Guilherme Brígido Rosa

Study of structure and properties of zeolites: 2Dlayered surfactant templated zeolites and EFAL species in H-ZSM-5 materials." ou "Estudo da estrutura e propriedades de zeólitos:zeólitos 2D lamelares e espécies EFAL em H-ZSM-5.

The aim of this Master thesis was to address a few of the open questions related with the structure and properties of zeolites, utilizing a plethora of techniques and previous experimental data available on the target systems. For this purpose, two main research goals were established. The first is related with the synthesis of 2D layered surfactant templated zeolites and the corresponding gemini bifunctional structure directing agents with three, four and five ammonium groups. The materials were then characterized by X-ray diffraction for structure determination and nitrogen physisorption for textural properties. The second goal involves the study of EFAL species in H-ZSM-5 zeolites. For this purpose, samples with differing degrees of dealumination were analysed by vibrational spectroscopy (infrared and INS), as well as by solid-state NMR to attempt a better understanding of the effect of various sample treatments, with a special focus on the generated EFAL species and their possible structures. This was aided by density functional theory simulations to better correlate signals and their variations to their corresponding atomic moieties.In this work, for the first time, the structural and regiochemistry preferences of 3,4-PEF have been studied using vibrational infrared spectroscopy and ab initio calculations. Additionally, the literature gap on 3,4-PEF thermal characterization was herein fulfilled. The results suggested that the 3,4-PEF EG moiety in crystalline domains, oppositely to what was previous reported for 2,5-PEF, had a predominance of the gauche/gaucheEG conformation. Moreover, the contributions of trans/transEG conformations are only detected in the amorphous domains, where intermolecular interactions play a lesser role leading to a distribution of multiple conformation patterns. Conversely, the conformation for the FDCA motif in the crystalline and amorphous domains was not attributed due to the lack of irrefutable spectroscopic features. The contribution of C-H…O interactions to the 3,4-PEF crystallization process was also studied and no significant differences were detected among the amount of C-H...O contacts in amorphous and semi-crystalline 3,4-PEF. Thermogravimetric and calorimetric analyses were performed to assess 3,4-PEF crystallization kinetics and its thermal properties. The first differential scanning calorimetry (DSC) analysis confirmed that the polymer has a glass transition temperature (Tg) and a melting temperature (Tm) of 39 °C and 155 °C, respectively. The low value obtained for Tm (comparing with 2,5-PEF) provided additional proof that in 3,4-PEF crystalline domains the major interaction contribution is not from hydrogen bonds. According to kinetic studies, the fastest crystallization rate for 3,4-PEF occurs at 110 °C, with a half crystallization time of 12 min. This is faster than the half crystallization time of 2,5-PEF found at its optimal crystallization temperature (170 °C), but still lower than PET at comparable molecular weights. 3,4-PEF presents itself as a promising polymer towards PET substitution. However, further studies are needed to clarify some structural and thermal aspects, such as the existence of polymorphic forms, the type and importance of other interactions besides hydrogen bonds in crystalline domains and the recycling process before 3,4-PEF can be considered a serious candidate in the ongoing processof total PET substitution.