Molecular Weight Cross-linking Research Articles

Effect of crosslinker molecular weight on the characteristics of thermoelectric ionogels

Abstract The present study investigates an ionic thermoelectric gel with adjustable functionality through the manipulation of crosslinker molecular weight. The thermoelectric properties of 2-hydroxyethyl acrylate (2-HEA) ionogels, prepared using PEGDA200, PEGDA575, and PEGDA1000 as crosslinkers, were thoroughly examined. Furthermore, dynamic thermal mechanical analysis (DMA) and X-ray diffraction (XRD) techniques were employed to elucidate the underlying reasons for variations in the thermoelectric material properties resulting from changes in crosslinker molecular weight. Notably, the thermoelectric gel synthesized with PEGDA575 exhibited a remarkable thermal power output of 19.19 mV•K-1 along with a tensile capacity of 231%. Additionally, the developed ionic thermoelectric capacitor demonstrated an impressive energy density of 4.288 J•m−2, thereby showcasing its potential application in flexible low-grade heat energy recovery devices.

Unconstrained dynamic gel swelling generates transient surface deformations.

Polymer gels are comprised of a three-dimensional, cross-linked network that can typically withstand the mechanical deformation associated with both swelling and de-swelling. Thus, gels can be designed with smart behaviors that require both stress generation and dissipation, making them well-suited to many applications including membrane technology, water capture devices, and drug delivery systems. In contrast to the fully swelled equilibrium state, limited research characterizes the unsteady-state swelling regime prior to equilibrium. It is in this regime where unique surface deformations can occur. Here we show how internal network constraints and external diffusive pressure can be leveraged to manipulate swelling kinetics and surface deformations in poly(ethylene glycol) gels during unconstrained, three-dimensional swelling. We find that increasing cross-linker molecular weight and swelling in ethanol, as opposed to water, are both effective routes to increase the time it takes to reach equilibrium but do so through different mechanisms. Networks with fewer internal constraints, manipulated via cross-linker chain-length, imbibe more solvent over a longer time. In contrast, swelling in ethanol reduces the amount of solvent imbibed by the network while increasing the time to reach equilibrium. Measurements of surface patterns during swelling establishes that an immediate, fast relaxation at the surface occurs during the first five minutes of swelling. However, the density and persistence of these features varies with solvent quality. These results establish a framework for how soft materials undergo dynamic deformation. Engineering transient surface properties while mitigating unwanted instabilities opens the door for emerging technologies such as smart anti-fouling and sensors.

Effect of using high molecular weight crosslinker on the physical properties of super porous hydrogel composite

Superporous hydrogel composite is widely utilized and investigated as a gastro retentive drug delivery system. Materials used in Superporous hydrogel formulation have a profound effect on its properties’, N-methylene bisacrylamide is the crosslinker of choice for the preparation of SPH.
 The purpose of this study is to determine if using a new high molecular weight crosslinker such as polyethylene glycol diacrylate will affect the physical characteristics of SPH and drug release behavior. For the preparation of super porous hydrogel polyvinyl alcohol, acrylamide, polyethylene glycol diacrylate 700, N, N-Methylene bisacrylamide, sodium bicarbonate, and tween 20 were used. Trifluoperazine HCl was used as a model drug. The buoyancy, porosity, density, drug release, drug content, swelling ratio, and swelling time were studied and compared. All the physical characteristics and medication release profiles were impacted by changing the formulation parameters. The formula with the best physical qualities had 300 µl of acrylamide (40 percent w/v), 20 mg of polyvinyl alcohol, 200 µl of Tween 20 (v/v), 5 µl of polyethylene glycol diacrylate 700, 45 µl ammonium persulfate, 45 µl TEMED and 50 mg of sodium bicarbonate. Around 80% of the drug was released over the course of 12 hours according to zero order kinetics. By modifying the formulation parameters using polyethylene glycol diacrylate, Superporous hydrogel was successfully manufactured and has the best properties to be employed as a gastro retentive drug delivery system.

Synthesis, selective decoration and photocrosslinking of self‐immolative poly(thioester)‐PEG hydrogels

AbstractSelf‐immolative polymers are a class of polymers that undergo linear depolymerization of the main chain, often triggered by a single initial degradation event. Chain‐unzipping immolation processes followed by low‐ceiling‐temperature polymers yield regenerated monomers, demonstrating the remarkable potential of these polymers in the development of reversible and recyclable materials. In this work, we describe the synthesis of an amino‐acid‐derived poly(thioester) self‐immolative polymer with pendent functional groups allowing for selective decoration of the polymer backbone with solubilizing and reactive functional groups for subsequent post‐polymerization modification. Crosslinking norbornene‐functionalized, water‐soluble derivatives of these polymers via the thiol‐ene photoclick reaction yielded mechanically robust hydrogels within 15 s of light exposure. These networks were capable of immolation in response to deprotonation of an end‐capping thiol, unzipping along the poly(thioester) backbone to yield constituent monomers and larger molecular weight crosslinker fragments. Finally, degelation rates were controlled with pH and temperature in aqueous buffers. At physiological pH and temperature, complete degradation of approximately 20 wt% hydrogels was observed after 16 h, and raising the buffer pH to 10 resulted in network dissolution within 5 h. © 2022 Society of Industrial Chemistry.

Structure and Temperature Induced Crystallization of Natural Rubber with Different Milling Times

Crystallization, a characteristic property of natural rubber, has great effect on the storage and application in industrial. Based on different milling times, natural rubber samples were prepared. Moreover, structure of natural rubber with different milling times, i.e. molecular weight, group transform, cross-link density (entanglement), and rheology were analyzed by gel permeation chromatograph (GPC), Fourier transform infrared spectrum (FTIR), and rubber processing analyzer (RPA), respectively. Furthermore, temperature induced crystallization parameters were mounted on differential scanning calorimeter (DSC). The results demonstrated that temperature induced crystallization rate decreased with the increment of milling times, whereas the average molecular weight measured by GPC decreased with milling times increasing. However, the average cross-link molecular weight increased which was compatible to the temperature induced crystallization rate. It was concluded that temperature induced crystallization rate was related to the average cross-link molecular weight, but not average molecular weight.

Reliable Condensation Curing Silicone Elastomers with Tailorable Properties.

The long-term stability of condensation curing silicone elastomers can be affected by many factors such as curing environment, cross-linker type and concentration, and catalyst concentration. Mechanically unstable silicone elastomers may lead to undesirable application failure or reduced lifetime. This study investigates the stability of different condensation curing silicone elastomer compositions. Elastomers are prepared via the reaction of telechelic silanol-terminated polydimethylsiloxane (HO-PDMS-OH) with trimethoxysilane-terminated polysiloxane ((MeO)3Si-PDMS-Si(OMe)3) and ethoxy-terminated octakis(dimethylsiloxy)-T8-silsesquioxane ((QMOEt)8), respectively. Two post-curing reactions are found to significantly affect both the stability of mechanical properties over time and final properties of the resulting elastomers: Namely, the condensation of dangling and/or unreacted polymer chains, and the reaction between cross-linker molecules. Findings from the stability study are then used to prepare reliable silicone elastomer coatings. Coating properties are tailored by varying the cross-linker molecular weight, type, and concentration. Finally, it is shown that, by proper choice of all three parameters, a coating with excellent scratch resistance and electrical breakdown strength can be produced even without an addition of fillers.

Crosslinking of Chitosan with Dialdehyde Chitosan as a New Approach for Biomedical Applications.

Materials based on natural high molecular compounds are particularly interesting for biomedical applications. It is known that the cross-linking agent used for preparation of biomacromolecule-based materials is as important as used biopolymer. Therefore, natural cross-linkers containing reactive carbonyl groups are of great interest especially for modifying properties of natural polysaccharides. One of the most popular cross-linking agents is glutaraldehyde. Nevertheless, the unreacted particles can be released from the cross-linked material and cause cytotoxic effects. This can be eliminated when using a cross-linker based e.g., on polysaccharides. This article describes quick and efficient synthesis of dialdehyde chitosan (DACS) and its application for the preparation of chitosan films. Materials obtained with different amount of DACS were fully characterized in terms of structure and surface morphology. Thermal and mechanical properties as well as hydrophilic character were also examined. The results obtained were compared with the materials obtained by cross-linking chitosan with low molecular weight glutaraldehyde and high molecular weight cross-linking agent based on polysaccharide–dialdehyde starch. Toxicity of all obtained materials was tested using the Microtox® test. It has been shown that due to better mechanical, thermal and surface properties as well as lower toxicity, dialdehyde chitosan is a very promising crosslinking agent.

Transparent, methacrylate‐based polymer networks with controlled crosslinker ductility

AbstractA series of transparent methacrylate‐based crosslinked polymer networks are prepared in which the crosslinker length is controlled as a means to investigate the effects of network ductility on mechanical and ballistic properties. In each network the optical clarity of pure poly(methyl methacrylate) (PMMA) is retained, as well as a low value of haze. Both the glass transition temperature (Tg) and the tensile modulus of the networks are highly tunable, with network values both above and well below that of pure PMMA or the pure crosslinker network. The ballistic performance is likewise affected, with performance values of up to 400% greater than neat PMMA. We examine the effects of the crosslinker molecular weight on the impact performance, finding that, in these systems, the molecular weight between crosslinks is not a driving factor for the impact performance, and this may broadly translate to polymer networks in general. We find that improvements in ballistic performance can be realized at low molecular weight between crosslinks, provided the crosslinking agent is of sufficient ductility.

Non-delaminating Polymer Hydrogel Coatings via C,H-Insertion Crosslinking (CHic) - A Case Study of Poly(oxanorbornenes).

Robust, non-delaminating polymer coatings and hydrogels are needed for technical and biomedical applications. This study focusses on surface-attached poly(oxanorbornene) hydrogels obtained by simultaneous UV-activated crosslinking and surface-immobilization. The synthesis and copolymerization of two oxanorbornene monomers carrying the UV-crosslinkers malonic acid diazoester or benzophenone, which can both undergo UV-triggered C,H-insertion crosslinking (CHic), is presented. The crosslinking efficiency and network stability of hydrogels made from these self-crosslinkable polymers are studied and compared to the properties of poly(oxanorbornene) networks obtained by UV-triggered thiol-ene-reactions involving a low molecular weight crosslinker. Smooth, defect-free, non-delaminating hydrogel coatings were obtained by CHic, not only on laboratory model surfaces but also on a technical product.

Crosslink-free collagen from Cichla ocellaris: Structural characterization by FT-IR spectroscopy and densitometric evaluation

Crosslink-free collagen of skin from peacock bass Cichla ocellaris was successfully isolated and had its structural characteristics analyzed mainly by the combination of two techniques: optical densitometry and FT-IR. The optical densitometry coupled to the electrophoretic profile showed two typical α chains (α1 and α2), lower content of dimmers and trimmers (β and ɣ chain, respectively) than other extraction methods and without formation of high molecular weight crosslinks (HMC and VMC). UV–visible absorption spectrum was 211 nm. FT-IR spectra analysis of the amide A, amide B, amide Ι, amide ΙI and amide ΙΙI bands were 3276, 2930, 1637, 1547 and 1240 cm−1, respectively, and showed maintenance of the triple helical chain stabilized by hydrogen bonds characterizing it as collagen. Moreover, PSC was soluble in the range from 0 to 3% of salt concentrations, as well as in alkaline media (pH 8). Our results indicate that the two main techniques used were able to identify and characterize the type 1 crosslinks-free collagen from C. ocellaris, which may be suitable for applications that requires higher purification degree.

Antimicrobial polymer coatings with efficacy against pathogenic and spoilage microorganisms

Antimicrobial polymer coatings with inherent self-sanitizing properties have been explored to support food safety and preservation. Materials with multiple antimicrobial modes of action represent a novel alternative. Herein, we evaluated the antimicrobial effect and storage stability of coatings with varied molecular weight styrene maleic anhydride (SMA) cross-linkers (6, 8, 120, and 250 kDa) and branched polyethyleneimine (PEI) coated onto polypropylene films. Infrared spectroscopy analyses suggested successful crosslinking between all varieties of SMA and PEI. Coatings were evaluated in their inherent form (cationic), and chlorinated as N-halamines. Surface concentration of primary amines ranged from 350 to 900 nmol/cm2, and N-halamine concentration ranged from 90 to 130 nmol/cm2, with values varying depending on SMA molecular weight. Surface energy decreased with increasing molecular weight of SMA. Optimal cross-linker molecular weight was determined based on antimicrobial performance, where the coated PP with 6 kDa SMA demonstrated enhanced biocidal effect against Escherichia coli O157:H7 in its chlorinated form. Further, the antimicrobial coating demonstrated efficacy between ∼3 and >5 logarithmic reductions in its unchlorinated and chlorinated forms against Escherichia coli O157:H7, Listeria monocytogenes, and Pseudomonas fluorescens. Storage studies supported the stability of the chlorinated N-halamines, with full chlorine retention over a 24 h study.

Effect of Crosslinker Length and Architecture on the Thermomechanical Properties of CNT-Loaded Elastomeric Polymer Matrix Composites.

An evolving understanding of elastomeric polymer nanocomposites continues to expand commercial, defense, and industrial products and applications. This work explores the thermomechanical properties of elastomeric nanocomposites prepared from bisphenol A diglycidyl ether and three amine-terminated poly(propylene oxides) (Jeffamines). The Jeffamines investigated include difunctional crosslinkers with molecular weights of 2000 and 4000 g mol-1 and a trifunctional crosslinker with a molecular weight of 3000 g mol-1 . Additionally, carbon nanotubes (CNTs) are added, up to 1.25 wt%, to each thermoset. The findings indicate that the T g and storage modulus of the polymer nanocomposites can be controlled independently within narrow concentration windows, and that effects observed following CNT incorporation are dependent on the crosslinker molecular weight. Finally, the impact of crosslinker length and architecture as well as CNT addition on the molecular weight between crosslink points in the glassy and rubbery states are discussed.

Radical Degradation Processes Initiated by Catalytic Nanoparticles of CoFe2O4 Towards Polymer Waste Application

Polymer waste presents a modern environmental challenge due to the long-term stability of these materials. Elastomer-based polymers (e.g., tires, pipelines and shoes) are unique in comprising numerous double bonds, which are typically sensitive to radical-initiated oxidative degradation leading to the scission of polymer chains. In this paper, we propose a new approach for radical-initiated oxidative degradation of polymers using cobalt ferrite (CoFe2O4) nanoparticles (NPs). We show that magnetic CoFe2O4 NPs can effectively catalyze the oxidative degradation of polybutadiene (PB), offering easy magnetic recycling and reuse without affecting their catalytic efficiency. The CoFe2O4 NPs were synthesized via a facile surfactant-free method based on a sonochemical reaction. We used methyl ethyl ketone peroxide (MEKP), a model system, to study the rate of radical decomposition catalyzed by the NPs. The radical decomposition rates were determined by following the discoloration of methylene blue (MB) using ultraviolet–visible (UV/Vis) spectroscopy; electron paramagnetic resonance (EPR) measurements were used to study radical formation. The radical-initiated oxidative degradation of PB was studied by thermogravimetric analysis with mass spectrometry detection (TGA–MS). Our results show that cobalt ferrite NPs lead to formation of polymers with low molecular weight fragments and crosslinking, indicating that these NPs are very effective catalysts for the radical degradation of PB. CoFe2O4 NPs are potentially suitable for other polymers, hence this approach may provide a novel route for the chemical (tertiary) recycling of polymers.

Preparation and Characterization of DGEBA/EPN Epoxy Blends with Improved Fracture Toughness

The physical and mechanical properties of blends composed of two kinds of epoxy resins of different numbers of functional groups and chemical structure were studied. One of the resins was a bifunctional epoxy resin based on diglycidyl ether of bisphenol A and the other resin was a multifunctional epoxy novolac resin. Attempt was made to establish a correlation between the structure and the final properties of cured epoxy samples. The blend samples containing high fraction of multifunctional epoxy resin showed higher solvent resistance and lower flexural modulus compared with the blends containing high fraction of bifunctional epoxy resin. The epoxy blends showed significantly higher ductility under bending test than the neat epoxy samples. The compressive modulus and strength increased with increasing of multifunctional epoxy in the samples, probably due to enhanced cross-link density and molecular weight. Morphological analysis revealed the presence of inhomogeneous sub-micrometer structures in all samples. The epoxy blends exhibited significantly higher fracture toughness (by 23% at most) compared with the neat samples. The improvement of the fracture toughness was attributed to the stick-slip mechanism for crack growth and activation of shear yielding and plastic deformation around the crack growth trajectories for samples with higher content of bifunctional epoxy resin as evidenced by fractography study.

Transport in PEG‐Based Hydrogels: Role of Water Content at Synthesis and Crosslinker Molecular Weight

Poly(ethylene glycol) (PEG) hydrogels are hydrophilic, high water content, polymeric networks that represent excellent candidates as engineering biomaterials for a broad range of applications. A key challenge for many biomedical applications is the control of transport properties within the resulting 3D crosslinked gels. The effects of the water content at synthesis and crosslinker molecular weights on gel chemical structure and equilibrium volumetric swelling ratio, Q, are studied for a series of PEG hydrogels. In addition, the translational diffusion coefficients of a model probe molecule, Rhodamine 110, are determined directly within the hydrogels by fluorescence correlation spectroscopy measurements. Increasing the water content at synthesis results in larger observed swelling behavior and faster particle transport within the formed PEG hydrogels for two different crosslinker molecular weights due to fewer physical crosslinks in the gels. Comparison of the particle translational diffusion coefficient to the swelling ratio shows a linear relationship for all crosslink densities examined. image

Synthesis, curing and properties of poly(phthalazione ether sulfone ketone) copolymers crosslinked by click chemistry

Functionalized poly(phthalazinone ether sulfone ketone) was synthesized by successive chloromethylation and azidation, followed by curing reaction with the propargyl end-groups of various molecular weight crosslinking agents in the presence of Cu(I) catalyst via the azide-alkyne click reaction. The influences of the chain length of crosslinking agents on the poly(phthalazinone ether sulfone ketone) system were studied. FTIR and DSC tests demonstrated certain crosslinking by azide-alkyne reaction with the formation of triazole ring. DSC results showed that curing temperature shifted to lower temperatures considerably in the presence of Cu(I) catalyst. TGA showed cured polymers were of much higher thermal stability, including higher thermal decomposition temperatures and higher char-yielding properties. After being cured, the polymers became insoluble in organic solvents and the gel fraction of the cured polymers exceeded 71%. Wide-angle X-ray diffraction results indicated there was a short distance order in the poly(ether sulfone) (PES) main chain except for the azido methyl poly(phthalazinone ether sulfone ketone) and 4,4’ -bis(2-propynyloxy) biphenyl ( AMPPESK-BP) system.

Spatiotemporal Modification of Stimuli-Responsive Hyaluronic Acid/Poly(N-isopropylacrylamide) Hydrogels.

Current methods to spatiotemporally modify stimuli response in hydrogels are typically subtractive and lead to a decrease in response. To increase the breadth of hydrogel applications and biomedical systems, new formulations are needed that can introduce and increase stimuli response spatiotemporally in hydrogels. In this work, the light-induced thiol-norbornene click chemistry reaction was used to modify the stimuli response of robust hyaluronic acid hydrogels through an additive process in spatiotemporal fashion, overcoming this limitation. These stimuli-responsive hydrogels were made from norbornene-functionalized hyaluronic acid (NorHA) cross-linked with thermoresponsive dithiol-terminated poly(N-isopropylacrylamide) (DTPN). Variation of the cross-linker molecular weight and gelation conditions led to a range of compression modulus (5 to 54 kPa) and mass loss (9 to 33%) upon heating to 37 °C while retaining a majority of NorHA in the hydrogel. The thermoresponse of these hydrogels could be controlled not only by the cross-link density but also by heating to 55 °C to increase the dewatering of the hydrogels. The stimuli response of the hydrogels was temporally increased by introducing additional DTPN and UV initiator to an original hydrogel with subsequent irradiation. This modification was extended to spatiotemporally changing the stimuli response by photopatterning DTPN into a NorHA hydrogel, yielding a hydrogel that changed shape and topology through heating. Furthermore, human mesenchymal stem cells could adhere and proliferate on the DTPN-patterned surface, demonstrating that the materials could be used for studies where cells are present.

Effect of protein concentrations on the properties of fish myofibrillar protein based film compared with PVC film.

The effect of protein concentrations on the properties of fish myofibrillar protein film (FMP) were investigated and compared with commercial wrap film (polyvinyl chloride; PVC). FMP (2%, w/v) showed the highest mechanical properties [tensile strength: 4.38MPa and elongation at break: 133.05%], and water vapor permeability [2.81×10(-10)gm(-1)s(-1)Pa(-1)]. FMP contained high molecular weight cross-links, resulting in complex film network, as indicated by lower film solubility (19-22%) and protein solubility (0.6-1.3%). FMP showed excellent barrier properties to UV light at the wavelength of 200-280nm. FMP had the thickness [0.007-0.032mm], color attributes and transparency similar to PVC film [thickness: 0.010mm]. Therefore, protein concentration majority influenced the properties of develop FMP. The protein content of 1% (w/v) had potential to be developed the biodegradable film with comparable properties to the commercial wrap film.

Effect of substrate type on sensory characteristics and antioxidant capacity of sunflower Maillard reaction products

The sensory characteristics and antioxidant capacity of Maillard reaction products (MRPs) from two substrates namely sunflower free amino acid and peptides, xylose with and without cysteine model systems (AXC, AX, PXC and PX, respectively) were evaluated and compared. The model systems were heated at 120 °C for 2.0 h and a pH of 7.4. Results showed that AXC had greater meat-like flavour and umami taste, while PXC showed great mouthfulness and continuity taste, and AX and PX showed higher caramel-like flavour and bitter taste. The addition of cysteine was found to accelerate high molecular weight peptide degradation while suppressing low molecular weight cross-linking and colour formation in PXC and AXC. Furthermore, it was observed that sensory attributes of MRPs were not significantly affected by the peptides size. Results also showed that caramel-like flavour and bitter taste were significantly and positively correlated with furans and most of the nitrogen-containing compounds while these compounds had significant and negative impact on mouthfulness, continuity and meat-like flavour. Additionally, sulphur-containing compounds showed significant and positive influence on meat-like flavour, while PXC and PX showed higher antioxidant activities than AXC and AX. It can therefore be concluded that sunflower peptides MRPs can be a good precursor of flavour enhancers with high antioxidant activity, while sunflower free amino acid MRPs can be used to produce meat-like flavour enhancers.

Print your own membrane: direct rapid prototyping of polydimethylsiloxane.

Polydimethylsiloxane is a translucent and biologically inert silicone material used in sealants, biomedical implants and microscale lab-on-a-chip devices. Furthermore, in membrane technology, polydimethylsiloxane represents a material for separation barriers as it has high permeabilities for various gases. The facile handling of two component formulations with a silicone base material, a catalyst and a small molecular weight crosslinker makes it widely applicable for soft-lithographic replication of two-dimensional device geometries, such as microfluidic chips or micro-contact stamps. Here, we develop a new technique to directly print polydimethylsiloxane in a rapid prototyping device, circumventing the need for masks or sacrificial mold production. We create a three-dimensional polydimethylsiloxane membrane for gas-liquid-contacting based on a Schwarz-P triple-periodic minimal-surface, which is inaccessible with common machining techniques. Direct 3D-printing of polydimethylsiloxane enables rapid production of novel chip geometries for a manifold of lab-on-a-chip applications.