Polymerization of Heterocyclics

PRZEMYS-fc AW KUBISA Center of Molecular and Macromolecular Studies, Polish Academy of Sciences, Lodz, Poland 

This chapter deals with the cationic polymerization of heterocyclic monomers, i.e., cyclic compounds containing one or more (identical or different) heteroatoms within the ring. Polymerization proceeds by a ring-opening reaction. Traditionally, this subject is discussed separately from the cationic polymerization of alkenyl monomers (vinyl polymerization) proceeding by opening of a double bond. This is justified, because both processes have their special features, making them distinctly different. 

On the other hand, however, these two areas of cationic polymerization are not completely separated fields. In spite of the differences, both processes proceed on electron-deficient active species cations or species with a partial positive charge. Thus, propagation in both cases involves attack of the nucleophile (double bond or heteroatom) on electrophilic active centers. Several basic principles will therefore hold for both vinyl and ring-opening cationic polymerization. 

With accumulating knowledge on both processes, the borderline between them becomes more diffuse and, indeed, if one looks at the active species in polymerization of vinyl ethers (typical vinyl polymerization) and 1,3-dioxolane (typical ring-opening polymerization), there is not much difference between their structures. 

Therefore, remembering all the differences, one should look for the similarities and analogies to prepare the ground for the uniform treatment of all polymerization processes proceeding by cationic mechanism [1], 

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Pencek, S., Kubisa, P. and Matyjaszewski, K. Cationic Ring-Opening Polymerization of Heterocyclic Monomers. Vol. 37, pp. 1 —149. 

Nucleophilic Polymerization of Heterocycles. Advances in Chemistry Series (American Chemical Society) 34, 208 (1962). 

We have compiled important preparations of heteroaryl halides, boranes and stannanes for each heterocycle. The large body of data regarding palladium-mediated polymerization of heterocycles in material chemistry is not focused here neither is coordination chemistry involving palladium and heterocycles. 

Penczek S, Cypryk M, Duda A, Kubisa P, Slomkowski S (2007) Living ring-opening polymerizations of heterocyclic monomers. Prog Polym Sci 32 247-282... 

Kubisa, P., Cationic Polymerization of Heterocyclics, Chap. 6 in Cationic Polymerizations Mechanisms, Synthesis, and Applications, K. Matyjaszewski, ed., Marcel Dekker, New York, 1996. 

Living Ring-Opening Polymerization of Heterocyclic Monomers with Aluminum Porphyrin-Organoaluminum Compound Systems... 

In conclusion, it has been shown that use of cryptates for the anionic polymerization of heterocyclic monomers leatis to a tremendous increase of the rates of polymerization. There are two main causes to the higher reaction rates observed with cryptates. The first one is a suppression of the association between ion pairs in the non polar media, and the second one is the possibility of ion pairs dissociation into free ions in ethereal solvents like THP or THF. By this way, it has been possible to make detailed studies of the propagation reaction for propylene sulfide, ethylene oxide, and cycloslloxanes. 

Uidal, B. et al. 1UPAC Is Intern. Symp. on Polymerization of Heterocycles. Warsaw-Yablonna,... 

Electrochemical polymerization of heterocycles is useful in the preparation of conducting composite materials. One technique employed involves the electro-polymerization of pyrrole into a swollen polymer previously deposited on the electrode surface (148—153). This method allows variation of the physical properties of the material by control of the amount of conducting polymer incorporated into the matrix film. If the matrix polymer is an ionomer such as Nafion (154—158) it contributes the dopant ion for the oxidized conducting polymer and acts as an effective medium for ion transport during electrochemical switching of the material. 

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