RESUMEN

Nanocomposites consisting of a polymer matrix and metallic nanoparticles can merge the functional, structural, and mechanical properties of the two components and are useful for applications that range from catalysis to soft electronics. Gaining spatial control over the nanoparticle incorporation is useful, for example to confine catalytic sites or create electrically conducting pathways. Here, we show that this is possible by the controlled disassembly of a metallosupramolecular polymer containing zerovalent platinum complexes to form nanoparticles in situ. To achieve this, a telechelic poly(ethylene-co-butylene) was end-functionalized with diphenylacetylene ligands and chain-extended through the formation of bis(η2-alkyne)Pt0 complexes. These complexes are stable at ambient conditions, but they can be dissociated upon heating or exposure to ultraviolet light, which allows producing Pt nanoparticles when and where needed and without auxiliary reagents or formation of byproducts. This approach was exploited to create objects with well-defined catalytically active areas.

RESUMEN

A modular approach for the design of two-component supramolecular polymer (SMP) networks is reported. A series of materials was prepared by blending two (macro)monomers based on trifunctional poly(propylene oxide) (PPO) cores that were end-functionalized with hydrogen-bonding 2-ureido-4[1H]pyrimidinone (UPy) groups. One monomer was based on a PPO core with a number-average molecular weight (Mn) of 440 g mol-1. The SMP formed by this building block is a glassy, brittle material with a glass transition temperature (Tg) of about 86 °C. The second monomer featured a PPO core with an Mn of 3000 g mol-1. The SMP formed by this building block adopts a microphase-segregated morphology that features a rubbery phase with a Tg of -58 °C and crystalline domains formed by the UPy assemblies, which act as physical cross-links and melt around 90-130 °C. Combining the two components allows access to microphase-segregated blends comprised of a rubbery phase constituted by the high-Mn cores, a glassy phase formed by the low-Mn component, and a crystalline phase formed by UPy groups. This allowed tailoring of the mechanical properties and afforded materials with storage moduli of 37-609 MPa, tensile strengths of 2.0-5.4 MPa, and melt viscosities of as low as 11 Pa s at 140 °C. The materials can be used as reversible adhesives.

RESUMEN

Materials with switchable mechanical properties are widespread in living organisms and endow many species with traits that are essential for their survival. Many of the mechanically morphing materials systems found in nature are based on hierarchical structures, which are the basis for mechanical robustness and often also the key to responsive behavior. Many "operating principles" involve cascades of events that translate cues from the environment into changes of the overall structure and/or the connectivity of the constituting building blocks at various levels. These concepts permit dramatic property variations without significant compositional changes. Inspired by the function and the growing understanding of the operating principles at play in biological materials with the capability to change their mechanical properties, significant efforts have been made toward mimicking such architectures and functions in artificial materials. Research in this domain has rapidly grown in the last two decades and afforded many examples of bioinspired materials that are able to reversibly alter their stiffness, shape, porosity, density, or hardness upon remote stimulation. This review summarizes the state of research in this field.

Asunto(s)

RESUMEN

We report a new series of supramolecular polymeric networks based on the isophthalic acid-pyridine (IPA-Py) H-bonding motif. The IPA units were attached as end-groups to telechelic poly(ethylene-co-butylene) to create a tetrafunctional macromonomer, which was cross-linked by the addition of various bispyridines. Some of the supramolecular polymer networks thus made display surprisingly good mechanical characteristics. We show that their structure and properties are strongly influenced by the nature of the bispyridine motif and by the fact that some of the IPA-Py motifs aggregate into particularly well-defined hard phases.

RESUMEN

An increasing number of reports on the syntheses of carbohydrate- and plant oil-based polymers has been published in ongoing efforts to produce plastic materials from renewable resources. Although many of these polymers are biodegradable and this is a desirable property for certain applications, in some cases non-degradable polymers are needed for long-term use purposes. Polyolefins are one of the most important classes of materials that have already taken their places in our daily life. On the other hand, their production relies on fossil resources. Therefore, within this contribution, we discuss synthetic routes toward a number of polyethylene mimics derived from fatty acids via thiol-ene and ADMET polymerization reactions in order to establish more sustainable routes toward this important class of polymers. Two different diene monomers were thus prepared from castor oil derived platform chemicals, their polymerization via the two mentioned routes was optimized and compared to each other, and their thermal properties were investigated.

Asunto(s)

RESUMEN

Control over molecular architectures obtained via ADMET polymerization is limited by the step-growth nature of this technique. A new approach to this polycondensation method is described allowing for the synthesis of diblock and star-shaped polymers with molecular weight control by using the selectivity of olefin cross-metathesis between acrylates and terminal olefins.

RESUMEN

Two decades have passed since the metathesis polymerisation of α,ω-dienes was successfully demonstrated by the group of Wagener and the term acyclic diene metathesis (ADMET) polymerisation was coined. Since then, the advances of metathesis chemistry have allowed to expand the scope of this versatile polymerisation reaction that nowadays finds applications in different fields, such as polymer, material, or medicinal chemistry. This critical review provides an insight into the historical aspects of ADMET and a detailed overview of the work done to date applying this versatile polymerisation reaction (221 references).

RESUMEN

We report on the catalytic activity of commercially available Ru-indenylidene and "boomerang" complexes C1, C2 and C3 in acyclic diene metathesis (ADMET) polymerization of a fully renewable α,ω-diene. A high activity of these catalysts was observed for the synthesis of the desired renewable polyesters with molecular weights of up to 17000 Da, which is considerably higher than molecular weights obtained using the same monomer with previously studied catalysts. Moreover, olefin isomerization side reactions that occur during the ADMET polymerizations were studied in detail. The isomerization reactions were investigated by degradation of the prepared polyesters via transesterification with methanol, yielding diesters. These diesters, representing the repeat units of the polyesters, were then quantified by GC-MS.

RESUMEN

The aza-Michael reaction, a variation of the Michael reaction in which an amine acts as the nucleophile, permits the synthesis of sophisticated macromolecular structures with potential use in many applications such as drug delivery systems, high performance composites and coatings. The aza-Michael product can be affected by a retro-Mannich-type fragmentation. A way of determining the reactions that are taking place and evaluate the quantitative evolution of the chemical species involved in the reactions is presented. The aza-Michael reaction between a modified fatty acid ester with alpha,beta-unsaturated ketone groups (enone containing methyl oleate (eno-MO)) and aniline (1:1) was studied isothermally at 95 degrees C and monitored in situ by near-infrared spectroscopy (NIR). The number of reactions involved in the system was determined analyzing the rank matrix of NIR spectra data recorded during the reaction. Singular value decomposition (SVD) and evolving factor analysis (EFA) adapted to analyze full rank augmented data matrices have been used. In the experimental conditions, we found that the resulting aza-Michael adduct undergoes a retro-Mannich-type fragmentation, but the final products of this reaction were present in negligible amounts. This was confirmed by recording the (1)H NMR spectra of the final product. Applying multivariate curve resolution-alternating least squares (MCR-ALS) to the NIR spectra data obtained during the reaction, it has been possible to obtain the concentration values of the species involved in the aza-Michael reaction. The performance of the model was evaluated by two parameters: ALS lack of fit (lof=1.31%) and explained variance (R(2)=99.92%). Also, the recovered spectra were compared with the experimentally recorded spectra for the reagents (aniline and eno-MO) and the correlation coefficients (r) were 0.9997 for the aniline and 0.9578 for the eno-MO.