The glass transition temperature and microstructure of polyurethane/epoxy resin interpenetrating polymer networks nanocomposites

Nanocomposites with various contents of organophilic montmorillonite (oMMT) have been prepared by adding oMMT to interpenetrating poly- mer networks (IPNs) of polyurethane and epoxy resin (PU/EP) which had been prepared by a sequential polymeric technique. DSC experiment indicates a novel phenomenon that the glass transition tem- perature (Tg) of the nanocomposites increases with the oMMT content up to 3 %, then decreases with further increasing oMMT content. In order to explain this phenomenon, crosslink density, hydrogen bond- ing in the hard segments, crystallization of the nanocomposites and the exfoliation degree of oMMT in the nanocomposites have been investigated by swelling method, FT-IR, XRD, SEM and TEM, re- spectively. The results indicate that the crosslink density and the hydrogen bonding index of the nanocomposites increase, but the crystallization de- gree of the nanocomposites decreases with increas- ing oMMT content. In addition, oMMT improves the network structure of PU/EP.