Poly(ethyleneoxide-b-styrene) copolymers as solid—liquid phase transfer catalysts

Di- and tri-block copolymers of ethylene oxide and styrene function as effective phase transfer catalysts in the reaction of solid potassium phenoxide with n-butylbromide in refluxing toluene to give virtually quantitative yields of n-butyl phenyl ether. A wide range of copolymer structures have been examined and the catalytic activity is found to increase with $\text{M}\text{?}{}_{\mathrm{n}}$ of both the styrene and the ethylene oxide segments levelling off at $\text{M}\text{?}{}_{\mathrm{n}}$ styrene block ～30 000 and $\text{M}\text{?}{}_{\mathrm{n}}$ ethylene oxide block ～60 000. Beyond $\text{M}\text{?}{}_{\mathrm{n}}$ ethylene oxide block ～100 000 rates of reaction drop again towards the value for a high molecular weight homopolymer of ethylene oxide. Kinetic analysis suggests the rate controlling process to be the bimolecular reaction between complexed potassium phenoxide and n-butyl bromide, and the activation energy for the reaction is the same as that for reactions catalysed by low molecular weight oligoethers. From the kinetic dependence of the concentration of copolymer catalysts, the dependence on the structure of individual copolymers and from the known physical behaviour of these copolymers in toluene solution, catalysis appears to involve micellar aggregates of copolymer chains.