Polyrotaxanes urethane

Similar to that in copoly(ester rotaxane)s 64, min for these poly(urethane rotax-ane)s increased with increasing BG, i.e. higher x values [116,117]. However, compared with the copoly(ester rotaxane), the dethreading occurred to lesser extent in these polyrotaxanes this is attributed to the fact that the NH groups retard dethreading by hydrogen bonding with the threaded crown ether as in structure 67. A linear relationship between min values and x was revealed. 

Beckham and coworkers studied the dynamic mechanical properties of poly(urethane-crown ether rotaxane)s [138]. No difference was observed between the backbone and polyrotaxane, probably because of the low min value (0.02). However, 13C solid-state NMR detected die presence of the crown ether as a mobile structure at room temperature. The same observation was seen in polyrotaxanes with ether sulfone and ether ketone backbones (77-80) [114]. Although no detailed properties were reported, the detection of the liquid-like crown ether provided very important information in terms of mechanical properties, because these properties are the result of molecular response to external forces. For example, mobile crown ethers can play the role of plasticizers and thus improve impact strength. 

To determine the efficiency of ordering of macrocycles in a swarm complex and its effrct on polyrotaxane synthesis, we studied styrene polymerization in the presence both of a complex of cyclourethanes with ZnCl (method with elements of directionality) and of cyclic urethanes (statistical method) The structure of tl compoimds... 

Conducting the polymerization under such conditions allowed us to assume the following medianism of polyrotaxane formation. First the sweUing of cyclic urethanes in the monomer occurs, i.e. styrene penetrates into the bulk of cyclourethanes or their comfdexes also including their interiors. Polymerization of styrme v4iich is both in the interior and on the outside results in the formation of a polymer whose molecules pierce the cycles, i.e. the possibility of formation of compounds with a polyrotaxane structure arises. 

The X-ray diffraction of the product after PS extraction turned out to be similar to the X-ray scattering by the initial diurethane. These results prove an absence of a chemical interaction between urethane and PC. The identical nature of CU and their linear analog made it reasonable to suggest an absence of the chemical bonding also in the c e of PS and CU. It follows that a medianical en gement between cyclourethanes and PS molecute occurs in the samples, i.e. polyrotaxane-structure compounds are formed. 

From the data in Table 1 it follows that styrene polymerization in the pmsence of cydourethane — ZnClj complexes results in products (PR-Al and PR-Bl) where the degree of penetration of rings by the growing chain is hitter than in polyrotaxanes produced by the statistical method (PR-A2 and PR-B2). Such a difference can be explained by the complexes of ZnCl with cyclic urethanes being more lengthy ordered systems than the initial urethane macrocycles. 

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