Novel hydrogels from diepoxy‐terminated poly(ethylene glycol)s and aliphatic primary diamines: synthesis and equilibrium swelling studies

Abstract

New hydrogels were prepared from diepoxy‐terminated poly(ethylene glycol)s of approximate molecular weights 600, 1000, 2000, and 4000 Da and aliphatic primary diamines with different numbers of carbon atoms (ethylenediamine, 1,4‐diaminobutane, hexamethylenediamine, 1,8‐octanediamine, 1,10‐decanediamine, 1,12‐dodecanediamine), in water or ethanol–water mixture, depending on the amine solubility. The swelling behavior of these gels was tested in distilled water/aqueous solution at constant temperature and the equilibrium swelling degree (ESD) was determined for structurally different hydrogels and under various environmental conditions. It was shown that ESD was influenced by the molecular weight of PEG oligomers, amine/epoxy groups mole ratio, amine chain length, temperature, pH, and concentration of salts present in the swelling medium. Higher ESDs were obtained for either longer‐chain PEGs, non‐stoichiometric amine/epoxy groups ratio, shorter amines, acidic pH, lower temperatures, or in the absence of salts. Copyright © 2009 John Wiley & Sons, Ltd.

Swelling and Diffusion Characteristics of Hydrogels Synthesized from Diepoxy-terminated Poly(ethylene glycol)s and Aliphatic Polyamines

“…We should mention that the difference in ESD using DETA (about 0.5 g water/g xerogel) cannot be ascribed to the experimental error in its determination, which was less than ±0.1 g water/g xerogel within a set of 3 experiments. Figure 1 also shows that irrespective of the amine used as cross-linker, ESD increased with increasing MW of the oligomer, as a result of the decreasing number of effective elastic chains per volume unit of dry network (22), confirming previous results obtained for other PEG hydrogels (18,19,(28)(29)(30)(31). On this ground, if a mixture of two well-defined oligomers of different MW is employed in conjunction with a certain cross-linking agent, by varying their ratio it may be possible to adjust the average MW of the elastic chains, and therefore to finely tune the ESD of the resulting hydrogel.…”

“…Except for some of the experiments investigating the influence of the reaction conditions, the soluble fraction of gels was less than 3% in all cases, indicative for a high degree of perfection of the networks prepared (27). Consequence of the stoichiometric ratio of reactants, no significant influence (less than 1%) of the molecular weight (MW) of DEPEG X upon this reaction parameter was noticed, as reported previously, as well (19).…”

“…f procedure already reported by us and others (19,25). The cross-linking occurs through the well-known reaction between the epoxy groups (EG) and primary and secondary aliphatic amines (Scheme 1), the functionality of the amine in this reaction being equal to its number of hydrogen atoms (H amine ).…”

“…Their hydroxyl numbers, determined by the acetylation method, were 185.52, 114.44, 54.55, and 27.99 mg KOH/g, respectively, corresponding to number average molecular weights (M n,PEG ) of 605 Da, 982 Da, 2060 Da and 4010 Da, calculated assuming the presence of two hydroxy groups within each PEG macromolecule. DEPEG X were synthesized through the reaction of the corresponding DHPEG X and epichlorohydrin (ECH), in benzene, in the presence of NaOH, as previously described (19). Their functionality ( ), as well as their polydispersity index (PDI) determined by SEC, are shown in Table 1.…”

“…The preparation and swelling behavior testing conditions were identical to those previously reported (19) in order to be able to compare the results. From the swelling degree versus time plots obtained, ESD was determined as the value corresponding to the curve plateau.…”