Article

Water-induced (nano) organization in poly(ethyl acrylate-co-hydroxyethyl acrylate) networks

Center for Biomaterials, Universidad Politécnica de Valencia, 46022 Valencia, Spain; Centro de Investigación Príncipe Felipe, Autopista del Saler 16, 46013 Valencia, Spain; CIBER en Bioingeniería, Biomateriales y Nanomedicina, Valencia, Spain
European Polymer Journal 01/2008; DOI: 10.1016/j.eurpolymj.2008.04.032

ABSTRACT The conformational changes in poly(ethyl acrylate-co-hydroxyethyl acrylate), P(EA-co-HEA) chains, which constitute a copolymer network hydrogel, induced by the presence of water are investigated by different experimental techniques and compared with the behaviour of the corresponding xerogel. The mechanical relaxation spectrum shows the presence of a new water-induced relaxation, the water content dependence of the glass transition is measured by DSC, and the dielectric relaxation assesses the effect of water for the lower concentrations. Hydrophilic and hydrophobic monomeric units in the P(EA-co-HEA) network are able to aggregate to form two separated (nano)phases in the presence of water due to hydrophobic interaction. Phase separation takes place when the water content of the sample is higher than a critical value estimated as two water molecules per –OH group in the copolymer chain. The existence of the hydrophobic domains is detected by their glass transition being nearly independent on the water content of the sample. Phase separation is also clearly revealed by phase angle measurements in AFM experiments.

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