Even mixed carboxylic acid esters could be synthesized easily that are of commercial interest. Phosphorus-containing polymers possess a growing interest in the biomedical field, mainly because of their properties such as biocompatibility, hemocompatibility, and protein adsorption resistance. Cellulose phosphates and phosphonates are promising biomaterials, are used to increase the flame retardancy of textile fibers and as cation exchange materials.