Developments in Solid-State NMR Spectroscopy of Polymer Systems

Solid-state nuclear magnetic resonance (NMR) has long emerged as a valuable technique for characterizing the molecular structure, conformation, and dynamics of polymer chains in various polymer systems. The principles of the solid-state 13C NMR cross-polarization experiment are described along with corresponding relaxation measurements. The ensuing recent applications of these techniques to different polymer systems are reviewed, with selected examples that have appeared in the recent literature. All of these applications of solid-state NMR to polymers have one feature in common: the interpretation of spectroscopic observations as related to the structural features and physical properties of the polymer

Hydrolytic degradation of poly(ε-caprolactone) with different end groups and poly(ε-caprolactone-co--Y-butyrolactone): characterization and kinetics of hydrocortisone delivery

7 páginas, 8 figuras, 2 tablas.-- El pdf es el borrador del artículo.Asymmetric telechelic alfa-hydroxyl-ω-(carboxylic acid)-poly(ε-caprolactone) (HA-PCL), alfa-hydroxyl-ω-(benzylic ester)-poly(ε-caprolactone) (HBz-PCL), and an asymmetric telechelic copolymer alfa-hydroxyl-ω-(carboxylic acid)-poly(ε-caprolactone-co-Y-butyrolactone) (HA-PCB) were synthesized by ring-opening polymerization of ε-caprolactone (CL). CL and CL/-butyrolactone mixture were used to obtain homopolymers and copolymer respectively at 150°C and 2 hr using ammonium decamolybdate (NH4) [Mo10O34] (Dec) as a catalyst. Water (HA-PCL and HA-PCB) or benzyl alcohol (HBz-PCL) were used as initiators. The three polylactones reached initial molecular weights between 2000 and 3000 Da measured by proton nuclear magnetic resonance (1H-NMR). Compression-molded polylactone caplets were allowed to degrade in 0.5 M aqueous p-toluenesulfonic acid at 37°C and monitored up to 60 days for weight loss behavior. Data showed that the copolymer degraded faster than the PCL homopolymers, and that there was no difference in the weight loss behavior between HA-PCL and HBz-PCL. Caplets of the three polylactones containing 1% (w/w) hydrocortisone were placed in two different buffer systems, pH 5.0 with citrate buffer and pH 7.4 with phosphate buffer at 37°C, and monitored up to 50 days for their release behavior. The release profiles of hydrocortisone presented two stages. The introduction of a second monomer in the polymer chain significantly increased the release rate, the degradation rate for HA-PCB being faster than those for HBz-PCL and HA-PCL. At the pH studied, only slight differences on the liberation profiles were observed. SEM micrographs indicate that hydrolytic degradation occurred mainly by a surface erosion mechanism.The financial support by Consejo Nacional de Ciencia y Tecnología and Universidad de Guanajuato is acknowledged. L.M.O.C. thanks Consejo Nacional de Ciencia y Technología (CONACYT) for a Ph.D. scholarship.Peer reviewe

One-Step Route to α-Hydroxyl-ω-(carboxylic acid) Polylactones Using Catalysis by Decamolybdate Anion

10 páginas, 12 figuras, 5 esquemas, 5 tablas.Asymmetric telechelic α-hydroxyl-ω-(carboxylic acid) poly(ε-caprolactone) (HA-PCL) and α-hydroxyl-ω-(carboxylic acid) poly(δ-valerolactone) (HA-PVL) were synthesized by ring-opening polymerization of ε-caprolactone (CL) and δ-valerolactone (VL), respectively. HA-PCL oligomers were obtained at 150 °C in 2 h using ammonium decamolybdate (NH4)8[Mo10O34] as catalyst and water as initiator. A control of the number-average molecular weight (measured by NMR) can be achieved in the range between 212 and 2198 Da, based on the initial monomer/initiator ratio. Number-average molecular weight (Mn) shows a linear dependence with CL/H2O ratio in this range. The nature of hydroxyl and carboxylic acid end groups of HA-PCL and HA-PVL was studied by MALDI-TOF and 1H and 13C NMR. Changes in the chemical shifts observed in the NMR spectra as a function of molecular weight were explained in terms of hydrophobic interactions. Formation of macrocyclic species was studied by MALDI-TOF. It was found that macrocyclic species are favored at longer reaction times. Insertion of alcohols and polycondensation reactions occurring after complete monomer conversion were also studied. Alcohol insertion for this system depends on the nature of alcohol. Polycondensation reactions vary with reaction times and affect the polymer molecular weight in a nonlinear manner. Finally, the α-hydroxyl-ω-(sodium carboxylate) PCL salt (HC-PCL) was prepared from HA-PCL and characterized by FT-IR and solution and solid-state NMR. Important differences between CP-MAS and MAS spectra are observed and discussed in terms of morphology and polarization transferFinancial support by Consejo Nacional de Ciencia y Tecnología (CONACYT), Consejo de Ciencia y Tecnología del Estado de Guanajuato (CONCYTEG), and Universidad de Guanajuato are acknowledged.Peer reviewe

Chemo-Enzymatic Syntheses of Polyester-Urethanes

9 páginas.-- Editores: H. N. Cheng y Richard A. Gross.The enzymatic synthesis of α-ω-telechelic polycaprolactone diols (HOPCLOH) and triblock copolymers was studied. Synthesis of α-ω-telechelic PCL diols was achieved by enzymatic ring opening polymerization with Yarrowia lipolytica lipase immobilized on a macroporous resin Lewatit VP OC 1026, and using diethylene glycol and poly(ethylene glycol) as initiators. Biodegradable linear polyester-urethanes were prepared from synthesized PCL diols and hexamethylenediisocyanate (HDI). Depending on the length of PCL in HOPCLOH, the polymers were amorphous or semicrystalline. Measured mechanical properties strongly depend upon the degree of crystallinity of HOPCLOH.Peer reviewe

Poly(-caprolactone) diols (HOPCLOH) and their poly(ester-urethane)s (PEUs): The effect of linear aliphatic diols [HO-(CH2)m-OH] as initiators

α,ω-Hydroxy telechelic poly(ε-caprolactones) were prepared by ring-opening polymerization of the ε-caprolactone catalyzed by ammonium decamolybdate in the presence of different aliphatic diols [HO–(CH2)m–OH, where m ¼ 2, 4, 6, 8, 10, 12, 14, and 16] as initiators to obtain a family of α,ω- hydroxy telechelic poly(ε-caprolactone) [HO–PCL–O–(CH2)m–O–PCL–OH, m ¼ 2, 4, 6, 8, 10, 12, 14, and 16]. The content of the alkyl group (AG) (–(CH2)m–) had an important effect on the crystallinity (xi) of α,ω-hydroxy telechelic poly(ε-caprolactone), showing a proportional relationship. In poly (ester-urethanes) derived from α,ω-hydroxy telechelic poly(ε-caprolactones) and 1,6- hexamethylene diisocyanate, the AG also showed a similar effect on the xi and eventually on the mechanical properties, increasing the values of the modulus. Therefore, AG content was a factor to induce a plastic behavior in poly(ester-urethanes). The effect of AG on the water uptake of poly(ester-urethanes) after 1 week was negligible.José E. Báez thanks the “Programa para el Desarrollo Profesional Docente (PRODEP, Protocolo 166155)”, Dirección de Apoyo a la Investigación y al Posgrado (DAIP) at University of Guanajuato (UG), Consejo Nacional de Ciencia y Tecnología (CONACYT) and “Sistema Nacional de Investigadores (SNI)” in Mexico for financial support of the work. José E. Báez also thanks Ángel Marcos-Fernández for believing in these ideas and providing financial support for the reagents. José E. Báez also thanks the UG for the recent opportunity to work as an Assistant Professor. Marvin was used for drawing, displaying, and characterizing chemical structures, substructures, and reactions (Marvin Sketch 6.1.3, 2013, ChemAxon; http://www.chemaxon.com); a free software program with an academic license was provided by ChemAxon. Finally, José E. Báez thanks to MSc Paulina Lozano and Dr. Ricardo Navarro Mendoza for the acquisition of SEM micrographs in the “National Laboratory for the Characterization of Physicochemical Properties and Molecular Structure” at the University of Guanajuato. Ángel Marcos-Fernández would like to thank the Ministry of Economy and Competitiveness (MINECO) for the financial support of this work within the framework of the Plan Nacional de IþDþI through the research project MAT2014-52644-R.Peer Reviewe

Obtención de Relaciones Cuantitativas Estructura-Propiedad en Cristales Líquidos Obtención de Relaciones Cuantitativas Estructura-Propiedad en Cristales Líquidos

<p>Sixty nine thermotropic liquid crystal molecules were analyzed by different chemometric methods, including Principal Component Analysis (PCA), Genetic algorithms and Quantitative Structure-Property Relationships (QSPR). Mathematical models to predict nematic transition temperatures (T_N) were derived. This is the first time that Principal Component Analysis was used to predict liquid crystal properties, leading to the derivation of local (specific) models for different molecule sets. Results indicate that local models have higher prediction capabilities than global models, which is consistent to our initial assumption. This methodology will be used in the study of liquid crystals used in pharmaceutical applications.</p><br><p>Una serie de 69 cristales líquidos termotrópicos se sometió a una colección de Métodos Quimiométricos incluyendo Análisis de Componentes Principales; Algoritmos Genéticos y Relaciones Cuantitativas Estructura Propiedad para la obtención de modelos matemáticos que permitan predecir las Temperaturas de Transición Nemática, (T_N). En este trabajo se aplica por primera vez el Análisis de Componentes Principales al estudio de cristales líquidos para la identifi cación de subconjuntos de moléculas para los cuales se obtuvieron modelos locales. Los resultados obtenidos muestran que la capacidad de predicción de los modelos locales es superior a la del modelo global, lo cual resultó consistente con la hipótesis planteada. La metodología utilizada se extenderá al estudio de cristales líquidoscon actividad farmacológica.</p

Enzymatic ring-opening polymerization of ε-caprolactone by Yarrowia lipolytica lipase in ionic liquids

12 páginas, 17 figuras, 1 esquema, 2 tablas.Yarrowia lipolytica (YLL), Candida rugosa (CRL), and porcine pancreatic lipase (PPL) were employed successfully as catalysts in the enzymatic ring-opening polymerization (ROP) of ε-caprolactone in the presence of 1-ethyl-3-methylimidazolium tetrafluoroborate ([EMIM][BF4]), 1-butyl-3-methylimidazolium tetrafluoroborate ([BMIM][BF4]), 1-butylpyridinium tetrafluoroborate ([BuPy][BF4]), 1-butylpyridinium trifluoroacetate ([BuPy][CF3COO]), 1-ethyl-3-methylimidazolium nitrate ([EMIM][NO3]) ionic liquids. Poly(ε-caprolactone)s (PCLs) with molecular weights (Mn) in the range of 300–9000 Da were obtained. 1H- and 13C-NMR analyses on PCLs formed by YLL, CRL, and PPL showed asymmetric telechelic -hydroxy-ω-carboxylic acid end groups. Differences between CP-MAS and MAS spectra are observed and discussed in terms of morphology. MALDI-TOF spectra show the formation of at least seven species. Differential scanning calorimetry (DSC) and Wide Angle X-Ray Scattering (WAXS) results demonstrate the high degree of crystallinity present in all the polyesters.Contract grant sponsor: Consejo Nacional de Ciencia y Tecnología (CONACyT); contract grant number: SEP-2004- C01-47173E. Contract grant sponsor: Consejo de Ciencia y Tecnología del Estado de Guanajuato (CONCYTEG). Contract grant sponsor: Universidad de Guanajuatato.Peer reviewe