Ring-opening Polymerization Reaction Research Articles

Upgrading of thermosets and composites via sequential frontal ring-opening metathesis polymerization and radical reactions

Upgrading of thermosets and composites via sequential frontal ring-opening metathesis polymerization and radical reactions

Effect of segment structure of monotrimethoxysilylethyl-terminated asymmetric polysiloxanes on the thermal management performance of AlN-filled silicone pastes

Three kinds of α-triethylsiloxyl-ω-trimethoxysilyethyl-terminated oligomers (TES-PDMS-TMOS, TES-PTFPMS-TMOS, and TES-PDES-TMOS) were synthesized through an anion catalyzed non-equilibrium ring-opening polymerization reaction of cyclotrisiloxanes and subsequent hydrosilylation reaction with vinyltrimethoxysilane. As the in situ surface modification agent for mixed-size AlN inorganic fillers (1, 20 and 50 μm blended in a mass ratio of 3:5:9), these oligomers have been mixed with Vi-PDMS in a mass ratio of 1:2. Relative to that of silicone pastes using Vi-PDMS as the polymer matrix, the thermal conductivity of silicone pastes made from AlN particles treated with these oligomers is enhanced, while their thermal resistances decreased. With the change of the repeating unit structure in the oligomers, the silicone pastes prepared from these oligomer-treated AlN fillers differ significantly in filler content, thermal conductivity, and thermal resistance. When TES-PTFPMS-TMOS is used and filled with 800 parts (70.3 vol%) of hybrid AlN powders, a silicone paste with a thermal conductivity of 4.56 W/(m. K) could be achieved, which was 37.8% higher than that silicone paste using pure Vi-PDMS as the matrix. When TES-PDES-TMOS is used and filled with 900 parts (72.7 vol%) of hybrid AlN powders, the thermal conductivity of the silicone paste reaches 4.13 W/(m. K). Despite its thermal conductivity being only 3.5% higher relative to the silicone paste using only Vi-PDMS as the polymer matrix, its thermal resistance decreased by 20.3%. When TES-PDMS-TMOS is used and filled with 1200 parts (78.0 vol%) of hybrid AlN powders, the thermal conductivity of the silicone paste could reach up to 4.59 W/(m. K), together with a thermal resistance 29.6% lower than that of silicone paste where 1000 parts (74.7 vol%) of hybrid AlN particles filled in the Vi-PDMS. The heat dissipation of the 30 W high-brightness LED chip also illustrated the excellent thermal conductivities of these silicone pastes. The effect of another terminal group on the monotrimethoxysilylethyl-terminated asymmetric polysiloxanes on the thermal resistance of thermal interface materials was also discussed in detail.

Machine learning and DFT coupling: A powerful approach to explore organic amine catalysts for ring-opening polymerization reaction

Recently, using well-known data to drive the chemical feature of catalysts for the specified reaction has emerged as a prevalent approach in catalysis science. Amines as essential compounds play crucial roles in living organisms, pharmaceutical, agricultural applications, and various chemical reactions. However, developing a systematic strategy for the screening of amine as an organic catalyst in ring-opening polymerization (ROP) remains a significant challenge. In predicting the catalytic performance of ROP reactions, the proton affinity (PA) of amines serves as a significant indicator, which reflects the basicity of the catalyst and the activity of the ROP reaction. Herein, we conducted a systematical analysis on a dataset of 259 unique amine compounds, involving the application of seven classical machine learning models and 23 molecular descriptors. The predictive model was constructed with molecular descriptors and DFT-calculated PA values. Among the regression results, the Support Vector Machine (SV) model exhibited the optimal performance, with R2, average mean absolute error (MAE) and root mean square error (RMSE) achieving 0.84, 8.38 kJ/mol and 13.77 kJ/mol, respectively. We further employed SHAP (SHapley Additive exPlanations) to evaluate feature significance and provide insights into screening amine catalysts for ROP reaction. The top 10 amines with high PA values are enumerated and discussed. This workflow of coupling machine learning and the DFT approach proves an effective way for screening amine catalysts in ROP reaction.

Latency for All: Enabling Latency of Hoveyda-Grubbs Second-Generation Catalysts by Adding Phosphite Ligands.

The Hoveyda-Grubbs catalyst (HG2, M720 Umicore) is among the most widely used catalysts in olefin metathesis reactions. Given the usefulness of HG2 and the great interest in developing latent olefin metathesis catalysts for numerous applications, we developed a method to introduce phosphite molecules as ancillary ligands into the precatalyst framework. This modification alters the geometry of the complex from an active trans-dichloro form to a latent cis-dichloro species. Most unusually, the ligands coordinate to HG2 only in solidified solutions (most likely due to entropic factors), providing latent catalysts that can be activated on demand by heat or light by regenerating the original HG2 catalyst. Of particular interest is the use of these latent catalysts in ring-opening metathesis polymerization (ROMP) reactions and 3D printing methods. Indeed, the novel complexes displayed the required latency toward ROMP monomers, even the most reactive dicyclopentadiene. Irradiation with 405 nm light readily results in the expedited formation of the desired polymers. This novel approach provides a general and straightforward way to access efficient and well-defined latent olefin metathesis catalysts.

Fully biobased epoxy resins from ring opening polymerization of epoxidized pennycress (Thlaspi arvense L.) oil with itaconic and citric acids

Fully biobased thermosetting epoxy resins were efficiently synthesized from non-edible field pennycress (Thlaspi arvense L.) oil following a two-step sequence in which the oil was epoxidized by in situ-generated performic acid and then cured with citric and itaconic acids. Ring opening polymerization reactions were self-catalyzed, solvent-free, and conducted at 120 °C for 5 – 25 h. Analogous polymers were prepared from epoxidized soybean oil to serve as reference comparisons. The influence of comonomer combination and curing time on properties of the resulting elastomeric, ductile, thermally stable (DTG > 379 °C), hydrophobic (contact angle > 70 °) epoxy resins is reported. Crosslink density, storage modulus at the glass transition temperature (6.8 – 14.4 MPa), tensile strength (0.3 – 1.1 MPa), and gel content (87 – 96%) increased with cure time. Citrate-based polymers had higher crosslink densities (317 mol m−3) than itaconate-based polymers (164 – 279 mol m−3) due to the greater functionality of citric acid versus itaconic acid, which resulted in higher glass transitions (> 21 °C), tensile strengths (> 0.6 MPa), and storage moduli in the rubbery state (> 2.6 MPa). Finally, the lower oxirane content of EPO versus ESO resulted in lower crosslink density, storage modulus, tensile strength, and elongation at break. Overall, the epoxy networks had promising thermal, mechanical, and viscoelastic properties that were tunable by selection of appropriate comonomer combinations and curing times.

Tuning the Latency by Anionic Ligand Exchange in Ruthenium Benzylidene Phosphite Complexes

Recently discovered cis-dichloro benzylidene phosphite complexes are latent catalysts at room temperature and exhibit exceptional thermal and photochemical activation behavior in olefin metathesis reactions. Most importantly, the study of these catalysts has allowed their introduction in efficient 3-D printing applications of ring-opening metathesis derived polymers and the control of chromatically orthogonal chemical processes. Moreover, their combination with plasmonic Au-nanoparticles has given rise to novel smart materials that are responsive to light. Given the importance of the ligand shell in the initiation and reactivity behavior of this family of complexes, we set out to investigate the effect of anionic ligand exchange. Thus, we report herein two new ruthenium benzylidene benzylphosphite complexes where the chloride anionic ligands have been replaced by bromide and iodide anions (cis-Ru-Phos-Br2 & cis-Ru-Phos-I2). The thermal and photochemical activations of these dormant catalysts in a variety of ring-closing and ring-opening metathesis polymerization (RCM and ROMP) reactions were thoroughly studied and compared with the previously known chloride precatalyst. Photochemical RCM studies provided similar results, especially in non-hindered reactions, with the UV-A wavelength being the best in all cases. On the other hand, the thermal activation profile exposed that the anionic ligand significantly affects reactivity. Notably, cis-Ru-Phos-I2 disclosed particularly impressive initiation efficiency compared to the other members of the family.

Determination of HOMO and LUMO of bis(β-diketonate)zirconium(IV) compound used as a catalyst in the ring opening polymerization of ε-Caprolactone and δ-Valerolactone

Poly(ε-caprolactone) (PCL) and poly(δ-valerolactone) (PVL) are aliphatic polyesters that can generally be used for basic medical materials such as bone and dental implant materials, drug delivery systems, and scaffolds in tissue engineering. PCL and PVL belong to the polylactone group which have superior properties such as good biocompatibility, nontoxicity, flexibility, thermoplastic and can be biodegraded in a controlled manner. These superior properties make it the main choice in producing medical materials. This study aims to determine the degree of polymerization of PCL and PVL catalyzed using a bis(β-diketonate)zirconium(IV) complex. In addition, analysis of the Highest Occupied Molecular Orbital (HOMO) and Lowest Unoccupied Molecular Orbital (LUMO) was also carried out on the catalyst complex. The ring-opening polymerization reaction (ROP) of ε-caprolactone (ε-CL) and δ-valerolactone (δ-VL) lasted for 4 h at 100 °C. The resulting PCL and PVL were then characterized for their chemical and thermal properties using FTIR, 1HNMR, XRD, DTA and TGA. Both PCL and PVL are semicrystalline. On the other hand, the resulting PCL has a melting point of 65.5 °C, with a degree of polymerization (DP) of 17. Meanwhile, the resulting PVL has a melting point of 63.4 °C with a DP of 8.

Cascade signal amplification electrochemical biosensor based on AgNPs and ring opening polymerization for determination of Ochratoxin A.

Anochratoxin A (OTA) electrochemical biosensor based on a cascade signal amplification strategy with Ag nanoparticles (AgNPs) and ring opening polymerization (ROP) was constructed. The large specific surface area of AgNPs was used to increase the loading of OTA aptamer on the electrode surface, enhancing the ability to capture OTA as a way to achieve the first signal amplification. The OTA antibody modified with polyethylenimine specifically recognizes the OTA, forming an aptamer-OTA-antibody sandwich structure. The amino group on polyethylenimine initiates the ROP reaction with α-amino acid-n-carboxylic anhydride-ferrocene (NCA-Fc) as the monomer. A large number of electrochemical signal units of ferrocene are introduced into the sensing system for a second signal amplification. By amplifying the signal twice, the sensitivity of the sensor is improved. Under the optimal conditions, the detection range of the sensor is 1pg·mL-1 ~ 1μg·mL-1, while the detection limit is as low as 117fg·mL-1. Moreover, the sensor has the advantages of high sensitivity, good stability and selectivity. Standard addition recovery experiment proved that the sensing system can be successfully used for the detection of OTA in four actual samples with recoveries in the range90.0 to 113% with RSDs of 0.6 to 5.2%, providing a new idea for the pollution assessment of mycotoxins.

Modification of wool fibre's structural properties as a cheap adsorbent for the elimination of Cr6+ and Rhodamine6g dye from aqueous solution

Wool, a naturally occurring biopolymer made up of amino acids, is employed as an adsorbent for both modified and unmodified forms of the dyes rhodamine6G (R6G) and Cr6+. The two-step procedure of (i) ring opening polymerization (ROP) and (ii) condensation reaction was used to modify the structure of wool fibre. Both the ROP and the condensation provide steric free chain expanding groups as well as adsorption-improving groups. The FT-IR spectrum, which showed peaks about 1725 and 1630 cm−1 corresponding to the CO and CN stretchings, respectively, confirmed the structural modification. By detecting a slight hump at 8.5 ppm, 1H NMR was able to validate the later functional group. DSC, TGA, FE-SEM, EDX, and water contact angle (WCA) were also used to characterize it. With the aid of a UV–visible spectrophotometer, the quantitative adsorption of both Cr6+ and R6G by modified and unmodified Wool fibre was monitored. For the adsorption of Cr6+ and R6G, the pseudo first order and pseudo second order kinetics were used. The multilayer coating of adsorbate onto adsorbent was confirmed by the Langmuir adsorption isotherm. Thermodynamic parameters were calculated and compared to values found in the literature.

Electrochemical biosensor for highly sensitive detection of cTnI based on a dual signal amplification strategy of ARGET ATRP and ROP

Cardiac troponin I (cTnI), a gold biomarker for the diagnosis of acute myocardial infarction (AMI), plays a vital role in the early diagnosis, treatment and prognosis analysis of AMI. In this paper, an electrochemical biosensor for the highly sensitive determination of cTnI was fabricated based on the dual signal amplification strategy of electron transfer atom transfer radical polymerization (ARGET ATRP) and ring-opening polymerization (ROP) for the first time. Briefly, the thiolate cTnI-aptamer 1, which was bonded to the electrode via Au–S bonds, specifically captured cTnI to the electrode surface. Then, cTnI-aptamer 2 (Apt2) was successfully introduced to the electrode surface to form Apt-cTnI-Apt sandwich structure. Subsequently, the initiator BIBB was connected to Apt2 through bromination reaction, and then the resulting ATRP polymer was employed as a macromolecular initiator for the succeeding reaction. Next, the monomers, α-amino acid-N-carboxylic acid anhydride ferrocene derivatives (NCA-Fc), used for the ROP reaction produced numerous electroactive polymers on the electrode surface. The dual action of ARGET ATRP and ROP significantly improved sensitivity of cTnI biosensor assay, the prepared biosensor displayed a wide linear detection range from 100 fg mL−1 to 100 ng mL−1, with a detection limit of 32.24 fg mL−1. The method exhibited favorable selectivity, simple operation and excellent stability. Furthermore, the biosensor still rendered satisfactory analytical performance in the detection of clinical serum samples, indicating the application potential in clinical diagnosis.

High performance of solid electrolyte endowed by SiO2 cross-linking agent towards lithium metal battery

A dual network solid polymer electrolyte is prepared, the cross-linked part is constructed using ring-opening polymerization reaction, in which SiO2 particles connect with polyethylene glycol diglycidyl ether (PEGDE) and polyetheramine (PEA) as cross-linking point. The introduction of SiO2 is conducive to reduce the crystallization of polymer matrix, improve the strength and promote the fast migration of Li ions. The abundant C-O segments in PEGDE and PEA are advantageous to the hopping behavior of Li ions and improve the ionic conductivity of electrolyte. Poly (vinylidenefluoride-hexaflouropropylene) (PVDF-HFP) is selected as linear part due to its robust mechanical behavior and outstanding electrochemical property. The obtained SiO2 functionalized PEGDE and PEA-PVDF-HFP solid polymer electrolyte (referred to as SGPP-ASPE) demonstrates excellent ionic conductivity of 2.4 × 10−4 S cm−1, high lithium-ion transference number of 0.54 and minor interfacial polarization of 0.09 V after 1000 h using Li//Li symmetrical cell. After assembling Li/LiFePO4 cell, a favorable cycling stability with the capacity retention of 93.8% after 100 cycles at 0.2 C is delivered. The reasonable design of advanced polymer electrolytes with dual network opens up a new path for the development of solid high-performance LMBs.

Design, Synthesis, and Comparison of PLA-PEG-PLA and PEG-PLA-PEG Copolymers for Curcumin Delivery to Cancer Cells.

Curcumin (CUR) has potent anticancer activities, and its bioformulations, including biodegradable polymers, are increasingly able to improve CUR's solubility, stability, and delivery to cancer cells. In this study, copolymers comprising poly (L-lactide)-poly (ethylene glycol)-poly (L-lactide) (PLA-PEG-PLA) and poly (ethylene glycol)-poly (L-lactide)-poly (ethylene glycol) (PEG-PLA-PEG) were designed and synthesized to assess and compare their CUR-delivery capacity and inhibitory potency on MCF-7 breast cancer cells. Molecular dynamics simulations and free energy analysis indicated that PLA-PEG-PLA has a higher propensity to interact with the cell membrane and more negative free energy, suggesting it is the better carrier for cell membrane penetration. To characterize the copolymer synthesis, Fourier transform-infrared (FT-IR) and proton nuclear magnetic resonance (1H-NMR) were employed, copolymer size was measured using dynamic light scattering (DLS), and their surface charge was determined by zeta potential analysis. Characterization indicated that the ring-opening polymerization (ROP) reaction was optimal for synthesizing high-quality polymers. Microspheres comprising the copolymers were then synthesized successfully. Of the two formulations, PLA-PEG-PLA experimentally exhibited better results, with an initial burst release of 17.5%, followed by a slow, constant release of the encapsulated drug up to 80%. PLA-PEG-PLA-CUR showed a significant increase in cell death in MCF-7 cancer cells (IC50 = 23.01 ± 0.85 µM) based on the MTT assay. These data were consistent with gene expression studies of Bax, Bcl2, and hTERT, which showed that PLA-PEG-PLA-CUR induced apoptosis more efficiently in these cells. Through the integration of nano-informatics and in vitro approaches, our study determined that PLA-PEG-PLA-CUR is an optimal system for delivering curcumin to inhibit cancer cells.

Wood Cellulose Nanofibers Grafted with Poly(ε-caprolactone) Catalyzed by ZnEu-MOF for Functionalization and Surface Modification of PCL Films.

Renewable cellulose nanofiber (CNF)-reinforced biodegradable polymers (such as polycaprolactone (PCL)) are used in agriculture, food packaging, and sustained drug release. However, the interfacial incompatibility between hydrophilic CNFs and hydrophobic PCL has limited further application as high-performance biomaterials. In this work, using a novel ZnEu-MOF as the catalyst, graft copolymers (GCL) with CNFs were grafted with poly(ε-caprolactone) (ε-CL) via homogeneous ring-opening polymerization (ROP), and used as strengthening/toughening nanofillers for PCL to fabricate light composite films (LCFs). The results showed that the ZnEu-MOF ([ZnEu(L)2(HL)(H2O)0.39(CH3OH)0.61]·H2O, H2L is 5-(1H-imidazol-1-yl)-1,3-benzenedicarboxylic acids) was an efficient catalyst, with low toxicity, good stability, and fluorescence emissions, and the GCL could efficiently promote the dispersion of CNFs and improve the compatibility of the CNFs and PCL. Due to the synergistic effect of the ZnEu-MOF and CNFs, considerable improvements in the mechanical properties and high-intensity fluorescence were obtained in the LCFs. The 4 wt% GCL provided the LCF with the highest strength and elastic modulus, which increased by 247.75% and 109.94% compared to CNF/PCL, respectively, showing the best elongation at break of 917%, which was 33-fold higher than CNF/PCL. Therefore, the ZnEu-MOF represented a novel bifunctional material for ROP reactions and offered a promising modification strategy for preparing high-performance polymer composites for agriculture and biomedical applications.

A mechanistic study on homo- and copolymerization of L-Lactide and ε-caprolactone catalyzed by an aluminum complex bearing a Bis(phenoxy)amine ligand: A DFT study

Polymerization of biodegradable lactide and lactone has been the subject of intense research during the past decade. We used density functional theory (DFT) calculations to investigate the initiation and first propagation for ring-opening polymerization (ROP) mechanisms of L-lactide (LA) and ε-caprolactone (CL) on aluminum complexes bearing the bis(phenoxy)-amine ligand with pyridine (Catalyst I) and diethylamine (Catalyst II) sidearm. Here, the ROP mechanisms of LA and CL on both catalysts were classified into 3 parts: (1) LA homopolymerization, (2) CL homopolymerization, and (3) LA and CL copolymerization. For homopolymerization, Catalyst I shows a greater performance than Catalyst II on both LA and CL due to its less bulky sidearm. However, CL homopolymerization on Catalyst I is more favorable than that of LA, which is caused by the stronger CL coordination on the catalyst. For LA and CL copolymerization, the amine sidearm variation and the vdW interactions of monomers on Catalysts I and II provide different copolymer products, the tapered and random copolymers, respectively. These calculated results are in good agreement with our previous experimental reports. The understanding gained in the current study might be helpful in the development of high-performance catalysts for the ROP reaction of biodegradable lactide and lactone.

Synthesis and Characterization of Poly(DL-lactide) Containing Fluorene Structures.

9,9-bis[4-(2-hydroxy-3-acryloyloxypropoxy)phenyl]fluorene (BPF) hydroxyl groups (-OH) were used as initiators in the ring-opening polymerization reaction with DL-lactide monomers at different molar ratios to synthesize a Poly(DL-lactide) polymer containing bisphenol fluorene structure and acrylate functional groups (DL-BPF). The polymer's structure and molecular weight range were analyzed using NMR (1H, 13C) and gel permeation chromatography. DL-BPF was then subjected to photocrosslinking using the photoinitiator Omnirad 1173, resulting in the formation of an optically transparent crosslinked polymer. Characterization of the crosslinked polymer involved analyzing its gel content, refractive index, thermal stability (via differential scanning thermometry (DSC) and thermogravimetric analysis (TGA)), as well as conducting cytotoxicity tests. The crosslinked copolymer exhibited a maximum refractive index of 1.5276, a maximum glass transition temperature of 61.1 °C, and cell survival rates higher than 83% in the cytotoxicity tests.

Adding Polypeptides to the Toolbox for Redox-Switchable Polymerization and Copolymerization Catalysis

Bis(imino)pyridine (BIP) iron alkoxide complexes act as catalysts to efficiently polymerize N-carboxyanhydrides (NCAs), including γ-benzyl-l-glutamate NCA (BLG-NCA) and sarcosine NCA (Sar-NCA), at room temperature. Reaction rates were greatly enhanced with the addition of mild Lewis acids, such as [CoCp2][BArF24], which work cooperatively with the iron-based catalysts to facilitate NCA polymerization. The reactivity of (2,6MeBIP)FeOCH2C(CH3)3 with Sar-NCA was combined with its known reactivity for ε-caprolactone polymerization to form diblock and triblock copoly(ester-b-peptides) through sequential addition of lactone and NCA monomers. Redox-switchable polymerization reactions were developed by iteratively exposing the catalyst to redox reagents and Sar-NCA or cyclohexene oxide. The orthogonal reactivity demonstrated by the catalyst in its oxidized and reduced states led to the synthesis of diblock and triblock copoly(ether-b-peptides). Polyether segments were synthesized with the catalyst in its oxidized state, while the polyamide segments were synthesized with the catalyst in its reduced state. Both copolymerization reactions developed here are rare examples where NCA polymerization reactions can be combined with other ring-opening polymerization reactions to make copolymers containing polypeptides and other functional monomers.

Dual signal amplified electrochemical aptasensor based on PEI-functionalized GO and ROP for highly sensitive detection of cTnI

Cardiac troponin I (cTnI) is considered as the gold standard for the diagnosis of acute myocardial infarction (AMI) because of its excellent specificity and sensitivity. Herein, a novel aptasensor based on the dual signal amplification strategy of Polyethyleneimine functionalized Graphene oxide (GO) and ring-opening polymerization (ROP) for the first time was successfully constructed to achieve high sensitivity detection of cTnI. Briefly, cTnI-aptamer 1 (Apt1) was immobilized on the surface of gold electrode by self-assembly of Au-S bonds to specifically capture cTnI. After specific recognition of cTnI, Apt2 coated PEI-functionalized GO composites acted as macroinitiators for the subsequent ROP reaction. Next, α-amino acid-N-carboxylic acid anhydride ferrocene derivatives (NCA-Fc), the monomer for ROP reaction, was added to the electrode surface. The combined application of PEI-functionalized GO and NCA-Fc better achieves the high sensitivity and signal amplification of the aptasensor. Under optimal conditions, the aptasensor exhibited a wide linear range of 10 fg mL−1 to 10 ng mL−1 and the limit of detection was 3.78 fg mL−1. Moreover, this method displayed the advantages of good selectivity, simple operation and excellent stability. Meanwhile, the aptasensor had good accuracy and applicability even in real serum samples analysis, demonstrating its considerable application potential in biomedical assays.

Phosphonate-Functionalized Polycarbonates Synthesis through Ring-Opening Polymerization and Alternative Approaches

Well-defined phosphonate-functionalized polycarbonate with low dispersity (Ð = 1.22) was synthesized using organocatalyzed ring-opening polymerization (ROP) of novel phosphonate-based cyclic monomers. Copolymerization was also performed to access different structures of phosphonate-containing polycarbonates (PC). Furthermore, phosphonate-functionalized PC was successfully synthesized using a combination of ROP and post-modification reaction.

Adsorption behavior and mechanism analysis of siloxane thickener for CO2 fracturing fluid on shallow shale soil

Reducing the adsorption of CO2 thickeners in soil particles of shallow shale is a pathway to protect the shale environment and water cycle. In this work, we first synthesized a siloxane-based thickener named AOB based on ring-opening polymerization and hydrosilylation reaction and discussed the influence of geological factors (including contents, pressure, temperature and shear rate) on the adsorption capacity of this thickener. The soil surface adsorption behavior of AOB was characterized by a self-assembled high-pressure soil adsorption device and the adsorption capacity was analyzed by Attenuated Total Reflectance Infrared Spectroscopy (ATR-FTIR). The results showed that AOB molecule belongs to the monolayer adsorption type on the soil surface by measuring the contents. Moreover, an inverse relationship was showed between pressure and adsorption capacity for AOB, while the significantly proportional relationship was presented for temperature and shear rate, respectively. It is found that the combined force formed by soil repulsion (originated from aromatic groups in AOB) and grid drag weakens the adsorption of AOB on the soil surface, resulting in a much lower adsorption capacity than the commercial PDMS. This work not only paves a new avenue for synthesizing siloxane-based polymer as CO2 thickener, but also provides an efficient measure to reduce the adsorption of thickener on the shallow soil.

Synthesis and Characterization of Zinc(II), Cadmium(II), and Palladium(II) Complexes with the Thiophene-Derived Schiff Base Ligand.

Zn(II), Pd(II), and Cd(II) complexes, [L TH MCl 2 ] (M = Zn, Pd; X = Br, Cl) and [L TH Cd(μ-X)X] n (X = Cl, Br; n = n, 2), supported by the (E)-N 1,N 1-dimethyl-N 2-(thiophen-2-ylmethylene)ethane-1,2-diamine (L TH ) ligand are synthesized and structurally characterized. Density functional theory (DFT) electronic structure calculations and variable-temperature NMR support the presence of two conformers and a dynamic interconversion process of the minor conformer to the major one in solution. It is found that the existence of two relevant complex conformers and their respective ratios in solution depend on the central metal ions and counter ions, either Cl- or Br-. Among the two relevant conformers, a single conformer is crystallized and X-ray diffraction analysis revealed a distorted tetrahedral geometry for Zn(II) complexes, and a distorted square planar and square pyramidal geometry for Pd(II) and Cd(II) complexes, respectively. It is shown that [L TH MCl 2 ]/LiO i Pr (M = Zn, Pd) and [L TH Cd(μ-Cl)Cl] n /LiO i Pr can effectively catalyze the ring-opening polymerization (ROP) reaction of rac-lactide (rac-LA) with 94% conversion within 30 s with [L TH ZnCl 2 ]/LiO i Pr at 0 °C. Overall, hetero-enriched poly(lactic acid)s (PLAs) were provided by these catalytic systems with [L TH ZnCl 2 ]/LiO i Pr producing PLA with higher heterotactic bias (P r up to 0.74 at 0 °C).