The first absolute gravity and height reference network in Sicily

The purpose of this work is to provide the methodological and instrumental framework for the establishment of a new absolute gravity and height reference network in Sicily. The aim of the network is to contribute to the new reference systems in the Italian area, useful for the scientific and technological activities related to the gravity field and to the proper definition of a modern height system in this region. The network is composed of 5 stations, evenly distributed to form a large mesh, which roughly covers the entire Sicily. Since four of the five selected stations were measured also in the 1990s, it was also possible to evaluate whether long-term gravity changes occurred at these sites (basic requirement for a reference network) and check the long-term ground deformation patterns, using data from the closest GPS/GNSS stations. The observed gravity changes over a time interval of about 30 years at the absolute stations and in the surrounding areas, confirm the long-term stability of the selected areas/sites

Reversible polymerization techniques leading to π-stacked polymers

Serendipity has often played a pivotal role in research and, in harmony with this function, it has had a fundamental responsibility in the discovery of the thermoreversible spontaneous polymerization of benzofulvene derivatives. After a decade from the discovery of poly-BF1, the present chapter narrates the history of polybenzofulvene derivatives from the discovery to the latest developments. Now that more than 50 polymers belonging to this family have been synthesized and the relevant studies have been published in the most important journals dealing with polymer science, the spontaneous polymerization of benzofulvene monomers and the special features of the corresponding polymers appear to become a well-established topic. The chapter provides an in-depth analysis of the literature on the subject, from the preparation methods to the characterization of polybenzofulvene derivatives, the study of their properties, and the evaluation of the possible applications

Combined Techniques for the Characterization of Polyfluorene Copolymers and Correlation with their Optical Properties.

New red- and green-emitting copolymers, hereafter <i>core</i>-copolymers, bearing a 4,7-bis­(thiophen-2-yl)­benzothiadiazole and a benzothiadiazole residue respectively as bridging <i>core</i> between two identical polymeric arms were synthesized by Suzuki coupling reaction of the dibromine derivative of such chromophores and essentially borolane-ended alternating copolymers [namely <b>P­(TPAF)</b>] of triphenylammine disubstituted fluorene and dialkylsubstituted fluorene. All polymer samples were characterized by ¹H NMR and in particular by MALDI–TOF MS. MALDI mass spectra allow the identification of many end groups of the initial blue-emitting macromers and therefore of the side reactions occurring during Suzuki polycondensation. The average molar masses were determined by two different SEC apparatus, one calibrated with conventional polystyrene narrow standards and the other with an absolute calibration curve built up by SEC/MALDI–TOF MS analysis of selected SEC fractions of polydisperse red and green <i>core</i>-copolymers. MALDI mass spectra of these fractions give reliable information on their composition, which combined with their integrated area calculated from the corresponding normalized SEC curves, enable the estimation, for the first time, of the percentage of macromolecules containing the dyes composing the neat <i>core</i>-copolymers. Optical characterization, performed by UV–visible absorption and photoluminescence measurements, of the same SEC fractions gives results in agreement with the different compositions determined by their MALDI mass spectra

A novel hybrid linear-hyperbranched poly(butylene adipate) copolymer as an epoxy resin modifier with toughening effect

A study was carried out on the effect of a hybrid linear-hyperbranched poly(butylene adipate) copolymer on the properties of a commercial epoxy resin. First, the synthesis of the hyperbranched systems was optimized. These systems were obtained by reacting linear oligomers with 1,1,1-tris(hydroxymethyl)propane used as branching agent and varying the reaction times from 16 to 44 h. The synthesized samples were characterized through matrix-assisted laser desorption ionization time-of-flight mass spectrometry, differential scanning calorimetry and thermogravimetric analysis. Results showed that for reaction times of 30 h a highly branched system, namely 5HB30, was obtained. This system was chosen as toughening agent for a commercial high-performance epoxy resin. A kinetics analysis of epoxy/5HB30 blends indicated that the hyperbranched system had no accelerator or catalytic effect on the crosslinking reaction in the resin. Furthermore, it was demonstrated that 5HB30 acted as an excellent toughening agent, increasing significantly impact resistance up to 90% with respect to neat epoxy resin. The toughness behaviours of epoxy-based blends were explained by investigating the fracture surface after impact tests through scanning electron microscopy before and after solvent etching. It was observed that the globular-like hyperbranch-rich domains, dispersed throughout the continuous epoxy resin, were able to absorb the impact energy without affecting thermal stability