Polymerization with Fluosulfonic Acid

Unlike the rather ill-defined acid sites of siliceous earth, with fluosulfonic acid the intensity of polymerization catalysis (i.e. the number of chain initiations) is clearly dictated by the quantity of fluosulfonic acid added to the THF. The more fluosulfonic acid is added, the more chains are initiated, which means that the more fluosulfonic acid is added, the lower will be the molecular weight of the polymer product. 

Against this background, the process for polymerizing THF with fluosulfonic acid can be outlined as follows  

To terminate the polymerization, 50 ml of water are added while the flask is being cooled and stirring is accelerated. The enforced termination reaction between the growing macrocation and water is shown below  

The macrocation is neutralized by a hydroxyl ion, thus leading to an OH end group, so that the final product is PTMEG. This reaction is the reason why, in the procedures described,wa-ter had to be scrupulously eliminated from the system as otherwise polymerization would not 

After addition of the water, the mixture in the reactor is heated to 80 °C for a period of 30 minutes. Due to this treatment, the major portion of the nonpolymerized THF (boiling point 65 °C) will be distilled off. After cooling, 500 ml of toluene are added, and the mixture is submitted to an extraction with 100 ml quantities of water in a separating furmel until the aqueous phase is neutral. The toluene phase is then mixed with 10 g of bleaching earth and submitted to filtration or centrifugation before being freed of the toluene in a rotary vacuum evaporator. 

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The polymerization of THF with SbCls starts in the same fashion as with fluosulfonic acid except that 250 ml of THF require only 15 ml of SbCls (instead of 30 ml of fluosulfonic acid). The addition of the SbCls causes the THF to assume a yellow to brown color. Some toluene is added to prevent any sudden rise in viscosity. A water bath is employed to take the mixture of THF, SbCls, and toluene to 40 °C for a period of 3 hours. During this time, the viscosity will be seen to increase significantly. 

These oligomers are prepared by polymerization of THF with protonic acid initiators, and according to the patent literature and other available information, fluosulfonic acid has been used on a technical scale. A recent paper describes the successful application of H2S04/S03 mixtures 11). The diol of Mn = 1000 is a white opalescent solid at 24 C it melts at 32 °C giving a syrupy liquid with a hydroxyl number of 112-116, an acid number less than 0.05, a carbonyl number less than 4.0 and a Ca content le>s than 5 ppm Na and K are less than 10 ppm 8). 

When fluosulfonic acid (FS03H) was used as the initiator of THF polymerization, the higher molecular weight polymer with DP > ([THFJo — [rHF]e/[FS03H]o was formed initially. In the further course of the reaction, the molecular weight decreased and approached calculated values. HF is formed during the polymerization and as determined by 19F-NMR its ultimate concentration equals that of FSOaH 13). The results of a typical polymerization are summarized in Table 6.2. 

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