Gerard Lligadas

Plant Oils as Platform Chemicals for Polyurethane Synthesis: Current State-of-the-Art

Plant oils are already one of the most important platform chemicals for the chemical industry due to its universal availability, inherent biodegradability, and low price. Nowadays, plant oils are already a commercial source of multifunctional monomers and oligomers for polyurethane synthesis, and the design of novel biobased polyols derived from them is an active area of research. By taking advantage of the wide variety of possibilities for chemical modification of plant oils, there is a broad palette of strategies to functionalize its structure with hydroxyl groups. The purpose of this review is to comprehensively overview recent developments on the preparation of biobased polyols from plant oils, covering from the general epoxidation and ring-opening approach to novel routes based on thiol-ene click chemistry as well as to highlight the properties of polyurethanes obtained from them.

Polybenzoxazines: new players in the bio-based polymer arena

Polybenzoxazines are phenol-like materials that have attracted significant attention from both academia and industry because of their unique advantages. The growth of this technology has always been linked to petro-based feedstocks. However, due to the incessant global energy crisis it is now finding a breakthrough through the preparation of their monomers from renewable resources. This mini-review focuses on the recent efforts to replace petro-based feedstocks with polybenzoxazine precursors.

Recent Developments in the Synthesis of Biomacromolecules and their Conjugates by Single Electron Transfer–Living Radical Polymerization

Single electron transfer-living radical polymerization (SET-LRP) represents a robust and versatile tool for the synthesis of vinyl polymers with well-defined topology and chain end functionality. The crucial step in SET-LRP is the disproportionation of the Cu(I)X generated by activation with Cu(0) wire, powder, or nascent Cu(0) generated in situ into nascent, extremely reactive Cu(0) atoms and nanoparticles and Cu(II)X2. Nascent Cu(0) activates the initiator and dormant chains via a homogeneous or heterogeneous outer-sphere single-electron transfer mechanism (SET-LRP). SET-LRP provides an ultrafast polymerization of a plethora of monomers (e.g., (meth)-acrylates, (meth)-acrylamides, styrene, and vinyl chloride) including hydrophobic and water insoluble to hydrophilic and water soluble. Some advantageous features of SET-LRP are (i) the use of Cu(0) wire or powder as readily available catalysts under mild reaction conditions, (ii) their excellent control over molecular weight evolution and distribution as well as polymer chain ends, (iii) their high functional group tolerance allowing the polymerization of commercial-grade monomers, and (iv) the limited purification required for the resulting polymers. In this Perspective, we highlight the recent advancements of SET-LRP in the synthesis of biomacromolecules and of their conjugates.

Thiol–yne reaction of alkyne-derivatized fatty acids: biobased polyols and cytocompatibility of derived polyurethanes

With the goal of obtaining renewable diols and polyols for polyurethane (PU) technology, the thiol–yne coupling reaction was applied to alkyne-derivatized fatty acids derived from naturally occurring oleic and 10-undecenoic acids. The resulting monomers were then polymerized with 4,4′-methylenebis(phenylisocyanate) to produce the corresponding PUs. The chemical structures and thermal and mechanical properties of the synthesized PUs have been evaluated by FTIR and NMR spectroscopy, DSC, TGA and tensile tests respectively. Moreover, the biocompatibilities of the synthesized PUs with human osteoblast-like cell line (MG63) have also been evaluated for tissue engineering purposes.

“Click” Synthesis of Fatty Acid Derivatives as Fast-Degrading Polyanhydride Precursors

Fast-degrading linear and branched polyanhydrides are obtained by melt-condensation of novel di- and tri-carboxylic acid monomers based on oleic and undecylenic acid synthesized using photoinitiated thiol-ene click chemistry. (1)H NMR spectroscopy, size exclusion chromatography, differential scanning calorimetry, thermogravimetric analysis, and FT-IR spectroscopy have been used to fully characterize these polymers. The hydrolytic degradation of these polymers was studied by means of weight loss, anhydride bond loss, and changes in molecular weight, showing fast degrading properties. Drug release studies from the synthesized polyanhydrides have also been conducted, using rhodamine B as a hydrophobic model drug, to evaluate the potential of these polymers in biomedical applications.

Convenient and solventless preparation of pure carbon nanotube/polybenzoxazine nanocomposites with low percolation threshold and improved thermal and fire properties

This work contemplates the use of pristine multiwalled carbon nanotubes (MWNTs) as nanofillers in the preparation of bisphenol A-based polybenzoxazine and diphenolic acid derived polybenzoxazine. These materials were prepared by using a solventless method varying the MWNT amount from 0.1 to 1.0 wt%. MWNTs were found to disperse well within both benzoxazine monomers and the dispersion also appears to be good in the cured system. Rheological and electrical percolation thresholds were obtained for MWNT concentrations lower than 0.1 wt% indicating the existence of good affinity between MWNTs and polybenzoxazine matrices. The characterization of the resulting nanocomposites revealed that MWNTs affected polybenzoxazines differently. The limiting oxygen index of the nanocomposites increased as a function of the nanotube content, from 35.2 to 38.7 for a bisphenol A-benzoxazine based system (BPA-PBz) and from 31.2 to 37.4 for a methyl-4,4′-bis-[6-(3-phenyl-3,4-dihydro-2H-1,3-benzoxazine)]pentanoate based system (MDP-PBz), respectively. Moreover, MWNTs positively influenced the thermo-mechanical, thermal and mechanical properties of the nanocomposites. The resulting attractive properties have been attributed to good interaction between the polybenzoxazines and the finely dispersed nanofillers.

Single-Electron Transfer Living Radical Polymerization Platform to Practice, Develop, and Invent

The most fundamental aspects of single-electron transfer (SET) principles are presented. They are discussed according to different definitions used by expert practitioners and are applied to SET living radical polymerization (SET-LRP) according to the definition of the division of organic chemistry of IUPAC that relies on principles elaborated by Taube, Eberson, Chanon, and Kochi. Additional definitions are also discussed to help clarify for the nonexpert contradictory literature reports. Subsequently, the principles and evolution of SET-LRP together with the methodologies currently available to practice it are discussed. It is expected that this Perspective will be able to help experts and nonexperts practice, develop, and invent new concepts and methodologies for SET-LRP to advance its status and the status of other living radical polymerization methods to the level of the most precise living polymerization methods.

Searching for efficient SET-LRP systems via biphasic mixtures of water with carbonates, ethers and dipolar aprotic solvents

The recently developed “programmed” water/organic solvent biphasic reaction medium is the most efficient approach to expand the advantages of SET-LRP to next generation solvents and to enhance the performance of the current solvents employed in this polymerization methodology. This system has been successfully applied to families of solvents not accessible so far by SET-LRP such as polar and nonpolar non-disproportionation solvents. Here we report a series of screening experiments on biphasic mixtures of water with linear diethyl and dimethyl carbonates, cyclic propylene and ethylene carbonates, the cyclic ethers THF and dioxane, and with dipolar aprotic solvents. Two general methodologies were applied in the catalytic process: the accelerated “multicomponent” Cu(0) generated by the in situ reduction of Cu(II)Br2 with NaBH4 and the “single component” Cu(0) wire. All carbonates and ethers provide linear kinetic SET-LRP experiments when solvent/water = 8/2, v/v were used while under the same conditions dipolar aprotic solvents increased their apparent rate constant of polymerization up to about 3.5 times from the values obtained in the absence of water. These remarkable results demonstrate the power of the biphasic water/organic solvent mixture to the elaboration of new solvent systems for SET-LRP.

SET-LRP mediated by TREN in biphasic water–organic solvent mixtures provides the most economical and efficient process

Tris(2-aminoethyl)amine (TREN) has been used as a replacement for tris(dimethylaminoethyl)amine (Me6-TREN) in the non-activated Cu(0) wire catalyzed SET-LRP of methyl and n-butyl acrylates performed in biphasic-binary mixtures containing an aqueous solution of Cu(II)Br2 and a ligand with water miscible or water immiscible organic solvents containing a monomer and a polymer. Dipolar aprotic solvents (DMF, DMSO, NMP, DMAc and sulfolane), cyclic carbonates (ethylene carbonate and propylene carbonate), cyclic ethers (THF and dioxane), alcohols (methanol, ethanol, and isopropanol), acetone, acetonitrile and 2-butanone were used as water soluble solvents while hexane, anisole, toluene and ethyl acetate were used as water insoluble solvents. The chain end functionality of the resulting polymers is close to 100%. All reagents used in this process including the ligand, the Cu(0) wire catalyst, the solvent and Cu(II)Br2 are air insensitive, and can be recycled and reused. In addition, since TREN is 80 times less expensive than Me6-TREN and some of these solvents are the least expensive commercial solvents available, we expect that this methodology, which most probably is the most economical and efficient metal-catalyzed living radical polymerization, can be transplanted to a continuous process of interest for technological applications.

Polyketoesters from oleic acid. Synthesis and functionalization

In this study, we exploited the reactivity of the methyl oleate enone derivative for the conversion of this renewable raw material to ketone-containing hydroxyesters. The radical-mediated thiol–ene addition to the conjugated double bonds has been investigated and low yields were obtained due to secondary reactions. The thiol-Michael addition under acidic and basic/nucleophilic conditions was also examined. While using vanadyl triflate (VO(OTf)2), a slight excess of thiol was necessary to complete the reaction, by using both basic/nucleophilic catalysts 1,5-diazabicyclo[4.3.0]non-5-ene (DBN) and 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU), quantitative conversion was achieved under stoichiometric conditions in shorter reaction times. The obtained hydroxyester, carrying sulphide and ketone functional groups, was used to obtain polyesters by Novozyme-435 enzymatic polymerization. The coupling between the ketone group of the repeating unit and a model oxyamine has been used to demonstrate the polyketoester functionalization via oxime formation.