Rotaxanes polymeric

As discussed in Section 7.3, conventional free radical polymerization is a widely used technique that is relatively easy to employ. However, it does have its limitations. It is often difficult to obtain predetermined polymer architectures with precise and narrow molecular weight distributions. Transition metal-mediated living radical polymerization is a recently developed method that has been developed to overcome these limitations [53, 54]. It permits the synthesis of polymers with varied architectures (for example, blocks, stars, and combs) and with predetermined end groups (e.g., rotaxanes, biomolecules, and dyes). 

Swager et al. prepared conjugated polymers with tethered rotaxane groups [76]. As a substrate, a rotaxane containing a diiodobiphenyl unit was synthesized for this purpose. Polymerization via microwave-assisted Sono-... 

Therefore, polyrotaxanes can be simply defined as polymeric materials containing rotaxane units. They are different from conventional linear homopolymers because they always consist of two components, a cyclic species mechanically attached to a linear species. They also differ from polymer blends as the individual species are interlocked together and from block copolymers since the two components are noncovalendy connected. Thus new phase behavior, mechanical properties, molecular shapes and sizes, and different solution properties are expected for polyrotaxanes. Their ultimate properties depend on the chemical compositions of the two components, their interaction and compatibility. This review is designed to summarize the syntheses of these novel polymers and their properties. 

In addition to the types of structure and chemical compositions, the properties of a polyrotaxane are determined by the amount of cyclic incorporated. To define such quantities, the min value was introduced [7, 12], Min, file threading efficiency, was defined for systems of Types 4-6, 9, and 10 as the average number of cyclic molecules per repeat unit [7, 12]. However, this definition seems a little awkward for polyrotaxanes of Types 7, 8, 11, and 12, because in these polyrotaxanes the linear component penetrates through the polymeric cyclic instead of the cyclic being threaded on to the linear species. To fit all the types in Table 1, we redefine min as the proportion of rotaxane repeat units in the polymer. 

In 1979, Maciejewski et al. also explored Method 3 for the preparation of main-chain poly(vinylidene chloride-/ -CD rotaxane) 35 [74, 75]. Radiation polymerization and AIBN-initiated solution polymerization of the complex of vinyli-dene chloride with 21 gave products with min = 0.34 and 0.49, respectively. However, the polyrotaxane via Method 1 had a much lower min (0.087) with much lower CD/monomer feed ratio than for those via the polymerization of the complex (1 1 ratio). Therefore, the reported min values are not comparable, so the difference between the two methods in terms of threading efficiencies cannot be distinguished. Although the authors did not see any threading via Method 2 for the same polyrotaxanes, Ogino and coworkers prepared a true CD-based polyrotaxane of Type 5 using metal complexes as stoppers [76]. It was also found that... 

Steinbrunn and Wenz recently reported poly(amide-CD rotaxane)s 53 via a very imaginative approach [90,91]. First, the CD was threaded on to an a,co-amino acid in water to give a pseudorotaxane monomer. An NMR study showed that two CD molecules were threaded per linear molecule for 11-aminoundecanoic acid. The X-ray powder pattern indicated that these rotaxanes stacked like channels in the solid state this provided the basis for solid state polymerization at 200°C to afford polyamide 53 with m/n=2 ... 

Poly(ether sulfone) and poly(ether ketone) rotaxanes 77, 78, 79, and 80 were reported by Xie and Gong via solution polymerization in a mixture of toluene and DMF in the presence of metal ions (K+ or Na+) and 30C10 [114, 123]. The min values depended on the reaction conditions and the amount of BG applied [114, 123]. Polyrotaxanes 77 and 78 were difficult to purify because these polymers formed emulsions in water or methanol. Because of different preparation conditions between those with or without BG, the absolute m/n values are not comparable and thus the effect of the BG on threading remains unknown. However, considering that a polar solvent, i.e., DMF, was used for polymerization, these m/n values are still significant. 

Paraquat, an ionic molecule, is more rigid than polymeric crown ethers. In addition, die crown ether has to adopt a restricted conformation for complexation to occur. The total increase of the rigidity for derived polyrotaxanes 84 depended on the min value [118, 119]. The higher the value of min, the higher Tg of the poly-rotaxane. Paraquat is a crystalline material but the polyrotaxanes are amorphous. 

It is necessary to point out that while various types of polyrotaxane have been conceived (Table 1), to date, only polyrotaxanes of Types 4, 5, 6, 7, 9, 10 and 11 have been reported. Polyrotaxanes of Types 8 and 12 are worth study this might provide more interesting information about the relationship between properties and structure. In addition to those discussed so far, other potential preparation approaches have also been conceived but have not been applied. These methods are simply summarized and demonstrated via those for the side-chain polyrotaxanes of Type 10 (Figure 18). They are (i) chemical conversion, (ii) polymerization of rotaxane monomers, (iii) clipping (cyclization in the presence of preformed polymer), and (iv) grafting. The corresponding methods for other types of polyrotaxanes in Table 1 are analogous [6-8, 12]. 

Greets Y (1999) Polycatenanes, poly[ 2]-catenanes and polymeric catenanes. In Sauvage JP, Dietrich-Buchecker CO (eds) Molecular Catenanes, Rotaxanes, and Knots. Wiley-VCH, Weinheim... 

The rotaxane assembly is adopted by many enzymes that operate on nucleic acids and proteins. In the case of processive enzymes, the catalytic reaction drives the sequential motion of the enzyme on its polymeric substrate. Therefore, these enzymes can be viewed as molecular motors powered by chemical reactions and moving one-dimensionally on a track, in which fuel is provided by the track itself. An initial attempt to carry out processive catalysis with a synthetic rotaxane has been described [69]. 

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