Examinando por Autor "Ezquerra, Tiberio A."

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    Inter and intra molecular dynamics in poly(trimethylene 2,5-furanoate) as revealed by infrared and Broadband Dielectric Spectroscopies
    (Elsevier, 2023-02-22) Gálvez González, Óscar; Toledano Sanz, Óscar; Hermoso,Francisco Javier; Linares, A.; Sanz Monasterio, Mikel; Rebollar, Esther; Nogales, Aurora; García Gutiérrez, Mari Cruz; Santoro, Gonzalo; Irska, Izabela; Paszkiewicz, Sandra; Szymczyk, Anna; Ezquerra, Tiberio A.
    Infrared spectroscopy (IR) and Broadband Dielectric Spectroscopy (BDS) experiments have been performed in poly(trimethylene 2,5-furanoate)(PTF) and poly(trimethylene terephthalate)(PTT) below their glass transition temperatures. The BDS experiments reveal a richer inter-molecular dynamic for PTT as characterized by a multimodal β relaxation in contrast with the monomodal one exhibited by PTF. The evolution with temperature of comparable IR absorption bands is very similar for PTF and PTT and shows small shifts in wavenumbers towards lower values, with exception of the band related to the stretching mode of the carbonyl group. In addition, a significant difference appears in the shape of the bands associated with the –Cdouble bondO stretching. While for PTT the absorption feature is comprised of a single component, that for PTF exhibits several components suggesting the presence of hydrogen bonds. This effect may be responsible for the monomodal shape of the β relaxation of PTF since a higher degree of intramolecular coupling between the furan ring and the rest of the monomer is expected. Density Functional Theory (DFT) calculations support the experimental results revealing that as temperature increases an increment of the syn conformations of the 2,5-furandicarboxylic acid (FDCA) moiety is likely to occur in the amorphous state. The energy gain from more stable anti to less stable syn isomers can be compensated by the formation of hydrogen bonds between interchain FDCA moieties in syn conformations. This effect may cause additional hindrance to the intermolecular dynamics of the dielectric β relaxation. It is conceivable that the hindrance exhibited by PTF in both intra and inter-molecular dynamics may play a role in the reduction of gas diffusion and permeability of PTF in comparison with PTT.