Similarly the glycol ether residue is derived from the mono ether of a glycol, the free hydroxyl group of the mono ether being esterified by theboric acid, the ether group being unreacted.The glycol which preferably contains up to 30 carbon atoms may be ethylene, propylene or butylene glycol, neopentyl glycol, or a polyglycol, i.e. a polyethylene or polypropylene glycol or a glycol derived from mi