Poly(oxy-1,2-ethanediyl), .alpha.-hydro-.omega.-hydroxy-, ether with N-2-bis(2-hydroxyethyl)methylammonioethyl-N,N-bis(hydroxyethyl)-N,N-dimethyl-N-octadecyl-1,2-ethanediaminium tris(methyl sulfate) (4:1) (salt)