Macromolecular Segments Research Articles

Study of the Thermal Phase Transition of Poly(N,N-diethylacrylamide-co-N-ethylacrylamide) Random Copolymers in Aqueous Solution.

N-alkyl-substituted polyacrylamides exhibit a thermal coil-to-globule transition in aqueous solution driven by an increase in hydrophobic interactions with rising temperature. With the aim of understanding the role of N-alkyl substituents in the thermal transition, this study focuses on the molecular interactions underlying the phase transition of poly(N,N-diethylacrylamide-co-N-ethylacrylamide) random copolymers. Poly(N,N-diethylacrylamide) (PDEAm), poly(N-ethylacrylamide) (PNEAm), and their random copolymers were synthesized by free radical polymerization and their chemical structure characterized spectroscopically. It was found that the values of the cloud-point temperature increased with PNEAm content, and particle aggregation processes took place, increasing the negative charge density on their surface. The cloud-point temperature of each copolymer decreased with respect to the theoretical values calculated assuming an absence of interactions. It is attributed to the formation of intra- and interchain hydrogen bonding in aqueous solutions. These interactions favor the formation of more hydrophobic macromolecular segments, thereby promoting the cooperative nature of the transition. These results definitively reveal the dominant mechanism occurring during the phase transition in the aqueous solutions of these copolymers.

Določanje obstojnosti funkcionaliziranih tekstilij na osnovi kopolimerov akrilonitrila na toplotno in toplotno-oksidativno razgradnjo

Acrylonitrile is widely used to produce carbon fibres, household textiles, artificial fur, etc. The modification of polyacrylonitrile fibres in an alkaline medium is extended in the production of textile sorbents. The scientific direction of fibre modification through surface activation using hydrogen peroxide is of scientific interest. However, the thermal and thermophysical properties of the samples are not examined. Therefore, interest arises when analysing the effect of polyacrylonitrile textile material functionalization on the resistance of fibres to thermal oxidation and thermal degradation. The study of thermogravimetry and differential thermogravimetry thermooxide of polyacrylonitrile – modified fibres is carried out using thermogravimetric analysis to research the thermal oxidation and thermal degradation of modified polyacrylonitrile fibre samples. A change in the rate of thermal oxidative-degradation in the process of functionalization was identified in this research. A change in the loss of mass of the sample under different conditions of functionalization was also identified. The total glass transition of the polyacrylonitrile was achieved by heating the polymer to 130 °C. The intensification self-regulation of the structure of the polymeric material through the formation of the mesophase was released at the temperature of around 100 °C. During the heating of the initial polyacrylonitrile textile material to the temperature of 70‒80 °C, a weakening of intermolecular contacts was observed, which led to an increase in the mobility of macromolecular segments. The temperature of 78 °С was considered to be the initial glass transition temperature Tg,t1 and Tg,t2 – 121 °С as the final temperature for the original sample. However, if the temperature exceeded 130 °C, chemical changes in the polymer occurred, in particular, the process of cyclization. The analysis of the thermogravimetry data of thermally oxidized samples resulted in the retention of the complex stepwise nature of decomposition inherent in the initial fibrous material based on acrylonitrile copolymers. The conducted analysis showed the absence of significant changes in the reasonable conditions of chemical modification and practical operation of textile materials. The physical and mechanical properties of functionalized textile materials based on acrylonitrile copolymers were studied. As a result of surface functionalization, an insignificant strength reduction of functionalized textile materials occurred.

Electret Properties of PET /AlOx Films with Protective Coating Based on Acrylic Copolymers

This paper describes the study of corona electrets made of a polyethylene terephthalate (PET) laminate film with an aluminum oxide nanolayer with a protective coating based on acrylic copolymers. Those films showed rather high and stable electret properties. At this, dipole polarization prevailed at the acrylic layer due to the orientation of oxygen-containing groups of atoms and macromolecular segments under the corona discharge, while injected charge carriers were located predominantly in polyethylene terephthalate layer at interfaces of both PET-aluminum oxide and amorphous-crystalline regions of the polymer.

Scalable micropatterned epoxy vitrimer films by thermo-triggered bond exchange for repairable and recyclable triboelectric nanogenerators

Triboelectric nanogenerators are believed to be a promising solution to energy crisis by mechanical-to-electrical energy conversion through the contact electrification between constituent tribo-materials. However, most of the current tribo-materials are difficult to be repaired if damaged, and recycled for their reuse or disposal, limiting the development for reusable and sustainable energy-harvesting devices. Therefore, we explore the development of durable, repairable and recyclable triboelectric nanogenerators based on an epoxy-derived vitrimer (EV) with thermo-reversible cross-linked networks. Rather than polymerizing the EVs by adding thermoplastic components, they are generated by a solvent-free, quasi-thermoforming and scalable process. Thanks to the flowability of cross-linked networks realized by thermo-triggered hydroxyl/ester bond-exchange reactions, surface-micropatterned EV film based tribo-materials are successfully fabricated by a thermal micro-imprinting process, showing 3D shape-adaptive thermoforming ability. The EV films exhibit excellent flexibility and ductility with the smaller elastic hysteresis under external deformations, whose molecular origin is revealed to be the achievable macromolecular segment relaxation and energy dissipation of networks. The favorable mechanical robustness and recoverability endow the EV-based nanogenerators (EV-TENG) with significantly durable electricity-generating performances under repeated compressions (≥10,000 cycles) and larger mechanical loads. More importantly, by taking the triboelectric signal as a probe for network evolution, repairability and recyclability of EV-TENGs are further evaluated quantitively. Interestingly, the introduction of EVs makes the device self-repairable simply by heating treatment with a higher healing efficiency of 98%. Moreover, the device could be recycled by both physical and chemical approaches, without losing the original triboelectric performance and structural integrity. Our results demonstrate the potential applications of vitrimers derived from industrial raw materials in developing repairable, recyclable and scalable energy-harvesting electronics with prolonged lifetimes and environmental sustainability.

Twin-screw extrusion molding of a cellulose-based vitrimer containing a crosslinkable macromolecular plasticizer

Cellulose-based vitrimers were prepared using a crosslinkable macromolecular plasticizer and acetylated carboxymethyl cellulose via twin-screw extrusion. The cellulose-based material was toughened by the entanglement between the macromolecular plasticizer segments, and the exudation of the plasticizer was avoided by crosslinking. The prepared materials exhibited excellent hydrophobicity and shape memory properties. The plasticizer was evidently effective, and the reprocessing was completed at 130 °C within 15 min. The materials could be reprocessed at a lower temperature over a short period of time without any obvious degradation. After reprocessing three times, the material performance did not decrease significantly, thus showing good potential for regeneration and recycling.

Para fluoro-thiol clicked diblock-copolymer self-assembly: Towards a new paradigm for highly proton-conductive membranes

Sulfonated sPPFS-b-PBuA diblock and statistical copolymers based on 2,3,4,5,6-pentafluorostyrene PFS and butyl acrylate BuA were elaborated for Proton Exchange Membrane Water Electrolyser (PEMWE) purposes. The block copolymers (BCP) were synthetized by Nitroxide Mediated Polymerization NMP, a controlled radical polymerization technique that yields a well-defined molar mass and a low dispersity material. These diblock-copolymers have the ability to self-assemble due to the immiscibility of the two macromolecular segments PPFS and PBuA. Statistical copolymers of the similar chemical composition were synthetized by both controlled radical polymerization NMP in solution and by free radical polymerization FRP in emulsion as waterborne dispersed polymer with highest molar mass. The copolymers were sulfonated by a mild click-reaction, namely an organo-catalyzed nucleophilic substitution reaction with sodium 3-mercapto-1-propanesulfonate (SMPS) at low temperature. The morphology of the sulfonated diblock-copolymer BCP was studied by SAXS and AFM, revealing a nano-phase-segregated sulfonated membrane. The mechanical properties of the membranes were improved by ionic crosslinking with polybenzimidazole (PBI-OO). Finally, the conductive properties of the sulfonated BCPs and statistical copolymers were investigated as a function of parameters such as the morphology of the BCP, the molar mass, and the sulfonation degree of the materials.

Effect of mechanical properties on the self‐healing behavior of waterborne polyurethane coatings

AbstractThe effect of structural parameters such as hard segment content and cross‐linking degree on the mechanical properties of waterborne self‐healing polyurethane and the effect of tensile strength, self‐healing conditions (temperature, time) on the self‐healing properties were investigated. These results demonstrated that as the increasing of the content of hard segments/the cross‐linking agent, the tensile strength of the sample increased and the self‐healing performance exhibited a downward trend. When the tensile strength reached 40 MPa, it could hardly healed, even if prolonging the self‐healing time or increasing the self‐healing temperature. Mechanism study demonstrated that the self‐healing ability was attributed to the dynamic exchange of disulfide bonds and the thermal reversibility of hydrogen bonds in the system. Hydrogen bonding could provide the initial self‐healing force and promote the dynamic exchange reaction of disulfide bonds, while high hydrogen bonding is not conducive to the movement of macromolecular segments, causing a decrease in the self‐healing efficiency.

High-density polyethylene composite filled with red mud: effect of coupling agent on mechanical and thermal properties

ABSTRACT In this study, red mud (RM) was modified with titanate coupling agent (triisostearoyl isopropoxy titanate, KR-TTS), and then the modified RM was melted blending with high-density polyethylene (HDPE) to prepare HDPE-based composite. The action mechanism of KR-TTS on the properties of HDPE composites was analysed combining with the movement mode of polyethylene macromolecular chain segments. The entanglement and mechanical interlocking of long alkyl chains of titanate coupling agent and the polyethylene molecular chains occurs in modified RM/HDPE composite, reflected by fracture morphology within tension process. The stronger interface interaction results in a decrease of polyethylene molecular chain segments motion under external loading, externally expressed as higher tensile strength and tensile modulus as well as storage modulus. Meanwhile, KR-TTS imparts modified RM/HDPE composite with higher elongation at break of uniaxial tension and lower damping ratio. The impact strength presents an improvement from 5.62 kJ/m2 of RM/HDPE composite to 6.56 kJ/m2 of modified RM/HDPE composite due to stronger interface strength. And modified RM/HDPE composite appears higher thermal stability, attributed to better particles dispersion and higher interface adhesion. Differential scanning calorimetric analysis shows that with the addition of coupling agent, the melt enthalpy of modified RM/HDPE composite decreases, indicating a decrement in the crystallinity of polyethylene composites (from 70.2% of RM/HDPE to 63.1% of modified RM/HDPE), resulted from the retarded stacking speed of chain segments into the crystal lattice during crystal growth.

Synergistic Effect of Copper Sulfate and Tetramethylthiuram Monosulfide Induced Metal‐Coordination Cross‐Linking in Nitrile–Butadiene Rubber

AbstractThe cross‐linking microstructure formed by the metal‐coordination bonds provides excellent properties for rubber materials. Copper sulfate (CuSO4) and tetramethylthiuram monosulfide (TMTM) are successfully compounded with nitrile–butadiene rubber (NBR) to fabricate vulcanizates by the coordination cross‐linking. The curing characteristics, mobility of macromolecular segment, mechanical properties, morphology analysis, swelling properties, and dynamic features under cyclic compression of the vulcanizates are investigated systematically. The results indicate that the microstructure of 3D cross‐linking is held together by the metal‐coordination bonds between Cu2+ and CN. The torque during static vulcanization, tensile strength, and cross‐linking density of the obtained NBR/CuSO4/TMTM vulcanizates are better than that of NBR/CuSO4 vulcanizates, which is attributed to the synergistic effect between the radicals formed by the splitting of TMTM under thermal activation and the Cu2+; moreover, the highly reactive [Cu(SnCNMe2)]•2+ complexes are formed by the synergistic effect and promote the coordination stability of NBR and CuSO4 effectively. The excellent tensile properties of the prepared NBR/CuSO4/TMTM vulcanizates via synergistic effect made the metal‐coordination cross‐linking attractive in the field of industrial application.

Biodegradable PLA/PBSA Multinanolayer Nanocomposites: Effect of Nanoclays Incorporation in Multinanolayered Structure on Mechanical and Water Barrier Properties.

Biodegradable PLA/PBSA multinanolayer nanocomposites were obtained from semi-crystalline poly(butylene succinate-co-butylene adipate) (PBSA) nanolayers filled with nanoclays and confined against amorphous poly(lactic acid) (PLA) nanolayers in a continuous manner by applying an innovative coextrusion technology. The cloisite 30B (C30B) filler incorporation in nanolayers was considered to be an improvement of barrier properties of the multilayer films additional to the confinement effect resulting to forced assembly during the multilayer coextrusion process. 2049-layer films of ~300 µm thick were processed containing loaded PBSA nanolayers of ~200 nm, which presented certain homogeneity and were mostly continuous for the 80/20 wt% PLA/PBSA composition. The nanocomposite PBSA films (monolayer) were also processed for comparison. The presence of exfoliated and intercalated clay structure and some aggregates were observed within the PBSA nanolayers depending on the C30B content. A greater reduction of macromolecular chain segment mobility was measured due to combined effects of confinement effect and clays constraints. The absence of both polymer and clays interdiffusions was highlighted since the PLA glass transition was unchanged. Besides, a larger increase in local chain rigidification was evidenced through RAF values due to geometrical constraints initiated by close nanoclay contact without changing the crystallinity of PBSA. Tortuosity effects into the filled PBSA layers adding to confinement effects induced by PLA layers have caused a significant improvement of water barrier properties through a reduction of water permeability, water vapor solubility and water vapor diffusivity. The obtaining barrier properties were successfully correlated to microstructure, thermal properties and mobility of PBSA amorphous phase.

Synthesis and properties of a stimulus-responsive block polymer.

In this study, the synthesis of small molecules and use of an improved “one-pot” method to synthesize the reversible addition–fragmentation chain transfer polymerization (RAFT) reagents have been reported. By comparing with the RAFT reagents synthesized by the traditional “step-by-step” method, it was observed that the reagents synthesized by the two methods had the same structure, however, the improved “one-pot” preparation method results in a significantly higher yield. Subsequently, two different macromolecular CTA segments (PVP-CTA-PVP and PDMAEMA-CTA-PDMAEMA) were prepared by RAFT polymerization, followed by the synthesis of the block polymer PDMAEMA-b-PVP-CTA-PVP-b-PDMAEMA. Through FITR, NMR, GPC and DLS analysis of the block polymer, it was observed that the isotacticity gradually became dominant as the degree of polymerization increased. Further, using NMR spectroscopy to study the effect of pH on the block polymer, the ionization degree of the synthesized polymer in the tumor tissue environment was observed to range between 86.32% to 99.50%, which proved that the synthesized polymers exhibit significant prospects in the medical application.

Influence of graphite particles in thermal properties of amylopectin/PVA-based hydrogels

The aim of the present work is to study the influence of graphite particles on the molecular structure of the hydrogel composed of amylopectin/poly(vinyl alcohol) hybrid matrix by thermogravimetric analysis, differential scanning calorimetry and dynamic mechanical thermal analysis techniques. Hybrid amylopectin/PVA hydrogels were prepared with and without particles, and their properties were measured. The results of the analyses showed that the presence of particles in the reaction medium decreased the formation of cross-links among macromolecular chain segments, modifying thermal and mechanical properties of hydrogel. Raman spectroscopy confirmed the obtaining of graphitic carbon particles. Besides, optical microscopy and atomic force microscopy showed a large distribution in particles dimensions.

X-Ray Structure and PMR Spectra of Polycaproamide Modified by a Polyfluorinated Alcohol

Effects on polycaproamide structure of a polyfluorinated alcohol immobilized on montmorillonite clay nanoparticles were studied using x-ray structure analysis and broad-line PMR spectroscopy. An exfoliated composite formed and caused the crystal and molecular structures of this heterochain polymer to reorganize. A composite based on the polyfluorinated alcohol changed the mobility of macromolecular chain segments and increased the fraction of planar trans-conformations.

Catalysis mechanism of Pd(II)@PVA membrane catalyst studied from the aspect of molecular level micro-defects by positron annihilation spectroscopy

In this study, an insightful understanding of the correlations of the molecular level micro-defects structure and catalytic performance of palladium species supported on polyvinyl alcohol (Pd(II)@PVA) membrane heterogeneous catalyst have been studied with positronium probe and other structural characterization methods. The micro-defects size both in crystalline region (Dc) and amorphous region (Da) of PVA matrix increases gradually with the Pd species loading and membrane catalyst recycle times. As a result of a synergism of micro-defects enlargement caused by solvents swelling and highly thermal motions of macromolecular segments at high temperature, a number of instantaneously connected micro-defects channel rather than a single micro-defect in the real reaction state might provide enough open spaces for the coupling reactions. This catalysis mechanism from the aspect of molecular level micro-defects structure is powerfully supported by comparing the catalytic performances of a common Pd(II)@PVA membrane catalyst and a PVA layer sealed Pd(II)@PVA membrane catalyst applied in Heck reactions. As the recycle times increases, the compactness and regularity of PVA molecular chain segments stacking decreases obviously, which promotes the Pd leaching and causes gradually decrease in catalytic efficiency of the recycled Pd(II)@PVA membrane catalyst. The mechanical properties, morphology, crystalline behavior, and swelling properties of the Pd(II)@PVA membrane catalysts are also characterized and explained in view of the changes of molecular level micro-defects structure.

A topical review on hybrid quasi-ceramic coatings for corrosion protection

AbstractA set of unique properties can be derived by a proper combination of organic and inorganic segments in a coating composition. The synthesis of such hybrid coatings is a challenging task due to that a number of variable parameters need to be optimized to achieve the desired results. Similar to the copolymerization of macromolecular segments in a common solvent, sol–gel chemistry could provide a viable alternate for the development of single-phase coating composition. The coating derived through sol–gel and wet chemistry displays homogenous physical and chemical characteristics. A large variety of chemical moieties containing labile functional groups are available for the development of new coating compositions. This article briefly reviews such studies that are reported in majority of the academic sector.

Synthesis and characteristics of pectiniform polyurethane‐modified polycarboxylate at room temperature

ABSTRACTIn this article, modified polyurethane prepolymer was synthesized by segmental synthesis method using isophorone diisocyanate, hydroxyl‐terminated silicone, polyether glycol dimethylolpropionic acid as raw materials. After that, pectiniform polycarboxylate, of which side chains were in roughly the same polymerization degree and main chains were in different lengths, was synthesized at room temperature in initiation system of hydrogen peroxide, ascorbic acid, and persulfate. Moreover, influence of various factors on the synthesis of polyurethane‐modified polycarboxylate at room temperature was discussed in detail and optimal synthesis process was determined. Results showed that redox initiation system, increasing initiator and monomer concentration, and extending reaction time needed to be adopted to complete the reaction. However, when the reaction time was over 4 h, water reducing of polycarboxylate declined rapidly. In addition, it could be found in Fourier transform infrared spectrum analysis that the CC double bonds in acrylic acid were opened and polymerized, macromolecular chain segments were successfully connected to polyoxyethylene chain segment, and resulting polycarboxylic acid molecule contained hydroxy, carboxyl, methyl, ester group, and other groups. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018, 135, 45873.

Synthesis of acrylate-based UV/thermal dual-cure coatings for antifogging

A dual-cure hydrophilic acrylate polymer was synthesized via radical polymerization with acrylic acid (AA), isophorone diisocyanate (IPDI), 2-acrylamide-2-methylpropane sulfonic acid (AMPS), hydroxyethyl acrylate (HEA), and 3-(trimethoxysilyl)propyl-2-methyl-2-methacrylate (MPS) as monomers, then used as prepolymer for antifog coating with tetraethylorthosilicate (TEOS) as a novel crosslinker. The prepolymer was mixed with crosslinking agent and photoinitiator to form coating formulas. The coating was characterized by nuclear magnetic resonance (NMR), Fourier-transform infrared (FTIR) spectroscopy, and contact angle measurements. The results indicated that the dosage of AMPS and TEOS had great influence on the antifog performance. With an increasing TEOS amount, the hardness, adhesion, water resistance, impact resistance, and thermal stability of the films were improved, at the expense of transparency; with increasing dosage of AMPS, the hydrophilicity of the film increased at the expense of water resistance. Optimum coating properties could be obtained when the amount of AMPS was 7% and that of TEOS was 5.5%. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) results showed that some SiO2 microspheres were formed and microphase separation occurred between the macromolecular segments, yielding the excellent coating properties.

Non-Isothermal Crystallization Behaviour and Kinetics of LLDPE/REDMUD Blends

The non-isothermal crystallization behaviour of pure LLDPE and LLDPE/REDMUD blends was investigated by differential scanning calorimetry (DSC), and the crystallization kinetics was analyzed by three methods, namely the Jeziorny, the Mo and the Ozawa. The results show that an optimal content of REDMUD (lower than10 wt.%) can enhance the kinetic crystallizability of the system because of heterogeneous nucleation, but excessive REDMUD, by physical hindrance, would impair the kinetic crystallizability. In non-isothermal crystallization kinetics, the Ozawa model did not fit well with the crystallization behaviour of these systems, while the Jeziorny and Mo models were found to be applicable. Furthermore, the activation energy ΔE calculated by the Kissinger method for the transport of macromolecular segments to the growing surface of crystal nucleus indicates that REDMUD could significantly reduce the crystallization migration activation energy of these blends.

Remarkable shape memory effect of a natural biopolymer in aqueous environment

Remarkable water-stimulated shape memory effect was revealed in a natural biopolymer of peacock's tail covert feathers of which the innate shape can almost be fully recovered after severe deformation by a short hydration step. The shape memory effect manifests a good stability of high recovery rate and ratio during cycles of deformation and subsequent recovery. Both strength and energy absorption efficiency of medullary foam can be recovered despite the apparent decrease in the first deformation stroke caused by structural damage. A kinetic model developed from non-equilibrium thermodynamic fluctuation theory was adopted to describe the shape recovery process by considering the viscoelastic relaxation. The effects of hydration on mechanical properties, recovery kinetics, activation process and dynamic mechanical behaviors were also evaluated. Mechanisms were explored based on the lubrication, swelling effect and structural changes of macromolecular chains or segments in terms of their mobility. This study is expected to aid in understanding the responses of natural biological materials to environmental stimuli and to provide useful information for synthetic shape memory materials from the bio-inspiration perspective.

Optical activity of solutions and films of chitosan acetate

The optical activity of solutions, oligomers, and films of chitosan acetate in a molecular weight (М) range of 660—640 000 g mol–1 was studied by the optical rotation dispersion method. Monotonic dispersion curves lying in the range of negative values of specific optical rotation [α] are observed for all samples in a wavelength range of 300—700 nm. The absolute value of [α] decreases as the degree of polymerization decreases for solutions of chitosan acetate. Three regions are observed on the dependence [α] = f(logМ): constant [α] values for solutions of highmolecular-weight chitosan samples, their relatively weak change for low-molecular-weight samples, and a sharp change for oligomers. The transition to the low-molecular-weight analog of the monomeric chitosan unit, d-glucosamine, is characterized by the inversion of the rotation sign as high positive values of [α] are attained. The nontrivial for high-molecular-weight compounds dependence [α] = f(logМ) was established for chitosan acetate films: the module of [α] of the films increases with a decrease in the degree of polymerization. It is shown that the module of optical activity of the studied samples is determined by the mobility of structural units of oligomer, polymer, or film. It is found by X-ray diffractometry that differences in optical activity of the solutions and films are due to restriction of the mobility of macromolecular segments during the formation of high-molecular-weight chitosan films and incomplete relaxation processes of film systems to the state of energetically favorable conformations.