Heidarzadeh, N.; Rafizadeh, M.; Taromi, F.; Puiggali, J.; del Valle, LJ.; Franco, M. Journal of polymer research Vol. 24, num. 10, p. 1-15 DOI: 10.1007/s10965-017-1318-0 Data de publicació: 2017-10 Article en revista
Random copolyesters having 1,4-butanediol units were synthesized from a transesterification process between homopolymers constituted by aliphatic dicarboxylates (i.e. succinate, adipate or sebacate) and the aromatic therephthalate derivative, as verified by NMR spectroscopy. Biodegradability of resulting copolyesters was studied via enzymatic hydrolysis using Pseudomonas cepacia lipase at pH = 7.2 and 37 °C. Kinetics of degradation showed that in all cases the degradation rate decreased after 19 days of exposure. The observed glass transition temperatures, Tg, of the random copolyesters showed a non-linear dependence on composition, a feature that was explained in terms of the internal stiffening effect of butylene terephthalate units. Copolymers with higher aliphatic (i.e. 50 and 70 mol-%) and methylene (i.e. adipate and sebacate units) contents showed double melting peaks in DSC thermograms. These copolyesters resulted in two different crystalline rich phases after melt-crystallization and subsequent cooling. The ratio between these phases logically depended on the predominant aliphatic or aromatic dicarboxylate content. The copolymers initially crystallized via the aromatic units through a heterogeneous nucleation and a spherulitic growth. The presence of aliphatic dicarboxylate units hindered the beginning of the crystallization process, but the overall growth kinetic constant was similar for all samples. The secondary nucleation constants were determined and showed higher values for samples with higher adipate and sebacate contents.
Polyalkylene dicarboxylates derived from 1,9-nonanediol and mixtures with different ratios of pimelic acid and azelaic acid were synthesized by thermal polycondensation. All samples had a high degree of crystallinity although it was found to decrease with the comonomer content. Crystallization kinetics of the two homopolymers and the copolymer with the eutectic composition was studied by calorimetric and optical microscopy techniques. Similar Avrami parameters were determined for the three samples and a spherulitic growth with heterogeneous nucleation was deduced. Spherulites showed negative birefringence and a fibrillar or ringed texture depending on the sample. Furthermore, clear differences were found in the primary nucleation density, the spherulitic growth rate and even in the secondary nucleation constant deduced from the Lauritzen-Hoffman treatment. The three studied samples had a similar arrangement of molecular chains, and consequently their WAXD patterns showed the same strong reflections related to the molecular packing. SAXS data revealed that a lamellar insertion mechanism was characteristic for non-isothermal crystallization from the melt. In addition, significant differences were found between the crystal lamellar thicknesses of the homopolymer and copolymer samples. Diffraction and spectroscopic data suggested that the lamellar crystals of the eutectic copolymer were mainly constituted by azelate units whereas the pimelate units were preferentially located in the amorphous regions including the interlamellar amorphous layer associated with the chain folds.
Scaffolds comprising different ratios of poly(ethylene glycol) (PEG) and polylactide (PLA) electrospun fibers were prepared by using a single rotary collector. Electrospinning parameters and solution conditions were optimized to obtain continuous fibers and a homogeneous distribution of both polymers in the final scaffold. Short needle-collector distances allowed good overlapping of the two incident and independent jets. The composition of the scaffold was effectively tuned by varying the flow rate of the PLA solution. PEG and PLA fibers could be well distinguished in the scaffold because of their smooth and rough texture, respectively, and diameters in the nanometer and micrometer range. Greater sizes corresponded to polylactide and clearly depended on the flow rate. Drugs such as triclosan and polyhexamethylene biguanide hydrochloride, which have different hydrophilic/hydrophobic character and molecular size, were loaded into PLA microfibers by electrospinning. The high water solubility of PEG justified its use as a sacrificial polymer. Thus, it was possible to prepare scaffolds with tuned porosity (from 40 to 80 %) by water immersion of dual samples having different PEG content. Porosity greatly affected the release rate; specifically, a practically instantaneous or a sustained release was determined for triclosan in an appropriate medium. Drug loaded scaffolds had a clear bactericidal effect that was more effective for Gram-positive bacteria. Cell proliferation studies indicate that fibroblast colonization increased by 20-25 % in PLA/PEG scaffolds with high PEG contents compared to the control, whereas this effect was not observed for epithelial cells.
Diaz, A.; Franco, M.; Casas, M.; del Valle, LJ.; Aymami, J.; Olmo, C.; Puiggali, J. Journal of polymer research Vol. 21, num. 11 DOI: 10.1007/s10965-014-0584-3 Data de publicació: 2014-10-15 Article en revista
Ultrasound micro-molding technology has been tested as a new method to get polymer/clay nanocomposites. Biodegradable polylactide (PLA) and poly (nona-methylene azelate) (PE99) have been used as polymer matrices, whereas different silicate clays have been assayed. The new technology is able to get specimens without evidences of degradation during processing. Only the use of organo-modified clays could give rise to a slight molecular weight decrease when the poly (alkylene dicarboxylate) sample was considered. Ultrasonic micro-molding has revealed effective to get directly nanocomposites with the final form required for a selected application, a homogeneous clay distribution up to a load of 6 wt-% and more interestingly exfoliated structures without being necessary the use of a compatibilizer agent between the organic polymer and the inorganic silicate clay. Transmission electron micrographs and X-ray diffraction profiles revealed exfoliated structure when N757, C20A, C25A, and N848 clays were employed.; Crystallization behavior of exfoliated PLA nanocomposites was highly peculiar since clay particles had an antinucleating effect that decreased the overall crystallization rate respect to the neat polymer. In addition, the incorporation of layers into growing spherulites increased the crystal growth rate. A typical crystallization effect was on the contrary observed for nanocomposites derived from the poly (alkylene dicarboxylate) sample.
Cordova, E.; Poater, J.; Teixeira-Dias, Bruno; Bertran, O.; Estrany, F.; del Valle, LJ.; Solà, M.; Aleman, C. Journal of polymer research Vol. 21, num. 10, p. 1-13 DOI: 10.1007/s10965-014-0565-6 Data de publicació: 2014-09-03 Article en revista
The interaction between morphine (MO), a very potent analgesic psychoactive drug, and five electroactive polymers, poly(3,4-ethylenedioxythiophene) (PEDOT), poly(3-methylthiophene) (P3MT), polypyrrole (PPy), poly(N-methylpyrrole (PNMPy) and poly[N-(2-cyanoethyl)pyrrole] (PNCPy), has been examined using theoretical calculations on model complexes and voltammetric measures considering different pHs and incubation times. Quantum mechanical calculations in model polymers predict that the strength of the binding between the different polymers and morphine increases as follows: PEDOT < PNMPy < Py < < P3MT a parts per thousand PNCPy. The most relevant characteristic of P3MT is its ability to interact with morphine exclusively through non-directional interactions. On the other hand, the variations of the electroactivity and the anodic current at the reversal potential evidence that the voltammetric response towards the presence of MO is considerably higher for P3MT and PNCPy than that for the other polymers at both acid (P3MT > PNMPy) and neutral (P3MT a parts per thousand PNCPy) pHs. Energy decomposition analyses of the interaction of MO with different model polymers indicate that the stronger affinity of MO for P3MT and PNCPy as compared to PEDOT, PNMPy, and PPy is due to more favorable orbital interactions. These more stabilizing orbital interactions are the result of the larger charge transfer from MO to P3MT and PNCPy model polymers that takes place because of the higher stability of the single occupied molecular orbital (SOMO) of these model polymers. Therefore, to design polymers with a large capacity to detect MO we suggest looking at polymers with high electron affinity.
Llorens, E.; del Valle, LJ.; Ferran, R.; Rodriguez, R.; Puiggali, J. Journal of polymer research Vol. 21, num. 2, p. 360-1-360-15 DOI: 10.1007/s10965-014-0360-4 Data de publicació: 2014-01-29 Article en revista
Electrospun mats were obtained from different mixtures of polylactide (PLA) and poly(ethylene glycol) (PEG). Processing conditions were optimized for all compositions and the resulting micro/nanofiber morphologies (i.e., diameter size and surface texture) were characterized by scanning electron microscopy (SEM). NMR and FTIR spectroscopies were employed to verify the final compositions, and thermal properties were evaluated by DSC and TGA. XPS spectroscopy revealed that PEG was mainly deposited on the surfaces of the electrospun micro/nanofibers, leading to smooth textures. Interestingly, PLA/PEG scaffold solubility in ethanol was very different to that in water, since a significant amount of PEG was effectively retained in the PLA matrix after immersion in ethanol whereas only a low level of PEG was retained in the PLA matrix after immersion in water. The hydrophilicities of the scaffolds obtained from PLA/PEG mixtures were consequently higher than that of the PLA, even after exposure to water. As PEG can be used as a sacrificial polymer due to its high solubility in water, it was possible to increase the porosity of PLA/PEG scaffolds. PLA/PEG scaffolds loaded with triclosan (TCS) had very different release profiles in hydrophilic (e. g., PBS) and hydrophobic (e. g., Srensen/ethanol 30: 70v/v) media, while differences were small between scaffolds with different PLA/PEG ratios. TCS-loaded scaffolds exhibited good antibacterial properties for all compositions and allowed the adhesion of epithelial cells (i.e., MDCK and VERO). Significant differences in cell proliferation were found between unloaded and TCS-loaded scaffolds due to the clear improvement in cell colonization observed with increasing PEG content.
del Valle, LJ.; Roa, M.; Diaz, A.; Casas, M.; Puiggali, J.; Rodriguez, R. Journal of polymer research Vol. 19, num. 2, p. 1-13 DOI: 10.1007/s10965-011-9792-2 Data de publicació: 2012-01 Article en revista
Gomes, A.L.; Casanovas Salas, Jordi; Bertran, O.; Sinezio , J.; Armelin, E.; Aleman, C. Journal of polymer research Vol. 18, num. 6, p. 1509-1517 DOI: 10.1007/s10965-010-9556-4 Data de publicació: 2011-11-04 Article en revista
The electronic structure of poly(thiophene-3-
methyl acetate) has been investigated using UV–vis absorption spectroscopy and quantum mechanical calculations. Experimental measures in chloroform solution indicate
that the π-conjugation length increases with the polymer concentration, which is reflected by the red shift of the absorbance peak of the π-π* transition. On the other hand, the energy required for the π-π* transition has been found to decrease with the volatility of the solvent for
concentrated polymer solutions, even though the influence of the solvent is very small for dilute solutions. Quantum mechanical calculations indicate that the interactions
between the π-conjugated backbone and the methyl acetate side groups are very weak. On the other hand, the lowest energy transition predicted for an infinite polymer chain
that adopts the anti-gauche and all-anti conformations is 2.8 and 1.9 eV, respectively. Finally, measurements on spincasted nanofilms reflect that the π-π* transition energy increases with the thickness, which has been attributed to
the distortion of the molecular conformation. In spite of
this, the energy gap obtained for the thinnest film (1.52 eV) is significantly smaller than that determined for dilute and
concentrated chloroform solutions (2.56 and 2.09 eV, respectively)
del Valle, LJ.; Camps, R.; Diaz, A.; Franco, M.; Rodriguez, R.; Puiggali, J. Journal of polymer research Vol. 18, num. 6, p. 1903-1917 DOI: 10.1007/s10965-011-9597-3 Data de publicació: 2011-11 Article en revista
Pfeiffer, P.; Armelin, E.; Estrany, F.; del Valle, LJ.; Yao, C.; Aleman, C. Journal of polymer research Vol. 15, num. 3, p. 225-234 DOI: 10.1007/s10965-007-9162-2 Data de publicació: 2008-06 Article en revista
Copolymers derived from mixtures of pyrrole and N-(hydroxypropyl)pyrrole have been prepared electrochemically using various concentration ratios. Copolymers were generated on stainless electrodes by chronoamperometry and cyclic voltammetry in a LiClO4 acetonitrile solution. Relevant physical (density and doping level) and electrochemical (electroactivity and electrostability) properties of the copolymers have been examined and compared with those of the two corresponding homopolymers, which were prepared using the same electrochemical procedures. Results show that the copolymer obtained using the 25:75 N-(hydroxypropyl)pyrrole:pyrrole molar ratio presents an interesting behavior. Finally, the ability of the latter copolymer to form specific interactions with plasmid DNA has been compared with that of polypyrrole.
Electrodeposition of poly(3,4-ethylenedioxythiophene) by electrochemical polymerization of 3,4-ethylenedioxythiophene has been performed on steel electrodes rather than on the typically used inert electrodes (Pt, Au, graphite carbon). The polymer was generated by cyclic voltammetry, chronopotentiometry and chronoamperometry from a 10 mM monomer solution in acetonitrile with 0.1 M LiClO4. Elemental analysis of the generated polymer indicated that the monomeric units support 0.54 positive charges balanced with CIO414- counterions. Electrochemical, electrical and structural properties of the prepared material have been characterized. The good adherence of films combined with its excellent properties indicate that poly(3,4-ethylenedioxythiophene) can be a suitable material for anticorrosion applications.