Free Radical Initiator Research Articles

The effect of free radical initiators on poly (butylene adipate-co-terephthalate) (PBAT) and its foaming performance

The effect of free radical initiators on poly (butylene adipate-co-terephthalate) (PBAT) and its foaming performance

Tumor Receptor-Mediated Morphological Transformation and In Situ Polymerization of Diacetylene-Containing Lipidated Peptide Amphiphile on Cell Membranes for Tumor Suppression.

In situ polymerization on cell membranes can decrease cell mobility, which may inhibit tumor growth and invasion. However, the initiation of radical polymerization traditionally requires exogenous catalysts or free radical initiators, which might cause side effects in normal tissues. Herein, we synthesized a Y-type diacetylene-containing lipidated peptide amphiphile (TCDA-KFFFFK(GRGDS)-YIGSR, Y-DLPA) targeting integrins and laminin receptors on murine mammary carcinoma 4T1 cells, which underwent nanoparticle-to-nanofiber morphological transformation and in situ polymerization on cell membranes. Specifically, the polymerized Y-DLPA induced 4T1 cell apoptosis and disturbed the substance exchange and metabolism. In vitro assays demonstrated that the polymerized Y-DLPA nanofibers decreased the migration capacity of 4T1 cells, potentially suppressing tumor invasion and metastasis. When administered locally to 4T1 tumor-bearing mice, the Y-DLPA nanoparticles formed a biomimetic extracellular matrix that effectively suppressed tumor growth. This study provides an in situ polymerization strategy that can serve as an effective drug-free biomaterial with low side effects for antitumor therapy.

Peroxide free radical grafting of maleic anhydride onto polyethylene under high melt temperature: A comprehensive approach

“Flash Reactive Extrusion” under very high temperatures (T=200–420°C) allowed to graft maleic anhydride onto polyethylene (PE) without the use of conventional free radical initiators such as peroxides. Herein, the use of unusual temperatures induced the formation of radicals through degradation/chain scission of the PE backbone and the latter radicals were able to react with maleic anhydride (MA) and yielding a MA grafting degree close to 1.4 wt% at 390°C. Moreover, the MA grafting mechanistic scheme was deeply discussed with the help of 1H NMR and 13C NMR analysis and it was pointed out that β-scissions reactions are favoured in comparison with the cross-linking ones at very high temperatures for the thermal initiation step with a MA grafting mainly onto the PE side chain.

Prussian Blue-Assisted NIR Triggered In-Situ Polymerized Nanocomposite Hydrogel for Wound Repair.

Hydrogels are commonly used as wound dressings to help maintain a moist environment around the wound and isolate contaminants, thus promoting healing. For irregular wounds, the slow healing process and even infection may occur due to the inability of dressings to adhere well to the wound. Prussian blue (PB) is a metal-organic framework (MOF) material with excellent photothermal conversion and superior stability. In this paper, a kind of near-infrared (NIR) light triggered in-situ polymerized antimicrobial hydrogel was prepared. The free radical initiator was encapsulated in the hollow PB by a phase change material (PCM) to maintain stability. The raised temperature triggered by NIR induced the release and decomposition of the initiator. The matrix was formed by the cross-linking of double bonds on modified chitosan. The quaternary amine groups of modified chitosan and the photothermal properties of PB enhanced the antimicrobial properties of the hydrogel. High-quality wound healing was demonstrated in the whole skin defect model. This study provides a new reference for the preparation of in-situ polymerized hydrogel dressings for irregular wounds.

Improved Performance of Polylactic Acid Biocomposites at High Lignin Loadings through Glycidyl Methacrylate Grafting of Melt-Flowable Organosolv Lignin.

Glycidyl methacrylate (GMA) was grafted onto a melt-flowable organosolv lignin, called bioleum (BL), using a melt mixing process. Then, up to 40 wt % of BL-g-GMA was blended with polylactic acid (PLA) in the presence of dicumyl peroxide as a free radical initiator utilizing a melt extrusion method. Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis, differential scanning calorimetry, scanning electron microscopy, and tensile testing were performed to characterize the biocomposites' performance. The FTIR results revealed a successful grafting of GMA onto BL. Overall, BL and PLA compatibility increased significantly with the grafting and resulted in decreased domain size of BL-g-GMA and thus enhanced all the tensile properties (strength, modulus, and elongation at break) at BL loadings as high as 40 wt %. For instance, in the biocomposites containing 30 wt % BL, the GMA grafting increased the tensile strength by 23%. The presence of BL and BL-g-GMA hindered PLA's crystallization even when it was cooled at a rate of 1 °C/min. However, the composites with BL-g-GMA showed a crystallinity value comparable to that of PLA during isothermal crystallization, but with a slower crystallization rate. This work reveals a facile and scalable method that can be adopted to enhance the performance of lignin-based biocomposites.

Enhanced Antibacterial Activity of Clindamycin Using Molecularly Imprinted Polymer Nanoparticles Loaded with Polyurethane Nanofibrous Scaffolds for the Treatment of Acne Vulgaris.

Acne vulgaris, a prevalent skin condition, arises from an imbalance in skin flora, fostering bacterial overgrowth. Addressing this issue, clindamycin molecularly imprinted polymeric nanoparticles (Clin-MIP) loaded onto polyurethane nanofiber scaffolds were developed for acne treatment. Clin-MIP was synthesized via precipitation polymerization using methacrylic acid (MAA), ethylene glycol dimethacrylate (EGDMA), and azoisobutyronitrile (AIBN) as functional monomers, crosslinkers, and free-radical initiators, respectively. MIP characterization utilized Fourier-transform infrared spectroscopy (FTIR) and transmission electron microscopy (TEM) before being incorporated into polyurethane nanofibers through electrospinning. Further analysis involved FTIR, scanning electron microscopy (SEM), in vitro release studies, and an ex vivo study. Clin-MIP showed strong antibacterial activity against S. aureus, with inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) values of 0.39 and 6.25 μg/mL, respectively. It significantly dropped the bacterial count from 1 × 108 to 39 × 101 CFU/mL in vivo and has bactericidal activity within 180 min of incubation in vitro. The pharmacodynamic and histopathology studies revealed a significant decrease in infected animal skin inflammation, epidermal hypertrophy, and congestion upon treatment with Clin-MIP polyurethane nanofiber and reduced pro-inflammatory cytokines (NLRP3, TNF-α, IL-1β, and IL-6) conducive to acne healing. Consequently, the recently created Clin-MIP polyurethane nanofibrous scaffold. This innovative approach offers insight into creating materials with several uses for treating infectious wounds caused by acne.

K2S2O8-Mediated or Azobisisobutyronitrile-Catalyzed Regioselective Aerobic Oxidative Cleavage of 1-Arylbutadienes to Cinnamaldehydes.

This work reveals the regioselective oxidative cleavage of 1-arylbutadienes to cinnamaldehydes mediated by K2S2O8 or catalyzed by azobisisobutyronitrile, a very common free radical initiator, in an easy to handle, simple procedure and free of transition metals. This approach demonstrates excellent regioselectivity, mild reaction conditions, and compatibility with a broad range of functional groups (45 examples).

Cleavable azobenzene linkers for the design of stimuli-responsive materials.

The azo linkage (NN) is one of the very few functional groups in organic chemistry that exhibits sensitivity towards thermal, chemical, photochemical, and biological stimuli. Consequently, this property has given rise to a distinct class of responsive materials. For example, thermal sensitivity has led to generation of free radical initiators useful in curing and polymerization applications. Chemically-induced cleavage has aided the development of self-immolative polymers and reactive scaffolds for proteomics applications. Photo-isomerization capability has given rise to photo-responsive systems. Azobenzene cleavage in biologically reducing environments, such as that of the colon, and under tumor hypoxia conditions has led to diagnostic, therapeutic, and delivery materials. Such conditions have also allowed for control over formation (assembly) and disruption (disassembly) of micellar nanoparticles. The aim of this review article is to look beyond the prevalent photosensitivity aspect of the aromatic azo compounds and draw attention to the azo scission reaction as a trigger of the change in the structure and properties of organic materials. Thus, the main discussion begins with the mechanism of the reductive cleavage. Then, its application in the design of molecules that can be activated as drugs and fluorescent sensors, (nano)materials with potential to release active substances, and polymers with side-chain and main-chain self-immolative capacity is discussed. Finally, the status and future challenges in this field are discussed.

Acceleration of Zeolite Crystallization: Current Status, Mechanisms, and Perspectives.

Zeolites are important classes of crystalline materials and possess well-defined channels and cages with molecular dimensions. They have been extensively employed as heterogeneous catalysts and gas adsorbents due to their relatively large specific surface areas, high pore volumes, compositional flexibility, definite acidity, and hydrothermal stability. The zeolite synthesis normally undergoes high-temperature hydrothermal treatments with a relatively long crystallization time, which exhibits low synthesis efficiency and high energy consumption. Various strategies, e.g., modulation of the synthesis gel compositions, employment of special silica/aluminum sources, addition of seeds, fluoride, hydroxyl (·OH) free radical initiators, and organic additives, regulation of the crystallization conditions, development of new approaches, etc., have been developed to overcome these obstacles. And, these achievements make prominent contributions to the topic of acceleration of the zeolite crystallization and promote the fundamental understanding of the zeolite formation mechanism. However, there is a lack of the comprehensive summary and analysis on them. Herein, we provide an overview of the recent achievements, highlight the significant progress in the past decades on the developments of novel and remarkable strategies to accelerate the crystallization of zeolites, and basically divide them into three main types, i.e., chemical methods, physical methods, and the derived new approaches. The principles/acceleration mechanisms, effectiveness, versatility, and degree of reality for the corresponding approaches are thoroughly discussed and summarized. Finally, the rational design of the prospective strategies for the fast synthesis of zeolites is commented on and envisioned. The information gathered here is expected to provide solid guidance for developing a more effective route to improve the zeolite crystallization and obtain the functional zeolite-based materials with more shortened durations and lowered cost and further promote their applications.

Mucus and Biofilm Penetrating Nanoplatform as an Ultrasound-Induced Free Radical Initiator for Targeted Treatment of Helicobacter pylori Infection.

Helicobacter pylori (H. pylori) infection is closely associated with the development of various gastric diseases. The effectiveness of current clinical antibiotic therapy is hampered by the rise of drug-resistant strains and the formation of H. pylori biofilm. This paper reports a sonodynamic nanocomposite PtCu3-PDA@AIPH@Fucoidan (PPAF), which consists of dopamine-modified inorganic sonosensitizers PtCu3, alkyl radicals (R•) generator AIPH and fucoidan, can penetrate the mucus layer, target H. pylori, disrupt biofilms, and exhibit excellent bactericidal ability. In vitro experiments demonstrate that PPAF exhibits excellent acoustic kinetic properties, generating a significant amount of reactive oxygen species and oxygen-independent R• for sterilization under ultrasound stimulation. Simultaneously, the produced N2 can enhance the cavitation effect, aiding PPAF nanoparticles in penetrating the gastric mucus layer and disrupting biofilm integrity. This disruption allows more PPAF nanoparticles to bind to biofilm bacteria, facilitating the eradication of H. pylori. In vivo experiments demonstrate that ultrasound-stimulated PPAF exhibited significant antibacterial efficacy against H. pylori. Moreover, it effectively modulated the expression levels of inflammatory factors and maintained gastrointestinal microbiota stability when compared to the antibiotic treatment group. In summary, PPAF nanoparticles present a potential alternative to antibiotics, offering an effective and healthy option for treating H. pylori infection.

Integrated drug delivery system loading ROS-generating antitumor drugs for signal-amplified photoacoustic imaging and multimodal tumor therapy

The usefulness of antitumor drugs that produce reactive oxygen species (ROS) in accurate tumor diagnosis and treatment has been underestimated. Here, β-Lapachone (Lapa, antitumor drugs), 2,2′-azino-bis (3-ethylbenzothiazoline-6-sulfonic acid) (ABTS, precursor photoacoustic agents) and 2, 2′-azobis[2-(2-imidazolin-2-yl) propane] dihydrochloride (AIPH, free radical initiators) were successfully loaded into zeolitic imidazolate framework (ZIF) in situ by a one-pot method and named Lapa/ABTS/AIPH@ZIF-67 nanoparticles (LBIZ NPs). After entering the tumor cell, the ZIF structure of LBIZ NPs is disrupted in the acidic tumor microenvironment, which results in the release of Co2+ and drugs. In one hand, Lapa and Co2+ together increased hydroxyl radicals (•OH) levels to achieve Enhanced-Chemodynamic therapy (ECDT). As the amount of •OH went up, the amount of ABTS•+, the oxidation product of ABTS, would also increase, thus increasing the sensitivity and contrast of photoacoustic imaging. In the other hand, the photothermal effect produced by ABTS•+ induces AIPH to crack and release alkyl radicals (•R) to achieve thermodynamic therapy. The LBIZ NPs achieved more effective tumor treatments by fully utilizing light and heat energy. Hence, this integrated drug delivery system is able to achieve signal-amplified photoacoustic imaging and Enhanced-Chemodynamic/Photothermal/Thermodynamic trimodal combination therapy. This work provides a new insight into the application of ROS-generating antitumor drugs to precise imaging of tumors.

Stable and efficient perovskite solar cells based on tert-butyl peroxy-2-ethylhexanoate modified hole transport layer

Nowadays, perovskite solar cells (PSCs) have gained significant attention as one of the most promising new energy technologies. However, the application of spiro-OMeTAD, a highly efficient organic hole transport material (HTM) in PSCs, is limited due to its inherent weaknesses in conductivity and hole mobility. Here, a free radical initiator, tert-butyl peroxy-2-ethylhexanoate (TBPEH) is introduced to induce the rapid and controllable oxidation of Spiro. TBPEH-modified hole transport layer (HTL) produces more free radical cations, increasing carrier mobility and electrical conductivity. A smoother surface of the modified HTL improves the charge transport efficiency. Additionally, trap-state density and defect-induced nonradiative recombination of TBPEH-modified device are decreased. In addition, better energy level matching between the HTL and perovskite layer enables more efficient hole transport. Consequently, the PSC doped with TBPEH achieves a champion power conversion efficiency (PCE) of 24.33 %, surpassing the PCE of 21.72 % obtained from the pristine device. Furthermore, the TBPEH-modified devices show better stability. Storing in the atmosphere at 30 % relative humidity for 42 days, the TBPEH-modified device maintains 90.8 % of its highest efficiency, compared to the 73.8 % of the pristine one.

Introducing sulfonic acid polymers into MOF nanochannels for ultra-high Ba2+ adsorption capacity and proton conductivity

Porous materials with a high concentration of sulfonic acid groups are highly desirable for applications such as radioactive Ba2+ adsorption, catalysis, and proton-conductive materials, but they are also challenging to synthesize. In this work, we introduce polymers containing sulfonic acid groups into the nanochannels of metal–organic frameworks (MOFs) through in-situ synthesis to enhance the sulfonic acid content. We use a alkene with sulfonic acid groups (2)-acrylamido-2-methylpropane sulfonic acid, AMPS) and a crosslinking agent N,N’-methylenebisacrylamide (MBAA) to synthesize two MOF composites, PAMPS@MIL-101 and PAMPS@MIL-101-SO3H, in the ultra-stable MIL-101 series through in-situ polymerization with free radical initiators. The two MOF composites have a high and uniform distribution of sulfonic acid groups in the MOF framework, which results in ultra-high barium ion adsorption capacity. The maximum adsorption amounts are 142.7 and 356.9 mg·g−1 for PAMPS@MIL-101 and PAMPS@MIL-101-SO3H, respectively, which are higher than those of most reported adsorbents. Importantly, the adsorption equilibrium can be achieved within 20 min. Moreover, both MOF composites, PAMPS@MIL-101 and PAMPS@MIL-101-SO3H, exhibit super proton conductivity, with values of 6.43 × 10−2 S·cm−1 and 1.43 × 10−1 S·cm−1 at 85 °C and 98 % RH, respectively. This method offers a new way of modifying MOF nanochannels with high sulfonic acid concentrations, and opens up new opportunities for developing radioactive Ba2+ adsorption materials and proton-conductive materials.

Lipid Peroxidation in Muscle Foods: Impact on Quality, Safety and Human Health.

The issue of lipid changes in muscle foods under the action of atmospheric oxygen has captured the attention of researchers for over a century. Lipid oxidative processes initiate during the slaughtering of animals and persist throughout subsequent technological processing and storage of the finished product. The oxidation of lipids in muscle foods is a phenomenon extensively deliberated in the scientific community, acknowledged as one of the pivotal factors affecting their quality, safety, and human health. This review delves into the nature of lipid oxidation in muscle foods, highlighting mechanisms of free radical initiation and the propagation of oxidative processes. Special attention is given to the natural antioxidant protective system and dietary factors influencing the stability of muscle lipids. The review traces mechanisms inhibiting oxidative processes, exploring how changes in lipid oxidative substrates, prooxidant activity, and the antioxidant protective system play a role. A critical review of the oxidative stability and safety of meat products is provided. The impact of oxidative processes on the quality of muscle foods, including flavour, aroma, taste, colour, and texture, is scrutinised. Additionally, the review monitors the effect of oxidised muscle foods on human health, particularly in relation to the autooxidation of cholesterol. Associations with coronary cardiovascular disease, brain stroke, and carcinogenesis linked to oxidative stress, and various infections are discussed. Further studies are also needed to formulate appropriate technological solutions to reduce the risk of chemical hazards caused by the initiation and development of lipid peroxidation processes in muscle foods.

Flocculation of kaolin and anion dye by cationic cellulose-based flocculant: RSM-optimized synthesis and experimental study

An efficient cellulose-based flocculant, CMA, was synthesized using a free radical initiation method in a NaOH/Urea aqueous solution. The optimal synthesis conditions were determined through single-factor and RSM experiments: a molar ratio of MCC to AA of 1:3.6, MCC to CTA of 1:8.2, and a reaction temperature of 45.8 °C. CMA was characterized using FTIR, SEM, XRD, DLS, XPS, and TG and applied successfully to the flocculation treatments of kaolin, simulated dyes, and actual dye wastewater. It exhibited low pH sensitivity, achieving over 90% removal efficiency at pH 3–12, with a maximum of 98.3%. In simulated dye wastewater, the removal efficiency of various dyes was greater than 95%, with a maximum of 97%. After CMA flocculation and ozone aeration, 86.5% of COD and 93.6% of turbidity were removed from the actual dye wastewater. CMA carried out the flocculated dye removal process via charge neutralization, double layer compression, and bridging adsorption, as revealed by various instrument characterization and analysis. A polysaccharide-based flocculant, CMA exhibits environmentally friendly properties, low pH sensitivity, and high efficiency in removing wastewater pollutants, making it a promising flocculant for highly turbid wastewater and anionic dye wastewater.

Self-heating mitochondrion-induced free radical blast for immunogenic cell death stimulation and HCC immunotherapy

Hepatocellular carcinoma (HCC) is an immunosuppressive tumor associated with high mortality. Photothermal and photodynamic therapies have been applied to induce immunogenic cell death (ICD) in HCC, successfully eliciting immune responses but facing limitations in penetration depth in clinical trials. Here, intrinsic mitochondrial hyperthermia was used to trigger thermosensitive drug release. The mitochondria were further self-heated through 2,4-dinitrophenol uncoupling, dramatically promoting free radical initiation and inducing tumor ICD. The synthesized mitochondrial-targeting TPP-HA-TDV nanoparticles specifically generated free radicals in the mitochondria without external stimulation, and obviously enhanced the release of ICD markers, subsequently evoking immune responses. The results showed that mitochondrial hyperthermia could be an endogenous target for thermosensitive drug release. Furthermore, self-heating mitochondria-induced free radical blast could be an efficient therapeutic for deep-seated tumor therapy.

THERMORESPONSIVE CELLULOSE NANOCRYSTALS PROTECTING MACROPHAGE CELLS FROM OXIDATIVE STRESS

Cellulose nanocrystals (CNCs) were grafted with poly(N-isopropylacrylamide) (PNIPAM) chains, by means of the grafting from route, using the TEMED/KPS redox pair as free-radical initiators. The confirmation of grafting was revealed by 13C NMR spectra. In a test with murine macrophages (RAW 264.7 cell line), CNC-g-PNIPAM copolymers did not affect cell viability nor RAW cell oxide nitric production. Raw cells exposed to oxidative stress induced by H2O2 decreased the cell viability (~ 60%) and increased lipid peroxidation, as revealed by malondialdehyde (MDA), glutathione (GSH) and superoxide dismutase (SOD) levels. The most effective protection against the oxidative damage, with cell viability of 100%, was provided by 50 µg mL-1 of CNC-g-PNIPAM synthesized with 1:1 CNC:NIPAM mass ratio. Furthermore, there was no significant difference between the levels of GSH, MDA and SOD between cells treated with the modified CNC and cells not exposed to peroxide. These results indicate that the antioxidant properties of CNC-g-PNIPAM may be useful in possible applications in health treatments.

Synthesis of tragacanth gum-based programmable adhesive for wood binding applications

Synthesis of graft copolymer [2-(methacryloyloxy) ethyl]trimethylammonium chloride (MAETMAC) grafted gum tragacanth was performed using the microwave-assisted technique using potassium persulfate (KPS) as a free radical initiator. The synthesized grades were optimized by varying the monomer and the initiator concentration. The intended grafting was ascertained through standard physico-chemical characterizations. The synthesized graft copolymer was studied as a water-soluble adhesive for fabrication of single lap joint. The failure shear stress of lap joint was obtained using the Universal Testing Machine (UTM). Further, the self-separation study of the lap joints was carried out by soaking the lap-joint under water until they got self-separated. The failure shear stress and self-separation time of the adhesive in water were compared with three commercial adhesives available. The properties “self separation time” in water and “failure shear stress” were programmable at the molecular level (molecular level programming) in terms of percentage grafting.

Effect of molecular weight and its modality on pressure-sensitive adhesives behavior of plant oil-based latexes

Semibatch emulsion polymerization of high oleic soybean oil-based monomer (HO-SBM), 2–ethylhexyl acrylate (2-EHA), and styrene (St) was applied to synthesize pressure-sensitive latex adhesives with up to 40 wt% of plant oil-based content. Ternary latex copolymers with similar chemical composition and broadly different molecular weight distribution (MWD) and modality were synthesized at varying temperatures and the mechanism of free-radical initiation. Conventional thermal initiation with ammonium persulphate at 80 °C and ascorbic acid/tert-butyl hydroperoxide redox system of lower reaction temperature up to 20 °C were employed. Linear, short-chain, and long-chain branched macromolecules are formed due to chain-breaking reactions of HO-SBM (chain transfer on allyl groups) and 2-EHA (inter- and intramolecular chain transfer on the polymer). The dominant effect of chain transfer on allyl group protons and subsequent decrease in molecular weight was observed at higher reaction temperatures, while extensively branched polymer with high molecular weight was obtained at reaction temperature close to 20 °C.The effect of MWD and branching on the PSAs performance of synthesized biobased latexes was studied using loop tack and peel strength and lap shear testing and compared to two commercial PSA tapes as a benchmark. A significant increase in shear strength (up to 0.23 MPa) was observed for latex adhesives due to high molecular weight fractions, maintaining satisfactory level of tack (3–7 N) and peel (3–6 N/in). Broad MWD of the copolymers can be beneficial for providing materials with high shear strength (0.25–0.33 MPA) while preserving the significant level of tack (2–4 N) and peel strength (9–12 N/in) on both glass and steel substrates.

Combining isosorbide and lignin-related benzoic acids for high-Tg polymethacrylates

The insertion of rigid aliphatic or aromatic building blocks in polymer structures is an efficient synthetic strategy towards high-Tg polymer materials. In the present work, we have functionalized isosorbide 5-methacrylate with various aromatic lignin-inspired esters to yield a series of isosorbide-2-aryl carboxylate-5-methacrylate monomers (ArIMAs) as single regioisomers. The selection of phenyl carboxylate side groups included benzoate, p-cyanobenzoate, meta/para-methoxybenzoates, and different vanillic acid esters. This afforded a range of seven bio-based monomers with different size, polarity, and substitutions. Polymerizations were carried out by conventional free radical initiation to obtain the corresponding high molecular-weight poly(aryl carboxylate isosorbide methacrylate)s (PArIMAs). The polymerizations were evaluated in different solvents, including toluene, EtOAc, γ-valerolactone, 2-MeTHF, and DMSO to identify the most suitable conditions. The polymers exhibited high glass transition temperatures in a broad range, from 80 to 168 °C, and were thermally stable up to 268 °C. Furthermore, dynamic rheology experiments indicated that the polymers were sufficiently stable for melt processing. The availability of the building blocks combined with the high stability of the polymers make these materials attractive for use as high-performance plastics and coatings.