Monomer Conversion Research Articles

Controlled polymerization of functional acrylamides by rare-earth aryloxide-based Lewis pairs

A series of amine-bridged bis(phenolate) rare-earth (Sc, Y) aryloxides were synthesized and characterized. These complexes were successfully used for the controlled Lewis pair polymerization (LPP) of functional acrylamides in combination with phosphines, affording a new type of polyacrylamides with predictable molecular weight and low molecular weight distribution. The living nature of this LPP was verified by near-quantitative initiation efficiencies, a linear increase of molecular weight vs monomer-to-initiator ratio and monomer conversion, chain extensions, and the synthesis of well-defined block copolymers. The mechanistic studies were performed through the isolation of a zwitterionic intermediate as well as the end-chain analysis of oligomers, showcasing a rare-earth/phosphine cooperation. Furthermore, the resultant polyacrylamides exhibit outstanding thermal stability and great potential for application in photovoltaic devices.

Conductive NR/PMMA-RAFT-CNT-rGO composites and their morphological, mechanical, and electrical properties

This study reports the synthesis of poly(methyl methacrylate) (PMMA)-carbon nanotube (CNT)-reduced graphene oxide (rGO) emulsions via reversible addition-fragmentation chain-transfer (RAFT)-mediated surfactant-free emulsion polymerization using a hydrophilic chain transfer agent. The rGO was prepared by the modified Hummers method and reduced with L-ascorbic acid. The effects of the CNT:rGO ratios and CNT and rGO contents on the conversion and stability of emulsion were investigated. Increasing the CNT and rGO contents from 1 to 4 wt% decreased the monomer conversion, while all the samples remained as colloidal dispersions. The morphology of PMMA-CNT-rGO composites showed the incorporated arrangement of a linear CNT portion connected with the rGO sheet dependent on the CNT:rGO ratio. Various PMMA-CNT-rGO filled natural rubber (NR) cast films were prepared. The NR/PMMA-CNT-rGO composite film with a 1 wt% filler loading at a CNT:rGO ratio of 1:1 presented a quite high modulus value (3.08 MPa) and sufficient intrinsic electrical conductivity (1.36 S/m) due to its strong filler-matrix interaction. Thus, the PMMA-RAFT-CNT-rGO composites at a very low filler content can be used as an effective reinforcement to enhance the mechanical and electrical properties of NR films with a high compatibility between the fillers and NR matrix.

Advancing photopolymerization and 3D printing: High-Performance NiII complexes bearing N2O2 Schiff-base ligands as photocatalysts

New high-performance photocatalysts based on metal structures are being developed for polymerization. However, using low-cost metals while ensuring effectiveness is challenging. In this study, two NiII complexes NiL1 and NiL2 were synthesized using N2O2 Schiff-base ligands bearing π-extended rings (naphthaldehyde (H2L1) and phenylsalicylaldehyde (H2L2) groups), respectively. These complexes were characterized by FTIR, UV–Vis and 1H NMR spectroscopy, elemental analysis, cyclic voltammetry, and MALDI-TOF mass spectrometry. NiL1 and NiL2 were evaluated in photoinitiating system as new photocatalysts for the Free Radical Photopolymerization of Ethoxylated (3) Trimethylolpropane Triacrylate (TMPETA) for violet and green light. Three-component systems were employed in the presence of Di-tert-butyl-diphenyl iodonium hexafluorophosphate (Iod) and ethyl dimethylaminobenzoate (EDB). The absorption, luminescence, and redox properties of nickel complexes and ligands were explored and compared for a better understanding of their structure/reactivity relationship. The designed nickel complexes showed good photoinitiation abilities. NiL2 exhibited the highest monomer conversion, and it was investigated in the on–off process under green light irradiation, demonstrating the efficiency of the system in reactivating the polymerization process. An oxidative pathway mechanism was proposed based on free energy, steady state photolysis and electron spin resonance spin trapping experiments. The best system was successfully applied in cationic photopolymerization and 3D printing.

Polymer dispersity modulation by statistical copolymerization of (α-alkyl)acrylate monomers with disparate reactivity: Enhanced monomer conversion and tailored dispersity for dielectric elastomer application

Polymer dispersity (Ð) is an important parameter in determining polymer properties. We report a new strategy for Ð modulation by statistically copolymerizing steric-hindered itaconates with methacrylate and acrylate monomers via organocatalyzed controlled radical polymerization. Due to the disparate monomer reactivity, Ð values can be tunable in a broad range (1.1–1.6) in a batch system. This strategy has demonstrated the sequential and topological generality for Ɖ modulations, serving as a model tool for Ð modulation in any segment of A-B diblock, B-A-B and A-B-A triblock, and 3-arm star A-B diblock copolymers. The unique aspects of this method are that the segment after Ð modulation can initiate polymerization of various types of monomers (e.g., methacrylate, acrylate) by the labile tertiary carbon-iodide chain-end without any external assistance or special initiator and monomer selection, the metal-free nature and the renewable substitution of petroleum-based methacrylate and acrylate monomers with bio-based itaconates without sacrificing inherent properties. This work broadens the application scope of Ð modulation to many other emerging technologies, such as antifreezing thermoplastic dielectric elastomers used as film capacitors in the field of energy storage.

Access to bromo-functionalized polyester by ring-opening polymerization of a bridged bicyclic lactone and application for grafted copolymers

Ring-opening polymerization (ROP) of bridged bicyclic lactones has been proved to be effective method for degradable polyesters, especially recyclable polymers. Herein, we reported a novel bromo-functionalized bridged bicyclic lactone (MBr) from a biobased olefin carboxylic acid. The investigation of polymerization system showed that urea/1,8-Diazabicyclo[5,4,0]undec-7-ene (DBU) catalyzed ROP of MBr is well-controlled. Quantitative monomer conversion (98 %) was achieved and bromo-functionalized polyesters (PMBr) with high molecular weights (up to 91800 g/mol) were produced. Cu(0)-mediated controlled radical polymerization of methyl acrylate with PMBr as macroinitiators afforded grafted copolymers. This strategy would provide more convenience for the synthesis of bromo-functionalized polyesters and grafted copolymers.

Copper Nanodrugs with Controlled Morphologies through Aqueous Atom Transfer Radical Polymerization.

Copper (Cu) nanodrugs can be facilely prepared through atom transfer radical polymerization (ATRP) in an aqueous medium. However, it is difficult to control the morphology of Cu nanodrugs and thereby optimize their anticancer activity. In this work, aqueous ATRP was combined with polymerization-induced self-assembly (PISA) to prepare Cu nanodrugs with various morphologies. We mapped the relationship between polymerization condition and product morphology in which each morphology shows a wide preparation window. Decreasing the reaction temperature and feeding more Cu catalysts can improve the mobility of chains, facilitating the morphology evolution from sphere to other high-order morphologies. The resultant Cu nanodrugs with high monomer conversion and high Cu loading efficiency could be easily taken by cancer cells, showing excellent anticancer efficacy in vitro. This work proposed a potential strategy to prepare Cu nanodrugs with a specific morphology in batches, providing the method to optimize the anticancer efficacy through morphology control.

Trace organic–inorganic hybrid lead halide perovskite nanocrystals as photocatalysts for PET-RAFT polymerization with high efficiency

Lead halide perovskite has emerged as a new class of materials in photocatalysis due to its promising photocatalytic performance. Here, we introduce organic–inorganic hybrid lead halide perovskite (OIHP) nanocrystals as photocatalysts (PCs) for efficient photoinduced electron/energy transfer–reversible addition–fragmentation chain transfer (PET-RAFT) polymerization. PET-RAFT polymerization is successfully conducted with 0.025 wt% PC loading under blue light (6 mW/cm2, 460 nm), yielding upwards of 90 % monomer conversion and polymer products with narrow dispersity (≤1.20) within 2 h, demonstrating a fast polymerization rate. Moreover, the oxygen resistance of the polymerization process has been demonstrated. Due to the advantages of low PC usage, fast polymerization rate and oxygen tolerance, OIHP mediated PET-RAFT polymerization is expected to be used for large-scale production and industrial applications.

Energy-efficient frontal polymerization of poly(DCPD-co-TCPD) with improving thermomechanical properties and chemical resistance

Polydicyclopentadiene (PDCPD) was attractive in marine, automotive and new energy fields, but limited by its lower rigidity. Herein, poly(dicyclopentadiene-co-tricyclopentadiene) (poly(DCPD-co-TCPD)), was prepared by rapid and energy-efficient frontal polymerization (FP). The flexural properties of copolymers prepared via FP were comparable to those prepared by long-term oven curing. Furthermore, the study explored the cis-trans isomerization of double bond, molecular weight between cross-links, density, swelling degree and monomer conversion to systematically analyze the influence of tricyclopentadiene (TCPD) incorporation. Notably, the selected comonomer TCPD was relatively simple in synthesis, and its incorporation resulted in remarkable enhancement of the thermomechanical properties and acid-base resistance of neat PDCPD. At an 80 wt% TCPD incorporation, the flexural modulus increased significantly from 1865 MPa to 2703 MPa, and the Tg elevated from 147 ℃ to 210 ℃. Compared to other widely used thermosets, poly(DCPD-co-TCPD) exhibited significant advantages in terms of being lightweight and heat-resistant. The resulting thermosets demonstrated considerable potential for applications as high-performance thermosets and in composites with adjustable thermomechanical properties.

Synthesis and properties of transparent PMMA/cellulose nanocomposites prepared by in situ polymerization in green solvent

AbstractIn order to contribute to the demanded sustainability transparent poly(methyl methacrylate) (PMMA) composites with cellulose nanocrystals (CNC) up to high shares of 50 wt% were prepared by in situ radical polymerization in green solvent Cyrene. The weight average molecular weights of PMMA were in the range from 144,000 to 160,000 g mol−1 and the dispersity was in the range of 1.49 to 1.89 with high conversion of monomer to polymer. The DSC thermal analysis showed that the glass transition temperature of pure PMMA was at 99°C while in composites increased from 103°C up to 129°C with the increase of CNC from 1 wt% to 50 wt%. TGA shows that the addition of CNC does not have a significant effect on the thermal stability of PMMA. In composites Young's modulus increases with the increasing CNC ratio and composites with 50 wt% of CNC showed more than twice the modulus of the PMMA matrix. The SEM images indicate uniform distribution of CNC in polymer matrix. The transparent and semitransparent PMMA/cellulose composites of improved sustainability with higher modulus of elasticity and glass transition temperature can be used as lightweight materials for a wide range of technical and everyday applications as well as optical lenses or acoustic lenses for ultrasound transducers and other devices.Highlights Cellulose nanocrystals/PMMA composites fabricated by a green in situ process. Synthesized PMMA matrices have high molecular weights. Improved elastic modulus and glass transition temperature were achieved. Prioritizing eco‐friendly chemicals for a greener production approach.

Evolution Kinetics of Stabilizing Pickering Emulsion by Brush-Modified Janus Particles: DPD Simulation and Experimental Insights.

In the present study, we report the evolution of stabilizing Pickering emulsions using brush-modified Janus particles (JPs), utilizing the dissipative particle dynamics (DPD) simulation technique. Our results are subsequently corroborated with experimental findings. Each JP has one-half of the hydrophobic surface, with the other half embedded with hydrophilic polymer brushes grown via atom transfer radical polymerization (ATRP). Our generic simulation model analyzes the chemical kinetics of polymer brush growth on one-half of the initiator-embedded microparticle (MP) surface, resulting in the formation of JP. This involves evaluating monomer conversion and reaction rates. Our results exhibit a substantial influence of the number of JPs, grafted brush density, and brush length on oil-in-water emulsion stability. We studied the evolution kinetics and stability of emulsion formation by analyzing the growth of average domain size and corresponding scaling functions up to a late time limit. This study aims to clarify the connection between the size, quantity, and functionality of JPs and the stability of Pickering emulsions.

A Systematic Study of Nonionic Di- and Multiborane Catalysts for the Oligomerization and Polymerization of Epoxides.

Borane catalysis has emerged as a powerful technology in epoxide polymerization. Still, the structure-activity correlations for these catalysts are not fully understood to date, especially regarding compounds with nonionic backbones. Thus, in this work, 13 different borane catalysts of this respective type are described and investigated for their epoxide oligomerization and polymerization performance, using propylene oxide (PO), 1-butylene oxide (BO) and allyl glycidyl ether (AGE) as monomers. Structurally, special emphasis is put on catalysts with different linker lengths and linker flexibilities as well as the introduction of more than two borane functionalities. Importantly, this screening is conducted both under typical polymerization conditions as well as under the chain transfer agent (CTA)-rich conditions relevant for large-scale production. It is found that suitable preorganization of the borane groups, such as present in biphenyl derivatives, offers a simple route to high-performing catalysts and quantitative monomer conversion of the investigated epoxides. Furthermore, it is demonstrated that a diborane-catalyzed oligomerization can be kept active over weeks, whereby repeated addition of monomer batches (14 steps) constantly results in full conversion and well-defined oligoethers, underlining the practical potential of this method. The absence of co-initiating counter ions is suggested as an inherent advantage of nonionic catalysts.

Investigation of the Degree of Monomer Conversion in Dental Composites through Various Methods: An In Vitro Study

The degree of monomer conversion (DC) values of three different dental composites were examined using three different methods: surface microhardness (ratio of bottom/top), Fourier-transform infrared (FT-IR), and differential scanning calorimetry (DSC). Two of the dental composites included in the study were nanohybrid (Dentsply Neo Spectra ST HV and Omnichroma), and one was a microhybrid-labeled newly marketed composite containing nanoparticles (Dentac Myra). Composite discs were prepared according to the methodology for all methods and analyzed (2 mm thickness × 5 mm diameter). Surface microhardness values were measured in Vickers Hardness Number (VHN), while FT-IR and DSC values were obtained in percentage (%). Significant differences were observed in both bottom/top surface microhardness values and DC values obtained from FT-IR. However, there was no statistical difference in the ratio of bottom/top microhardness values. Neo Spectra ST HV exhibited superior performance in both microhardness and monomer conversion compared to the other two composites. Newly marketed Myra showed values close to Omnichroma. It was found that the values obtained by the DSC method were parallel to those obtained by FT-IR. In conclusion, the structure of dental composites leads to different mechanical properties. Additionally, DSC measurements and FTIR spectra were found to be complementary techniques for characterizing monomer conversion values.

An in Vitro Comparative Evaluation for Internal and Marginal Integrity and the Degree of Monomer Conversion of Alkasite Restorative Material

An in Vitro Comparative Evaluation for Internal and Marginal Integrity and the Degree of Monomer Conversion of Alkasite Restorative Material

Selection strategy of curing depth for vat photopolymerization 3D printing of Al2O3 ceramics

Vat photopolymerization (VPP) 3D printing technology allows the fabrication of complex ceramic structure components through the layer-by-layer stacking strategy. The curing depth is a crucial parameter for the stacking process, as it directly impacts the printing quality. Furthermore, this parameter exerts a profound effect on the final quality of the printed part. However, there is currently a lack of comprehensive research on how the curing depth affects VPP ceramic 3D printing. This study aims to thoroughly evaluate the impact of curing depth parameters on critical aspects of the 3D printing process, including the forming accuracy, surface quality, monomer conversion, resin pyrolysis, interlayer defects, and mechanical properties. The results of our investigation clearly demonstrate the significant influence of curing depth on the precision and performance of VPP 3D printed ceramic parts. Ceramic samples produced with higher curing depth exhibited superior surface quality (Ra<1.6 μm) but lower forming accuracy. Increasing the curing depth improved interlayer adhesion but excessive depth led to a decreased monomer conversion content from 5.2 % to 2.0 % and an internal stress in the green body. Moreover, increasing the curing depth intensified the pyrolysis process and increased the propensity for cracks forming, as confirmed by simultaneous thermal analysis and microstructure observations. The flexural strength of the sintered samples reached its maximum value of 630 MPa at three times the printing layer thickness. This study provides valuable insights for selecting appropriate curing depth parameters in VPP ceramic 3D printing.

Ethanolysis of enzymatic hydrolysis lignin with Ni catalysts on different supports: The roles of catalytic sites

Catalytic lignin solvolysis (CLS) holds promise for efficient lignin utilization, yielding small molecules with minimal or no char formation. However, the role of different active sites of catalyst in CLS are rarely discussed. Here, Ni catalysts on different supports, i.e., SiO2, Al2O3, MgO, and ZrO2, were prepared with the aim of manipulating the relative importance of metal and acid-base functionalities to investigate the role of different active sites in the enzymatic hydrolysis of lignin (EHL) ethanolysis. The main ether linkage, i.e., β-O-4, in EHL is cleaved without the participation of a catalyst. Metal sites suppress repolymerization through hydrogenating active intermediates, while acid and base sites facilitate the conversion of phenolic monomers into complex alkylated and etherified products and also promote repolymerization reactions. Among the catalysts, Ni/SiO2 demonstrated the highest hydrogenation activity and yielded the most monomers (24.7 wt %) at 280 °C for 6 h under 2 MPa H2 in ethanol. These findings shed light on the catalytic mechanisms in CLS, offering valuable insights for future catalyst design.

Selective and Controlled Grafting from PVDF-Based Materials by Oxygen-Tolerant Green-Light-Mediated ATRP.

Poly(vinylidene fluoride) (PVDF) shows excellent chemical and thermal resistance and displays high dielectric strength and unique piezoelectricity, which are enabling for applications in membranes, electric insulators, sensors, or power generators. However, its low polarity and lack of functional groups limit wider applications. While inert, PVDF has been modified by grafting polymer chains by atom transfer radical polymerization (ATRP), albeit via an unclear mechanism, given the strong C-F bonds. Herein, we applied eosin Y and green-light-mediated ATRP to modify PVDF-based materials. The method gave nearly quantitative (meth)acrylate monomer conversions within 2 h without deoxygenation and without the formation of unattached homopolymers, as confirmed by control experiments and DOSY NMR measurements. The gamma distribution model that accounts for broadly dispersed polymers in DOSY experiments was essential and serves as a powerful tool for the analysis of PVDF. The NMR analysis of poly(methyl acrylate) graft chain-ends on PVDF-CTFE (statistical copolymer with chlorotrifluoroethylene) was carried out successfully for the first time and showed up to 23 grafts per PVDF-CTFE chain. The grafting density was tunable depending on the solvent composition and light intensity during the grafting. The initiation proceeded either from the C-Cl sites of PVDF-CTFE or via unsaturations in the PVDF backbones. The dehydrofluorinated PVDF was 20 times more active than saturated PVDF during the grafting. The method was successfully applied to modify PVDF, PVDF-HFP, and Viton A401C. The obtained PVDF-CTFE-g-PnBMA materials were investigated in more detail. They featured slightly lower crystallinity than PVDF-CTFE (12-18 vs 24.3%) and had greatly improved mechanical performance: Young's moduli of up to 488 MPa, ductility of 316%, and toughness of 46 × 106 J/m3.

Organocatalytic ring-opening polymerization of lactide by bis(thiourea) H-bonding donating cocatalysts with binaphthyl-amine framework

Development of H-bonding organo-catalysts with high catalytic activity and high degree of control is significantly important for the metal-free polyesters that are potentially suitable for biomedical usage. The concomitant use of base and commercially available thiourea generally suffered from prolonged reaction time and resulted in incomplete monomer conversion in some cases. Introducing one or more (thio)urea H-bonding donating arms to the parent thiourea has been proved to be an effective method for substantially increasing the activity of thiourea H-bonding donors. Consequently, we synthesized bis-thioureas derived from binaphthyl-amine bearing different substituents and investigated their catalytic performance in ROPs of lactide in this work. The density functional theory (DFT) calculations suggested that the “activated-thiourea” mode is more preferred for the bis(thiourea) containing binaphthyl-amine framework. The bis(thiourea)/base binary systems could effectively promote the LA polymerization using benzyl alcohol as initiator. The polymerization rates and the degree of control over the polymerization are highly dependent on the structures of the bis(thiourea) and base. Bis(thiourea)/1,5,7-triazabicyclo[4.4.0]dec‑5-ene pairs exhibited highest catalytic activity compared to other bis(thiourea)/base pairs, and the turnover frequency is high up to 1980 h–1 at 75 °C. In addition, the bulky hindrance and axial chirality of the binaphthyl-amine framework could enable stereoselective ROP of rac-LA to produce isotactic-rich and crystalline PLAs at relatively low temperature (0 °C). Mechanistic studies indicated that both enantiomorphic site control (ESC) and chain end control (CEC) concurrently occurred in the rac-LA polymerization catalyzed by bis(thiourea)/base binary systems. This work will inspire future design of H-bonding donors with high catalytic performance.

Critical interplay between ruthenium oxide and water for the catalytic conversion of lignin to sustainable aviation fuel

The production of renewable drop-in fuels from lignocellulosic biomass is desirable for achieving net-zero carbon emissions in the transportation sector. However, the high irregularity of lignin and its resistance to complete ring saturation and deoxygenation hinder its conversion to sustainable aviation fuels (SAFs) such as C7–C16 isoparaffins and alkylated cycloalkanes. In this study, we achieve the direct production of SAFs from lignin-derived oil over a nonacidic Ru/C catalyst in water. Hydrogen atoms generated by H2 dissociation combine with neighboring water molecules to produce hydronium ions, which are then transferred via H-shuttling to attack the double bonds and cyclic –OH groups of adsorbed reactants and intermediates. Density functional theory calculations suggest that hydrodeoxygenation in water decreases the activation energy for the direct hydrogenolysis of cyclic –OH groups over oxygen-vacant ruthenium oxide sites. The critical interplay between oxygen-vacant ruthenium oxide and water results in the almost-complete conversion of lignin-derived monomers, dimers, and bio-oils to desirable SAF components.

Development of Ring-Expansion RAFT Polymerization of tert-Butyl Acrylate with a Cyclic Trithiocarbonate Derivative toward the Facile Synthesis of Cyclic Polymers.

Polymers with cyclic topology have no terminal structure and, therefore, exhibit various unique physical and functional properties compared to those of linear analogs. In this paper, we report an innovative methodology for the synthesis of cyclic polymers via ring-expansion RAFT (RE-RAFT) polymerization of vinyl monomers using a cyclic trithiocarbonate derivative (CTTC) as a RAFT agent. RE-RAFT of tert-butyl acrylate (TBA) was performed to yield a mixture of polymers exhibiting a bimodal size exclusion chromatography (SEC) trace. Both the peak top molecular weights shifted to higher-molecular-weight regions as the monomer conversion increased. The structure of the resulting polymer mixture was examined by 1H NMR and MALDI-TOF-MS. Detailed studies indicated that the obtained polymer of higher molecular weight was one of the large-sized cyclic polymers generated by the fusion of smaller-sized cyclic polymers during the RE-RAFT polymerization process. This approach opens the door to the simple synthesis of well-controlled cyclic polymers with complex structures, such as alternating and multi-block repeat unit sequences.

Thermoplastic elastomer obtained by photopolymerization‐induced concomitant macrophase and microphase separations

AbstractWe report on concomitant photoinitiated polymerization‐induced macrophase and microphase separation strategies to produce hierarchically structured recyclable poly(n‐butyl acrylate) based elastomeric materials. The investigated crosslinker‐free formulations are composed of n‐butyl acrylate monomer and a UV photo‐initiator mixed with poly(methyl methacrylate)‐b‐poly(n‐butyl acrylate)‐poly(methyl methacrylate) ABA triblock copolymers. Two different pre‐synthesized copolymers are used to control the macrophase separation. One synthesized by nitroxide‐mediated radical polymerization (NMRP), and a second by anionic polymerization (AP). Essentially, NMRP route leads to copolymer with unsaturated chain ends, activated during UV photopolymerization. On the other hand, the copolymer synthesized by AP are chemically inert. That dissimilarity is also highlighted by time‐resolved FTIR and SAXS, performed to monitor respectively monomer conversion and nanostructure evolution during photopolymerization. The experimental data demonstrate that the reactivity of the triblock copolymer impacts drastically the polymerization kinetics and the self‐assembly processes. Finally, the rheological analysis shows that the produced materials present a solid‐like behavior at low frequencies despite a large PnBA content (i.e., 85 wt%). This property is associated to the phase segregation and to the sample hierarchical morphology.