Mechanism Of Cross-linking Reaction Research Articles

Preparation and characterization of UV-curable coatings based on waterborne polyurethane acrylate/g-C3N4 co-crosslinked network for wood materials

Wood materials are often damaged due to exposure to environmental factors including humidity changes, temperature fluctuations, and ultraviolet radiation, resulting in surface aging, deformation, and cracking. Therefore, developing a new wood coating with good mechanical properties and weather resistance is conducive to improving the usability and service life of wood as an outdoor material. In this study, graphitic carbon nitride (g-C3N4) with a characteristic crystal structure was synthesized using melamine as raw material. By constructing a g-C3N4 /polyurethane acrylate co-crosslinked network, a UV-curable wood coating with excellent interfacial adhesion was prepared, which retained the natural aesthetic texture of the wood and imparted good wear resistance, anti-wetting property, and aging resistance to the wood material. Subsequently, the formation process and cross-linking reaction mechanism of the coating were revealed by XRD, FTIR and XPS measurements. Compared with untreated samples, coatings with a cross-linked network structure exhibited enhanced resistance to external environmental changes. As the content of the g-C3N4 increased (>1.0 %), the mechanical properties were significantly improved, with the mass loss rate and damaged area decreasing by 56.9 % and 60.0 %. Meanwhile, with the increased cross-link density of the coating, the water and heat resistance of the wood increased by 22.77 % and 260 %, respectively. After a seven-day UV aging resistance test, the ΔE values only changed by 10.28 %, showing good weathering resistance. This design and synthesis of wood coating provides an effective technology for the long-term use of outdoor wood material.

Effect of polymer crosslinking to the failure behavior of thermoplastic composite remelting interface: Molecular dynamics simulation and experimental verification

AbstractThe forming interface is the weak link of thermoplastic composite complex structures. To explore the effect of polymer crosslinking on the failure behavior of thermoplastic composite remelting interface using “Preforming + Remelting bonding” process, the all‐atom models of different types of interfaces were established, and a molecular dynamics (MD) simulation was conducted on the uniaxial tensile failure process of the remelting interface. The failure behavior of the remelting interface with different preforming processes was tested to verify the correctness of MD simulation, and the influencing mechanism of polymer crosslinking reactions in the preforming stage to the remelting interface properties was clarified. The results showed that the yield stress of the uncrosslinked interface reaches 283.2 MPa and 16.0% and 50.6% higher than that of the unilateral and bilateral crosslinked interfaces respectively. The polymer crosslinking reaction during the preforming stage will reduce the interlaminar bonding performance. The interlaminar shear strength (ILSS) of the uncrosslinked interface is 87.46 MPa and 7.21% and 27.36% higher than that of the unilateral and bilateral crosslinked interface respectively, and only 3.95% lower than that of the non‐remelting sample formed by standard process. This research provides a new approach for predicting and analyzing the effect of polymer crosslinking on remelting interface properties of thermoplastic composite using “Preforming + Remelting bonding” process.Highlights The failure behavior of different thermoplastic composite remelting interfaces was studied. MD simulation was conducted on the uniaxial tensile failure process of the remelting interface. The influencing mechanism of polymer crosslinking reactions in the preforming stage to the remelting interface properties was clarified. It is effective to explore the failure mechanism of thermoplastic remelting interface by MD simulation.

In-situ crosslinking reaction of graphene oxide & waterborne epoxy resin to construct continuous phase anticorrosive coating

The mechanism of using graphene oxide as a two-dimensional filler to increase the path length of the corrosive medium to the metal surface is limited to improving the corrosion resistance of the coating. This study propose novel dispersion and in-situ crosslinking reaction mechanism for constructing water-based heavy-duty anticorrosive coatings by using graphene oxide (GO) and waterborne epoxy resin (WEP). The results showed that GO can be uniformly dispersed directly into WEP without complex functional modifications. Oxygen-containing functional groups on moleculars structure of GO&WEP co-polymerized with diethylenetriamine (DETA) forming a continuous phase film which improved the density of the coating. Characterization techniques such as Fourier-transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), scanning electron microscopy (SEM), thermal conductivity measurement instrument, pencil hardness tester, adhesion tester, salt spray corrosion test chamber, and electrochemical impedance spectroscopy (EIS) were used to evaluate coating structure and performance properties. The results showed that graphene characteristics enhanced physical properties and anti-corrosion performance of composite coatings. The construction mechanism of the coating is different from that of the current GO modified and dispersed in the coating as a two-dimensional filler to extend the path length of the corrosive medium to the metal surface. The coatings prepared by adding the optimum mass ratio of 0.1–0.2 % GO to WEP have the best physical properties and anti-corrosion properties. When the GO content is 0.2 wt%, the thermal conductivity increases by 86.0 %. After added 0.025 wt% GO, the coating hardness is increased by two grades directly from 2B to HB. With the addition of GO concentration increased to 0.05 wt%, the adhesion is increased from 2 to level 1.When the GO content exceeds 0.05 %, the coating will not bulge off after 4 months of salt water immersion experiment.

Thermal crosslinking and cyclodehydration assisted fabrication of chemically robust thin-film composite (TFC) membranes for ultrafast polar solvents filtration

Organic solvent nanofiltration (OSN) offers an energy-efficient alternative to conventional thermal distillation processes for organic solvent separations. However, the fabrication of polymeric OSN membranes with adequate chemical stability in strong polar aprotic solvents remains a remarkable challenge. In this work, chemically robust polyamide thin-film composite (TFC) OSN membranes were fabricated by utilizing an innovative chemical modification of polyimide (PI) nanofiber substrate via one-step crosslinking and thermal cyclodehydration of terephthalic hydrazide (TPDH). The crosslinking and cyclodehydration reaction mechanisms were thoroughly elucidated and the effects of TPDH loading and thermal treatment conditions on solvent resistance and pore structure of the resulting TPDH/PI nanofiber substrates as well as the formation of the polyamide selective layer were systematically studied. The resulting TFC membranes show excellent stability in polar aprotic solvents (i.e., DMF, DMAC, and NMP), and a high DMF permeance of 9.4 L m−2 h−1 bar−1 was achieved with a 99.8% rejection to Rose Bengal at 2.0 bar. The outstanding long-term performance stability revealed the robust structure of the developed TFC OSN membranes. This work demonstrates a facile strategy to address the chemical stability limitations of TFC OSN membranes through a multifaceted yet generalizable approach of chemical crosslinking and thermal cyclodehydration. We believe this strategy can be broadly applied to different substrates, enabling TFC membranes to address a wide variety of unmet OSN needs.

Optimization of Nickel(II) adsorption by sodium tripolyphosphate crosslinked chitosan using response surface methodology (RSM)

This study aimed to synthesize chitosan crosslinked by sodium tripolyphosphate with different concentrations and optimize it for Ni(II) adsorption in a batch adsorption system. The BET analysis and the solubility/swelling test showed that as the crosslinking degree increased, the surface area and total pore volume decreased while the physicochemical properties improved. The effect of the initial pH and temperature on the adsorption of Ni(II) was studied in a batch adsorption system, and thermodynamic parameters were calculated. In order to enhance the adsorption capacity of crosslinked chitosan, Response Surface Methodology (RSM) was employed to establish a correlation between two independent experimental factors, namely pH and crosslinking degree, and the Ni(II) adsorption capacity. By changing these factors, the aim was to optimize the adsorption capacity of crosslinked chitosan. The constructed model was well-aligned with the experimental data with an R2 = 96.05%. According to the model, an adsorption capacity of 31.94 mg/g could be achieved at a pH of 7.21 and a crosslinking degree of 2.93% (w/v). Among isotherm models investigated, the Langmuir model was found to be more appropriate for studying Ni(II) adsorption with maximum adsorption capacity in the order of chitosan beads> crosslinked chitosan beads. The mechanism of adsorption and crosslinking reaction was also investigated using FT-IR and SEM-EDS techniques, implying that the amine groups were the primary sites for metal ions uptake as well as crosslinking reaction. A mixture of NaCl and H2SO4 could release the sorbed Ni(II) ions from STPP-CB5% with a recovery of 83% after one sorption-desorption cycle.

Kinetic and thermodynamic investigation on diffusion-limited crosslinking reaction behaviors of peroxide-induced low-density polyethylene

Crosslinking reaction behaviors can determine the network morphology and further influence macroscopic properties of polymers, while the current comprehension about crosslinking reaction behaviors of peroxide-induced low-density polyethylene (PLDPE) is quite lacking, which seriously limits its development and application. Here, for the first time, the crosslinking reaction behaviors of PLDPE are fully characterized and analyzed by combining kinetic and thermodynamic analysis. The kinetic behaviors are investigated by non-isothermal DSC and isothermal rheology methods, and thermodynamic characteristics of crosslinking reaction are analyzed by Arrhenius law and transition state theory. The results demonstrate that the crosslinking reaction of PLDPE involves complex order and autocatalysis reactions. Notably, the autocatalysis reaction is considered as the driving force of the whole crosslinking reaction. Furthermore, the autocatalysis reaction is proved to be strongly dependent on the diffusion of macromolecular chains under isothermal conditions, whereas the effect of diffusion on order reaction can be ignored. Given that, a new kinetic model incorporates the single diffusion factor to significantly describe the diffusion effect on the autocatalysis reaction during crosslinking, which grasps the complexity of crosslinking reaction mechanism. This model is able to characterize and predict the kinetic results of PLDPE crosslinking reaction very well. It provides an effective analysis methodology and an accurate kinetic model for characterizing and predicting the diffusion-limited crosslinking reaction behaviors of polymers.

Theoretical study on the cross-linking reaction mechanism of cellulose nanofibrils initiated by fluorine

Theoretical investigation on the cross-linking reaction process and mechanism of cellulose nanofibrils (CNFs) initiated by fluorine is accomplished by density functional theory. Three reaction pathways generated aldehyde and ester are identified. The reaction potential energy information of the ten reaction channels at B3LYP/6-311+G(d,p) level are obtained. The calculation results show that the reaction pathway of forming ester thereafter acyl fluoride has realized the cross-linking of cellulose. The reaction pathway of forming ester is more kinetically and thermodynamically favorable than the others of forming aldehyde with the lower energy barriers. The oxidation site mainly occurred at the methylene hydrogen of the hydroxymethyl group in the cellulose. The cross-linking of two cellulose molecules initiated by fluorine forming a covalent ester bond would be beneficial to improve cellulose mechanical properties of the insulating paper, which is better to add cellulose nanofibrils served as a “bridge” for strengthening the connection between celluloses.

Diselenide as a Dual Functional Mechanophore Capable of Stress Self-Reporting and Self-Strengthening in Polyurethane Elastomers

Diselenide as a Dual Functional Mechanophore Capable of Stress Self-Reporting and Self-Strengthening in Polyurethane Elastomers

Mechanically Robust and Flame-Retardant Polylactide Composites Based on In Situ Formation of Crosslinked Network Structure by DCP and TAIC.

The addition of intumescent flame retardant to PLA can greatly improve the flame retardancy of the material and inhibit the dripping, but the major drawback is the adverse impact of the mechanical properties of the material. In this study, we found that the flame retardant and mechanical properties of the materials can be improved simultaneously by constructing a cross-linked structure. Firstly, a cross-linking flame-retardant PLA structure was designed by adding 0.9 wt% DCP and 0.3 wt% TAIC. After that, different characterization methods including torque, melt flow rate, molecular weight and gel content were used to clarify the formation of crosslinking structures. Results showed that the torque of 0.9DCP/0.3TAIC/FRPLA increased by 307% and the melt flow rate decreased by 77.8%. The gel content of 0.9DCP/0.3TAIC/FRPLA was 30.8%, indicating the formation of cross-linked structures. Then, the mechanical properties and flame retardant performance were studied. Results showed that, compared with FRPLA, the tensile strength, elongation at break and impact strength of 0.9DCP/0.3TAIC/FRPLA increased by 34.8%, 82.6% and 42.9%, respectively. The flame retardancy test results showed that 0.9DCP/0.3TAIC/FRPLA had a very high LOI (the limiting oxygen index) value of 39.2% and passed the UL94 V-0 level without dripping. Finally, the crosslinking reaction mechanism, flame retardant mechanism and the reasons for the improvement of mechanical properties were studied and described.

Novel Photoreactive Pressure-Sensitive Adhesives (PSA) Based on Acrylics Containing Additionable Photoinitiators.

A new class of additionable ultraviolet photoinitiators that can be used, through addition, for modification of the acrylic polymer chain and their influence of main properties of acrylic pressure-sensitive adhesives (PSAs) is described here. The photoinitiators studied are based on benzophenone, dibenzofuran and anthraquinone chromophores. The propyleneimine carbonyl is the reactive additionable group incorporated in the photoinitiator structure. First, the solvent-borne acrylic pressure-sensitive adhesive was synthesized and characterized. Then, a photoinitiator suitable for addition to the acrylic polymer chain possessing a carboxyl group was added before UV-irradiation. A mechanism of UV-initiated cross-linking reaction of acrylic PSA with additionable photoinitiators was done as well. The influence of the concentration and type of photoinitiator, UV-crosslinking time and UV-dose on peel adhesion, shear strength and tack of solvent-borne acrylic pressure-sensitive adhesives cross-linked by UV light was studied and presented here. It was found that the tack depends on the UV-dose and photoinitiator concentration. An increase of UV dose results in an increase of shear strength of acrylic pressure-sensitive adhesive (PSA) formulations.

Preparation of highly porous SiC via ceramic precursor conversion and evaluation of its thermal insulation performance

ABSTRACT Porous SiC ceramics were prepared based on precursor conversion method using liquid hyperbranched polycarbosilane (LHBPCS) as the preceramic polymer and expandable microsphere (EMS) as the pore foaming agent. By optimising the content of free radical initiator, the cross-linking process of LHBPCS is synchronised with the foaming process of EMS. The addition of EMS had no serious effect on the cross-linking reaction mechanism and rate of LHBPCS, and the cross-linking of LHBPCS did not significantly confine the foaming of EMS. After 1000°C pyrolysis, EMS decomposed, but its spherical shape with sizes of 20–30 μm homogeneously embedded in the pyrolysed LHBPCS. As a result, a highly porous SiC foam with density of 0.211 g cm–3 and porosity of 91.2% was obtained and its thermal conductivity at room temperature was as low as 0.05 W (m K)–1. In addition, with increasing test temperature, its thermal conductivity increased slowly, indicating a good thermal insulation property.

Mechanism of crosslinking in benzoyl peroxide‐initiated functionalization of vinyltriethoxysilane onto polypropylene in the water medium

AbstractSilane grafting and moisture crosslinking is one of the most common methods in the production of crosslinked polyolefin. A remarkable increase in the percentage of gel in the product was observed in benzoyl peroxide‐mediated aqueous suspension grafting of vinyltriethoxysilane onto polypropylene. Aimed to explore the crosslinking reaction mechanism in this functionalization process, comprehensive experiments had been conducted and the grafted products were characterized by mass spectrometry, 1H NMR, and 29Si NMR spectroscopy. Finally, a novel crosslinking mechanism was proposed based on the characterization results.

UV-Initiated Crosslinking Reaction Mechanism and Electrical Breakdown Performance of Crosslinked Polyethylene.

The ultraviolet (UV) irradiation crosslinking reactions of polyethylene and the electronic properties of photo-initiators and reaction products are theoretically investigated by the first-principles calculations. The crosslinked polyethylene (XLPE) materials are prepared in experiments that employ the UV-initiated crosslinking technique with different photon-initiation systems. Infrared spectrum and the alternating current dielectric breakdown strength of UV-initiated XLPE are tested to explore the effect of reaction products on the breakdown characteristics in combination with the electron structure calculations. The theoretical calculations indicate that the 4-hydroxybenzophenone laurate, which is compatible with polyethylene, can effectively initiate crosslinking reactions of polyethylene molecules under UV photon excitation and will produce reaction by-products from carbonyl radicals; as a macromolecular auxiliary crosslinker, the monomer or homopolymer of dioleyl-2,2′,4,4′-tetraallyl isocyanurate can form chemical connections with multiple polyethylene molecules acting as a crosslinking node in a photon-initiated reaction process. The carbonyl, hydroxyl, or ester groups of reaction by-products are capable of capturing hot electrons to prevent polyethylene molecules from impact ionization, and thus will increase the breakdown electric field. The macromolecular auxiliary crosslinker and the macromolecular photon initiator as well as its reaction by-product can convert the energy of their captured high-energy electrons into heat, which can act as a voltage stabilizer. The molecule characterization of infrared spectra demonstrates that the characteristic absorption peaks of the carbonyl in the macromolecular photon initiator and the allyl in the macromolecular auxiliary crosslinking agent are gradually decreasing in intensity as the crosslinking reaction proceeds, which is consistent with the conclusion from theoretical calculations. Compared with the small molecular photon-initiation system generally used in the photon-initiated crosslinking process, the higher dielectric breakdown field of XLPE being prepared by utilizing a macromolecular photon-initiation system is in good agreement with the calculation results of electronic affinity and ionization potential. The consistent results of the experiments and first-principles calculations elucidate the fundamental mechanism of the UV-initiation crosslinking technique and suggest a prospective routine to improve the insulation strength for developing high-voltage XLPE insulating materials.

Tannin Gels and Their Carbon Derivatives: A Review.

Tannins are one of the most natural, non-toxic, and highly reactive aromatic biomolecules classified as polyphenols. The reactive phenolic compounds present in their chemical structure can be an alternative precursor for the preparation of several polymeric materials for applications in distinct industries: adhesives and coatings, leather tanning, wood protection, wine manufacture, animal feed industries, and recently also in the production of new porous materials (i.e., foams and gels). Among these new polymeric materials synthesized with tannins, organic and carbon gels have shown remarkable textural and physicochemical properties. Thus, this review presents and discusses the available studies on organic and carbon gels produced from tannin feedstock and how their properties are related to the different operating conditions, hence causing their cross-linking reaction mechanisms. Moreover, the steps during tannin gels preparation, such as the gelation and curing processes (under normal or hydrothermal conditions), solvent extraction, and gel drying approaches (i.e., supercritical, subcritical, and freeze-drying) as well as the methods available for their carbonization (i.e., pyrolysis and activation) are presented and discussed. Findings from organic and carbon tannin gels features demonstrate that their physicochemical and textural properties can vary greatly depending on the synthesis parameters, drying conditions, and carbonization methods. Research is still ongoing on the improvement of tannin gels synthesis and properties, but the review evaluates the application of these highly porous materials in multidisciplinary areas of science and engineering, including thermal insulation, contaminant sorption in drinking water and wastewater, and electrochemistry. Finally, the substitution of phenolic materials (i.e., phenol and resorcinol) by tannin in the production of gels could be beneficial to both the bioeconomy and the environment due to its low-cost, bio-based, non-toxic, and non-carcinogenic characteristics.

Investigation of chemical reaction during sodium alginate drop impact on calcium chloride film

The objective of this work is to study the chemical reaction between sodium alginate drop and calcium chloride film and instantaneous formation of calcium alginate gel. The complexity of this work is the simultaneous effect of both liquid and solid surface on drop impact gelation process. The sodium alginate concentration in the drop fluid, liquid film thickness, and drop impingement height are varied and the observations are captured using a high speed camera. Several interesting phenomena like splashing and jet break up occur depending on the drop impingement velocity, drop concentration, and film thickness. Crosslinking reaction and mixing mechanisms are schematically explained accounting the role of capillary wave propagation within the liquid film. A mathematical model on drop spreading on the solid surface after penetrating the liquid film is developed to predict the theoretical gel length for ultrathin and thin film regimes. Maximum spreading diameter of the drop postimpact on the liquid film is predicted from the model. However, the experimentally measured solidified gel length deviates from the theoretical values and these deviations are utilized to measure the rate of crosslinking gelation and instantaneous solidification. Different hydrodynamic parameters such as the crater depth, crater contact time, and crater dissipation energy are evaluated for the dynamics of gelation. Finally, the kinetics of gelation with the variation of liquid film thickness are determined for alginate drop concentrations and drop impingement heights.

Mechanism of formation of chromium acetate(Cr3+)/ phenol-formaldehyde resin prepolymer(PRP) complex and its compound cross-linking reaction with polymer for conformance control

For the heterogeneous oil reservoir with high water cut, the conformance control by using polymer gels is good for increasing oil production and decreasing excessive water. However, facing the current situation of low oil prices, how to improve the exploitation efficiency and reduce the production cost in the maximum extent are still drawing the attention of petroleum engineers. Therefore, it is necessary to further study the polymer gels to achieve this purpose. Among the polymer gels, the polymer/Cr3+ system and polymer/phenolic-formaldehyde compounds system are the most common used, which are suitable for the low temperature reservoir and high temperature reservoir, respectively. Based on the properties of each other, the combination of Cr3+ and phenol-formaldehyde resin prepolymer (PRP) as a type of cross-linking agent can not only improve the thermal stability of polymer/Cr3+ gel, but also enable polymer/PRP gel to be applied to low-medium temperature reservoirs, which can further improve the application effect of polymer gels. However, the mechanism of compound cross-linking reaction of Cr3+-PRP and polymer is still unclear. In this paper, the properties of Cr3+-PRP solution is first tested and then the process of crosslinking reaction of Cr3+-PRP and polymer is study. In the Cr3+-PRP solution, a new polynuclear olation complex ion of chromium (Cr3+-PRP complex) is formed, of which the properties is different from PRP solution or chromium acetate solution. The cross-linking reaction of Cr3+-PRP complex and polymer is compound. During the compound reaction at the temperature of 45 °C, the reaction of Cr3+ and polymer has an impact on that of PRP and polymer, so that the reaction of Cr3+-PRP complex and polymer is different from the superposition of the two reaction processes of Cr3+/polymer system and PRP/polymer system. The formed Cr3+-PRP complex can resist salt to 70,000 mg/L. The experimental results can provide a theoretical guidance for the high efficient practical application of conformance control by using polymer/Cr3+ system or polymer/phenolic-formaldehyde compounds system.

Understanding the effect of silane crosslinking reaction on the properties of PP/POE blends

The effect of silane crosslinking reaction on properties and structure of polypropylene (PP)/ethylene–octene elastomer (POE) blends had been carried out. FTIR and gel content tests confirmed the grafting and crosslinking reaction mechanism of PP/POE blends. The incorporation of POE phase enhanced the crosslinking degree and thermal stability of blends. Crystallinity of silane-crosslinked PP/POE blends decreased sharply, and the melting points change a little with the POE content increasing. The rheological curves of silane-crosslinked PP/POE blends showed an obvious “gel point”, corresponding to the dynamic crosslinking network. Solvent resistance tests suggested crosslinking had a great improvement of solvent resistance. The blends with 30% POE had good comprehensive mechanical properties. Scanning electron microscopy images exhibited that crosslinking had a great influence on the morphologies of silane-crosslinked PP/POE blends. Characterization results indicated the “gel point” acquired from rheology had some corresponding relationship with mechanical properties and solvent resistance.

Study of Cellulose Nanocrystals and Zinc Nitrate Hexahydrate Addition in Chitosan Hydrogels

In this study, chitosan hydrogels were produced with 0, 2, 4 and 6 wt% of cellulose nanocrystals (CNC) using hexahydrate zinc nitrate (Zn(NO3)2.6H2O) as a catalyst for chitosan crosslinking reaction. CNC´s size was estimated by dynamic light scattering (DLS) and surface charge by zeta potential. Hydrogels were characterized by rotational rheometer, swelling test, uniaxial compression test, in vitro degradation, scanning electron microscopy (SEM) and microtomography. Results showed that zinc nitrate and CNC addition did not influence mechanical properties, degradation, and morphology of the hydrogels. However, zinc nitrate decreased 36.54% of the gel time and 41.37% of the swelling degree, and increased the crosslinking degree of the chitosan hydrogels, proving not only its catalytic effect but also its participation in the crosslinking reaction. Porosity was slightly reduced after addition of zinc nitrate and incorporation of CNC. In the mechanism of crosslinking reaction, a competition between CNC and zinc nitrate was observed.

Gelation studies on acrylic acid‐based hydrogels via in situ photo‐crosslinking and rheology

ABSTRACTThe gelation characteristics of acrylic acid (AA)‐based hydrogels were investigated using real time in situ photocrosslinking and rheological measurements. The gel point and gelation times were established using Winter–Chambon criteria. Frequency independence of tan δ was observed in all cases, such that G′ and G″ scaled as ∼ωn. The Flory–Stockmayer theory was used alongside other indices in order to probe the gelation and the post‐gelation characteristics of the critical gels and the fully formed hydrogels. Network relaxation exponents (n) were influenced by the concentrations of AA and methylene bis‐acrylamide. The gel stiffness (S) decreased with an increase in the concentration of the monomer and of the concentration of the crosslinker, while network branching decreased (lower fractal dimensions) at the gel point. The conversion at the gel point was found to be iso‐conversion with respect to the intensity of the UV irradiance used in the photocrosslinking reactions (1–20 mW/cm2). Thus, network clusters and the crosslinking reaction mechanism were the same irrespective of radiation intensity, although the rates of the reactions were affected. Having sufficient amounts of reactive species at the time of cure drive the crosslinking reactions beyond the gel point to greater crosslink density and smaller mesh sizes. The effects of auto‐acceleration and free‐volume were observed and shown to have key effects on the gelation mechanisms and the branching topographies of the network, when the concentration of the known polyacrylamide medium were not controlled. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018, 135, 46691.

Application of Molecular Mass Spectrometry for The Structural Characterization of a DNA-Protein Cross-Links

<p>To date, many different analytical methods have been used to investigate the cross-linking reaction mechanism and to obtain the chemical structure of DNA-Protein Cross-links (DPCs). Direct MS analysis of DPCs is challenging because of the ionization properties of DNA and the protein. However, peptide sequencing and mass spectrometry (MS) as analytical techniques are playing increasingly important roles for the structure determination of DPCs model. In our previous study, a novel approach was presented for purification, detection and quantification of DPCs by newly developed inductively coupled plasma mass spectrometry (ICPMS/MS), which allows sub-ppb detection of S and P, key heteroelements in DNA and proteins.</p><p>In this study, we enhanced our previously developed method and it was complemented by the use of molecular MS to allow complete characterization of a DNA-protein cross-link. First, a small molecule model is utilized to identify the adduct structure that will likely occur in an intact DNA-protein cross-link. We investigate the thermal stability of DNA-protein cross-links, both in an intact DPC and a small molecule adduct to determine feasibility of digestion/thermal degradationof DNA without the cross-link information being lost. Thermal degradation was conducted to reduce the cross-linked DNA into a single nucleoside. The remaining protein-nucleoside adduct then was proteolytically digested, generating a peptide-nucleoside adduct. The absence of the phosphate moiety allows for facile structural characterization <em>via</em> electrospray ionization mass spectrometry (ESI-MS). Additional calculations were done for peptide matching allowing us to determine the cross-link location in the protein, made possible <em>via</em> MS/MS analysis. Additionally, we show that steric effects play an important role in DPC formation.</p>