Linear Polyamides Research Articles

Quantitative analyzing the effect of pore distribution on formation of active layer for forward osmosis membrane

The morphology and performance of polyamide active layer can be controlled by the pore size and surface porosity of support layer. Nevertheless, further investigation is required to elucidate the impact of pore distribution and the specific role of each pore. Therefore, by introducing polyetherimide (PEI) as a sacrificial top layer, the support layer with a wide pore distribution was prepared by co-casting method. A mathematical model was developed to enable the estimation of the impact of each pore radius and pore distribution on the structure and performance of the active layer. During interfacial polymerization process, the surface pore size and distribution of the support layer influenced the incipient film which consists of the polyamide colloids and dominates the successive growth of polyamide layer. It was suggested that both average pore radius and pore distribution contributed to the composite of incipient film. The overall η of 1.77 for S75 corresponded to an incipient film composed of linear polyamide terminated with MPD and fully cross-linked polyamide, resulting in the best performing membrane (C75) with DC of 0.75 and structural parameter as low as 230 μm. A comparison of C75 with C0 revealed an increase in water flux of 138 % and a minor increase in salt flux of 6.37 %. This work presents a novel approach to enhancing the performance of FO membranes and offers a new perspective on the structure-effect relationship.

Nylons with Applications in Energy Generators, 3D Printing and Biomedicine.

Linear polyamides, known as nylons, are a class of synthetic polymers with a wide range of applications due to their outstanding properties, such as chemical and thermal resistance or mechanical strength. These polymers have been used in various fields: from common and domestic applications, such as socks and fishing nets, to industrial gears or water purification membranes. By their durability, flexibility and wear resistance, nylons are now being used in addictive manufacturing technology as a good material choice to produce sophisticated devices with precise and complex geometric shapes. Furthermore, the emergence of triboelectric nanogenerators and the development of biomaterials have highlighted the versatility and utility of these materials. Due to their ability to enhance triboelectric performance and the range of applications, nylons show a potential use as tribo-positive materials. Because of the easy control of their shape, they can be subsequently integrated into nanogenerators. The use of nylons has also extended into the field of biomaterials, where their biocompatibility, mechanical strength and versatility have paved the way for groundbreaking advances in medical devices as dental implants, catheters and non-absorbable surgical sutures. By means of 3D bioprinting, nylons have been used to develop scaffolds, joint implants and drug carriers with tailored properties for various biomedical applications. The present paper aims to collect evidence of these recently specific applications of nylons by reviewing the literature produced in recent decades, with a special focus on the newer technologies in the field of energy harvesting and biomedicine.

Thermodynamic characteristics of the aliphatic polyamide crystal structures: Enhancement of nylon 66α, 610α and 77γ polymers

Despite the polymer industry's reliance on nylon polymers, numerous questions remain about their crystal structures, modeling, and other features. This work discusses the thermodynamic properties and molecular modeling of a polyamides nylon 66α, 610α, and 77γ crystal structure systems for use in various electronics and Nano-devices that feature distinct properties such as exceptional optoelectronic properties at a low cost compared to other structures. This study looked at the crystal structure of a linear polyamide chain made up of repeating units. The influence of the thermal expansion coefficient and thermodynamic parameters on crystal structures' characteristics at different temperatures has previously been explored. The findings of this study demonstrate, on the one hand, the influence of the amorphous phase on the final thermodynamic characteristics of semi-crystalline polymers and, on the other hand, pave the way for greater improvement in the durability of these polymers by increasing their crystalline features. The values of the thermodynamic parameters for nylon 66α, 610α and 77γ such as enthalpy (ΔHExp.) were 35.08, 40.25, and 1.44 kJ/mol, entropy (ΔSExp.) 113.75, 128.84, and 15.10 J/mol-K, free energy (ΔGExp.) was −44.57, −46.62, and −6.86 kJ/mol, respectively. When the nylon data is compared, the nylon 610α exhibits a significantly higher free energy, at high temperatures, the process is spontaneous and exergonic, making it a potentially viable material for use as fibers and engineering thermoplastics.

Chemical Characterization of Leachables in Catheter Device.

Extractables or leachables of biomaterials or residues of additives used in the manufacturing process that are potentially released from a medical device may have an adverse effect on a patient. Chemical characterization of leachable chemicals and degradation products in a medical device is an important aspect of its overall biocompatibility assessment process, which helps to ensure that the therapeutical benefits exceed the potential biological risks associated with the use of the device or its components or materials. By evaluating the types and amounts of chemicals that may migrate from a device to a patient during clinical use, potential toxicological risks can be assessed. A semipolar solvent, 40% ethanol in water (v/v), an appropriate surrogate for blood and blood related substances, was used as an extraction medium to mimic the body fluid in contact with a medical device. The extraction was conducted at 37 °C for 24 h for limited exposure medical devices per ISO 10993-12:2021. From gas chromatography-mass spectrometry (GC-MS) and liquid chromatography-mass spectrometry (LC-MS) analysis, leachable chemicals of polylactams, linear polyamides, cyclic polytetramethylene ether (PTME), poly(tetramethylene ether) glycol (PTMEG), cyclic and linear poly(tetramethylene ether) glycol adipate (PTMEGA), cyclic and linear poly(tetramethylene ether) glycol adipamide (PTMEGAA) were structurally elucidated. The workflow presented in this study was proven to be a successful approach for rapid extractable and leachable profiling and identification with confidence.

The Potential for the Direct and Alternating Current-Driven Electrospinning of Polyamides.

The paper provides a description of the potential for the direct current- and alternating current-driven electrospinning of various linear aliphatic polyamides (PA). Sets with increasing concentrations of selected PAs were dissolved in a mixture of formic acid and dichloromethane at a weight ratio of 1:1 and spun using a bar electrode applying direct and alternating high voltage. The solubility and spinnability of the polyamides were investigated and scanning electron microscopy (SEM) images were acquired of the resulting nanofiber layers. The various defects of the spun fibers and their diameters were detected and subsequently measured. Moreover, the dynamic viscosity and conductivity were also subjected to detailed investigation. The most suitable concentrations for each of the PAs were determined according to previous findings, and the solutions were spun using a NanospiderTM device at the larger scale. The fiber diameters of these samples were also measured. Finally, the surface energy of the fiber layers produced by the NanospiderTM device was measured aimed at selecting a suitable PA for a particular application.

Thermal, morphological and mechanical properties of glass fiber reinforced star‐branched polyamide 6

AbstractUsing star‐branched polyamide 6 (SPA6) with hexafunctional cyclotriphosphazene core as a matrix resin and glass fiber (GF) as a reinforcing material, star‐branched polyamide 6/glass fiber (SPA6/GF) composites with different GF content were prepared by melt‐compounding method. The star‐branched structure of SPA6 and GF content have great effects on the properties of SPA6/GF composites. Compared with linear polyamide 6 (LPA6), SPA6 with star‐branched structure has low viscosity, high melt flowability and good impregnation and adhesion to GF, which endow SPA6/GF composites outstanding processability, good surface qualities and excellent mechanical properties even when the content of GF reaches 60 wt%. The use of SPA6 resin with star‐branched structure fundamentally solves the industry problem of traditional LPA6 resin in high‐filled modification. Such high‐performance SPA6/GF composites will provide great promise for large‐scale applications.

Properties and solvatochromic change of crosslinked polyamide complexes synthesized through Michael addition and coordination

A new and simple method is established to prepare crosslinked polyamide complexes (cPACs) through Michael addition and coordination. A linear polyamide with terminal acrylamide groups (t-AA-PA) was prepared by a Michael addition of N,N′-methylenebisacrylamide and piperazine. Crosslinking reaction of the t-AA-prePA was conducted with different aliphatic diamines, and three crosslinked polyamides containing piperazine rings (P-cPAs) were synthesized. Differential scanning calorimetry and wide angle X-ray diffraction verified the crystallization feature of P-cPAs. They possessed Tg around 78 °C, Tm around 203 °C, and tensile strength up to 24 MPa. After P-cPAs were coordinated with Co2+ ions and dried fully, cPACs with removed chelating water (r-cPACs) were prepared. Chelating P-cPAs with Co2+accompanied a color change, the increase in Tg, and the loss of crystallization ability. When r-cPAC-Co2+s were immerged in water or methanol, an evident solvatochromic change was observed, and a reversible color change occurred after heated above 80 °C.

Synthesis of triptycene-based linear polyamide membrane for molecular sieving of N2 from the VOC mixture

In this study, triptycene-based carboxylic acid (triptycene-2,3,6,7-tetracarboxylic acid) was synthesized for polycondensation with two amino compounds to ultimately form linear polyamides with different backbone structures. Characterizations, including nuclear magnetic resonance (NMR) spectroscopy, X-ray photoelectron spectroscopy (XPS), and Fourier transform infrared (FTIR) spectroscopy, were performed to confirm the polycondensation, and the structural properties were determined. Solubility of the synthesized polyamides was also measured. Subsequently, these polyamides were fabricated into membranes to investigate the separation of N2 over the VOCs, and their stability and separation performance under different operating conditions were determined. Good separation performance, such as a rejection rate above 95%, was obtained during the studied separation range for the N2/VOC mixture, indicating that a linear polymer can also be used for the separation of a condensable gas/vapor mixture and only the rotation of polymer chains can be restricted to a certain extent by the side groups.

Controlling water dynamics for kinetic inhibition of clathrate hydrate

Subsea natural gas drilling and gas transport is challenged by the catastrophic formation of gas clathrate hydrate in production lines. Polymer inhibitors are vital to mitigate this technical problem in subsea gas drilling operation. However, physico- chemical factors affecting their performance are not yet completely known. Herein, we report that the activities of synthetic kinetic inhibitors of clathrate hydrates are correlated to the surrounding water dynamics. Two types of linear polyamide inhibitors are found to be capable of producing immobilized nonfreezable water molecules with fast transverse relaxation in sub-millisecond to millisecond time-scale as revealed by NMR relaxometry. Such a unique state of water can be construed as a form of nonfreezable bound water measured by differential scanning calorimetry. The quantity of such water species can be tuned by the size of the hydrophobic groups introduced to the polyamides and result in longer inhibition time before the rapid growth of the hydrate crystals. Addition of a single hydroxyl side group in the polymer structural unit can also affect the dependence of the kinetic inhibition time on the amount of the supercooled water. Both the hydrophobic and hydrophilic groups in the polymer inhibitors exert coordinated influence on the dynamic properties of the bound water, which are responsible for the early recognition and inhibition of the clathrate hydrate clusters.

Construction of dendritic structure by nano-SiO2 derivate grafted with hyperbranched polyamide in aramid fiber to simultaneously improve its mechanical and compressive properties

Weak transverse interaction of aramid fiber leads to low compressive strength, which is a prominent problem for its further application. In this study, a novel strategy by constructing dendritic structure in aramid fiber was conducted to solve the problem. Hyperbranched aromatic polyamide and linear aromatic polyamide are grafted on nano-SiO2 respectively, which will present absolutely different conformations. Structure of the SiO2 derivates was analyzed in detail by Fourier transform infrared spectroscopy (FTIR), dynamic laser scattering (DLS) and X-ray photoelectron spectroscopy (XPS). Compared with linear polyamide, hyperbranched polyamide tends to grow in multiple directions during polymerization due to significant steric effect, which can be confirmed by molecular simulation. When the SiO2 derivates were blended in aramid fiber, three-dimensional dendritic structure will be constructed by utilizing distinctive conformation of the hyperbranched polyamide. When loading content of nano-SiO2 derivate modified by hyperbranched polyamide in aramid fiber is 0.5 wt%, compressive strength of the fiber is improved by nearly 114%. Moreover, tensile strength and modulus are improved by nearly 13% and 9% respectively. Therefore, comprehensive performance of the aramid fiber can be remarkably improved by utilizing unique conformation of the hyperbranched polyamide, even if loading content of the SiO2 derivate is relatively low.

Synthesis and Gas-Permeation Characterization of a Novel High-Surface Area Polyamide Derived from 1,3,6,8-Tetramethyl-2,7-diaminotriptycene: Towards Polyamides of Intrinsic Microporosity (PIM-PAs).

A triptycene-based diamine, 1,3,6,8-tetramethyl-2,7-diamino-triptycene (TMDAT), was used for the synthesis of a novel solution-processable polyamide obtained via polycondensation reaction with 4,4′-(hexafluoroisopropylidene)bis(benzoic acid) (6FBBA). Molecular simulations confirmed that the tetrasubstitution with ortho-methyl groups in the triptycene building block reduced rotations around the C–N bond of the amide group leading to enhanced fractional free volume. Based on N2 sorption at 77 K, 6FBBA-TMDAT revealed microporosity with a Brunauer–Emmett–Teller (BET) surface area of 396 m2 g−1; to date, this is the highest value reported for a linear polyamide. The aged 6FBBA-TMDAT sample showed moderate pure-gas permeabilities (e.g., 198 barrer for H2, ~109 for CO2, and ~25 for O2) and permselectivities (e.g., αH2/CH4 of ~50) that position this polyamide close to the 2008 H2/CH4 and H2/N2 upper bounds. CO2–CH4 mixed-gas permeability experiments at 35 °C demonstrated poor plasticization resistance; mixed-gas permselectivity negatively deviated from the pure-gas values likely, due to the enhancement of CH4 diffusion induced by mixing effects.

Renewable polyamides via thiol-ene ‘click’ chemistry and long-chain aliphatic segments

Thiol-ene ‘click’ chemistry was utilised to prepare dicarboxylic acid monomers containing two sulphur units within the backbone, which subsequently underwent polycondensation to yield a series of renewable, long-chain, fatty-acid derived linear polyamides. The linear sulphur-containing polyamides displayed number-average molecular weights of 8000–55,000 g·mol−1 and broad polydispersities biased towards higher weight fractions. Glass transition values were slightly above room temperature (31–35 °C), while melting temperatures ranged from 121 to 170 °C. This novel class of polymers exhibited an impressive property profile, most notably exceptional impact resistance, tear strength, high elasticity, very low water absorption yet high oxygen- and water vapour permeability. The presence of sulphur and the increased aliphatic segment length influenced a wide spectrum of polyamide properties due to the reduced amide linkage (and inter-chain hydrogen bonding) density and less-effective chain packing ability due to the increased atomic radii of the sulphur atoms. The data highlights the technical advantages of these polymers, while also expanding the repertoire and structure-property relationships of both long-chain- and sulphur-containing polyamides, and encouraging further development of polyamide derivatives from renewable sources.

Novel Facial Conducting Polyamide-Based Dithiophenylidene Cyclyhexanone Moiety Utilized for Selective Cu2+ Sensing

ABSTRACTThe present work is aimed to synthesize a novel series of linear polyamides (PAs) 4a–d based on di(thiazolyl-thiophenylidene)cyclyhexanone as well as carries aliphatic and aromatic species in the polymer main backbones. The polymerization process was occurred by solution polycondensation technique by the interaction of the newly synthesized monomer 3 with adepoyl, sebacoyl, terphthaloyl, and isophthaloyldiacid chlorides. Before polymerization, the structure of monomer 3 was confirmed by elemental and spectral analyses. The structures of polymers were also investigated by elemental, spectral analysis, thermal analysis, and Field-Emission Scanning Electron Microscopy (FE-SEM) micrographs. Film draw temperatures for all the polymers were evaluated in the range 509.0–542.3°C. Here, the heavy metallic sensors are developed with the polyamide-fabricated glassy carbon electrode (GCE) by reliable current vs. voltage technique. A thin layer of PA onto GCE was fabricated with conducting coating agents (5% nafion) to fabricate a selective heavy metal ions, Cu2+ sensor in short response time in phosphate buffer phase. The fabricated sensor was also exhibited higher sensitivity, lower detection limit, large dynamic concentration ranges, long-term stability, and improved electrochemical performances toward Cu2+ sensor. The calibration plot is linear (r2: 0.9956) over the large Cu2+ ion concentration ranges (1.0 nM to 10.0 mM). The sensitivity and detection limit is 3.4177 µA cm−2 µM−1 and 0.36 nM (signal-to-noise ratio of 3) respectively. This novel effort is initiated a well-organized way of efficient cationic sensor improvement with conductive polymers for heavy metallic pollutants in environmental and health-care fields in large scales.

What makes aromatic polyamide membranes superior: New insights into ion transport and membrane structure

Polyamide composites are instrumental to modern desalination technology; however, reasons for the superior performance of polyamide membranes have been unclear. Models usually view membranes as an array of charged nanopores, however, observed discrepancies and inconsistencies call for more insights. Here ion conductance in polyamide membranes was analyzed using electrochemical impedance spectroscopy, focusing on the effects of salt type, concentration, and pH, which are compared with the conductance obtained for a dense linear polyamide Nomex® of similar superficial thickness. The results rule out the common view of polyamide membranes as homogeneous layers or nanopore arrays and indicate that they essentially behave as thin films of Nomex. The salt exclusion in both materials is so strong that uptake of protons (rather than sodium) dominates membrane conductivity, yielding a similar concentration-dependence. However, the conductivity of polyamide membranes is much higher and equivalent to sub-10nm Nomex films. These findings are explained by the sponge-like structure of polyamide, containing voids separated by thin polymer films, which can be adequately modeled as a 3D random resistor network. This unique structure, combining very dense (hence highly selective) and extremely thin (hence reasonably permeable) films supported within a ~100nm porous layer is what enables exceptional performance of polyamide membranes.

PH and reduction sensitive bio-based polyamides derived from renewable dicarboxylic acid monomers and cystine amino acid

ABSTRACTNew reduction biodegradable and pH-sensitive linear nonpeptidic polyamides were synthesized by interfacial polycondensation of diamines and cystine amino acid with dicarbonyl dichlorides derived from renewable dicarboxylic acids. The polymer degradability by glutathione is enhanced by the introduction of disulfide linkages, and the response to pH change is enhanced by introducing pendant carboxylic acid functions. The results of pH sensitivity tests indicated that protonation–deprotonation of the carboxylic acid group at about pH of 4.1 with cation exchange capacity 4.5 meq g−1 and the disulfide bonds in polyamides were effectively cleaved.

Chemical Sensors Based on New Polyamides Biobased on (Z) Octadec‐9‐Enedioic Acid and β‐Cyclodextrin

The synthesis of new biobased polyamides from different β‐cyclodextrin monomers and the (Z) octadec‐9‐enedioic acid is investigated. The aim of this study is to design different sensors, having different sensibilities and selectivities to a set of various volatile organic compounds (VOC) relevant in the early detection of lung cancer. The sensors are obtained from the synthesized polyamides, using multiwalled carbon nanotubes as conductive nanofillers and a layer by layer process. The conductive polymer nanocomposites (CPC) designed from the heptakis‐6‐amino β‐cyclodextrin and 6A,6D diamino β‐cyclodextrin have a high affinity for polar protic solvents, while the CPC having a matrix based on 6A,6D diamino 2A‐G,3A‐G,6B,6C,6E,6F,6G nonadeca‐O‐benzyl‐β‐cyclodextrin develops hydrophobic interactions with nonpolar solvents. Due to a higher accessibility of cyclodextrin, the chemoresistive response of the hydrophilic linear polyamide CPC is larger than one of the hydrophilic branched polyamide CPC. As required, the VOC diffusion/desorption phenomenon is reversible for all the sensors. image

A family of cationic polyamides for in vitro and in vivo gene transfection

The purpose of this study is to develop biodegradable cationic polyamides for non-viral gene delivery and elucidate their structural effects on gene transfection activity. To this end, a group of novel cationic polyamides were synthesized by polycondensation reaction between different di-p-nitrophenyl esters and tertiary amine-containing primary diamines. These linear polyamides have flexible alkylene group (ethylene or propylene), protonable amino group and bioreducible disulfide linkage in the polyamide main chain. The alkylene group and disulfide linkage in these polyamides have a distinct effect on their gene delivery properties including buffering capacity, gene binding ability and intracellular gene release profile. Those cationic polyamides containing disulfide linkage and 1,4-bis(3-aminopropyl)piperazine (BAP) residue exhibited high buffering capacity (endosomal escape ability), high gene binding ability, and intracellular gene release ability, thus inducing fast gene nucleus translocation and robust gene transfection in vitro against different cell lines and rat bone marrow mesenchymal stem cells. Moreover, the transfection efficiencies in vitro were comparable or higher than those of 25kDa branched polyethylenimine and Lipofectamine 2000 transfection agent as positive controls. These cationic polyamides and their polyplexes were of low cytotoxicity when an optimal transfection efficacy was achieved. In vivo transfection tests showed that bioreducible BAP-based polyamides were applicable for intravenous gene delivery in a mouse model, leading to higher level of transgene expression in the liver as compared to 22kDa linear polyethylenimine as a positive control. These cationic polyamides provide a useful platform to elucidate the relationship between chemical functionalities and gene transfection activity.

Elaboration of novel biosourced AA–BB polyamides with dangling chains from methyl ricinoleate

The existence of entirely biobased AA–BB polyamides is very limited because of the low availability of biosourced diamines. In this work, saturated and unsaturated diamines, with dangling hexyl chain, were successfully synthesized from methyl ricinoleate. These new monomers were reacted with several diacids to prepare novel partially to totally biobased AA–BB polyamides. Linear polyamide analogues were also prepared from commercial monomers. The physico‐chemical properties of the obtained polymers were assessed by DSC and TGA analysis. An auto‐plasticizing effect owing to the dangling chains was evidenced. The new branched monomers and polymers are expected to be used when modification of the properties of existing polyamides are required.Practical applications: The new branched monomers and polymers are expected to be used as green and renewable plasticizers for modification of the properties of existing polyamides. Furthermore, the presence of the carbon–carbon double bonds in the main chains would be beneficial to perform polyamide chemical modifications at the molten state or to achieve cross‐linking reactions suitable for coating applications.Elaboration of new branched renewable polyamides

Synthesis and Characterization of Complex Mixtures Consisting of Cyclic and Linear Polyamides from Ethyl Bis-Ketal Galactarates

Bis-ketal-protected diethyl galactarate was condensed with different diamines to prepare sugar-based polyamides. Ketal-protected polyamides, which are soluble in organic solvents, were deprotected with 90% trifluoroacetic acid to yield water insoluble materials. FTIR, NMR, GPC, MALDI-TOF, ESI and TGA techniques were used to characterize the structure and the properties of these biodegradable materials. D-galactaric acid-based polyamides are complex mixtures of cyclic and linear structures. High molecular weight linear polymer formation was limited by competitive cyclization reactions. The percentage of cyclization was highly dependent on the nature of the diamine used. Polycondensation with linear aliphatic diamines favored the formation of macrocycles, identified by MALDI-TOF and ESI.

Highly functionalized, aliphatic polyamides via CuAAC and thiol-yne chemistries

The first step in the synthesis of functionalized polyamides consisted in the introduction of alkyne side groups in several types of linear polyamides by interfacial step-growth polymerization of hexane-1,6-diamine or 4,9-dioxadodecane-1,12-diamine in combination with on one hand adipoyl or sebacoyl chloride and on the other hand an alkyne-containing building block, i.e. 2-methyl-2-propargylmalonic acid dichloride. Both homo- and copolyamides were synthesized, creating a large range of alkyne-containing polyamides with degrees of functionalization ranging between 5% and 100%. Subsequently, these polyamide chains have been modified with two types of linking chemistries, respectively with azides through the copper(I)-catalyzed Huisgen 1,3-dipolar cycloaddition or with thiols through the thiol-yne addition reaction.