Vaccine adjuvant and vaccine

A method of synthesizing a composition consisting of a polyoxypropylene/polyoxyethylene block copolymer having the following general formula:

• HO(C.sub.2 H.sub.4 O).sub.a (C.sub.3 H.sub.6 O).sub.b (C.sub.2 H.sub.4 O).sub.a H
• wherein "b" represents a number such that the molecular weight of the hydrophobe (C.sub.3 H.sub.6 O) is greater than 15,000 Daltons and "a" represents a number such that the percentage of hydrophile (C.sub.2 H.sub.4 O) is between approximately 3% and 30% by weight, said method comprising:
• (a) adding propylene glycol to an oxygen free reactor vessel containing cesium hydroxide (CsOH.H.sub.2 O) and maintaining a temperature of between approximately 90.degree. C. and 120.degree. C., wherein the mole ratio of the cesium hydroxide to the propylene glycol is between approximately 12 to 1:8;
• (b) adding propylene oxide to the reactor vessel under conditions allowing the formation of a polyoxypropylene molecule, the propylene oxide being added by rate limiting vapor phase addition, minimizing excess propylene oxide, and the propylene oxide being added until the molecular weight of the polyoxypropylene molecule is greater than 15,000 Daltons;
• (c) adding ethylene oxide to the reactor vessel under conditions allowing the formation of polyoxyethylene blocks on each end of the polyoxypropylene molecule, thereby forming polyoxypropylene/polyoxyethylene block copolymer in the reactor vessel, the ethylene oxide being added until the percentage of polyoxyethylene is between approximately 3% to 30% by weight of the block copolymer, the block copolymer having significantly reduced level of unsaturation.
• (d) removing any remaining cesium hydroxide in the block copolymer.