Five generations of nitroxyl-functionalized dendrimers

The prepn. and ESR spectroscopy of a series of fully functionalized poly(propylenimine) dendrimers (DAB-dendr-(NH2)n; n = 2, 4, 8, 16, 32, 64) with 3-carboxy-PROXYL radical end groups is described. The pendant nitroxyl end groups exhibit a strong exchange interaction. As a consequence, the ESR spectrum directly reveals the no. of end groups from the splitting between the hyperfine transitions for the lower generations. For the higher generations an increasingly exchanged-narrowed ESR spectrum is obsd. The temp. and solvent dependency of the exchange interaction is used to assess the dynamic behavior of the dendritic branches. FT-IR spectroscopy shows that a hydrogen-bonded network between the amide functionalities is present, consistent with the obsd. solvent effect on the ESR spectr

Toughening and healing of continuous fibre reinforced composites by supramolecular polymers

\u3cp\u3eInterleaves comprising self-healing materials based on hydrogen bonded supramolecular polymers (SP) were successfully incorporated in the mid-plane of unidirectional (UD) carbon fibre reinforced polymers (CFRPs). The fracture toughness of these hybrid composites and their healing capability were measured under mode I loading. The fracture toughness appeared to have increased considerably since the maximum load (P\u3csub\u3emax\u3c/sub\u3e) of the hybrid composite had increased approximately 5 times, and the fracture energy I (G\u3csub\u3eIC\u3c/sub\u3e) displayed a dramatic increase by almost one order of magnitude when compared to the reference composite without the SP. Furthermore, the double cantilever beam (DCB) hybrid composites displayed a healing efficiency (H.E.) value for the mode I interlaminar characteristics around 60% for the P\u3csub\u3emax\u3c/sub\u3e and the G\u3csub\u3eIC\u3c/sub\u3e after the first healing cycle, dropping to 20-30% after the seventh cycle. During the mode I interlaminar fracture toughness tests the acoustic emission (AE) activity of the samples was also monitored. It was found that AE-activity strongly reduced due to the presence of the SP. Moreover, optical microscopy not only showed that the epoxy matrix at the interface is partly infiltrated by the SP, but it also revealed that cross-sections of both fractured surfaces were covered with the SP comprising pulled-out carbon fibres, indicating a strong interfacial adhesion. Finally it was shown that the SP fractured surfaces were partially covered with pulled-out carbon fibres emanating from the edges of the SP film in which the epoxy system exists.\u3c/p\u3

Supramolecular polypropylene with self-complementary hydrogen bonding system

\u3cp\u3eNovel supramolecular polypropylenes (PP) having self-complementary quadruple hydrogen bonding 2-ureido-4[1H]-pyrimidinone (UPy) groups (UPy-PP) have been synthesized by functionalizing of PP. The mechanical properties donated by the network structure formed by the multiple hydrogen bonding were studied with rheological analyses and tensile tests of the UPy-PP. Unusual melt viscosity of the UPy-PP indicated that the hydrogen bonding network of the UPy was maintained in the solid state at ambient temperature whereas the hydrogen bonding was dissociated in the melting PP matrix at high temperatures of around 190 °C. Tensile tests showed that the elongation at break of the UPy-PP drastically increased at higher temperatures compared to that of non-functionalized PP (nf-PP). The results indicated that a pseudo-high molecular weight PP was easily obtained through the UPy hydrogen bonding aggregation of low molecular weight PP. These findings are applicable to improving the mechanical properties of various nonpolar polyolefins by introducing self-complementary quadruple hydrogen bonding groups as a thermal reversible network system.\u3c/p\u3

Multi-component supramolecular fibers with elastomeric properties and controlled drug release

\u3cp\u3eSupramolecular materials based on hydrogen bonding ureido-pyrimidinones (UPy) are highly versatile substrates for tissue engineering, as they provide a platform in which specific functions can be introduced in a modular fashion by means of components with matching supramolecular motifs. In this work, a core-shell fiber mesh is generated by coaxial electrospinning of a robust elastomeric UPy-poly(hexamethylene carbonate) (UPy-PC) core with a hydrophilic shell of poly(ethylene glycol) (UPy-PEG), which is exploited to confer drug release properties to the load-bearing core. The effect of PEG chain length and supramolecular crosslink density on mechanical properties and drug elution profiles is investigated. Hydrated UPy-PC/UPy-PEG meshes containing 30 mol% of UPy-PEG have a Young's modulus matching that of UPy-PC meshes of approximately 0.5 MPa, and elongation at break of 600%. Drug release experiments with low molecular weight drugs encapsulated in the UPy-PEG shell during electrospinning reveal a combined role of drug and matrix hydrophilicity on the elution profile. Our results indicate that a hydrophobic drug is retained in the UPy-PEG shell for several days with a maximum drug release of 56 ± 8% after 14 days, a highly water soluble drug undergoes burst release within one day, and the UPy-modification of a highly water soluble compound increases its retention in the UPy-PEG shell up to multiple weeks. Taken together, our results indicate that the proposed multi-component system is a drug delivery vehicle of excellent versatility for applications requiring strong and durable materials.\u3c/p\u3

A multi-O\u3csub\u3e2\u3c/sub\u3e complex derived from a copper(I) dendrimer

\u3cp\u3eThe high-pressure reaction of 2-vinylpyridine with the primary amines of four consecutive generations of poly(propylene imine) dendrimers (DAB-dendr- (NH\u3csub\u3e2\u3c/sub\u3e)(n)) (n = 4, 8, 16, 32) yielded dendrimers with bis[2-(2- pyridyl)ethyl]-amine (PY2) ligands. The complexation of the new dendrimers with metal ions was investigated by a variety of techniques. The reaction of the first- and fourth-generation dendrimers (n=4 and 32, respectively) with Zn(II)(ClO\u3csub\u3e4\u3c/sub\u3e)\u3csub\u3e2\u3c/sub\u3e was studied by \u3csup\u3e1\u3c/sup\u3eH NMR titration, and the complexation of all new dendrimers with Cu(II)(ClO\u3csub\u3e4\u3c/sub\u3e)\u3csub\u3e2\u3c/sub\u3e was investigated by UV/Vis and EPR spectroscopy. Quantitative coordination of one metal ion per PY2 group was demonstrated in all cases. A UV/Vis titration of the fourth-generation dendrimer DAB-dendr-(PY2)\u3csub\u3e32\u3c/sub\u3e in dichloromethane with [Cu(I)(CH\u3csub\u3e3\u3c/sub\u3eCN)\u3csub\u3e4\u3c/sub\u3e](ClO\u3csub\u3e4\u3c/sub\u3e) in acetonitrile revealed that approximately 30 Cu(I) ions were bound. Low-temperature UV/Vis spectroscopy of this complex in dichloromethane at -85°C in the presence of dioxygen showed that approximately 60-70% of the copper centers can bind dioxygen, corresponding to 10-11 of these molecules per dendrimer molecule. This complex can be considered a synthetic analogue of hemocyanin, the copper-containing oxygen transport protein from the hemolymph of molluscs and arthropods.\u3c/p\u3

Terminal Terrestre Yerbateros como regenerador urbano

Elabora una investigación en torno al transporte terrestre interprovincial que llega y sale de Lima, que permita diseñar un terminal con la capacidad de descongestionar la zona intervenida, mediante el agrupamiento de empresas transportistas y el ordenamiento de sus flujos vehiculares. Además, se busca comprender las necesidades básicas para garantizar el buen funcionamiento del terminal y su activación mediante la implementación de características intermodales y usos complementarios. Finalmente, se analizarán las condicionantes y problemáticas de la zona para comprender la posibilidad de regeneración y beneficios que brindaría un diseño enfocado hacia el peatón mediante la implementación de espacio público

Crowned dendrimers : pH-responsive pseudorotaxane formation

With the end goal of incorporating the unique structural and phys. properties of dendrimers into supramol. assemblies, bis(m-phenylene)-32-crown-10-functionalized poly(propyleneimine) dendrimers of the first and third generations have been synthesized and their interaction with paraquat diol has been investigated. Using 1H NMR, we detd. that binding to the 4 or 16 crown ether sites occurred in an anti-cooperative fashion, most likely a result of steric influences. Upon protonation of the tertiary amines in the dendritic interior, binding became independent, i.e., statistical, and the av. apparent assocn. const. increased by nearly 5-fold; this effect is attributed to rigidification of the dendrimer, which makes its binding sites more accessible and less crowded

Self-healing supramolecular polymers in action

\u3cp\u3eSophisticated polymeric materials with responsive properties, such as self-healing, are beginning to reach the market. Supramolecular polymers, i.e., polymers that owe their mechanical properties primarily to the reversible, non-covalent interactions, such as hydrogen bonding interactions, between the macromolecules, have frequently been employed as self-healing materials. The quadruple hydrogen bonding ureidopyrimidinone (UPy) unit is a particularly effective and versatile design motif, since it forms very strong but reversible linkages, and can be incorporated into virtually any type of polymer backbone, leading to materials with increased mechanical properties. Supramolecular polymers are presented, with an emphasis on those based on the UPy-unit, and their use in self-healing applications is highlighted and discussed. Supramolecular polymers are eminently useful in self-healing applications. The reversible nature of supramolecular polymers allows for self-healing processes to take place, using a contact pressure trigger or a heat trigger. Several materials are presented with an emphasis on ureidopyrimidinone (UPy) comprising supramolecular polymer.\u3c/p\u3

Novel supramolecular block copolymer of isotactic polypropylene and ethylene-co-propylene connected by complementary quadruple hydrogen bonding system

\u3cp\u3eSupramolecular block copolymers comprising isotactic polypropylene (iPP) and ethylene-propylene random copolymers (EP) with complementary quadruple hydrogen bonding junctions have been prepared by melt-mixing of iPP having a 2-ureido-4[1H]-pyrimidinone (UPy) group (iPP-UPy) and elastic EP bearing a 2,7-diamido-1,8-naphthyridine (Napy) group (EP-Napy). Transmission electron microscope (TEM) analysis of the iPP-UPy/EP-Napy composite showed that the elastic EP domains were well dispersed in the iPP matrix compared with the traditional iPP/EP impact polypropylene copolymer (IPC). The iPP-UPy/EP-Napy hydrogen-bonded pseudo block copolymer effectively acts as a compatibilizer in the IPC and contributes to improved mechanical properties of the resulting iPP/EP composite. There is good correlation between impact strength of the IPC and EP domain size observed by the TEM analysis. The use of the complementary quadruple hydrogen bonding system for blending two immiscible polymers has been shown to result in smaller domain sizes of the EP-phase in the iPP and consequently improved mechanical properties of the supramolecular iPP/EP blends.\u3c/p\u3