Self-assembly of epoxy-based polymers

Abstract

Amphiphilic polymers have proved to be very versatile precursors for the synthesis of nanostructured systems by self-assembly. Dendrimers, polysoaps and block copolymers have successfully been used to obtain micelles, nanostructured films and mesophases with different levels of organization.1-3 Hydrophobic interactions are important in the formation of many kinds of organized polymer aggregates and gels. We can find good examples of the role of van der Waals interactions between long alkyl chains in the self assembly of metal nanoparticles 4 and metal thiolates.5 In this chapter we will show that proper combination of epoxy monomers with long alkyl chains co-monomers enables the synthesis of nanostructured systems through self-assembly of the alkyl chains. Both linear and crosslinked nanostructured polymers may be synthesized using appropriate chemistries. Linear polymers with hydrophobic pendant chains are easily obtained in bulk by the polycondensation reaction of diglycidylether of bisphenol A (DGEBA) with a long alkyl chain monoamine like dodecylamine. The resulting product exhibits typical properties of a thermoplastic epoxy (e.g., high solubility in a variety of solvents). However, when stored above its glass transition temperature it undergoes a nanostructuration process by the self-assembly of alkyl chains leading to a physical gel that is insoluble in most solvents. The sol-gel transition is reversible with temperature. Physical properties of the obtained networks and their dependence with the length of the alkyl chain are discussed. Crosslinked nanostructured networks may be obtained by a two-step procedure. In a first step the alkylamine is reacted with a monofunctional epoxy monomer bearing a multifunctional group capable of polymerizing in a second step. Glycidoxypropyl(trimethoxy)silane (GPMS) is a convenient epoxy monomer for these purposes. After end-capping the alkylamine with GPMS, self-assembly of the alkyl chains takes place in solution. The nanostructure generated is fixed by the hydrolytic polycondensation of methoxy groups (sol-gel reaction) that takes place simultaneously with solvent evaporation. The use of these systems as hosts of nanoparticles (NPs) coated by hydrophobic organic groups (e.g. dodecyl chains), is discussed.