Chain Microstructure Research Articles

Estimation of ethylene/1-butene copolymerization conditions using the autoencoder model

Chain microstructures of ethylene/1-butene copolymers produced at specific polymerization conditions can be calculated using the copolymerization kinetic model. However, this kinetic model cannot be solved inversely to estimate polymerization conditions from desired microstructures. In this work, the autoencoder (AE) model, the machine learning techniques based on artificial neural network (ANN) concept, was developed to help estimate polymerization conditions to produce polymers with desired microstructures (e.g., molecular weight distribution (MWD), chemical composition distribution (CCD), and number and weight average molecular weight). Two models were developed in this work: one with only microstructural distributions (MWD and CCD) and the other with additional information on average microstructures and polymer yield. The results showed that the proposed AE models can adequately estimate polymerization conditions from desired microstructures with acceptable mean square error (MSE). More specific microstructures lead to better estimation of polymerization conditions with lower MSE.

Copolymerization of Ethylene with Selected Vinyl Monomers Catalyzed by Group 4 Metal and Vanadium Complexes with Multidentate Ligands: A Short Review.

This paper gives a short overview of homogeneous post-metallocene catalysts based on group 4 metal and vanadium complexes bearing multidentate ligands. It summarizes the catalytic behavior of those catalysts in copolymerization of ethylene with 1-olefins, with styrenic monomers and with α,ω-alkenols. The review is focused on finding correlations between the structure of a complex, its catalyst activity and comonomer incorporation ability, as well as the microstructure of the copolymer chains.

Crystallization behavior of impact copolymer polypropylene revealed by fast scanning chip calorimetry analysis

The crystallization behaviors of two impact copolymer polypropylenes (ICP) were investigated by using fast scanning chip calorimetry (FSC) and micro-focus wide-angle X-ray diffraction (WAXD) techniques. Different crystallization peaks of these two samples during cooling were observed at cooling rates from 50 to 4000 K/s. For ICP-A, the crystallization of polypropylene (PP) matrix into α crystallites, polyethylene (PE) sequences in ethylene-propylene segmented copolymer (EsP), PP segments in ethylene-propylene block copolymer (EbP), and PP matrix into mesophase successively occurred from high to low temperatures. As the cooling rate increased, the crystallization of PP matrix into α crystallites, PP segments, and mesophase were suppressed one by one. Nevertheless, the crystallization of PE segments was hardly suppressed. For ICP-B, it showed almost the same crystallization behavior as ICP-A, except for the absence of independent crystallization peak of PP segments. The different crystallization performance in these two samples could be ascribed to their different chain microstructures.

In-Depth Analysis of the Nonuniform Chain Microstructure of Multiblock Copolymers from Chain-Shuttling Polymerization

In-Depth Analysis of the Nonuniform Chain Microstructure of Multiblock Copolymers from Chain-Shuttling Polymerization

Polymerization-Induced Phase Separation in Rubber-Toughened Amine-Cured Epoxy Resins: Tuning Morphology from the Nano- to Macro-scale

Polymerization-induced phase separation enables fine control over thermoset network morphologies, yielding heterogeneous structures with domain sizes tunable over 1–100 nm. However, the controlled chain-growth polymerization techniques exclusively employed to regulate the morphology at these length scales are unsuitable for a majority of thermoset materials typically formed through step-growth mechanisms. By varying the composition of a binary curing agent mixture in a classic rubber-toughened epoxy thermoset, where the two curing agents are selected based on disparate compatibility with the rubber, we demonstrate facile tunability over morphology through a single compositional parameter. Indeed, this method yields morphologies spanning the nano-scale to the macro-scale, controlled by the relative reactivities and thermodynamic compatibility of the network components. We further demonstrate a profound connection between chain dynamics and microstructure in these materials, with the tunable morphology enabling exquisite variations in glass transition. In addition, previously unattainable control over tensile mechanical properties is realized, including atypical increase of elongation at failure while maintaining the modulus and ultimate strength.

Theoretical and experimental assessment of UV resistance of high‐density polyethylene: Screening and optimization of hindered amine light stabilizers

AbstractHindered amine light stabilizers (HALS) are widely used chemical stabilizers for preventing polymer degradation. In this study, the effects of type of HALS and its content in high‐density polyethylene (HDPE) over the stabilization process are investigated employing density functional theory (DFT) and experimental approach. The electrophilicity index of four types of commercial HALS are compared by DFT to select the most effective one. Besides, the HDPE sample containing a phenolic antioxidant and different contents of the selected HALS are experimentally exposed to UV irradiation. The effect of HALS content on the changes in chain microstructure and molecular weight of HDPE are evaluated using gel permeation chromatography and frequency sweep rheometry. In the absence of HALS, HDPE suffers degradation and the phenolic antioxidant causes chain scission. However, by adding HALS, the chain branching and crosslinking mechanisms are predominant. The results of FTIR, DSC, and tensile analyses follow similar trends, revealing that the best stabilization performance corresponds to adding 600 ppm HALS to HDPE.

Influence of the Polyacrylic Acid Binder Neutralization Degree on the Initial Electrochemical Behavior of a Silicon/Graphite Electrode.

The role of the physicochemical properties of the water-soluble polyacrylic acid (PAA) binder in the electrochemical performance of highly loaded silicon/graphite 50/50 wt % negative electrodes has been examined as a function of the neutralization degree x in PAAH1-xLix at the initial cycle in an electrolyte not containing ethylene carbonate. Electrode processing in the acidic PAAH binder at pH 2.5 leads to a deep copper corrosion, resulting in a significant electrode cohesion and adhesion to the current collector surface, but the strong binder rigidity may explain the big cracks occurring on the electrode surface at the first cycle. The nonuniform binder coating on the material surface leads to an important degradation of the electrolyte, explaining the lowest initial Coulombic efficiency and the lowest reversible capacity among the studied electrodes. When processed in neutral pH, the PAAH0.22Li0.78 binder forms a conformal artificial solid electrolyte interphase layer on the material surface, which minimizes the electrolyte reduction at the first cycle and then maximizes the initial Coulombic efficiency. However, the low mechanical resistance of the electrode and its strong cracking explain its low reversible capacity. Electrodes prepared at intermediate pH 4 combine the positive assets of electrodes prepared at acidic and neutral pH. They lead to the best initial performance with a notable areal capacity of 7.2 mA h cm-2 and the highest initial Coulombic efficiency of around 90%, a value much larger than the usual range reported for silicon/graphite anodes. All data obtained with complementary characterization techniques were discussed as a function of the PAA polymeric chain molecular conformation, microstructure, and surface adsorption or grafting, emphasizing the tremendous role of the binder in the electrode initial performance.

Microstructural insight on strain-induced crystallization of ethylene/propylene(/diene) random copolymers

The tensile properties and the structural transformations occurring by effect of deformation of un-vulcanized ethylene/propylene(/diene) elastomers with ethylene contents ranging from 57 to 83 mol% are analyzed and interpreted in terms of the chain microstructure. It is shown that the samples with ethylene contents larger than or equal to 73 mol% experience a slight but significant increase of crystallinity upon stretching and partial melting of the new oriented crystals formed by stretching after releasing the tension. The degree of crystallinity, the tensile properties, the incremental crystallinity achieved upon stretching and the residual crystallinity left upon release of the tension all show well-defined correlations with the average ethylene content and the ethylene sequence length distribution. The tensile properties and the strain hardening behavior are correlated with the incremental crystallinity achieved upon stretching at high strain.

Influence of the Polymer Microstructure over the Phase Separation of Thermo-Responsive Nanoparticles.

Thermo-responsive nanoparticles (NPs), i.e., colloids with a sharp and often reversible phase separation in response to thermal stimuli, are coming to the forefront due to their dynamic behavior, useful in applications ranging from biomedicine to advanced separations and smart optics. What is guiding the macroscopic behavior of these systems above their critical temperature is mainly the microstructure of the polymer chains of which these NPs are comprised. Therefore, a comprehensive understanding of the influence of the polymer properties over the thermal response is highly required to reproducibly target a specific behavior. In this study, we synthesized thermo-responsive NPs with different size, polymeric microstructure and hydrophilic-lipophilic balance (HLB) and investigated the role of these properties over their phase separation. We first synthesized four different thermo-responsive oligomers via Reversible Addition-Fragmentation Chain Transfer (RAFT) Polymerization of poly(ethylene glycol)methyl ether methacrylate. Then, exploiting the RAFT living character, we chain-extended these oligomers with butyl methacrylate obtaining a library of NPs. Finally, we investigated the NP thermo-responsive behavior, their physical state above the cloud point (Tcp) as well as their reversibility once the stimulus is removed. We concluded that the solid content plays a minor role compared to the relative length of the two blocks forming the polymer chains. In particular, the longer the stabilizer, the more favored the formation of a gel. At the same time, the reversibility is mainly achieved at high HLB, independently from the absolute lengths of the block copolymers.

Influence of isothermal crystallization temperature on the temperature rising elution fractionation for a poly(1-butene-co-ethylene) resin

Temperature Rising Elution Fractionation (TREF) is effective for separating polyolefin resins according to crystallizability. A relatively low isothermal crystallization temperature is necessary to fractionate poly(1-butene) (PB-1) resin because of its slow crystallization kinetics. This study aims to investigate the influence of isothermal crystallization temperature of TREF on the fractionation and chain microstructure of eluted fractions for one poly(1-butene-co-ethylene) with 5.8 mol% ethylene. The resin is fractionated using P-TREF under four different isothermal crystallization temperatures, i.e. 0 °C, −5 °C, −10 °C, and −30 °C, and then the fractions are characterized by high-temperature gel permeation chromatography (HT-GPC), 13C nuclear magnetic resonance spectroscopy (13C NMR), and differential scanning calorimetry (DSC) to acquire their chain microstructure information. The isothermal crystallization temperature significantly affects the nucleation and growth of the crystals, which consequently results in differences in the relative content of eluted fractions. With the decrease of isothermal crystallization temperature from 0 °C to −30 °C, the copolymer is fractionated more effectively since fractions are more evenly distributed among elution temperatures rather than concentrated at lower elution temperatures. Furthermore, the isothermal crystallization temperature influences the chain microstructure of fractions obtained at the same elution temperature, which are different in ethylene content, isotacticity, and average sequence length. The distribution of ethylene content and isotacticity becomes broader with the decrease in isothermal crystallization temperature. Lower isothermal crystallization temperature is conducive to effective separation of the fractions with weak crystallizability. These results are of great significance for the selection of fractionation conditions and chain microstructure analysis of poly(1-butene-co-ethylene) resins.

Enabling Oxygen-Sulfur Exchange Reaction to Produce Semicrystalline Copolymers from Carbon Disulfide and Ethylene Oxide.

This work describes the first example of semicrystalline poly(thiocarbonate)s from carbon disulfide (CS2 ) and ethylene oxide (EO), two mass producible low-cost monomers. Lewis acid/base pairs (LPs) exhibit high activity (EO conversion up to >99%, 8h) in catalyzing the copolymerization under low Lewis pair/monomer ratio of 1:1500. Oxygen-sulfur exchange reaction (O-S ER) during the copolymerization of CS2 and EO, the generation and mutual copolymerization with COS, CO2 , and episulfide, is harnessed to introduce crystallizable segments [SC(O)O and SC(S)S] in the copolymer. The type of Lewis base is found to have a great impact on the chain microstructure and the crystalline properties. The formed copolymers with melting point from 117.7 to 245.3°C are obtained. The maximum crystallinity is estimated to be 78% based on the powder wide-angle X-ray diffraction pattern. This work provides a general method to prepare semicrystalline sulfur-containing polymers.

Chain flexibility and glass transition temperatures of poly(n-alkyl (meth)acrylate)s: Implications of tacticity and chain dynamics

The relationship between chain microstructure and glass transition temperature (Tg) is complicated for poly(alkyl methacrylate)s and poly(alkyl acrylate)s. Despite intensive studies, relationships between the structures of these polymers and their properties, including solution characteristics and Tg, are still controversial. Solution properties, chain conformations, including Flory's characteristic ratio (C∞), persistence length (lp), and chain diameters, and Tg are reported for series of poly(n-alkyl acrylate)s and poly(n-alkyl methacrylate)s having alkyl side chain lengths (n) ranging from 1 to 10 carbons in length, with uniform and well-characterized tacticities. Chain flexibilities of both series of polymers decrease as n increases, reflecting increased hindrances to rotation about backbone bonds as side chains become longer. Conversely, the Tgs for both series of polymers decrease substantially as n increases, reflecting the greater side chain mobilities of long alkyl substituents. For shorter alkyl chain lengths, Tgs for the poly(n-alkyl acrylate)s are much lower than for the corresponding poly(n-alkyl methacrylate)s, a difference which has been attributed in the past to the presumed reduced chain flexibility of polymethacrylates due to the presence of the α-methyl substituent. However, contrary to such expectations, C∞ and lp values for these two series of polymers are nearly identical at a given n value, except for the longest n-alkyl substituents. Instead, the differences in Tg may be attributed to the differences in tacticity of the two series – almost ideally atactic for the poly(n-alkyl acrylate)s but high in syndiotacticity for the poly(n-alkyl methacrylate)s. The Tgs for the two series of polymers approach that of polyethylene at longer alkyl chain lengths. In addition, the effects of tacticity and chain dynamics on C∞, lp, and Tg of poly(methyl methacrylate) is discussed.

Synthesis of Amphiphilic Copolymers of Acrylic Acid and Styrene with the Desired Microstructure and Their Properties

The regularities of the controlled synthesis of amphiphilic copolymers of styrene and acrylic acid mediated by dithiobenzoate and trithiocarbonates as reversible addition fragmentation chain transfer agents in a 1,4-dioxane solution are considered. The influence of the general composition and chain microstructure on the dispersion stability and hydrodynamic sizes of polymer particles of copolymers containing from 40 to 90 mol % of acrylic acid units is studied. It is shown that in dilute aqueous media random copolymers are dispersed to individual compacted coils owing to the intrachain hydrophobic association of styrene units. The addition of two poly(acrylic acid) blocks to such a copolymer improves its dispersibility in water, and the attachment of two polystyrene blocks makes it insoluble in water because of the interchain association of polystyrene units. The synthesized copolymers possess surface activity, and when applied to a hydrophilic glass surface, they moderately hydrophobize it. In general, this synthetic approach opens up broad prospects for obtaining a wide range of new polymer macromolecules with different properties from one pair of traditional monomers.

Comparison of chain microstructure between two propylene−ethylene copolymer resins with bimodal melting temperature distribution

Polypropylene (PP) has been commonly used as packaging materials due to the favorable mechanical and optical properties related to its diverse and complex chain microstructure which can be better understood through effective fractionation. In this work, two commercial PP resins (A and B) with similar bimodal melting temperature distribution in the range of 100–160 °C but different ethylene content (9.1–12.3 mol%) are fractionated by preparative temperature rising elution fractionation (P-TREF) and relevant fractions are characterized by a variety of techniques such as high temperature-gel permeation chromatography (HT-GPC), differential scanning calorimetry (DSC), 13C nuclear magnetic resonance (NMR) spectroscopy, Fourier transform-infrared (FT-IR) spectroscopy, and wide-angle X-ray diffraction (WAXD). The chain microstructures of the two resins used as food packaging film exhibit heterogeneity and some differences, which are mainly caused by broad and different distribution of ethylene comonomers. Resin B contains more ethylene units than resin A, and the ethylene units are incorporated into the PP chains in the forms of individual unit or very short segments, resulting in large amount of fractions with relatively low isotacticity and crystallinity that eluted at the temperature range of 35–90 °C. These fractions account for 84.07 wt% of resin B, whereas 59.66 wt% of resin A. The propylene sequences of different isotacticity and crystallinity generated by the insertion of ethylene comonomers in resin B are mainly responsible for its biomodal melting behavior. However, ethylene comonomers tend to insert into the PP chains of resin A in the forms of long polyethylene (PE) blocks and generate propylene−ethylene block copolymers with high crystallizability which can be eluted at high temperatures of 120–140 °C. These fractions constitute 3.16 wt% of resin A, but barely exist in resin B. Moreover, 35.83 wt% of resin A were eluted at 110 °C, whereas only 13.22 wt% of resin B can be eluted at this temperature. These fractions with high isotacticity and molecular weight eluted at high temperatures contribute to the higher flexural modulus of resin A. Both long ethylene blocks and propylene sequences of different lengths contribute to the biomodal melting peaks on the thermogram of resin A.

Structure and Properties of Isotactic Polypropylene/Polybutene-1 In-reactor Alloys

The composition and structure of polymer largely determine the properties of its final products. As a novel polymer material, the composition, structure, and properties of the isotactic polypropylene/polybutene-1 in-reactor alloy (iPP/iPB alloy) synthesized by sequential two-stage polymerization with Ziegler-Natta catalyst were correlated for the first time in this work. The iPP/iPB alloy was fractionated by temperature rising elution fractionation (TREF) in a broad temperature ranged from −30 °C to 140 °C, and the chain microstructures and sequence distributions of isolated fractions were analyzed by DSC, GPC, 13C-NMR, and FTIR. The iPP/iPB alloy was composed of five components, namely high isotactic PB (iPB, 85.8 wt%), medium isotactic PB (mPB, 5.1 wt%), poly((butene-1)-block-propylene) copolymers (PB-b-PP, 4.1 wt%) which contained PB and PP blocks with different lengths according to the isolation temperature, isotactic PP (iPP, 2.7 wt%), and atactic PB (aPB, 2.3 wt%). Compared to other commercial pipe materials, the iPP/iPB alloy presented outstanding thermal creep resistance and gas permeability resistance, high strength and low deformation at high temperature, and appropriate flexural strength. The roles of PP and PB-b-PP components in the alloy were interpreted. This work is expected to elucidate the potential application of iPP/iPB alloy as pipe materials and provide solutions for the design and synthesis of high performance pipe materials.

Dynamic Monte Carlo Simulation for Chain‐Shuttling Polymerization of Olefin Block Copolymers in Continuous Stirred‐Tank Reactor

AbstractA dynamic Monte Carlo model coupling with residence time distribution is developed to simulate chain microstructures of olefin block copolymers (OBCs) produced with the chain‐shuttling polymerization in a continuous stirred‐tank reactor (CSTR). The simulated results provide information on how polymer chain microstructures (i.e., average molecular weight, average comonomer content, and microstructural distributions) evolve in a CSTR system and show a good agreement with previously reported theoretical and experimental results. The model is also used to investigate effect of reaction conditions (i.e., catalyst feed compositions, monomer feed compositions, and mean residence time) on time evolution of OBC chain microstructures.

The chain microstructure and condensed structure of polyethylene resin used for Biaxially stretched film

AbstractTo explore the desirable chain structure and condensed structure of polyethylene used for biaxial stretching, the blends of two polyethylenes (PE1 and PE2) with different molecular weight and branch distribution were investigated. Their condensed structure including relaxation and crystallization behavior was studied by rheology, dynamic mechanical analysis (DMA), and non‐isothermal crystallization kinetics. And the chain microstructure was characterized by preparative temperature rising elution fractionation (P‐TREF), and successive self‐nucleation and annealing (SSA). It was demonstrated that the structural variables were not changing monotonically with the increment of the PE1 content. The longest relaxation time, lowest and less varied crystallization rate always appeared when the blend contained 15 wt% of PE1. This excellent structure was owing to the formation of more branches on the short chains, resulting in the uniform distribution of lamellae size and thus showing the widest biaxial stretchable temperature range (i.e., 8°C).

Auditory ossicles in ScanningElectron Microscopy.

<b>Introduction: </b>Knowledge about the physiology of a healthy middle ear is essential for understanding the activity and mechanics of the ear as well as the basics of ossiculoplasty. Trauma of the epithelial lining of the tympanic cavity as well as the ossicular chain may be the result of chronic inflammation and surgery. Depending on the observed changes of the middle ear lining, there are several types of distinguished chronic inflammatory changes: simple, with cholesteatoma, with the formation of inflammatory granulation tissue, in course of specific diseases. <br><b>Purpose: </b>The aim of the article is presentation of the microstructure and vasculature of the ossicular chain in the Scanning Electron Microscope. Particular attention is drawn to the anatomical aspects of the structure and connections of auditory ossicles as vital elements for reconstruction of the conduction system of the middle ear. <br><b>Material and method: </b>The analysis covered auditory ossicles standardly removed in accordance with the methodology of the investigated surgical procedures. The preparations were evaluated in a scanning electron microscope. <br><b>Results: </b>The exposure of bone surface promotes deep erosion. The advanced process of destruction of bone surface in the case of chronic otitis media correlates with a significant degree of damage to both the lining covering the auditory ossicles and that surrounding articular surfaces. <br><b>Conclusions: </b>(1) The ossicles in the image of the Scanning Electron Microscope are covered with lining. It passes from the surface of the ossicles to the vascular bundles, forming vascular sheaths; (2) Damage to lining continuity on the surface of the auditory ossicles promotes the rapid destruction of bone tissue in the inflammatory process; (3) The dimensions of the individual ossicles are respectively: malleus - 8.36 +/- 0.01, incus - 8.14 +/- 0.0, stapes - 3.23 +/- 0.01 mm. Behavior of the anatomical length of ossicular chain during tympanoplasty appears to be essential to maintaining adequate vibration amplitude of the conductive system of the middle ear.

Plasticization- and aging-resistant membranes with venation-like architecture for efficient carbon capture

Plasticization and physical aging due to the undesirable deformation of chain microstructure under high pressure or long-term operation hamper the practical application of polymer membranes. Fixing the polymer chain architecture without sacrificing the internal free volume and thereby the membrane permeability remains a grand challenge. The venation architecture in plant leaf, featured by its stable vein structure with abundant interveinal spaces, offers us an inspiration for designing a highly permeable and stable chain architecture. Here, we construct a venation-like chain architecture in polyphenylene oxide (PPO) membrane by introducing numerous interchain crosslinking bridges using Friedel-Crafts-based hypercrosslinking reaction. These crosslinking bridges rigidify the chains and prevent them from dense packing, inhibiting the microstructural deformation, while simultaneously generating abundant free volume. The resulting membranes display ultrahigh CO2 permeability of 5130 Barrer (73-fold higher than pristine PPO membrane), along with superior structural stability. Particularly, the plasticization is fully suppressed under high pressure even up to 70 bar and the physical aging-induced loss of CO2 permeability is reduced remarkably down to as low as 19% after 360 days, transcending most of the state-of-the-art membranes. This venation-like chain architecture opens a new avenue to solving the current permeability-stability dilemma for the implementation of polymer membrane technology.

Amphiphilic Copolymers of Acrylic Acid and n-Butyl Acrylate with the Predetermined Microstructure: Synthesis and Properties

Features of the synthesis of n-butyl acrylate copolymers with acrylic acid in 1,4-dioxane by free radical reversible addition-fragmentation chain transfer (RAFT) polymerization mediated by symmetric trithiocarbonates are considered. It is shown that the living mechanism of polymerization is realized in the studied systems. The chemical nature of the RAFT agent dictates different chain microstructures (random block or random) of the copolymers. The effect of chain microstructure on the properties of the copolymers containing about 90 mol % of acrylic acid units is studied by differential scanning calorimetry, contact angle measurements, turbidimetry, potentiometric titration, and dynamic light scattering. It is demonstrated that all the copolymers in the solid phase have similar properties: a single glass transition temperature close to the glass transition temperature of polyacid and a good water wettability. In dilute aqueous solutions, the properties of the copolymers are different: at the inherent pH, random copolymer macromolecules form large associates, while random block copolymers are dispersed into individual coils or micelles. All the copolymers are weaker polyacids compared with PAA; the random block copolymers are characterized by the compaction of macromolecules at small degrees of ionization. Our studies provide evidence that reversible addition-fragmentation chain transfer polymerization is an efficient tool for the targeted insertion of nonpolar units into a polyelectrolyte chain and it can be used for the fine-tuning of its properties.