Such a polyhydroxy compound includes, for example, bivalent alcohols such as ethylene glycol and propylene glycol, trivalent alcohols such as glycerol, trimethylolpropane and hexanetriol, and tetravalent or higher valent alcohols such as pentaerythritol, diglycerol, dextrose, sorbitol and sucrose, as well as polyoxyalkylene alcohols having lower molecular weights than the desired products obtained