Breathable Lignin Nanoparticles as Reversible Gas Swellable Nanoreactors.

The design of stimuli-responsive lignin nanoparticles (LNPs) for advanced applications has hitherto been limited to the preparation of lignin-grafted polymers in which usually the lignin content is low (<25 wt.%) and its role is debatable. Here, the preparation of O2 -responsive LNPs exceeding 75 wt.% in lignin content is shown. Softwood Kraft lignin (SKL) is coprecipitated with a modified SKL fluorinated oleic acid ester (SKL-OlF) to form colloidal stable hybrid LNPs (hy-LNPs). The hy-LNPs with a SKL-OlF content ranging from 10 to 50 wt.% demonstrated a reversible swelling behavior upon O2 /N2 bubbling, increasing their size - ≈35% by volume - and changing their morphology from spherical to core-shell. Exposition of hy-LNPs to O2 bubbling promotes a polarity change on lignin-fluorinated oleic chains, and consequently their migration from the inner part to the surface of the particle, which not only increases the particle size but also endows hy-LNPs with enhanced stability under harsh conditions (pH < 2.5) by the hydration barrier effect. Furthermore, it is also demonstrated that these new stimuli-responsive particles as gas tunable nanoreactors for the synthesis of gold nanoparticles. Combining a straightforward preparation with their enhanced stability and responsiveness to O2 gas these new LNPs pave the way for the next generation of smart lignin-based nanomaterials.

Biosourced All-Acrylic ABA Block Copolymers with Lactic Acid-Based Soft Phase.

Lactic acid is one of the key biobased chemical building blocks, given its readily availability from sugars through fermentation and facile conversion into a range of important chemical intermediates and polymers. Herein, well-defined rubbery polymers derived from butyl lactate solvent were successfully prepared by reversible addition-fragmentation chain transfer (RAFT) polymerization of the corresponding monomeric acrylic derivative. Good control over molecular weight and molecular weight distribution was achieved in bulk using either monofunctional or bifunctional trithiocarbonate-type chain transfer agents. Subsequently, poly(butyl lactate acrylate), with a relative low Tg (-20 °C), good thermal stability (5% wt. loss at 340 °C) and low toxicity was evaluated as a sustainable middle block in all-acrylic ABA copolymers using isosorbide and vanillin-derived glassy polyacrylates as representative end blocks. Thermal, morphological and mechanical properties of copolymers containing hard segment contents of <20 wt% were evaluated to demonstrate the suitability of rubbery poly(alkyl lactate) building blocks for developing functional sustainable materials. Noteworthy, 180° peel adhesion measurements showed that the synthesized biosourced all-acrylic ABA copolymers possess competitive performance when compared with commercial pressure-sensitive tapes.

Dual Biochemically Breakable Drug Carriers from Programmed Telechelic Homopolymers.

Well-defined hydrophilic telechelic dibromo poly(triethylene glycol monomethyl ether acrylate)s were prepared by single-electron transfer living radical polymerization employing a hydrophobic difunctional initiator containing acetal and disulfide linkages. Although the resulting homopolymers have low hydrophobic contents (<8.5 wt % of the entire structure), they are able to self-assemble in water into nanoscale micellelike particles via chain folding. Acetal and disulfide linkages were demonstrated to be "keystone" units for their dual stimuli-responsive behavior under biochemically relevant conditions. Their site-selective middle-chain cleavage under both acidic pH and reductive conditions splits the homopolymer into two equal-sized fragments and results in the breakdown of the nanoassemblies. The drug loading/delivery potential of these nanoparticles was investigated using curcumine combining in vitro drug release, cytotoxicity, and cellular uptake studies with human cancer cell lines (HT-29 and HeLa). Importantly, this strategy may be extended to prepare innovative nanoplatforms based on hydrophilic homopolymers or random copolymers for intelligent drug delivery.

SET-LRP from Programmed Difunctional Initiators Encoded with Double Single-Cleavage and Double Dual-Cleavage Groups.

The use of stimuli-cleavable difunctional initiators containing a discrete single-type cleavable junction represents a general strategy to prepare mid-chain-degradable vinylic polymers. Here, we present a series of α-haloester-type programmed initiators encoding multiple single-type and dual-type cleavable junctions. Multiple single-cleavage groups increase the cleavage rate, whereas double-dual sites provide access to multiple mechanisms for cleavage. Single-electron transfer living radical polymerization was employed to generate well-defined mid-chain-cleavable poly(methyl acrylate)s designed with low-pH, low-pH/reduction, or low-pH/UV light cleavable linkages. Kinetic studies demonstrated that the polymerizations are living when using various catalytic Cu(0) sources (wire and powder), ligands (Me6-TREN and TREN), and solvent sources (homogeneous and "programmed" biphasic). Moreover, structural analyses by NMR and matrix-assisted laser desorption/ionization-time-of-flight confirmed the near-perfect chain-end functionality of these stimuli-cleavable polymers derived from programmed initiators. A rigorous gel permeation chromatography study demonstrated that the combination of multiple acetal, disulfide, or 2-nitroresorcinol-derived acetal junctions offer attractive possibilities in terms of selective cleavage and orthogonal degradation.

Polyacrylates Derived from Biobased Ethyl Lactate Solvent via SET-LRP.

The precise synthesis of polymers derived from alkyl lactate ester acrylates is reported for the first time. Kinetic experiments were conducted to demonstrate that Cu(0) wire-catalyzed single electron transfer-living radical polymerization (SET-LRP) in alcohols at 25 °C provides a green methodology for the LRP of this forgotten class of biobased monomers. The acrylic derivative of ethyl lactate (EL) solvent and homologous structures with methyl and n-butyl ester were polymerized with excellent control over molecular weight, molecular weight distribution, and chain-end functionality. Kinetics plots in conventional alcohols such as ethanol and methanol were first order in the monomer, with molecular weight increasing linearly with conversion. However, aqueous EL mixtures were found to be more suitable than pure EL to mediate the SET-LRP process. The near-quantitative monomer conversion and high bromine chain-end functionality, demonstrated by matrix-assisted laser desorption ionization time-of-flight analysis, further allowed the preparation of innovative biobased block copolymers containing rubbery poly(ethyl lactate acrylate) poly(ELA) sequences. For instance, the poly(ELA)- b-poly(glycerol acrylate) block copolymer self-assembled in water to form stable micelles with chiral lactic acid-derived block-forming micellar core as confirmed by the pyrene-probe-based fluorescence technique. Dynamic light scattering and transmission electron microscopy measurements revealed the nanosize spherical morphology for these biobased aggregates.

SET-LRP of Bio- and Petroleum-Sourced Methacrylates in Aqueous Alcoholic Mixtures.

Single-electron transfer-living radical polymerization (SET-LRP) in "programmed" aqueous organic biphasic systems eliminates the judicious choice of solvent and also provides accelerated reaction rates. Herein, we report efforts to expand the monomer scope for these systems by targeting methacrylic monomers and polymers. Various environmentally friendly aqueous alcoholic mixtures were used in combination with Cu(0) wire catalyst, tris(2-dimethylaminoethyl)amine (Me6-TREN) ligand, and p-toluenesulfonyl chloride (Ts-Cl) initiator to deliver well-defined polymethacrylates from methyl methacrylate, butyl methacrylate, and other monomers derived from biomass feedstock (e.g., lactic acid, isosorbide, furfural, and lauric acid). The effect of water on the nature of the reaction mixture during the SET-LRP process, reaction rate, and control of the polymerization is discussed. The control retained under the reported conditions is demonstrated by synthesizing polymers of different targeted molar mass as well as quasi-block AB copolymers by "in situ" chain extension at high conversion. These results highlight the capabilities of SET-LRP to provide sustainable solutions based on renewable resources.

pH-Responsive Micellar Nanoassemblies from Water-Soluble Telechelic Homopolymers Endcoding Acid-Labile Middle-Chain Groups in Their Hydrophobic Sequence-Defined Initiator Residue.

A middle-chain cleavable telechelic poly(oligoethylene glycol) methyl ether acrylate) (MCCT-POEGA-Br) was synthesized by single-electron transfer living radical polymerization (SET-LRP) initiated from an acetal-containing hydrophobic sequence-defined difunctional initiator. In aqueous medium, above a certain concentration, this hydrophilic homopolymer self-assembled into nanogel-like large micelles that exhibit an encapsulating capacity for both hydrophobic and hydrophilic cargo. The sequence-defined cleavage pattern encoded in the initiator residue allowed precise middle-chain cleavage, leading to quantitative disassembly of the corresponding nanoobjects. Dye release studies performed in an acidic environment demonstrated the potential of this new design concept in the preparation of pH-responsive nanocarriers. In addition, fluorescently tagged nanoassemblies could also be obtained via the thio-bromo "click" modification of MCCT-POEGA-Br prior to self-assembly. This strategy may provide facile access to a diversity of multistimuli-responsive nanocarriers based on commercially available hydrophilic monomers and sequence-defined difunctional initiators synthesized by this simple design strategy.

SET-LRP of the Hydrophobic Biobased Menthyl Acrylate.

Cu(0) wire-catalyzed single electron transfer-living radical polymerization (SET-LRP) of (-)-menthyl acrylate, a biobased hydrophobic monomer, was investigated at 25 °C in ethanol, isopropanol, ethyl lactate, 2,2,2-trifluoroethanol (TFE), and 2,2,3,3-tetrafluoropropanol (TFP). All solvents are known to promote, in the presence of N ligands, the mechanistically required self-regulated disproportionation of Cu(I)Br into Cu(0) and Cu(II)Br2. Both fluorinated alcohols brought out their characteristics of universal SET-LRP solvents and showed the proper polarity balance to mediate an efficient polymerization of this bulky and hydrophobic monomer. Together with the secondary alkyl halide initiator, methyl 2-bromopropionate (MBP), and the tris(2-dimethylaminoethyl)amine (Me6-TREN) ligand, TFE and TPF mediated an efficient SET-LRP of MnA at room temperature that proceeds through a self-generated biphasic system. The results presented here demonstrate that Cu(0) wire-catalyzed SET-LRP can be used to target polyMnA with different block lengths and narrow molecular weight distribution at room temperature. Indeed, the use of a combination of techniques that include GPC, 1H NMR, MALDI-TOF MS performed before and after thioetherification of bromine terminus via "thio-bromo" click chemistry, and in situ reinitiation copolymerization experiments supports the near perfect chain end functionality of the synthesized biobased hydrophobic polymers. These results expand the possibilities of SET-LRP into the area of renewable resources where hydrophobic compounds are widespread.

SET-LRP in the Neoteric Ethyl Lactate Alcohol.

Ethyl lactate (EtLa), a green and safe agrochemical solvent, is gifted with some properties that make it a good candidate for SET-LRP. It dissolves CuBr2, mediates an efficient disproportionation of CuBr in the presence of tris(2-(dimethylamino)ethyl)amine (Me6-TREN), and is capable to dissolve both aqueous (polar) and hydrocarbon (nonpolar) soluble monomers and polymers. Here, we report that EtLa is an excellent solvent for the Cu(0) wire-catalyzed SET-LRP to produce both hydrophilic and hydrophobic polyacrylates that exhibit precise chain end functionality. These results will expand the table of SET-LRP solvents with a new green member of biological origin that is also biodegradable and, therefore, are expected to contribute to continue expanding the use of SET-LRP in the field of biomacromolecules, bioconjugates, and other biology and medicine related disciplines.

Antimicrobial polyurethane thermosets based on undecylenic acid: synthesis and evaluation.

In the present study, plant oil-derived surface-modifiable polyurethane thermosets are presented. Polyol synthesis is carried out taking advantage of thiol-yne photopolymerization of undecylenic acid derivatives containing methyl ester or hydroxyl moieties. The prepared methyl ester-containing polyurethanes allow surface modification treatment to enhance their hydrophilicity and impart antimicrobial activity through the following two steps: i) grafting poly(propylene glycol) monoamine (Jeffamine M-600) via aminolysis and ii) Jeffamine M-600 layer complexation with iodine. The antimicrobial activity of the iodine-containing polyurethanes is demonstrated by its capacity to inhibit the growth of Staphylococcus aureus, and Candida albicans in agar media.

Thermoplastic polyurethanes from undecylenic acid-based soft segments: structural features and release properties.

A set of thermoplastic polyurethanes is synthesized, combining undecylenic acid-derived telechelic diols as soft segments and 1,4-butanediol/4,4'-methylenebis(phenylisocyanate) as a hard segment (HS). These polymers are fully chemically and physically characterized by means of NMR and Fourier transform IR (FTIR) spectroscopy, size-exclusion chromatography (SEC), DSC, thermogravimetric analysis (TGA), tensile testing, and contact angle measurements. The obtained results reveal that both the molecular weight of the diol and the HS content greatly influence the physical and mechanical properties of these polymers. In addition, given the potential use of these materials for biomedical applications, hydrolytic degradation, their biocompatibility using a human fibroblast cell line, and performance as drug delivery carriers are evaluated.

Enhancement of fatty acid-based polyurethanes cytocompatibility by non-covalent anchoring of chondroitin sulfate.

For tissue engineering purpose biopolymer chondroitin sulfate (CS), one of the major components of cartilage and bone extracellular matrix, was immobilized onto the surface of amino-functionalized polyurethane (PU) films derived from naturally occurring oleic and 10-undecenoic acids. The amino-functionalized PUs were prepared by aminolysis with 1,6-hexamethylenediamine of synthesized PUs containing methyl ester groups. FTIR-ATR, XPS, SEM, and water contact angle measurements were used to confirm the surface changes at each step of treatment, both in morphologies and chemical composition. Cytotoxicity and cell morphology analysis using osteoblast cell line MG63 showed that PU-CS films are suitable materials for cell growth, spreading, and differentiation.

"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.

Aza-Michael reaction with enone-modified vegetable oils: evidence of the keto-enolic equilibrium by NIR chemical imaging and evolving factor analysis.

The existence of an enone-dienol tautomerism in enone-containing triglyceride, obtained from high oleic sunflower oil, was detected in an image set captured at 95 °C by fixed-size image window-evolving factor analysis. A (1)H NMR spectrum and a UV-Visible spectrum of the enone-containing triglyceride at 25 °C and at 95 °C were measured to corroborate the presence of the enol form. The presence of this equilibrium explains the different behaviour of the curing reaction between an enone-containing triglyceride and diaminodiphenylmethane, which was evaluated following the spectral evolution of two pixels that differ in the presence or absence of the enol form. As the enol form acts as a inert species in the reaction, it leads to different degree of advance depending on which growing zone is observed.

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.

Rapid approach to biobased telechelics through two one-pot thiol-ene click reactions.

The application of environmentally friendly thiol-ene chemistry to the preparation of biobased telechelics is presented in this work. This methodology is based on two one-pot photoinitiated thiol-ene click processes: step-growth polymerization using a 3,6-dioxa-1,8-octanedithiol and end-group postpolymerization modification with three functional thiols: 2-mercaptoethanol, 3-mercaptopropionic acid, and 3-mercaptopropyltrimethoxysilane. We applied this approach to a potentially 100% biomass-derived monomer, allyl ester of 10-undecenoic acid (UDA). To show the generality and scope of this methodology, a series of well-defined telechelics with molecular weight ranging from 1000-3000 g/mol and hydroxyl, carboxyl, or trimethoxysilyl groups at the polymer terminus were prepared. An exhaustive (1)H NMR and MALDI-TOF MS analyses demonstrates the highly end-group fidelity of this methodology being an interesting procedure for the accelerated preparation of telechelics derived from divinyl monomers. UDA-based thelechelic diol prepared using this methodology was reacted with 4,4'-methylenebis(phenylisocyanate) and 1,4-butanediol as the chain extender to obtain multiblock poly(ester urethane).

Silicon-containing soybean-oil-based copolymers. Synthesis and properties.

New silicon-containing soybean-oil-based copolymers were prepared from soybean oil, styrene, divinylbenzene, and p-trimethylsilylstyrene by cationic polymerization using boron trifluoride etherate as initiator. Soxhlet extraction and NMR spectroscopy indicate that the copolymers consist of a cross-linked network plasticized with varying amounts of oligomers and unreacted oil. This soluble fraction increases when the SiST content in the feed increases, according to a lower reactivity of this monomer. The thermal, dynamomechanical, and flame-retardant properties of these materials were examined. Thermosets with glass transition temperatures ranging from 50 to 62 degrees C, which are thermally stable below 350 degrees C, and with LOI values from 22.6 to 29.7 were obtained. Their properties suggest that these materials may prove to be useful alternatives for current non-renewable-based thermosets and that the flame-retardant properties of vegetable-oil-based thermosets can be improved by adding covalently bonded silicon to the polymer.

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.

Spectroscopic and quantitative analysis of spiroorthoester synthesis by two-dimensional correlation and multivariate curve resolution methods of NIR data.

The spiroorthoester synthesis includes several competitives reactions. A way of determining the reactions that are taking place and their sequential order, is presented. The reaction between the phenylglycidylether and gamma-butyrolactone to obtain a spiroorthoester has been monitored by near-infrared spectroscopy (NIR). In addition to the formation of the corresponding spiroorthoester, some parallel processes can occur. By means of two-dimensional correlation analysis, only one reaction is postulated, the one corresponding to the spiroorthoester formation. This was confirmed by recording the NMR spectra of the final product. Applying multivariate curve resolution-alternating least squares (MCR-ALS) to the NIR spectra obtained during the reaction, it has been possible to obtain the concentration values of the species involved in the reaction. The recovered spectra were compared with the experimentally recorded spectra for the reagents (phenylglycidylether, gamma-butyrolactone) and the final product (spiroorthoester) and the correlation coefficients were, in all cases, higher than 0.990. The maximum and minimum limits associated with the ALS solutions were calculated, making it possible to limit to a considerable extent the ambiguity that is characteristic of these curve resolution methods.