Structure and swelling behaviour of hydrophilic epoxy networks investigated by SANS

Structure of hydrophilic epoxy networks swollen in deuterated water has been investigated by small-angle neutron scattering (SANS). Two series of the networks were prepared by end-linking reaction of α,ω-diamino terminated poly(oxypropylene)-block-poly(oxyethylene)-block-poly(oxypropylene) (POP-POE-POP), α,ω-diamino terminated poly(oxypropylene) (POP) and diglycidyl ether of Bisphenol A propoxylate (PDGEBA). In the first series, prepared using functionalized POP-POE-POP and PDGEBA, hydrophilicity of the networks was controlled via cross-linking density of the networks, changing the initial ratio of reactives. In the second series, POP-POE-POP was gradually substituted by POP of the same molecular weight, enabling a control of hydrophilicity of the networks at essentially constant crosslinking density in this way. Microphase separated structure of the networks swollen in deuterated water with composition variations on nanometer scale was found by SANS. The scattering data were fitted to the Percus-Yevick model, approximating the swollen network by an idealized system of spheres dispersed in the matrix. Satisfactory fits in the region of the interference scattering peak were obtained giving values 30-70 Å for the average radius of the spherical regions. Radius of the spheres increases with increasing hydrophobicity of the networks (growing POP content and/or network crosslinking density).