Gamma-irradiation of cellulose nanocrystals (CNCs): investigation of physicochemical and antioxidant properties

Gamma irradiation is a common process mostly used for sterilization against bacteria growth. However, when the process is applied to a material, physical and chemical changes may alter its integrity and behaviour. The aim of this study was to observe the effect of γ-irradiation on the surface chemistry of CNCs. The carbonyl content (both carboxylic acid and aldehyde functionalities) was followed to investigate the influence of the irradiation dose. Thermal stability, wettability and antioxidant properties were also measured. Conductometric titration showed that the carboxylic acid groups content (COOH) was increased from 43 mmol COOH kg^?1 CNCs for native CNCs to 631 mmol COOH kg^?1 CNCs when a dose of 80 kGy was applied. These changes were confirmed by FTIR and fluorescence spectroscopy. At high irradiation doses, a significant decrease of approximately 30% was observed in the cellulose degree of polymerization while the aldehyde groups content was increased to 379 mmol CHO kg^?1 CNCs due to the cleavage of glycosidic linkages. These physicochemical changes led to enhanced antioxidant properties of CNCs.     

Hybrid fluorescent nanoparticles from quantum dots coupled to cellulose nanocrystals

Carboxylated cellulose nanocrystals (CNCs) were decorated with CdSe/ZnS quantum dots (QDs) using a carbodiimide chemistry coupling approach. The one-step covalent modification was supported by nanoscale imaging, which showed QDs clustered on and around the CNCs after coupling. The QD–CNC hybrid nanoparticles remained colloidally stable in aqueous suspension and were fluorescent, exhibiting the broad excitation and narrow emission profile characteristic of the QDs. QD–CNCs in nanocomposite films imparted strong fluorescence within CNC-compatible matrices at relatively low loadings (0.15 nmol QDs/g of dry film), without altering the overall physical properties or self-assembly of the CNCs. The hybrid QD–CNCs may find applications in nanoparticle tracking, bio-imaging, optical/sensing devices, and anti-counterfeit technologies.     

High-performance natural rubber nanocomposites with marine biomass (tunicate cellulose)

Due to the importance in economic and environmental benefits, marine biomass has gained increasing attention in recent years. In this work, marine biomass-based materials were prepared and characterized. Highly reinforcing cellulose nanocrystals (CNCs) with length of 1–2 μm and aspect ratio of ~75 were extracted from tunicates (t-CNCs), and CNCs with length of 100–300 nm and aspect ratio of ~15 from cotton (c-CNCs) were presented for comparison. In order to enhance interfacial interactions between CNCs and rubber, modification of natural rubber (NR) was conducted via epoxidation reaction to obtain epoxidized NR (ENR). Fully bio-based rubber nanocomposites were produced by latex mixing. Compared with NR nanocomposites, hydrogen bonding formed between ENR and CNCs, which led to homogeneous dispersion of CNCs and enhanced interfacial adhesion between them. Moreover, t-CNCs with longer length and larger aspect ratio facilitate filler entanglements, which led to higher reinforcing efficiency. Consequently, both hydrogen bonding and filler entanglements contributed to the improved mechanical properties of ENR/t-CNCs nanocomposites.     

Optimized preparation and preliminary evaluation of [64Cu]–DOTA–trastuzumab for targeting ErbB2/Neu expression

Breast cancer radioimmunoscintigraphy targeting HER2/neu expression is a growing field of work in nuclear medicine research. Trastuzumab is a monoclonal antibody that binds with high affinity to HER2/neu, which is over expressed on breast and other tumors. Developing new tracers for the detection of this cancer is of great interest. In this study, trastuzumab was successively labeled with [⁶⁴Cu]CuCl₂ after conjugation with DOTA-NHS-ester. The conjugate was purified by molecular filtration, the average number of DOTA conjugated per mAb was calculated and total concentration was determined by spectrophotometric method. DOTA–trastuzumab was labeled with ⁶⁴Cu produced by ⁶⁸Zn(p,αn)⁶⁴Cu nuclear reaction (30 MeV protons at 180 μA). Radiochemical purity, integrity of protein after radiolabeling and immunoreactivity of radiolabeled mAb trastuzumab with HER2/neu antigen and SkBr3 cell line were performed by RIA. In vitro stability of radiolabeled mAb in human serum was determined by thin layer chromatography. In vitro internalization studies were performed with the SkBr3 cell line and the tissue biodistribution of the ⁶⁴Cu–DOTA–trastuzumab was evaluated in wild-type rat (90 ± 5.5 μCi, 2, 6, 12, 24 h p.i.). The radioimmunoconjugate was prepared with a radiochemical purity of higher than 96 ± 0.5 % (ITLC) and specific activity as high as 5.3 μCi/μg. The average number of chelators per antibody for the conjugate used in this study was 5.8/1. The sample was showed to have similar patterns of migration in the gel electrophoresis. The ⁶⁴Cu–DOTA–trastuzumab showed high immunoreactivity towards HER2/neu antigen and SkBr3 cell line. In vitro stability of the labeled product was found to be more than 94 % in PBS and 82 ± 0.5 % in human serum over 48 h. In vitro internalization studies of the ⁶⁴Cu–DOTA–trastuzumab showed that up to 11.5 % of the radioimmunoconjugate internalized after 10 h. The accumulation of the radiolabeled mAb in liver, skin, intestine, lung, spleen, kidney and other tissues demonstrates a similar pattern to the other radiolabeled anti-HER2 immunoconjugates. ⁶⁴Cu–DOTA–trastuzumab is a potential compound for molecular imaging of PET for diagnosis and treatment studies and follow-up of HER2 expression in oncology.     

Acryloyl-modified cellulose nanocrystals: effects of substitution on crystallinity and copolymerization with acrylic monomers

Cellulose nanocrystals (CNCs) are crystalline nano-rods that have high specific strength with hydroxyl surface chemistry. A wide range of chemical modifications have been performed on the surface of CNCs to increase their potential to be used in applications where compatibilization with other materials is required. Understanding the surface chemistry of CNCs and critically examining the functionalization technique are crucial to enable control over the extent of modification and the properties of CNCs. This work aims to optimize the surface modification of wood-derived CNCs with isocyanatoethyl methacrylate (IEM), a bifunctional molecule carrying both isocyanate and vinyl functional groups. We studied the effect of modification reaction time and temperature on the degree of substitution, crystallinity, and morphology of the CNCs. We found that the degree of modification is a strong and increasing function of reaction temperature over the range studied. However, the highest temperature (65 °C) and the longest time of reaction (6 h) resulted in shorter, thinner, and less crystalline CNCs. We obtained surface hydroxyl conversion of 60.1?±?6% and percent crystallinity of 84% by keeping the reaction shorter (30 min) at 65 ºC. Also, the copolymerization ability of modified CNCs was verified by polymerizing attached IEM groups with acrylic monomers via solution polymerization. The polymer-grafted CNCs (6% w/w) dispersed better in an acrylic polymer matrix compared to unmodified CNCs (umCNCs), resulting in approximately 100% improvement in the tensile strength and about 53% enhancement in the hardness of the acrylic, whereas addition of 6% w/w umCNCs did not influence the strength and hardness.

Graphic abstract

     

Cellulosic nanocomposite membranes from hydroxypropyl cellulose reinforced by cellulose nanocrystals

Cellulosic nanocomposite membranes were prepared by incorporation of cellulose nanocrystals (CNCs) into a hydroxypropyl cellulose (HPC) matrix using a mixing/evaporation technique. CNCs were obtained from filter paper using the sulfuric acid hydrolysis method with the aid of ultrasonication. The relationship between the microstructure and mechanical properties of the CNCs/HPC nanocomposite membranes was studied. Scanning electron microscopy showed that the CNCs were well dispersed in the HPC matrix, and the fracture surface demonstrated a fibrous characteristic. With increasing CNCs content, the tensile strength and Young’s modulus of the CNCs/HPC nanocomposite membranes gradually increased. At 5 wt% content of CNCs, the strength was increased by 525 % and the Young’s modulus by 124 % compared with pure HPC membrane. Moreover, the effect of the phase change of HPC on the mechanical properties of the CNCs_5wt%/HPC nanocomposite membranes and the corresponding mechanism were also studied.     

Cellulose nanocrystals as promising adsorbents for the removal of cationic dyes

Cellulose nanocrystals (CNCs) prepared from cellulose fibre via sulfuric acid hydrolysis was used as an adsorbent for the removal of methylene blue (MB) from aqueous solution. The effects of pH, adsorbent dosage, temperature, ionic strength, initial dye concentration were studied to optimize the conditions for the maximum adsorption of dye. Adsorption equilibrium data was fitted to both Langmuir and Freundlich isotherm models, where the Langmuir model better described the adsorption process. The maximum adsorption capacity was 118 mg dye/g CNC at 25 °C and pH 9. Calculated thermodynamic parameters, such as free energy change (ΔG = ?20.8 kJ/mol), enthalpy change (ΔH = ?3.45 kJ/mol), and entropy change (ΔS = 0.58 kJ/mol K) indicates that MB adsorption on CNCs is a spontaneous exothermic process. Tunability of the adsorption capacity by surface modification of CNCs was shown by oxidizing the primary hydroxyl groups on the CNC surface with TEMPO reagent and the adsorption capacity was increased from 118 to 769 mg dye/g CNC.     

Sustainable stabilization of oil in water emulsions by cellulose nanocrystals synthesized from deep eutectic solvents

There is an urgent global need to develop novel types of environmentally safe dispersing chemicals from renewable resources in order to reduce the environmental impact of oil spills. For this goal, cellulose, the most abundant natural polymeric source, is a promising green, nontoxic alternative that could replace the current synthetic surfactants. In this study, cellulose nanocrystals (CNC) synthesized using a deep eutectic solvent (DES) and two commercially available cellulose nanocrystals were used as marine diesel oil–water Pickering emulsion stabilizers. In particular, oil in water (o/w) emulsion formation and stability of emulsified oil during storing were addressed using a laser diffraction particle size analyzer, image analysis, and oil emulsion volume examination. The particle size of the o/w reference without CNCs after dispersing was over 50 µm and coalescence occurred only a few minutes after the emulsifying mixing procedure. All three investigated CNCs were effective stabilizers for the o/w system (oil droplets size under 10 µm) by preventing the oil droplet coalescence over time (6 weeks) and resulting in a stable creaming layer. The CNCs prepared using green DES systems boasted performance comparable to that of commercial CNCs, and they showed effectiveness at 0.1% dispersant dosage.     

Effect of oligosaccharide deposition on the surface of cellulose nanocrystals as a function of acid hydrolysis temperature

Recent findings indicate there is only a small window of sulfuric acid concentration (60–65 %) and temperature (45–65 °C) which allows efficient extraction of cellulose nanocrystals in significant quantities from bleached chemical pulp. In the present report, we develop a systematic explanation for how hydrolysis temperature, at a specific acid concentration, governs CNC surface properties. We demonstrate that CNCs with different suspension viscosity, stability in electrolyte-containing solutions, and optical properties can be produced, based on the presence or not of a precipitated oligosaccharide layer (OSL) on the surface of the nanocrystals. At hydrolysis temperatures below 65 °C, the degree of polymerization (DP) distribution of cellulose chains in CNC samples exhibits a bimodal distribution, indicating an accumulation of oligosaccharides on the CNC surface which increases as the hydrolysis temperature is decreased. At low hydrolysis temperature (45 °C), the oligosaccharides dissolved in the strong acid phase have a DP between 7 and 20 and precipitate onto CNCs when the reaction is quenched by diluting with water. As the temperature of hydrolysis is increased (50–60 °C), the dissolved oligosaccharides are hydrolyzed faster and their DP decreases such that they remain soluble after quenching. At 65 °C, no precipitated oligosaccharides can be detected on the CNC surface. Based on these results, we propose possible explanations to account for the effects of the OSL on the CNC suspension viscosity and stability and on optical properties of CNC films.     

Liquid crystalline thermosets based on anisotropic phases of cellulose nanocrystals

A new class of liquid crystalline thermosets (LCTs) was successfully produced containing lyotropic cellulose nanocrystals (CNCs) as the primary mesogenic component (up to 72 wt%) by the addition of non-mesogenic epoxy monomers. Cellulose-based LCTs were produced by totally aqueous processing methods and ultimately cured at elevated temperatures to produce ordered networks of ‘frozen’ liquid crystalline (LC) phases. Various degrees of birefringence were obtained via self-assembly of CNCs into oriented phases as observed by polarized optical microscopy and transmission electron microscopy. X-ray diffraction measurements highlighted the effects of texture of CNCs within LCT films compared to lyophilized CNCs. Cellulose-based LCT films uniquely exhibited thermo-mechanical properties of both traditional LCTs and LC elastomers, such as high elastic modulus (~1 GPa) under ambient conditions and low glass transition temperature (~?25 °C), respectively. The development of LCTs based on CNCs and aqueous processing methods provides a renewable pathway for designing high performance composites with ordered network structures and unique optical properties.     

A Novel Process for Direct Production of Acetone–Butanol–Ethanol from Native Starches Using Granular Starch Hydrolyzing Enzyme by Clostridium saccharoperbutylacetonicum N1-4

In this work, a new approach for acetone–butanol–ethanol (ABE) production has been proposed. Direct fermentation of native starches (uncooked process) was investigated by using granular starch hydrolyzing enzyme (GSHE) and Clostridium saccharoperbutylacetonicum N1-4. Even the process was carried out under suboptimal condition for activity of GSHE, the production of ABE was similar with that observed in conventional process or cooked process in terms of final solvent concentration (21.3?±?0.4 to 22.4?±?0.4 g/L), butanol concentration (17.5?±?0.4 to 17.8?±?0.3 g/L) and butanol yield (0.33 to 0.37 g/g). The production of solvents was significantly dependent on the source of starches. Among investigated starches, corn starch was more susceptible to GSHE while cassava starch was the most resistant to this enzyme. Fermentation using native corn starch resulted in the solvent productivity of 0.47 g/L h, which was about 15 % higher than that achieved in cooked process. On the contrary, uncooked process using cassava and wheat starch resulted in the solvent productivity of 0.30 and 0.37 g/L h, which were respectively about 30 % lower than those obtained in cooked process. No contamination was observed during all trials even fermentation media were prepared without sterilization. During the fermentation using native starches, no formation of foam is observed. This uncooked process does not require cooking starchy material; therefore, the thermal energy consumption for solvent production would remarkably be reduced in comparison with cooked process.     

Comparison of polyethylene glycol adsorption to nanocellulose versus fumed silica in water

The recent intensification of industrially produced cellulose nanocrystals (CNCs) and cellulose nanofibrils has positioned nanocelluloses as promising materials for many water-based products and applications. However, for nanocelluloses to move beyond solely an academic interest, a thorough understanding of their interaction with water-soluble polymers is needed. In this work, we address a conflicting trend in literature that suggests polyethylene glycol (PEG) adsorbs to CNC surfaces by comparing the adsorption behaviour of PEG with CNCs versus fumed silica. While PEG is known to have strong hydrogen bonding tendencies and holds water tightly, it is sometimes (we believe erroneously) presumed that PEG binds to cellulose through hydrogen bonding in aqueous media. To test this assumption, the adsorption of PEG to CNCs and fumed silica (both in the form of particle films and in aqueous dispersions) was examined using quartz crystal microbalance with dissipation, isothermal titration calorimetry, rheology and dynamic light scattering. For all PEG molecular weights (300–10,000 g/mol) and concentrations (100–10,000 ppm) tested, strong rapid adsorption was found with fumed silica, whereas no adsorption to CNCs was observed. We conclude that unlike silanols, the hydroxyl groups on the surface of CNCs do not readily hydrogen bond with the ether oxygen in the PEG backbone. As such, this work along with previous papermaking literature supports the opinion that PEG does not adsorb to cellulose surfaces.     

High performance poly (vinyl alcohol)/cellulose nanocrystals nanocomposites manufactured by injection molding

Polyvinyl alcohol (PVA)/cellulose nanocrystals (CNCs) compounds were successfully melt-processed by injection molding. During the processing, water was involved in the system as both the dispersion medium for CNCs and the plasticizer for PVA. Meanwhile, formamide was added to prevent the evaporation of water and to co-plasticize PVA. Thermal gravimetric analysis and differential scanning calorimetry indicated the melt processing window of PVA was expanded by 40 °C. Tensile tests showed that the mechanical properties of injection-molded samples were significantly improved with the addition of CNCs. The tensile strength of the composites increased from 32 to 58 MPa, and modulus increased from 175 to 1,252 MPa when 7 wt% CNCs was added. Moreover, the volume shrinkage of PVA nanocomposites upon drying as well as their water leaching rate could be remarkably reduced in the presence of CNCs.     

Preparation and quality control and biodistribution studies of [90Y]-DOTA-cetuximab for radioimmunotherapy

Yttrium-90 is a useful radionuclide for radioimmunotherapy (RIT) and the anti-epidermal growth factor receptor (anti-EGFR) antibody cetuximab is clinicsally approved for the treatment of EGFR-expressing metastatic colorectal cancer and advanced head and neck cancer. Thus in this work radiolabeling of monoclonal anti-EGFR with ⁹⁰Y for radioimmunotherapy (RIT) is targetted. Cetuximab was successively labeled with [⁹⁰Y] chloride (74 MBq) 2 mCi after conjugation with macrocyclics bifunctional chelating agent, 1,4,7,10-tetraazacyclododecane-N,N′,N″,N″′-tetraacetic acid mono-(N-hydroxysuccinimidyl) ester (DOTA-NHS), purified and concentrated by centrifugation using an Amicon Ultra-15 filter (Millipore, MWCo, 30000). ⁹⁰Y chloride was obtained by ⁹⁰Sr/⁹⁰Y generator. Radiolabeling was completed in 2 h by the addition of DOTA-cetuximab conjugate at 42 °C. The stability of radiolabeled was studied in human serum. Biodistribution studies in normal rats were carried out to determine the radioimmunoconjugate distribution up to 96 h. Radiochemical purity of 92 % (using ITLC) was obtained for final radioimmunoconjugate (Specific activity = 0.55 GBq/mg). Stability of radiolabeled protein in presence of human serum was tested at 37 °C for up to 24 h. Biodistribution studies demonstrated the highest ID/g % in the blood (2.62 ± 0.005 at 24 h) and the liver (2.19 ± 0.001). This study demonstrated that ⁹⁰Y-DOTA-cetuximab is a potential compound for the treatment of EGFR-expressing cancers.     

Magneto-responsive hybrid materials based on cellulose nanocrystals

We fabricated self-standing films of cellulose nanocrystals (CNC) and electrospun composite fibers with CNC and polyvinyl alcohol both with magnetic properties arising from cobalt iron oxide nanoparticles in the CNC matrix. Aqueous dispersions of cobalt-iron oxide nanoparticles (10–80 nm diameter) and CNCs (ca. 150 nm length) were used as precursor systems for the films and composite fibers. The properties of the hybrid material were determined by electron and atomic force microscopy, X-ray diffraction, thermogravimetry and magnetometry. The CNC-inorganic system was ferromagnetic, with a saturation magnetization of ca. 20 emu g^?1 of the magnetic phase. We demonstrate potential applications of the precursor dispersions, including magnetic fluid hyperthermia and highlight possible uses of the CNC-based magneto-responsive systems in biomedical and magneto-optical components.     

Interplay of colloidal stability of cellulose nanocrystals and their dispersibility in cellulose acetate butyrate matrix

Cellulose nanocrystals (CNC) prepared from eucalyptus cellulose CNCs were modified by the reaction with methyl adipoyl chloride, CNCm, or with a mixture of acetic and sulfuric acid, CNCa. The CNC were either dispersed at 0.1 wt% in the pure solvents ethyl acetate (EA), tetrahydrofuran (THF) and dimethylformamide (DMF) or in cellulose acetate butyrate (CAB) solutions prepared in these solvents at 0.9 wt%. The colloidal behavior of these dispersions was systematically investigated using a phase separation analyzer LUMiReader^®. The mechanical properties and morphological features of the films resulting from the mixtures of CAB and CNC were determined by dynamic mechanical analysis, optical microscopy and atomic force microscopy, respectively. Regardless the functional group attached to the surface of CNC, the best colloidal stability was observed for dispersions prepared in CAB/DMF solution. Higher degree of substitution of modified CNCs favored the colloidal stability in EA and THF. Composite films prepared from CAB/DMF solutions were more homogeneous and presented better mechanical performance than those prepared in CAB/EA or CAB/THF. The mechanical performance of composites and neat CAB prepared from DMF was CAB/CNCs > CAB/CNCm > CAB/CNCa > CAB, indicating that the modification weakens the percolation process, which is mediated by H bonding.     

Molecularly imprinted polymer for selective determination of Δ9-tetrahydrocannabinol and 11-nor-Δ9-tetrahydrocannabinol carboxylic acid using LC-MS/MS in urine and oral fluid

The use of molecularly imprinted polymers (MIPs) for solid phase extraction (MISPE) allows a rapid and selective extraction compared with traditional methods. Determination of Δ⁹-tetrahydrocannabinol (THC) and 11-nor-Δ⁹-tetrahydrocannabinol carboxylic acid (THC-COOH) in oral fluid (OF) and urine was performed using homemade MISPEs for sample clean-up and liquid chromatography tandem mass spectrometry (LC-MS/MS). Cylindrical MISPE shaped pills were synthesized using catechin as a mimic template. MISPEs were added to 0.5 mL OF or urine sample and sonicated 30 min for adsorption of analytes. For desorption, the MISPE was transfered to a clean tube, and sonicated for 15 min with 2 mL acetone:acetonitrile (3:1, v/v). The elution solvent was evaporated and reconstituted in mobile phase. Chromatographic separation was performed using a SunFire C18 (2.5 μm; 2.1?×?20 mm) column, and formic acid 0.1 % and acetonitrile as mobile phase, with a total run time of 5 min. The method was fully validated including selectivity (no endogenous or exogenous interferences), linearity (1–500 ng/mL in OF, and 2.5–500 ng/mL in urine), limit of detection (0.75 and 1 ng/mL in OF and urine, respectively), imprecision (%CV <12.3 %), accuracy (98.2–107.0 % of target), extraction recovery (15.9–53.5 %), process efficiency (10.1–46.2 %), and matrix effect (<?55 %). Analytes were stable for 72 h in the autosampler. Dilution 1:10 was assured in OF, and Quantisal? matrix effect showed ion suppression (<?80.4 %). The method was applied to the analysis of 20 OF and 11 urine specimens. This is the first method for determination of THC and THC-COOH in OF using MISPE technology.     

Mercury speciation analysis in human hair by species-specific isotope-dilution using GC–ICP–MS

We optimized a mercury (Hg) speciation extraction method for human hair in combination with species-specific isotope-dilution analysis by gas chromatography–inductively coupled plasma–mass spectrometry (GC–ICP–MS). The method was validated on human hair reference material RM (IAEA-086), which is recommended for analysis of monomethylmercury (MMHg) and inorganic mercury (IHg). Three reagents, hydrochloric acid (HCl), nitric acid (HNO₃), and tetramethylammonium hydroxide (TMAH), and three extraction procedures, at ambient temperature for 12 h, microwave-assisted at 75 °C for 6 min, and oven heated at 80 °C for 2 h were tested. Extraction efficiency, recovery, and potential species transformations were evaluated for each method. The most efficient procedures, with recovery of ~90 % for each species with limited demethylation (<5 %) and methylation (0 %), were HNO₃ digestion, irrespective of temperature, and microwave-assisted TMAH extraction. Acidic extraction with HCl induces significant demethylation, with production of artifacts. To correct for potential demethylation artifacts we recommend spiking with isotopically enriched standards before the extraction step.     

Thermoresponsive poly(poly(ethylene glycol) methylacrylate)s grafted cellulose nanocrystals through SI-ATRP polymerization

We report a series of thermoresponsive cellulose nanocrystals (CNCs) decorated with poly(poly(ethylene glycol) methylacrylate) copolymers (poly(PEGMA)-g-CNCs) synthesized by surface initiated-atom transfer radical polymerization (SI-ATRP). The chemical structures and surface morphologies were subsequently confirmed by FT-IR, XPS, and AFM measurements. With regard to thermally responsive behavior, poly(PEGMA)-g-CNCs show tunable lower critical solution temperature (LCST) values in the range of 34–66 °C by varying the feeding ratios of comonomers. The reversible morphological transformation from individual nano-rod structures to larger globule aggregates was further verified by AFM during the LCST transition. These functionalized CNCs have potential as smart film filters and biosensors.     

Synthesis and structures of mono(β-diiminato) copper complexes and their catalytic performances for homo- and copolymerizations of methyl acrylate

A series of mono(β-diiminato) copper complexes bearing different coordinating anions and with different fluorine substitution patterns on the β-diiminato ligands were synthesized. All of the complexes were characterized by physicochemical and spectroscopic methods, and in addition, the structures of two of them were confirmed by X-ray diffraction. The crystal structures revealed a four-coordinate mode around the copper center in a slightly distorted square planar geometry, with the β-diimine and the carboxyl groups coordinated to give six- and four-membered chelate rings. The conjugation of C=C and C=N in the β-diiminato ligands and the resonance between C–O and C=O in the carboxyl groups resulted in extensive delocalization of electrons and the formation of conjugated N–C–C–C–N and O–C–O π-bonds, respectively. When activated by modified methylaluminoxane (MMAO), these complexes can effectively catalyze methacrylate (MA) polymerization with activities up to 54.5 kg/mol Cu h, as well as MA/1-hexene copolymerization with the incorporation of MA over 80 %.