Physical Cross-linking Points Research Articles

Nano-injectable pH/NIR-responsive hydrogel for chemo-photothermal synergistic drug delivery.

Conventional cancer treatments are highly toxic and ineffective; therefore, it is essential to develop less toxic and minimally invasive treatment methods. A pH/Near Infra-red (NIR) dual-responsive, nano-injectable smart hydrogel was fabricated by incorporating CuS nanoparticles into the hydrogel networks formed by a random copolymer of N-isopropylacrylamide (NIPAM) and double-bond functionalized uracil. Microstructural characterizations of synthesized polymer and hydrogels were carried out using transmission electron microscope (TEM), scanning electron microscope (SEM), nuclear magnetic resonance (NMR) and fourier transform infrared spectroscopy (FT-IR). Multiple hydrogen bonding interactions between uracils function as physical cross-linking points to construct the network structure of the polymeric nanogel without the addition of additional cross-linking agents, ensuring the material's safety. The amino group on the structure of uracil gives the uracil-modified polymeric hydrogel excellent pH responsiveness. Notably, as a temperature-responsive material, poly (N-isopropylacrylamide) (PNIPAM) nanogel solution can achieve in situ gel formation (within 100 s at 37°C) above its lower critical solution temperature (LCST), granting injectability to polymeric solutions. Moreover, using a hierarchical construction strategy, the variable loading of DOX and CuS was achieved. First, a heterogeneous system was created by encapsulating doxorubicin (DOX) inside the nanogel via hydrophobic and π-π stacking interactions, followed by the introduction of CuS nanoparticles as photosensitizers outside of the nanogels. Due to the presence of CuS nanoparticles, the gel is able to convert NIR light into local heat to enhance the destruction of tumor cells while simultaneously achieving rapid in situ gel formation. The in situ-forming hydrogel showed promising tissue biocompatibility. The in vitro antitumor test demonstrated the capacity of the nanocomposite hydrogel for chemo-photothermal synergistic therapy. Therefore, this prepared platform has the potential to become a safe and effective, smart-responsive drug carrier for chemotherapy and PTT synergy, a minimally invasive material for tumor treatment.

Robust and stretchable Ti3C2Tx MXene/PEI conductive composite dual-network hydrogels for ultrasensitive strain sensing

The development of high-performance hydrogels with superior strength, stretchability, and conductivity is critical to the practical application of flexible sensors. In this study, we employed a strategy that involves introducing physical cross-linking points, creating a double network, and adding nanofillers. By utilizing a two-step method that involves thermal cross-linking and post-immersion cross-linking, and using two common metal ions to crosslink different polymer networks, we successfully developed a conductive composite dual-network hydrogel. In addition, the incorporation of modified MXene has significantly improved the strength and toughness of the hydrogel. The resulting hydrogel exhibits impressive mechanical properties, including a tensile strength of 2.64 MPa and elongation at break of 689%, as well as high toughness of 10.25 MJ·m−3 and conductivity of 1.89 S/m. When applied as a flexible sensor in electronic skin, the sensor demonstrates a wide operating range (>300%), high sensitivity (GF = 4.64), and excellent linear detection ability (R2 = 0.99).

Liquid crystal elastomer film actuators with anti-strain robustness

Thermotropic monodomain liquid crystal elastomers (mLCEs) exhibit reversible contractile actuation properties along the collimated direction of mesogens when stimulated by external temperature, similar to those of biological skeletal muscle, and have great potential applications in flexible actuators and artificial muscles. However, the existence of flexible chain segments causes mLCEs to elongate under a small load, making calibration under different loads necessary when they are used as an actuator. In this study, a physical crosslinking point between flexible segments is provided through the introduction of designed long-chain molecules (LHS) containing amide bonds on the main chain of LCEs. The 5% LHS-mLCEs with enhanced anti-strain robustness achieved essentially constant original length over a range of loads (0–0.25 MPa) and maintained a reversible contraction ratio of 39.4%, comparable to biological skeletal muscle. Furthermore, a nonreconfigurable topological structure of a metal electrothermal layer with lossless compression properties was designed and prepared on the surface of mLCEs. The film actuators exhibit higher frequency oscillatory actuation (0.1 Hz 9.2%; 0.2 Hz 6.3%; 0.5 Hz 2%) relative to previously reported actuators, benefitting from the optimized heat dissipation structure of LCEs/Ag/air. This study provides valuable references and ideas for applying thermotropic mLCEs in practice.

A green and efficient synthetic strategy for the preparation of PBS ionomers with high molecular weight, high ionic group content and good combined properties

The conventional direct esterification and polycondensation is difficult to obtain kilogram scale of poly(butylene succinate) (PBS) ionomers with both high molecular weight and high ionic group content. Therefore, the investigation of relationship between the content of ion group and performance (such as mechanical properties) is impossible. In this work, the preparation of PBS ionomers with high molecular weight and high ion group content was achieved by transesterification method using sodium dimethyl isophthalate-5-sulfonate (SIPM) as the ionic monomer, and the polycondensation time decreased significantly with the increase of SIPM content. The mechanism of reducing the polycondensation time of PBS prepared by transesterification is proposed. The tensile strength, flexural strength and impact strength of PBS ionomers increased significantly with increasing SIPM content. At high ion group content, the formed multiplets-clusters among ion groups, which act as reversible physical crosslinking points and nano-fillers, substantially improved the mechanical properties. The tensile strength, flexural strength and impact strength improved and reached to 50.1 MPa, 40.9 MPa and 13.1 kJ/m2 at high ion group content from 34.2 MPa, 24.1 MPa and 5.8 kJ/m2 for PBS, respectively. It showed a totally opposite trend from the previous research. In addition, the hydrophilicity and processing properties of PBS ionomers improved significantly with the increase of the ion group content, and the contact angle reduced to 41.1° after the introduction of ions.

Construction and Evaluation of Alginate Dialdehyde Grafted RGD Derivatives/Polyvinyl Alcohol/Cellulose Nanocrystals IPN Composite Hydrogels.

To enhance the mechanical strength and cell adhesion of alginate hydrogel, making it satisfy the requirements of an ideal tissue engineering scaffold, the grafting of Arg-Gly-Asp (RGD) polypeptide sequence onto the alginate molecular chain was conducted by oxidation of sodium periodate and subsequent reduction amination of 2-methylpyridine borane complex (2-PBC) to synthesize alginate dialdehyde grafted RGD derivatives (ADA-RGD) with good cellular affinity. The interpenetrating network (IPN) composite hydrogels of alginate/polyvinyl alcohol/cellulose nanocrystals (ALG/PVA/CNCs) were fabricated through a physical mixture of ion cross-linking of sodium alginate (SA) with hydroxyapatite/D-glucono-δ-lactone (HAP/GDL), and physical cross-linking of polyvinyl alcohol (PVA) by a freezing/thawing method, using cellulose nanocrystals (CNCs) as the reinforcement agent. The effects of the addition of CNCs and different contents of PVA on the morphology, thermal stability, mechanical properties, swelling, biodegradability, and cell compatibility of the IPN composite hydrogels were investigated, and the effect of RGD grafting on the biological properties of the IPN composite hydrogels was also studied. The resultant IPN ALG/PVA/CNCs composite hydrogels exhibited good pore structure and regular 3D morphology, whose pore size and porosity could be regulated by adjusting PVA content and the addition of CNCs. By increasing the PVA content, the number of physical cross-linking points in PVA increased, resulting in greater stress support for the IPN composite hydrogels of ALG/PVA/CNCs and consequently improving their mechanical characteristics. The creation of the IPN ALG/PVA/CNCs composite hydrogels' physical cross-linking network through intramolecular or intermolecular hydrogen bonding led to improved thermal resistance and reduced swelling and biodegradation rate. Conversely, the ADA-RGD/PVA/CNCs IPN composite hydrogels exhibited a quicker degradation rate, attributed to the elimination of ADA-RGD by alkali. The results of the in vitro cytocompatibility showed that ALG/0.5PVA/0.3%CNCs and ADA-RGD/PVA/0.3%CNCs composite hydrogels showed better proliferative activity in comparison with other composite hydrogels, while ALG/PVA/0.3%CNCs and ADA-RGD/PVA/0.3%CNCs composite hydrogels displayed obvious proliferation effects, indicating that PVA, CNCs, and ADA-RGD with good biocompatibility were conducive to cell proliferation and differentiation for the IPN composite hydrogels.

Natural UCST hydrogel with long-term stability, recyclability, thermoplasticity, frost resistance and adhesive properties

Thermosensitive hydrogels have received great research interest, but the elaborate experimental design, inferior mechanical and anti-freeze properties have limited the practical application of thermosensitive hydrogels. For address these challenges, here, polyol (glycerol, xylitol, and sorbitol) and deionized water were selected as mixed solvents to fabricate multifunctional natural gelatin UCST hydrogels by simple physical blending. XRD and FT-IR indicate that the polyol assists the gelatin molecular chain to form short-range β-sheets without affecting the triple helix structure. The short-range β-sheets acts as the physical cross-linking point, which leads to a denser three-dimensional network of the hydrogel. The results indicate that the phase transition temperature and mechanical properties of UCST hydrogels can be modulated by simply changing the amount of polyol in the solvent mixture. In addition, the polyol forms extensive hydrogen bonds with water, which gives the hydrogel excellent freeze resistance, anti-drying and adhesive properties. In this paper, natural UCST gelatin hydrogels with long-term stability, recyclability, thermoplasticity, anti-freeze and adhesive properties were prepared by a simple scheme, and the facile process and cheap cost lays the foundation for the application of UCST hydrogels in drug delivery, skincare products and wearable devices.

A dual-crosslinked zwitterionic hydrogel with load-bearing capacity and ultra-low friction coefficient

Due to similar properties to that of cartilage, hydrogels are considered as promising candidates for cartilage repair. However, it is still a challenge to synthesize hydrogel combining high strength and low friction like natural cartilage. In this work, we synthesized a dual-crosslinked zwitterionic P(AAm-co-AAc-co-SBMA)/Fe3+ hydrogel, in which a zwitterionic monomer [2-(methacryloyloxy)ethyl]dimethyl-(3-sulfopropyl)(SBMA) was used to improve the hydrophilicity of the polymer chain. The results showed that the hydrogel exhibited significantly improved tensile strength (9.9 MPa) and compressive strength (207.6 MPa), which was due to the physical crosslinking points introduced by SBMA. Moreover, the zwitterionic hydrogel achieved an ultra-low friction coefficient (CoF) of 0.04 in water. The results provide a new approach for cartilage repair materials with considerable strength and low friction.

Initiator-Free Photocuring 3D-Printable PVA-Based Hydrogel with Tunable Mechanical Properties and Cell Compatibility.

Poly(vinyl alcohol) (PVA)-based hydrogels have attracted great attention and been widely used in biological tissue engineering. With the development of modern medicine, precision medicine requires the customization of medical materials. However, lacking of photocurable functional groups or the performance of rapid phase transition makes PVA-based hydrogels difficult to be customizable molded through photocuring 3D printing technique. In this research, customizable PVA-based hydrogels with high performance through 3D photocurable printing and freezing-thawing (F-T) process are obtained. The ability of 3D-printable is endowed by the introduction of polyvinyl alcohol-styrylpyridine (PVA-SBQ), which can be photo-crosslinked quickly without photoinitiator. Meanwhile, the tunable mechanical properties are achieved by adjusting the mass ratio of PVA-SBQ to PVA, and PVA can offer the physical crosslinking points through freezing-thawing (F-T) process. The hydrogels with high resolution are prepared by digital light procession 3D printing with the mass ratio 1:1 of PVA-SBQ to PVA solution. Attributed to the absence of initiator, and no small molecule residues inside the hydrogels, the hydrogels have good biocompatibility and have the potential to be applicated in the field of biological tissue engineering.

Cross-section and pore size regulation of hydroxyurea-modified polyacrylonitrile membrane by NH2-CNT and Si(OEt)4 filler and heat treatment for dye removal application at medium temperature

The preparation of ultrafiltration (UF) membranes for dye removal at higher temperature is a challenging task. In this study, hydroxyurea-modified polyacrylonitrile (PAN-Hu) was used to prepare hydrophilic UF membrane. The further addition of NH2-grafted carbon nanotube (CNT) and tetraethoxysilane(TEOS) resulted in a change of the cross-section morphology of the membrane from half-sponge to an asymmetrical one, with an increased pore size due to the hydrophobic nature of the fillers. The resulting PHT/Si membrane showed a higher pure water flux (130 L/m2 h at 1 bar) than PAN-Hu, with a 98% rejection rate of Congo red (CR) from a 0.1% NaCl aqueous solution. The dye rejection mechanism was explained based on the molecular size and surface charge density of dyes, as well as force analysis inside the spongy skin layer. Subsequently, two heating methods were adopted to stabilize the structure of membrane, and improve its thermal stability for filtration at medium temperature (60 °C). After heating in water at 60 °C for 5 days, the rejection rate of Methyl blue (MB) in a 0.1% NaCl solution increased by 80%, but the flux of membrane decreased by more than 50%. On the other hand, heating at 100 °C in glycerol for 10 hrs led to a similar increase in dye rejection but a lower decrease in flux. Specifically, the heated PHT/Si membrane showed a dye flux of 64 L/m2 h, and an MB rejection rate of 94% from water, 80% from a 0.1% NaCl solution at 20 °C. Additionally, all membranes showed a higher flux and slightly lower rejection at 60 °C compared with that at 20 °C. Instrumental characterization revealed that morphology change of membrane was caused by the shrinkage effect through chain rearrangement as a result of heat treatment. But PAN-Hu showed a greater decrease in pore size than PHT/Si membrane. The reason lies in that CNT or SiO2 in PHT/Si membrane acts as physical crosslinking point. Their dimension stabilization effect limits the free movement of polymer chains and affects the pore size change of membrane. Overall, this study can help to tailor the porous structure of UF membranes for dye removal under different temperatures.

Hydrogelation from Self-Assembled and Scaled-Down Chitin Nanofibers by the Modification of Highly Polar Substituents.

Chitin nanofibers (ChNFs) with a bundle structure were fabricated via regenerative self-assembly at the nanoscale from a chitin ion gel with an ionic liquid using methanol. Furthermore, the bundles were disentangled by partial deacetylation under alkaline conditions, followed by cationization and electrostatic repulsion in aqueous acetic acid to obtain thinner nanofibers called scaled-down ChNFs. This review presents a method for hydrogelation from self-assembled and scaled-down ChNFs by modifying the highly polar substituents on ChNFs. The modification was carried out by the reaction of amino groups on ChNFs, which were generated by partial deacetylation, with reactive substituent candidates such as poly(2-oxazoline)s with electrophilic living propagating ends and mono- and oligosaccharides with hemiacetallic reducing ends. The substituents contributed to the formation of network structures from ChNFs in highly polar dispersed media, such as water, to produce hydrogels. Moreover, after the modification of the maltooligosaccharide primers on ChNFs, glucan phosphorylase-catalyzed enzymatic polymerization was performed from the primer chain ends to elongate the amylosic graft chains on ChNFs. The amylosic graft chains formed double helices between ChNFs, which acted as physical crosslinking points to construct network structures, giving rise to hydrogels.

Improving the Energy Storage Performance of a Chlorinated Poly(vinyl chloride) Film at Elevated Electric Field and Temperature via a Simple Annealing Process

High energy density and efficiency are crucial factors for polymeric dielectrics to satisfy the emerging demand in high-pulse metallized film capacitors. However, achieving high energy density in polar polymeric dielectrics is usually accompanied by a sharp decline in the energy discharge efficiency at elevated electric fields and temperatures. In this work, we investigated the dielectric and energy storage properties of chlorinated poly(vinyl chloride) (CPVC) with moderate polarity. Due to the random distribution of chlorine atoms on the polymer chain, CPVC displays a medium permittivity of about 3 and low loss. Moreover, high-temperature annealing is used to promote the rearrangement of CPVC chain segments, which contributes to the formation of CPVC microcrystals. Consequently, the storage modulus and glass transition temperature (Tg) along with the thermal stability of CPVC are improved due to the microcrystals as physical cross-linking points. Compared to pristine CPVC, heat-treated CPVC shows reduced dielectric loss and elevated breakdown strength. As a result, a high energy density of 9.4 J/cm3 and a discharge efficiency of 82.7% at 625 MV/m are obtained in heat-treated CPVC. This work offers a straightforward approach to improving the energy storage properties of CPVC so that it can be used for high-pulse metallized film capacitors.

High-Expansion Open-Cell Polylactide Foams Prepared by Microcellular Foaming Based on Stereocomplexation Mechanism with Outstanding Oil-Water Separation.

Biodegradable polylactic acid (PLA) foams with open-cell structures are good candidates for oil-water separation. However, the foaming of PLA with high-expansion and uniform cell morphology by the traditional supercritical carbon dioxide microcellular foaming method remains a big challenge due to its low melting strength. Herein, a green facile strategy for the fabrication of open-cell fully biodegradable PLA-based foams is proposed by introducing the unique stereocomplexation mechanism between PLLA and synthesized star-shaped PDLA for the first time. A series of star-shaped PDLA with eight arms (8-s-PDLA) was synthesized with different molecular weights and added into the PLLA as modifiers. PLLA/8-s-PDLA foams with open-cells structure and high expansion ratios were fabricated by microcellular foaming with green supercritical carbon dioxide. In detail, the influences of induced 8-s-PDLA on the crystallization behavior, rheological properties, cell morphology and consequential oil-water separation performance of PLA-based foam were investigated systemically. The addition of 8-s-PDLA induced the formation of SC-PLA, enhancing crystallization by acting as nucleation sites and improving the melting strength through acting as physical cross-linking points. The further microcellular foaming of PLLA/8-s-PDLA resulted in open-cell foams of high porosity and high expansion ratios. With an optimized foaming condition, the PLLA/8-s-PDLA-13K foam exhibited an average cell size of about 61.7 μm and expansion ratio of 24. Furthermore, due to the high porosity of the interconnected open cells, the high-absorption performance of the carbon tetrachloride was up to 37 g/g. This work provides a facile green fabrication strategy for the development of environmentally friendly PLA foams with stable open-cell structures and high expansion ratios for oil-water separation.

Tough, Photoluminescent, Self-Healing Waterborne Polyurethane Elastomers Resulting from Synergistic Action of Multiple Dynamic Bonds

Polymers that integrate multiple functions into one system broaden the application range of materials, but it remains a great challenge to obtain polymer materials with simultaneously high strength, high toughness, and high self-healing rate. In this work, we prepared waterborne polyurethane (WPU) elastomers using Schiff bases containing disulfide and acylhydrazone bonds (PD) as chain extenders. Acylhydrazone forming a hydrogen bond not only acts as a physical cross-linking point, which promotes the microphase separation of polyurethane to increase the thermal stability, tensile strength, and toughness of the elastomer, but also serves as a "clip" to integrate various dynamic bonds together to synergistically reduce the activation energy of the polymer chain movement and endow the molecular chain with faster fluidity. Therefore, WPU-PD exhibits excellent mechanical properties at room temperature, such as a tensile strength and a fracture energy of 25.91 MPa and 121.66 kJ m-2, respectively, and a high self-healing efficiency of 93.7% in a short time under moderate heating conditions. In addition, the photoluminescence property of WPU-PD enables us to track its self-healing process by monitoring change of the fluorescence intensity at the cracks, which helps to avoid the accumulation of cracks and improve the reliability of the elastomer. This self-healing polyurethane has a great potential application value in optical anticounterfeiting, flexible electronics devices, functional automobile protective films, and so on.

Enhanced heat resistance and expansion ratio of biodegradable poly (lactic acid)/poly (butylene adipate-co-terephthalate) composite foams via synergistic effect of nucleating agent and chain extension

Abstract Environmentally friendly foams have been studied extensively to handle the plastic pollution caused by disposable tableware. Herein, biodegradable poly (lactic acid) (PLA) – poly (butylene adipate-co-terephthalate) (PBAT) composites were first fabricated by melt blending, in which a reactive chain extender (ADR) was incorporated to enhance the interfacial compatibility and melt strength, a nucleating agent (TMC) was applied to improve the crystallinity. Subsequently, the foaming behavior of the composites was investigated via supercritical CO2 foaming. Specifically, a spherulite and shish-kebab-like nanoporous structure was observed from PLA and PLA/TMC foams, respectively, when the soaking temperature was far below melting temperature. With an increase of foaming temperature, the unmelted completely crystals served as physical cross-linking points, also contributing to a high melt strength. Combined with chain extension reaction of ADR, the PLA–PBAT/ADR/TMC foams showed the largest cell diameter and expansion ratio, which were 19 μm and 8.9, respectively. Furthermore, the heat resistance of PLA–PBAT/ADR/TMC foams was also significantly improved, owing to the high crystallinity induced by TMC. Consequently, the composite foams with superior heat resistance and toughness were obtained to broaden its application as biodegradable disposable tableware for hot food.

ナノ触診原子間力顕微鏡を用いた熱可塑性エラストマーの変形挙動解析

Due to its unique elastic deformation characteristics, rubber is used in all kinds of industrial products. However, the huge amount of energy consumed during the vulcanization and molding processes and the recyclability of rubber, which has been used industrially in the past, have become problems. Thermoplastic elastomers (TPEs) are attracting attention as a material to solve this problem. TPEs are microphase-separated into the hard segment (HS) phase and the soft segment (SS) phase. The SS phase serves as the rubber component that provides softness, while the HS phase is fluid at high temperatures but serves as a physical cross-linking point that prevents deformation at room temperature. As a result, it is attracting attention as an alternative material to rubber because it is easy to mold and process and can be recycled. In this study, Styrene-ethylene-butylene-styrene triblock copolymers (SEBS) , which is a styrenic-based thermoplastic elastomer, and α-methylstyrene-ethylene-butylene-α-methylstyrene triblock copolymers, in which the PS blocks are replaced by α-methylstyrene is prepared and differences in structure and physical properties at the nanoscale were discussed using a nano-palpation atomic force microscopy (AFM) .

Mussel-inspired interfacial reinforcement of thermoplastic polyurethane based energetic composites

The interfacial interaction and the microstructure evolution play a vital role in the mechanical properties of thermoplastic polyurethane (TPU) based energetic composites. In this work, inspired by the strong adhesion of mussels, 2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane (CL-20) energetic crystals were coated with polydopamine (PDA) via in-situ polymerization of dopamine and then dispersed in TPU matrix. The core-shell structure of CL-20@PDA was confirmed by in-depth structural characterizations. The uniform and compact PDA shell gave rise to a high thermal stability with phase transition temperature of CL-20 crystals increased by 11.5 °C. Moreover, the PDA modification endowed the TPU based composites with excellent mechanical properties. A striking increase in mechanical properties and creep resistance was achieved with 6 h polymerization time of PDA. Compared with the PBX-Raw with untreated CL-20 crystals, the compressive and tensile strength after PDA coating increased by 115% and 57%, and the compressive and tensile fracture energy increased by 148% and 68%. The storage modulus at 25 °C was 40% higher than PBX-Raw. The enhancement effectivity could be ascribed to both interfacial interaction and the microstructure evolution of TPU binder. The theoretical simulations by molecular dynamics demonstrated the strong interfacial interaction mechanism between CL-20 and PDA. Moreover, the abundant hydrogen bonds between the hard segments of TPU and functional groups of PDA facilitated the formation of more hard microdomains which acted as physical crosslinking points to promote the phase separation. This work provides a potential method for the mechanical and thermal enhancement for TPU based energetic materials based on dopamine chemistry.

Role of the Branched PEG-b-PLLA Block Chain in Stereocomplex Crystallization and Crystallization Kinetics for PDLA/MPEG-b-PLLA-g-glucose Blends with Different Architectures.

The isothermal crystallization behavior and corresponding morphology evolution of poly(d-lactic acid) (PDLA) blends with PLLA6.7k or MPEG-b-PLLA6.7k-g-glucose with different architectures and different PLLA-grafted copolymer contents were investigated. The formation of stereocomplexes (SCs) in between the chain branched structure of MPEG-b-PLLA6.7k-g-glucose and PDLA chains acting as the physical crosslinking points slows down the motion of PDLA chains, but the SCs could act as a heterogeneous nucleating agent for the late formation of homocrystals (HCs) in the blend system, accelerating the crystallization kinetics of HCs through enhancing the nucleation density. For PDLA/MPEG-b-PLLA6.7k-g-glucose blends, the mobility of SCs in the blend system and the nucleation density of SCs in the blends exhibit oppositional behavior during the isothermal crystallization at a Tc of 130 °C. The evolution of the crystal growth and structure during the isothermal crystallization process by rheometry has revealed the interesting role of the branched chains of MPEG-b-PLLA6.7k-g-glucose in the mechanism of the crystallization in PDLA blends.

Highly toughened poly(ʟ-lactide) by poly(ᴅ-lactide)-containing crosslinked polyurethane shows excellent malleability, flexibility and shape memory property

The brittle nature of poly(ʟ-lactide) (PLLA) limits its extensive application. In the present work, PLLA was toughened by crosslinked polyurethane (CPU), which was formed by reactive blending of poly(ε-caprolactone) (PCL), poly(d-lactide) (PDLA), hexamethylene diisocyanate (HDI) and glycerol. PCL segments in the network acted as soft segments while PDLA segments served as hard segments to form stereocomplex (SC) crystallites as physical crosslinking points. The disappearing peak at 2270 cm−1 and the emerging absorption peak appeared at 1530 cm−1 in the FTIR spectrum proved the formation of the network in the modified PLLA. The melt-quenched specimens containing the network showed significant increase in elongation at break, and the CPU80/18/2 blend showed a maximum value of 428.6%. Tensile-fractured surfaces of all the blends exhibited fibril-like morphologies because of the matrix shear yielding caused by large deformation. And the crystallization rate could be accelerated because of the PDLA chains in the sample comparing to the CPU80/20 without PDLA. Interestingly, when SC crystallites could be formed after annealing of the melt-quenched specimens at 110 °C for 1h, CPU80/18/2 still owned a maximum value of 152.8% of elongation at break. It was found that the CPU phase was presented as continuous phase in the material. Due to the compatibility, the added PDLA chains were distributed in the interface of CPU and PLLA phase, which provided additional interfacial adhesion, improved the stress transmission and endowed the material with enhanced toughness. The CPU80/18/2 sample also showed the malleability, flexibility and shape memory capacity, implying great application potential as biodegradable green composites.

Facile Method for the Synthesis of PCL-b-PA6-b-PCL Using Amino-Terminated PA6 as a Macroinitiator and Its Characterization

Polyesteramides have attracted much attention due to their intriguing properties. However, the synthesis of di- or triblock polyesteramides based on polyamide 6 (PA6) remains challenging owing to their harsh reaction conditions. In this work, we introduced a new strategy to synthesize poly(ε-caprolactone)-block-PA6-block-poly(ε-caprolactone) (PCL-b-PA6-b-PCL) in a mild way. A series of well-designed copolymers were characterized by gel permeation chromatography, 1H, DOSY, and 13C NMR, and their crystallization and melting behavior, degradation rate, and compatibilization effect on PA6/PCL blends were found to be strongly composition dependent. Interestingly, the copolymers exhibited diverse spherulite morphologies, including curving stems and banded spherulites, which also correlated with the different relative content of PA6. Besides, PA6 nanodomains could act as physical cross-linking points to improve the tensile strength and Young’s modulus of PCL. This work fills the synthesis gap of well-defined PA6-based triblock polyesteramides, providing new materials for material modification and elucidation of some basic scientific questions.

Tough antifouling organogels reinforced by the synergistic effect of oleophobic and dipole–dipole interactions

Slippery organogels have gained increasing interest as competitive candidates for antifouling applications. However, it remains challenging to develop tough organogels suitable for fouling resistance in dynamic and flexible application scenarios. Herein, a kind of physically crosslinked organogels with a combination of desirable properties, including high toughness, transparency, surface slipperiness, and fouling resistance is developed. The representative pAL organogels, constructed by poly(acrylonitrile-co-lauryl acrylate) (pAL) copolymer and infiltrated with n-hexadecane as a lubricating solvent, possess high tensile fracture stress, fracture strain, Young’s modulus, and toughness of 4.28 MPa, 517%, 2.52 MPa, and 11.19 MJ m−3. In the organogels, the polar cyano groups from the pAN segments serve as physical cross-linking points, where the synergistic effects played by oleophobic and dipole–dipole interactions significantly toughen the materials. Meanwhile, the soft oleophilic poly(lauryl acrylate) chains offer considerable solvent content, giving rise to satisfactory surface slipperiness. Therefore, the organogels bring about a 57.16% and 81.50% reduction of protein and bacteria adhesion in comparison to the control. The satisfactory antifouling performance has been further confirmed with Spirulina platensis. It is deemed that this organogel may provide great potential for various applications in the future such as anti-adhesion materials and self-cleaning coating.