ABSTRACT
I. Mechanically Interlocked Macromolecules . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 257 II. Polycatenanes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 258 III. Main-Chain Polyrotaxanes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 267 IV. Side-Chain Polyrotaxanes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 282 V. Mechanically Interwoven Polymer Chains . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 284 VI. Interwoven Dendrimers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 288 VII. Polyrotaxanes via Post-Assembly Modification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 290 VIII. Properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 291 IX. Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 293 Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 294 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 294
I. MECHANICALLY INTERLOCKED MACROMOLECULES
Macromolecules incorporating repeat units connected by covalent bonds are widespread in nature [1]. Synthetic procedures for the construction of their artificial counterparts are well established [2]. Furthermore, the properties of these unnatural macromolecules are now rather well understood [2] and, indeed, polymeric materials have found [2] applications in numerous branches of science and technology. In recent years, synthetic chemists have learnt [3] how to introduce mechanical bonds (Figure 1) into small molecules. Mechanically interlocked “rings,” as well as “wheels” mechanically trapped onto “axles,” can be constructed efficiently to afford molecular compounds, named catenanes and rotaxanes, respectively. (The term catenane derives from the Latin word catena meaning chain. The term rotaxane derives from the Latin words rota and axis meaning wheel and axle, respectively.) Metal coordination [4,5], donor/acceptor interactions [6,7], hydrogen bonds [8,9], and/or hydrophobic interactions [10] among appropriate components have all been
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employed to template [11] the formation of these exotic molecules. Making the transition from simple catenanes and rotaxanes to their macromolecular counterparts — namely, polycatenanes and polyrotaxanes, respectively — offers the possibility of generating a range of novel polymeric materials. Indeed, the fundamental difference between “conventional” macromolecules and these “unconventional” polymers — that is, the presence of mechanical bonds — is expected to confer unusual properties upon them, which could have profound technological implications. Mechanically interlocked macromolecules can be regarded as the molecular-sized counterparts of macroscopic objects, such as abacuses, bearings, chains, and joints, which could become the components of some of the smallest possible devices sometime in the future.
