Lucas Montero de Espinosa

Renewable Polyethylene Mimics Derived from Castor Oil

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.

A new approach for modular polymer–polymer conjugations via Heck coupling

Heck coupling reactions are introduced as a modular, very efficient and highly orthogonal method for polymer–polymer conjugation. Several diblock and triblock copolymers (5200 Da ≤ Mn ≤ 17300 Da, 1.08 ≤ PDI ≤ 1.33) were prepared via Heck coupling reactions of acrylate-terminated and aryliodide-terminated polymers. The coupling reactions were performed using the so-called Jefferys conditions, which allowed the use of equimolar amounts of reacting polymers and low reaction temperatures. Acrylated poly(ethylene glycol) monomethyl ether (PEG), poly(e-caprolactone) (PCL) and polymers synthesized via head-to-tail selective acyclic diene metathesis (ADMET) polymerisation have been successfully conjugated with both a PEG and PCL containing an aryliodide moiety.

Olefin Metathesis of Renewable Platform Chemicals

Olefinic double bonds are often found in the structure of natural compounds. This makes olefin metathesis a powerful tool for their transformation into valuable renewable platform chemicals and, in some cases, directly for targeted chemical products. Natural products display many different structures and functional groups, which in some cases challenge catalyst performance. In this respect, new catalysts with improved performance are constantly developed providing new application possibilities. This chapter covers the research performed in the field of olefin metathesis with renewable chemicals, starting from the early days of this chemical reaction to the present situation. Special attention is given to renewables naturally containing double bonds, like oleochemicals or terpenes. On the other hand, the introduction of double bonds in the structure of non-olefinic renewables, such as carbohydrates, amino acids, or peptides, and their use as olefin metathesis substrates are discussed. This chapter is subdivided in two main parts covering the synthesis of platform chemicals and the synthesis of polymers, respectively.

Sulfur-containing fatty acid-based plasticizers via thiol–ene addition and oxidation: synthesis and evaluation in PVC formulations

A new family of sulfur-containing plasticizers derived from fatty acids has been developed. The synthetic approach is based on the thiol–ene addition of alkyl thiols to the double bond of technical oleic acid, followed by oxidation of the sulfide group to either sulfoxide or sulfone groups. It has been found that both sulfide and sulfoxide derivatives are not suitable as plasticizers due to their unpleasant odor and limited thermal stabilities. However, the sulfone derivatives are odorless, thermally stable, and show plasticizing properties similar to those of established PVC plasticizers such as cyclohexane-1,2-dicarboxylic acid diisononyl ester (ELATUR® CH) and diisononyl phthalate (VESTINOL® 9). A wide range of application tests is reported to support this conclusion. Furthermore, a mixture of fatty acids obtained from commercial rapeseed oil has been used as a cheap and readily available alternative source of oleic acid to obtain such plasticizers.

Acyclic Diene Metathesis Polymerization and Heck Polymer–Polymer Conjugation for the Synthesis of Star‐shaped Block Copolymers

Three- and four-arm star shaped polymers, as well as diblock copolymers, are synthesized via acyclic diene metathesis (ADMET) polymerization. This is accomplished by using an asymmetric α,ω-diene containing a terminal double bond and an acrylate, which is polymerized in the presence of multifunctional acrylates as selective and irreversible chain transfer agents using Hoveyda-Grubbs second generation catalyst. High cross-metathesis selectivities are achieved at low temperatures enabling good control over molecular weights. Furthermore, additional polyethyleneglycol (PEG) blocks are attached to these polymers via Heck coupling of the acrylate end-groups of these polymers with aryl iodide functionalized PEG, obtaining three- and four-arm star shaped di- and triblock copolymers with molecular weights up to 31 kDa.

Side‐Chain Modification and “Grafting Onto” via Olefin Cross‐Metathesis

Olefin cross-metathesis is introduced as a versatile polymer side-chain modification technique. The reaction of a poly(2-oxazoline) featuring terminal double bonds in the side chains with a variety of functional acrylates has been successfully performed in the presence of Hoveyda-Grubbs second-generation catalyst. Self-metathesis, which would lead to polymer-polymer coupling, can be avoided by using an excess of the cross-metathesis partner and a catalyst loading of 5 mol%. The results suggest that bulky acrylates reduce chain-chain coupling due to self-metathesis. Moreover, different functional groups such as alkyl chains, hydroxyl, and allyl acetate groups, as well as an oligomeric poly(ethylene glycol) and a perfluorinated alkyl chain have been grafted with quantitative conversions.

About the activity and selectivity of less well-known metathesis catalysts during ADMET polymerizations

Summary 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.

Chemometric resolution of NIR spectra data of a model aza-Michael reaction with a combination of local rank exploratory analysis and multivariate curve resolution-alternating least squares (MCR-ALS) method.

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.