Joaquín Palacios-Alquisira

Poly (Hexahydrotriazine) Membranes Prepared by Coupling Reaction Between Diamines and Aldehydes

The preparation of membranes based on new polymers by using paraformaldehyde and five aromatic diamines was studied using N-methyl-2-pyrrolidone (NMP) as a solvent. A conventional heating activation method was used. Films were cast out from the new polymeric materials; these new polymers were characterized by spectroscopic and calorimetric methods, and their basic physicochemical properties were determined. Theoretical methods were used to estimate the FFV and predict the gas permeability of these materials.

Characterization and study of microwave activation effects on the polystyrene tacticity

ABSTRACT 13C Nuclear magnetic resonance proved to be an advantageous tool to determine the stereoregularity of polystyrene polymers. The latter was achieved through the analysis of the signal of the quaternary carbon and that of the carbon-p in the aromatic ring too. Styrene was polymerized through microwaves and conventional heating activation using two different polymerization techniques: emulsion and bulk. Microwave activation was performed in a mono-modal type device under the following experimental conditions: various initiator concentrations, an average irradiation power of 50 W, temperature of 70°C, and using a batch reactor for emulsion and bulk experiments. The results obtained in these experiments were compared with those obtained by conventional heating activation polymerization under the same initiator concentration and temperature conditions. Microwave-activated reactions resulted in shorter reaction times and higher yields. The tacticity of the polymer samples was not significantly altered, which lead to the conclusion that, in this case, the stereoregularity of polystyrene was not influenced by microwave irradiation.

Nanopigmented acrylic resin cured indistinctively by water bath or microwave energy for dentures

The highlight of this study was the synthesis of nanopigmented poly(methyl methacrylate) nanoparticles that were further processed using a water bath and/or microwave energy for dentures. The experimental acrylic resins were physicochemically characterized, and the adherence of Candida albicans and biocompatibility were assessed. A nanopigmented acrylic resin cured by a water bath or by microwave energy was obtained. The acrylic specimens possess similar properties to commercial acrylic resins, but the transverse strength and porosity were slightly improved. The acrylic resins cured with microwave energy exhibited reduced C. albicans adherence. These results demonstrate an improved noncytotoxic material for the manufacturing of denture bases in dentistry.

Kinetic modeling of vinyl acetate telomerization catalyzed by metal transition complexes under thermal and microwave heating

ABSTRACT A kinetic model for the redox-initiated radical telomerization of vinyl acetate activated by microwave irradiation is presented. Four approaches based on the “microwave” or “thermal” effects were used to study the cases under microwave irradiation. One of the models assumes microwave-induced generation of radicals from monomer. The second model considers higher reaction temperatures than those reported in the experiments. The third model assumes that microwave radiation affects specifically catalyst-involved reactions. The fourth model is a combination of the second and third ones. The kinetic model captures well the effect of initiator, catalyst and solvent contents, as well as absence or presence of microwave irradiation, on polymerization rate and molecular weight development. Limiting monomer conversions and fairly constant values of number average molecular weight and molar mass dispersity were predicted by the model, which agrees with experimental observations.

Eaton’s reagent in polybenzimidazole synthesis: The influence of temperature and microwave irradiation

The polycondensations of 3,3′-diaminobenzidine with two acids, 4,4′-oxybis(benzoic acid) and hexafluoroisopropylidene bis(benzoic acid), were conducted in Eaton’s reagent at the unusually high temperature of 180°C and under microwave irradiation at 90°C. Both protocols resulted in soluble polybenzimidazoles, OPBI and CF3PBI, of high molecular weights in very short reaction times. The synthesized polybenzimidazoles exhibited high thermostability and excellent mechanical properties. The influence of the reaction conditions on the polymer structure and molecular weights was studied. The “microwave effect” was demonstrated by comparison of the polycondensations conducted under microwave irradiation and conventional heating.

Preparation of an Adhesive in Emulsion for Maxillofacial Prosthetic

Maxillofacial prostheses is a dental medicine specialty aimed at restoring anatomical facial defects caused by cancer, trauma or congenital malformations through an artificial device, which is commonly attached to the skin with the help of an adhesive. The purpose of our research was to develop a pressure-sensitive adhesive (PSA) based on acrylic monomers, characterizing and determining its drying kinetics, that is to say the time it takes to lose 50 to 90% of its moisture. The adhesive synthesis was realized by means of emulsion polymerization; the composition of formulations was: (AA-MMA-EA) and (AA-MMA-2EHA) with different molar ratios. The formulation based on (AA-MMA-2EHA) with 50 w% of solids, presented good adhesive properties such as tack, bond strength, and short drying time. We propose this formulation as a PSA, because it offers an alternative for systemically compromised patients, by less irritation compared to organic solvent-based adhesives.

Calculation of the Molecular Parameters of Poly(Acrylic Acid) Using Intrinsic Viscosity Data

Abstract A detailed review of the available methods for calculating molecular parameters from viscosimetry measurements, is presented. A comparative study utilizing those theories for the case of Poly(Acrylic Acid) was carried out, revealing that only one of the approaches yields predictions agreeable to the experimental results.