Ring-opening addition polymerization, ionic

There are three principal ionic ring-opening polymerization reactions of epoxides acid-initiated, base-initiated, and coordinate-initiated polymerizations. The acid-initiated reaction involves addition of an active hydrogen compound, HY, such as ethanol, to an epoxide ring and is catalyzed by an acid, HX, such as perchloric acid. The reaction sequence involves formation of an oxonium complex, followed by ring opening by an 8 2 cleavage of an oxonium carbon bond. 

Fig. 15.2 Schematic representation for covalent attachment of hydroxyl groups to MWCNTs by free radical addition of 4,4 -azobis(4-cyanopentanol) in water and subsequent surface-initiated ring-opening polymerization of -caprolactone in room-temperature ionic liquids (BmimBF )...

Random copolymers have grown to be the most versatile, economical, and easily synthesized types of copolymers. A wide variety of free-radical, ionic-addition, and ring-opening polymerization techniques, as well as many step-growth reactions, are employed. 

Addition polymerizations proceed either by free-radical or by ionic mechanisms and can be carried out either in bulk solution, i.e., on the neat monomer, or in suspension or emulsion. Each method has its own advantages and disadvantages. The choice of method of polymerization also depends to a very great extent both on the nature of the monomer and on the product desired. Polycondensations or step-reactions proceed according to the mechanism demanded by the reactive functional groups. Some common step-reactions are esterification, amidification, and urethane formation, as well as ring-opening or transesterification. 

In the early distinction by Carrothers (1) between condensation and addition polymers, polyesters were uniformly considered as examples of the former. However it was soon appreciated that a large family of polymers could be made which were functionally "polyesters" but did not fall into the synthesis based definition of condensation polymers. This family of polymers are usually prepared by ionic routes, generally a ring opening polymerization, and are structurally different from the condensation polyesters by having a chain sense i.e. the crystalline chain conformation possesses an intrinsic dipole moment. Accordingly, a structurally based definition of polyesters in terms of "polar and non-polar" crystalline conformations will be used in this report. The non-polar molecules considered will be aromatic polyesters and the polar molecules will be polyalkanoates. 

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