New Architectures based on Isotactic Polypropylene: Synthesis and Molecular Characterization, Competition between Polymorphs (monoclinic / orthorhombic / mesomorphic / trigonal), and Properties Evaluation

Tesis doctoral inédita leída en la Universidad Autónoma de Madrid, Facultad de Ciencias, Departamento de Química Física Aplicada. Fecha de lectura: 23-11-2015El polipropileno isotáctico se encuentra presente en una enorme variedad de aplicaciones, que lo sitúan en la segunda posición de los polímeros con mayor demanda mundial, los denominados “commodities”. Las necesidades del mercado, la expansión de su uso así como nuevas políticas, medioambientales entre otras, están detrás de los numerosos esfuerzos que se llevan a cabo a diario para mejorar las arquitecturas existentes y diseñar otras nuevas basadas en ellas, con objeto de optimizar y ampliar su espectro de propiedades. El presente trabajo de investigación tiene, por tanto, el propósito último de incidir en las posibilidades que ofrecen los copolímeros y terpolímeros de propileno con alfa-olefinas de longitudes intermedias como comonómeros (1-penteno, 1-hexeno y 1-hepteno), motivado por el hallazgo en 2005 de una nueva estructura cristalina (celdilla trigonal) en copolímeros de propileno con 1-penteno y 1-hexeno a elevados contenidos. Para ello, se han sintetizado diferentes familias de copolímeros de propileno-co-1-penteno, propileno-co-1-hexeno y propileno-co-1-hepteno en intervalos amplios de composición de los comonómeros, así como terpolímeros de propileno-co-1-penteno-co-1-hexeno y propileno-co-1-penteno-co-1-hepteno, en los que, además, se varió el ratio entre comonómeros a una composición global dada. Se han preparado también los homopolímeros correspondientes, es decir, el polipropileno isotáctico, el poli(1-penteno), el poli(1-hexeno) y el poli(1-hepteno). Los numerosos materiales obtenidos presentan pesos moleculares suficientemente elevados así como una alta isotacticidad, características que garantizan unas buenas prestaciones mecánicas, como se ha comprobado. Un entendimiento adecuado de las estructuras cristalinas que pueden generarse y, consecuentemente, de las propiedades finales que pueden manifestar estos materiales, ha requerido una minuciosa evaluación de su microestructura. De ella se ha deducido que la inserción de los monómeros durante la polimerización se produce al azar. A continuación, se ha realizado un estudio pormenorizado sobre las diferentes estructuras cristalinas existentes, la competencia entre los diversos polimorfos y sus transiciones de fase, para cada una de las familias sintetizadas, en función de la composición, la velocidad de cristalización y el ratio entre comonómeros. Se ha prestado especial atención a las condiciones para obtener la mesofase y la nueva modificación trigonal. Finalmente, se ha procedido al estudio de algunas propiedades que se han considerado de interés para futuras posibles aplicaciones, haciendo incidencia en su comportamiento mecánico, su caracterización óptica y sus propiedades de transporte. Además, se ha realizado un estudio pionero sobre la estabilidad térmica de los copolímeros de propileno con 1-penteno y 1-hexeno. En general, las propiedades han resultado ser muy sensibles tanto a la cristalinidad total como a la naturaleza de las diversas fases presentes, lo que ha permitido obtener materiales polímeros en un extenso espectro de propiedades, que se pueden modular a voluntad en un amplio intervaloIsotactic polypropylene can be found in an enormous variety of applications, and, consequently, its demand is extraordinary high between those polymers denominated as “commodities”. Requirements of markets joined to expansion of its uses and new environmental policies, among others factors, are underneath the numerous efforts that are being carried out in order to enhance the existing architectures and to design new ones, aiming optimization and expansion of its properties range. The present research work has the final purpose of exploring the possibilities offered by copolymers and terpolymers based on propylene and alpha-olefins of different lengths as comonomers (1-pentene, 1-hexene, and 1-heptene), primarily motivated by the discovery in 2005 of a new crystalline structure (trigonal lattice) in propylene copolymers at high contents of 1-pentene or 1-hexene. For that, different families of propylene-co-1-pentene, propylene-co-1-hexene and propylene-co-1- heptene copolymers have been synthesized in a wide range of comonomer compositions, as well as propylene-co-1-pentene-co-1-hexene and propylene-co-1- pentene-co-1-heptene terpolymers, where the ratio between comonomers has been additionally varied at a given global composition. Moreover, the corresponding homopolymers have been also prepared, namely isotactic polypropylene, poly(1- pentene), poly(1-hexene) and poly(1-heptene). All these numerous materials prepared present sufficiently high molecular weights and high isotacticity, both features ensuring good mechanical performance, as observed. The adequate understanding of the different crystalline structures that can be developed and, consequently, of the final properties exhibited by these materials, required a detailed and thorough evaluation of the microstructure. From that, a random inclusion of the monomers during polymerization has been deduced. In addition, the different existing crystalline lattices, the competence between the various polymorphs and their phase transitions have been studied in detail for the different materials synthesized, as function of composition, crystallization rate and comonomers ratio. Special attention has been paid to the conditions for obtaining the mesophase and the new trigonal modification. Finally, some properties of interest for possible future applications have been studied, especially the mechanical behavior, optical response, and transport properties. In addition, a pioneer study on the thermal stability of propylene copolymers with 1-pentene and 1-hexene has been performed. In general, properties have turned out very sensitive both to the global crystallinity and to the nature of the phases involved, so that polymer materials covering a broad spectra of properties have been obtained and their ultimate performance can be widely tailore

On the Political Determinants of Intergovernmental Grants in Decentralized Countries: The Case of Spain

This paper studies the effect of political variables on the gains obtained by Spanish regions in periodical bargaining of the intergovernmental financing agreements and on the regional distribution of discretional earmarked grants over the period 1987-2008. First, we find that the relationship between gains in transferred revenues and on regional public debt stocks depends on the period and the specific issues discussed in the corresponding negotiation, aside from political affinity. Second, we show that the most discretional program of earmarked grants is strongly driven by electoral strategy. National incumbents tend to allocate intergovernmental transfers where there are competitive regional elections. We also show that earmarked grants are allocated in those regions where the incumbent performs better in national elections and, especially, in those where there are more seats to be won. Hence we prove that both strategies are complementary rather than exclusive.España. Ministerio de Ciencia e Innovación ECO2010-1555

On the econometric estimates of regional spending needs: are they robust enough?

El objetivo de este artículo es identificar y cuantificar econométricamente el impacto de los determinantes de las necesidades de gasto de las Comunidades Autónomas. La combinación de efectos fijos individuales que capturen diferencias interterritoriales no observables en preferencias o eficiencia de gasto, por un lado, con factores determinantes del gasto de escasa variabilidad, por otro, plantea problemas para los estimadores tradicionales. Para solventar esta limitación, se exploran especificaciones econométricas y estimadores alternativos. Los resultados muestran que los coeficientes estimados y su significatividad cambian sustancialmente, por lo que no está claro que puedan garantizar la robustez necesaria para sustentar una discusión política adecuada. Es necesario apostar por otras estrategias para el trabajo empírico que permitan estudiar las preferencias de gasto de las Comunidades Autónomas.The aim of this paper is to identify and quantify econometrically the determinants of the spending needs of the Autonomous Communities. The combination of individual fixed effects that capture unobservable inter-territorial differences in spending preferences or efficiency, on the one hand, with expenditure determinants of low variability, on the other poses problems for traditional estimators. To overcome this limitation, alternative econometric specifications and estimators are explored. The results show that the estimated coefficients and their significance change substantially, not being able to guarantee the necessary robustness to sustain an adequate political discussion. Therefore, it is necessary to bet on other strategies for empirical work that allow us to the spending preferences of the Autonomous Communities

Do political factors affect fiscal consolidation? Evidence from spanish regional governments

This paper empirically examines the political factors behind the different fiscal consolidation paths across Spanish regions over the period 2004 to 2017. Spanish regions provide an interesting case study due to both the strong fiscal decentralization and the deep impact of the so-called “Great Recession” on subcentral budget constraints in Spain. The estimates confirm that governments react to fiscal imbalances by reducing expenditure growth, but this reaction depends on the electoral budget cycle and the results of elections. Fiscal consolidation tends to stop in election years and is boosted by changes in the incumbent. By contrast, neither ideology nor fragmentation of government systematically affects the dynamics of fiscal adjustment.Agencia Estatal de Investigación | Ref. CSO2017-85024-C2-2-

Anticancer applications of nanostructured silica-based materials functionalized with titanocene derivatives: Induction of cell death mechanism through TNFR1 modulation

This article belongs to the Special Issue Nanomaterials for Biomedical ApplicationsA series of cytotoxic titanocene derivatives have been immobilized onto nanostructured silica-based materials using two different synthetic routes, namely, (i) a simple grafting protocol via protonolysis of the Ti-Cl bond; and (ii) a tethering method by elimination of ethanol using triethoxysilyl moieties of thiolato ligands attached to titanium. The resulting nanostructured systems have been characterized by different techniques such as XRD, XRF, DR-UV, BET, SEM, and TEM, observing the incorporation of the titanocene derivatives onto the nanostructured silica and slight changes in the textural features of the materials after functionalization with the metallodrugs. A complete biological study has been carried out using the synthesized materials exhibiting moderate cytotoxicity in vitro against three human hepatic carcinoma (HepG2, SK-Hep-1, Hep3B) and three human colon carcinomas (DLD-1, HT-29, COLO320) and very low cytotoxicity against normal cell lines. In addition, the cells' metabolic activity was modified by a 24-h exposure in a dose-dependent manner. Despite not having a significant effect on TNFalfa or the proinflammatory interleukin 1alfa secretion, the materials strongly modulated tumor necrosis factor (TNF) signaling, even at sub-cytotoxic concentrations. This is achieved mainly by upregulation of the TNFR1 receptor production, something which has not previously been observed for these systems.We gratefully acknowledge financial support from FEDER and the Ministerio de Economía y Competitividad, Spain (grant no. CTQ2015-66164-R) and the Romanian UEFISCDI Exploratory Research Project PN-III-P4-ID-PCE-2016-0870, IMPRESS. We would also like to thank Universidad Rey Juan Carlos and Banco de Santander for supporting our Research Group of Excellence QUINANOAP. Finally, we thank D. Pérez for valuable discussion and S. Carralero and C. Forcé for their assistance with solid-state NMR experiments

Does fiscal consolidation hurt economic growth? Empirical evidence from Spanish regions

This article brings empirical evidence on the effect of fiscal consolidation in decentralized countries. The focus on Spain is justified by three reasons. First, it is one of the OECD countries most affected by the Great recession in terms of both GDP and public deficit. Second, Spain is one of the most decentralized countries in the world. Third, compliance with fiscal consolidation targets has been very diverse across regions. Using both time series econometrics and the Synthetic Control Method approach (SCM), we show that compliance with fiscal targets at the regional level has not involved lower GDP growth rates in the short-run. Openness and economic integration of regional economies involve that fiscal multipliers tend to fade. Hence, while a fiscal stimulus would not work on this scale, the opposite is also true: the potentially negative demand effects of a stronger regional fiscal consolidation strategy would be exported to other regions.Agencia Estatal de Investigación | Ref. CSO2017-85024-C2-2-

Effect of hydrophobic interactions on lower critical solution temperature for poly(N-isopropylacrylamide-co-dopamine methacrylamide) copolymers

For the preparation of thermoresponsive copolymers, for e.g., tissue engineering scaffolds or drug carriers, a precise control of the synthesis parameters to set the lower critical solution temperature (LCST) is required. However, the correlations between molecular parameters and LCST are partially unknown and, furthermore, LCST is defined as an exact temperature, which oversimplifies the real situation. Here, random N-isopropylacrylamide (NIPAM)/dopamine methacrylamide (DMA) copolymers were prepared under a systematical variation of molecular weight and comonomer amount and their LCST in water studied by calorimetry, turbidimetry, and rheology. Structural information was deduced from observed transitions clarifying the contributions of molecular weight, comonomer content, end-group effect or polymerization degree on LCST, which were then statistically modeled. This proved that the LCST can be predicted through molecular structure and conditions of the solutions. While the hydrophobic DMA lowers the LCST especially the onset, polymerization degree has an important but smaller influence over all the whole LCST range.This research was funded by Shenzhen Fundamental Research Funds number KC2014ZDZJ0001A, the Shenzhen Sci & Tech research grant number ZDSYS201507141105130, and the China Postdoctoral Science Foundation Grant number 2018M633119

Hydrogen bonds in blends of poly(N-isopropylacrylamide), poly(n-ethylacrylamide) homopolymers, and carboxymethyl cellulose

Recently, it was reported that the physical crosslinking exhibited by some biopolymers could provide multiple benefits to biomedical applications. In particular, grafting thermoresponsive polymers onto biopolymers may enhance the degradability or offer other features, as thermothickening behavior. Thus, different interactions will affect the different hydrogen bonds and interactions from the physical crosslinking of carboxymethyl cellulose, the lower critical solution temperatures (LCSTs), and the presence of the ions. This work focuses on the study of blends composed of poly(N-isopropylacrylamide), poly(N-ethylacrylamide), and carboxymethyl cellulose in water and water/methanol. The molecular features, thermoresponsive behavior, and gelation phenomena are deeply studied. The ratio defined by both homopolymers will alter the final properties and the gelation of the final structures, showing that the presence of the hydrophilic groups modifies the number and contributions of the diverse hydrogen bonds.The authors want to acknowledge the funding obtained from the National Science Foundation of China (21574086), Shenzhen Fundamental Research Funds (No. KC2014ZDZJ0001A), Shenzhen Sci & Tech research grant (ZDSYS201507141105130), and China Postdoctoral Science Foundation Grant (2018M633119)

Preparation, thermoresponsive behavior, and preliminary biological study of functionalized poly(N-isopropylacrylamide-co-dopamine methacrylamide) copolymers with an organotin(IV) compound

Recent advances focused on smart polymers have demonstrated the numerous advantages regarding other structures because they can adapt the behavior depending on physicochemical properties. In this way, functionalized thermoresponsive polymers with organometallic complexes were profoundly analyzed. Consequently, novel catalytic systems or biomedical devices could be developed. This publication focuses on the facile preparation of poly(N-isopropylacrylamide-co-dopamine methacrylamide) copolymers functionalized with triphenyltin chloride by protonolysis through the -OH of catechol groups. The presence of hydrophobic organotin(IV) derivatives could modify the solubility, thermoresponsive behavior, and other properties regarding pure copolymers. Also, sensitive analysis of the microstructure could help to understand the changes associated with the lower critical solution temperature by rheology, UV-vis spectroscopy, and calorimetry. In addition, a preliminary biological study against MDA-MB-231 cancer cells and peripheral blood mononuclear cells showed that the functionalized copolymers could be a potential platform to be explored in the future in the fight against cancer.The financial support obtained from the National Science Foundation of China (21574086), Shenzhen Fundamental Research Funds (No. KC2014ZDZJ0001A), Shenzhen Sci & Tech research grant (ZDSYS201507141105130) and China Postdoctoral Science Foundation Grant (2018M633119) are acknowledged. Also, these researchers would like to thank the former Ministerio de Ciencia, Innovación y Universidades of Spain (current Ministerio de Ciencia e Innovación of Spain) for the grant RTI2018-094322-B-I00 and the Dirección General de Investigación e Innovación, Consejería de Educación e Investigación de la Comunidad de Madrid for the predoctoral grant PEJD-2017-PRE/BMD-3512 (I. M.-P.)