The concept of the polyrotaxane gel is important not only in the creation of highperformance gels or rubbers, but also as a new framework for artificial molecular motors based on the sliding motion just like actin and myosin. [20±26] Experimental Polyrotaxane Preparation: PEG-BA (0.9 g) and a-CD (3.6 g) were dissolved in water (30 mL) at 80 C and kept at 5 C overnight to yield the white paste of the inclusion complex. We dried the paste, added an excess of 2,4-dinitrofluorobenzene (2.4 mL) together with dimethylformamide (10 mL) and stirred the mixture in a nitrogen atmosphere at room temperature overnight. The reaction mixture was dissolved in DMSO (50 mL) and precipitated from a 0.1 % sodium chloride aqueous solution (800 mL) twice to give a yellow product. The product was collected, washed with water and methanol (three times, respectively), and dried to produce the polyrotaxane (1.25 g).
Gelation: The polyrotaxane (100 mg) was dissolved in 1 N NaOH (0.5 mL) at 5 C. The hydroxyl groups of a-CD are ionized under a strong base, which results in Coulombic repulsion between adjacent CDs in the polyrotaxane. Cyanuric chloride (35 mg), dissolved in 1 N NaOH (0.5 mL), was mixed with the solution to initiate the cross-linking reaction. After 3 h at room temperature, we got a transparent yellow polyrotaxane gel. Figure 4 shows the 1 H NMR spectra of a) the polyrotaxane in DMSO-d 6 and b) the polyrotaxane gel swollen in DMSO-d 6 and disrupted with a sonicator (Sonifier Cell Disruptor 200, Branson Sonic Power Co.). Compared with the polyrotaxane, all the peaks of the 1 H NMR spectrum of the polyrotaxane gel are broadened, indicating that the CDs became polymeric. The peak at 5.66 ppm due to the C-2 OH of a-CD decreased, and the peak at 5.50 ppm due to the C-3 OH splits into three signals.
These results indicate that the cyanuric chloride mainly reacted with C-2 OH and that the a-CD structure was distorted.