liquid chromatography at critical conditions (LCCC) and NMR was used for the analysis of block copolymers. Polyisoprene-b-poly(methyl methacrylate) (PI-b-PMMA) copolymers synthesized by living anionic polymerization were separated regarding chemical composition by LCCC using single solvents as mobile phases. The analysis of the chemically different LCCC fractions was conducted by on-flow 1 H NMR. To separate the copolymers from the respective homopolymers, critical conditions of polyisoprene (PI) and poly(methyl methacrylate) (PMMA) were used. Critical conditions were obtained by varying the column temperature. The comprehensive chemical composition and microstructure analysis by 1 H NMR revealed that quantitative information on the PI/PMMA content as well as the microstructure of PMMA (isotactic, atactic, and syndiotactic triads) and PI (1,2-PI, 1,4-PI, 3,4-PI) was obtained. For the first time the determination of the true molar masses and true chemical compositions of the block copolymers was achieved by determining the microstructure distribution.

Characterisation of blends of polyisoprene and polystyrene by on‐line hyphenation of HPLC and 1H‐NMR: LC‐CC‐NMR at critical conditions of both homopolymers

“…We have published the application of LC-CC-NMR for the complete characterisation of PS-b-PMMA copolymers and blends of homopolymers of both PS and PMMA by operating at the critical conditions of both PS [17] as well as PMMA [18]. Recently we have shown that by the online coupling of LCCC and NMR using single solvents it is possible to determine the true molar masses, true chemical composition and microstructure information in a single experiment [19].…”

Advanced fractionation methods for the microstructure analysis of complex polymers

“…[52] Making use of the different chemical shifts for the different structural and isomeric moieties, the distribution of the PMMA triads and the PI isomeric structures can be directly calculated from the individual NMR chromatograms. The separations were conducted at LCCC conditions for PI and PMMA, and therefore, the molar masses of the PMMA and the PI blocks, respectively, could be analyzed in addition to the microstructural compositions.…”

“…For the comprehensive analysis of the blend components, 2D-LC was used with interaction chromatography in the first dimension and SEC in the second dimension. [52] with permission). PI, polyisoprenes; LCCC, liquid chromatography at critical conditions; LAC, liquid adsorption chromatography; SEC, size exclusion chromatography.…”

Structural characterization of telechelic polyisobutylene diol

“…Previous researchers have tried to utilize size exclusion chromatography (SEC) for the determination of chemical heterogeneity of polymers [5] and copolymers. [6] However, SEC can only provide limited information on the chemical composition of a polymer, if only interfaced with NMR [7] or mass spectrometry. [8] Subsequently, liquid adsorption chromatography (LAC) in a gradient mode was developed.…”