The synthesis of several difunctional monomers, derived from the introduction of two 4-styrenesubstituted moieties into a covalent skeleton, is described. The more rigid ones, built around malonate moieties and more preorganized to give 3,3′-cyclophane repeating units, failed completely to give soluble, ordered cyclopolymers. The introduction of a certain degree of flexibility in the tethering moiety afforded, by using freeradical initiation, structurally stable cyclopolymers with a high degree of cyclization and good degrees of polymerization. Theoretical calculations detail and strongly support the experimental results. Further chemical elaboration of the obtained cyclopolymeric backbones, by means of the removal of a ketal group, is possible in mild conditions to give systems which can be easily cross-linked thermally, with the loss of H 2 O, at temperatures higher than 100 °C.

Polyurethane prepolymers prepared from toluene 2,4-diisocyanate, toluene 2,6-diisocyanate, and polypropylene glycol with a ratio between the isocyanate and hydroxyl groups equal to 2 were analyzed by 1 H nuclear magnetic resonance (NMR) spectroscopy in acetone-d 6 . Different temperatures and concentrations were used. Toluene 2,4-dimethylurethane and toluene 2,6-dimethylurethane were synthesized and used as model compounds to assign prepolymers signals. Measurements of spin-lattice relaxation time T 1 by "inversion recovery" experiments were carried out on toluene 2,4-diisocyanate, toluene 2,6-diisocyanate, toluene 2,4-dimethylurethane, toluene 2,6-dimethylurethane, and polyurethane prepolymers. Differences in T 1 times were used to interpret prepolymers spectra, by means of the strong observed effect on protons due to the presence of adjacent isocyanate groups.

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