Cristian-Dragos Varganici

Studies on new hybrid materials prepared by both Diels–Alder and Michael addition reactions

New polyurethane chemically crosslinked networks containing silica were synthesized by both Diels–Alder polymerization and Michael addition reaction. Structural characterization of the products was evidenced by proton nuclear magnetic resonance and attenuated total reflectance in conjunction with Fourier transform infrared spectroscopy techniques. Differential scanning calorimetry was used to demonstrate the thermally remendable character of the materials obtained through Diels–Alder polymerization. The influence of increasing silica content on the glass transition temperatures was studied. It was observed that the glass transition temperatures increased with increasing silica content. Absolute heat capacities and crosslinking densities were determined for the thermoreversible materials. A comparison between materials obtained through Diels–Alder process and Michael addition method was studied. A kinetic study was conducted via an isoconversional method. Morphological studies were conducted by atomic force microscopy technique.

Highly efficient copper(II) ion sorbents obtained by calcium carbonate mineralization on functionalized cross-linked copolymers.

A new type of Cu(II) ion sorbents is presented. These are obtained by CaCO3 mineralization from supersaturated solutions on gel-like cross-linked polymeric beads as insoluble templates. A divinylbenzene-ethylacrylate-acrylonitrile cross-linked copolymer functionalized with weakly acidic, basic, or amphoteric functional groups has been used, as well as different initial inorganic concentrations and addition procedures for CaCO3 crystal growth. The morphology of the new composites was investigated by SEM and compared to that of the unmodified beads, and the polymorph content was established by X-ray diffraction. The beads, before and after CaCO3 mineralization, were tested as sorbents for Cu(II) ions. The newly formed patterns on the bead surface after Cu(II) sorption were observed by SEM, and the elemental distribution on the composites and the chemical structure of crystals after interaction with Cu(II) were investigated by EDAX elemental mapping and by FTIR-ATR spectroscopy, respectively. The sorption capacity increased significantly after CaCO3 crystals growth on the weak anionic bead surface (up to 1041.5 mg Cu(II) /g sample) compared to that of unmodified beads (491.5 mg Cu(II) /g sample).

Studies on Diels–Alder thermoresponsive networks based on ether–urethane bismaleimide functionalized poly(vinyl alcohol)

Thermoreversible networks obtained by the Diels–Alder cycloaddition reaction of poly(vinyl furfural) with urethane bismaleimides containing polyether chain were synthesized. The formation of the networks was confirmed by attenuated total reflectance in conjunction with Fourier transform infrared spectroscopy (ATR–FTIR). The materials thermal properties were investigated using differential scanning calorimetry (DSC) and a coupling of dynamic thermogravimetry with Fourier transform infrared spectroscopy and mass spectrometry (TG–FTIR–MS) for pyrolysis behaviour under nitrogen atmosphere. A thermal decomposition mechanism of the networks and poly(vinyl furfural) was discussed via evolved gas analysis. The thermoreversibility of the networks was demonstrated by the presence of the endothermic peak characteristic to the retrodienic process on the DSC heating curves and also the appearance of the exothermic peak, due to the dienic process, on the DSC cooling curve. The dynamic contact angle and free surface energy values of the networks were determined. Measures of the heterogeneity and roughness of the surfaces suggested that the surfaces of the networks’ films are more homogenous than the initial poly(vinyl furfural) surface. Dynamic water vapour sorption studies were conducted.

Supramolecular Aggregation in Organic Solvents of Discrete Copper Complexes Formed with Organosiloxane Ligands

Three complexes of copper with organosiloxane ligands of bis-azomethine type derived from 1,3-bis(3-aminopropyl)tetramethyldisiloxane and 2-hydroxybenzaldehyde (1), 5-nitro-2-hydroxybenzaldehyde (2), and 3,5-di-tert-butyl-2-hydroxybenzaldehyde (3) having well-established structures were investigated for their ability to form aggregates in organic solvents, namely dimethylformamide. The thermal behavior in solid state was investigated by thermogravimetrical analysis (TGA) and differential scanning calorimetry (DSC), the results being correlated with the structure and intermolecular interactions highlighted by crystallographic analysis. The co-existence in these structures of nonpolar 1,3-bis(propyl)tetramethyldisiloxane moiety and a polar one, consisting in metal complexed through hydroxy-azomethine groups, makes them able to self-assemble both in solid state and in solution. The surface activity of the complexes was evaluated by surface tension measurements, whereas the formation of the aggregates in solution was emphasized by UV-Vis spectroscoppy, dynamic light scattering (DLS) and small-angle X-ray scattering (SAXS) analyses. The DSC curves recorded in solution revealed the presence of large endotherms in the range 30–100°C, which prove the presence of the aggregates. The preservation of these assemblies after solvent evaporation was studied by transmission electron microscopy (TEM) and atomic force microscopy (AFM).

Physico-chemical properties investigation of softwood surface after treatment with organic anhydride

AbstractWood originating from a softwood species was subjected to chemical treatment by reaction with succinic anhydride in N, N-dimethylformamide at different concentration values. Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy analysis were used to study changes that occurred on a softwood surface. The extent of chemical treatment on softwood was evaluated by determining the weight percent gain values. Thermal properties of modified softwood and the water absorption were also evaluated. The chemical treatment with succinic anhydride influenced the thermal stability of the softwood samples with increasing anhydride concentration levels.

Multicomponent Polymer Materials: Photodegradation Mechanism

The chapter follows two pathways into polymer photodegradation. The first one consists of an introduction into the obtaining of photodegradable polymers by inserting several photolabile entities, such as o-nitrobenzyl, coumarin-4-ylmethyl, p-hydroxyphenacyl or acetal, with emphasis on the o-nitrobenzyl group. The second and main pathway of the chapter encompasses literature studies related to photochemical decomposition mechanisms occurring in different types of multicomponent polymer systems. UV radiations, oxygen, temperature and humidity represent the main driving forces in polymer irreversible photochemical deterioration, occurring through radical intermediates (hydroperoxides, chromophore carbonyl groups or conjugated double bonds) as chained mechanisms.

Thermal Degradation of Thermosetting Blends

The chapter coalesces literature studies on recent advances concerning the thermal behavior of different thermosetting blends. The introduction debates the general issue concerning polymer blends, that being the occurrence of phase separation phenomena and lists a series of possibilities to overcome these undesired aspects. The introduction section also presents the most common polymers used as crosslinked scaffolds either individual or for different multicomponent polymeric materials. The subchapters that follow are focused on recent studies on the thermal stability and degradation of thermosetting blends, effect of reinforcement and nanofillers on the thermal stability of thermosetting blends and applications and future trends of thermosetting blends, dealing with the latest issues and trying to reveal solutions.

Theoretical Aspects Regarding Polymer Photochemistry

The chapter encompasses literature studies related to the basic photochemical decomposition processes occurring in polymers. Ultraviolet (UV) radiations from light, oxygen from air, temperature and humidity are the main factors producing chemical and/or physical irreversible damages in polymers. UVA radiations (λ = 315–400 nm) possess sufficiently high energy for generating most macromolecular chain bonds cleavage leading to initiation of important chemical modifications through radical intermediates such as oxides and hydroperoxides, chromophore carbonyl groups or conjugated double bonds. The presence of oxygen leads to occurrence of photo-oxidative processes through chained mechanisms.

Life-Time Prediction of Multicomponent Polymeric Materials

Since the continuous emerging of new technologies and outdoor applications of polymers and polymer based materials, and thus a dire need in increasing their lifetime service quality, the number of methods predicting aging has also experienced growth. Most of such methods are reported on natural and artificial aging and may be based on accelerated aging predictions, different damage models and empirical formulas. The present chapter is a systematization of literature studies focused on discovering new means for accurate linking of laboratory and field exposure results, which represent the actual and future main challenges in estimating and assessing quality and service lifetime of polymeric materials.

Changes induced in the properties of dielectric silicone elastomers by the incorporation of transition metal complexes

Three new, cheap, and easily obtained complexes of triethanolamine with Cu(II), Ni(II), and Co(II) were incorporated in a high-molecular-weight polydimethylsiloxane-α,ω-diol (number-average molecular weight = 440,000 g mol−1) together with silica nanoparticles. While silica has a well-known mechanical reinforcing role, adding the metal complexes with high dielectric permittivity aims to increase values for this characteristic of the prepared silicone composites in order to be useful for electromechanical applications. A simple procedure was employed for the incorporation of fillers by mechanical mixing in bulk without a solvent. The composites were processed as films and stabilized by curing initiated with 2,4-dichlorobenzoyl peroxide at high temperature (180°C) and pressure. The cross-linking yield was estimated on the basis of swelling in chloroform, while the cross-linking density was calculated from differential scanning calorimetry traces. The filler’s effect on mechanical and dielectric properties was assessed by appropriate measurements (tensile testing and dielectric spectroscopy). Changes in dielectric behavior as a result of the repeated deformation by stretching were also highlighted. Electromechanical sensitivity and ultimate tensile toughness values were estimated on the basis of these results as primary indices on suitability of these materials in transducers. The dielectric strength of the composite films was also evaluated by electrical breakdown field measurements.