Establishing the relationship among the composition, structure and property of the associated materials at the molecular level is of great significance to the rational design of high-performance electrical insulating Epoxy Resin (EP) and its composites. In this paper, the molecular models of pure Diglycidyl Ether of Bisphenol A resin/Methyltetrahydrophthalic Anhydride (DGEBA/MTHPA) and their nanocomposites containing nano-SiO 2 with different particle sizes were constructed. The effects of nano-SiO 2 dopants and the crosslinked structure on the micro-structure and thermomechanical properties were investigated using molecular dynamics simulations. The results show that the increase of crosslinking density enhances the thermal and mechanical properties of pure EP and EP nanocomposites. In addition, doping nano-SiO 2 particles into EP can effectively improve the properties, as well, and the effectiveness is closely related to the particle size of nano-SiO 2 . Moreover, the results indicate that the glass transition temperature (T g ) value increases with the decreasing particle size. Compared with pure EP, the T g value of the 6.5 Å composite model increases by 6.68%. On the contrary, the variation of the Coefficient of Thermal Expansion (CTE) in the glassy state demonstrates the opposite trend compared with T g . The CTE of the 10 Å composite model is the lowest, which is 7.70% less than that of pure EP. The mechanical properties first increase and then decrease with the decreasing particle size. Both the Young's modulus and shear modulus reach the maximum value at 7.6 Å, with noticeable increases by 12.60% and 8.72%, respectively compared to the pure EP. In addition, the thermal and mechanical properties are closely related to the Fraction of Free Volume (FFV) and Mean Squared Displacement (MSD). The crosslinking process and the nano-SiO 2 doping reduce the FFV and MSD value in the model, resulting in better thermal and mechanical properties.

Investigating the relationship between microstructure and macroscopic properties of epoxy resin (EP) materials for high-voltage insulation at the molecular level can provide theoretical guidance for the synthetic design of EP. Here, using diglycidyl ether (DGEBA) as the resin matrix and methyl tetrahydrophthalic anhydride (MTHPA) as the curing agent, a set of crosslinked EP molecular models at different curing stages were constructed based on the proposed crosslinking method. We studied the influences of crosslinking density on micro-parameters and macro-properties employing molecular dynamics (MD) simulations. The results indicate that crosslinking of DGEBA/MTHPA is a contraction and exothermic process. The structural parameters and macroscopic properties are closely related to the degree of crosslinking. With the increase of crosslinking density, the mean square displacement (MSD) of the system decreases, and the segment motion in the models is weakened gradually, while, the fractional free volume (FFV) first decreases and then increases. In addition, the thermal and mechanical properties of DGEBA/MTHPA have a significant dependence on the crosslinking density. Increasing crosslinking density can improve the glass transition temperature (Tg), reduce the coefficient of thermal expansion (CTE), and enhances the static mechanical properties of DGEBA/MTHPA system. Furthermore, the relationship between microparameters and properties has been fully investigated. Free volume is an important factor that causes thermal expansion of DGEBA/MTHPA. Moreover, there is a negative correlation between MSD and mechanical moduli. By elevating temperature, the decline in mechanical moduli may be due to the exacerbated thermal motion of the molecules and the increasing MSD values.

An investigation of the relationship between the microstructure parameters and thermomechanical properties of epoxy resin can provide a scientific basis for the optimization of epoxy systems. In this paper, the thermomechanical properties of diglycidyl ether of bisphenol A (DGEBA)/methyl tetrahydrophthalic anhydride (MTHPA) and DGEBA/nadic anhydride (NA) were calculated and tested by the method of molecular dynamics (MD) simulation combined with experimental verification. The effects of anhydride curing agents on the thermomechanical properties of epoxy resin were investigated. The results of the simulation and experiment showed that the thermomechanical parameters (glass transition temperature (Tg) and Young’s modulus) of the DGEBA/NA system were higher than those of the DGEBA/MTHPA system. The simulation results had a good agreement with the experimental data, which verified the accuracy of the crosslinking model of epoxy resin cured with anhydride curing agents. The microstructure parameters of the anhydride-epoxy system were analyzed by MD simulation, including bond-length distribution, synergy rotational energy barrier, cohesive energy density (CED) and fraction free volume (FFV). The results indicated that the bond-length distribution of the MTHPA and NA was the same except for C–C bonds. Compared with the DGEBA/MTHPA system, the DGEBA/NA system had a higher synergy rotational energy barrier and CED, and lower FFV. It can be seen that the slight change of curing agent structure has a significant effect on the synergy rotational energy barrier, CED and FFV, thus affecting the Tg and modulus of the system.

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eye, exhibiting long lifetimes, large stokes shifts, and significant signal-to-noise ratio. [1] Among all the UOP materials, UOP polymers have advantages in terms of amorphous, flexibility, stretchability, and low cost are better candidates for future applications of bioimaging, information encryption, and foldable electronic devices. [2] Nevertheless, long-lived triplets can be easily quenched via intermolecular collision or energy transfer and thus make it difficult to achieve efficient polymeric UOP. [3] Generally, the presupposition of polymer matrix is considered as follows: (i) perfect oxygen and moisture resistance to reduce triplet excitons quenching, (ii) rigid microenvironment with rich intermolecular interactions to restrict the nonradiative pathways, (iii) high singlet and triplet energy levels to suppress the reversed energy transfer from emission center to matrix, and (iv) good mechanical strength for wide applications. [4,5] Regard to this, several linear polymers with abundant intraand intermolecular hydrogen bond are successfully used in fabrication of amorphous UOP by doping or grafting organic phosphors into the rigid matrix, such as polyvinyl alcohol, [6] poly(lactic acid), [7] polymethyl methacrylate, [8] and polyacrylamids. [9] However, hydrogen bond in such polymers is very sensitive to humidity and unfavorable for long-term stability in air. [10] Compared to these processible thermoplastics, polymeric UOP materials with covalent cross-linked bond which can supply stronger interactions between the molecular chains exhibit superior environmental resistance, higher quantum efficiently (Φ P ), and longer lifetime (τ) due to efficient suppression of excited-state vibrations in the rigid networks. [2,11] Unfortunately, cross-linked polymers are regularly defined as traditional thermosets that lack recyclability, reprocessing, and environmental friendly features. [1b] Besides, the full-wavelength range color tuning with good purity in cross-linked polymeric UOP is rarely demonstrated.In 2011, vitrimers which rely on reversible transesterifications in epoxy/acid and epoxy/anhydride polyester networks with dynamic bond exchange mechanism were developed by Leibler's group (Figure 1a and Figure S1, Supporting Information). [12] The exchangeable covalent bonds triggered above topology freezing transition temperature (T v ) enable covalent cross-linked thermosets with features such as self-healing, Polymeric materials displaying ultralong organic phosphorescence (UOP) have drawn much attention in the fields of optoelectronics, bioimaging, and information encryption. However, it is challenging to realize polymeric UOP materials with variable mechanical strength, self-healing, and superior processability. This work presents a low-cost strategy to achieve polymeric UOP with full-color-emission (doping vitrimers with different phosphorescent emitters) by introducing exchangeable covalent cross-linked bonds. These amorphous polymers show ultralong lifetimes up to 1.75 s under ambient conditions. Impress...