A simple and green procedure to prepare poly(ethylene glycol) networks: Synthesis and properties

Poly(ethylene glycol) networks have been prepared by reaction between dihydroxy-terminated poly(ethylene glycol) (PEG) and diepoxy-terminated poly(ethylene glycol) (DEPEG) (M approximate to 600 g mol(-1)) in concentrated aqueous NaOH solutions by a process involving alkoxide-epoxy-type reactions. Yields of formation of the networks depend on the concentration of NaOH used, being maximum (>80%) for concentrations of 20% by weight. The PEG/DEPEG molar ratio in the feed plays a decisive role in both the yield of the reaction and the properties of the obtained network, controlling the degree of crosslinking. High PEG/DEPEG ratios lead to hydrogels with a great swelling capacity. The swelling capacity can also be controlled by varying the PEG molecular weight for a same PEG/DEPEG ratio. By employing PEG samples of molecular weights 600, 1500 and 3000 g mol(-1), and different PEG/DEPEG ratios, hydrogels with degrees of swelling ranging from 3.4 to 21.6 have been obtained. The thermal transitions in the networks, i.e. the glass transition (T-g) and/or the melting temperature (T-m) show a linear dependence on the PEG/DEPEG ratio.