Non-ionic water-soluble cellulose ethers modified with 3-azido-2-hydroxypropyl groups bound via an ether link are provided having a molar degree of substitution MSAHP in the range from 0.001 to 0.50. Exemplary cellulose ethers are alkyl cell doses, including methyl, hydroxyalkyl (e.g. hydroxyethyl hydroxypropyl) or alkylhydroxyalkyl cellulose (e.g. methylhydroxyethyl). Reaction products with alkyne compounds are also provided, resulting in a terminal alkyne group. The reaction of azide with the alkyne proceeds as a 1,3-dipolar cycloaddition reaction, advantageously with Cu(I) or ruthenium catalysts. A multiplicity of cellulose ethers can be obtained from the conversion reaction. Variations in the macroscopic properties can be achieved by controlled modification, ranging from increased or reduced viscosity. The reaction, taking place within a few seconds, requires only minimal catalyst. Gel formation is reversible by adjustment of the pH such that a monophasic system (high-viscous fluid) arises again from a biphasic system (gel+low-viscous water phase).