Sequential Copolymerization Research Articles

Selective aerobic oxidation of cumene to acetophenone via N-hydroxymaleimide fabricated by a sequential copolymerization and imidization

Selective oxidation of cumene to value-added acetophenone is of great importance and environmental friendliness. N-hydroxymaleimide (NHMI) was immobilized on a polymer substrate via co-polymerization followed by an imidization in this work, and the catalyst was characterized and tested for oxidation of cumene to acetophenone. The catalyst was found active and selective for the transformation from cumene to acetophenone. The optimized catalyst exhibited a cumene conversion of 93.3 % and a selectivity to acetophenone of 79.2 %. The cumene oxidation catalyzed by the immobilized NHMI copolymers may proceed in the presence of the cocatalyst Co2+ by a radical way based on the key intermediates or free radicals for the chain propagation of the auto-oxidation reaction observed. Accordingly, a reaction network and mechanism were proposed. The synthesized NHMI catalysts and the fabrication method may shed some light on the development of immobilized catalysts for the activation and selective oxidation of benzylic C−H bonds.

Effect of Different Monomer Sequence of Polyacrylate Copolymers with Coumarin Moieties on their Photodimerization Reaction

Effect of Different Monomer Sequence of Polyacrylate Copolymers with Coumarin Moieties on their Photodimerization Reaction

Pd(II)-Porphyrin-sensitized smart star polymer photocatalysts: A light-harvesting strategy using fluorescence resonance energy transfer effects

Photochemistry has become a popular topic in the field of sustainability. In particular, photocatalysts are a promising method to deal with environmental pollution, but only a few light sources with limited wavelengths are utilized to activate photosensitizers. Herein, we broaden the range of activation wavelengths of porphyrin-core amphiphilic star polymer photocatalysts by light harvesting. The coumarin moiety was polymerized from the porphyrin core while maintaining the amphiphilic microenvironment of the star polymer. The fluorescence resonance energy transfer (FRET) between porphyrin and coumarin leads to the activation of photocatalysts under both UV-A and UV-B light. Moreover, the copolymer sequence and polymer swelling effects on the FRET efficiency are discussed. The amphiphilic star block copolymer exhibited superior energy transfer efficiency in polar solvents, and its photocatalytic activity was evaluated via 2,5-dimethylfuran (2,5-DMF) photooxidation.

Preparation of acrylate-cationic monomer block copolymers by RAFT and their flotation oil removal properties

With the development of oilfields, the liquid volume of oily wastewater gets larger. Thus, more efficient flotation agents must be developed. In this regard, cationic polyacrylates with amphiphilic structures are potentially efficient flotation agents. Many studies have explored the effect of monomer type on flotation performance. However, there is a lack of investigations on the effect of block sequences on flotation performance. In this paper, acrylates (including methyl acrylate (MA) and ethyl acrylate (EA)) and cationic monomers (including acryloxyethyl trimethyl ammonium chloride (DAC), methylacryloxyethyl trimethyl ammonium chloride (DMC) and acryloxyethyl benzyl dimethyl ammonium chloride (DBC)) were used as raw materials, random, diblock and triblock copolymers were prepared through free radical polymerization and reversible addition-fragmentation chain transfer (RAFT) polymerization. The effect of the copolymer sequence on flotation performance was studied, and triblock copolymer P(DBC-b-MA-b-DBC) had better flotation performance than those of other copolymers. The synthesis conditions of P(DBC-b-MA-b-DBC) were successively optimized using the single-factor and response surface methods, and the optimal synthesis conditions were obtained as follows: monomer concentration of 51 wt%, the first section m(DBC): the second section m(MA): the third section m(DBC) = 1.5:1:1.5, initiator concentration of 0.28 wt%, reaction time of each section of 2 h, and reaction temperature of 73 °C. Under flotation temperature of 25 °C, P(DBC-b-MA-b-DBC) concentration of 70 mg/L, aeration flow rate of 2.0 L/min and flotation time of 10 min, the oil removal of oily wastewater with initial oil content of 822 mg/L reached 96.5 %. The results of the study can provide reference for the research and development of oily wastewater treatment agents.

Control of Solution Phase Behavior through Block–Random Copolymer Sequence

Control of Solution Phase Behavior through Block–Random Copolymer Sequence

Tuning network structures of hydrophobic hydrogels by controlling polymerization solvent

Hydrophobic hydrogels with various copolymer sequences and network structures are prepared by tuning the solvent condition of the reaction solution, which exhibit different appearance and properties under the same monomer composition.

Precise Synthesis of Tetrablock Copolymers of Different Acrylamide Derivatives via Iterative Aqueous Cu(0)-Mediated Polymerization

The accessibility of specific synthesis of tetrablock copolymers is reported. In a specific synthesis, four acrylamide monomers are gradually added using an iterative aqueous Cu(0)-mediated reversible-deactivation radical polymerization (RDRP) method. Essential to the success of this approach is the ability to design and polymerize ABCD copolymer sequence with no need for immediate purification steps. The simple in-situ sequential polymerization method allowed for essentially perfect control of accurately well-defined tetrablock copolymers, which are composed of four tiny blocks, each of which contains an average of ten functional monomer units of acrylamide derivatives, resulting in a variety of functional groups. While the final molecular weight distributions have very narrow despersities (Đ < 1.10), the efficient successive chain extension polymerization proceeded with high monomer conversions (>99%), delivering excellent block purification in a short period of time. The tetrablock poly(NIPAM-DMA-HEAA-DEA) was characterized by NMR and GPC and showed beneficial end-group fidelity, allowing quantitative monitoring of the system’s alive nature after each synthetic cycle. Importantly, these one-pot syntheses are carried out at a below temperature of 0.0 °C in water as the solvent and can be implemented for applications of molecular biology. We also investigate the potential for a copper-amide complex to develop with acrylamide monomer, which could have an adverse effect on the end group’s functioning. Finally, we believe that this approach makes it easier to create a novel category of advanced polymeric materials.

Copolymer Brush Particle Hybrid Materials with "Recall-and-Repair" Capability.

The effect of sequence structure on the self-healing and shape-memory properties of copolymer-tethered brush particle films was investigated and compared to linear copolymer analogs. Poly(n-butyl acrylate-co-methyl methacrylate), P(BA-co-MMA), and linear and brush analogs with controlled gradient and statistical sequence were synthesized by atom transfer radical polymerization (ATRP). The effect of sequence on self-healing in BA/MMA copolymer brush particle hybrids followed similar trends as for linear analogs. Most rapid restoration of mechanical properties was found for statistical copolymer sequence; an increase of the high Tg (MMA) component provided a path to raise the material's modulus while retaining self-heal ability. Creep testing revealed profound differences between linear and brush systems. While linear copolymers featured substantial viscous deformation when exposed to constant stress in the linear regime, brush analogs displayed minimal permanent deformation and featured shape restoration. The reduction of flow was interpreted to be a consequence of slow cooperative relaxation due to the complex microstructure of brush particle hybrids in which long-range motions are constrained through entanglements and slow-diffusing particle cores. The rubbery-like response imparts BA/MMA copolymer brush material systems concurrent "shape-memory" and "self-heal" capability. This ability to "recall-and-repair" could find application in the design of functional hybrid materials, for example, for soft robotics.

Conventional Non-Fluorescent Polymers: Unconventional Security Inks for Data Storage and Multidimensional Photonic Cryptography.

Traditional security inks relying on fluorescent/phosphorescent molecules are facing increasing risks of forgery or tampering due to their simple readout scheme (i.e., UV-light irradiation) and the advancement of counterfeiting technologies. In this work, a multidimensional data-encryption method based on non-fluorescent polymers via a "lock-key" mechanism is developed. The non-fluorescent invisible polymer inks serve as the "lock" for data-encryption, while the anti-rigidochromic fluorophores that can distinctively light up the polymer inks with programed emissions are "keys" for decryption. The emission of decrypted data is prescribed by polymer chemical structure, molecular weight, topology, copolymer sequence, and phase structure, and shows distinct intensity, wavelength, and chirality compared with the intrinsic emission of fluorophores. Therefore, the data is triply encrypted and naturally gains a high-security level, e.g., only one out of 20000 keys can access the only correct readout from 40000000 possible outputs in a three-polymers-based data-encryption matrix. Note that fluorophores lacking anti-rigidochrimism cannot selectively light up the inks and fail in data-decryption. Further, the diverse topologies, less well-defined structures, and random-coiled shapes of polymers make it impossible for them to be imitated. This work offers a new design for security inks and boosts data security levels beyond the reach of conventional fluorescent inks.

Synthesis of sulfur-containing polycarbonate block copolymers via Salen-metal catalyzed copolymerization of CO2, propylene oxide, and phthalic thioanhydride

Sulfur-containing ABA-type polycarbonate triblock copolymers were synthesized via sequential copolymerization of propylene oxide (PO) and carbon dioxide (CO2), followed by propylene oxide (PO) and phthalic thioanhydride (PTA) in the presence of water and Salen-Metal catalysts. The reaction was catalyzed using Salen-Co(III)-Cl/[PPN]Cl and Salen-Cr(III)-Cl/[PPN]Cl catalyst systems. The content of thioester units in the copolymer chain could be adjusted by varying the feed ratios of PTA. These triblock polymers displayed a higher refractive index, reaching up to 1.561.

Reversible Thermo-Optical Response Nanocomposites Based on RAFT Symmetric Triblock Copolymers (ABA) of Acrylamide and N-Isopropylacrylamide and Gold Nanoparticles.

The development of composite materials with thermo-optical properties based on smart polymeric systems and nanostructures have been extensively studied. Due to the fact of its ability to self-assemble into a structure that generates a significant change in the refractive index, one of most attractive thermo-responsive polymers is poly(N-isopropylacrylamide) (PNIPAM), as well as its derivatives such as multiblock copolymers. In this work, symmetric triblock copolymers of polyacrylamide (PAM) and PNIPAM (PAMx-b-PNIPAMy-b-PAMx) with different block lengths were prepared by reversible addition-fragmentation chain-transfer polymerization (RAFT). The ABA sequence of these triblock copolymers was obtained in only two steps using a symmetrical trithiocarbonate as a transfer agent. The copolymers were combined with gold nanoparticles (AuNPs) to prepare nanocomposite materials with tunable optical properties. The results show that copolymers behave differently in solution due to the fact of variations in their composition. Therefore, they have a different impact on the nanoparticle formation process. Likewise, as expected, an increase in the length of the PNIPAM block promotes a better thermo-optical response.

Development of a chemometric approach to improve the accuracy of copolymer sequence information obtained from pyrolysis gas-chromatography mass-spectrometry data

Number-average copolymer sequence length information can be obtained by pyrolysis-gas chromatography (Py-GC) by comparing the ratios of formed oligomers (i.e. dimers and trimers). The formation constants of the oligomers and their detection efficiency are not constant for all fragments, however. This can lead to unrepresentative peak ratios in the chromatogram. In these cases, calibration with an external method (e.g. NMR) is required. In this work, we introduce an algorithm that improves the copolymer sequence accuracy yielded from chromatograms with unrepresentative peak areas. The algorithm even functions in cases where oligomer data is missing as the rate of formation of certain oligomers is too low to detect them. One Py-GC measurement and one NMR measurement are required to train the developed algorithm for the determination of average monomer reactivity ratios and relative pyrolysis constants. Afterwards, Py-GC measurements of copolymers containing the same monomers, albeit with different compositions, can be corrected using the previously estimated constants. The algorithm was tested on various styrene-acrylate copolymers, yielding more accurate sequence information, even when limited oligomer information was available.

Using the SAFT-γ-Mie to Generate Coarse-Grained Force Fields Useable in Molecular Dynamics Simulations: Describing the Micellar Phases of Polyalkylglycols in Aqueous Solutions

In this work, we showcase the potential of the SAFT-γ-Mie equation of state to obtain, in a top-down approach, coarse-grained molecular models capable of describing micellization phenomena. For this purpose, we selected polyethylene oxide (PEO)/polypropylene oxide (PPO) triblock copolymers in aqueous solutions as a case study. The model was fitted to reproduce the thermophysical properties─liquid densities and vapor pressures─of small PEO/PPO oligomers as well as the activity coefficients or liquid–liquid phase diagrams of their binary mixtures with water. At low concentrations, the MD simulations show the formation of spherical micelles of morphology comparable to experiments, with the characteristic star-shaped or flower-shaped morphology depending on the polymer block sequence. The local structure and molecular conformations were analyzed, showing distinctions between the two types of aggregates. At higher concentrations, depending on the co-polymer sequence, the molecules form larger micelles or coalesce into larger aggregates when signs of phase separation are observed, as expected.

Copolymers with Nonblocky Sequences as Novel Materials with Finely Tuned Properties

The copolymer sequence can be considered as a new tool to shape the resulting system properties on demand. This perspective is devoted to copolymers with "partially segregated" (or nonblocky) sequences. Such copolymers include gradient copolymers and copolymers with random sequences as well as copolymers with precisely controlled sequences. We overview recent developments in the synthesis of these systems as well as new findings regarding their properties, in particular, self-assembly in solutions and in melts. An emphasis is put on how the microscopic behavior of polymer chains is influenced by the chain sequences. In addition to that, a novel class of approaches allowing one to efficiently tackle the problem of copolymer chain sequence design─data driven methods (artificial intelligence and machine learning)─is discussed.

Polyethylene Glycol-Isophorone Diisocyanate Polyurethane Prepolymers Tailored Using MALDI MS.

The reaction of diols with isocyanates, leading to mono-functional and di-functional prepolymers may be investigated using various characterization methods which show the overall conversion of isocyanate monomers. On the other hand, matrix-assisted laser desorption ionization mass spectrometry (MALDI MS) polymer characterization can be employed to identify the monomer units, the end-group functionalities, molecular weight averages, and to determine the copolymer sequence. Herein, we focus on prepolymer synthesis using isophorone diisocyanate (IPDI), a widely used diisocyanate for prepolymers preparation, especially in waterborne polyurethane materials. Thus, the reaction between polyethylene glycol diol and IPDI was in-depth investigated by mass spectrometry to determine the influence of the reaction parameters on the prepolymer's structure. The relative content of the different functional oligomer species at given reaction times was determined in the reaction mixture. More specifically, the offline analysis revealed the influence of reaction parameters such as reaction temperature, the concentration of reactants, and the amount of dibutyltin dilaurate catalyst. The established MALDI MS analysis involved measurements of samples, first, directly collected from the reaction mixture and secondly, following derivatization with methanol. The obtained results revealed the effects of reaction parameters on the functionalization reaction with isocyanates, allowing to achieve a better reaction control.

A focus on how latent "codons" are unravelled in synthetic copolymers.

We contextualize and highlight an innovative methodology for copolymer analysis introduced by Hibi et al. in Chemical Science (Y. Hibi, S. Uesaka and M. Naito, Chem. Sci., 2023, https://doi.org/10.1039/D2SC06974A). The authors introduce an advanced mass spectrometric method driven by a learning algorithm, termed 'reference-free quantitative mass spectrometry' (RQMS) for decoding sequences of copolymers in real time, including as a function of reaction progress. We highlight potential future implications and applications of the RQMS technique, as well as look forward to where else RQMS could be utilized within the soft matter materials space.

Improving the accuracy of copolymer sequence length determination by pyrolysis gas chromatography: A comprehensive study

Many industrial polymers which find application in contemporary materials are copolymers. Copolymers feature multiple distributions, that govern their physical properties, including the sequence distribution. Styrene-acrylate copolymers are an important class of polymers, their monomer sequence is typically determined by 13C NMR which suffers from low sensitivity and spectral resolution. A series of studies have shown that Py-GC can be applied to determine the sequence length of copolymers. The accuracy of the trimer assignments and the appropriate calibration approaches yielding reliable data have however not yet been validated. In the present study we propose a comprehensive workflow to ensure the accuracy of the sequence determination by Py-GC, next to NMR. In-depth analysis of the trimers observed in the Py-GC pyrograms of model styrene-acrylate copolymers was performed and specific MS fragments relating to the trimer sequence were assigned. A comparison of a series of copolymers yielded reliable assignments for the trimer signals. The obtained sequence lengths were in agreement with those calibrated with the benchmark method, 13C NMR. Py-GC was found to consistently underestimate the acrylate sequence length. Py-GC calibration with 13C NMR was thus found to be indispensable for the accurate absolute quantification of the sequence length by Py-GC. The calculated randomness did not vary significantly after NMR calibration, indicating that NMR calibration might not be required in all cases to obtain (relative) information on the sequence of a copolymer.

Efficient enumeration-selection computational strategy for adaptive chemistry

Design problems of finding efficient patterns, adaptation of complex molecules to external environments, affinity of molecules to specific targets, dynamic adaptive behavior of chemical systems, reconstruction of 3D structures from diffraction data are examples of difficult to solve optimal design or inverse search problems. Nature inspires evolution strategies to solve design problems that are based on selection of successful adaptations and heritable traits over generations. To exploit this strategy in the creation of new materials, a concept of adaptive chemistry was proposed to provide a route for synthesis of self-adapting molecules that can fit to their environment. We propose a computational method of an efficient exhaustive search exploiting massive parallelization on modern GPUs, which finds a solution for an inverse problem by solving repetitively a direct problem in the mean field approximation. One example is the search for a composition of a copolymer that allows the polymer to translocate through a lipid membrane at a minimal time. Another example is a search of a copolymer sequence that maximizes the polymer load in the micelle defined by the radial core-shell potentials. The length and the composition of the sequence are adjusted to fit into the restricted environment. Hydrogen bonding is another pathway of adaptation to the environment through reversible links. A linear polymer that interacts with water through hydrogen bonds adjusts the position of hydrogen bonds along the chain as a function of the concentration field around monomers. In the last example, branching of the molecules is adjusted to external fields, providing molecules with annealed topology, that can be flexibly changed by changing external conditions. The method can be generalized and applied to a broad spectrum of design problems in chemistry and physics, where adaptive behavior in multi-parameter space in response to environmental conditions lead to non-trivial patterns or molecule architectures and compositions. It can further be combined with machine learning or other optimization techniques to explore more efficiently the parameter space.

Emergent Sequence Biasing in Step-Growth Copolymerization: Influence of Non-Bonded Interactions and Comonomer Reactivities.

The phase behavior and material properties of copolymers are intrinsically dependent on their primary comonomer sequences. Achieving precise control over monomer sequence in synthetic copolymerizations is challenging, as sequence determination is influenced not only by the reaction conditions and the properties of the reactants but also by the statistical nature of the copolymerization process itself. Mayo-Lewis reactivity ratios are often used to predict copolymer composition and sequence and are based on ratios of static reactivity constants. However, prior results have demonstrated that in a generic, solution-based step-growth A,B-copolymerization, relatively weak non-bonded attractions between certain monomer pairs induce emergent microphase separations. Such polymerization-driven separations lead to deviations from standard kinetics due to the emergent heterogeneities in reactant concentrations, which can also cause significant shifts in the resulting copolymer sequences. Previously, these effects were observed in systems where the activation energies were equal for all reaction pathways, that is, between all monomer pair combinations. In this work, we explore the combined effects on copolymerization kinetics of differences in both activation energies and non-bonded attractions between monomers and examine the sequences produced within this same step-growth copolymerization model. Our results indicate that altering activation energies influences the kinetics and sequences in a manner that also depends on the non-bonded attractions, showing that these effects may work in concert or in opposition to one another to bias the sequences formed. Non-standard kinetic behaviors and long-range sequence biasing are observed under certain conditions, and the extent of each clearly shifts as the reaction proceeds. These findings provide insight into the complex interplay between sequence and nascent oligomer phase behavior, highlighting the potential for exploiting emergent phase properties in the informed design of advanced sequence-biased materials.

Expansion of the application range of pyrolysis-gas chromatography to copolymer sequence determination: Acrylate copolymers

The sequence distribution, which describes the order of monomers in a copolymer, is notoriously hard to study. The current standard in polymer sequence determination, NMR, is limited to simple copolymers due to lack in resolution and sensitivity. Therefore, an alternative method to determine the sequence of complex copolymers in the form of a developed pyrolysis-GC-MS method was investigated. Pyrolysis-GC-MS was applied to various acrylate copolymers; in the obtained pyrograms clear trimer distributions were observed and identified. Based on these results the sequence of these systems was calculated. The determined sequence values were found to be in line with expectations, demonstrating that the method was suitable for the sequence determination of binary acrylate copolymers. The developed method was also applied on various tertiary acrylate copolymers. Tertiary copolymers form many more distinct trimers rendering assignment more challenging. Nevertheless, based on a combination of chromatographic and mass spectrometric data, all formed trimers were assigned. To the best of our knowledge, this is the first time that a tertiary acrylate is sequenced by pyrolysis-GC.