CHARAKTERIZACE HYDROXYLEM KONČENÝCH POLYBUTADIENŮ KAPALINOVOU CHROMATOGRAFIÍ

Significance of the Topic

Low‐molecular‐weight hydroxyl‐terminated polybutadienes serve as essential precursors in adhesives, sealants and industrial polyurethane formulations. Their end‐group functionality and molecular weight distribution critically influence curing behavior, network formation and mechanical properties of final elastomers.

Study Objectives and Overview

This study aims to develop a combined chromatographic strategy for simultaneous characterization of molecular weight distribution and hydroxyl functionality distribution in polybutadienes. The approach integrates size exclusion chromatography (SEC/GPC) with universal calibration and normal‐phase liquid adsorption chromatography at the critical adsorption point, complemented by acetylation titration for total hydroxyl content.

Methodology and Instrumentation

SEC analyses employed a Waters 600E solvent delivery system, dual HR4E columns at 30 °C, a Waters W410 refractive index detector and Millenium data manager. Universal calibration used polystyrene standards and Mark–Houwink parameters specific for polybutadiene.

Normal‐phase HPLC was performed on a TSP P200 gradient pump with Rheodyne injector, alloy columns packed with Nucleosil 1000‐NH2 (7 μm) at 60 °C and detection by either RI or evaporative light scattering (PL EMD 960) detectors. The mobile phase comprised 2.7 % dioxane in n‐heptane, set to match the critical adsorption point. Acetylation of hydroxyl end groups was carried out with acetic anhydride and p‐toluenesulfonic acid in ethyl acetate, followed by titration with KOH in methanol.

Key Results and Discussion

SEC profiles showed narrow molecular weight distributions consistent with anionic polymerization. The critical adsorption composition (2.7 % dioxane/97.3 % heptane) yielded retention times independent of molecular weight, enabling baseline separation of non‐functional, mono‐ and di‐functional fractions.

• Refractive index detection exhibited concentration‐independent response factors across the polymer mass range.
• Evaporative light scattering response varied significantly with molecular weight and concentration, requiring dual calibration.

The comparison of number‐ and weight‐average functionality confirmed negligible higher functionality fractions, validating the chromatographic assignments.

Benefits and Practical Applications of the Method

This combined analytical approach provides comprehensive quality control by resolving both chain length and end‐group distribution. It supports precise formulation of hydroxyl‐terminated polybutadienes for tailored polyurethane elastomers, adhesives and sealants, ensuring consistent network density and performance.

Future Trends and Potential Applications

Advances may include coupling gradient NP‐HPLC with mass spectrometric detection for direct identification of polyfunctional species. Integration with automated data processing could streamline in‐line monitoring in pilot and production environments.

Conclusion

The synergy of universal calibration SEC and critical‐point NP‐HPLC achieves accurate, distribution‐resolved characterization of hydroxyl‐terminated polybutadienes. Refractive index detection offers robust quantitation, while evaporative light scattering extends sensitivity and gradient capability, together delivering a powerful toolset for polymer end‐group analysis.

Instrumentation

• Waters 600E pump with dual HR4E columns and W410 refractive index detector
• TSP P200 gradient pump with Nucleosil 1000‐NH2 columns and PL EMD 960 evaporative light scattering detector
• Nicolet Magna 550 FT‐IR spectrometer for microstructure assessment

References

1. Muenker A H, Hudson B E J Macromol Sci Part A 7 1465 1969
2. Ninan K N, Balagangadharan V P, Catherine K B Polymer 32 628 1991
3. Baczek S K, Anderson J N, Adams H E J Appl Polym Sci 19 2269 1975
4. Law R D J Polym Sci 9 589 1971
5. Varghese A, Scariah K J, Bera S C, Rama Rao M, Sastri K S Eur Polym J 32 79 1996
6. Rama Rao M, Scariah K J, Ravindran P V, Chandrasekharan G, Alwan S, Sastri K S J Appl Polym Sci 49 435 1993
7. Ono K et al J Appl Polym Sci 21 3223 1977
8. Takahashi M F K, Lima M, Polito W L Polym Bull 38 455 1997
9. Bielsa R O, Brandolini M C, Akcelrud L, Meira G R J Appl Polym Sci 54 2125 1994
10. Montaudo G Trends Polym Sci 4 81 1996
11. Panicker S S, Ninan N N Polym Int 37 255 1995
12. Ninan K N, Balagangadharan V P, Ambikadevi K, Catherine K B Polym Int 31 255 1993
13. Amato R, Marot G J Liq Chromatogr 14 79 1991
14. Pokorny S et al J Liq Chromatogr 4 1 1981
15. Estrin J I, Kasumova L T Zh Fiz Khim 68 1784 1994
16. Pasch H, Much H, Schulz G, Gorshkov A LC-GC Int 5/2 38 1994
17. Philipsen H J A, Klumperman B, van Herk A M, German A L J Chromatogr A 727 13 1996
18. Berek D Macromol Symp 110 33 1996
19. Entelis S G, Evreinov V V, Gorshkov A V Adv Polym Sci 7(5) 131 1986
20. Dawkins J V in Steric Exclusion Liquid Chromatography of Polymers Marcel Dekker 1984
21. Cools P J C H, van Herk A M, German A L, Staal W J Liq Chromatogr 17 3133 1994
22. Lew R, Barth H G 9th Int Symp Polym Anal Charact Bl Oxford 1996
23. Bear G R J Chromatogr 459 91 1988
24. Chance R R et al Int J Polym Anal Charact 1 3 1995