Polyoxy(methyl-1,2-ethanediyl), .alpha.-hydro-.omega.-hydroxy-, ether with 2-ethyl-2-(hydroxymethyl)-1,3-propanediol (3:1), polymer with .alpha.-hydro-.omega.-hydroxypolyoxy(methyl-1,2-ethanediyl) and 1,1-methylenebis4-isocyanatobenzene, isocyanate-termin