M. Eugenia Muñoz

Facile Synthesis of Supramolecular Ionic Polymers That Combine Unique Rheological, Ionic Conductivity, and Self‐Healing Properties

A new family of supramolecular ionic polymers is synthesized by a simple method using (di-/tri-)carboxylic acids and (di-/tri-)alkyl amines. These polymers are formed by carboxylate and ammonium molecules that are weakly bonded together by a combination of ionic and hydrogen bonds, becoming solid at room temperature. The supramolecular ionic polymers show a sharp rheological transition from a viscoelastic gel to a viscous liquid between 30 and 80 °C. This sharp viscosity decrease is responsible for an unprecedented jump in ionic conductivity of four orders of magnitude in that temperature range. As a potential application, this chemistry can be used to develop polymeric materials with self-healing properties, since it combines properties from supramolecular polymers and ionomers into the same material.

New injectable and radiopaque antibiotic loaded acrylic bone cements.

The use of antibiotic loaded bone cements (ALBCs) has become a common clinical practice in the prevention and treatment of prosthesis-related infections. However, due to antibiotic resistance, there is a general interest in broadening the antibacterial spectrum of currently used drugs. The aim of this work is to formulate ALBCs for specific use in vertebroplasty and kyphoplasty, and to study the effect of the addition of ciprofloxacin alone and in combination with vancomycin on some properties of the cement. The cements were formulated using bismuth salicylate as the radiopacifier. The setting properties, residual monomer content, release of antibiotics, rheological behavior, injectability, and mechanical properties of these formulations were studied. They showed long setting times and low curing temperatures. From the release studies, antibacterial properties are assumed because the concentration of released antibiotic was higher than the minimum effective. Although the experimental cements had slightly reduced mechanical properties, the other alterations shown were negligible.

Viscoelastic measurements on main-chain thermotropics

Abstract Rheological properties, determined by torsion experiments, of three main-chain thermotropics are investigated. Stable, time-independent measurements are obtained in two of these polymers, and the corresponding dynamic viscoelastic and first normal difference results are analysed. In the nematic state both storage and loss moduli scale as G′, G″ ∝ ω 1 2 , and no shear modulus associated with an entanglement network is detected. Recoverable compliances J0e, which are determined from steady-state N1 values, are several orders of magnitude higher than those of isotropic polymers. For one of the polymers, the characteristic molecular weight between entanglements, Mc, is determined from Newtonian viscosities of isotropic solutions. Although the molecular weight of our sample is above Mc, viscoelastic measurements at temperatures corresponding to the nematic state show no vestige of the entanglement network

New supramolecular ionic networks based on citric acid and geminal dicationic ionic liquids

A new family of supramolecular ionic networks was synthesized by a straightforward method using citric acid and germinal dicationic ionic liquids. The networks were formed by the ionic boding of multi carboxylate and cationic molecules. The resulting networks are solid soft material at room temperature, which exhibited a thermoreversible transition, becoming a viscoelastic liquid at high temperatures. Thus, each supramolecular ionic network was characterized by an elastic modulus, Ge, and a network-liquid transition temperature, Tnl. The glass transition temperature, Tg, of the systems was evaluated by differential scanning calorimetry (DSC) measurements, which, however, were not able to detect the Tnl. Considering the effect of the employed dicationic ionic liquids, the three characteristic parameters of the networks, Ge, Tnl and Tg, followed the same trend, as they increased following the sequence: citrate-1,3-propanedipyridinium > citrate-1,3-propanedimethylimidazolium > citrate/1,3-propanedimethylpyrrolidinium and citrate/1,3-propanedibenzylimidazolium. The nature of the dication and its substituents determined the basic parameters of the elastic network, Ge and Tnl. The observed effect of the chemical structure on Tg was assumed to be due to a reduction of the free volume as Ge augments.

Highly Conducting Polyaniline Gels

An improved method, based on mechanical stirring and a controlled solvent evaporation process, is proposed to obtain PANI(CSA) 0.5 /m-cresol solutions, which lead to gels with conductivities in the range 3 to 150 S/cm, preserving the elasticity associated to the gel network. Such high conductivity values have only been found for brittle films cast from PANI solutions. According to our experimental results, there is no justification for an analogy between the elastic moduls and the conductivity of physical networks.

Syneresis and fibrillation of conducting polyaniline gels

The results of the analysis of the morphology of highly conducting polyaniline/m-cresol gels are reported. It is shown that the procedure used to prepare gels of conductivities ranging from 3 to 150 S/cm implies: (a) syneresis, associated with phase separation, which is provoked by a lowering of the quality level of the solvent due to absorption of humidity, (b) fibrillar morphology, due to the facility of the stiff, fully protonated, polyaniline chains to be orientated.

Physical features of blends based in a liquid crystalline polymer: the effect of the mixing devices

Abstract Rheology, viscoelastic measurements and morphological aspects of blends of a commercial liquid crystalline polymer (LCP) and a polyarylate of bisphenol A (PAr) are presented. Viscoelastic results reveal incompatibility between the components and in the case of 60 LCP/40 PAr blends the physical properties are different, depending on the mixing method. This is attributed to the relationship between rheology, morphology and properties. The influence of the composition and the draw ratio on the storage tensile modulus is also studied.