Contreras M.M.,Laboratorio Of Polimeros |
Contreras M.M.,TU Ilmenau |
Mattea C.,TU Ilmenau |
Rueda J.C.,Laboratorio Of Polimeros |
And 3 more authors.
Designed Monomers and Polymers | Year: 2015
Poly(2-isopropyl-2-oxazoline) and block copolymers of 2-isopropyl-2-oxazoline (ISOXA) and ester derivative 2-oxazoline (Methyl 3-(oxazol-2-yl)propionate) (ESTER-OXA) were prepared by a cationic ring-opening polymerization. The lower critical solution temperature (LCST) of the aqueous polymer solutions was investigated. While the LCST of poly(2-isopropyl-2-oxazoline) was 44.7°C, slightly higher values were found for the block copolymers. The segment of poly(ESTER-OXA) of the block copolymers was hydrolyzed under mild conditions so that only hydrolysis of ester groups took place, avoiding hydrolysis of the amide groups. The values of LCST of the hydrolyzed block copolymers showed only weak pH sensitivity due to the relatively short segment of poly(ESTER-OXA) in comparison with the segment of poly(ISOXA) and to the fact that the poly(ISOXA) and poly(ESTER-OXA) segments are in separated blocks. In addition to turbidimetric experiments, diffusion and relaxation were measured by NMR for studying the molecular motions of the polymers in aqueous solutions in a broad temperature range covering the LCST, and to determine the variation in hydrodynamic radius of the molecules. © 2014 Taylor & Francis.
Paleo A.J.,University of Minho |
Silva J.,Case Western Reserve University |
Van Hattum F.W.J.,University of Minho |
Lanceros-Mendez S.,University of Minho |
Ares A.I.,Laboratorio Of Polimeros
Journal of Polymer Science, Part B: Polymer Physics | Year: 2013
Two different types of carbon nanofibers (CNF) were incorporated in the same polypropylene (PP) matrix by twin-screw extrusion. The electrical characterization of both CNFs/PP composites as a function of volume fraction show different electrical performance: conducting and nonconducting. The objective of this work is to study the rheological behavior of both composites with the aim of relating it to the electrical behavior. The results indicate that the rheological behaviors are different, suggesting that rheology differentiates the microstructural variations responsible for the electrical performance. Furthermore, the main rheological parameters were correlated to the electrical conductivity. The results show that G′/G″ and G′ are the most sensitive parameters when compared with the onset of electrical percolation. Finally, in spite of the intrinsic measuring differences between electrical and rheological analysis, the two calculated thresholds are very similar: ∼0.5 for the rheological and ∼0.4 for the electrical. © 2012 Wiley Periodicals, Inc.
Medeiros S.F.,Laboratorio Of Polimeros |
Santos A.M.,Laboratorio Of Polimeros |
Fessi H.,University Claude Bernard Lyon 1 |
Elaissari A.,University Claude Bernard Lyon 1
Journal of Polymer Science, Part A: Polymer Chemistry | Year: 2010
The goal of this study was to develop a new route to prepare thermally responsive polymer nanogels. Poly (N-vinylcaprolactam) nanogels were prepared via inverse miniemulsion polymerization (W/O) at 70°C using n-hexadecane as a nonpolar continuous phase, potassium persulfate as an initiator, and N,N′-methylenebisacrylamide as a crosslinker. Sorbitan monooleate (Span 80) was used as surfactant and its influence on the polymerization kinetics and on the colloidal characteristics of the nanogels were principally investigated. It was observed that the addition of a strong "lipophobe" is required to stabilize the resulting miniemulsion. The nanogels were characterized in terms of morphology, size, zeta potential, and thermoproperties using transmission electron microscopy and dynamic light scattering. It was observed that all the nanogels obtained collapsed when the lower critical solution temperature (LCST) was raised. © 2010 Wiley Periodicals, Inc.
Escalante M.,Laboratorio Of Analisis Organico |
Santos I.,Laboratorio Of Analisis Organico |
Rojas L.B.,Institute Investigaciones |
Velasquez C.L.,Laboratorio Of Polimeros
Avances en Quimica | Year: 2012
The Soxhlet extraction, using n-hexane as solvent, of the orange seed oil from waste residues obtained in street sales of fruit juices of Merida, Venezuela, was studied. Yields of 5.1% oil (w/w) and 42.7% (w/w) relative to the initial mass of the residue and dry seeds, respectively, were obtained. The oil was subjected to a transesterification process with methanol and the main components of the mixture of methyl esters achieved were quantified by gas chromatography coupled to mass spectrometry (GC-MS), which turned out to be: linoleate (31±1% ), oleate (31±1%), palmitate (30±3%) and magnesium stearate (7.1±0.5%). The mixture of methyl esters was subjected to the hydrolysis reaction in aqueous alkaline medium yielding the respective acid mixture which, after a precipitation process in HCl aqueous solution and its re-crystallization in n-hexane, generated an acid mixture with a higher content of unsaturated acids.