Pendant Hydroxyl Research Articles

The Synthesis and Optical Property of a Ternary Hybrid Composed of Aggregation-Induced Luminescent Polyfluorene, Polydimethylsiloxane, and Silica

Tetraphenylethene (TPE) is known as a molecule that exhibits aggregation-induced emission (AIE). In this study, pendant hydroxyl groups were introduced onto polyfluorene with a TPE moiety. Sol-gel reactions of polydiethoxysiloxane (PDEOS) were carried out in the presence of hydroxyl-functionalized AIE polyfluorene (TPE-PF-OH) and polydimethylsiloxane carrying pendant hydroxyl groups (PDMS-OH) to immobilize AIE polyfluorene into a PDMS/SiO2 hybrid in an isolated dispersion state. The luminescence intensity from this three-component hybrid increased with the increase in silica content. The luminescence intensity decreased with increasing external temperature. For the control experiment, sol-gel reactions of PDEOS were carried out in the presence of hydroxyl group-free polyfluorene (TPE-PF) and PDMS to obtain ternary composites. We found that the luminescence from this composite was not significantly affected by the silica content or external temperature. We synthesized temperature-responsive AIE materials without changing the concentration or aggregation state of the AIE molecules.

Carbon Dioxide-Based Cross-Linked Poly(hydroxyurethane-urea) Elastomers: Synthesis and Modification Utilizing Pendent Hydroxyl Groups

Carbon Dioxide-Based Cross-Linked Poly(hydroxyurethane-urea) Elastomers: Synthesis and Modification Utilizing Pendent Hydroxyl Groups

Oxidative Photochemical Cyclisations to Access Spiroketals

AbstractThe spiroketal moiety is an important substructure within many biological natural products. One method to access them is via the oxidative cyclisation of a pendant hydroxyl group on to a pre‐formed pyran. However applications of this methodology have been severely limited by requiring the use of toxic oxidants, such as lead (IV) tetraacetate or mercuric oxide. Herein we report a high yielding photochemical route to prepare complex spiroketals using an oxidative photochemical approach employing iodine monochloride and sodium acetate and demonstrate the methodology to the synthesis of a number of insect pheromones.

Self-immolative Polymer Hydrogels via In Situ Gelation.

Hydrogels are of interest for a wide range of applications. The ability to control when the hydrogel degrades can provide beneficial properties such as controlled degradation in the environment or the stimulated release of drugs or cells. Self-immolative polymers are a class of degradable polymers that undergo complete end-to-end depolymerization upon the application of a stimulus. They have been explored for hydrogel development, but the ability to prepare and selectively degrade self-immolative hydrogels under neutral aqueous conditions has so far been limited. We describe here the preparation of water-soluble polyglyoxylamides with cross-linkable pendent azides and their cross-linking to form hydrogels with 4-arm poly(ethylene glycol)s having unstrained and strained alkynes using copper-assisted and strain-promoted azide-alkyne click chemistry respectively. The influence of pendent azide density and solution polymer content on the resulting hydrogels was evaluated. A polyglyoxylamide with a 70 : 30 ratio of pendent hydroxyl:azide successfully provided hydrogels with compressive moduli ranging from 1.3-6.3 kPa under copper-free conditions at 10-20 % (w/w) of polymer in phosphate-buffered saline. Selective depolymerization and degradation of the hydrogels upon irradiation with light was demonstrated, resulting in reductions in the compressive moduli and the release of depolymerization products that were detected by NMR spectroscopy.

Combining Siloxane-Based polybenzoxazine with Poly(ethylene-co-vinyl acetate/hydroxyl) for tougher, more Stable, and Self-Healable materials

Cross-linked EVOH containing dynamic silyl ether bonds with improved toughness and processability have been prepared by taking advantage of both ethylene vinyl alcohol (EVOH) and benzoxazine chemistry. For that, the cross-linked EVOH was synthesized through a trans etherification reaction between siloxane mono-functional benzoxazine and pendant hydroxyl groups on ethylene vinyl alcohol (EVOH) copolymer. The precursor EVOH copolymer was obtained by hydrolysis of the commercially available and inexpensive ethylene–vinyl acetate copolymer (EVA). The chemical structures of polymers were analyzed by proton nuclear magnetic resonance (1H NMR) spectra and Fourier transform infrared (FTIR) spectroscopy. The curing and thermal stability were researched by using differential scanning calorimetry (DSC) and a thermogravimetric analyzer (TGA), respectively. The mechanical properties via the stress–strain analysis were examined to identify the effect of the benzoxazines with the silyl ether group on the toughness and self-healing ability of the modified EVOH.

Topology-Accelerated and Selective Cascade Depolymerization of Architecturally Complex Polyesters.

Despite considerable recent advances already made in developing chemically circular polymers (CPs), the current framework predominantly focuses on CPs with linear-chain structures of different monomer types. As polymer properties are determined by not only composition but also topology, manipulating the topology of the single-monomer-based CP systems from linear-chain structures to architecturally complex polymers could potentially modulate the resulting polymer properties without changing the chemical composition, thereby advancing the concept of monomaterial product design. To that end, here, we introduce a chemically circular hyperbranched polyester (HBPE), synthesized by a mixed chain-growth and step-growth polymerization of a rationally designed bicyclic lactone with a pendent hydroxyl group (BiLOH). This HBPE exhibits full chemical recyclability despite its architectural complexity, showing quantitative selectivity for regeneration of BiLOH, via a unique cascade depolymerization mechanism. Moreover, distinct differences in materials properties and performance arising from topological variations between HBPE, hb-PBiLOH, and its linear analogue, l-PBiLOH, have been revealed where generally the branched structure led to more favorable interchain interactions, and topology-amplified optical activity has also been observed for chiral (1S, 4S, 5S)-hb-PBiLOH. More intriguingly, depolymerization of l-PBiLOH proceeds through an unexpected, initial topological transformation to the HBPE polymer, followed by the faster cascade depolymerization pathway adopted by hb-PBiLOH. Overall, these results demonstrate that CP design can go beyond typical linear polymers, and rationally redesigned, architecturally complex polymers for their unique properties may synergistically impart advantages in topology-augmented depolymerization acceleration and selectivity for exclusive monomer regeneration.

ProPhos: A Ligand for Promoting Nickel-Catalyzed Suzuki-Miyaura Coupling Inspired by Mechanistic Insights into Transmetalation.

Nickel-catalyzed Suzuki-Miyaura coupling (Ni-SMC) offers the potential to reduce the cost of pharmaceutical process synthesis. However, its application has been restricted by challenges such as slow reaction rates, high catalyst loading, and a limited scope of heterocycles. Despite recent investigations, the mechanism of transmetalation in Ni-SMC, often viewed as the turnover-limiting step, remains insufficiently understood. We elucidate the "Ni-oxo" transmetalation pathway, applying PPh2Me as the ligand, and identify the formation of a nickel-oxo intermediate as the turnover-limiting step. Building on this insight, we develop a scaffolding ligand, ProPhos, featuring a pendant hydroxyl group connected to the phosphine via a linker. The design preorganizes both the nucleophile and the nickel catalyst, thereby facilitating transmetalation. This catalyst exhibits fast kinetics and robust activity across a wide range of heteroarenes, with a catalyst loading of 0.5-3 mol %. For arene substrates, the catalyst loading can be further reduced to 0.1 mol %.

Synergistic global and local flexibilities in Zr-based metal-organic frameworks enable sequential sieving of hexane isomers.

Separating hexane isomers based on the branching degree is crucial for their efficient utilization in the petrochemical industry, yet remains challenging due to their similar properties. Here we report a temperature-responsive Zr-based metal-organic framework, Zr-fum-FA, capable of sequentially sieving linear, mono-, and di-branched hexane isomers. Notably, the pore structure of Zr-fum-FA dynamically transforms from segmented triangular channels to an integrated rhombic configuration as the temperature increases, leading to distinct sieving effects. At low temperatures, the narrow triangular pores allow the exclusive adsorption of n-hexane while excluding branched isomers. In contrast, the expanded rhombic pores at high temperatures enable the sieving of mono- and di-branched isomers. Mechanistic studies reveal that this unique dual-sieving behavior originates from the synergistic effects of the global framework flexibility and the local dynamics of pendent hydroxyl groups. Furthermore, we demonstrate the decoupling of global and local flexibilities via two strategies: incorporating steric hindrance to dampen the global framework dynamics and enhancing the metal node rigidity to limit the local vibrations. These findings not only provide a promising adsorbent for the challenging separation of hexane isomers but also offer rational design principles for harnessing flexibility in MOFs.

3-oxetanylmethanol as additive to PEDOT:PSS for improved conductivity and water-resistance and applications in ink-jet printed electrochemical transistors

3-oxetanylmethanol is used as additive to poly (3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS) water dispersions and the properties of thin films, prepared by spin-coating and ink-jet printing, either on glass or flexible polyethylene terephthalate (PET) substrates, are investigated. 1H NMR studies revealed that 3-oxetanylmethanol is reactive within the PEDOT:PSS medium during the film drying step at 120 °C, to form polyether compounds. Chemical cross-linking established through the esterification reaction of pendant hydroxyl groups in polyether chains, resulting from the 3-oxetanylmethanol in situ polymerization, and sulfonate groups from PSS, is also identified by the 1H NMR studies. Spin-cast films prepared from this formulation on either glass or PET exhibited electrical conductivity enhanced by more than two orders of magnitude, when compared to films obtained with the pristine PEDOT:PSS dispersion, reaching maximum values of around 596 and 682 Scm−1 for films on glass and PET, respectively, together with improved water-resistance. Atomic force microscopy and Raman spectroscopic studies, indicating that PEDOT chains are organized in more ordered domains in the films of the oxetane-based formulations, suggest that the polyether compounds modify the PEDOT:PSS phase segregation and promote charge transport across conducting PEDOT segments. Subsequently, improved conductivities and stability were also found for films prepared by high-resolution ink-jet printing of the formulations that led to the most conductive spin coated films. The potential application of the new ink formulations in printed electrodes interfacing aqueous media was assessed by ink-jet printing PEDOT-based electrochemical transistors operating with aqueous KCl electrolyte.

Bifunctional Carbosilane Dendrimers for the Design of Multipurpose Hydrogels with Antibacterial Action.

The emergence of antibiotic resistance is a serious global health problem. There is an incessant demand for new antimicrobial drugs and materials that can address this global issue from different angles. Dendritic hydrogels have appeared as a promising strategy. A family of bifunctional amphiphilic carbosilane dendrimers was designed and employed as nanosized cross-linking points for the synthesis of high-swelling hydrogels using the highly efficient Thiol-Ene click reaction for their preparation. Both stoichiometric and off-stoichiometric conditions were studied, generating hydrogels with pendant hydroxyl or alkene moieties. These hydrogels were found to be tunable antibacterial materials. They can easily be postmodified with relevant antibiotic moieties through covalent attachment on the hydroxyl or alkene pendant groups, generating ammonium-decorated networks with temperature and pH-responsive properties. Additionally, they can efficiently encapsulate drugs with poor solubility in water, like ciprofloxacin, and perform a sustained release over time, as demonstrated in preliminary assays against Staphylococcus aureus.

The Synthetic Progress of Fused Bicyclic N,O-acetals

Abstract: Owing to the prevalent occurring in natural products and abundant bioactivities, the effective synthetic methods of fused bicyclic N,O-acetals skeletons are of great interest to chemists. This mini-review summarized the thus far synthetic progress of fused bicyclic N,O-acetals. These works were elaborated according to the different reaction types, including a) hetero-Diels-Alder cycloaddition of cyclic enamines with oxadienes; b) step-by-step reactions between cyclic enamines and electrophiles with pendant hydroxyl groups; c) [3+2] cycloaddition of indole with quinone or its equivalent and d) other novel strategies. The catalytic systems and reaction mechanisms are mainly described.

Crosslinked succinic acid based non-isocyanate polyurethanes for corrosion resistant protective coatings

Non-isocyanate polyurethanes (NIPUs) are considered as safer alternatives to toxic isocyanate-based polyurethanes (PUs). However, NIPU coatings are generally known for their poor water resistance due to the presence of pendant hydroxyl groups in the structure unlike traditional PUs. In this work, solvent-borne crosslinkable NIPU coating formulations were developed in a non-toxic solvent, diethylene glycol diethyl ether, and their coatings properties were evaluated. The crosslinking chemistry involved acid catalyzed transetherification of a commercially available crosslinking agent hexa(methoxymethyl) melamine (HMMM) with the NIPU hydroxyl groups. The crosslinked NIPU coatings showed good thermal stability (up to 245 °C), high pencil hardness (up to 3H), strong adhesion to metal substrates (adhesive strength up to 9.04 MPa), high resistance to water and good salt-water corrosion resistance. The formulations were also applied successfully for dip coating of copper specimens with complex and hard to reach surfaces. Finally, pigmented solvent-borne coating formulations were also demonstrated. All these results highlight the potential of NIPU resins for the application in industrial coatings substituting traditional petroleum-based polyol resins used currently.

Evaluation of the adhesive properties of vanillin‐derived polyhydroxy urethanes

AbstractPoly(hydroxy urethanes) (PHUs) have been considered attractive and safer variants of conventional polyurethanes (PUs). To improve the prerequisites of green and sustainable chemistry herein, we propose the synthesis and utilization of cyclic carbonate monomers majorly derived from vanillin, a lignin derivative, and CO2 for the development of PHUs. Kinetic evaluation on the polymerization temperature ascertained 80°C as the optimum condition for PHU synthesis. The structural evaluation of PHUs was carried out by various spectroscopic techniques, such as FTIR, 1HNMR, and 13C‐NMR, molar masses were determined by gel permeation chromatography (Mn varied between 2500 and 11,100 g/mol), and thermal properties evaluated by differential scanning calorimeter (Tg in the ranges of 28–42°C), and thermogravimetric analysis (stable above 180°C). Since the PHUs are enriched with pendant hydroxyl groups on their backbone which can promote adhesion, lap shear studies on the aluminum substrate exhibited a maximum shear strength of 1.65 ± 0.37 MPa. This study demonstrates an attractive and environment‐friendly pathway for developing novel PHUs network using renewable biobased resources and further explores its applicability as adhesives.

Synthesis and Evaluation of Antimicrobial Biobased Waxes as Coating Materials.

The objective of this study was to synthesize and evaluate the efficacy of antimicrobial waxes to be used as both physical and biological protection to perishable fruits and vegetables. The existing wax materials used in postharvest coating applications do not provide this antimicrobial functionality. One class of such waxes was obtained by covalently linking quaternary ammonium compounds (QACs) featuring alkyl, benzyl, and stearyl ester hydrophobic side groups to the terminal position of a bromo stearyl ester. A second class was obtained by linking these QACs to the pendant hydroxyl group of an aliphatic diamide made of 12-hydroxystearic acid, stearic acid, and ethylene diamine. In total, six distinct structures having three different QAC groups were synthesized. Compounds containing QACs with C8 alkyl groups exhibited potent inhibition toward the growth of both bacteria and fungi. Notably, the complete inhibition of Penicillium italicum and Geotrichum candidum, two fungi detrimental to the postharvest quality of fruits, as well as the complete destruction of viable cells for Gram-positive and Gram-negative bacteria was observed when these organisms were incubated in contact with QAC waxes or dispersed in an aqueous system at a concentration of 1.0 mM. Comparatively, benzalkonium chloride with an alkyl chain length of 10 carbon can completely inhibit Staphylococcus aureus at a concentration of 1.44 mM. The properties of the attached hydrophobic groups appeared to exert a strong influence on antimicrobial activity presumably due to differences in molecular orientation, size, and differences among microbial cellular structures.

Direct Synthesis of Aliphatic Polyesters with Pendant Hydroxyl Groups from Bio-Renewable Monomers: A Reactive Precursor for Functionalized Biomaterials.

Introducing desired functionalities into biomaterials is an effective way to obtain functionalized biomaterials. A versatile platform with the possibility of postsynthesis functionalization is highly desired but challenging in biomedical engineering. In this work, linear aliphatic polyesters with pendant hydroxyl (PEOH) groups were directly synthesized using renewable malic acid/tartaric acid as raw materials under mild conditions through the polyesterification reaction promoted by 1,1,3,3-tetramethylguanidine (TMG). The hydroxyl groups on PEOH provide an active stepping stone for the fabrication of demanded functionalized polyesters. We demonstrated the possibility of the PEOH as a reactive precursor for functional group transformation, coupling of bioactive molecules, and formation of crosslinking networks. Moreover, a theranostic nanoplatform (mPEG-b-(P7-asp&TPV)-b-mPEG NPs) was synthesized using PEOH as a reactive stepping stone by the programmable combination of the above functionalization methods. Overall, these hydroxyl-containing polyesters have great potential in biological applications.

AGGREGATION BEHAVIORS OF PENDANT PHOSPHORYLCHOLINE GROUPS AND THEIR INFLUENCE ON POLYISOPRENE PROPERTIES

ABSTRACT Terminal phospholipid groups contribute considerably to the excellent comprehensive properties of NR, but their aggregation behaviors and influence on polyisoprene properties during storage and use have not yet been revealed at the molecular level. To begin to address these phenomena, two sequentially different polyisoprene copolymers were suspended with phosphorylcholine groups to disclose their influence on phase separation, network dynamics, mechanical properties, and crystallization differences. Phosphorylcholine groups attached to polymer chains can form aggregates that increase the storage modulus of rubbers, and this process is accelerated at elevated temperatures due to faster chain movement. In addition, phosphorylcholine groups act as crosslinking points in unvulcanized and vulcanized rubbers and increase mechanical properties by promoting strain-induced crystallization (SIC). By contrast, the polymers with pendant hydroxyl groups present sequence-dependent SIC properties that are ascribed to their non-aggregation nature.

Biodegradable Block Poly(ester amine)s with Pendant Hydroxyl Groups for Biomedical Applications.

The article presents the results of the synthesis and characteristics of the amphiphilic block terpolymers, built of a hydrophilic polyesteramine block, and hydrophobic blocks made of lactidyl and glycolidyl units. These terpolymers were obtained during the copolymerization of L-lactide with glycolide carried out in the presence of previously produced macroinitiators with protected amine and hydroxyl groups. The terpolymers were prepared to produce a biodegradable and biocompatible material containing active hydroxyl and/or amino groups, with strong antibacterial properties and high surface wettability by water. The control of the reaction course, the process of deprotection of functional groups, and the properties of the obtained terpolymers were made based on 1H NMR, FTIR, GPC, and DSC tests. Terpolymers differed in the content of amino and hydroxyl groups. The values of average molecular mass oscillated from about 5000 g/mol to less than 15,000 g/mol. Depending on the length of the hydrophilic block and its composition, the value of the contact angle ranged from 50° to 20°. The terpolymers containing amino groups, capable of forming strong intra- and intermolecular bonds, show a high degree of crystallinity. The endotherm responsible for the melting of L-lactidyl semicrystalline regions appeared in the range from about 90 °C to close to 170 °C, with a heat of fusion from about 15 J/mol to over 60 J/mol.

3D printing of dynamic covalent polymer network with on-demand geometric and mechanical reprogrammability

Delicate geometries and suitable mechanical properties are essential for device applications of polymer materials. 3D printing offers unprecedented versatility, but the geometries and mechanical properties are typically fixed after printing. Here, we report a 3D photo-printable dynamic covalent network that can undergo two independently controllable bond exchange reactions, allowing reprogramming the geometry and mechanical properties after printing. Specifically, the network is designed to contain hindered urea bonds and pendant hydroxyl groups. The homolytic exchange between hindered urea bonds allows reconfiguring the printed shape without affecting the network topology and mechanical properties. Under different conditions, the hindered urea bonds are transformed into urethane bonds via exchange reactions with hydroxyl groups, which permits tailoring of the mechanical properties. The freedom to reprogram the shape and properties in an on-demand fashion offers the opportunity to produce multiple 3D printed products from one single printing step.

Selective removal of copper (II) ions from aqueous solution using pyridyl-bridged mesoporous organosilica hybrid adsorbent

The incorporation of active functional groups into the mesoporous organosilica hybrid materials is efficient for various applications. A newly designed mesoporous organosilica adsorbent was prepared using diaminopyridyl groups bridged-(bis-trimethoxy)organosilane (DAPy) precursor by using Pluronic P123 as structure directing template via sol-gel co-condensation method. The hydrolysis reaction of DAPy precursor and tetraethyl orthosilacate (TEOS) with a DAPy content of about 20 mol% to TEOS were incorporated into the mesopore walls of the mesoporous organosilica hybrid nanoparticles (DAPy@MSA NPs). Low-angle XRD and FT-IR, N2 adsorption-desorption analysis, SEM, TEM, and TG analysis were used to characterize the synthesized DAPy@MSA NPs. The DAPy@MSA NPs exhibit an order mesoporous structure with a high surface area, mesopore size and pore volume of approximately ∼465 m2/g, 4.4 nm and 0.48 cm3/g, respectively. The pyridyl groups integrated DAPy@MSA NPs showed the selective adsorption of Cu2+ ions from the aqueous medium by metal-ligand complex coordination of Cu2+ ions with the integrated pyridyl groups and the pendant hydroxyl (-OH) functional groups present into the mesopore walls of the DAPy@MSA NPs. In the presence of other competitive metal ions (Cr2+, Cd2+, Ni2+, Zn2+, and Fe2+), the DAPy@MSA NPs showed relatively high adsorption of Cu2+ ions (276 mg/g) from aqueous solution as compared to the other competitive metal ions at the same concentration (100 mg/L) of initial metal ion solution.

Intramolecular oxypalladation-initiated domino sequence: One-pot, two-step regioselective synthesis of isoquinolines

A palladium-catalyzed one-pot, two-step sequential reaction of 2-alkynylarylaldehydes and ketones was established to access isoquinolines under mild conditions. The initial palladium-triggered 6-endo-dig cyclization-hydration-ring opening sequence afforded the 1,5-dicarbonyl compounds and the subsequent annulation in the presence of ammonium acetate delivered the isoquinoline derivatives in good to excellent yields (up to 97%) in short reaction times. The challenging alkynes bearing pendant hydroxyl and amino functionalities have shown significant reactivity in accessing the corresponding isoquinolines in good yields. The developed domino sequence was highly regioselective and completely evaded the competitive 5-exo-dig cyclization leading to indenones unlike the gold-catalyzed literature precedent.