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 byLCCCusingsinglesolventsasmobilephases.Theanalysis ofthechemically differentLCCCfractionswas 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 thefirst time thedetermination ofthetruemolarmasses and truechemicalcompositions ofthe block copolymers was achieved by determining the microstructure distribution.