Utility of chromatographic and spectroscopic techniques for a detailed characterization of poly(styrene-b-isoprene) miktoarm star copolymers with complex architecture
AuthorsŠmigovec Ljubič, Tina
KAUST DepartmentBiological and Environmental Sciences and Engineering (BESE) Division
KAUST Catalysis Center (KCC)
Physical Sciences and Engineering (PSE) Division
Chemical Science Program
Polymer Synthesis Laboratory
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AbstractWe 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. © 2012 American Chemical Society.
SponsorsThe authors gratefully acknowledge the financial support of the Ministry of Higher Education, Science and Technology of the Republic of Slovenia through (a) the Slovenian Research Agency (Program P2-0145) and (b) the Centre of Excellence - Polymer Materials and Technologies for MALDI-TOF MS analysis.
PublisherAmerican Chemical Society (ACS)