As R, --CH(CH.sub.3)CH.sub.2-- is particularly preferable.The main chain skeleton of the polyoxyalkylene polymer as the component (A) is obtained, for example, by ring-opening polymerization of monoepoxide in the presence of an initiator and a catalyst.Specific examples of the initiator may include dihydric alcohols and polyhydric alcohols such as ethylene glycol, propylene glycol, butanediol, hex