Rate of Polymerization in THF-Protonic Acid System

The rates of THF polymerization initiated by protonic acids having anions that are capable of forming covalent bonds, are affected by the existence of macroion-macro-ester equilibria (cf. Adv. Pol. Sci. 37 Sect. 5.1.2). 

When Ae = CF3SOf, propagation by macroions is approximately 100 times faster than by macroestersl6). Thus, only 2% macroions (of all of the growing species) counterbalance the contribution of growth by macroesters. 

While k for the sulfate ester (e.g.. ..—O—(CH2)40S03H) is unknown, it is certainly much lower than that of the triflate ester (the higher the nucleophilicity of the parent anion the lower the reactivity of the ester). 

Since the equilibrium constant of ion-ester interconversion is also unknown, the relative contribution of ionic and covalent growth cannot be predicted. 

The rate of polymerization is very low even at high acid concentrations (up to 20 mol %) n). To increase the polymerization rate to acceptable values it is necessary to decrease the nucleophilicity of the sulfate anion. This can be done in various ways one that is practical involves the addition of S03 U). Most likely the pyrosulfate anions thus produced increase the proportion of ions (as compared with sulfate anions) and/or yield more reactive macroesters. We are inclined to think that the first explanation is valid. 

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