Fluorinated polyurethanes with hydroxy functionality, process for preparing them and their use for the treatment of lithoidal material

Low molecular weight non-film forming fluorinated polyurethanes with hydroxy functionality obtained from (1) the reaction of at least one organic diisocyanate with at least one hydroxy-capped perfluoropolyether to produce a product and (2) reacting the product with a polyol, having a functionality of least 2, and in which the ratio of the equivalents of isocyanate groups to total hydroxy groups is lower than or equal to 1, said low molecular weight fluorinated polyurethane having an average molecular weight between greater than 1,000 and 5,000, a hydroxy functionality greater than or equal to 2, a fluorine content larger than 30% by weight, and said fluorinated polyurethane is soluble in organic solvents.