Synthetic photocrosslinkable polysaccharide sulfates

Photoactive derivatives of dextran and pullulan with high degree of substitution were prepared by an efficient and mild esterification of the biopolymers with [(4-methyl-2-oxo-2H-chromen-7-yl)oxy] acetic acid via in situ activation of the carboxylic acid with N,N′- carbonyldiimidazole. Subsequently, sulfation was carried out with the gentle and easily manageable SO3/DMF complex as reagent. Thus, water soluble polyelectrolytes decorated with high amounts of photochemically active moieties were obtained. The structures of the novel polysaccharide esters and the polyelectrolytes were evaluated by means of NMR and IR spectroscopy. Moreover, the photochemistry of both the carboxylic acid esters and their sulfated derivatives was studied by means of UV–Vis spectroscopy in the dissolved state. The changes observed may be used to control the properties and are thus of interest in the design of smart materials.