Utility of Chromatographic and Spectroscopic Techniques for a Detailed Characterization of Poly(styrene-b-isoprene) Miktoarm Star Copolymers with Complex Architecture

Abstract

We analyzed various miktoarm star copolymers of the PS(PI) x type (x = 2, 3, 5, 7), which consist of one long polystyrene (PS) arm (82 or 105 kDa) and various numbers of short polyisoprene (PI) arms (from 11.3 to 39.7 kDa), prepared by anionic polymerization and selective chlorosilane chemistry. The length of the PI arm in stars decreases with the number of arms, so that the chemical compositions of all PS(PI) x samples were comparable. Our aim was to determine the purity of samples and to identify exactly the constituents of individual samples. For this purpose we used a variety of separation techniques (size-exclusion chromatography (SEC), reversed-phase liquid-adsorption chromatography (RP-LAC), and two-dimensional liquid chromatography (2D-LC)) and characterization techniques (UV-MALS-RI multidetection SEC system, NMR, and MALDI-TOF MS). The best separation and identification of the samples’ constituents were achieved by RP-LAC, which separates macromolecules according to their chemical composition, and a subsequent analysis of the off-line collected fractions from the RP-C18 column by SEC/UV-MALS-RI multidetection system. The results showed that all PS(PI) x samples contained the homo-PS and homo-PI in minor amounts and the high-molar-mass (PS) y (PI) z (y > 1) species, the content of which is higher in the samples PS(PI)5 and PS(PI)7 than in the samples PS(PI)2 and PS(PI)3. The major constituent of the PS(PI)2 sample was the one with the predicted structure. On the other hand, the major components of the PS(PI) x (x = 3, 5, and 7) samples were the stars consisting of a smaller number of PI arms than predicted from the functionalities of chlorosilane coupling agents. These results are in agreement with the average chemical composition of samples determined by proton NMR spectroscopy and characterization of the constituents by MALDI-TOF MS.

Star Polymers

“…TGIC has high sensitivity toward the length of the more strongly absorbing species, while LCCC provides information by making one of the species (i.e., one arm-type) chomatographically "invisible" (in that it does not contribute to retention time). 387 TGIC is an effective way to separate polymer species by MW and is almost independent of polymer architecture, making it particularly suited to the analysis of star polymers. When stars are prepared with a single arm-type and MW, the MWs of each star macromolecule with different N arm values can often be resolved via TGIC, with the peaks appearing "quantized" by the MW of the arm precursor.…”

“…It was observed that all of the star products investigated showed small quantities of linear impurities (both PS and PI) as well as star impurities of higher and/or lower N arm value. 387 The experimental setup for 2D chromatography is relatively straightforward, although additional software may be required to analyze and present the 2D contour plots obtained. A typical combination of LCCC × GPC 2D-LC is displayed schematically in Figure 65.…”

Cost‐efficient modeling of distributed molar mass and topological variations in graft copolymer synthesis by upgrading the method of moments

“…In 2D‐LC, the effluents from the first dimension (1st‐D) need to be analyzed by the second dimension (2nd‐D) following another (ideally orthogonal) separation mode. Here, one separates copolymers by CCs or by MM of the specific monomer sequences (e.g., PB or PS segments in the context of the present work) 73–78 . In this way, the bivariate distributions correlating two different molecular parameters can be accessible so that higher resolution and more informative data are in principle delivered.…”

“…As highlighted above, D‐NF‐MoM allows to theoretically obtain CC‐MMDs so that is worthwhile to evaluate the feasibility of typical 2D‐LC combinations and also try to figure out the preferential separation mode for GC structural analysis. Here, one can refer to the experimental study of Ljubič et al in which poly(styrene‐ block ‐isoprene) star copolymer has been characterized as 1st‐D by solvent gradient interaction chromatography (SGIC; separation by CC) and with SEC as the 2nd‐D 73 …”

Influence of the Chain Architecture and the Presence of End-Groups or Branching Units Chemically Different from Repeating Structural Units on the Critical Adsorption Point in Liquid Chromatography

“…Another advantage of LCCC is the ability to separate polymers with respect to their chain architecture. − It was theoretically predicted that cyclic polymers can be separated from their linear counterpart at the CAP of the linear polymers. − It was demonstrated experimentally that LCCC separation is the best available method for the purification of cyclic polymers from linear polymer byproducts which are present in samples synthesized by a ring-closure reaction of telechelic precursors. − The high purity of cyclic polymers is very important since it was found that very small contamination by the linear chains changes the melt viscoelasticity of cyclic polymers dramatically . We recently reported that linear and cyclic polymers exhibited their own CAP behaviors.…”