Theoretical study on the grafting reaction of maleimide containing 2-hydroxy-benzophenone onto polyethylene.

A theoretical study on the multi-channel hydrogen addition of maleimide containing 2-hydroxy-benzophenone onto polyethylene in ultra-violet (UV) radiation cross-linking process was carried out using density functional theory (DFT) method at the B3LYP/6-311 + G(d,p) level. The energetic information and the minimum energy path (MEP) are calculated for nine reaction channels. The electrophilic addition reactions at two positions in the target molecule (maleimide containing 2-hydroxy-benzophenone) were investigated, which are on the C atom of C = C groups and on the O atom of C = O groups. Frontier molecular orbitals (MOs) and natural bond orbital (NBO) charge population of the target molecule have been analyzed in detail. As a result, the reaction site of C in C = C group is more active than the site of O in C = O groups. The target molecule can be used as a multi-functional additive candidate. The predicted mechanism may provide a theoretical basis for the real application of cross-linked polyethylene (XLPE) high-voltage insulation cables.

Theoretical study on the hydrogen addition reactions to bismaleimide in the ultra-violet radiation cross-linking process of polyethylene.

Theoretical investigation on the multiple-channel addition reactions of hydrogen in polyethylene to bismaleimide in the Ultra-violet (UV) radiation cross-linking process is accomplished by density functional theory. Their energetic information of the nineteen reaction channels at B3LYP/6-311 + G(d,p) level is obtained. Two types of electrophilic addition reaction, one is the 4-position hydrogen in 4-methylheptane to C of C=C groups in bismaleimide and the other one is the 4-position hydrogen in 4-methylheptane to O of C=O groups in bismaleimide, are identified. The effects of introducing the heteroatom O and/or the benzene ring among both ends of the two maleimide rings have been evaluated. The results show that the addition reaction potential barrier height to O in C=O groups is lower than that of the C in C=C groups in the conjugative bismaleimide system.The founding of the addition reaction channel to O in C=O groups could clear further the mechanism of grafting bismaleimide to polyethylene.

Further discussion on the reaction behaviour of triallyl isocyanurate in the UV radiation cross-linking process of polyethylene: a theoretical study.

Further theoretical investigation on the reaction behaviour of triallyl isocyanurate (TAIC) in the UV radiation cross-linking process of polyethylene (PE) is accomplished by density functional theory for high voltage cable insulation materials. The reaction potential energy information of the 13 reaction channels at B3LYP/6-311 + G(d,p) level are identified. These have been explored that the TAIC take part in the reaction behaviour on ground state during UV radiation cross-linking process and TAIC intra-molecular isomerization reaction itself. In addition, the results show that the effect of multiplication and acceleration for the cross-linking reaction of trimethylopropane trimethacrylate (TMPTMA) would be better than that of TAIC. It has further clarified the reasons why UV radiation cross-linking reaction of PE had been initiated by benzophenone (Bp), and the TAIC or TMPTMA needed to take part. The results obtained in the present study could directly guide both the optimization of UV radiation cross-linking PE process and the development of the insulation material of high-voltage cable in real application.

The role of inserted polymers in polymeric insulation materials: insights from QM/MD simulations.

In this study, we performed a quantum chemical molecular dynamics (QM/MD) simulation to investigate the space charge accumulation process in copolymers of polyethylene (PE) with ethylene acrylic acid (EAA), ethylene vinyl acetate (EVA), styrene-ethylene-butadiene-styrene (SEBS), and black carbon (BC). We predicted that BC, especially branched BC, would possess the highest electron affinity and is identified as the most promising filler in power cable insulation. Following incorporations of 0-4 high-energy electrons into the composites, branched BC exhibited the highest stability and almost all electrons were trapped by it. Therefore, PE was protected efficiently and BC can be considered as an efficient filler for high voltage cables and an inhibitor of tree formation. On the contrary, although EAA, EVA, and SEBS can trap high-energy electrons, the latter can be supersaturated in composites of EAA, EVA, and SEBS with PE. The inserted polymers was unavoidably destroyed following C-H and C-O bond cleavage, which results from the interactions and charge transfer between PE and inserted polymers. The content effects of -COOH, benzene, and -OCOCH3 groups on the electron trapping, mobility and stability of PE were also investigated systematically. We hope this knowledge gained from this work will be helpful in understanding the role of inserted polymers and the growth mechanisms of electrical treeing in high voltage cable insulation.

A density functional theory study of the role of functionalized graphene particles as effective additives in power cable insulation.

The role of a series of functionalized graphene additives in power cable insulation in suppressing the growth of electrical treeing and preventing the degradation of the polymer matrix has been investigated by density functional theory calculations. Bader charge analysis indicates that pristine, doped or defect graphene could effectively capture hot electrons to block their attack on cross-linked polyethylene (XLPE) because of the π-π conjugated unsaturated structures. Further exploration of the electronic properties in the interfacial region between the additives and XLPE shows that N-doped single-vacancy graphene, graphene oxide and B-, N-, Si- or P-doped graphene oxide have relatively strong physical interaction with XLPE to restrict its mobility and rather weak chemical activity to prevent the cleavage of the C-H or C-C bond, suggesting that they are all potential candidates as effective additives. The understanding of the features of functionalized graphene additives in trapping electrons and interfacial interaction will assist in the screening of promising additives as voltage stabilizers in power cables.

Theoretical Study on the Grafting Reaction of Maleimide to Polyethylene in the UV Radiation Cross-Linking Process.

Theoretical investigation of the reaction of graft maleimide to polyethylene in the UV radiation cross-linking process is accomplished at the B3LYP/6-311+G(d,p) level for high-voltage cable insulation materials. The reaction potential energy surface of the nine reaction channels is identified. The results show that the N,N'-ethylenedimaleimide can connect two 4-methylheptane molecules and act as the cross-linking agent. The calculated reaction potential barrier of forming 4-methylheptane radical by maleimide is higher than that of maleic anhydride. The study is expected to provide a basis for optimizing the UV radiation cross-linking polyethylene process and development more than 500 kV high-voltage cable insulation materials in practical applications.

Doping Effect of Graphene Nanoplatelets on Electrical Insulation Properties of Polyethylene: From Macroscopic to Molecular Scale.

The doping effect of graphene nanoplatelets (GNPs) on electrical insulation properties of polyethylene (PE) was studied by combining experimental and theoretical methods. The electric conduction properties and trap characteristics were tested for pure PE and PE/GNPs composites by using a direct measurement method and a thermal stimulated current (TSC) method. It was found that doping smaller GNPs is more beneficial to decrease the conductivity of PE/GNPs. The PE/GNPs composite with smaller size GNPs mainly introduces deep energy traps, while with increasing GNPs size, besides deep energy traps, shallow energy traps are also introduced. These results were also confirmed by density functional theory (DFT) and the non-equilibrium Green's function (NEGF) method calculations. Therefore, doping small size GNPs is favorable for trapping charge carriers and enhancing insulation ability, which is suggested as an effective strategy in exploring powerful insulation materials.

Theoretical study on the mechanisms of polyethylene electrical breakdown strength increment by the addition of voltage stabilizers.

A theoretical investigation on the mechanisms of electrical breakdown strength increment of polyethylene at the atomic and molecular levels is accomplished. The addition of aromatic carbonyl and carboxyl compounds as voltage stabilizers may increase the electrical breakdown strength of polyethylene. The HOMO-LUMO energy gaps, the ionization potentials, the electron affinities, and the reorganization energies at the ground states of a series of aromatic carbonyl and carboxyl compounds are obtained at the B3LYP/6-311+G(d,p) level. The 24 isomerization reactions at the S0 and T1 states, including the harmonic vibration frequencies of the equilibrium geometries and the minimum energy path (MEP) by the intrinsic reaction coordinate (IRC) theory, are obtained at the same level. The results show that 4,4'-didodecyloxybenzil (Bd) molecule, which has much smaller HOMO-LUMO energy gap, much larger reorganization energy than others, and excellent compatibility with polymers matrix, can increase the electrical breakdown strength effectively. This result is in good agreement with the available experimental findings.

Mechanisms on electrical breakdown strength increment of polyethylene by aromatic carbonyl compounds addition: a theoretical study.

A theoretical investigation is accomplished on the mechanisms of electrical breakdown strength increment of polyethylene at the atomic and molecular levels. It is found that the addition of aromatic carbonyl compounds as voltage stabilizers is one of the important factors for increasing electrical breakdown strength of polyethylene, as the additives can trap hot electrons, obtain energy of hot electrons, and transform the aliphatic cation to relatively stable aromatic cation to prevent the degradation of the polyethylene matrix. The HOMO-LUMO energy gaps (E(g)), the ionization potentials (IPs), and electron affinities (EAs) at the ground states of a series of aromatic carbonyl compounds are obtained at the B3LYP/6-311+G(d,p) level. The theoretical results are in good agreement with the available experimental findings, show that 2,4-dioctyloxybenzophenone (Bzo) and 4,4'-didodecyloxybenzil (Bd) molecules can effectively increase the electrical breakdown strength when they are doped into polyethylene because of their much smaller E g values than all the other studied aromatic carbonyl molecules and excellent compatibility with polymers matrix.

Mechanisms on electrical breakdown strength increment of polyethylene by acetophenone and its analogues addition: a theoretical study.

A theoretical investigation is completed on the mechanism of electrical breakdown strength increment of polyethylene. It is shown that it is one of the most important factors for increasing electrical breakdown strength of polyethylene through keto-enol isomerization of acetophenone and its analogues at the ground state S0 and the lowest triplet state T1. The minimum structures and transition states of the keto- and the enol-tautomer of acetophenone and its analogues at the S0 and T1 states are obtained at the B3LYP/6-311+G(d,p) level, as well as the harmonic vibration frequencies of the equilibrium geometries and the minimum energy path (MEP) by the intrinsic reaction coordinate (IRC) theory at the same level. The two C-C bond cleavage reaction channels have been identified in acetophenone. The calculated results show that the energy barriers of keto-enol isomerization of acetophenone and its analogues at S0 and T1 states are much smaller than the average C-C bond energy of polyethylene, and the acetophenone doping or bond linked into polyethylene can increase the electrical breakdown strength and inhibit polyethylene electrical tree initiation and aging.

Mechanisms on inhibition of polyethylene electrical tree aging: a theoretical study.

A theoretical investigation is completed on inhibition mechanism of polyethylene electrical tree aging. Foremost it elucidates that it is one of the important factors for inhibiting initiation and propagation of polyethylene electrical tree through keto-enol tautomerism of acetophenone and its analogues. Geometries of the keto tautomer and the enol tautomer of acetophenone and its analogues, and its transition states are optimized at the B3LYP/6-311+G(d,p) level, the harmonic vibration frequencies of the equilibrium geometries are calculated at the same level. The minimum energy path (MEP) is obtained by the intrinsic reaction coordinate (IRC) theory at the same level. The calculated results show that the energy barriers of keto-enol tautomerism of acetophenone and its analogues are smaller than the average C-C bond energy of polyethylene, the acetophenone and its analogues adulterated in polyethylene composites can improve the strength of alternate current puncture that PE can endure as well as inhibit polyethylene electrical tree from initiation and propagation.

Modification of antimicrobial peptide with low molar mass poly(ethylene glycol).

PEGylation of peptide drugs prolongs their circulating lifetimes in plasma. However, PEGylation can produce a decrease in the in vitro bioactivity. Longer poly(ethylene glycol) (PEG) chains are favourable for circulating lifetimes but unfavourable for in vitro bioactivities. In order to circumvent the conflicting effects of PEG length, a hydrophobic peptide, using an antimicrobial peptide as a model, was PEGylated with short PEG chains. The PEGylated peptides self-assembled in aqueous solution into micelles with PEG shell and peptide core. In these micelles, the core peptides were protected by the shell, thus reducing proteolytic degradation. Meanwhile, most of the in vitro antimicrobial activities still remained due to the short PEG chain attached. The stabilities of the PEGylated peptides were much higher than that of the unPEGylated peptides in the presence of chymotrypsin and serum. The antimicrobial activities of the PEGylated peptides in the presence of serum, an ex vivo assay, were much higher than that of the unPEGylated peptide.