Synthesis of copolyamides based on PA 66 bearing lithium sulfonate groups and having unique thermal properties

Copolyamides of PA 66/6 lithium 5‐sulfoisophthalic acid (LiSIPA) containing up to 40 mol % of LiSIPA were prepared in a 1L‐pilot reactor operating at high pressures and high temperatures. Interestingly, the presence of lithium sulfonate moieties highly impacted the glass transition temperature of the polyamide. The T_g increased from 59 °C for PA 66 to 155 °C for a copolymer containing about 40 mol % of LiSIPA. 1,3‐Dihexylbenzenedicarboxamide and lithium p‐toluenesulfonate were synthesized as model compounds to investigate the interaction of lithium sulfonate moieties and amide functions. Infrared spectroscopy using ATR technology performed on mixture of both compounds showed that the carbonyl group of amide functions interacts with the lithium cation of lithium sulfonate moieties. Similar S? O and C? O adsorption bands were observed in copolyamides PA 66/6LiSIPA and in mixture of model compounds, which strongly suggest the formation in the copolyamides of physical cross‐linking points centered on lithium cations coordinated by carbonyl groups of amide functions. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Photoresponsive polymers and block copolymers by molecular recognition based on multiple hydrogen bonds

A new methacrylate containing a 2,6‐diacylaminopyridine (DAP) group was synthesized and polymerized via RAFT polymerization to prepare homopolymethacrylates (PDAP) and diblock copolymers combined with a poly(methyl methacrylate) block (PMMA‐b‐PDAP). These polymers can be easily complexed with azobenzene chromophores having thymine (tAZO) or carboxylic groups with a dendritic structure (dAZO), which can form either three or two hydrogen bonds with the DAP groups, respectively. The supramolecular polymers were characterized by spectroscopic techniques, optical microscopy, TGA, and DSC. The supramolecular polymers and block copolymers with dAZO exhibited mesomorphic properties meanwhile with tAZO are amorphous materials. The response of the supramolecular polymers to irradiation with linearly polarized light was also investigated founding that stable optical anisotropy can be photoinduced in all the materials although higher values of birefringence and dichroism were obtained in polymers containing the dendrimeric chromophore dAZO. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 3173–3184     

Responsive Linear‐Dendritic Block Copolymers

The combination of dendritic and linear polymeric structures in the same macromolecule opens up new possibilities for the design of block copolymers and for applications of functional polymers that have self‐assembly properties. There are three main strategies for the synthesis of linear‐dendritic block copolymers (LDBCs) and, in particular, the emergence of click chemistry has made the coupling of preformed blocks one of the most efficient ways of obtaining libraries of LDBCs. In these materials, the periphery of the dendron can be precisely functionalised to obtain functional LDBCs with self‐assembly properties of interest in different technological areas. The incorporation of stimuli‐responsive moieties gives rise to smart materials that are generally processed as self‐assemblies of amphiphilic LDBCs with a morphology that can be controlled by an external stimulus. Particular emphasis is placed on light‐responsive LDBCs. Furthermore, a brief review of the biomedical or materials science applications of LDBCs is presented.

     

The separation of the enantiomers of diquats by capillary electrophoresis using randomly sulfated cyclodextrins as chiral selectors

Diquats, derivatives of the widely used herbicide diquat, represent a new class of functional organic molecules. A combination of their special electrochemical properties and axial chirality could potentially result in their important applications in supramolecular chemistry, chiral catalysis, and chiral analysis. However, prior to their practical applications, the diquats have to be prepared in enantiomerically pure forms and the enantiomeric purity of their P- and M-isomers has to be checked. Hence, a chiral capillary electrophoresis (CE) method has been developed and applied for separation of P- and M-enantiomers of 11 new diquats. Fast and better than baseline CE separations of enantiomers of all 11 diquats within a short time 5–7 min were achieved using acidic buffer, 22 mM NaOH, 35 mM H₃PO₄, pH 2.5, as a background electrolyte, and 6 mM randomly sulfated α-, β-, and γ-cyclodextrins as chiral selectors. The most successful selector was sulfated γ-cyclodextrin, which baseline separated the enantiomers of all 11 diquats, followed by sulfated β-cyclodextrin and sulfated α-cyclodextrin, which baseline separated enantiomers of 10 and nine diquats, respectively. Using this method, a high enantiopurity degree of the isolated P- and M-enantiomers of three diquats with a defined absolute configuration was confirmed and their migration order was identified.     

Thermal characterization of nitrile butadiene rubber (NBR)/PVC blends

Summary Nitrile butadiene rubber (NBR) and NBR/PVC blends were produced using 2,2,4-trimethyl-1,2-dihydroquinoline (TMQ) or not as antioxidant. Controlled ozone degradation was performed in several samples. Thermal, compositional and morphological analysis was performed by means of differential scanning calorimetry, thermogravimetry, chemical analysis and scanning electron microscopy. Thermogravimetry analysis shows four mass loss processes related to plastizicer, complex rubber degradation and metallic oxides and other additives. In NBR (NBR/PVC blends) the onset temperature of the first degradation process varies between 227-231°C (259-262°C) and the apparent activation energy between 26 and 36 kJ mol^-1 (36-57 kJ mol^-1), the NBR/PVC samples non degraded presents the higher thermal stability.     

Neurochemical studies on catecholamines and indoleamines by high-performance liquid chromatography with electrochemical detection

Summary This communication reports the HPLC separation and quantitative ECD assay of dopamine (DA) and its metabolites DOPAC and HVA, 5-HT and its metabolite 5-HIAA and the noradrenaline metabolites MHPG and VMA, in samples of rat brain extracts and human CSF. The separation is carried out by reversed-phase with a methanolic phosphate/citrate buffer as mobile phase. Response is linear within 10pg-20 ng. Rat brain homogenates of cortex plus striatum were centrifuged and 10–20 l aliquots injected in the column. CSF samples were directly injected without any further manipulation. The method has been applied to the study of the possible neuromodulating role of T on the catecholaminergic and serotonergic transmission. For this purpose rats are injected intraperitoneally (ip) with T (150 mg/kg) and killed after 30 min. Relative to control rats, the results show that for n=12, T does not affect the basal level of DA and DOPAC whereas HVA increases a 99.3% and 5HT and 5HIAA show variations of 23% and — 4.1%, respectively. Aside from the fall of 5HIAA, it is interesting to note that the turnover rate of 5HT decreases, which might prove of functional significance.Presented at the 14th International Symposium on Chromatography London, September, 1982     

Non-isothermal approach to crystallization process of a Co-rich alloy

In this work we have investigated the crystallization of a Co-rich alloy obtained by melt-spinning. The same process was repeated by applying a magnetic field at the moment of the solidification process. Furthermore, the melt-spun amorphous ribbons were subjected to mechanical alloying in a planetary ball-milling. The milling conditions were chosen to develop a material in a like-powdered form. The samples are amorphous as determined by X-ray diffraction patterns. Non-isothermal experiments were carried out by differential scanning calorimetry. An isoconversional method is applied to perform the kinetic analysis in order to obtain the activation energy and de Jhonson–Mehl–Avrami parameter. It was found a decrease of 15–25% in the activation energy of the main crystallization process in mechanically alloyed samples.     

Off-diagonal magnetoimpedance effect in Fe80B20 amorphous ribbons

Both the axial and off-diagonal magnetoimpedance (MI) effect in Fe₈₀B₂₀ amorphous ribbons were measured trough the voltage across the sample and using a pick-up coil wound around it, respectively. Two different ribbons were studied; one in the as-quenched state and other was produced under a transverse magnetic field of 0.07 T in the ribbon plane (field quenched). In spite of the small anisotropy induced in the ribbon during this field quenching procedure, the off-diagonal MI allowed us to differentiate both samples. Asymmetric two-peak behavior of the field dependence of the off-diagonal MI was observed, which can be related to the inhomogeneous induced anisotropy in field-quenched samples.