Difunctional Epoxy Research Articles

Regulating Cationic Polymerization of Difunctional Epoxy Resin through Structural Variations of the Thermal Initiator

Regulating Cationic Polymerization of Difunctional Epoxy Resin through Structural Variations of the Thermal Initiator

Synthesis of Hybrid Epoxy Methacrylate Resin Based on Diglycidyl Ethers and Coatings Preparation via Cationic and Free-Radical Photopolymerization

A series of difunctional epoxy methacrylate resins (EAs) containing at least one epoxy and at least one methacrylate group were synthesized by means of an addition reaction between epoxy-terminated diglycidyl ethers and methacrylic acid. In order to investigate the impact of polymer architecture on the course of addition reactions and further coating properties, several different types of diglycidyl ethers, i.e., linear, containing aliphatic or aromatic rings, with a short or polymeric backbone, were employed in the synthesis. The carboxyl-epoxide addition esterification reactions have been found to, in a relatively straightforward manner, control the extent of acrylation depending on the substrate feed ratio and reaction time. The structure of obtained pre-polymers was evaluated by FT-IR and NMR methods. At the same time, the extent of addition reactions was validated via quantitative analysis, including non-volatile matter content (NV), acid value (PAVs), and epoxy equivalent value (EE) analysis. The modification was carried out in a manner likely to create a compound with one epoxy and one carbon-carbon pendant group. Hence, due to the presence of both functionalities, it is possible to crosslink compositions based on synthesized EAs via two distinct mechanisms: (i) cationic polymerization or (ii) free-radical polymerization. Synthesized epoxy methacrylate pre-polymers were further employed for use in formulate photocurable coating compositions by the cationic or radical process. Furthermore, the photopolymerization behavior and properties of cured coatings were explored regarding some structural factors and parameters. The investigated polymeric materials cure in a short time to obtain coatings with good properties, which is why they can be successfully used to produce protective and decorative coatings for many industries.

Synthesis of a bio-based and intrinsically anti-flammable epoxy thermoset and the application of its carbonized foam as an efficient CO2 capture adsorbent

The production of multifunctional carbon foams from biomass has attracted great interest due to the increasing awareness of green and sustainable development. Here, we report a bio-based epoxy thermoset prepared by curing a furan-derived di-functional epoxy monomer (5-hydroxymethyl-2-furaldehyde (HMF)-3, 5-diamino-1,2,4-triazole (GU)-EP) with a furan-derived curing agent, 5,5′-methylenedifurfurylamine (DFA). For comparison, the cured commercial diglycidyl ether of bisphenol-A was used as a thermoset epoxy resin. Due to its unique structure rich in aromatic and nitrogenous structures, the cured HMF-GU-EP/DFA thermoset possessed exceptional charring ability. This fully bio-based epoxy thermoset had a very high char yield (55.8 wt%) at 800 °C under nitrogen, while the cured diglycidyl ether of bisphenol-A/4, 4′-diaminodiphenylmethane was only 13.6 wt%. Due to this excellent carbonization ability, the cured HMF-GU-EP/DFA was carbonized at 700 °C to obtain a carbon foam as a CO2 absorbent. The Brunauer–Emmett–Teller surface area and total pore volume were measured to be 472 m2/g and 0.22 cm3/g, respectively. The amounts of CO2 adsorbed with this carbon foam were 4.72 and 2.15 mmol/g at 273 and 298 K, respectively. In conclusion, this study provides a bio-based, strong and rigid, inherently flammable, and highly carbonizable epoxy thermoset and the potential application of its carbonized foam as an efficient adsorbent for CO2 capture.

Preparation and characterization of a low viscosity epoxy resin derived from m-divinylbenzene

To explore thermal and mechanical properties of epoxy material, difunctional aromatic epoxy--divinylbenzene dioxide (DVBDO) had been synthesized by epoxidizing divinylbenzene, using the metal acetylacetone compound grafted Fe3O4 particles as the catalyst. The catalyet had high conversion and epoxy selectivity and could be recyclable. Then the polymerization of DVBDO with different diamine curing agents were reported. The structure and viscosity of DVBDO were firstly characterized. Because it had low molecular weight and viscosity, DVBDO had excellent liquidity and formability. Subsequently to clarify the properties of epoxy thermosets, experiments to determine thermal and mechanical performances were carried out, such as differential scanning calorimetry (DSC), thermal gravimetric (TGA), dynamic mechanical analysis (DMA) and tensile test. It could be observed that the thermoset polymers using DVBDO as epoxy matrix had excellent thermal (Tg was about 201°C) and mechanical properties (tensile strength was 131.99Mpa). Possibly considering that this kind of thermoset polymers had higher rigidity and crosslink density. In conclusion, a new type of one-component liquid epoxy encapsulant material with low viscosity, good filling fluidity, strong heat resistance and excellent storage performance had been developed.

Determination of the formulation and curing conditions of thermosetting epoxy resins for optimizing their properties and future use in gelcasting process

AbstractThis work investigates the suitability of epoxy resins for possible use in an industrial gelcasting process. Two different formulations are studied using complementary experimental techniques. Both reactive formulations are based on a difunctional epoxy prepolymer (aliphatic BDGE or aromatic RDGE) mixed with a polyamine hardener (TEPA). The combination of analytical chemistry (NMR and FTIR spectroscopy) and calorimetric measurements (DSC) are used to determine the optimal epoxy/amine ratio for each reactive formulation. The gelation and vitrification times are investigated by dynamic rheometry through kinetic analyses over a large range of fixed temperature. It is found that the RDGE‐TEPA mixture is more reactive than BDGE‐TEPA with shorter curing starting times. The thermomechanical analyses performed on both optimized formulations show that the RDGE‐TEPA material presents better performances after curing (Tg close to 80°C) than the BDGE‐TEPA system (Tg lower than ambient temperature). Then, the effects of the cooling cycle on the thermomechanical profile of each polymer are investigated. The RDGE‐TEPA formulation is found to be much more subject to the formation of internal stresses created during the cross‐linking and cooling step than the BDGE‐TEPA material. Considering all these criteria, the BDGE‐TEPA system is ultimately more suitable for the gelcasting process than RDGE‐TEPA.

Thermal, mechanical, and electrical properties of difunctional and trifunctional epoxy blends with nanoporous materials

In the present study, the aim is to synthesize the particulate nanocomposites with difunctional and trifunctional epoxy blend as matrix and synthesized nanoporous materials as fillers. Organic/inorganic hybrid networks were prepared by the novel solvent free method. Viscoelastic, thermal, and electrical properties of di- and trifunctional epoxy and the effect of different nanoparticles in the particulate nanocomposites have been studied by dynamic mechanical analyzer, thermogravimetry (TGA), and dielectric strength. Epoxy mixed with different compositions of TGPAP and particulate nanocomposites by the addition of different types of nanomaterials shows higher storage modulus than the pure epoxy. The addition of TGPAP and nanofillers decreases the thermal stability of epoxy matrix. The evolved gas analysis (TG-FTIR) was also done in order to study the products formed during degradation. An increase in dielectric strength and impact strength (4%) was also observed in the particulate nanocomposites.

Highly thermally stable copolymers of epoxy and trifunctional polybenzoxazine

In this work, we report the copolymerization of a triamine-based benzoxazine and a commercial difunctional epoxy resin, and investigate their synergistic effect on improved thermal properties using differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). Results showed that a glass transition temperature increase of up to 268 °C was obtained for the copolymer with as low as 25 wt% epoxy. A higher thermal performance was also achieved with an onset degradation of nearly 400 °C and char yield of 39 wt% at 800 °C for the copolymer with 52 wt% epoxy. The behavior was compared to previously reported benzoxazine/epoxy combinations and was found to be advantageous. The curing behavior of different copolymer compositions was also investigated via DSC and a methodology for matching each peak with its corresponding reaction was developed. Results showed that the alternating favorability of the reactions was dependent on the benzoxazine/epoxy ratio. Overall, the prepared PBZ/epoxy copolymers displayed higher thermal stability than their individual components, indicating suitability for a number of potential extended uses including utility in higher temperature applications.

Benzoxazine Copolymers with Mono- and Difunctional Epoxy Active Diluents with Enhanced Tackiness and Reduced Viscosity

The influence of epoxy active diluents, 1,4-butanediol diglycidyl ether (BD) and furfuryl glycidyl ether (FUR), in the mixtures with benzoxazine monomer based on bisphenol A, formaldehyde and m-toluidine (BA-mt), on the properties of a matrix was disclosed in this work. Resins were modified to achieve good tackiness at room temperature and reduced viscosity. The influence of mono- and difunctional modifiers on the process of curing was studied by way of differential scanning calorimetry and oscillatory rheology. The addition of BD and FUR shifted the curing peak to higher temperatures and significantly reduced viscosity. Preferable tackiness at ambient temperature was achieved with 10 phr of epoxy components in mixtures. However, cured blends with difunctional epoxy BD had an advantage over monofunctional FUR in enhanced tensile strength with remaining glass transition temperature at the level of neat benzoxazine (217 °C).

Wetting Simulations of High-Performance Polymer Resins on Carbon Surfaces as a Function of Temperature Using Molecular Dynamics.

Resin/reinforcement wetting is a key parameter in the manufacturing of carbon nanotube (CNT)-based composite materials. Determining the contact angle between combinations of liquid resin and reinforcement surfaces is a common method for quantifying wettability. As experimental measurement of contact angle can be difficult when screening multiple high-performance resins with CNT materials such as CNT bundles or yarns, computational approaches are necessary to facilitate CNT composite material design. A molecular dynamics simulation method is developed to predict the contact angle of high-performance polymer resins on CNT surfaces dominated by aromatic carbon, aliphatic carbon, or a mixture thereof (amorphous carbon). Several resin systems are simulated and compared. The results indicate that the monomer chain length, chemical groups on the monomer, and simulation temperature have a significant impact on the predicted contact angle values on the CNT surface. Difunctional epoxy and cyanate ester resins show the overall highest levels of wettability, regardless of the aromatic/aliphatic nature of the CNT material surface. Tetrafunctional epoxy demonstrates excellent wettability on aliphatic-dominated surfaces at elevated temperatures. Bismaleimide and benzoxazine resins show intermediate levels of wetting, while typical molecular weights of polyether ether ketone demonstrate poor wetting on the CNT surfaces.

Trans‐limonenedioxide, a promisingbio‐basedepoxy monomer

AbstractVast quantities of the natural terpene (R)‐limonene can be collected from food waste. Epoxidation of its two double bonds provides limonene dioxide (LDO), a difunctional epoxy monomer. However, LDO is a mixture of four isomers, two of which (trans‐LDO) are actually difunctional while the others (cis‐LDO) have one epoxide group which is significantly less reactive, as revealed by Fourier transformed infrared spectroscopic analysis of formulations cross‐linked with polyethylene imine. These results are also confirmed when preparing epoxy formulations using respectivelycisortransisomers. From DFT calculations, the reactivity of each epoxide group of LDO has been assessed in model reactions with primary and secondary amines, in the presence of amine or alcohol hydrogen‐bond donors. The kinetics of cross‐linking has also been probed by differential scanning calorimetry. As measured by dynamic mechanical analysis, the resulting epoxy resins based ontransisomers have a storage modulus ofca1GPa at room temperature and a glass transition temperature (Tg) of 70°C. These results demonstrate thattransLDO is a promising bio‐based epoxy monomer, which could be used as an alternative to petroleum‐based epoxy monomers.

Enhancing the loading and swelling capacity of cellulose crystal through difunctional and multifunctional epoxy crosslinkers and the effects on the elasticity and plasticity: A computational study

Cellulose is known to have wide industrial applications because of its natural abundance and possibility of enhancing its physical properties through modification with crosslinkers. This study considers the impacts of the difunctional long chain and multifunctional epoxy crosslinkers. Strong agreement was observed between the computed and experimental properties which include low porosity, higher network, compactness and elasticity of multifunctional over the difunctional long-chain epoxy modified cellulose (called hydrogels). These consequentially affect the dynamic fluctuation of cellulose, plasticity, glass temperature, viscosity and conductivity. Hydrogels that were experimentally found to have higher porosity, swelling and loading ability were also observed to have stronger water interaction and gas absorption. The multivariance analysis and partial least squares (PLS) established a good relationship between the experimental and computational results. The general order of gases diffusion through the hydrogels is N2 > CH4 > O2 > CO2 with some slight variation in the specific hydrogels.

Viscoelastic characterization of polymers for deployable composite booms

Deployable space structures are being built from thin-walled fiber-reinforced polymer composite materials due to their high specific strength, high specific stiffness, and designed bistability. However, the inherent viscoelastic behavior of the resin matrix can cause dimensional instability when the composite is stored under strain. The extended time of stowage between assembly and deployment in space can result in performance degradation and in the worst case, mission failure. In this study, the viscoelastic properties of candidate commercial polymers consisting of difunctional and tetrafunctional epoxies and thermoplastic and thermosetting polyimides were evaluated for deployable boom structures of solar sails. Stress relaxation master curves of the candidate polymers were used to predict the relaxation that would occur in 1 year at room temperature under relatively low strains of about 0.1%. A bismaleimide (BMI) showed less stress relaxation (about 20%) than the baseline novolac epoxy (about 50%). Carbon fiber composites fabricated with the BMI resin showed a 44% improvement in resistance to relaxation compared to the baseline epoxy composite.

Influence of temperature and BN nanoparticles on UV, thermal and dark curing of a cycloaliphatic epoxy resin

The influence of boron nitride (BN) nanoparticles on cationic photopolymerization of an epoxy resin at different temperatures was investigated employing photo-DSC. A difunctional cycloaliphatic epoxy resin was polymerized in the presence of triarylsulfonium hexafluoroantimonate salts (cationic photoinitiator). BN-epoxy dispersions containing 5 mass% of BN were obtained by sonication. The epoxy conversion during UV irradiation was determined at seven temperatures, from 30 to 90 °C. The conversion reached was strongly dependent on temperature, and lower conversions were obtained in the presence of BN. After the UV curing, the samples were thermally postcured by dynamic heating in the DSC. The thermal postcuring shows two exothermal peaks, being the main one dependent on the temperature of the previous UV curing and on the composition. The total achieved conversion (65–77%) is lower for the samples containing BN compared to neat epoxy. The UV-irradiated samples at 40 °C reached conversions between 24 and 36%; afterward, they were kept under isothermal dark curing (40 °C) up to 1 month leading to significant conversion increases, independently of the composition and reaching a final conversion between 60 and 70%. DMTA measurements of dark-cured specimens evidence a heterogeneous epoxy matrix, thus needing higher postcuring temperatures to get homogeneity. The Tg of the epoxy matrix is reduced in the presence of BN nanoparticles.

Facile synthesis of bio-based phosphorus-containing epoxy resins with excellent flame resistance

The development of high-performance biomass-derived epoxy thermosets with excellent flame resistance is vital to various applications (i.e., composites, coatings and adhesives). Herein, a difunctional epoxy monomer bis(2-methoxy-4-(oxiran-2-ylmethyl)phenyl) phenyl phosphate (BEU-EP) was synthesized from abundant and biobased eugenol. In addition, BEU-EP was cured by 4,4′-diaminodiphenyl methane (DDM) and the cured resin diglycidyl ether of bisphenol A (DGEBA)/DDM was used as a reference. Results indicated that BEU-EP/DDM not only showed a 58.1%, 28.8% and 35.1% increase in residual char (at 700 °C), flexural and storage modulus (at 30 °C) compared with DGEBA/DDM, but also exhibited excellent flame resistance and smoke suppression. BEU-EP/DDM passed V-0 rating (in UL-94 testing) with limiting oxygen index (LOI) of 38.4% and greatly decreased the peak heat release rate (pHRR) and total smoke production (TSP) by 84.9% and 80.5%, respectively. The mechanism analysis confirmed that the phosphorus-containing group and aromatic structure from BEU-EP contributed both the gas and condensed-phase flame retardation of BEU-EP/DDM network. This work provides an efficient and scalable route for synthesizing biobased epoxy thermosets with high integrated performance and superior flame resistance.

Examining the influence of carboxylic anhydride structures on the reaction kinetics and processing characteristics of an epoxy resin for wind turbine applications

The cure of a low molecular weight (approximate EEW = 184 g/mol), difunctional epoxy resin based on bisphenol A has been studied in the presence of three carboxylic anhydrides: 3- or 4-methyl-1,2,3,6-tetrahydrophthalic anhydride, 3- or 4-methyl-hexahydrophthalic anhydride, and methyl-3,6-endomethylene-1,2,3,6-tetrahydrophthalic anhydride, and a tertiary amine (Ancamine K54). The formulated blends display complex viscosities ranging from 36 to 58 mPa.s and at 75 °C, the blends take between 56 and 73 min to reach gelation, with the highest viscosity and longest gel time observed for the blend containing methyl-3,6-endomethylene-1,2,3,6-tetrahydrophthalic anhydride. Rate constants of 6.8 to 14 s−1 at 75 °C and activation energies of 69 to 78 kJ/mol are determined using dynamic differential scanning calorimetry. Glass transition temperatures for the cured blends are similar, at 100 °C, with conversions of 83 to 89% observed. The cured blend containing methyl-3,6-endomethylene-1,2,3,6-tetrahydrophthalic anhydride displays the poorest thermal stability in terms of the onset of degradation, while yielding the highest char yield of the blends studied.

On the use of benzaldehyde to improve the storage stability of one-pot, epoxy ionic liquid formulations

A series of adducts were prepared based on the reaction of 1-ethyl-3-methylimidazolium acetate and benzaldehyde in various stoichiometries (from equimolar reaction to benzaldehyde in 10-fold excess) and the resulting adducts were characterized using nuclear magnetic resonance spectroscopy (1H, 13C, DEPT, and HQSC experiments). Differential scanning calorimetry was used to examine the initiating behaviour of the adducts towards mono- and di-functional epoxy resins and the data were used to determine kinetic parameters for the polymerization. The lower temperature peak, due to carbene formation, is sensitive to adduct concentration; the residual ionic liquid in the adduct mixture contributes towards the initiation of the curing reaction. When a monofunctional epoxy and the 1:1 adduct was subjected to a 2-week period of storage at room temperature and sub-zero temperatures in the freezer, the profiles of the thermograms for the frozen samples do not change considerably over the storage period and the formulation retains a light yellow colour (rather than the viscous, dark red appearance of the formulation stored at room temperature).

Polyether Sulfone-Based Epoxy Toughening: From Micro- to Nano-Phase Separation via PES End-Chain Modification and Process Engineering.

The toughness of a high-performance thermosetting epoxy network can be greatly improved by generating polyether sulfone−based macro- to nano-scale morphologies. Two polyethersulfones (PES) which only differ by their chain-end nature have been successively investigated as potential tougheners of a high-Tg thermoset matrix based on a mixture of trifunctional and difunctional aromatic epoxies and an aromatic diamine. For a given PES content, morphologies and toughness of the resulting matrices have been tuned by changing curing conditions and put into perspective with PES chain-end nature.

Modelling the properties of a difunctional epoxy resin cured with aromatic diamine isomers

Group Interaction Modelling has been extended to predict a range of thermo-mechanical properties of diglycidyl ether of bisphenol A cured with two isomers of diaminodiphenyl sulphone. The meta-meta and para-para positions of the substituents on the phenylene rings in the curing agent cause differences in packing efficiency, reaction kinetics and conformational freedom. Experimental data in the form of dynamic mechanical, static mechanical and density measurements are acquired in order to provide validation for the model. The model has proven capable of accurately reproducing the experimental measurements to well within experimental errors in most cases. Both the experimental measurements and model predictions have highlighted a number of subtle differences in behaviour of the resins cured with the two diamine isomers. In particular, variation of the amine/epoxy ratio has revealed how the secondary phase transitions of the resins are influenced. Variation of the glass and beta transitions in amine rich, stoichiometric or epoxy rich mixtures is described in terms of the molecular motions responsible for the transitions and the underlying network structural differences between the meta and para isomers.

Superhydrophobic/oleophobic coatings based on a catalyst driven thiol‐epoxy‐acrylate ternary system

ABSTRACTSuperhydrophobic surfaces have attracted much attention for their exceptional properties such as self‐cleaning, anti‐fouling, and anti‐fogging. This study presents a facile approach for creating superhydrophobic coatings that are also oleophobic by utilizing spray deposition of polymers mixed with silica particles as an easy and effective route to control the surface roughness of the coatings. The polymer precursors formulated here are based on a ternary thiol‐epoxy‐acrylate mixture that reacts in the presence of a strong base without a need for external initiation (such as light). This system employs tetrafunctional thiol monomers as hubs where both the acrylate and the epoxy components can covalently bond. The acrylate component contains a perfluorinated side chain offering low surface energy properties and the difunctional epoxy monomers crosslink the thiol hubs to provide strength. Addition of a strong base catalyst (1,8‐diazabicycloundec‐7‐ene, or DBU) to the coating precursors initiates the polymerization reaction without the need for light. To identify the optimal formulation, Fourier transformed infrared spectroscopy (FTIR) measurements quantified the kinetics of the polymerization, X‐ray photoemission spectroscopy analysis revealed the surface composition, an optical goniometer evaluated the wetting behavior, and scanning electron microscopy and confocal laser the microscopy provided information about the surface topography of the coatings. Based on the results from FTIR, addition of 0.08 mol % of DBU effectively carries out the reaction within 10 min on the substrate while providing long solution shelf life for the spray coating process. The goniometer results showed that water contact angle of >150°, n‐dodecane contact angle of >110° and diiodomethane contact angle of >130° is achievable upon optimization of the coating precursors. This simple route to create superhydrophobic and oleophobic coatings by spraying may be useful for packaging, protective coatings, and other surface modifications. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018, 135, 46710.

Preparation of self-healing, recyclable epoxy resins and low-electrical resistance composites based on double-disulfide bond exchange

Vitrimers have been emerged as a new class of polymers with many attractive properties of material processing such as reshaping, recycling and repairing. Herein, a new type of vitrimers (BDSER) based on thermosetting dynamic epoxy network with double disulfide bonds was synthesized by the reaction of a difunctional epoxy monomer containing disulfide bonds with 4,4′-disulfanediyldianiline (4-AFD). Our results demonstrated that the relaxation time of BDSER at 200 °C was as short as 9 s without any catalyst. The storage modulus of BDSER was up to about 2.2 GPa and its glass transition temperature was higher than 130 °C. Additionally, the thermodynamic and chemical properties of BDSER were no significant loss after 3 cycles of continuous breaking/compression molding. Furthermore, the resistance of CNT/PPy/Vitrimer composites (CPV), synthesized by doped BDSER with the polypyrrole (PPy) decorated multi-walled carbon nanotubes (WMCNTs), was decreased to 109 Ω even the mass ratio was only 1%wt, which could be used a promising candidate as self-repairing materials in the field of antistatic.