Though the stress, strain, and temperature dependence for an ideal rubber is fairly well establis... more Though the stress, strain, and temperature dependence for an ideal rubber is fairly well established, the relation between network structural features like crosslinks, dangling ends, and entanglements and mechanical response is uncertain. The modulus-structure relations recently derived by Miller and Macosko for several types of networks are tested here with a model system: the hydrosilation crosslinking of vinyl-terminated polydimethylsiloxane chains with a tetra-functional silane. Results of shear modulus as a function of extent of reaction and of stoichiometric imbalance are in good agreement with the theory.
For the first time, order–order and order–disorder transitions were detected and characterized in... more For the first time, order–order and order–disorder transitions were detected and characterized in a model diblock copolymer of poly(butadiene-1,3) and poly(dimethylsiloxane) (PB-b-PDMS). This model PB-b-PDMS copolymer was synthesized by the sequential anionic polymerization (high vacuum techniques) of butadiene 1,3 (B) and hexamethylciclotrisiloxane (D3), and subsequently characterized by nuclear magnetic resonance (1H and 13C NMR), size exclusion chromatography (SEC), Fourier Transform
Spectroscopic features in the Raman spectra of semicrystalline polyolefins that characterize diff... more Spectroscopic features in the Raman spectra of semicrystalline polyolefins that characterize different phase morphologies are reported. With growing incorporation of different 1-olefins, changes in the spectra due to different short chain branches are identified for polyethylene and polypropylene, both isotactic and syndiotactic. Bands were assigned to crystalline, semicrystalline and amorphous contents, and quantification was approached with the use of internal reference bands. The degree of crystallinity and the conformational order of the copolymers decrease with the increase in short chain branches content, and the behavior of larger short chains is different depending on the type of polymer analyzed. A semi ordered interphase was found, assigned and followed in all cases, as well as the evolution of amorphous phase with comonomer incorporation.
Block copolymers constitute a fascinating group of polymeric materials belonging to the "sof... more Block copolymers constitute a fascinating group of polymeric materials belonging to the "soft matter" family. These materials are formed by blocks of polymeric chains from different monomers. In most cases, these blocks are thermodynamically incompatible, but the covalent bonds between them impose specific arrangements, generating particular morphologies both in bulk and in solution. In this book, the authors present current research in the study of the phase morphology, material applications and future challenges of block copolymers. Topics discussed include the different experimental skills developed to synthesize model block copolymers; the macromolecular design of stereo block polylactides showing high performance; ion-containing block copolymers and their applications; self-assembled block copolymers for the preparation of advanced materials; the electrical properties of polythylene-b-polyethylene oxide diblock copolymers; and triblock copolymers as tougheners for PMMA matrices.Fil: Ninago, Mario Daniel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Planta Piloto de Ingeniería Química. Universidad Nacional del Sur. Planta Piloto de Ingeniería Química; ArgentinaFil: Satti, Angel Jose. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto de Química del Sur. Universidad Nacional del Sur. Departamento de Química. Instituto de Química del Sur; ArgentinaFil: Gomez, Leopoldo Raimundo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto de Física del Sur. Universidad Nacional del Sur. Departamento de Física. Instituto de Física del Sur; ArgentinaFil: Vega, Daniel Alberto. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto de Física del Sur. Universidad Nacional del Sur. Departamento de Física. Instituto de Física del Sur; ArgentinaFil: Ciolino, Andrés Eduardo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Planta Piloto de Ingeniería Química. Universidad Nacional del Sur. Planta Piloto de Ingeniería Química; ArgentinaFil: Villar, Marcelo Armando. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Planta Piloto de Ingeniería Química. Universidad Nacional del Sur. Planta Piloto de Ingeniería Química; ArgentinaFil: Valles, Enrique Marcelo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Planta Piloto de Ingeniería Química. Universidad Nacional del Sur. Planta Piloto de Ingeniería Química; Argentin
Publisher Summary This chapter provides an overview of viscoelastic properties of model silicone ... more Publisher Summary This chapter provides an overview of viscoelastic properties of model silicone networks with pendant chains. Model silicone networks, i.e., those prepared by end-linking of functionally terminated polymer chains, are extensively utilized to explain the influence of molecular structure on mechanical properties. An important number of studies are focused on the contribution of elastically active chains and trapped entanglements to equilibrium properties. When a rubber network is stretched only those chain sections extending between crosslinking points are permanently oriented by the external stress and contribute to the elastic equilibrium modulus. Dangling chains are temporarily oriented by a deformation, but they can relax, reptating from the free ends towards their permanent junction with the network. At infinite times these chains do not contribute to the elastic force, but they do have a strong effect on time-dependent properties. Model polymer networks are materials prepared in a way that provides independent information on their structure. Synthetic procedures that link long chains of a given linear pre-polymer by their ends are quite successful in obtaining these kinds of materials.
The widespread uses of ultra-high molecular weight polyethylene, UHMWPE, lead to the urgent devel... more The widespread uses of ultra-high molecular weight polyethylene, UHMWPE, lead to the urgent development of approaches aiming to improve its performance. This is essential to fulfill its continuous market demands with tailored mechanical and/or thermal properties. Among these methods, the melt blending of UHMWPE with other polymers, different mineral particles, or addition of reinforcements [1-4] have proved to be an interesting strategy to attain these goals. Between polymers, high density polyethylene, HDPE, is a low price commodity, with good flow properties and feasible transformation by traditional processes, like extrusion, injection, blow molding, and rotational molding. Consequently, blends of UHMWPE and HDPE seem to be very interesting since the outstanding properties of UHMWPE and the good processability of HDPE under conventional techniques could be combined. Nevertheless, homogeneous HDPE/UHMWPE blends are rather difficult 344
DOAJ (DOAJ: Directory of Open Access Journals), 2016
Se estudió la síntesis de copolímeros bloque de poli (estireno) y poli (metil metacrilato) (PS-b-... more Se estudió la síntesis de copolímeros bloque de poli (estireno) y poli (metil metacrilato) (PS-b-PMMA) empleando polimerización radicalaria por transferencia atómica (ATRP). Se realizaron distintos experimentos variando las relaciones molares de monómero, ligando e iniciador para determinar su influencia en la síntesis de copolímeros PS-b-PMMA con masas molares determinadas y estructura homogénea. Los polímeros sintetizados se caracterizaron químicamente por espectroscopia infrarroja con Transformada de Fourier (FTIR) y cromatografía por exclusión de tamaños (SEC), empleando un detector de índice de refracción. Se obtuvieron los copolímeros bloque propuestos, con un buen control de su estructura macromolecular (Mw/Mn < 1,90).
The synthesis of bidirectional anionic initiators by the reaction between metallic lithium (Li) a... more The synthesis of bidirectional anionic initiators by the reaction between metallic lithium (Li) and naphthalene (Naph), under mild conditions, in non-polar (benzene) or low-polarity media (benzene/THF mixtures) is reported. The efficiency of these initiators to provide macromolecules with well-defined structures was demonstrated. Model linear homopolymers from styrene (S) or hexamethyl(ciclotrisiloxane) (D3) monomers were synthesized using classical anionic polymerization (high-vacuum techniques). The model polymers obtained were analyzed using the conventional analytical techniques, and showed narrow molar mass distributions, a broad range of molar masses (from 3000 to 1,000,000 g/mol) and polydispersity indexes (Mw/Mn) lower than 1.1. High molar mass polymers were obtained using pure benzene as solvent, whereas lower molar masses were obtained in benzene/THF mixtures in which the concentration of THF was lower than 10 % v/v. The ratio [Li]/[Naph] and the nature of the reaction medium are the experimental parameters to be controlled to obtain the desired lithium naphthalenides.
The successive self nucleation and annealing (SSA) methodology has been shown to be successful to... more The successive self nucleation and annealing (SSA) methodology has been shown to be successful to characterize the lamellae structure of many polyolefins. The differences in molecular structure of metallocenic a-olefin copolymers with varied comonomer type and content were characterized by this technique with a conventional DSC. This thermo-structural characterization process was also applied to analyze the changes induced on a 1-octadecene-ethylene copolymer modified with different postreactor methods: several doses of gamma-radiation, peroxide modification and oxidative degradation. These modifications induced crosslinking and branching on the original copolymer affecting its molecular weight and the crystalline structure. The SSA technique revealed detailed changes in the lamellae formation of the materials obtained as a consequence of the different methods of modification employed in this work. Mainly, crosslinking and branching sites restrained the mobility and length of CH 2 sequences to form lamellae, while degradation led to preferential chain scission at branched carbons making easier the formation of higher melting temperature lamellae.
Nowadays, the understanding of the interaction of ionizing radiations with polymeric materials is... more Nowadays, the understanding of the interaction of ionizing radiations with polymeric materials is becoming increasingly important. It is well known that many parameters regarding the synthesis of the polymers noticeably affect the irradiation process. In this work, an analysis of the effect of the type and the position of unsaturations in the molecular structure of crosslinkable polymers is performed. For such purpose, two solid semycristalline metallocenic ethylene 1-olefin copolymers (mEOC) which contain a low concentration of unsaturations from the synthesis, and their hydrogenated samples, were irradiated along with liquid poly(dimethylsiloxane) (PDMS) homo and copolymers containing different location and concentration of vinyl groups, which were structurally tailored through anionic synthesis. The source of irradiation was 60 Co, under vacuum at room temperature, in all the cases. The results indicated that terminal vinyls drastically accelerate the crosslinking to lower doses, even at much lower concentrations than other type and location of unsaturations for both, mEOC and PDMS, type of polymers.
The polypropylene produced in most industrial polymerization processes is a resin which has excel... more The polypropylene produced in most industrial polymerization processes is a resin which has excellent mechanical properties but broad molecular weight distribution and high molecular weight tails w...
A good knowledge of the molecular structure of polymer networks allows to relate rheological prop... more A good knowledge of the molecular structure of polymer networks allows to relate rheological properties with different molecular parameters. In this work we analyze the influence of low concentrations of pendant chains on the viscoelastic properties of polymer networks. Model networks, with a well defined structure, were synthesized by reacting a commercial a,u-divinyl poly(dimethylsiloxane) (B 2) with a trifunctional cross-linker bearing silane groups (A 3) and known amounts of an anionic u-vinyl poly(dimethylsiloxane) (B 1). The structure of the networks was predicted with a molecular model based on a mean field approach (recursive model) taking into account the initial composition of the reactants. Rheological characterization was carried out in a rotational rheometer by dynamic and stress relaxation test. Viscoelastic properties of the networks depend on both concentration and molecular weight of pendant chains. Relaxation modulus was adjusted by the empirical Chasset-Thirion equation. It was found that it provides a very good fit to the behavior of these networks prepared by end-linking. The fitting parameter m in the Chasset-Thirion equation shows a strong dependence with the molecular mass of pendant chains, but it is rhougly independent of concentration. The results agree remarkably well with the predictions of a theoretical model previously reported by our group.
SE HA SUGERIDO QUE UN DEFECTO EN LOS SISTEMAS DEFENSIVOS LOCALES O SISTEMICOS PODRIA PREDISPONER ... more SE HA SUGERIDO QUE UN DEFECTO EN LOS SISTEMAS DEFENSIVOS LOCALES O SISTEMICOS PODRIA PREDISPONER A INFECCIONES RESPIRATORIAS EN PACIENTES CON ENFERMEDADES OBSTRUCTIVAS DE LAS VIAS AEREAS. ES CONOCIDO QUE ALGUNOS TIPOS DE BRONQUIECTASIAS, TIENEN SU ORIGEN EN DEFECTOS INMUNOLOGICOS PRIMARIOS QUE AFECTAN FUNDAMENTALMENTE A LA INMUNIDAD HUMORAL. LA PREVALENCIA DE ENFERMEDADES ATOPICAS EN PACIENTES CON DEFICIT PRIMARIO DE INMUNOGLOBULINA A ES MAYOR QUE EN LA POBLACION NORMAL. A PESAR DE SER MAS FRECUENTES LOS DEFICITS DE INMUNIDAD HUMORAL, EXISTE TAMBIEN LA POSIBILIDAD DE QUE EXISTA UNA PROPORCION DEFICIENTE DE CELULAS EFECTORAS DE LA INMUNIDAD. LOS OBJETIVOS DE ESTE TRABAJO SON: 1) COMPARAR ALGUNOS PARAMETROS DE LA INMUNIDAD HUMORAL Y CELULAR EN PACIENTES DIAGNOSTICADOS DE ENFERMEDAD PULMONAR OBSTRUCTIVA CRONICA, ASMA Y BRONQUIECTASIAS, ASI COMO EN UN GRUPO DE PERSONAS SANAS. 2) DETERMINAR LA PREVALENCIA DE LOS DEFICITS PRIMARIOS DE INMUNOGLOBULINAS EN LOS MISMOS ENFERMOS. 3) RELACIONAR LA SITUACION INMUNITARIA DE ESTOS ENFERMOS CON LA EVOLUCION CLINICO FUNCIONAL. SE CONCLUYE QUE: 1. NO EXISTEN DIFERENCIA ESTADISTICAMENTE SIGNIFICATIVAS EN LOS NIVELES DE INMUNOGLOBULINAS, SUBPOBLACIONES LINFOCITARIAS Y FRACCIONES C3 Y C4 DEL COMPLEMENTO ENTRE LOS DIFERENTES GRUPOS DE ENFERMOS. 2. LAS INMUNODEFICIPRIMARIAS CONSTITUYEN UN 20% DE CASOS DE BRONQUIECTASIAS DE CAUSA NO ACLARADA, UN 8% DE LOS CASOS DE ASMA Y UN 1.98 DE LOS CASOS DE EPOC. 3. LOS ESTUDIOS INMUNOLOGICOS DEBEN DE ENTRAR A FORMAR PARTE EN EL PROTOCOLO DE ESTUDIO DE LOS PACIENTES CON BRONQUIECTASIAS DE CAUSA NO ACLARADA, ESPECIALMENTE EN JOVENES, NO FUMADORES Y CON ANTECEDENTES DE PROCESOS INFECCIOSOS DE VIAS ALTAS O BAJAS.
A novel liquid-crystalline polyurethane (LCPU) was synthesized by the condensation of 2,4-toluene... more A novel liquid-crystalline polyurethane (LCPU) was synthesized by the condensation of 2,4-toluenediisocyanate and 4,4'-bis(6-hydroxyhexoxy)biphenyl. Solution polymerization in dimethylformamide produced intrinsic viscosities in the range 0.30-0.57 dL/g. Differential scanning calorimetry shows a crystalline melting transition that is highly dependent on molecular weight and thermal history and a clearing transition that is virtually independent of both. Parallel-plate rheometry results are consistent with the presence of a liquid-crystalline phase, coexisting with a small amount of three-dimensional crystallinity, between 152 and 166 °C. Dynamic mechanical measurements reveal an unusually high elastic modulus of 180 MPa in the plateau region above Tg, compared with 6 MPa for an amorphous polyurethane with a chemical structure based on 1,4-butanediol.
Branched polypropylenes (PPb) with markedly improved melt strength were produced without signific... more Branched polypropylenes (PPb) with markedly improved melt strength were produced without significantly affecting the processability of the original PP. A two-step process of functionalization with MA and crosslinking with m-XDA was used, both by batch mixing and by extrusion. Branching degrees of~0.06 LCB/1000 monomer units or smaller were obtained. All PPbs display clear and significant strain hardening, being the PPb obtained by extrusion the one that shows the largest melt strength. This polymer has a zero-shear-rate viscosity slightly smaller than that of PP while its strain-hardening index is about 10 times higher. Moreover, the nonlinear behavior of PP at elongation begins at a time similar to its terminal relaxation time or larger, while the ratio of these times reduces significantly with branching. PP/PPb blends were prepared to extend the range of obtainable melt strength in PP. They display rheological behavior between those of the mixed polymers with slight positive deviation.
Trapped entanglements, cross-linker functionality, and elastically effective chains are the sourc... more Trapped entanglements, cross-linker functionality, and elastically effective chains are the sources of elasticity of polymer networks and gels. However, despite more than 80 years of theoretical and experimental research in this field, still little is known about their relative contribution to network elasticity. In this work, we use double quantum nuclear magnetic resonance (DQ NMR) experiments to characterize the elasticity of model polymer networks prepared with cross-linkers of mixed functionality and control of structural defects. An order parameter that condensates the elastic response within the theoretical framework of the entangled phantom theory for rubber elasticity was identified. Standard lore dictates that low molecular weight precursors for the elastically active chains leads to a negligible contribution of trapped entanglements. Here we show that the contribution of trapped entanglements may equal the contribution coming from elastically active material and that it is independent of network topology.
A reaction between a linear polypropylene functionalized with maleic anhydride (PPg) and epoxy re... more A reaction between a linear polypropylene functionalized with maleic anhydride (PPg) and epoxy resin (bisphenol A diglycidyl ether) was carried out on the molten state to generate long-chain branches (LCB) in the molecular structure of the PPg. Concentrations of epoxy resin (ER) of up to 3.15 wt% were employed to obtain different levels of branching. FTIR spectroscopy analysis indicates that during the reaction, anhydride groups in PPg are consumed and new ester groups are formed. The presence of branches was verified using multiple-detection size-exclusion chromatography and rheology. The degree of long-chain branching induced in PPg augments with increasing concentration of ER. Furthermore, the materials modified with higher content of ER display gel-like behavior. The long-chain branched polymers also display thermo-rheological complexity. Thermal characterization studies show that LCBs have a nucleating effect during crystallization and cause the augment of the crystallization activation energy of PPg.
International journal of pharmaceutics, Jan 25, 2016
The aim of this work was to design and characterize cross-linked hyaluronic acid (HA)-itaconic ac... more The aim of this work was to design and characterize cross-linked hyaluronic acid (HA)-itaconic acid (IT) films loaded with dexamethasone sodium phosphate salt (DEX) for topical therapy of inflammatory ocular surface diseases. Films were chemically cross-linked with polyethylene glycol diglycidyl ether (PEGDE), then physical and mechanical characterization by stress-strain, X-ray diffraction, X-ray fluorescence spectrometry and swelling assays was conducted. A sequential in vitro therapeutic efficacy model was designed to assess changes in interleukin (IL)-6 production in an inflamed human corneal epithelial (HCE) cell line after film exposure. Changes in cell proliferation after film exposure were assessed using the alamarBlue(®) proliferation assay. Experimental findings showed desirable mechanical properties and in vitro efficacy to reduce cell inflammation. A moderately decreased proliferation rate was induced in HCE cells by DEX-loaded films, compared to commercial DEX eye drops...
The hydrogenation of benzene on a nickel catalyst has been studied by means of a pulse micmrataly... more The hydrogenation of benzene on a nickel catalyst has been studied by means of a pulse micmratalyt~ic reactor in the lOO-150°C temperature range. It is shown that, the treatjment of experiment,al dat)a using equations derived for power-law and Langmuir-Iiinshelwond rate models allows the determination of similar kinetic paramePers as obtained from steady-state flow react,ors.
Though the stress, strain, and temperature dependence for an ideal rubber is fairly well establis... more Though the stress, strain, and temperature dependence for an ideal rubber is fairly well established, the relation between network structural features like crosslinks, dangling ends, and entanglements and mechanical response is uncertain. The modulus-structure relations recently derived by Miller and Macosko for several types of networks are tested here with a model system: the hydrosilation crosslinking of vinyl-terminated polydimethylsiloxane chains with a tetra-functional silane. Results of shear modulus as a function of extent of reaction and of stoichiometric imbalance are in good agreement with the theory.
For the first time, order–order and order–disorder transitions were detected and characterized in... more For the first time, order–order and order–disorder transitions were detected and characterized in a model diblock copolymer of poly(butadiene-1,3) and poly(dimethylsiloxane) (PB-b-PDMS). This model PB-b-PDMS copolymer was synthesized by the sequential anionic polymerization (high vacuum techniques) of butadiene 1,3 (B) and hexamethylciclotrisiloxane (D3), and subsequently characterized by nuclear magnetic resonance (1H and 13C NMR), size exclusion chromatography (SEC), Fourier Transform
Spectroscopic features in the Raman spectra of semicrystalline polyolefins that characterize diff... more Spectroscopic features in the Raman spectra of semicrystalline polyolefins that characterize different phase morphologies are reported. With growing incorporation of different 1-olefins, changes in the spectra due to different short chain branches are identified for polyethylene and polypropylene, both isotactic and syndiotactic. Bands were assigned to crystalline, semicrystalline and amorphous contents, and quantification was approached with the use of internal reference bands. The degree of crystallinity and the conformational order of the copolymers decrease with the increase in short chain branches content, and the behavior of larger short chains is different depending on the type of polymer analyzed. A semi ordered interphase was found, assigned and followed in all cases, as well as the evolution of amorphous phase with comonomer incorporation.
Block copolymers constitute a fascinating group of polymeric materials belonging to the "sof... more Block copolymers constitute a fascinating group of polymeric materials belonging to the "soft matter" family. These materials are formed by blocks of polymeric chains from different monomers. In most cases, these blocks are thermodynamically incompatible, but the covalent bonds between them impose specific arrangements, generating particular morphologies both in bulk and in solution. In this book, the authors present current research in the study of the phase morphology, material applications and future challenges of block copolymers. Topics discussed include the different experimental skills developed to synthesize model block copolymers; the macromolecular design of stereo block polylactides showing high performance; ion-containing block copolymers and their applications; self-assembled block copolymers for the preparation of advanced materials; the electrical properties of polythylene-b-polyethylene oxide diblock copolymers; and triblock copolymers as tougheners for PMMA matrices.Fil: Ninago, Mario Daniel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Planta Piloto de Ingeniería Química. Universidad Nacional del Sur. Planta Piloto de Ingeniería Química; ArgentinaFil: Satti, Angel Jose. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto de Química del Sur. Universidad Nacional del Sur. Departamento de Química. Instituto de Química del Sur; ArgentinaFil: Gomez, Leopoldo Raimundo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto de Física del Sur. Universidad Nacional del Sur. Departamento de Física. Instituto de Física del Sur; ArgentinaFil: Vega, Daniel Alberto. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto de Física del Sur. Universidad Nacional del Sur. Departamento de Física. Instituto de Física del Sur; ArgentinaFil: Ciolino, Andrés Eduardo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Planta Piloto de Ingeniería Química. Universidad Nacional del Sur. Planta Piloto de Ingeniería Química; ArgentinaFil: Villar, Marcelo Armando. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Planta Piloto de Ingeniería Química. Universidad Nacional del Sur. Planta Piloto de Ingeniería Química; ArgentinaFil: Valles, Enrique Marcelo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Planta Piloto de Ingeniería Química. Universidad Nacional del Sur. Planta Piloto de Ingeniería Química; Argentin
Publisher Summary This chapter provides an overview of viscoelastic properties of model silicone ... more Publisher Summary This chapter provides an overview of viscoelastic properties of model silicone networks with pendant chains. Model silicone networks, i.e., those prepared by end-linking of functionally terminated polymer chains, are extensively utilized to explain the influence of molecular structure on mechanical properties. An important number of studies are focused on the contribution of elastically active chains and trapped entanglements to equilibrium properties. When a rubber network is stretched only those chain sections extending between crosslinking points are permanently oriented by the external stress and contribute to the elastic equilibrium modulus. Dangling chains are temporarily oriented by a deformation, but they can relax, reptating from the free ends towards their permanent junction with the network. At infinite times these chains do not contribute to the elastic force, but they do have a strong effect on time-dependent properties. Model polymer networks are materials prepared in a way that provides independent information on their structure. Synthetic procedures that link long chains of a given linear pre-polymer by their ends are quite successful in obtaining these kinds of materials.
The widespread uses of ultra-high molecular weight polyethylene, UHMWPE, lead to the urgent devel... more The widespread uses of ultra-high molecular weight polyethylene, UHMWPE, lead to the urgent development of approaches aiming to improve its performance. This is essential to fulfill its continuous market demands with tailored mechanical and/or thermal properties. Among these methods, the melt blending of UHMWPE with other polymers, different mineral particles, or addition of reinforcements [1-4] have proved to be an interesting strategy to attain these goals. Between polymers, high density polyethylene, HDPE, is a low price commodity, with good flow properties and feasible transformation by traditional processes, like extrusion, injection, blow molding, and rotational molding. Consequently, blends of UHMWPE and HDPE seem to be very interesting since the outstanding properties of UHMWPE and the good processability of HDPE under conventional techniques could be combined. Nevertheless, homogeneous HDPE/UHMWPE blends are rather difficult 344
DOAJ (DOAJ: Directory of Open Access Journals), 2016
Se estudió la síntesis de copolímeros bloque de poli (estireno) y poli (metil metacrilato) (PS-b-... more Se estudió la síntesis de copolímeros bloque de poli (estireno) y poli (metil metacrilato) (PS-b-PMMA) empleando polimerización radicalaria por transferencia atómica (ATRP). Se realizaron distintos experimentos variando las relaciones molares de monómero, ligando e iniciador para determinar su influencia en la síntesis de copolímeros PS-b-PMMA con masas molares determinadas y estructura homogénea. Los polímeros sintetizados se caracterizaron químicamente por espectroscopia infrarroja con Transformada de Fourier (FTIR) y cromatografía por exclusión de tamaños (SEC), empleando un detector de índice de refracción. Se obtuvieron los copolímeros bloque propuestos, con un buen control de su estructura macromolecular (Mw/Mn < 1,90).
The synthesis of bidirectional anionic initiators by the reaction between metallic lithium (Li) a... more The synthesis of bidirectional anionic initiators by the reaction between metallic lithium (Li) and naphthalene (Naph), under mild conditions, in non-polar (benzene) or low-polarity media (benzene/THF mixtures) is reported. The efficiency of these initiators to provide macromolecules with well-defined structures was demonstrated. Model linear homopolymers from styrene (S) or hexamethyl(ciclotrisiloxane) (D3) monomers were synthesized using classical anionic polymerization (high-vacuum techniques). The model polymers obtained were analyzed using the conventional analytical techniques, and showed narrow molar mass distributions, a broad range of molar masses (from 3000 to 1,000,000 g/mol) and polydispersity indexes (Mw/Mn) lower than 1.1. High molar mass polymers were obtained using pure benzene as solvent, whereas lower molar masses were obtained in benzene/THF mixtures in which the concentration of THF was lower than 10 % v/v. The ratio [Li]/[Naph] and the nature of the reaction medium are the experimental parameters to be controlled to obtain the desired lithium naphthalenides.
The successive self nucleation and annealing (SSA) methodology has been shown to be successful to... more The successive self nucleation and annealing (SSA) methodology has been shown to be successful to characterize the lamellae structure of many polyolefins. The differences in molecular structure of metallocenic a-olefin copolymers with varied comonomer type and content were characterized by this technique with a conventional DSC. This thermo-structural characterization process was also applied to analyze the changes induced on a 1-octadecene-ethylene copolymer modified with different postreactor methods: several doses of gamma-radiation, peroxide modification and oxidative degradation. These modifications induced crosslinking and branching on the original copolymer affecting its molecular weight and the crystalline structure. The SSA technique revealed detailed changes in the lamellae formation of the materials obtained as a consequence of the different methods of modification employed in this work. Mainly, crosslinking and branching sites restrained the mobility and length of CH 2 sequences to form lamellae, while degradation led to preferential chain scission at branched carbons making easier the formation of higher melting temperature lamellae.
Nowadays, the understanding of the interaction of ionizing radiations with polymeric materials is... more Nowadays, the understanding of the interaction of ionizing radiations with polymeric materials is becoming increasingly important. It is well known that many parameters regarding the synthesis of the polymers noticeably affect the irradiation process. In this work, an analysis of the effect of the type and the position of unsaturations in the molecular structure of crosslinkable polymers is performed. For such purpose, two solid semycristalline metallocenic ethylene 1-olefin copolymers (mEOC) which contain a low concentration of unsaturations from the synthesis, and their hydrogenated samples, were irradiated along with liquid poly(dimethylsiloxane) (PDMS) homo and copolymers containing different location and concentration of vinyl groups, which were structurally tailored through anionic synthesis. The source of irradiation was 60 Co, under vacuum at room temperature, in all the cases. The results indicated that terminal vinyls drastically accelerate the crosslinking to lower doses, even at much lower concentrations than other type and location of unsaturations for both, mEOC and PDMS, type of polymers.
The polypropylene produced in most industrial polymerization processes is a resin which has excel... more The polypropylene produced in most industrial polymerization processes is a resin which has excellent mechanical properties but broad molecular weight distribution and high molecular weight tails w...
A good knowledge of the molecular structure of polymer networks allows to relate rheological prop... more A good knowledge of the molecular structure of polymer networks allows to relate rheological properties with different molecular parameters. In this work we analyze the influence of low concentrations of pendant chains on the viscoelastic properties of polymer networks. Model networks, with a well defined structure, were synthesized by reacting a commercial a,u-divinyl poly(dimethylsiloxane) (B 2) with a trifunctional cross-linker bearing silane groups (A 3) and known amounts of an anionic u-vinyl poly(dimethylsiloxane) (B 1). The structure of the networks was predicted with a molecular model based on a mean field approach (recursive model) taking into account the initial composition of the reactants. Rheological characterization was carried out in a rotational rheometer by dynamic and stress relaxation test. Viscoelastic properties of the networks depend on both concentration and molecular weight of pendant chains. Relaxation modulus was adjusted by the empirical Chasset-Thirion equation. It was found that it provides a very good fit to the behavior of these networks prepared by end-linking. The fitting parameter m in the Chasset-Thirion equation shows a strong dependence with the molecular mass of pendant chains, but it is rhougly independent of concentration. The results agree remarkably well with the predictions of a theoretical model previously reported by our group.
SE HA SUGERIDO QUE UN DEFECTO EN LOS SISTEMAS DEFENSIVOS LOCALES O SISTEMICOS PODRIA PREDISPONER ... more SE HA SUGERIDO QUE UN DEFECTO EN LOS SISTEMAS DEFENSIVOS LOCALES O SISTEMICOS PODRIA PREDISPONER A INFECCIONES RESPIRATORIAS EN PACIENTES CON ENFERMEDADES OBSTRUCTIVAS DE LAS VIAS AEREAS. ES CONOCIDO QUE ALGUNOS TIPOS DE BRONQUIECTASIAS, TIENEN SU ORIGEN EN DEFECTOS INMUNOLOGICOS PRIMARIOS QUE AFECTAN FUNDAMENTALMENTE A LA INMUNIDAD HUMORAL. LA PREVALENCIA DE ENFERMEDADES ATOPICAS EN PACIENTES CON DEFICIT PRIMARIO DE INMUNOGLOBULINA A ES MAYOR QUE EN LA POBLACION NORMAL. A PESAR DE SER MAS FRECUENTES LOS DEFICITS DE INMUNIDAD HUMORAL, EXISTE TAMBIEN LA POSIBILIDAD DE QUE EXISTA UNA PROPORCION DEFICIENTE DE CELULAS EFECTORAS DE LA INMUNIDAD. LOS OBJETIVOS DE ESTE TRABAJO SON: 1) COMPARAR ALGUNOS PARAMETROS DE LA INMUNIDAD HUMORAL Y CELULAR EN PACIENTES DIAGNOSTICADOS DE ENFERMEDAD PULMONAR OBSTRUCTIVA CRONICA, ASMA Y BRONQUIECTASIAS, ASI COMO EN UN GRUPO DE PERSONAS SANAS. 2) DETERMINAR LA PREVALENCIA DE LOS DEFICITS PRIMARIOS DE INMUNOGLOBULINAS EN LOS MISMOS ENFERMOS. 3) RELACIONAR LA SITUACION INMUNITARIA DE ESTOS ENFERMOS CON LA EVOLUCION CLINICO FUNCIONAL. SE CONCLUYE QUE: 1. NO EXISTEN DIFERENCIA ESTADISTICAMENTE SIGNIFICATIVAS EN LOS NIVELES DE INMUNOGLOBULINAS, SUBPOBLACIONES LINFOCITARIAS Y FRACCIONES C3 Y C4 DEL COMPLEMENTO ENTRE LOS DIFERENTES GRUPOS DE ENFERMOS. 2. LAS INMUNODEFICIPRIMARIAS CONSTITUYEN UN 20% DE CASOS DE BRONQUIECTASIAS DE CAUSA NO ACLARADA, UN 8% DE LOS CASOS DE ASMA Y UN 1.98 DE LOS CASOS DE EPOC. 3. LOS ESTUDIOS INMUNOLOGICOS DEBEN DE ENTRAR A FORMAR PARTE EN EL PROTOCOLO DE ESTUDIO DE LOS PACIENTES CON BRONQUIECTASIAS DE CAUSA NO ACLARADA, ESPECIALMENTE EN JOVENES, NO FUMADORES Y CON ANTECEDENTES DE PROCESOS INFECCIOSOS DE VIAS ALTAS O BAJAS.
A novel liquid-crystalline polyurethane (LCPU) was synthesized by the condensation of 2,4-toluene... more A novel liquid-crystalline polyurethane (LCPU) was synthesized by the condensation of 2,4-toluenediisocyanate and 4,4'-bis(6-hydroxyhexoxy)biphenyl. Solution polymerization in dimethylformamide produced intrinsic viscosities in the range 0.30-0.57 dL/g. Differential scanning calorimetry shows a crystalline melting transition that is highly dependent on molecular weight and thermal history and a clearing transition that is virtually independent of both. Parallel-plate rheometry results are consistent with the presence of a liquid-crystalline phase, coexisting with a small amount of three-dimensional crystallinity, between 152 and 166 °C. Dynamic mechanical measurements reveal an unusually high elastic modulus of 180 MPa in the plateau region above Tg, compared with 6 MPa for an amorphous polyurethane with a chemical structure based on 1,4-butanediol.
Branched polypropylenes (PPb) with markedly improved melt strength were produced without signific... more Branched polypropylenes (PPb) with markedly improved melt strength were produced without significantly affecting the processability of the original PP. A two-step process of functionalization with MA and crosslinking with m-XDA was used, both by batch mixing and by extrusion. Branching degrees of~0.06 LCB/1000 monomer units or smaller were obtained. All PPbs display clear and significant strain hardening, being the PPb obtained by extrusion the one that shows the largest melt strength. This polymer has a zero-shear-rate viscosity slightly smaller than that of PP while its strain-hardening index is about 10 times higher. Moreover, the nonlinear behavior of PP at elongation begins at a time similar to its terminal relaxation time or larger, while the ratio of these times reduces significantly with branching. PP/PPb blends were prepared to extend the range of obtainable melt strength in PP. They display rheological behavior between those of the mixed polymers with slight positive deviation.
Trapped entanglements, cross-linker functionality, and elastically effective chains are the sourc... more Trapped entanglements, cross-linker functionality, and elastically effective chains are the sources of elasticity of polymer networks and gels. However, despite more than 80 years of theoretical and experimental research in this field, still little is known about their relative contribution to network elasticity. In this work, we use double quantum nuclear magnetic resonance (DQ NMR) experiments to characterize the elasticity of model polymer networks prepared with cross-linkers of mixed functionality and control of structural defects. An order parameter that condensates the elastic response within the theoretical framework of the entangled phantom theory for rubber elasticity was identified. Standard lore dictates that low molecular weight precursors for the elastically active chains leads to a negligible contribution of trapped entanglements. Here we show that the contribution of trapped entanglements may equal the contribution coming from elastically active material and that it is independent of network topology.
A reaction between a linear polypropylene functionalized with maleic anhydride (PPg) and epoxy re... more A reaction between a linear polypropylene functionalized with maleic anhydride (PPg) and epoxy resin (bisphenol A diglycidyl ether) was carried out on the molten state to generate long-chain branches (LCB) in the molecular structure of the PPg. Concentrations of epoxy resin (ER) of up to 3.15 wt% were employed to obtain different levels of branching. FTIR spectroscopy analysis indicates that during the reaction, anhydride groups in PPg are consumed and new ester groups are formed. The presence of branches was verified using multiple-detection size-exclusion chromatography and rheology. The degree of long-chain branching induced in PPg augments with increasing concentration of ER. Furthermore, the materials modified with higher content of ER display gel-like behavior. The long-chain branched polymers also display thermo-rheological complexity. Thermal characterization studies show that LCBs have a nucleating effect during crystallization and cause the augment of the crystallization activation energy of PPg.
International journal of pharmaceutics, Jan 25, 2016
The aim of this work was to design and characterize cross-linked hyaluronic acid (HA)-itaconic ac... more The aim of this work was to design and characterize cross-linked hyaluronic acid (HA)-itaconic acid (IT) films loaded with dexamethasone sodium phosphate salt (DEX) for topical therapy of inflammatory ocular surface diseases. Films were chemically cross-linked with polyethylene glycol diglycidyl ether (PEGDE), then physical and mechanical characterization by stress-strain, X-ray diffraction, X-ray fluorescence spectrometry and swelling assays was conducted. A sequential in vitro therapeutic efficacy model was designed to assess changes in interleukin (IL)-6 production in an inflamed human corneal epithelial (HCE) cell line after film exposure. Changes in cell proliferation after film exposure were assessed using the alamarBlue(®) proliferation assay. Experimental findings showed desirable mechanical properties and in vitro efficacy to reduce cell inflammation. A moderately decreased proliferation rate was induced in HCE cells by DEX-loaded films, compared to commercial DEX eye drops...
The hydrogenation of benzene on a nickel catalyst has been studied by means of a pulse micmrataly... more The hydrogenation of benzene on a nickel catalyst has been studied by means of a pulse micmratalyt~ic reactor in the lOO-150°C temperature range. It is shown that, the treatjment of experiment,al dat)a using equations derived for power-law and Langmuir-Iiinshelwond rate models allows the determination of similar kinetic paramePers as obtained from steady-state flow react,ors.
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Papers by Enrique Valles