Hydrogen Bonding in Copoly(ether−urea)s and Its Relationship with the Physical Properties

Impact of the Configurational Microstructure of Carboxylate-Rich Chitosan Beads on Its Adsorptive Removal of Diclofenac Potassium from Contaminated Water

A novel adsorbent-contaminant system was investigated for its ability to remove a contaminant of emerging concern, diclofenac potassium, from contaminated water. Bio-based crosslinked chitosan beads functionalized with poly(itaconic acid) side chains were examined for their potential to remove the emerging contaminant. To evaluate the impact of the polymeric microstructure on its adsorptive capacity, several adsorbent samples were prepared using different combinations of initiator and monomeric concentrations. Fourier Transform Infrared (FTIR) analysis confirmed the crosslinking of the chitosan chains and the incorporation of the carboxylic groups on the surface of the final chitosan beads. After the grafting copolymerization process, an additional peak at 1726 cm-1 corresponding to the carboxylic C=O groups of the grafted chains appeared, indicating the successful preparation of poly(IA)-g-chitosan. Thermal stability studies showed that the grafting copolymerization improved the thermal stability of the beads. X-ray and Scanning Electron Microscopy confirmed the successful grafting of the itaconic acid on the surface of the beads. The study revealed that the higher the initiator concentration, the greater the number of side chains, whereas the higher the monomeric concentration, the longer the length of these side chains. The adsorption mechanism involved hydrogen bonding to the carboxylic groups of the grafted chains along with n-π* stacking interaction between the amino group of the chitosan and the aromatic rings of diclofenac potassium. The adsorption efficiencies of diclofenac potassium onto the grafted beads were significantly improved compared to the unfunctionalized chitosan beads, reaching values above 90%. The removal efficiency of grafted chitosan increased with an increase in the concentration in the range of 10-30 ppm and then flattened out in the range of 30-50 ppm. The removal efficiencies of 1-50 ppm of DCF ranged between about 75% and 92% for the grafted chitosan and 30-45% for the crosslinked chitosan. Rapid adsorption occurred within 20 min for all grafted sample combinations, and the adsorption kinetics followed a pseudo-second-order model with qe values ranging from 28 to 44.25 g/mg and R2 values greater than 0.9915. The results highlight the potential of grafted chitosan beads in removing emerging contaminants from contaminated water without harming the environment.

Molecular Resolution Nanostructure and Dynamics of the Deep Eutectic Solvent-Graphite Interface as a Function of Potential

Interest in deep eutectic solvents (DESs), particularly for electrochemical applications, has boomed in the past decade because they are more versatile than conventional electrolyte solutions and are low cost, renewable, and non-toxic. The molecular scale lateral nanostructures as a function of potential at the solid-liquid interface-critical design parameters for the use of DESs as electrochemical solvents-are yet to be revealed. In this work, in situ amplitude modulated atomic force microscopy complemented by molecular dynamics simulations is used to probe the Stern and near-surface layers of the archetypal and by far most studied DES, 1:2 choline chloride:urea (reline), at the highly orientated pyrolytic graphite surface as a function of potential, to reveal highly ordered lateral nanostructures with unprecedented molecular resolution. This detail allows identification of choline, chloride, and urea in the Stern layer on graphite, and in some cases their orientations. Images obtained after the potential is switched from negative to positive show the dynamics of the Stern layer response, revealing that several minutes are required to reach equilibrium. These results provide valuable insight into the nanostructure and dynamics of DESs at the solid-liquid interface, with implications for the rational design of DESs for interfacial applications.

Supramolecular Polycaprolactone-Based Polyurethanes with Thermally Activated Shape-Memory Behavior

In this work, using supramolecular polyurethanes theories, two polycaprolactone-based polyurethanes with 2-ureido-4-[1H]-pyrimidinone (UPy) motifs capable of forming quadruple hydrogen bonds were synthetized and characterized, focusing our attention on their capability to show thermally activated shape-memory response. In particular, ¹H NMR analyses confirmed the chemical structure of the supramolecular polyurethanes, while DSC showed their totally amorphous morphology. DMTA in tensile mode was used to study their thermally activated shape-memory properties. In our case, the UPy units are the switching domains while the network formed by the segregated hard segments is the permanent domain obtained materials with excellent shape-memory response at both 100 and 85 °C. These materials are promising for multi-responsive materials where bio-based and potentially recyclable polymers with excellent shape-memory properties are needed.

Effect of microcrystalline cellulose on the preparation and performance of rigid polyurethane foam

In order to study the effect of microcrystalline cellulose on the reaction kinetics of polyurethane, in this work, the multi-scale microcrystalline cellulose was added to the foaming system of multifunctional polyether and multifunctional MDI polyurethane. While the chemical reaction was carried out, it was found through in situ FTIR combined with in situ rheological analysis that what was different from the usual inorganic fillers, the hydroxyl on the surface of the microcrystalline cellulose could preferentially react with MDI to generate urethane under the action of the catalyst. In the initial 5–6 min of the reaction, the reaction of soft segment chain growth was the main reaction. Then the main reaction quickly converted to the cross-linking reaction, which greatly increased the viscosity of the system. The addition of microcrystalline celluloses accelerated the improvement of the cross-linking degree and viscosity of the system. The higher the surface hydroxyl content of microcrystalline cellulose, the more significant this trend become. In addition, although the amount of microcrystalline cellulose added was different, the ratio of the reaction rate of the isocyanate group with the hydroxyl group and the amine group eventually tended to be constant, which indicated that there was a stable reactivity rate in the gradual addition reaction during the cross-linking reaction. Combined with SEM analysis, it was found that 25–60 μm microcrystalline cellulose with large hydroxyl content could act as a nucleating agent when the addition amount was less than 0.1%, which was beneficial to increase the cell density and reduce the pore size and improved the impact performance of the foam. The microcrystalline cellulose with a length of more than 90 μm continuously penetrated through several cell walls and destroyed integrity of the cell structure, which would consequently reduce the impact strength of the foam. This paper provided theoretical guidance for polyurethane modified by microcrystalline cellulose.

Role of Air Bubble Inclusion on Polyurethane Reaction Kinetics

In this study, we investigated the influence of mixing conditions on the foaming process of water blown polyurethane (PU) foams obtained at different mixing speeds (50, 500, 1000 and 2000 rpm). In particular, the morphological evolution during the foaming process, in terms of the bubble size and bubble density, was studied via optical observations, while the effects on the reaction kinetics were monitored using in situ FTIR spectroscopy. At the slow mixing speed (50 rpm), no air bubbles were included and the early foaming process was characterized by the formation of new bubbles (CO₂ nucleation), provided by the blowing reaction. Later on, it was observed that the coalescence affected the overall foaming process, caused by the gelling reaction, which was inhibited by the indigent mixing conditions and could not withstand the bubbles expansion. As a result, a PU foam with a coarse cellular structure and an average bubble size of 173 µm was obtained. In this case, the bubbles degeneration rate, dN/dt, was −3095 bubble·cm⁻³·s⁻¹. On the contrary, at 500 rpm, air bubbles were included into the PU reaction system (aeration) and no formation of new bubbles was observed during the foaming process. After this, the air bubbles underwent growth caused by diffusion of the CO₂ provided by the blowing reaction. As the gelling reaction was not strongly depleted as in the case at 50 rpm, the coalescence less affected the bubble growth (dN/dt = −2654 bubble·cm⁻³·s⁻¹), leading to a PU foam with an average bubble size of 94 µm. For the foams obtained at 1000 and 2000 rpm, the bubble degeneration was first affected by coalescence and then by Ostwald ripening, and a finer cellular structure was observed (with average bubble sizes of 62 µm and 63 µm for 1000 rpm and 2000 rpm, respectively). During the first foaming stage, the coalescence was less predominant in the bubble growth (with dN/dt values of −1838 bubble·cm⁻³·s⁻¹ and −1601 bubble·cm⁻³·s⁻¹, respectively) compared to 50 rpm and 500 rpm. This occurrence was ascribed to the more balanced process between the bubble expansion and the PU polymerization caused by the more suitable mixing conditions. During the late foaming stage, the Ostwald ripening was only responsible for the further bubble degeneration (with dN/dt values of −89 bubble·cm⁻³·s⁻¹ and −69 bubble·cm⁻³·s⁻¹, respectively).

High-Performance Polyurethane Nanocomposite Membranes Containing Cellulose Nanocrystals for Protein Separation

With the aim of exploring new materials and properties, we report the synthesis of a thermoplastic chain extended polyurethane membrane, with superior strength and toughness, obtained by incorporating two different concentrations of reactive cellulose nanocrystals (CNC) for potential use in kidney dialysis. Membrane nanocomposites were prepared by the phase inversion method and their structure and properties were determined. These materials were prepared from a polyurethane (PU) yielded from poly(1,4 butylene adipate) as a soft segment diol, isophorone diisocyanate (IPDI) and hexamethylenediamine (HMDA) as isocyanate and chain extender, respectively (hard segment), filled with 1 or 2% w/w CNC. Membrane preparation was made by the phase inversion method using N,N-dimethylformamide as solvent and water as nonsolvent, and subjected to dead-end microfiltration. Membranes were evaluated by their pure water flux, water content, hydraulic resistance and protein rejection. Polymers and nanocomposites were characterized by scanning electronic and optical microscopy, differential scanning calorimetry, infrared spectroscopy, strain stress testing and ¹³C solid state nuclear magnetic resonance. The most remarkable effects observed by the addition of CNCs are (i) a substantial increment in Young’s modulus to twenty-two times compared with the neat PU and (ii) a marked increase in pure water flux up to sixty times, for sample containing 1% (w/w) of CNC. We found that nanofiller has a strong affinity to soft segment diol, which crystallizes in the presence of CNCs, developing both superior mechanical and pure water flow properties, compared to neat PU. The presence of nanofiller also modifies PU intermolecular interactions and consequently the nature of membrane pores.

Blends of sodium deoxycholate-based poly(ester ether)urethane ionomer and hydroxypropylcellulose with mucosal adhesiveness

New mucoadhesive blends of sodium deoxycholate-based poly(ester ether)urethane ionomer (PU) and hydroxypropyl cellulose (HPC) are prepared. The presence of the intermolecular interactions between the polymeric components has been investigated by FTIR spectroscopy indicating their miscibility in the solid phase. DSC studies also revealed a single glass transition of the blends, which is indicative of miscibility of PU and HPC in the amorphous phase. The amount of HPC in the blends influences strongly the physicochemical and mucoadhesion/bioadhesion properties. It was found that the value of area attributed to ordered hydrogen bonding (FTIR), the onset temperature values of thermal degradation in N₂ flow (TG/DTG), the values of the sorption capacity (Dynamic Vapor Sorption-DVS), the values of the apparent viscosity (rheological measurements) and mucoadhesion/bioadhesion properties increased by increasing the HPC content in the blends. Complex viscosity revealed shear thinning behavior for all the studied solutions evidencing the contributive role of polymer viscoelasticity on mucoadhesion. It was found that both G' and G" increase with an increase in angular frequency and G">G' which is characteristic for liquid-like (sol state) behavior for all blended solutions and this behavior is helpful in the adhesion with mucosa surface. Mucoadhesion of PU/HPC blends was assessed in the stomach mucosa at pH 2.6 and 37 °C. Bioadhesion test was performed at pH 7.4 and 37 °C and revealed a stronger interaction of PU/HPC blends with cellulose membrane than with stomach mucosa. The similar nature of the HPC and cellulose membrane determines additional adhesion forces and implicity high adhesion properties. The HPC component increases the hydrophilicity of the blends as DVS analysis revealed, but also leads to hydrolytic degradation. FTIR spectroscopy analysis was used to evaluate the hydrolytic stability in acid (pH 2.6) and slightly alkaline (pH 7.4) PBS media and a mechanism of degradation has been proposed.

Optimization of mechanical and dielectric properties of poly(urethane–urea)-based dielectric elastomers via the control of microstructure

In this work, we fabricated hydroxyl-terminated butadiene–acrylonitrile copolymer-based poly(urethane–urea) dielectric elastomers, and investigated the relationship between multi-length scale structure and dielectric, mechanical properties.

Fibronectin adsorption on surface-modified polyetherurethanes and their differentiated effect on specific blood elements related to inflammatory and clotting processes

After the introduction of a medical device into the body, adhesive proteins such as fibronectin (Fn) will adsorb to the surface of the biomaterial. Monocytes (MCs) will interact with these adsorbed proteins, and adopt either a proinflammatory and/or prowound healing phenotype, thereby influencing many blood interaction events including thrombogenesis. In this work, Fn adsorption as well as subsequent MC response and thrombus formation were investigated on two surfaces-modified polyetherurethanes (PEUs) using different surface modifiers: an anionic/dihydroxyl oligomeric (ADO) additive, known to enable cell adhesion, and a fluorinated polypropylene oxide oligomer (PPO), known to reduce platelet adhesion. Results indicated that at 24 h of MC culture, PEU-ADO and PEU-PPO promoted an anti-inflammatory character relative to the base PEU. Longer clotting times, based on a free hemoglobin assay, were also found on the two surface-modified PEUs relative to the native one, suggesting their potential for the reduction of thrombus formation. In presence of a Fn monolayer, the surface-modified PEUs conserved a lower thrombogenic character than the base PEU, and was however significantly decreased when compared to prior protein adsorption. Furthermore, Fn coatings increased the MC production levels of tumor necrosis factor-α and interleukin-10 at 24 h, while not affecting the anti-inflammatory effect of the modifications relative to the base PEU. This finding was most prominent on PEU-PPO, suggesting that the interaction of the adsorbed Fn with blood cells was different for the two additives. Hence, the results highlighted differentiating effects of Fn adsorption on specific blood activating processes related to inflammatory and thrombotic responses.

Self-healing poly(siloxane-urethane) elastomers with remoldability, shape memory and biocompatibility

The poly(siloxane-urethane) elastomers with microphase separation structure and Diels–Alder bonds show high healing efficiency, good mechanical property and good biocompatibility.

Microphase separation induced in the melt of Pluronic copolymers by blending with a hydrogen bonding urea-urethane end-capped supramolecular polymer

Blending with a hydrogen-bonding supramolecular polymer is shown to be a successful novel strategy to induce microphase-separation in the melt of a Pluronic polyether block copolymer. The supramolecular polymer is a polybutadiene derivative with urea-urethane end caps. Microphase separation is analysed using small-angle X-ray scattering and its influence on the macroscopic rheological properties is analysed. FTIR spectroscopy provides a detailed picture of the inter-molecular interactions between the polymer chains that induces conformational changes leading to microphase separation.

Synthesis and characterization of acrylic acid-2-hydroxyethyl methacrylate IPN hydrogels

Three different methods have been developed to crosslink the poly(acrylic acid-2-hydroxyethyl methacrylate) to form the hydrogels having tunable swelling, rheological and morphological properties with applicability in dye and heavy metal removal.

Comparative studies on the accumulation of strain and recovery ratio of Veriflex®, a shape-memory polymer

A comparative investigation on thermomechanical cycles including programming, cooling, unloading and heating to trigger the one-way effect (1-WE) was carried out for Veriflex® between temperature ( T) and glass transition temperature ( Tg) at 62°C ( T <  Tg) and 72°C ( T >  Tg) for 140% strains and 10 min recovery time. Accumulation of strain and recovery ratios was estimated during the treatments. It turns out that the process causes an increase in irreversible strain and is associated with a corresponding decrease in intensity of the 1-WE in particular during the first thermomechanical cycle. The confocal laser scanning microscopic study shows a very little wavy surface structure evolved at 72°C. Infrared study features the chemical nature of Veriflex.

Biodegradable polyurethane ureas with variable polyester or polycarbonate soft segments: effects of crystallinity, molecular weight, and composition on mechanical properties

Biodegradable polyurethane urea (PUU) elastomers are ideal candidates for fabricating tissue engineering scaffolds with mechanical properties akin to strong and resilient soft tissues. PUU with a crystalline poly(ε-caprolactone) (PCL) macrodiol soft segment (SS) showed good elasticity and resilience at small strains (<50%) but showed poor resilience under large strains because of stress-induced crystallization of the PCL segments, with a permanent set of 677 ± 30% after tensile failure. To obtain softer and more resilient PUUs, we used noncrystalline poly(trimethylene carbonate) (PTMC) or poly(δ-valerolactone-co-ε-caprolactone) (PVLCL) macrodiols of different molecular weights as SSs that were reacted with 1,4-diisocyanatobutane and chain extended with 1,4-diaminobutane. Mechanical properties of the PUUs were characterized by tensile testing with static or cyclic loading and dynamic mechanical analysis. All of the PUUs synthesized showed large elongations at break (800-1400%) and high tensile strength (30-60 MPa). PUUs with noncrystalline SSs all showed improved elasticity and resilience relative to the crystalline PCL-based PUU, especially for the PUUs with high molecular weight SSs (PTMC 5400 M(n) and PVLCL 6000 M(n)), of which the permanent deformation after tensile failure was only 12 ± 7 and 39 ± 4%, respectively. The SS molecular weight also influenced the tensile modulus in an inverse fashion. Accelerated degradation studies in PBS containing 100 U/mL lipase showed significantly greater mass loss for the two polyester-based PUUs versus the polycarbonate-based PUU and for PVLCL versus PCL polyester PUUs. Basic cytocompatibility was demonstrated with primary vascular smooth muscle cell culture. The synthesized families of PUUs showed variable elastomeric behavior that could be explained in terms of the underlying molecular design and crystalline behavior. Depending on the application target of interest, these materials may provide options or guidance for soft tissue scaffold development.

Studies on the cycling, processing and programming of an industrially applicable shape memory polymer Tecoflex® (or TFX EG 72D)

The present investigations were undertaken to find out whether and how often cycling, processing and programming can be repeated, whether repeated programming affects the one way effect and how much irreversible strain the shape memory polymeric material accumulates at a particular temperature. The effect was investigated in dependence of different stress levels, and the effect of both recovery temperature and recovery time was considered. As a model material the commercially and industrially applicable amorphous shape memory polymer Tecoflex® was examined and subjected to 50 programming cycles. Tecoflex® is characterized by a glass transition temperature, Tg, of 74 °C, above which it looses all its strength. During tensile testing at 20 °C (T < Tg), stresses a steady increase to 26 MPa as strains approached the rupture strain of 25%. It is observed that at 60 °C (T < Tg, but near Tg) the material can be strained to more than 2500% before rupture occurs while stresses slowly increase to values less than 0.3 MPa. It turns out that programming, cooling, unloading and heating to trigger the one way effect causes an increase of irreversible strain that is associated with a corresponding decrease of the intensity of the one way effect during the first thermomechanical cycles.

Bifurcated hydrogen bonds stabilize fibrils of poly(L-glutamic) acid

Model fibrillating homopolypeptides have been providing many insightful analogies to the clinically important phenomena of protein misfolding and amyloidogenesis. Here we show that the beta(2) structural variant of poly(l-glutamic) acid forms fibrils with an amyloid-like morphology, ability to enhance fluorescence of thioflavin T, and seeding properties. The beta(2) fibrils are formed upon heating of aqueous solutions of alpha-helical poly(l-glutamic) acid, which leads to a significant increase of pD (pH) of unbuffered samples and a concomitant precipitation of fibrils with unusual infrared traits: amide I' band being dramatically red-shifted to 1596 cm(-1), and the -COOD stretching band split into two peaks around 1730 and 1719 cm(-1). We are proposing that formation of three-center hydrogen bonds involving bifurcated peptide carbonyl acceptors (>C=O) and main chains' NH, as well as side chains' -COOH proton donors is likely to underlie the observed infrared characteristics of beta(2) fibrils. Such bonds provide additional conformational constraints in a tightly packed environment around glutamate side chains resulting in the decreased overall acidity of the polypeptide. The presence of bifurcated hydrogen bonds in amyloid fibrils may be an overlooked factor in fibrils' robustness, thermodynamic stability and the ability to propagate their own growth.