New routes to macrocyclic polymers of controlled dimensions

Since the early 1950s a number of theoretical studies have dealt with the prediction of the dimensions and behaviour of macrocyclic polymers. However, owing to the difficulty of synthesis, the comparison of theories with experimental data still remains restricted to a small number of macromolecules. The first cyclic polymers studied were those produced from systems in which ring-chain equilibrium exists, but it is only in the last decade that a method for the preparation of ring-shaped vinylic polymers of controlled dimensions has become available. The method involves the bimolecular end-to-end ring closure of an anionically prepared α,ω-difunctional linear polymer using a coupling agent. Low cyclization yields are generally observed. Besides theoretical considerations the experimental conditions which may lead to these results have been examined. In this paper a new approach to the synthesis of macrocyclic polymers with controlled dimensions is examined. In contrast to previous procedures, it involves a single unimolecular ring-closure process which is much less sensitive to the extremely low concentrations required for cyclizations. It is achieved by the direct end-coupling of an α,ω-heterodifunctional linear polymer precursor after the appropriate activation under high dilute conditions of one of its two end-functions. The advantages of this new approach are discussed both on theoretical and experimental grounds. Its application to the preparation of poly(vinyl ether)s, polystyrenes and poly(vinyl ether-b-styrene) diblock copolymers of controlled dimensions with a macrocyclic architecture is described.