A patent was issued this month that used tetrabutylammonium bromide as a bromide source that can be used to carefully control at will not only the initiation of the polymerization of propylene oxide or epichlorohydrin, but also control the ratio of repeating units to a cationic end group at only one side of the polymer. This is useful for preparing an effective dispersion of a nanocarbon material in an aqueous phase.
The inventors of the patent Hoang, T.; Ohta, K.; Hayano, S.; Tsunogae, Y.; (Zeon Corporation) US Patent 10,344,124, 09-Jul-2019, found that a nanocarbon material is more favorably and more stably dispersed in a polyether-based polymer that contains a cation on only one terminal side. Examples of such polyethers that contain a cation on one side are polypropylene oxide or polyepichlorohydrin that has an onium salt on one side that can be produced by reacting an amine or a nitrogen heterocycle with a polypropylene oxide or polyepichlorohydrin that has a bromide at only one end.
For this purpose, in one example the inventors polymerized propylene oxide in the presence of a carefully chosen amount of tetrabutylammonium bromide (TBAB) as an organic soluble bromide source (21.5:1 molar ratio of PO:TBAB), triethylaluminum as polymerization catalyst and toluene as the solvent at 0 C for 2 hours. When the reaction was complete, the inventors added isopropanol to terminate the reaction and obtain polypropylene oxide with an average of 20 PO units, having a bromomethyl group at the polymerization starting terminal and a hydroxyl group at the polymerization terminating terminal.
The polypropylene oxide with bromomethyl at one end and hydroxyl at the other end was quaternized with 1-methyl imidazole or butyl dimethyl amine.
In other examples, the inventors reduced the amount of TBAB which increased the number of PO repeating units to 50, 100 and 200 at will and by design, in order to test for the optimal chain length for the stable dispersion of the nanocarbon material.
While this application is not strictly phase-transfer catalysis, it does leverage the concept of controlling a reaction by using a phase-transfer agent to introduce an anion into a reaction phase in a specific well-controlled quantity to achieve desired performance targets.
In our 2-day PTC course, we show other examples of using TBAB to initiate nucleophilic reactions induced by bromide that star with ring opening. Now register for the public PTC course in Prague in October 2019 or bring the PTC course in-house to your company to improve your personal performance, your department’s performance and your company’s performance. The increased profit your company will achieve from low-cost high-performance green chemistry using phase-transfer catalysis, may save jobs, perhaps your job.
