Chemical structure determination cationic polymerization

Correlations of structures and reactivities for anionic and cationic ring-opening polymerization are reviewed. The following topics are discussed chemical structure of active species and their isomerism, determination of active centers concentration, covalent vs ionic growth and correlations between structures of active centers or monomers and their reactivities. 

This paper descriBes problems outlined above, methods of determination of the chemical structures in both anionic and cationic ring-opening polymerizations, equilibria between different active species, the corresponding mechanisms of propagation and related rate constants of propagation on these species, and finally the available correlations. 

The chemical structures of the monomers also determine their reactivity toward cationic polymerizations. Electron-donating groups enhance the electron densities of the double bonds. Because the monomers must act as nucleophiles or as electron donors in the course of propagation, increased electron densities at the double bonds increase the reaction rates. It follows, therefore, that electron-withdrawing substituents on olefins will hinder cationic polymerizations. They will, instead, enhance the ability for anionic polymerization. The polarity of the substituents, however, is not the only determining factor in monomer reactivity. Steric effects can also exert considerable controls over the rates of propagation and the modes of addition to the active centers. Polymerizations... 

As discussed in Section IV.B, a general structural feature of single-site polymerization catalyst ion pairs is the presence of weak donor—acceptor interactions involving the cation and anion moieties or a solvent molecule. Many of these weak interactions still persist in solution and thus likely stabilize the chemically very reactive ion pairs. These stabilization forces, along with complexation with functional monomers In the presence of polymerizable monomers, doubtless play a key role in determining catalyst high-temper-ature stability, lifetime, and overall kinetic profile, as well as polymerization characteristics. 

---