Carbohydrate-based polyamides and polyesters: an overview illustrated with two selected examples

An overview on the synthesis, structure and properties of polyamides and aromatic copolyesters produced by using monomers derived from carbohydrates is provided. Two examples are selected for illustration: (a) aliphatic polyamides prepared from aldaric acids and (b) aromatic copolyesters containing alditols units. Polycondensation in solution of n-alkanediamines (n taking even values from 6 to 12) with activated pentaric (L-arabino and xylo) and hexaric (galacto and D-manno) acids bearing the secondary hydroxyl groups protected as methyl ether, afforded linear polyaldaramides PA-nSu with Mw oscillating between 25 000 and 150 000 g mol 1. They are stable above 300 C and are semicrystalline even so only PA-nMn are stereoregular. Melting temperatures of PA-nSu range between 140 and 230 C and most of them are able to crystallize from the melt at a rate that increases with the length of the polymethylene segment. Both melting and glass transition temperatures decrease with the content in sugar units. Spherulitic films, oriented fibers and lamellar single crystals could be obtained from PA-nSu. All these polyamides seem to adopt a common crystal structure made of hydrogen-bonded sheets with the sugar residue skewed to attain an efficient side-by-side packing of the polymer chains. Aromatic homopolyesters and copolyesters derived from terephthalic acid and mixtures of butylene glycol and O-methylated alditols were prepared by polycondensation in the melt with Mw in the 20 000–50 000 g mol 1 range and a random microstructure. The thermal properties of PBT containing alditols units are very depending on the sugar constitution and copolyester composition. In general they are thermally stable above 300 C and display crystallinity for contents in alditols up to 30%. Melting temperatures decrease with the content in alditols whereas an opposite trend is observed for glass transition temperatures. The crystalline structure of PBT is preserved in the crystalline copolyesters whereas a different crystal lattice is adopted by homopolyesters entirely made of alditol units. In general, polyamides and polyesters containing sugar derived units are widely soluble in organic solvents, markedly hydrophilic and more susceptible to hydrolysis than their parent polymers.Postprint (published version

Evaluación de la condición física y somatotipo de la población escolar indígena de 12 a 14 años en la unidad educativa Zuleta 2018

Evaluar la Condición Física y Somatotipo de la población escolar Indígena de Bachillerato 12 a 14 años de la Unidad Educativa Zuleta 2018.Esta investigación, evalúo la condición física y somatotipo, de la población escolar indígena de 12 a 14 años en la Unidad Educativa Bilingüe Zuleta, utilizando los test de evaluación de salto horizontal a pies juntos, sit and reach, marcha de 6 minutos, realizándose un estudio de tipo descriptivo, cuantitativo, de diseño no experimental y corte transversal; donde se evaluó a 26 estudiantes. Dentro de la Condición Física, para medir la Fuerza, el género masculino tuvo una valoración como aceptable y buena con el 23%, mientras que en el género femenino su valoración es aceptable con el 35%; En cuanto al nivel de flexibilidad, el género femenino presento una valoración de tipo Excelente con un 27%, y el género masculino presento una flexibilidad de tipo buena con un 27%; en cuanto a la resistencia cardiorrespiratoria, se demostró que, la distancia obtenida, tanto para el género masculino como femenino, se encuentran dentro de los rangos normales al igual que, la toma de signos vitales “pre test y post test, no existiendo cambios de mayor relevancia. Finalmente, para la determinación del somatotipo, se evidencio que el género masculino presenta un somatotipo mesomórfico con el 50% mientras que, en el género femenino un 31%, de somatotipo endomorfico.Licenciatur

Validation of smart nanoparticles as controlled drug delivery systems: loading and pH-dependent release of pilocarpine

Micelles are good devices for use as controlled drug delivery systems because they exhibit the ability to protect the encapsulated substance from the routes of degradation until they reach the site of action. The present work assesses loading kinetics of a hydrophobic drug, pilocarpine, in polymeric micellar nanoparticles (NPs) and its pH-dependent release in hydrophilic environments. The trigger pH stimulus, pH 5.5, was the value encountered in damaged tissues in solid tumors. The new nanoparticles were prepared from an amphiphilic block copolymer, [(HEMA19%-DMA31%)-(FMA5%-DEA45%)]. For the present research, three systems were validated, two of them with cross-linked cores and the other without chemical stabilization. A comparison of their loading kinetics and release profiles is discussed, with the support of additional data obtained by scanning electron microscopy and dynamic light scattering. The drug was loaded into the NPs within the first minutes; the load was dependent on the degree of cross-linking. All of the systems experienced a boost in drug release at acidic pH, ranging from 50 to 80% within the first 48 h. NPs with the highest degree (20%) of core cross-linking delivered the highest percentage of drug at fixed times. The studied systems exhibited fine-tuned sustained release features, which may provide a continuous delivery of the drug at specific acidic locations, thereby diminishing side effects and increasing therapeutic rates. Hence, the studied NPs proved to behave as smart controlled drug delivery systems capable of responding to changes in pH.Peer ReviewedPostprint (published version

Sugar-based bicyclic monomers for aliphatic polyesters: a comparative appraisal of acetalized alditols and isosorbide

Three series of polyalkanoates (adipates, suberates and sebacates) were synthesized using as monomers three sugar-based bicyclic diols derived from D-glucose (Glux-diol and isosorbide) and D-mannose (Manx-diol). Polycondensations were conducted in the melt applying similar reaction conditions for all cases. The aim was to compare the three bicyclic diols regarding their suitability to render aliphatic polyesters with enhanced thermal and mechanical properties. The ensuing polyesters had molecular weights (Mw) in the 25,000–50,000 g mol-1 range with highest values being attained for Glux-diol. All the polyesters started to decompose above 300 °C and most of them did not display perceivable crystallinity. On the contrary, they had glass transition temperatures much higher than usually found in homologous polyesters made of alkanediols, and showed a stress– strain behavior consistent with their Tg values. Glux-diol was particularly effective in increasing the Tg and to render therefore polyesters with high elastic modulus and considerable mechanical strength.Peer ReviewedPostprint (published version

Triblock copolyesters derived from lactic acid and glucose: synthesis, nanoparticle formation and simulation

ABA triblock copolyesters were synthesized by ring-opening polymerization (ROP) of l-lactide in solution initiated by a telechelic d-glucose-based polyester macroinitiator. The macroinitiator with a number-average molecular weight about 2500 g mol-1 was synthesized by non-stoichiometric polycondensation in the melt of 2,4:3,5-di-O-methylene-d-glucitol and dimethyl succinate. Two triblock copolyesters of Mn ranging between ~6000 and ~9000 g mol-1, and differing in the length of the polylactide blocks were prepared. These copolyesters started to decompose when heated at ~220 °C and degraded slowly upon aqueous incubation under physiological conditions. They did not display any perceivable crystallinity and showed a single glass transition temperature (Tg) around 60 °C with the higher value corresponding to the larger content in glucitol units. The copolyesters were able to form nanoparticles with average diameters of ~100–130 nm and satisfactory dispersity. The effect of the block lengths on size, ¿-potential values and physical stability of the nanoparticles was evaluated. A molecular dynamics simulation study allowed modelling the two-phase structure of the nanoparticles and evidenced the preference of the glucose-based block to be peripherally located.Peer ReviewedPostprint (author's final draft

Crystalline structure and thermotropic behavior of alkyltrimethylphosphonium amphiphiles

Quaternary organophosphonium salts bearing long alkyl chains are cationic surfactants of interest owing to their physical and biological properties. In the present work, the crystal structure and thermotropic behavior of the homologous series of alkyltrimethylphosphonium bromides (nATMP·Br), with the alkyl chain containing an even number (n) of carbon atoms from 12 to 22, have been examined within the 0–300 °C range of temperatures. These compounds were shown to be resistant to heat up to ~390 °C. The phases adopted at different temperatures were detected by DSC, and the structural changes involved in the phase transitions have been characterized by simultaneous WAXS and SAXS carried out in real-time, and by polarizing optical microscopy as well. Three or four phases were identified for n = 12 and 14 or n = 16, respectively, in agreement with the heat exchange peaks observed by DSC. The phase existing at room temperature (Ph-I) was found to be fully crystalline and its crystal lattice was determined by single-crystal X-ray diffraction methods. Ph-II consisted of a semicrystalline structure that can be categorized as Smectic-B with the crystallized ionic pairs hexagonally arranged in layers and the molten alkyl chain confined in the interlayer space. Ph-II of 12ATMP·Br and 14ATMP·Br directly isotropicized upon heating at ~220 °C, whereas for n = 16, it converted into a Smectic-A phase (Ph-III) that needed to be heated above ~240 °C to become isotropic (Ph-Is). The correlation existing between the thermal behavior, phase structure and length of the alkyl side chain has been demonstrated.Peer ReviewedPostprint (published version

Isohexide and sorbitol-derived, enzymatically synthesized renewable polyesters with enhanced Tg

Sugar-based polyesters derived from sorbitol and isohexides were obtained via solvent-free enzymatic catalysis. Pendant hydroxyl groups, coming from the sorbitol units, were present along the polyester backbone, whereas the two isohexides, namely, isomannide and isoidide dimethyl ester monomers, were selected to introduce rigidity into the polyester chains. The feasibility of incorporating isomannide as a diol compared to the isoidide dimethyl ester as acyl-donor via lipase-catalyzed polycondensation was investigated. The presence of bicyclic units resulted in enhanced Tg with respect to the parent sorbitol-containing polyester lacking isohexides. The different capability of the two isohexides to boost the thermal properties confirmed the more flexible character provided by the isoidide diester derivative. Solvent-borne coatings were prepared by cross-linking the sugar-based polyester polyols with polyisocyanates. The increased rigidity of the obtained sugar-based polyester polyols led to an enhancement in hardness of the resulting coatings.Peer ReviewedPostprint (author's final draft

Fully bio-based aromatic–aliphatic copolyesters: poly(butylene furandicarboxylate-co-succinate)s obtained by ring opening polymerization

Poly(butylene 2,5-furandicarboxylate-co-succinate) copolyesters (coPBFxSy) have been synthesized by ring opening polymerization (ROP). Cyclic butylene 2,5-furandicarboxylate and butylene succinate oligomer mixtures, to be used as monomers for ROP, were prepared by high dilution condensation and enzymatic cyclization reactions, respectively. Two different catalytic systems, tin dioctanoate and supported Candida antarctica lipase B (CALB), were used for polymerization. Thus two series of copolyesters covering the whole range of compositions were prepared and their properties comparatively examined. In both cases, random copolyesters with compositions close to those used in their respective feeds were obtained. The influence of composition on reaction kinetics with respect to time and temperature was evaluated for the two series. Chemically catalyzed ROP rendered copolyesters with Mw in the ~50 000–65 000 g mol-1 range, whereas values between 15 000 and 45 000 g mol-1 were attained when the ROP reaction was assisted by CALB. The thermal behavior of coPBFxSy obtained by ROP was similar to that reported for such copolymers prepared by melt polycondensation. They all start to decompose above 300 °C and display melting enthalpy and temperatures that decrease with copolymerization, attaining minimum values when the comonomer contents are approximate to balance. On the contrary, the glass-transition temperature increased almost linearly with the content of butylene furandicarboxylate units, covering the whole range of values between those of the two parent homopolyesters. Small deviations in thermal properties observed between the two series could be attributed to their differences in molecular weights. Hydrolytic and enzymatic degradation studies revealed that coPBFxSy became more degradable with increasing content of succinic units, whereas the homopolyester PBF remained practically unaffected when incubated under similar conditions.Peer ReviewedPostprint (author's final draft

Ring opening polymerization of macrocyclic oligoesters derived from renewable sources

Macrocyclic oligoesters (MCOs) derived from biomass such as those prepared from alkylene alkanedioates and 2,5-furandicarboxylates are suitable compounds for ring opening polymerization (ROP) to produce high molecular weight bio-based polyesters. The synthetic procedures that have been recently developed to obtain these MCOs in good yields, their ROP either alone or together with other cyclic compounds, and their recovery by cyclodepolymerization of the final polyesters are the main topics covered in this review. Both organometallic compounds and enzymes such as Candida antarctica lipase B are the catalytic systems used for all reactions. This synthetic approach based on ROP of MCOs derived from renewable sources opens a green pathway for a circular economy in plastics.Postprint (author's final draft

Controlling the isothermal crystallization of isodimorphic PBS-ran-PCL random copolymers by varying composition and supercooling

In this work, we study for the first time, the isothermal crystallization behavior of isodimorphic random poly(butylene succinate)-ran-poly(e-caprolactone) copolyesters, PBS-ran-PCL, previously synthesized by us. We perform nucleation and spherulitic growth kinetics by polarized light optical microscopy (PLOM) and overall isothermal crystallization kinetics by differential scanning calorimetry (DSC). Selected samples were also studied by real-time wide angle X-ray diffraction (WAXS). Under isothermal conditions, only the PBS-rich phase or the PCL-rich phase could crystallize as long as the composition was away from the pseudo-eutectic point. In comparison with the parent homopolymers, as comonomer content increased, both PBS-rich and PCL-rich phases nucleated much faster, but their spherulitic growth rates were much slower. Therefore, the overall crystallization kinetics was a strong function of composition and supercooling. The only copolymer with the eutectic composition exhibited a remarkable behavior. By tuning the crystallization temperature, this copolyester could form either a single crystalline phase or both phases, with remarkably different thermal propertiesPeer ReviewedPostprint (published version