Preparation and swelling behavior of end-linked hydrogels prepared from linear poly(ethylene glycol) and dendrimer-star polymers

Linear diepoxide-terminated poly(ethylene glycol) (PEG) of molar mass 600, 1000 and 2000 g mol−1 was end-linked with dendrimer-star polymer (PAMAM) of generations 1.0 in water to prepare architecturally well-defined copolymer hydrogels. The structures and properties of the products were characterized using infrared, 1H NMR, DSC measurements, scanning electron microscopy (SEM) and swelling behavior tests. The swelling behavior of these hydrogels was tested in distilled water at constant temperature and the equilibrium swelling ratio (ESR) was determined for structurally different hydrogels and various environmental conditions, which showed that ESR was influenced by the molecular weight of PEG, the molar ratio of H amine groups/epoxy groups, temperature and pH. Higher ESR was obtained for either longer-chain PEG, non-stoichiometric H amine/epoxy groups ratio, acidic pH or lower temperatures. When the hydrogel was switched from 10 °C to 65 °C and pH 3.5 to 11.5, the swelling behavior of the hydrogels showed good reversibility for swelling–deswelling. When the molecular weight of PEG was changed in the range of 600–2000, the lower critical solution temperature (LCST) of hydrogel increased from 30 to 40 °C. When the molar ratio of H amine/epoxy groups was changed, the LCST was not significantly changed.