Novel linear–globular thermoreversible hydrogel ABA type copolymers from dendritic citric acid as the A blocks and poly(ethyleneglycol) as the B block

The syntheses of novel linear–dendritic thermoreversible hydrogel copolymers were achieved via two procedures. In the first procedure synthesis of linear–dendritic copolymers carried out through an esterification step using thionylchloride and pyridine. In the second procedure linear–dendritic copolymers were prepared using dicyclohexylcarbodiimide and pyridine. The citric acid as the monomer unit was used for the preparation of ester-linked fragments. Diacid poly(ethyleneglycol) was chlorinated and diacyl halide poly(ethyleneglycol) prepared and used as the core. The formation of water soluble inclusion complexes with a variety of small size guest molecules is also described. Moreover, the thermoreversible behavior of the prepared hydrogels of both citric acid–poly(ethyleneglycol)–citric acid (CA–PEG–CA) triblock copolymers and the complexes derived from CA–PEG–CA triblock copolymers with various drugs have been investigated. The structure definition and analysis of the new resulted triblock copolymers and their complexes were carried out using NMR, optical microscopy, viscosimetry, FT–IR and UV–VIS spectrometry methods.