Characterization of linear and 3-arm star block copolymers by liquid chromatography at critical conditions

LCCC for polyMA homopolymers was established in order to analyze the polyMA-polySt linear and star block copolymers. The validity of the assumption that under the LCCC for polyMA, the polyMA segment in the poly MA-containing block copolymer is chromatographically invisible was verified. It was found that within the scale of investigation ((M) over bar (n,polyMA) <= 5 (M) over bar (n,polySt)), the molecular weight and architecture of the polyMA segments had no evident influence on the retention behavior of the polySt-polyMA block copolymers and the polyMA block in the copolymer was invisible. The critical conditions of polyMA were used for quantitative analysis of the polySt block in the linear and 3-arm star polyMA-polySt block copolymers, which were synthesized by AGET ATRP in miniemulsion. It was shown that the copolymer had completely different elution peak from its MI. The calculated molecular weights of polySt blocks in the block copolymers were similar to those obtained from normal SEC analysis. Transferring the eluates from the LCCC (the first dimension) column to a SEC column (the second dimension) produced LCCC x SEC two-dimensional chromatogram, which contained information on both chemical composition and molecular weight of the synthesized copolymers. The combination of these liquid chromatography methods clearly confirmed the high initiation efficiency of the polyMA MIs during the synthesis of block copolymers and the presence of a byproduct formed by radical-radical coupling.