The effect of the chemical modification of poly(propylene glycol) (PPG) end groups on the molecular dynamics under 2D confinement and the polymer/matrix interactions (including interfacial energies) was investigated by a combination of differential scanning calorimetry (DSC), broadband dielectric spectroscopy (BDS), surface tension and contact angle measurements. The replacement of −OH groups in native PPG allowed to modify the interactions with the hydroxyl groups attached to the pore walls of nanoporous aluminum oxide (AAO) membranes of various pore diameter. It was found that the observed reduction in the glass transition temperature (T g) of the core polymers correlates well with a general trend (the higher the solid–liquid interfacial tension, γSL, the lower T g,confined) reported earlier. Moreover, we demonstrated that although the interfacial solid–liquid energy seems to be almost the same for each studied herein material, a clear change in the crossover temperature (T c), related to the vitrification of the polymers adsorbed to the pore walls, is noted. Interestingly, the shift in T c with respect to the glass transition temperature of the bulk polymer scales well according to the decreasing ability in the formation of H bonds in the order PPG–OH → PPG–NH2 → PPG–OCH3 for the constant γSL. One can add that no such effect is found for the glass transition of the core polymers, where a similar shift of the T g was recorded. This finding has been discussed in the context of various sensitivity of the studied materials to the density fluctuations, equilibration phenomena occurring below T c, etc. We believe that our finding will help in a better understanding of an interplay between interfacial and core molecules and contribute significantly to the discussion on the impact of interfacial interactions on the molecular dynamics of polymers under 2D confinement.
The kinetics of polymerization of Bisphenol-A diglycidyl ether (DGEBA), a well-known epoxy resin, with two ionic amines 1-(3-aminopropyl)-3-butylimidazolium bis(trifluoromethylsulfonyl)imide ([apbim][NTf2]) and the tetrabutylammonium leucine ([N4444][Leu]) have been studied with the use of differential scanning calorimetry (DSC) and broadband dielectric spectroscopy (BDS) at various temperatures. We found many fundamental differences between the progress of this reaction with respect to the classical system (curing of epoxy resin with ordinary nonconducting hardeners). One of the most significant differences is related to the mechanism of polymerization. It is worthwhile to mention that usually the autocatalytic model is used to describe the curing of DGEBA with ordinary amines. However, herein, the kinetic curves followed a clearly exponential shape characteristic of first-order kinetics. We claim that the change in mechanism of polymerization is related to the presence of a conducting amine that acts as both the substrate and the catalyst of this specific chemical conversion. Also, it is presented that the pace of the reaction only weakly depends on temperature, which is reflected in the relatively low activation energy. On the other hand, the degree of monomer conversion stays around 45%–70% as typically reported for the polymerization of DGEBA with nonconducting hardeners. In addition, we measured the time evolution of dc conductivity as the reaction proceeded and observed that a change in this parameter correlates very well with the monomer conversion in contrast to the reaction of nonconducting systems. Finally, ionic conductivity of the resulted cured samples was investigated and found to be quite significant at the glass transition temperature with respect to other polymerized ionic liquids.
Broadband dielectric spectroscopy (BDS) and differential scanning calorimetry (DSC) have been employed to probe dynamics and charge transport of 1-butyl-3-vinylimidazolium bis(trifluoromethanesulfonyl)imide ([bvim][NTf]) confined in native uniaxial AAO pores as well as to study kinetics of radical polymerization of the examined compound as a function of the degree of confinement. Subsequently, the electronic conductivity of the produced polymers was investigated. As observed, polymerization carried out at T = 363 K proceeds faster under confinement with some saturation effect observed for the sample in pores of smaller diameter. Obtained results were discussed in the context of the very recent reports showing that the free volume of the confined material is higher with respect to the bulk one. It was also noted that conductivity of poly[bvim][NTf] is significantly higher with respect to the macromolecules obtained upon bulk polymerization. Moreover, charge transport of the confined macromolecules is even higher when compared to the bulk monomeric ionic liquid at some thermodynamic conditions. Additionally, the molecular weight, M, of the confined-synthesized polymers is significantly higher with respect to the bulk-synthesized material. Interestingly, both parameters, (i) the enhancement of σ and (ii) the increase in M, can be tuned and controlled by the application of the appropriate confinement. Consequently, those results are quite promising in the context of development of the fabrication of polymerized ionic liquids (PILs) nanomaterials with unique properties and morphologies, which can be further easily applied in the field of nanotechnology.
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