Jean-Francois GERARD1, Houssem CHABANE1, Sébastien LIVI1, Jannick DUCHET-RUMEAU1
1IMP UMR CNRS 5223 - Université de Lyon, Villeurbanne, France
Designing innovative (multi)functional polymers represents a major challenge in materials science. For such a purpose, it is now known that it is necessary to work both on macromolecular architectures and also to structure matter at a nanometric scale, for example by introducing inorganic nano-objects such as nanosilica, layered silicates, etc. This lecture will describe the synthesis of novel polyhedral oligomeric silsesquioxane-supported imidazolium ionic liquid (IL-g-POSS) and their used as ionic inorganic-organic hybrid nano-objects to design nanostructured polymer networks. In fact, polyoligomeric silsesquioxanes, denoted POSS, were considered as core of imidazolium ionic liquids from end-capping reactions of non-closed T8 silicon-oxo clusters. For example, denoted heptaisobutyl-trisilanol POSS (POSSIB-triol) and heptaphenyl-trisilanol POSS (POSSPh-triol) have been covalently grafted by an ionic liquid-funtionalized silane, denoted Si-g-Im-Cl, and characterized by 29Si-NMR and mass spectrometry (MALDI-TOF). Chloride (Cl-) and bistrifluoromethanesulfonimidate (NTf2-) counter anions were considered. The thermal properties of the IL-g-POSS have been investigated by thermogravimetric analysis (TGA) highlighting a significant enhancement of the thermal stability (> 400 °C). These hybrid organic-inorganic nano-objects (5 wt %) have been incorporated into a diglycidyl ether of bisphenol A (DGEBA) epoxy prepolymer which was copolymerized the isophorone diamine (IPD) in order to synthesize nanostructured networks. An excellent dispersion of IL-g-POSS characterized by the formation of spherical or ellipsoïdal inorganic-rich nanoparticles with sizes included between 10 to 80 nm for IL-g-POSSIB and from 20 nm to 50 nm for IL-g-POSSPh were obtained. The resulting nanostructured polymer networks display an excellent thermal stability (> 400 °C) compared to the neat corresponding network, a pronounced hydrophobic character (23 mJ.m-2) and good mechanical performances, i.e. the combination of fracture toughness and stiffness enhancements. In addition, these O/I nanostructured networks demonstrate an improved fire resistance according to pyrolysis-combustion flow calorimetry (PCFC) and cone calorimetry analyses. In fact, the use of low amounts of imidazolium ionic liquid-modified polyhedral oligomeric silsesquioxanes induce a significant decrease of heat release rate, i.e. (about 55 %, as well as an enhancement of the ignition time (close to 29 %) compared to the neat epoxy-amine network.
On another hand, epoxy-amine networks derived from imidazolium ionic liquid epoxy monomers (ILMs) were also nanostructured by three types of POSS®Ph, i.e. unmodified trisilanol phenyl POSS® (POSS®Ph-triol) and two ionic liquid-modified POSS®Ph (IL-g-POSS®Ph) having chloride (Cl-) and bis-trifluoromethanesulfonimidate (NTf2-) counter anions. 5 wt% of unmodified and IL-modified POSS®Ph have been introduced into the ILMs and copolymerized with the isophorone diamine in order to design ionic nanostructured epoxy-amine networks. A (nano)phase separation occurred during the polymerization resulting in a good distribution of the POSS®Ph as nanoscale aggregates (diameters from 80 to 400 nm) into epoxy networks. As a consequence, IL-g-POSS®Ph nanodispersion into ILM/IPD networks led to a high decrease of the glass transition temperature (45 vs 71 °C) combined with an enhancement of the thermal stability (> 380 °C). Moreover, a significant increase of the hydrophobic character and high oil repellency of the surfaces could be obtained by incorporating IL.NTf2-g-POSS®Ph