Distinguishing channel-type crystal structure from dispersed structure in β-cyclodextrin based polyrotaxanes via FTIR spectroscopy

Abstract

Combining with XRD analysis, Fourier transform infrared (FTIR) spectroscopy is employed to discern the self-assembled structures of β-cyclodextrins (β-CDs) threaded onto the polymer backbone in the polyrotaxanes (PRs) by means of the relative changes of absorption intensity of the characteristic peaks of β-CDs at 1153 and 1025 cm^-1. For quantitative analysis, six parameters are proposed to describe the relative absorption intensity variations of these peaks associated with a channel-type crystal structure or a dispersed structure of β-CDs entrapped. Among them, absorbance ratio (AR), relative absorbance difference (RAD) and transmittance difference (TD) values are suitable. When the AR, RAD and TD data get below 1.04, 4.8 and 1.27, respectively, the PRs obtained would possess a dispersed structure. If these values go beyond 1.32, 34.5 and 9.47, respectively, they would hold a channel-type crystal structure. This finding provides a useful judgment to distinguish the self-assembled structures of β-CDs residing along the polymer backbone in the PRs.

Keywords

FTIR / polyrotaxane / β-cyclodextrin / self-assembled structure

References

[1] Harada A, Kamachi M. Complex formation between poly(ethylene glycol) and α-cyclodextrins.Macromolecules, 1990, 23(10): 2821–2823 10.1021/ma00212a039
[2] Wenz G, Han B H, Muller A. Cyclodextrin rotaxanes and polyrotaxanes.Chemical Reviews , 2006, 106(3): 782–817 10.1021/cr970027+
[3] Harada A, Takashima Y, Yamaguchi H. Cyclodextrin-based supramolecular polymers.Chemical Society Reviews, 2009, 38(4): 875–882 10.1039/b705458k
[4] Araki J, Ito K. Recent advances in the preparation of cyclodextrins-based polyrotaxanes and their application to soft materials.Soft Matter, 2007, 3(12): 1456–1473 10.1039/b705688e
[5] Sarvothaman M K, Ritter H. Discriminating influence of α- and methylated β-cyclodextrins on complexation and polymerization of diacrylate and dimethacrylate monomers.Macromolecular Rapid Communications, 2004, 25(23): 1948–1952 10.1002/marc.200400348
[6] Ito K. Novel cross-linking concept of polymer network: synthesis, structure, and properties of slide-ring gels with freely movable junctions.Polymer Journal, 2007, 39(6): 489–499 10.1295/polymj.PJ2006239
[7] Michels J J, O’Connell M J, Taylor P N, et al. Synthesis of conjugated polyrotaxanes.Chemistry - A European Journal, 2003, 9(24): 6167–6176 10.1002/chem.200305245
[8] Zhang X W, Zhu X Q, Tong X M, et al. Novel main-chain polyrotaxanes synthesized via ATRP of HPMA in aqueous media.Journal of Polymer Science, Part A: Polymer Chemistry, 2008, 46(15): 5283–5293 10.1002/pola.22856
[9] Tong X M, Zhang X W, Ye L, et al. Novel main-chain polyrotaxanes synthesized via ATRP of HEMA initiated with polypseudorotaxanes comprising BriB-PEG-iBBr and α-CDs.Polymer, 2008, 49(21): 4489–4493 10.1016/j.polymer.2008.08.036
[10] Zhang X W, Zhu X Q, Ke F Y, et al. Preparation and self-assembly of amphiphilic triblock copolymers with polyrotaxane as a middle block and their application as carrier for the controlled release of amphotericin B.Polymer, 2009, 50(18): 4343–4351 10.1016/j.polymer.2009.07.006
[11] Tong X M. Zhang X W, Ye L, et al. Synthesis and characterization of block copolymers comprising a polyrotaxane middle block flanked by two brush-like PCL blocks.Soft Matter, 2009, 5(9): 1848–1855 10.1039/b818819j
[12] Zhang X W, Ke F Y, Han J, et al. The self-aggregation behaviour of amphotericin B-loaded polyrotaxane-based triblock copolymers and their hemolytic evaluation.Soft Matter, 2009, 5(23): 4797–4803 10.1039/b914664d
[13] Wang J, Gao P, Ye L, et al. Solvent- and thermoresponsive polyrotaxanes with β-cyclodextrin dispersed/aggregated structures on a Pluronic F127 backbone.The Journal of Physical Chemistry B, 2010, 114(16): 5342–5349 10.1021/jp101068b
[14] Wang J, Gao P, Wang P J, et al. Novel polyrotaxanes comprising γ-cyclodextrins and Pluronic F127 end-capped with poly(N-isopropylacrylamide) showing solvent-responsive crystal structures.Polymer, 2011, 52(2): 347–355 10.1016/j.polymer.2010.12.014
[15] Wang J, Ye L, Zhang A Y, et al. Novel triblock copolymers comprising a polyrotaxane middle block flanked by PNIPAAm blocks showing both thermo- and solvent-response.Journal of Materials Chemistry, 2011, 21(9): 3243–3250 10.1039/c0jm02803g
[16] Wang J, Gao P, Ye L, et al. Dual thermo-responsive polyrotaxane-based triblock copolymers synthesized via ATRP of N-isopropylacrylamide initiated with self-assemblies of Br end-capped Pluronic F127 with β-cyclodextrins.Polymer Chemistry, 2011, 2(4): 931–940 10.1039/c0py00360c
[17] Xie Z G, Hou D D, Ye L, et al. Enzyme-catalyzed preparation of supramolecular structured hydrogel of polypseudorotaxanes derived from the self-assembly of α-CDs with 3-arm p-hydroxyphenylpropionate terminated PEG.Frontiers of Materials Science in China , 2007, 1(4): 1–6
[18] Hou D D, Geng X, Ye L, et al. Novel supramolecular hydrogels made via Michael-type addition reaction of dithiothreitol with self-assembly of α-cyclodextrins and acryloyl-terminated 3-arm PEG.Frontiers of Materials Science in China, 2010, 4(1): 70–77 10.1007/s11706-010-0010-7
[19] Koening J L, Antoon M K. Thermally induced conformational changes in poly(vinyl chloride). Journal of Polymer Science, Polymer Physics Edition, 1977, 15(8): 1379–1395 10.1002/pol.1977.180150806
[20] Painter P C, Havens J, Hart W W, et al. A Fourier transform infrared spectroscopic investigation of polyethylene single crystals. I. Methylene wagging mode.Journal of Polymer Science: Polymer Physics Edition, 1977, 15(7): 1223–1235 10.1002/pol.1977.180150708