The invention relates to method for preparation of a specific product from a polysaccharide in which at least one hydroxyl of a saccharide unit is substituted with an ether or ester moiety. Said ether or ester moiety is provided with ethenyl and / or epoxy functionality for preparing an activatable polysaccharide polymer and the activatable polysaccharide polymer with ethenyl and / or epoxy functionality is optionally reacted with an additional coupling reagent, having at least two coupling functionality for preparing polysaccharide polymer with additional activatable crosslinker. Thereafter the activatable polysaccharide polymer or the polysaccharide polymer with an additional activatable crosslinker, is activated for crosslinking said polysaccharide polymer with another polysaccharide polymer by reacting said activatable polysaccharide polymer or polysaccharide polymer with an additional activatable crosslinker with a crosslinking iniator for crosslinking the polysaccharide polymer chains with each other,for preparing a product such as hydrogel, film, coating or membrane with polysaccharide backbone.