Enhanced and Reusable Poly(hydroxy urethane)-Based Low Temperature Hot-Melt Adhesives

Poly(hydroxy urethane)s (PHUs) based on 5-membered cyclic carbonates have emerged as sustainable alternatives to conventional isocyanate-based polyurethanes. However, while from the point of view of sustainability they represent an improvement, their properties are still not competitive with conventional polyurethanes. In this work, the potential of PHUs as reversible hot-melt adhesives is discussed. We found that with a judicious choice of reagents (i.e., the dicyclic carbonate and diamine), the detrimental hydrogen bonding between the soft segment of the chains and the pendant hydroxyl groups was partially avoided, thus imparting PHUs with hot-melt adhesion properties (i.e., adhesion at elevated temperatures and cohesiveness at a temperature lower than T_g/T_m). The importance of a balanced hard to soft segment ratio, along with the relevance of the chain extender in the final properties, is highlighted. Addition of aliphatic diamines (HMDA, 1,12-DAD) resulted in rubbery materials, while the employment of cycloaliphatic (CBMA) or aromatic ones (MXDA, PXDA) led to materials with hot-melt adhesive properties. The thermoreversibility of all compositions was assessed by rebonding specimens after lap-shear tests. Lap-shear strength values that were comparable to the virgin adhesives were observed. The breaking and reformation of hydrogen bonding interactions was demonstrated by FTIR measurements at different temperatures, as well as by rheological frequency sweep experiments. In order to mitigate the negative impact of the low molar mass PHUs and to enhance the service temperature of the adhesives, a hybrid PHU was prepared by adding a small amount of an epoxy resin, which acts as a cross-linker. These hybrid PHUs maintain the thermoreversibility displayed by thermoplastic PHUs while providing better adhesion at elevated temperatures. We believe that this work provides some important insights into the design of PHU-based hot-melt adhesives.

Hydrogen Bond Strength-Mediated Self-Assembly of Supramolecular Nanogels for Selective and Effective Cancer Treatment

This study provides a significant contribution to the development of multiple hydrogen-bonded supramolecular nanocarrier systems by demonstrating that controlling the hydrogen bond strength within supramolecular polymers represents a crucial factor to tailor the drug delivery performance and enhance the effectiveness of cancer therapy. Herein, we successfully developed two kinds of poly(ethylene glycol)-based telechelic polymers Cy-PEG and UrCy-PEG having self-constituted double and quadruple hydrogen-bonding cytosine (Cy) and ureido-cytosine (UrCy) end-capped groups, respectively, which directly assemble into spherical nanogels with a number of interesting physical characteristics in aqueous solutions. The UrCy-PEG nanogels containing quadruple hydrogen-bonded UrCy dimers exhibited excellent long-term structural stability in a serum-containing biological medium, whereas the double hydrogen-bonded Cy moieties could not maintain the structural integrity of the Cy-PEG nanogels. More importantly, after the drug encapsulation process, a series of in vitro experiments clearly confirmed that drug-loaded UrCy-PEG nanogels induced selective apoptotic cell death in cancer cells without causing significant cytotoxicity to healthy cells, while drug-loaded Cy-PEG nanogels exerted nonselective cytotoxicity toward both cancer and normal cells, indicating that increasing the strength of hydrogen bonds in nanogels plays a key role in enhancing the selective cellular uptake and cytotoxicity of drugs and the subsequent induction of apoptosis in cancer cells.

Quadruple Hydrogen Bond-Containing A-AB-A Triblock Copolymers: Probing the Influence of Hydrogen Bonding in the Central Block

This work reveals the influence of pendant hydrogen bonding strength and distribution on self-assembly and the resulting thermomechanical properties of A-AB-A triblock copolymers. Reversible addition-fragmentation chain transfer polymerization afforded a library of A-AB-A acrylic triblock copolymers, wherein the A unit contained cytosine acrylate (CyA) or post-functionalized ureido cytosine acrylate (UCyA) and the B unit consisted of n-butyl acrylate (nBA). Differential scanning calorimetry revealed two glass transition temperatures, suggesting microphase-separation in the A-AB-A triblock copolymers. Thermomechanical and morphological analysis revealed the effects of hydrogen bonding distribution and strength on the self-assembly and microphase-separated morphology. Dynamic mechanical analysis showed multiple tan delta (δ) transitions that correlated to chain relaxation and hydrogen bonding dissociation, further confirming the microphase-separated structure. In addition, UCyA triblock copolymers possessed an extended modulus plateau versus temperature compared to the CyA analogs due to the stronger association of quadruple hydrogen bonding. CyA triblock copolymers exhibited a cylindrical microphase-separated morphology according to small-angle X-ray scattering. In contrast, UCyA triblock copolymers lacked long-range ordering due to hydrogen bonding induced phase mixing. The incorporation of UCyA into the soft central block resulted in improved tensile strength, extensibility, and toughness compared to the AB random copolymer and A-B-A triblock copolymer comparisons. This study provides insight into the structure-property relationships of A-AB-A supramolecular triblock copolymers that result from tunable association strengths.

Quadruple Hydrogen Bonding Supramolecular Elastomers for Melt Extrusion Additive Manufacturing

This manuscript describes the versatility of highly directional, noncovalent interactions, i.e., quadruple hydrogen bonding (QHB), to afford novel polyurea segmented supramolecular polymers for melt extrusion three-dimensional (3D) printing processes. The molecular design of the polyurea elastomers features (1) flexible polyether segments and relatively weak urea hydrogen-bonding sites in the soft segments to provide elasticity and toughness, and (2) strong ureido-cytosine (UCyt) QHB in the hard segments to impart enhanced mechanical integrity. The resulting polyureas were readily compression-molded into mechanically-robust, transparent, and creasable films. Optimization of polyurea composition offered a rare combination of high tensile strength (95 MPa), tensile elongation (788% strain), and toughness (94 MJ/m³), which are superior to a commercially available Ninjaflex elastomer. The incorporation of QHB facilitated melt processability, where hydrogen bonding dissociation provided low viscosities at printing temperatures. During cooling, directional self-assembly of UCyt QHB facilitated the solidification process and contributed to part fidelity with the formation of a robust physical network. The printed objects displayed high layer fidelity, smooth surfaces, minimal warpage, and complex geometries. The presence of highly directional QHB effectively diminished mechanical anisotropy, and the printed samples exhibited comparable Young's moduli along (x-y direction, 0°) and perpendicular to (z-direction, 90°) the layer direction. Remarkably, the printed samples exhibited ultimate tensile strains approaching 500% in the z-direction prior to failure, which was indicative of improved interlayer adhesion. Thus, this design paradigm, which is demonstrated for novel polyurea copolymers, suggests the potential of supramolecular polymers with enhanced mechanical performance, melt processability, recyclability, and improved interlayer adhesion for melt extrusion additive manufacturing processes.

Change of Characterization and Film Morphology Based on Acrylic Pressure Sensitive Adhesives by Hydrophilic Derivative Ratio

Hydrophilic acrylic pressure-sensitive adhesives (PSAs) were synthesized by controlling the contents of 2-ethylhexyl acrylate (EHA), isobornyl acrylate (IBOA), and 2-hydroxyethyl acrylate (HEA); especially, the characteristic change of the HEA content was analyzed. Surface contact angle of acrylic PSA film decreased from 77.87° to 70.23° in the case of Acryl-2 to Acryl-8 (below HEA 10 wt %). However, the surface contact angle of Acryl-10 to Acryl-40 (HEA 10 wt % to 40 wt %) increased up to 92.29°, indicating hydrophobicity. All acrylic PSA films showed high adhesive force above 1800 gf/25 mm. According to X-ray diffraction (XRD) measurement, hydrophilic acrylic PSAs exhibited amorphous property and it was confirmed that the morphology of acrylic PSA film was significantly affected by the flexibility of the polymer chain and the strength of hydrogen bonding. The affinity with hydrophilic materials for acrylic PSA films was evaluated by T-type peel test, confirming that the affinity with hydrophilic materials is determined by the hydrophilicity of the acrylic PSA film. The synthesized acrylic PSA film is non-toxic regardless of the hydrophilicity.

Cytosine-functionalized bioinspired hydrogels for ocular delivery of antioxidant transferulic acid

Contact lenses (CLs) are being pointed out as feasible platforms for controlled delivery of ophthalmic drugs. Bioinspired strategies may endow CLs with affinity for a given drug by mimicking its physiological receptor using adequate functional monomers and tuning their conformation in the space through the molecular imprinting technology. However, there are some active substances, such as efficient antioxidant agents, that cannot be used as templates because they degrade during polymerization or even hinder the polymerization itself. Therefore, the development of CLs able to sustain the release of antioxidants for the prevention and/or treatment of several age-related and light-induced eye diseases has not been explored yet. Searching for an alternative bioinspired strategy, the present work relies on the fact that some drugs owe their therapeutic action to their ability to interact with nucleotides that build up DNA and RNA. Thus, the aim of this work was to design hydrogels functionalized with the nitrogenous base cytosine for the controlled uptake and release of transferulic acid (TA) having a complementary chemical structure in terms of hydrogen bonding and π-π stacking ability. Hydrogels were prepared from mixtures of 2-hydroxyethyl methacrylate (HEMA), glycidyl methacrylate (GMA) and ethyleneglycolphenylether methacrylate (EGPEM). GMA was used as a bridge to immobilize cytosine after hydrogel synthesis, while EGPEM was added to reinforce hydrophobic interactions with TA. The hydrogels were characterized in terms of suitability to be used as CLs (swelling, light transmission, mechanical properties, biocompatibility) and capability to host TA and sustain its release in lachrymal fluid while maintaining the antioxidant activity. Relevantly, the bioinspired CLs favored TA accumulation in cornea and sclera tissues.

Evading the strength–ductility trade-off dilemma of rigid thermosets by incorporating triple cross-links of varying strengths

A new class of rigid thermosets with simultaneously enhanced strengths and ductilities have been successfully designed and synthesised.

Order–disorder transition in supramolecular polymer combs/brushes with polymeric side chains

Three groups of supramolecular comb/brush polymers with polymeric side chains are developed, showing different mechanical properties and morphologies.

Vat photopolymerization of charged monomers: 3D printing with supramolecular interactions

Vat photopolymerization of a trimethylammonium ethyl acrylate chloride solution (TMAEA) resulted in a well-defined, fully soluble, 3D printed rook.

Surface modification and pattern formation by nucleobases and their coordination complexes

This review presents recent progress concerning the organization of nucleobases on highly ordered pyrolytic graphite (HOPG), mica, Cu(110) and Au(111) surfaces, followed by their studies using microscopy methods such as atomic force microscopy (AFM), scanning tunneling microscopy (STM) and transmission electron microscopy (TEM). Interesting research prospects related to surface patterning by nucleobases, nucleobase-functionalized carbon nanotubes (CNTs) and metal–nucleobase coordination polymers are also discussed, which offer a wide array of functional molecules for advanced applications. Nucleobases and their analogs are able to invoke non-covalent interactions such as π–π stacking and hydrogen bonding, and possess the required framework to coordinate metal ions, giving rise to fascinating supramolecular architectures. The latter could be transferred to conductive substrates, such as HOPG and gold, for assessment by high-end tunneling microscopy under various conditions. Clear understanding of the principles governing nucleobase self-assembly and metal ion complexation, and precise control over generation of functional architectures, might lead to custom assemblies for targeted nanotechnological and nanomaterial applications.

This review highlights recent advancements in surface patterning of nucleobases, their analogs including nucleobase-CNT hybrids and metal complexes, using various microscopy techniques for nanotechnological applications.

Preparation of supramolecular silicone elastomersviahomo- and hetero-assembly

Supramolecular silicone elastomers were preparedviaself-assembly and they exhibit ultra-low temperature resistance and tunable mechanical properties.

3D Printing Polymers with Supramolecular Functionality for Biological Applications

Supramolecular chemistry continues to experience widespread growth, as fine-tuned chemical structures lead to well-defined bulk materials. Previous literature described the roles of hydrogen bonding, ionic aggregation, guest/host interactions, and π-π stacking to tune mechanical, viscoelastic, and processing performance. The versatility of reversible interactions enables the more facile manufacturing of molded parts with tailored hierarchical structures such as tissue engineered scaffolds for biological applications. Recently, supramolecular polymers and additive manufacturing processes merged to provide parts with control of the molecular, macromolecular, and feature length scales. Additive manufacturing, or 3D printing, generates customizable constructs desirable for many applications, and the introduction of supramolecular interactions will potentially increase production speed, offer a tunable surface structure for controlling cell/scaffold interactions, and impart desired mechanical properties through reinforcing interlayer adhesion and introducing gradients or self-assembled structures. This review details the synthesis and characterization of supramolecular polymers suitable for additive manufacture and biomedical applications as well as the use of supramolecular polymers in additive manufacturing for drug delivery and complex tissue scaffold formation. The effect of supramolecular assembly and its dynamic behavior offers potential for controlling the anisotropy of the printed objects with exquisite geometrical control. The potential for supramolecular polymers to generate well-defined parts, hierarchical structures, and scaffolds with gradient properties/tuned surfaces provides an avenue for developing next-generation biomedical devices and tissue scaffolds.

Molecular design through computational simulation on the benzo[2,1-b;3,4-b′]dithiophene-based highly ordered donor material for efficient polymer solar cells

Donor–acceptor (D–A) copolymers have been proved to be excellent candidates for efficient polymer solar cells (PSCs).