Heterogeneous Polymerization Research Articles

Deformation and Failure Mechanism of Particulate Filled and Short Fiber Reinforced Thermoplastics: Detection and Analysis by Acoustic Emission Testing.

Acoustic emission, the detection of signals during deformation, is a frequently used method for the study of local deformation processes occurring in heterogeneous polymer systems. Most of these processes result in the evolution of elastic waves which can be detected by appropriate sensors. The analysis of several parameters characterizing the waves offers valuable information about the possible deformation mechanism. The acoustic emission testing of composites may yield very different number of signals from a few hundred to more than 100,000. This latter was proved to be affected mainly by particle size, interfacial adhesion and composition, but other factors, such as matrix modulus and specimen size, also influence it. Local deformation processes are claimed to have a strong effect on macroscopic properties. Indeed, a close correlation was found between the initiation stress of the dominating particle related process derived from acoustic emission testing and the tensile strength in both polypropylene (PP) and poly(lactic acid) (PLA) composites. However, in polyamide (PA)-based heterogeneous polymer systems, deformations related to the matrix dominated composite properties. Besides forecasting failure, the method makes possible the determination of the inherent strength of lignocellulosic fibers being around 40 MPa as well as the quantitative estimation of adhesion strength for composites in which interactions are created by mechanisms other than secondary forces. The proposed approach based on acoustic emission testing proved that in PP/CaCO3 composites, the strength of adhesion can be increased by ten times from about 100 mJ/m2 to almost 1000 mJ/m2 in the presence of a functionalized polymer.

Identification and Quantification of Glycans in Whole Cells: Architecture of Microalgal Polysaccharides Described by Solid-State Nuclear Magnetic Resonance.

Microalgae are photosynthetic organisms widely distributed in nature and serve as a sustainable source of bioproducts. Their carbohydrate components are also promising candidates for bioenergy production and bioremediation, but the structural characterization of these heterogeneous polymers in cells remains a formidable problem. Here we present a widely applicable protocol for identifying and quantifying the glycan content using magic-angle-spinning (MAS) solid-state NMR (ssNMR) spectroscopy, with validation from glycosyl linkage and composition analysis deduced from mass-spectrometry (MS). Two-dimensional 13C–13C correlation ssNMR spectra of a uniformly 13C-labeled green microalga Parachlorella beijerinckii reveal that starch is the most abundant polysaccharide in a naturally cellulose-deficient strain, and this polymer adopts a well-organized and highly rigid structure in the cell. Some xyloses are present in both the mobile and rigid domains of the cell wall, with their chemical shifts partially aligned with the flat-ribbon 2-fold xylan identified in plants. Surprisingly, most other carbohydrates are largely mobile, regardless of their distribution in glycolipids or cell walls. These structural insights correlate with the high digestibility of this cellulose-deficient strain, and the in-cell ssNMR methods will facilitate the investigations of other economically important algae species.

Separation and catalytic depolymerization of empty palm fruit bunch lignin

Lignin is a heterogeneous and complex polymer and a potential renewable source of aromatic compounds as precursors to many industrially useful products. Microbial biotransformations for lignin valorization are reported but require not only its separation from biomass matrix but also breakdown into its monomeric components. Abundantly available empty palm fruit bunch was used as the lignin-rich biomass to process it to obtain a mixture of lignin-derived monomeric aliphatic and aromatic compounds. A two-step acid-alkali treatment was deployed to extract lignin and its breakdown into smaller fragments. Dilute nitric acid treatment could extract 80% of the lignin and the hydrolysate was fractionated through a series of nanofiltration membranes. The residual polymeric lignin obtained after monomer separation was catalytically depolymerized using Cu/Al2O3 under optimized conditions i.e., 180 °C, 7 MPa, 60 min, methanol: water ratio as 1:1 to give 80% conversion. Lignin mixture at every step was analyzed by GC-MS and gel permeation chromatography (GPC). The scheme resulted in 37% of the overall lignin being obtained as monomers.

Emerging Contributions of Solid-State NMR Spectroscopy to Chromatin Structural Biology.

The eukaryotic genome is packaged into chromatin, a polymer of DNA and histone proteins that regulates gene expression and the spatial organization of nuclear content. The repetitive character of chromatin is diversified into rich layers of complexity that encompass DNA sequence, histone variants and post-translational modifications. Subtle molecular changes in these variables can often lead to global chromatin rearrangements that dictate entire gene programs with far reaching implications for development and disease. Decades of structural biology advances have revealed the complex relationship between chromatin structure, dynamics, interactions, and gene expression. Here, we focus on the emerging contributions of magic-angle spinning solid-state nuclear magnetic resonance spectroscopy (MAS NMR), a relative newcomer on the chromatin structural biology stage. Unique among structural biology techniques, MAS NMR is ideally suited to provide atomic level information regarding both the rigid and dynamic components of this complex and heterogenous biological polymer. In this review, we highlight the advantages MAS NMR can offer to chromatin structural biologists, discuss sample preparation strategies for structural analysis, summarize recent MAS NMR studies of chromatin structure and dynamics, and close by discussing how MAS NMR can be combined with state-of-the-art chemical biology tools to reconstitute and dissect complex chromatin environments.

A Multipore Model for Heterogeneous Catalytic Polymerization: Structure–Performance Relationships

AbstractA novel single‐particle model is developed for the physicochemical processes involved in the heterogeneous catalytic polymerization. The model considers the reaction kinetics together with the detailed initial pore structure and explicitly describes the support fragmentation. It captures some of the most widely observed morphological features of heterogeneous catalysis for both before and after starting fragmentation, including the possibility of occurrence of both known fragmentation mechanisms. All the monomer mass conservation equations are solved using a robust semianalytical approach. The results show that the catalyst pore structure, which can be tuned during chemical preparations, has a vital role in determining the catalyst performance through changing the contribution of each of the two fragmentation mechanisms in the overall fragmentation process and that decreasing the propagation rate constant and/or increasing diffusion coefficient intensifies the continuous bisection mechanism. A potential fragmentation index is proposed in order to relate the fragmentation phenomenon to structural features of the catalyst. By defining a weighted average fill factor, it is shown that the fragmentation index is in fact a measure of how much the pores closer to the center relative to the pores closer to the surface are filled up at the fragmentation moment.

Coating Process Optimization and Self-Healing Performance Evaluation of Shellac Microcapsules Coated with Melamine/Rice Husk Powder

To explore the implication of the coating process on the comprehensive properties of water-based coating containing shellac microcapsules coated with melamine/rice husk powder on the Tilia cordata surface, the optical properties, mechanical properties, liquid resistance, aging resistance, chemical composition, and microstructure of the coating were analyzed comprehensively. After the best coating process was determined, compared with the coating without microcapsules, the self-repairing performance of the water-based coating containing shellac microcapsules coated with melamine/rice husk powder was explored via aging resistance test and scratch test. The results showed that the best comprehensive performance of the coating was obtained by three times primer, two times finish, and 6.0% shellac microcapsules coated with melamine/rice husk powder added in the primer. The coating with shellac microcapsules had significant stability, aging resistance, and self-healing performance, which can repair cracks in a certain period of time and inhibit the formation of cracks. At the core wall ratio of 0.75, the shellac which plays a role of the repair agent as the core material can effectively fill the microcracks in the coating to repair by flowing from the broken microcapsule because it can be physically cured at room temperature. The modification of waterborne coatings with shellac microcapsules coated with melamine/rice husk powder contributes the improved self-repairing properties of surface coatings containing heterogeneous natural polymer composites.

Conformational Variations for Surface-Initiated Reversible Deactivation Radical Polymerization: From Flat to Curved Nanoparticle Surfaces

Although progress in surface-initiated reversible deactivation radical polymerization (SI-RDRP) has already enabled the production of increasingly novel and advanced polymer structures on solid surfaces, fundamental kinetic questions remain regarding the impact of reaction conditions on the molecular properties of synthesized tethered chains. In the current work, we put forward a matrix-based kinetic Monte Carlo (kMC) model, which is based on an implicit SI-RDRP reaction scheme and continuous three-dimensional (3D) representations, capable of following the temporal evolution of the molecular properties of individual free and surface-tethered polymer chains. This is uniquely possible for variable surface curvature (nanoparticle radii from 4.5 to 32 nm; 353 K; monomer: methyl methacrylate), also including the comparison with the limiting case of a flat surface and addressing various (average) RDRP initiator surface coverages. For the tethered chains, we emphasize the prediction of the variation of the molecular height, monomer occupancy, and radius of gyration and also focus on the simulation of the chain length distribution (CLD) to enable a comparison with solution RDRP results. It is shown that confinement effects on the surface lead to the formation of heterogeneous polymer layers with a marked bimodality in the number CLD. This bimodality is, however, wiped out in experimental analysis based on log-molar mass distributions. It is also shown that an increase in the size of the spherical particles and, hence, a decrease in their curvature results in a deterioration of the control over molecular properties, leading to behavior more similar to that of flat surfaces. Average molecular heights and monomer occupancies can vary with a factor of 2. The impact of the targeted chain length is shown to be of lower importance.

Valorization and Mechanical Recycling of Heterogeneous Post-Consumer Polymer Waste through a Mechano-Chemical Process.

In this paper, a sustainable strategy to valorize and recycle heterogeneous polymer-based post-consumer waste is proposed. This strategy is based on a high-energy mechano-chemical treatment and has been applied to a polyolefin-rich fraction, coded as FIL/S, deriving from household plastic waste collection. This processing, performed in a planetary ball mill, allowed us to obtain fine grinding and, consequently, to induce an intimate mixing of the different polymer fractions and contaminants composing the FIL/S, as demonstrated by SEM analysis. As a result, an improvement in the deformability of the treated material was obtained, recording values for elongation at the break which were two and half times higher than the neat FIL/S. Finally, the addition of small amounts of organic peroxide during mechano-chemical treatment was tested, determining a more homogeneous morphology and a further improvement in mechanical parameters.

On the evolution of particle size distributions during the bulk synthesis of high-impact polystyrene using PBM: Towards morphology and phase inversion prediction

The mechanism of the phase inversion (PI) process that occurs during the bulk polymerization of High Impact Polystyrene (HIPS) is studied in this article. Transmission electron micrographs (TEM) were obtained for different operating conditions, varying initiator concentration, temperature, and stirring speed from a previous work. Particle size distributions were retrieved from such micrographs, and were compared to theoretical predictions. To this end, a population balance model, coupled with a heterogeneous polymerization module, was developed. The evolution of particle growth, break-up and coalescence is discussed to assess the breakage/coalescence imbalance that is thought to occur at the inversion point. Results indicate that a different criterion for PI seems to be needed in this system.

Collapse transition of a heterogeneous polymer in a crowded medium.

Long chain molecules can be entropically compacted in a crowded medium. We study the compaction transition of a heterogeneous polymer with ring topology by crowding effects in a free or confined space. For this, we use molecular dynamics simulations in which the effects of crowders are taken into account through effective interactions between chain segments. Our parameter choices are inspired by the Escherichia coli chromosome. The polymer consists of small and big monomers; the big monomers dispersed along the backbone are to mimic the binding of RNA polymerases. Our results show that the compaction transition is a two-step process: initial compaction induced by the association (clustering) of big monomers followed by a gradual overall compaction. They also indicate that cylindrical confinement makes the initial transition more effective; for representative parameter choices, the initial compaction accounts for about 60% reduction in the chain size. Our simulation results support the view that crowding promotes clustering of active transcription units into transcription factories.

A new silver coordination polymer based on 4,6-diamino-2-pyrimidinethiol: synthesis, characterization and catalytic application in asymmetric Hantzsch synthesis of polyhydroquinolines

A highly efficient and stable heterogeneous coordination polymer (CP) was successfully prepared by hydrothermal combination of silver and 4,6-diamino-2-pyrimidinethiol. The prepared coordination polymer was characterized by FT-IR, XRD, TGA, SEM, EDX, X-ray mapping and Nitrogen adsorption–desorption analysis. The prepared Ag–CP exhibit excellent catalytic activity in multicomponent Hantzsch synthesis of polyhydroquinolines under mild reaction conditions in relatively short reaction times. The heterogeneity of the catalyst was confirmed by the hot filtration test; also, the catalyst was reused for at least four times under the optimized reaction conditions without any significant loss of its catalytic activity.

Iminopyridyl ligands bearing polyethylene glycol unit for nickel catalyzed ethylene polymerization

Influence of polyethylene glycol unit on nickel catalyzed ethylene polymerization have attracted increasing interest. The Lewis basic oxygen atoms on polyethylene glycol group can form interactions with Lewis acidic metal additives. In this contribution, a series of iminopyridyl ligands (L-O1, L-O2 and L-O3) bearing polyethylene glycol units and corresponding nickel complexes (Ni-O1, Ni-O2 and Ni-O3) were designed, synthesized and characterized. By the activation of alkylaluminium cocatalysts, the nickel complexes and their corresponding MgCl2-supported nickel precatalysts (Ni-O1-Mg, Ni-O2-Mg and Ni-O3-Mg) were investigated in catalytic homogeneous and heterogeneous ethylene polymerization, respectively. The molecular weight of products increased with the number of oxygen atoms on polyethylene glycol unit increasing. The introduction of the MgCl2 support resulted in much higher molecular weights and much lower branched densities of polyethylenes than those of products generated in the homogeneous polymerizations. The polymers generated in heterogeneous polymerizations have excellent polymer powder morphology to prevent reactor fouling, facilitating potential industrial applications.

High-Temperature Proton Conduction in Covalent Organic Frameworks Interconnected with Nanochannels for Reverse Electrodialysis.

The crystalline porous organic framework offers a highly ordered and stable structure under hydrated conditions at high temperatures. Here, we demonstrated a method for preparing high-performance membrane buildup using "heterogeneous networks" and "polymer phase-separated nanochannels". A well-interconnected "nanochannel" with a "crystalline organic framework" forms a highly stable hybrid membrane above 80 °C under 100% hydration under acidic and basic conditions. The prepared structure provides a self-standing membrane that easily overcomes the problem faced by conventional high ion-exchange capacity (IEC)-based membranes such as swelling, gelling, fragility, and dissolving at elevated temperatures. Apart from structural stability, it also shows better chemical stability with enhanced proton conduction at elevated temperatures. This proton conduction with better structural stability in the high IEC sample confirms from thermal analysis, whereas it also offers relatively low in-plane membrane swelling as compared to the conventional membranes. These hybrid membranes were further combined with the FAA-3 membrane to manufacture a reverse electrodialysis system for generating a power output. We also evaluated the maximum power density (Pmax) of the stack theoretically and experimentally. The determined net power density (Pnet) is reported to be 0.45 W m-2 at a flow rate of 40 mL min-1. These results confirm that the developed membrane can withstand robustly under realistic ambient conditions maintaining stable cell performance.

Regulating the Self-Discharge of Flexible All-Solid-State Supercapacitors by a Heterogeneous Polymer Electrolyte.

Supercapacitors with high power density and an ultralong cyclic lifetime have been intensively investigated. However, the crucial challenge of their rapid self-discharge process is often neglected in most cases. A heterogeneous interface formed between two layers of polymer electrolytes is designed, in which a polyanion and a polycation are added into a common matrix of polymer electrolyte, respectively. By using the heterogeneous polymer electrolyte (HPE) as the separator simultaneously, the resultant supercapacitors exhibit comparable electrochemical performance to that of devices based on traditional polymer electrolytes. The HPE-based supercapacitors using both electric double-layer capacitive and pseudocapacitive electrodes show at least one time longer self-discharge time than that of devices based on homogenous polymer electrolyte, especially for the electrode in an electrolyte containing polyanion served as a positive pole during the charging process. Because of the same polymer matrix used, the heterojunction structure of the HPE exhibits excellent stability without obvious phase separation during thousands of charge/discharge and repeated bending cycles. This novel strategy by interface engineering of electrolyte to suppress the self-discharge behavior of supercapacitors is very meaningful to promote their practical applications.

Mechanistic Insights into Oxygen Tolerance of Graphitic Carbon Nitride-Mediated Heterogeneous Photoinduced Electron Transfer-Reversible Addition Fragmentation Chain Transfer Polymerization

Mechanistic Insights into Oxygen Tolerance of Graphitic Carbon Nitride-Mediated Heterogeneous Photoinduced Electron Transfer-Reversible Addition Fragmentation Chain Transfer Polymerization

Multi-Walled Carbon Nanotubes and Carbon Black Incorporated Heterogeneous Layered Polymer Composites with Enhanced Electrical Features

The present work is centered on the study of electrical properties of three different types of composites i.e. single layer carbon black (CB) and multi-walled carbon nanotubes (MWCNTs) based PMMA composites, CB/PMMA and MWCNTs/PMMA, and bilayer polymer composites CB/PMMA-MWCNTs/PMMA, prepared by solution mixing method using chloroform as dispersion medium. It is expected that two layers in bilayer polymer composites would show increased interfacial interactions resulting in improved electrical character especially dielectric properties. Prepared composites have been characterized by UV-Vis and FTIR spectroscopy for successful synthesis. Electrical properties, conductivity, dielectric constant and tangent loss of all composites were measured at frequency range of 40Hz to 1MHz by using LCR meter. Percolation threshold value was obtained by using data of electrical conductivity as a function of volume fraction of fillers. The obtained value of percolation threshold was much lower for bilayer polymer composites i.e. 0.01 vol% as compared to the single layer polymer composites. Observed data of dielectric constant encourages the synthesis of composites with this kind of structure.

Fabrication of kinetically stable micropolymofoam particles and the spontaneous induction of morphological transformation

We report fabrication of low-density polymeric microparticles (micropolymofoam particles [μPFPs]) using the piezoelectric inkjet method. After ejecting a polymer solution prepared by dissolving polymers in a volatile organic solvent, microdroplets are periodically generated through an inkjet nozzle in the air. Rapid evaporation of the solvent as it falls through the air leads to a highly porous surface and internal morphology. Optical microscope observation confirms that the inside of the μPFPs is filled with air. Notably, the use of more than two different polymers results in kinetically stable particles, in which the heterogeneous polymer chains are randomly entangled. Shape transformation of the kinetically stable μPFPs occurs upon adding a swelling solvent, spontaneously changing their geometry from porous and rugged-shaped to a Janus-like structure with a clear phase boundary. This transformation is directly monitored using an optical microscope. The surface free energy calculation reveals that particles are transformed to adopt a thermodynamically stable structure; this is achieved by imparting fluidity to the randomly entangled polymer chains, which is energetically unfavorable. In addition, porosity control can be possible by selectively removing one polymer phase of kinetically stable particles comprising two different polymers. Furthermore, the developed inkjet method can be applied for producing composite particles encapsulated with functional nanoparticles and coating or patterning them directly onto a substrate.

Ionic liquids: From a solvent for polymeric reactions to the monomers for poly(ionic liquids)

Ionic liquids (ILs) have created their niche as a solvent of choice in the realm of synthetic chemistry. More specifically, in polymer chemistry, these designer solvents are utilized as the potential media for carrying out the polymeric reactions and sometimes as reactive constituents of polymeric materials. None of the polymeric reactions is left to explore the ability of ILs as a solvent for homogeneous/ heterogeneous polymerization systems to develop specialty polymers making use of their versatile properties viz. non-toxicity, high thermal stability, negligible vapor pressure, and large electrochemical window. Interestingly, over some time, another aspect of these ILs has been explored i.e. their ability of getting polymerized, and their inherent properties are further enhanced in this form. Such polymerized ionic liquids (PILs) exhibit particular properties and find many newer applications such as in electrochemical devices as polyelectrolyte, development of nanocomposites, optoelectronics, gas membranes, smart materials, building blocks in materials science, and also in other areas such as environment, energy, analytical chemistry, and catalysis. A comprehensive review of both the aspects of ILs i.e. solvent of choice in the polymeric reactions and various aspects of its polymeric form i.e. [poly(ionic liquids)] is presented in this article.

Utilization of Poor RAFT Control in Heterogeneous RAFT Polymerization

Heterogeneous reversible addition–fragmentation chain transfer (RAFT) polymerization exhibits considerable promise in polymer and colloid synthesis. During the research of RAFT polymerization, good RAFT control is always an important goal to achieve while poor RAFT control is considered to be a lack of success. Herein, we develop heterogeneous RAFT polymerization from an unusual angle by deliberately using RAFT agents with poor RAFT controllability. The utilization of poor RAFT control in heterogeneous RAFT polymerization led to the formation of samples contain high-molecular-weight block copolymers, uncontrolled homopolymers, and the unreacted macro-RAFT agent. Remarkably, uniform polymer spheres with precise size could be obtained via heterogeneous RAFT polymerization, although molecular weight distributions of the obtained polymers were broad. In-depth studies of heterogeneous RAFT polymerization mediated by a binary mixture of RAFT agents with different controllability, the RAFT agent with good controllability dominated the polymerization while the RAFT agent with poor controllability was mainly inactivated or unreacted. On the basis of the unique mechanism provided, we have been able to prepare block copolymer assemblies with rich pendant RAFT groups on the surface by one-step heterogeneous RAFT polymerization using a macro-RAFT agent with divergent RAFT end groups. The reactivity of pendant RAFT groups on the surface provides a landscape for further functionalization of block copolymer assemblies. These proof-of-concept experiments demonstrate that the utilization of poor RAFT control in heterogeneous RAFT polymerization is a promising strategy to a variety of polymer particles that are challenging to be prepared by traditional heterogeneous RAFT polymerizations.

Upgrading poly(styrene‐co‐divinylbenzene) beads: Incorporation of organomodified metal‐free semiconductor graphitic carbon nitride through suspension photopolymerization to generate photoactive resins

AbstractThe inclusion of the metal free semiconductor graphitic carbon nitride (g‐CN) into polymer systems brings a variety of new options, for instance as a heterogeneous photoredox polymer initiator. In this context, we present here the decoration of the inner surface of poly(styrene‐co‐divinylbenzene) beads with organomodified g‐CN via one pot suspension photopolymerization. The resulting beads are varied by changing reaction parameters, such as, crosslinking ratio, presence of porogens, and mechanical agitation. The photocatalytic activity of so‐formed beads was tested by aqueous rhodamine B dye photodegradation experiments. Additionally, dye adsorption/desorption properties were examined in aqueous as well as in organic solvents. Photoinduced surface modification with vinylsulfonic acid and 4‐vinyl pyridine is introduced. Overall, metal‐free semiconductor g‐CN donates photoactivity to polymer networks that can be employed for dye photodegradation and acid–base catalyst transformation through facile photoinduced surface modifications.