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.

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.

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.

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.

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.

Polybenzoxazines: new players in the bio-based polymer arena

This mini-review focuses on the recent efforts to replace petro-based feedstocks with polybenzoxazine precursors.

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.

Steric Communication of Chiral Information Observed in Dendronized Polyacetylenes

Structural and retrostructural analysis of helical dendronized polyacetylenes (i.e., self-organizable polyacetylenes containing first generation dendrons or minidendrons as side groups) synthesized by the polymerization of minidendritic acetylenes with [Rh(nbd)Cl]2 (nbd = 2,5-norbornadiene) reveals an approximately 10% change in the average column stratum thickness (l) of the cylindrical macromolecules with a chiral periphery, through which a strong preference for a single-handed screw-sense is communicated. The cylindrical macromolecules reversibly interconvert between a three-dimensional (3D) centered rectangular lattice (Phi r-c,k) exhibiting long-range intracolumnar helical order at lower temperatures and a two-dimensional (2D) hexagonal columnar lattice (Phi h) with short-range helical order at higher temperatures. A polymer containing chiral, nonracemic peripheral alkyl tails is found to have a larger l as compared to the achiral polymers. In methyl cyclohexane solution, the same polymer exhibits an intense signal in circular dichroism (CD) spectra, whose intensity decreases upon heating. The observed change in l indicates that the chiral tails alter the polymer conformation from that of the corresponding polymer with achiral side chains. This change in conformation results in a relatively large free energy difference (DeltaGh) favoring one helix-sense over the other (per monomer residue). The capacity to distort the polymer conformation and corresponding free energy is related to the population of branches in the chiral tails and their distance from the polymer backbone by comparison to recently reported first and second generation dendronized polyphenylacetylenes.

Novel Silicon-Containing Polyurethanes from Vegetable Oils as Renewable Resources. Synthesis and Properties

Hydrosilylation of methyl 10-undecenoate (UDM) with phenyl tris(dimethylsiloxy)silane (PTDS) followed by a reduction of carboxylate groups was used to obtain a silicon-containing polyol with terminal primary hydroxyl groups (PSi194). Biobased silicon-containing polyurethanes, with a silicon content between 1.7% and 9.0%, were prepared from epoxidized methyl oleate-based polyether polyol (P184), PSi194, and 4,4'-methylenebis(phenyl isocyanate) (MDI). The thermal, mechanical, and flame-retardant properties of these materials were examined. The most notable change resulting from the incorporation of PSi194 is the appearance of melting endotherms of variable enthalpy and position and a downward shift in the T(g). The incorporation of silicon does not change the thermal stability but enhances the stability of the char under air atmosphere. Polyurethanes with higher silicon content no longer burn in ambient air without complementary oxygen, which suggests that these biobased materials are very interesting for applications that require fire resistance.