Synthesis of hydrophobic poly(alkylene oxide)s and amphiphilic poly(alkylene oxide) block copolymers

The anionic ring-opening polymerization of alkylene oxides, except ethylene oxide, is accompanied by strong side reactions, leading to high molecular weight and low molecular weight byproducts. In this work we investigated the anionic polymerization of hydrophobic alkylene oxides at different temperatures, solvents, and initiating systems. For polymers synthesized in the temperature range between 40 and 80 degrees C and employing potassium and cesium alcoholate initiators significant amounts of byproducts were found. With the help of crown ethers the temperature could be reduced to -23 degrees C without extending polymerization times too much. This measure allowed eliminating byproducts almost completely. The best results were obtained with potassium alcoholates and 18-crown-6 in toluene at -10 to -23 degrees C. Poly(1,2-butylene oxide), poly(1,2-hexylene oxide), and poly(1,2-octylene oxide) homopolymers were synthesized up to molecular weights in the range of 50 000-100 000 and M(w)/M(n) < 1.1. Furthermore, the method was employed to synthesize amphiphilic block copolymers of the hydrophobic poly(alkylene oxide)s with poly(ethylene oxide) as the hydrophilic moiety. Block molecular weights reached up to 50 000. Even at those high molecular weights the contents of homopolymer byproduct did not exceed 1%. The results indicate that side reactions usually involved in the anionic polymerization of alkylene oxides were largely suppressed using the employed polymerization technique.