Strained cyclic unit, stabilization

The intra- and intermolecular interaction between cationic center and tt-electron system have attracted many chemists and much knowledge on the interaction has been accumulated (1). In 1975, we intended to apply such a kind of interaction to cyclopolymerization. Thus, it is expected that the transition state leading to a strained cyclic unit in the polymerization could be stabilized by the intramolecular attractive interaction between cationic growing-end and ir-system There had been few examples of cyclopolymerizations giving strained units. A paracyclophane unit was employed as a strained cyclic unit in the polymer main chain. In Table I are summarized some cyclophanes with their strain energies. 

The test was conducted with a constant internal pressure of 1 MPa and a cyclic in-plane displacement equivalent to given ATm. Tests indicated that the stabilized strain growth at the crown per unit ATm is 7x10 % / K at room temperature. Extrapolation to the prototype under operating temperature yields 174 K. Since the maximum ATm is only 50 K, ratcheting is not possible for prototype pipe. 

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