Ionic copolyesters and their nanocomposites: synthesis, characterization and properties

A polymer containing small amounts of ionic groups either along the polymer backbone chains or as pendant groups is defined as ionomer. As originally proposed by Eisenberg, the interaction between ionic groups leads to the formation of multiplets containing a small number of ion pairs, and also to ionic clusters, which constitute a second phase made of many multiplets as well as portions of the hydrocarbon chains. These ionic structures have been shown to act as strong electrostatic cross-links, which provide altered physical properties, such as enhanced mechanical properties and high melt viscosity, among others. Both aromatic polyesters as aliphatic are polymeric materials widely used today. Their most familiar applications are in clothing, food packaging and water and carbonated soft drinks bottles. Major part of biodegradable synthetic polymers are polyesters, and in particular, aliphatic polyesters. Monomers for the latter can be synthesized from renewable resources. Biodegradable polyesters play a key role in medical applications due to their biodegradability and versatile synthesis able to afford tailored properties; they are currently employed as biomaterials for medical purposes such as surgical sutures, scaffolds, screws and reinforcing plates as well as controlled release drug carriers, since they are biocompatible and nontoxic. This thesis is focused to the chemical modification of aromatic and aliphatic polyesters through the incorporation of various concentration and different ionic groups. We synthesized poly(hexamethylene terephthalate) and poly(butylene succinate)-based ionomers and investigated the effects of the ionic substitution on physical properties, crystallization rates and hydrodegradability of these polyester ionomers. In addition, we also studied the influence of the ionic interaction with nanoclays in the formation of ionomers-based nanocomposites. This thesis embodies a multidisciplinary task work that includes synthesis, spectroscopy characterization, evaluation of thermal and mechanical properties, hydrolytic degradation and nanocomposites preparation: the synthesis procedure of copolyesters was made in all cases by polycondensation in melt-phase. Different conditions of temperature, catalyst and time required were used for each family of copolyesters depending on both the stability and the reactivity of the comonomers involved in the synthesis. The copolyesters synthesized incorporated sulfonated, ammonium, trimethylamonium and tributylphosphonium ionic groups into their chains. The hydrolytic degradation results suggest that the insertion of sulfonated groups in the copolyesters make them more hydrophilic allowing better solvation and an easier attack of water on the ester groups. Nanocomposites with nanoclays were obtained by using different approaches for mixing and in some cases by making use of compatibilizers. Octadecyltrimethylammonium, 1,12-dodecylenediammonium salts and a terpolyester ionomer were used for compatibilization. The clay was used either unmodified or modified with alkylammonium soaps. Results obtained by the different procedures were compared and the effect of the compatibilizers on the mixing efficiency and composite properties were evaluated. Characterization was carried out by 1H and 13C nuclear magnetic resonance (NMR) spectroscopy, FTIR spectroscopy, gel permeation chromatography (GPC), differential scanning calorimetry (DSC), and thermogravimetry analysis (TGA). The changes in crystal structure upon copolymerization were followed by X-ray diffraction (XRD).Un polímero que contiene pequeñas proporciones de grupos iónicos, ya sea a lo largo de la cadena principal como en los grupos laterales, es definido como ionómero. Según lo propuesto originalmente por Eisenberg, la interacción entre los grupos iónicos conduce a la formación de multipletes que contienen un grupo reducido de pares iónicos, y también a la formación de clusters, los cuales constituyen una segunda fase compuesta de muchos multipletes, así como de porciones de cadena hidrocarbonada. Estas estructuras iónicas han demostrado actuar como enlaces electrostáticos fuertes entrecruzados, los cuales producen modificacion en las propiedades físicas tales como una mejora de las propiedades mecánicas y un incremento en la viscosidad en fundido, entre otras. Tanto los poliésteres aromáticos como los alifáticos son materiales poliméricos usados ampliamente en la actualidad. Sus aplicaciones más conocidas van desde el campo textil hasta el envasado de alimentos y líquidos como el agua o bebidas carbónicas. La mayoría de los polímeros sintéticos biodegradables son poliésteres alifáticos. Estos poliésteres suelen ser biocompatibles y no tóxicos y juegan un papel clave en aplicaciones médicas debido a su síntesis versátil capaz de proporcionar propiedades a medida. Actualmente se vienen empleando como biomateriales en suturas quirúrgicas, implantes óseos porosos, tornillos y placas de refuerzo, así como portadores de fármacos de liberación controlada. Esta tesis está enfocada en la modificación química de poliésteres aromáticos y alifáticos mediante la incorporación de diferentes grupos iónicos y con diversas concentraciones. Se han sintetizado ionómeros en base al poli(hexametilen tereftalato) y poli(butilen succinato) y se han investigado los efectos de la sustitución iónica sobre las propiedades físicas, velocidades de cristalización e hidrodegradabilidad de estos poliésteres. Además, se ha estudiado la influencia de las interacciones iónicas con nanoarcillas en la formación de nanocompuestos a base de ionómeros. Esta tesis supone un trabajo multidisciplinar que incluye síntesis, caracterización espectroscópica, evaluación de propiedades térmicas y mecánicas, estudio de la degradación hidrolítica y preparación de nanocompuestos; el proceso de síntesis de los poliésteres ha sido realizado en todos los casos mediante policondensación en estado fundido. Se han utilizado condiciones diferentes de temperatura, catalizador y tiempo para cada familia de poliésteres dependiendo de la estabilidad y de la reactividad de los comonomeros involucrados en la síntesis. Los copoliésteres sintetizados incorporaron en sus cadenas grupos iónicos sulfonados, amonio, trimetilamonio y tributil fosfonio. Los resultados de la degradación hidrolítica sugieren que la inserción de grupos sulfonados en los poliésteres, los hace más hidrofílicos permitiendo una mejor solvatación y un ataque más fácil del agua a los grupos éster. Los nanocompuestos con nanoarcillas fueron obtenidos mediante diferentes metodologías de mezclado y en algunos casos haciendo uso de compatibilizadores. Para la compatibilización se usaron el bromuro de octadeciltrimetilamonio, el dicloruro de 1,12-dodecildiamonio y un ionómero terpoliéster. Se empleó la arcilla montmorillonite tanto sin modificar como modificada con grupos alquilamonio. Se compararon los resultados obtenidos mediante los diferentes procedimientos y se evaluaron los efectos de los compatibizadores en la eficacia de mezclado y en las propiedades de los composites. La caracterización se llevó a cabo mediante resonancia magnética nuclear de 1H y 13C (NMR), espectroscopia de infrarrojo, cromatografía de exclusión molecular (GPC), calorimetría diferencial de barrido (DSC), y análisis de termogravimétrico (TGA). Los cambios en la estructura cristalina debidos a la copolimerización fueron seguidos mediante difracción de rayos X (XRD)

Poly(butylene succinate) ionomers with enhanced hydrodegradability

A series of poly(butylene succinate) (PBS) ionomers containing up to 14 mol%of sulfonated succinate units have been synthesized by polycondensation in the melt-phase. The copolyesters were obtained with weight average molecular weights oscillating between 33,000 and 72,000 g·mol-1. All copolyesters were semicrystalline with melting temperatures and enthalpies decreasing and glass transition temperatures increasing with the content of ionic units. The thermal stability of PBS was slightly reduced by the incorporation of these units, and it was also found that the copolyesters were stiffer but also more brittle than PBS. The hydrolytic degradability of PBS was enhanced by copolymerization, an effect that was much more pronounced in basic media.Peer ReviewedPostprint (published version

Poly(butylene succinate) ionomers and their use as compatibilizers in nanocomposites

A series of low-molecular-weight poly(butylene succinate-co-glutarate-co-2-trimethylammonium chloride glutarate) terpolyester ionomers containing 35% mol of total glutarate units but varying in the content of charged units were synthesized by polycondensation at mild temperatures using a scandium catalyst. The terpolyester ionomers started to decompose at the temperatures of >175°C and all of them were semicrystalline and have glass transition temperature similar to poly(butylene succinate) (PBS). These terpolyesters were used to compatibilize the nanocomposites made of PBS-cloisite (CL) prepared by melt extrusion. X-ray diffraction revealed that an intercalated structure was present in these nanocomposites. The thermal properties of the three-component mixtures did not differ substantially from those of PBS–CL but the mechanical properties were significantly improved by the addition of the ionomer, in particular tenacity. The beneficial effect afforded by the terpolyester ionomer was attributed to its ability for strengthening the binding between the PBS and the nanoclay.A series of low-molecular-weight poly(butylene succinate-co-glutarate-co-2-trimethylammonium chloride glutarate) terpolyester ionomers containing 35% mol of total glutarate units but varying in the content of charged units were synthesized by polycondensation at mild temperatures using a scandium catalyst. The terpolyester ionomers started to decompose at the temperatures of >175°C and all of them were semicrystalline and have glass transition temperature similar to poly(butylene succinate) (PBS). These terpolyesters were used to compatibilize the nanocomposites made of PBS-cloisite (CL) prepared by melt extrusion. X-ray diffraction revealed that an intercalated structure was present in these nanocomposites. The thermal properties of the three-component mixtures did not differ substantially from those of PBS–CL but the mechanical properties were significantly improved by the addition of the ionomer, in particular tenacity. The beneficial effect afforded by the terpolyester ionomer was attributed to its ability for strengthening the binding between the PBS and the nanoclay.Peer ReviewedPostprint (author's final draft

Cationic poly(butylene succinate) copolyesters

The synthesis, characterization and comparative evaluation of properties of two series of cationic PBS copolyesters bearing respectively ammonium and tributylphosphonium side groups, are reported. The copolyesters with contents in ionic units up to 50 mole-% as well as the fully ionic homopolyesters were prepared by polycondensation in the melt catalyzed by CALB or TBT. Their Mn ranged between 20,000 and 5000 g mol-1 depending of composition and the type of ionic group that is involved. All the copolyesters were non-water soluble and showed good thermal stability. They were semicrystalline with melting temperatures and enthalpies decreasing with the ionic contents. The interactions interplayed by the ionic groups restricted largely the molecular mobility and caused a significant increase in the melt viscosity and glass transition temperature of PBS and a decrease in crystallization rate. Both ammonium and phosphonium containing PBS copolyesters were able to be coupled with sulfonated PBS to generate ionic polymer blends with modified crystallizability. The presence of both ammoniums and phosphoniums provided PBS with remarkable antimicrobial activity against gram-positive and gram-negative bacteria.Peer ReviewedPostprint (author's final draft

Poly(butylene succinate) Ionomers with Enhanced Hydrodegradability

A series of poly(butylene succinate) (PBS) ionomers containing up to 14 mol% of sulfonated succinate units have been synthesized by polycondensation in the melt-phase. The copolyesters were obtained with weight average molecular weights oscillating between 33,000 and 72,000 g·mol−1. All copolyesters were semicrystalline with melting temperatures and enthalpies decreasing and glass transition temperatures increasing with the content of ionic units. The thermal stability of PBS was slightly reduced by the incorporation of these units, and it was also found that the copolyesters were stiffer but also more brittle than PBS. The hydrolytic degradability of PBS was enhanced by copolymerization, an effect that was much more pronounced in basic media

Sulfonated poly(hexamethylene terephthalate) copolyesters: enhanced thermal and mechanical properties

A series of poly(hexamethylene terephthalate- co -hexamethylene 5-sodium sulfoisophthalate) copolyesters containing from 5 to 50 mol % of sulfonated units as well as the two parent homopolymers are prepared by melt polycondensation. The polyesters are obtained with high molecular weights, which decrease with the increased content of sulfonated units in the copolymer. Polyesters with 5 and 10 mol % of sulfonated units are semicrystalline whereas for contents equal or above 20 mol % they are unable to crystal- lize from the melt. Thermogravimetric analysis show that the thermal stability decreases with the content in sulfonated units. Isother- mal crystallizations of semicrystalline copolyesters show that the insertion of the sulfonated units causes a reduction of crystallizabil- ity, most probably due to the occurrence of ionic aggregations. It is observed a synergistic effect on the mechanical properties for copolymers with contents of around 5 mol % where the elongation at break increases drastically. Moreover, the hydrolytic degrada- tion of the copolymer is enhanced with the content in sulfonated unitsPeer ReviewedPostprint (published version

Poly(butylene succinate) ionomers and their use as compatibilizers in nanocomposites

A series of low-molecular-weight poly(butylene succinate-co-glutarate-co-2-trimethylammonium chloride glutarate) terpolyester ionomers containing 35% mol of total glutarate units but varying in the content of charged units were synthesized by polycondensation at mild temperatures using a scandium catalyst. The terpolyester ionomers started to decompose at the temperatures of >175°C and all of them were semicrystalline and have glass transition temperature similar to poly(butylene succinate) (PBS). These terpolyesters were used to compatibilize the nanocomposites made of PBS-cloisite (CL) prepared by melt extrusion. X-ray diffraction revealed that an intercalated structure was present in these nanocomposites. The thermal properties of the three-component mixtures did not differ substantially from those of PBS–CL but the mechanical properties were significantly improved by the addition of the ionomer, in particular tenacity. The beneficial effect afforded by the terpolyester ionomer was attributed to its ability for strengthening the binding between the PBS and the nanoclay.A series of low-molecular-weight poly(butylene succinate-co-glutarate-co-2-trimethylammonium chloride glutarate) terpolyester ionomers containing 35% mol of total glutarate units but varying in the content of charged units were synthesized by polycondensation at mild temperatures using a scandium catalyst. The terpolyester ionomers started to decompose at the temperatures of >175°C and all of them were semicrystalline and have glass transition temperature similar to poly(butylene succinate) (PBS). These terpolyesters were used to compatibilize the nanocomposites made of PBS-cloisite (CL) prepared by melt extrusion. X-ray diffraction revealed that an intercalated structure was present in these nanocomposites. The thermal properties of the three-component mixtures did not differ substantially from those of PBS–CL but the mechanical properties were significantly improved by the addition of the ionomer, in particular tenacity. The beneficial effect afforded by the terpolyester ionomer was attributed to its ability for strengthening the binding between the PBS and the nanoclay.Peer Reviewe

Poly(butylene succinate) ionomers with enhanced hydrodegradability

A series of poly(butylene succinate) (PBS) ionomers containing up to 14 mol%of sulfonated succinate units have been synthesized by polycondensation in the melt-phase. The copolyesters were obtained with weight average molecular weights oscillating between 33,000 and 72,000 g·mol-1. All copolyesters were semicrystalline with melting temperatures and enthalpies decreasing and glass transition temperatures increasing with the content of ionic units. The thermal stability of PBS was slightly reduced by the incorporation of these units, and it was also found that the copolyesters were stiffer but also more brittle than PBS. The hydrolytic degradability of PBS was enhanced by copolymerization, an effect that was much more pronounced in basic media.Peer Reviewe

Sulfonated poly(hexamethylene terephthalate) copolyesters: enhanced thermal and mechanical properties

A series of poly(hexamethylene terephthalate- co -hexamethylene 5-sodium sulfoisophthalate) copolyesters containing from 5 to 50 mol % of sulfonated units as well as the two parent homopolymers are prepared by melt polycondensation. The polyesters are obtained with high molecular weights, which decrease with the increased content of sulfonated units in the copolymer. Polyesters with 5 and 10 mol % of sulfonated units are semicrystalline whereas for contents equal or above 20 mol % they are unable to crystal- lize from the melt. Thermogravimetric analysis show that the thermal stability decreases with the content in sulfonated units. Isother- mal crystallizations of semicrystalline copolyesters show that the insertion of the sulfonated units causes a reduction of crystallizabil- ity, most probably due to the occurrence of ionic aggregations. It is observed a synergistic effect on the mechanical properties for copolymers with contents of around 5 mol % where the elongation at break increases drastically. Moreover, the hydrolytic degrada- tion of the copolymer is enhanced with the content in sulfonated unitsPeer Reviewe