Monodisperse Polymer Research Articles

A foundational framework for the mesoscale modeling of dynamic elastomers and gels

Discrete mesoscale network models, in which explicitly modeled polymer chains are replaced by implicit pairwise potentials, are capable of predicting the macroscale mechanical response of polymeric materials such as elastomers and gels, while offering greater insight into microstructural phenomena than constitutive theory or macroscale experiments alone. However, whether such mesoscale models accurately represent the molecular structures of polymer networks requires investigation during their development, particularly in the case of dynamic polymers that restructure in time. We here introduce and compare the topological and mechanical predictions of an idealized, reduced-order mesoscale approach in which only tethered dynamic bonding sites and crosslinks in a polymer’s backbone are explicitly modeled, to those of molecular theory and a Kremer–Grest, coarse-grained molecular dynamics approach. We find that for short chain networks (∼12 Kuhn lengths per chain segment) at intermediate polymer packing fractions, undergoing relatively slow loading rates (compared to the monomer diffusion rate), the mesoscale approach reasonably reproduces the chain conformations, bond kinetic rates, and ensemble stress responses predicted by molecular theory and the bead–spring model. Further, it does so with a 90% reduction in computational cost. These savings grant the mesoscale model access to larger spatiotemporal domains than conventional molecular dynamics, enabling simulation of large deformations as well as durations approaching experimental timescales (e.g., those utilized in dynamic mechanical analysis). While the model investigated is for monodisperse polymer networks in theta-solvent, without entanglement, charge interactions, long-range dynamic bond interactions, or other confounding physical effects, this work highlights the utility of these models and lays a foundational groundwork for the incorporation of such phenomena moving forward.

Multi-functional RAFT reagent to prepare fluorescent hyper-branched macromolecular probes for the detection of Fe3+ ions

Reversible addition-fragmentation chain transfer (RAFT) polymerization has the advantages of precise control, high yield, and narrow molecular weight distribution. These merits make it an ideal method for the preparation of hyper-branched fluorescent polymers (FL-HBPs). In this work, a multi-functional RAFT reagent (AVCT-NLP) was prepared for the synthesis of monodisperse FL-HBPs. Firstly, dithionate compound (CN1) containing a CC double bond was synthesized by the reaction of 4-nitrophenol with 1-(bromomethyl)-4-vinylbenzene. Subsequently, the NO2 group on CN1 was reduced to NH2, and the −Br on the 4-bromo-1,8-naphthalic anhydride was substituted to emit fluorescence. Finally, the fluorophore was introduced by the reaction of NH2 with the anhydride on the naphthalene ring to obtain AVCT-NLP which contains fluorophore, dithionate, and CC double bond in one molecule. AVCT-NLP was then used to synthesize the homopolymer (PAVCT-NLP) as both monomer and RAFT reagent. Moreover, PAVCT-NLP served as a macromolecular RAFT reagent, and hydrophilic monomer methacrylic acid (MAA) or 3-butene-1,2-diol were polymerized to obtain amphiphilic hyper-branched polymers (FL-AHBP-1, FL-AHBP-2). All the as-prepared macromolecules (PAVCT-NLP, FL-AHBP-1, and FL-AHBP-2) exhibited specific recognition and high sensitivity for Fe3+. The fluorescence quenching reached up to 74.4 %, with the limit of detection (LOD) as low as 1.82 nM. Additionally, the probe demonstrated pH stability and environmental adaptability. Due to the multi-functional structures of AVCT-NLP, it could be subjected to RAFT polymerization to obtain a monodisperse hyper-branched polymer. All polymers have a high fluorophore density and the polydispersity index (PDI) of the polymer is close to 1.00. This paper provided an effective approach for synthesizing polymer fluorescent probes with versatile structure and fluorescence properties in future applications.

Non-university of Constraint Release Relaxation in Entangled Linear Polymers of Various Chemical Structures

Abstract Extensive experiments have established that the constraint release (CR) relaxation takes place in binary blends of chemically identical long and short polymer chains wherein the long chains are dilute and entangled only with the short chains. Recently, Hannecart and coworkers focused on polymers of various chemical structures, polystyrene (PS), polyisoprene (PI), polybutadiene (PB), and poly(methyl methacrylate) (PMMA), and compared the CR relaxation time of the long chains in the binary blends of each polymer species (Hannecart, Clasen, and van Ruymbeke, Polymers 15, 1569 (2023)). From this comparison, they concluded that a normalized lifetime of the entanglement obstacle, with ZL = ML/Me (entanglement number of the long chain) and τe being the Rouse relaxation time of the entanglement segment, is determined only by the entanglements number of the short chain, ZS = MS/Me, irrespective of the chemical structure of the chains. This universality (independence from chemistry) would be an important feature if it were unequivocally concluded from experimental data. However, the values of the molecular weights utilized in their comparison, ML, MS, and Me, should have unavoidably included experimental uncertainties, which disturbs rigid conclusion of the universality. Aiming at a rigid experimental test avoiding those uncertainties, this study focuses just on data of the linear viscoelastic moduli G* of entangled monodisperse polymers of various chemical structures, PS, PI, PMMA, and poly(t-butyl styrene) (PtBS). We were able to find several pairs of chemically different but viscoelastically equivalent monodisperse polymers exhibiting indistinguishable G*GN data (with GN being the plateau modulus) from the local Rouse relaxation zone to the terminal relaxation zone. For binary blends of those equivalent polymers in each chemical species, i.e., long-X/short-X blends with X = PS, PI, PMMA, or PtBS, our experiments revealed that the CR relaxation of the dilute long chain does not complete at the same reduced frequency wte even when the chemically different component chains were viscoelastically equivalent in their monodisperse bulk state. It turned out that the CR relaxation is slower in the order of PS (slowest) < PMMA < PI < PtBS (fastest) and this difference was by a factor of 3-4 in total (well above the experimental resolution limit), rigidly showing the non-universal character of CR. An origin of this non-universality is briefly discussed within the framework of existing CR models, for example, Graessley’s CR model that already involved a chemistry-dependent parameter z representing a number of local CR hopping sites per entanglement segment.

Living Self-Assembly of Monodisperse Micron-Sized Polymer Vesicles.

Artificial vesicles are recognized as powerful platforms for a large body of research across the disciplines of chemistry, physics and biology. Despite the great progress, control of the size distribution to make uniform vesicles remains fundamentally difficult due to the highly uncontrollable growth kinetics, especially for micron-sized vesicles. Here we report a template-free living self-assembly method to prepare monodisperse vesicles around 1 μm from an alternating copolymer. The polymer forms nanodisks (ca. 9 nm) in N,N-dimethylformamide (DMF), acting as seeds for subsequent growth. By adding water, the nanodisks gradually grow into larger circular bilayer nanosheets, which bend to crowns and continue to grow into uniform micron-sized vesicles. The first-order growth kinetics as well as the small size polydispersity index (<0.1) suggests the living self-assembly characteristics. This work paves a new way in both living self-assembly and monodisperse polymer vesicles.

Living Self‐Assembly of Monodisperse Micron‐Sized Polymer Vesicles

AbstractArtificial vesicles are recognized as powerful platforms for a large body of research across the disciplines of chemistry, physics and biology. Despite the great progress, control of the size distribution to make uniform vesicles remains fundamentally difficult due to the highly uncontrollable growth kinetics, especially for micron‐sized vesicles. Here we report a template‐free living self‐assembly method to prepare monodisperse vesicles around 1 μm from an alternating copolymer. The polymer forms nanodisks (ca. 9 nm) in N,N‐dimethylformamide (DMF), acting as seeds for subsequent growth. By adding water, the nanodisks gradually grow into larger circular bilayer nanosheets, which bend to crowns and continue to grow into uniform micron‐sized vesicles. The first‐order growth kinetics as well as the small size polydispersity index (&lt;0.1) suggests the living self‐assembly characteristics. This work paves a new way in both living self‐assembly and monodisperse polymer vesicles.

A monodispersed metal-complexing peptide-based polymer for mass cytometry enabling spectral applications

We report the synthesis of a novel class of metal-complexing peptide-based polymers, which we name HyperMAPs (Hyper-loaded MetAl-complexed Polymers). The controlled solid-phase synthesis of HyperMAPs’ scaffold peptide provides our polymer with a well-defined molecular structure that allows for an accurate on-design assembly of a wide variety of metals. The peptide-scaffold features a handle for direct conjugation to antibodies or any other biomolecules by means of a thiol-maleimide-click or aldehyde-oxime reaction, a fluorogenic moiety for biomolecule conjugation tracking, and a well-defined number of functional groups for direct incorporation of metal-chelator complexes. Since metal-chelator complexes are prepared in a separate reaction prior to incorporation to the peptide scaffold, polymers can be designed to contain specific ratios of metal isotopes, providing each polymer with a unique CyTOF spectral fingerprint. We demonstrate the complexing of 21 different metals using two different chelators and provide evidence of the application of HyperMAPs on a 13 parameter CyTOF panel and compare its performance to monoisotopic metal-conjugated antibodies.

Continuous synthesis of monodisperse polymer nanoparticles: New insights into the effects of experimental variables under controlled mixing conditions

A robust microreactor with a sudden expansion structure was employed to facilitate controllable mixing with a mixing time ranging from 5.3 to 225.8 ms for water-acetonitrile mixing. Using this well-established mixing setup, a comprehensive investigation was conducted to analyze the inherent effects of various experimental variables on the size of PEG-PLGA NPs during nanoprecipitation. A consistent observation was that the size of PEG-PLGA NPs decreased as the mixing time decreased, ultimately reaching a limited size that no longer changed with the mixing time. This trend led to the classification of the nanoparticle formation process into slow and fast mixing stages. In the fast mixing stage, polymer concentration had minimal impact on particle size, while the anti-solvent to solvent flow rate ratio, solvent pair, and salt concentration influenced particle size by altering the solution environment. Lastly, the smallest attainable particle sizes of PEG-PLGA NPs under various experimental variables were revealed.

Enhanced molecular recognition with longer chain crosslinkers in molecularly imprinted polymers for an efficient separation of TR active substances.

Molecular imprinting technology has been widely studied as a technique to obtain molecular recognition by artificial means. Selecting functional monomers or polymerization conditions plays a key role to optimize molecularly imprinted polymer (MIP) synthesis. To date, there have been few reports well exploiting the effect of crosslinkers. Here, in this study, we synthesized the MIPs using poly(ethyleneglycol) dimethacrylate with different units of ethylene oxide (n = 1 to 23) as crosslinkers to observe the molecular recognition abilities. The MIPs were attached to the surface of mono-dispersed polymer beads. The obtained spherical MIPs and non-imprinted polymers were filled in a column for high performance liquid chromatography. Then the retention selectivity toward TR active substances was evaluated. The result revealed that the recognition ability did not improve regardless of the amount of ethylene oxide. With the crosslinker (n = 9), extremely high retention selectivity was observed, which provides at most around ten times as large imprinting factors in comparison with other MIPs. Interestingly, we obtained the highest recognition ability at around polymerization temperature from the evaluation of the recognition ability toward temperature shift using the MIP (n = 9). In general, hydrogen bonding based on MIPs provides high recognition ability at low temperature, whereas, this study indicates that the use of flexible crosslinkers may enable the synthesis of MIPs that precisely memorize the conditions of polymerization. Lastly, we simultaneously analyzed the TR active substances using the column filled with MIPs (n = 9). The result showed relatively linear correlation between the retention strength of each substance and phycological activity toward TR obtained by yeast assay. Therefore, we can conclude that an induced fit like the receptor emerged by constructing the flexible molecular recognition field.

The influence of the 8OCB liquid crystal concentrations on the ST-AA photonic crystal synthesis

This study presents the synthesis of polymer dispersed liquid crystals (PDLCs) composed of polymer particles and 4′-octyloxy-4-cyanobiphenyl (8OCB) liquid crystal. The motivation of this study resides in the great application prospects in widespread advanced technique fields for the obtained polymer-8OCB colloids and the possibility to implement the synthesis method for other types of LCs. The synthesis procedure involved soap-free emulsion polymerization in the presence of liquid crystal. This preliminary study describes for the first time the synthesis of nearly monodisperse PDLC polymer particles, as evidenced by SEM and DLS. The particles do not have the capacity to self-assemble. This study highlights the mechanism of generating PDLC particles, where 8OCB favors the chain transfer reactions and acts as a plasticizer between the polymer chains. These aspects were ascertained using GPC, DSC, SEM and EDX analysis. Increasing the 8OCB concentration in the system leads to lower molecular weights. The particle size was proportional to the amount of 8OCB. The limitations of the present synthesis approach are the reduced solubility of 8OCB in the monomer mixture. In consequence, a certain limit of LC concentration in the polymer matrix cannot be surpassed.

Shear banding in monodisperse polymer melt

We performed a series of molecular dynamics simulations on monodisperse polymer melts to investigate the formation of shear banding. Under high shear rates, shear banding occurs, which is intimately accompanied by the entanglement heterogeneity. Interestingly, the same linear relationship between the end-to-end distance Ree and entanglement density Z is observed at homogeneous flow before the onset of shear banding and at the shear banding state, where Ree ∼ ln(Wi0.87)−ξ0Z is proposed as the criterion to describe the dynamic force balance of the molecular chain in flow with a high rate. Deviating from this relation leads to a force imbalance and results in the emergence of shear banding. We establish a scaling relation between the disentanglement rate Vd and the Weissenberg number Wi as Vd∼Wi0.87 for stable flow in homogeneous shear and shear banding states. The formation of shear banding prevents chains from further stretching and disentanglement. The transition from homogeneous shear to shear banding partially dissipates the increased free energy from shear and reduces the free energy of the system.

Interpenetration and Friction of Brush-Coated Surfaces under External Load: Analytical Theory and SCF Calculations

We studied the compression and interpenetration properties of two opposing monodisperse polymer brushes under external load by analytical theory and by a numerical self-consistent field (SCF) approach. Analytical expressions are proposed for the brush density profiles in the interpenetration zone and verified by numerical SCF calculations. We quantify the interpenetration of two opposing brushes by the characteristic penetration length and by two integral parameters: the overlap integral, Γ, representing the number of interbush contacts, and the number of brush monomer units in the foreign half-space, Σ. The interpenetration parameters are studied in two conjugate ensembles as functions of the brush separation and of the external pressure. We propose a theoretical description of the solvent-mediated friction force in the low shearing rate regime on the basis of the Brinkman equation for two compressed brushes sliding against each other. We demonstrate that the total friction force which also includes direct brush–brush friction is expressed in terms of Γ and Σ. The SCF data for the interpenetration parameters Γ and Σ and hence for the total sliding friction force in the pressure ensemble collapse onto universal master curves when rescaled by the factor (N/σ)1/3 as suggested by the theory, where N is the chain length and σ is the surface grafting density. Finally, we define the kinetic friction coefficient as a function of the external pressure and analyze its universal rescaled behavior in the two limits of nondraining and free-draining brushes.

Monolithic light concentration by core–shell TiO2 nanostructures templated by monodisperse polymer colloidal monolayers

Nanostructured dielectric overlayers can be used to increase light absorption in nanometer-thin films used for various optoelectronic applications. Here, the self-assembly of a close-packed monolayer of polystyrene nanospheres is used to template a core–shell polystyrene-TiO2 light-concentrating monolithic structure. This is enabled by the growth of TiO2 at temperatures below the polystyrene glass-transition temperature via atomic layer deposition. The result is a monolithic, tailorable nanostructured overlayer fabricated by simple chemical methods. The design of this monolith can be tailored to generate significant absorption increases in thin film light absorbers. Finite-difference, time domain simulations are used to explore the design polystyrene-TiO2 core–shell monoliths that maximize light absorption in a 40 nm GaAs-on-Si substrate as a model for a photoconductive antenna THz emitter. An optimized core–shell monolith structure generated a greater than 60-fold increase of light absorption at a single wavelength in the GaAs layer of the simulated model device.

Review on Preparation of Polystyrene Microspheres

The traditional preparation methods of polystyrene microspheres are emulsion polymerization and suspension polymerization. The diameter of the microspheres prepared by the former is generally less than 0.5 m, and the diameter of the microspheres prepared by the latter is about several hundred microns and is difficult to control. With the continuous development of science and technology, scientists have found multiple methods to prepare micron-sized monodisperse polymer microspheres in recent years. Such as soap-free or low-soap emulsion method, dispersion polymerization method, liquid-phase synthesis method. The four preparation methods of dispersion polymerization, emulsion polymerization, liquid-phase synthesis, suspension polymerization and their respective advantages and disadvantages are discussed in detail, and the prospect of synthetic application is prospected.

Photo‐induced fusion of monodisperse polymer microspheres: A novel strategy for constructing topological microsphere clusters with improved stability

AbstractThe preparation of monodisperse azobenzene (Azo) polymer microspheres by dispersion polymerization was reported. The photo‐induced fusion of Azo polymer microspheres was successfully achieved during the process of reversible trans‐cis‐trans photoisomerization of Azo units, and induced various unique “microsphere molecular” clusters or “microsphere polymers”. Encouraged by this interesting phenomenon, microsphere clusters of different topological structures were stabilized by the in situ acetal cross‐linking chemistry. The photo‐induced fusion polymerization of monodisperse polymer microspheres provides a new strategy for designing photo‐responsive clusters and allows for control over the mechanical properties of microspheres with high spatiotemporal resolution.

Extremely early onset of nonlinear viscoelasticity in dynamic shear of ideally monodisperse DNA

AbstractThis work reports that the rheology of ideally monodisperse lambda () phage DNA solutions is extremely sensitive to the applied strain in dynamic oscillatory experiments. DNA exhibits nonlinearity at strains far smaller than what is observed in conventional synthetic polymers. However, it is found that polydisperse calf thymus DNA does not exhibit the extreme strain sensitivity. By mixing samples of monodisperse DNA with the polydisperse calf thymus DNA, we correlate the molecular weight distribution (or polydispersity) to the onset of nonlinear viscoelasticity. We demonstrate that the strain sensitivity weakens as the polydispersity index increases. This is the first work correlating the inception of nonlinear viscoelasticity in entangled polymer system such as lambda DNA solution to the polydispersity of the samples. The experimental data suggests that ideally monodisperse polymer systems are very sensitive to the applied strain and have a very early transition to the nonlinear regime. We conclude that nominally monodisperse synthetic polymers are not sufficiently monodispersed to exhibit the early onset.

Protecting-Group-Free Iterative Divergent/Convergent Method for Preparing Sequence-Defined Polymers

A new iterative growth method is reported to prepare monodisperse sequence-defined polymers by combining the chain growth mechanisms of the traditional iterative sequential growth (ISG) and iterative exponential growth (IEG) strategies. Using three orthogonal click reactions to couple three groups of monomers, each containing two orthogonal clickable groups. This method grows monodisperse sequence-defined polymers in a protecting-group-free divergent/convergent way. Each iterative cycle of this method involves two divergent sequential growth steps and one convergent exponential growth step, which endows the new method with the chain growth advantages of both traditional ISG and IEG. The two divergent sequential growth reactions introduce new monomer structures into main chains and provide the resultant sequence-defined polymers with varied monomer sequences, while the convergent exponential growth reaction guarantees the method a fast chain growth speed. The repetition of the abovementioned iterative cycle allows this method to grow monodisperse sequence-defined polymers with a fast chain growth manner of 3 × 2n–2.

Secondary structure and stability of a gel-forming tardigrade desiccation-tolerance protein.

Protein-based pharmaceuticals are increasingly important, but their inherent instability necessitates a "cold chain" requiring costly refrigeration during production, shipment, and storage. Drying can overcome this problem, but most proteins need the addition of stabilizers, and some cannot be successfully formulated. Thus, there is a need for new, more effective protective molecules. Cytosolically, abundant heat-soluble proteins from tardigrades are both fundamentally interesting and a promising source of inspiration; these disordered, monodisperse polymers form hydrogels whose structure may protect client proteins during drying. We used attenuated total reflectance Fourier transform infrared spectroscopy, differential scanning calorimetry, and small-amplitude oscillatory shear rheometry to characterize gelation. A 5% (wt/vol) gel has a strength comparable with human skin, and melts cooperatively and reversibly near body temperature with an enthalpy comparable with globular proteins. We suggest that the dilute protein forms α-helical coiled coils and increasing their concentration drives gelation via intermolecular β-sheet formation.

Cyclization assisted iterative growth method for synthesizing monodisperse polymers

A fast iterative growth method is reported to prepare monodisperse polymers assisted by a cyclization technique. This novel method uses a di-functional and a tri-functional compounds as monomer pairs. The di-functional monomer is designed to have an azide and a hydroxyl end groups, while the tri-functional monomer is designed to have an alkyne and a sym-dibenzo-1,5-cyclooctadiene-3,7-diyne containing two strained alkynes. One iterative cycle of this novel method is composed by four step reactions. First, the self-accelerating double-strain-promoted azide-alkyne click reaction is used to couple two monomers/oligomers having an azide and a hydroxyl end group pairs with one tri-functional monomer by reacting the azide and strained alkyne groups. This coupling reaction increases chain length and produces an elongated oligomers having two hydroxyl end groups and one alkyne group in the middle position of main-chain. Second, the esterification between anhydride and hydroxyl is used to modify the hydroxyl end groups to endow the elongated oligomers with two azide end groups. Third, copper(I)-catalyzed azide-alkyne click reaction is then used to ring-close the elongated oligomers by reacting the middle alkyne and one terminal azide groups to prepare a tadpole-shaped oligomers with one azide end group. Fourth, the 2,3-dichloro-5,6-dicyano-p-benzoquinone oxidized deprotection reaction is used to cleave the preset methoxybenzyl ether bond in the ring of the tadpole-shaped oligomers and rebuild an azide and a hydroxyl end group pairs for the elongated oligomers. The repetition of above iterative cycle can synthesize the monodisperse polymers with a fast chain-growth manner of 2n+1-1.

Aggregation-Induced Emission Enabled Visualization of Anisotropic Seed Emulsion Polymerization to Synthesize Monodisperse Polymer Hemispheres

Aggregation-Induced Emission Enabled Visualization of Anisotropic Seed Emulsion Polymerization to Synthesize Monodisperse Polymer Hemispheres

Independent control over sizes and surface properties of polystyrene-based particles using multiple comonomers

Polystyrene (PSt)-based particles are versatile components for composite materials, and their sizes and surface properties play a vital role in composite processes. In this study, we developed highly useful PSt-based particles by soap-free emulsion polymerization. The size and surface properties of monodisperse PSt-based particles were controlled using an ionic comonomer of sodium p-styrenesulfonic acid (NaSS) and a nonionic comonomer of N-isopropylacrylamide (NIPAM). The particle sizes decreased with increasing NaSS concentration. A weak dependence of particle sizes on NIPAM concentration was observed at a fixed NaSS concentration of 2 mM. The particles synthesized at an NIPAM ratio of 10 mol% or more exhibited shrinking behavior at 50°C, although an increase in NaSS concentration suppressed the shrinking behavior of the particles. Compared to the results of previous reports, the ratio of the nonionic (NIPAM) and the ionic (NaSS and initiator) components corresponds to the shrinking degree of PSt-based particles copolymerized with NIPAM. Surface tensions of the suspensions were measured to evaluate the surface properties of the PSt-based particles because poly(N-isopropylacrylamide) (PNIPAM) has an intrinsic property of surface activity. The surface tension decreased with increasing NIPAM ratio up to 10 mol%. An analysis using a fluorescence probe of Laurdan experimentally indicated that the addition of NIPAM formed a localized hydrophobic environment on the particle surfaces, resulting in surface activity. These results suggest that the employments of ionic comonomer and NIPAM enable independent controls over sizes and surface activities of PSt-based particles, which is required for development of new functional materials incorporating monodisperse polymer particles as building blocks.