Coupling of NMR and liquid chromatography at critical conditions: A new tool for the block length and microstructure analysis of block copolymers
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 1H 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 1H 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. © 2010 American Chemical Society.