Recent developments in supramolecular chemistry, such as the construction of molecules with constructing components topologically interlocked by non-covalent interactions, have attracted interest in a wide range of fields in polymer science and nano technology [1][2][3][4][5]. Typical candidates for supramolecules include (poly)rotaxane, (poly)catenan, and callixallene [1]. One of the most widely investigated of these molecules is polyrotaxane, which contains many rings penetrated by an axis carrying two bulky end groups that prevents "dethreading" of the rings [2][3][4][5]. Harada et al. [6] and Wenz [7] conducted a series of pioneering studies on spontaneous inclusion complexation between a linear synthetic polymer, such as poly(ethylene glycol) (PEG), and cyclodextrins (CDs), cyclic oligosaccharides of α-D-glucose [8], which have contributed to the development of facile synthetic methods for polyrotaxane [9][10][11][12]. 1 Polyrotaxanes, consisting of PEG as the axis and α-cyclodextrins (α-CDs) as ring molecules, have been used for microscopic applications such as molecular tubes [13,14], insulated molecular wire [15,16], drug delivery systems [17], multivalent ligand formation [18], and for macroscopic applications such as crosslinked polyrotaxane Abstract The preparation of polyrotaxane fibers by wet spinning of polyrotaxane, consisting of poly(ethylene glycol) (PEG) and α-cyclodextrins (α-CDs), was examined using three different types of dope solvents: dimethylacetamide (DMAc) containing 8 wt% lithium chloride (LiCl), dimethylformamide (DMF) containing 8 wt% LiCl, and dimethylsulfoxide (DMSO). In DMSO, polyrotaxane concentrations of 20 and 30 wt% were favorable for the smooth spinning of fibers with sufficient tenacity, while other polyrotaxane concentrations (10, 15, and 40 wt%) were unsuitable for the wet spinning of durable fibers. All of the fibers had nearly identical scanning electron microscopy (SEM) images and X-ray diffraction patterns. Although the values for tenacity at break and initial modulus also were similar for all fibers, elongation at break of fibers from DMSO was higher than the values for the other two fibers. The poorer physical properties of the latter two fibers may be affected by the slight amount of lithium salt remaining in the fibers.

Polyrotaxane (PR), a typical example of topological supramolecular architecture, consists of multiple cyclic molecules threaded onto a linear polymer backbone and capped with bulky end-groups. The PR system of polyethylene glycol and α-cyclodextrin (α-CD) has been extensively studied for its facile synthesis, unique molecular structure, and possible applications for various smart materials. We have previously demonstrated the fabrication of PR-based fibers without chemical cross-links by wet spinning of PR solution. In this paper, we investigate the crystal structure of α-CDs in PR fibers and the effect of drawing on it. The α-CDs in PR fiber are found to form hexagonal channel-type structure. The drawing process promotes formation of the packing arrangement of α-CDs in the c-axis because of the sliding of α-CD molecules along the polymer backbone. In addition, we demonstrate the preparation of an elastomeric PR film having similar network structure to the fibers and ethylene glycol oligomer as plasticizer.

Polyrotaxane fibers prepared with wet spinning of polyrotaxane consisting of poly(ethylene glycol) and cyclodextrins (CDs) were cross-linked with two different cross-linking reagents, i.e., divinyl sulfone (DVS) and ethylene glycol diglycidyl ether (EGDE), to improve tensile properties of the fibers. By cross-linking with DVS, the values for the tenacity at break and the initial modulus were increased with cross-linking time, while the elongation at break was improved only moderately. On the other hand, drastic improvements in elongation at break were observed after EGDE cross-linking, up to 645% of its original length, although the tenacity at break and the initial modulus showed only slight improvements. After cross-linking, only minor changes in the degree of crystallinity fibers were observed by wide-angle X-ray scattering (WAXS) measurements.Keywords: polyrotaxane fibers, cyclodextrins, cross-linking, tensile measurements -2 - IntroductionIn our previous paper [1] on the functional polyrotaxane fibers, we reported a successful preparation of pure polyrotaxane fibers by wet spinning from polyrotaxane dope solution in various polyrotaxane solvents, i.e., dimethylsulfoxide (DMSO), dimethylacetamide (DMAc) containing lithium chloride (LiCl), and dimethylformamide (DMF) containing LiCl. Electron microscopy observations revealed a smooth and crack-free surface texture of the as-spun polyrotaxane fibers. By tensile measurements, the fibers spun from these three solvent systems showed similar levels of initial modulus and tenacity at break, whose values were relatively lower than those of commercial fibers such as polyesters and rayons. The values for elongation at break, however, were extremely high: up to 388% at 50% RH and 972% at 95% RH. The fiber spun from the DMSO dope solution showed a higher value of the elongation at break than the fibers from DMF/LiCl and DMAc/LiCl. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 -3 -The results also imply a successful preparation of novel spandex-like fibers exhibiting high levels of elongation at break and elastomeric properties.Cross-linking treatments of spun fibers are widely used for the preparation of functional fibers and improvements in physical properties of fibers. For example, previous studies showed remarkable improvements in wet and dry mechanical properties of chitosan fibers by cross-linking [7,8]. Poly(vinyl alcohol) fibers cross-linked with boric acid also showed improved strength and Young's modulus [9]. Cross-linking treatments are also applied to the preparation of rayons [10] and ultra-high-molecular weight polyethylene fibers [11] with improved physical properties, as well as finishing of fabrics such as crease-resistant finishing [12]. Recent investigations have utilized novel bio-mimetic cross-linking mechanisms, mediated by the action of enzymes or oxidation ...