The anhydrides of the very strong acids, CF 3 SO 3 H and FSO 3 H, polymerize tetrahydrofuran (THF) to give a living polyether having cationic activity at each chain end. The surprising fact that both chain ends are cationically active necessitates the postulation of a reaction mechanism wherein the YSO,-ester end group (Y=CF 3 or F) formed as an intermediate in the polymerization generates an oxonium ion by a subsequent O-alkylation reaction involving either a THF molecule or a nearest neighbor ether group of the polymer chain. Kinetic studies of polymerizations involving (CF, SO,) 2 0 and the bis-ester, CF 3 SO 3 —C 4 H 5 —O 3 SCF 3 , as initiators indicate that chain growth is much faster where an oxonium ion rather than an ester is the end group. The chemistry of poly-THF dications is discussed. These are strong alkylating agents which make possible the facile preparation of unusual copolymers, block copolymers, and functionally terminated polymers.

The Preparation and Chemistry of Dicationically Active Polymers of Tetrahydrofuran

Following a short introduction and a brief discussion of thermodynamics of propagation, the kinetics and mechanisms of anionic polymerization are reviewed. The systems involving living polymers, a term introduced by this writer, are discussed in greater detail because the existence of various ionic species participating in polymerization was clearly revealed by their studies. Indeed, a large part of this review is concerned with the methods used in identification of these species and determination of their role in various polymerizing systems. The results of such studies are compared with those derived from investigations of radical-anions, carbanions and other ionic species.

Living Polymers and Mechanisms of Anionic Polymerization

Advances in the major areas of the cationic ring-opening polymerizations are discussed. In the first part synthesis of new polymers is reviewed; this includes mainly novel block and graft copolymers based on the di- and multicationically ended living polyacetals and polyethers (polyTHF).



Recent data on thermodynamics of nonideal systems, giving dependence of [M]e on [M]o, are summarized with special emphasize of the differences between monomers due to variation of their nucleophilicities.



Discussion of kinetics and mechanisms of polymerization of cyclic acetals and ethers is focused on the macroring formation and reactivities of active centers.



The reactivity of covalent and various ionic growing species are compared in the polymerization of cyclic ethers (THF and oxepane) and oxazolines. Reasons for much lower reactivity of covalent than ionic species and reasons for similar reactivities of macroion-pairs and macroions are presented.



It is shown, that the kinetically controlled proportions of macrorings in the polymerization of these and other heterocyclic monomers depend on the structure of the end-groups, formed upon initiation. Initiation with acids, giving H-X∼ (where X=heteroatom) end-groups, leads to the kinetically enhanced proportion of macrorings. This is particularly important for the low degrees of polymerization.

M. P. Dreyfuss

Papers

The Reaction of Trityl Salts with 2-Methyltetrahydrofuran and with Tetrahydrofuran