Molecular Structure Parameters Research Articles

Is the analysis of molecular electronic structure of corrosion inhibitors sufficient to predict the trend of their inhibition performance

The often used approach in the corrosion inhibition studies employing quantum chemical calculations that relies on the correlation between molecular electronic structure parameters and inhibition effectiveness is critically examined. It is shown that the inhibition performance of three selected triazole-based corrosion inhibitors for copper – 3-amino-1,2,4-triazole (ATA), benzotriazole (BTAH), and 1-hydroxybenzotriazole (BTAOH) – cannot be explained on this basis in a sound manner. As the effectiveness of inhibitors is due to several phenomena, the outcome depends on the interplay between them and although molecular electronic parameters may provide many necessary elements, the involved effects can be estimated only approximately which may not always suffice. This supports the proposition that in general molecular electronic properties cannot be directly related to inhibition effectiveness – the actual relation is more involved – thus emphasizing the importance of a rigorous modeling of the inhibitor–surface interaction in the corrosion inhibition studies.

Anharmonic vibrational spectroscopy and investigation of intramolecular mode couplings in adenine

Vibrational frequencies for the nucleobase adenine are calculated by the vibrational self-consistent field (VSCF) and correlation corrected vibrational self-consistent field (CC-VSCF) methods using Hartree–Fock (HF), density functional theory (DFT) and second order Møller–Plesset (MP2) theories. A large number of potential energy surface (PES) points were computed in the anharmonic calculations corresponding to each method. The quartic force field (QFF) approximation was used to generate the full grid of points for the VSCF solver. We have implemented our new procedure for computing the mode–mode coupling integrals in the 2-mode coupling representations of the quartic force field (2MR-QFF) for prediction of coupling magnitudes. Calculations were performed using the 6-31G(d,p) basis set. Comparison of the calculated ab initio anharmonic spectra with Ar matrix experimental data of adenine reported in the literature reveals that, the CC-VSCF (DFT) wavenumbers show the best agreement. The experimental geometric parameters of adenine are compared with the theoretically optimized molecular structural parameters. These are found to be in good agreement. Vibrational assignments are based on the calculated potential energy distribution (PED) values.

Estrogenic Activity of Anthraquinone Derivatives:In VitroandIn SilicoStudies

Comprehension of the ligand-receptor interactions is a prerequisite for constructing mechanism based quantitative structure-activity relationship (QSAR) models on xenoestrogenic activity. Molecular docking was performed to simulate the interactions between anthraquinone derivative (AQs) molecules and the estrogen receptor alpha (ERalpha). Hydrogen bonding, hydrophobic, and pi-pi interactions were found to be the dominant interactions between AQs and the receptor, which implied the estrogenic activities of the compounds. The recombinant yeast-based assay was employed to determine the estrogenic activities of 20 AQs. On the basis of the observed interactions between the AQs and ERalpha, appropriate molecular structural parameters were computed to develop a QSAR model. The polarizability term, the binding energy, the average molecular polarizability, the most negative formal charge in the molecule, and the average of the negative potentials on the molecular surface were significant parameters explaining the estrogenicity. The developed QSAR model had good robustness, predictive ability, and mechanism interpretability. The interactions between the AQs and ERalpha and the partition ability of the AQs into the biophase are main factors governing the estrogenic activities. Moreover, the applicability domain of the model was described.

Principal Component Analysis of HPLC Retention Data and Molecular Modeling Structural Parameters of Cardiovascular System Drugs in View of Their Pharmacological Activity

Evaluation of relationships between molecular modeling structural parameters and high-performance liquid chromatography (HPLC) retention data of 11 cardiovascular system drugs by principal component analysis (PCA) in relation to their pharmacological activity was performed. The six retention data parameters were determined on three different HPLC columns (Nucleosil C18 AB with octadecylsilica stationary phase, IAM PC C10/C3 with chemically bounded phosphatidylcholine, and Nucleosil 100-5 OH with chemically bounded propanodiole), and using isocratically acetonitrile: Britton-Robinson buffer as the mobile phase. Additionally, molecular modeling studies were performed with the use of HyperChem software and MM+ molecular mechanics with the semi-empirical AM1 method deriving 20 structural descriptors. Factor analysis obtained with the use of various sets of parameters: structural parameters, HPLC retention data, and all 26 considered parameters, led to the extraction of two main factors. The first principal component (factor 1) accounted for 44–57% of the variance in the data. The second principal component (factor 2) explained 29–33% of data variance. Moreover, the total data variance explained by the first two factors was at the level of 73–90%. More importantly, the PCA analysis of the HPLC retention data and structural parameters allows the segregation of circulatory system drugs according to their pharmacological (cardiovascular) properties as shown by the distribution of the individual drugs on the plane determined by the two principal components (factors 1 and 2).

Relationship of protein molecular structure to metabolisable proteins in different types of dried distillers grains with solubles: a novel approach

To date, there has been no study of protein molecular structures affected by bioethanol processing in relation to protein nutritive values of the new co-products of bioethanol production. The objective of the present study was to investigate the relationship between protein molecular structures (in terms of protein α-helix and β-sheet spectral intensity and their ratio and amide I to amide II spectral intensity and their ratio) and protein rumen degradation kinetics (rate and extent), estimated protein intestinal digestibility and total truly absorbed protein in small intestine (metabolisable protein) in different types of dried distillers grains with solubles (DDGS), such as wheat DDGS, maize DDGS and blend DDGS (wheat:maize = 70:30). The protein molecular structures of the different types of DDGS affected by processing were identified using diffuse reflectance IR Fourier transform spectroscopy. The results showed that the protein structure α-helix to β-sheet ratio in the DDGS had a strongly negative correlation with estimated intestinal digestibility of ruminally undegraded protein (%dRUP, R - 0.95, P = 0.04), tended to have a significant correlation with the protein PC subfraction (which was undegradable and contained proteins associated with lignin and tannins and heat-damaged proteins) (R 0.91, P = 0.09) and had no correlation (P>0.10) with rumen degradation kinetics (rate and extent), total intestinally absorbed protein supply and degraded protein balance. However, the protein amide I to amide II ratio in the DDGS had a strongly positive correlation with soluble crude protein (CP) (R 0.99, P < 0.01), protein PA subfraction (which was instantaneously solubilised at time zero) (R 0.99, P < 0.01), protein PB2 subfraction (which was intermediately degradable) (R - 0.95, P = 0.04) and total digestible CP (R 0.95, P = 0.04). The amide I to amide II ratio also had strongly negative correlations with ruminally undegraded protein (%RUP: R - 0.96, P = 0.03) and the degraded protein balance (OEB: R - 0.97, P = 0.02), but had no correlation (P>0.10) with the total intestinally absorbed protein supply. Multiple regression results show that the protein structure α-helix to β-sheet ratio was a better predictor of %dRUP with R² 0.92. The amide I to II ratio was a better predictor of the degraded protein balance with R² 0.93 in the DDGS. In conclusion, the changes in the protein molecular structure α-helix to β-sheet ratio and the amide I to amide II ratio during bioethanol processing (either due to fermentation processing or due to heat drying) were highly associated with estimated protein intestinal digestibility and degraded protein balance, but were not associated with total intestinally absorbed protein supply from the DDGS to dairy cattle. The present study indicates that a potential novel method could be developed based on the protein molecular structure parameters to improve the estimation of protein value after a validation in a large-scale in vivo study is done.

Linear vs Exponential Formation of Molecular-Based Assemblies

Here we present the critical role of the molecular structure and reaction parameters on the nature of thin-film growth, using a versatile two-step assembly method with organic and metal-organic chromophores cross-linked with palladium. It was found that the polypyridyl complexes exhibit exponential growth, whereas, under identical conditions, the organic systems exhibit linear behavior. The internal film morphology plays a pivotal role in the storage and usage of the palladium, where a more porous structure results in exponential growth. Interestingly, through proper tuning of the reaction conditions, the growth of the molecular assemblies can be controlled, resulting in a changeover from exponential to linear growth. These findings unequivocally demonstrate the importance of both the internal film structure and deposition conditions on the assembly of molecular-based films.

ChemInform Abstract: Liquid Crystals as Solvents in NMR Spectroscopy: Current Developments in Structure Determination

Nuclear Magnetic Resonance (NMR) spectroscopy of molecules aligned in liquid crystalline media provides information on molecular structure and order parameters. The partial alignment of the molecules in the anisotropic phase of the liquid crystals gives rise to residual intramolecular dipolar couplings which are dependent on the internuclear distances and therefore yield information on the geometry of molecules. The spectra of these aligned molecules become rapidly complex with the increase in the number of interacting spins and with decrease in the symmetry of the molecules. The spectra of these molecules are generally strongly coupled and are complex. Thus the first order analysis of the spectra as applicable to liquid state is generally not applicable and one should resort to numerical analysis using computers. In this report problems associated with the analyses of such complex spectra, methods developed to aid such analyses and the precision of the structural parameters derived are discussed. Use of mixed liquid crystals of opposite diamagnetic susceptibility anisotropies to extract information which is otherwise not possible to derive using single liquid crystals is highlighted. Current developments in the field with special emphasis on the discovery of a novel liquid crystal with low order parameter and the use of natural abundance deuterium NMR spectra of the probe molecules for the analyses of complex spectra are discussed.

The Localization Model of Rubber Elasticity

AbstractWhile the unusual elastic properties of rubbery polymer materials have been studied for literally centuries, a quantitative theoretical description of these properties in terms of molecular structural parameters remains a challenging task. Classical network elasticity theories are based on the concept of flexible volumeless network chains fixed into a network in which there are no excluded volume, or even topological, interactions between the chains and where the chains explore accessible configurations by Brownian motion. In this type of model, the elasticity of the deformed network derives from the entropic changes in this idealized network arising from a deformation of the network junction positions. The shortcoming of this approach is clear from the observation that unswollen rubbery materials are nearly incompressible, reflecting the existence of strong intermolecular interactions that restrict the polymer chains to an exploration of their local molecular environments. The imposition of a deformation of these solid rubbery materials then necessitates a consideration of how local molecular packing constraints become modified under deformation and the impact of these changes on the macroscopic elasticity of the material as a whole. Many researchers have struggled with this difficult problem, but we focus on the simple ‘localization model’ of rubber elasticity introduced by Gaylord and Douglas (GD), which provides an attractive and mathematically simple minimal model for the network elasticity of rubbers having strong intermolecular interactions in the dense polymer state. GD assume that the network chain segments are localized at the network junctions, as in classical elasticity theory, but they also consider the chains to be localized along their contours by a local harmonic potential arising from inter‐particle packing interactions, as in atoms in a simple harmonic crystal. This is the familiar Edwards‐De Gennes ‘tube’ model of polymers in the condensed state. The existence of the tube means that the entropy of the network chains is reduced relative to chains without this constraint, but the crucial problem is how this entropy change becomes modified as the material becomes deformed. GD approach this problem by first observing that both the volume of the material and the network chains are essentially invariant under deformation so they require that the dimensions of the confining tube to also be a deformation invariant where this constraint is applied at a segmental level. The properties of the resulting ‘localization model’ of elasticity of dry and swollen rubbers are summarized and some extensions of the model to describe chain finite extensibility and stiff polymer networks are briefly summarized.

Study on the structure and properties of SSBR with large-volume functional groups at the end of chains

Solution polymerized styrene-butadiene rubber (SSBR) and SSBR with tert-Butylchlorodiphenylsilane (TBCSi, large-volume functional groups) at the two ends of macromolecular chains (T-SSBR) were prepared by anionic polymerization. The molecular structure parameters of T-SSBR and SSBR were characterized and the ratio of the amount of macromolecular chain ends connected with TBCSi to total macromolecular chain ends (i.e., end-capping efficiency) was calculated. The comprehensive properties of T-SSBR and SSBR composites filled with carbon black (CB) were investigated. The results showed that T-SSBR composites presented lower Payne effect (namely better CB dispersion) than those of SSBR composites, which led to decrease in hardness, internal friction, dynamic compression heat built-up and permanent set of T-SSBR composites, significant increase in tensile strength, elongation at break, tear strength and resilience of T-SSBR composites, and excellent balance between wet-skid resistance and rolling resistance. However, compared with SSBR composites, T-SSBR composites presented longer stress-relaxation time, bigger die-swell and higher apparent viscosity, as well as slightly inferior dynamic-cutting resistance. All the above, owing to the end-capping of TBCSi, which could immobilize the free chain ends of T-SSBR (i.e., to reduce the friction loss of molecular chains and create a greater degree of orientation in the force field), and adsorb CB, the comprehensive performances of T-SSBR were better than those of SSBR and T-SSBR terminated with styrene-TBCSi (TS-SSBR) were far superior to those of T-SSBR terminated with butadiene-TBCSi (TB-SSBR). Accordingly, the former was suitable for the tread of green tires.

Retention indices and quantum-chemical descriptors of aromatic compounds on stationary phases with chemically bonded copper complexes

In this paper, Kováts retention indices determined on stationary phases with chemically bonded copper complexes were correlated with molecular structural parameters for aromatic compounds. Principal component regression (PCR) was applied to extract principal components from the set of 13 descriptors compiled in 5 theoretical models. Extracted components were used to model theoretical retention indices. Significant correlations were found among the retention indices of these compounds and, among others: molecular surface and molecule area, boiling point, HOMO and LUMO energies, dipole moment, dielectric energy, and double bond count. These correlations provide insights into the mechanism of chromatographic retention at the molecular level for the packings and the compounds under study.

Aromatization of Naphthenic Ring Structures and Relationships between Feed Composition and Coke Formation during Heavy Oil Carbonization

Selected characteristics and molecular structural parameters of a wide range of heavy oils originating from paraffinic, naphthenic, and intermediate crude oils were estimated, and carbonization was then performed in the form of delayed coking or the Conradson carbon residue (CCR) test to elucidate the aromatization fate of naphthenic ring structures and thus the feed composition, coke formation relationships during heavy oil carbonization. The results show that the heavy oils have very different characteristics such as density, viscosity, CCR content, asphaltene content, etc. Heavy oil may be rich in naphthenic ring structures found in molecules such as naphthenes of varying sizes; its aromaticity increases upon delayed coking, during which solid, liquid, and gaseous products are obtained. Further CCR tests of the heavy liquid products from delayed coking and the other heavy oils show that any single structural parameter such as aromaticity, aromatic ring size, or naphthenic ring size fail to account for coke product formation when heavy oils are carbonized under atmospheric pressure. However, the condensed ring (including aromatic and naphthenic) structures with no fewer than four rings fundamentally end in the coke product, showing essential aromatization and coke formation of the naphthenic structures. Because of the higher concentration of naphthenic structures, heavy oils from the naphthenic or intermediate crude oils tend to form more coke than those from the paraffinic ones.

Morphological characteristics of selenium-containing nanostructures based on rigid-chain molecules

Selenium-containing nanostructures of rigid-chain polymers with close molecular masses were studied by flow birefringence (FB) and static and dynamic light scattering at a fixed selenium to polymer mass ratio ν = 0.1 in solution. The group of polymers under study included the cationic polyelectrolyte poly-N,N,N,N-trimethylmethacryloyloxyethylammonium methyl sulfate, anionic polyelectrolyte carboxymethylcellulose, and nonionogen polymer oxyethylcellulose. High-molecular selenium-containing polymer nanostructures were found in all cases. Nanostructures with a maximum molecular mass and the largest number of constituent macromolecules were obtained using oxyethylcellulose. At ν = 0.1 the mean square radii of inertia of the nanostructures were almost independent of the nature of the polymer matrix. The thermodynamic state of the solutions of nanostructures was close to the ideal one in all cases. For the region where stable dispersions formed, the Gibbs energies of macromolecule-selenium nanoparticle interactions were calculated and shown to be almost independent of the nature of the polymer matrix at ν = 0.1. The close mean square radii of inertia Rg* of the nanostructures, the Gibbs energies of interaction, and the equivalence of the thermodynamic state of the solutions of nanostructures obtained for all polymer matrices at ν = 0.1 suggest that ν = 0.1 corresponds to the ultimate adsorption capacity of selenium nanoparticles; the considerable differences between the molecular masses (for close Rg* values), mean densities, and structural conformation parameters ρ* point to different packings of macromolecules in the nanostructures under study.

Young's Modulus and Degree of Conversion of Different Combination of Light-Cure Dental Resins

Objectives:To evaluate Young's modulus and degree of conversion of several combinations of bisGMA, UEDMA, TEGDMA light-cure dental resin.Methods:Young's modulus and DC% were studied for 21 different resin combinations of bisGMA, TEGDMA and UEDMA. Small universal testing machine and photo-calorimetry were used for the tests. The results were evaluated using ANOVA and Duncan's multiple range tests and regular t-test.Results:Young's modulus varied between 2.37±0.2 GPa (100% TEGDMA) and 4.15±0.2 GPa (100% bisGMA). By adding TEGDMA to bisGMA or UEDMA, the Young's modulus decreased significantly (p<0.05). Degree of conversion was significantly (p<0.05) higher when the wt% of TEGDMA was high in the mixtures than for highly concentrated bis-GMA (resin mixtures with TEGDMA in comparison to mixture with bisGMA had higher degree of conversion). DC% was significantly higher (p<0.05) for binary mixtures of UEDMA and TEGDMA, and significantly lower for 100 wt% bis-GMA (p<0.05). The DC% values were between 53.1%±0.9% (100% bisGMA) and 85.6%±1% (80% UEDMA-20% TEGDMA). The concentration of bisGMA, in the monomer mixture, affected DC% and Young's modulus oppositely.Conclusions: The differences in the values for DC% were mostly justified by the differences in the molecular structures of the different monomers. It was also revealed that higher DC% does not always result in a higher Young's modulus, because molecular and network structural parameters play major roles in the final physical properties of the mixtures.

Adsorption of difluoromethane on titanium dioxide: Investigation of the FTIR spectra and quantum-mechanical studies of the adsorbate–substrate structures

The interaction of difluoromethane (CH 2F 2) with the TiO 2 surface (P25 Degussa) at room temperature has been studied by Fourier-transform infrared spectroscopy for the first time. From the comparison between the adsorption characteristics and the gas-phase spectra it can be deduced that the molecule adsorbs through an acid–base interaction between one F atom and the surface Lewis acid site (Ti 4+) and an H-bond between the CH 2 group and the surface Lewis basic site (OH − or O 2−). In order to obtain more information about the orientation geometry and the variation of the molecular structural parameters, a quantum-mechanical investigation at DFT/B3LYP level has been also performed, considering the anatase (1 0 1) surface and focusing on the O 2− as Lewis basic site. The resulting adsorbate–substrate structures involve the formation of an acid–base interaction between one F atom and the Ti 4+ ion and differ for the number of the involved H-bonds. According to the scaled vibrational frequencies, the simulated adsorption model which better agrees with the experimental data corresponds to that in which the CH 2 group interacts with the surface by only one H-bond.

Bridging Theory with Experiment: A Benchmark Study of Thermally Averaged Structural and Effective Spectroscopic Parameters of the Water Molecule

Extending our previous study on the equilibrium structures of the major isotopologues of the water molecule (Csaszar et al. J. Chem. Phys. 2005, 122, 214305), temperature-dependent averaged structural parameters (for example, r(g)- and r(a)-type distances, their related root-mean-square amplitudes, and moments corresponding to the probability distribution functions of interatomic distances), effective rotational constants, and low-order vibration-rotation interaction constants have been determined for two major symmetric isotopologues of water, H(2)(16)O and D(2)(16)O. The nuclear motion treatments employed full quantum mechanical variational procedures which utilized the accurate adiabatic semiglobal PESs of water isotopologues named CVRQD (Barletta et al. J. Chem. Phys. 2006, 125, 204307). The temperature-dependent molecular structural parameters are based on expectation value computations and Boltzmann averaging in the temperature range 0-1500 K. The precise computed average internuclear, inverse internuclear, rms amplitude, and anharmonicity parameters could support a future gas electron diffraction (GED) investigation, though water isotopologues are far from being ideal species for GED analyses. Using a clearly defined and general formalism applicable to molecules of any size, we have evaluated vibrationally averaged effective rotational constants as expectation values using inertia tensor formulas in the Eckart frame for vibrational states of H(2)(16)O and D(2)(16)O. While such variationally determined rotational constants do not correspond strictly to constants resulting from fits performed by spectroscopists, the expected good agreement is found for the A and B rotational constants for both isotopologues. Low-order vibration-rotation interaction constants, the so-called alpha- and gamma-constants, have also been determined from the computed rotational constants; the latter were derived for the first time.

Directed mechanical motion in nonequilibrium nanosystems: Occurrence conditions and kinematic controllability

AbstractThe directed mechanical motion of nanoscale objects along a phase boundary can result from strongly nonequilibrium processes, which transfer the energy of various external sources to the system. This effect is particularly relevant in Brownian (molecular or biological) motors known for their high efficiency of chemical‐to‐kinetic energy conversion. Here, we formulate the necessary conditions for nanoparticle surface‐parallel motion to occur under the action of external nonequilibrium fluctuations of various nature; the ways to provide such conditions are also considered. As shown, the magnitude and sign of the average directed velocity are dictated by the competition between the spatial and temporal asymmetry of the potential energy. The theoretical models are exemplified by high‐efficiency Brownian nanoengines, molecular pumps, dipole rotators, and photo‐induced molecular motors. The latter serve to illustrate the kinematic controllability of motors by varying their molecular structure and photoexcitation parameters. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2010

Modeling photoinduced toxicity of PAHs based on DFT-calculated descriptors

Quantitative structure–activity relationships (QSARs) were established for photoinduced toxicity of polycyclic aromatic hydrocarbons (PAHs) to two aquatic species. Partial least squares (PLS) regression and molecular structural parameters calculated by density functional theory (DFT) were employed for model development. Two QSAR models were established and their high R 2 and Q CUM 2 values indicated their good goodness-of-fit, robustness and internal predictive power. The descriptors that describe the partition behavior, light absorbance, and generation of reactive free radicals were found to be successful in modeling the photoinduced toxicity. The average molecular polarizability ( α), energy gap ( E GAP) between the energy of the lowest unoccupied molecular orbital and the highest occupied molecular orbital, lowest triplet excitation energy ( E T1) and vertical electron affinity at the lowest excited triplet ( VEA T1) were the main molecular structural factors. Polarizability which determines the partition of PAHs between water and lipid governs the photoinduced toxicity of selected PAHs. Moreover, the photoinduced toxicity increased with the decreasing of E GAP probably due to better spectral overlap. The parameter, VEA T1 that characterizes the ability of PAH anion radical (PAH −) generation from excited triplet state PAH ( 3PAH ∗), is also related with the photoinduced toxicity. This investigation will make us gain more insight into the photoinduced toxicity mechanism and assess the applicability of various DFT-based descriptors to toxicological QSARs.

Phase behavior and photo‐responsive studies of photoactive liquid crystalline hyperbranched polyethers containing benzylidene moiety

AbstractTwo sets of hyperbranched polyether epoxies were synthesized to study the effect of substituent, rigidity, and nature of photoactive unit on the thermal and photoresponsive properties. Each set was comprised of one molecule with an acyclic moiety in the repeating unit, and two molecules with a cyclic moiety of varying rigidity (cycle size) in the repeating unit. Two substituents on aromatic rings in the repeating unit were present in one set, and other set was without a substituent. The mesogenic and photoresponsive properties were studied and correlated to the varied structural parameters. The effects of varied molecular structural parameters on phase behavior and photoresponsive properties were very prominent. Out of six monomeric diols, only four have exhibited liquid crystalline phase while the polymers corresponding to all monomeric diols revealed mesophase. The findings in photoresponsive properties were further supported by molecular modeling studies. The changes in refractive index, photoviscosity, and fluorescence intensity with irradiation time substantiated the spectral pattern observed in UV‐Vis spectroscopy. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 2774–2786, 2009

A density functional study of 1,1,5‐tris(4‐dimethylaminophenyl)‐3‐methyl‐divinylene

AbstractThe optimized molecular structural parameters and UV‐vis, IR and Raman spectra of a dye molecule with an open formula of 1,1,5‐Tris(4‐dimethylaminophenyl)‐3‐methyl‐divinylene are determined by means of density functional theory (DFT) calculations using B3LYP/6‐31G** formalism. Neutral and cationically charged molecules are used for DFT computations. CC, CC, and NC bond distances of dimethylaminophenyl groups of the dye molecule are in reasonable agreement with the experimental and theoretical CC, CC, and NC bond lengths of the group reported in the literature. Because Vis‐NIR region is near UV‐Vis region in the electromagnetic spectra, calculated maximum wavelengths of UV‐vis spectra are close to those of the experimental VIS‐NIR spectra reported. CC stretching frequencies calculated for dimethylaminophenyl, alkene, and benzene ring groups are also in good agreement with experimentally reported values. All calculated frequencies fall within 2.2% of the experimental frequency region. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2010

Effect of polymer structure and additives on silane grafting of polyethylene

Silane method is a preferred method in crosslinking polyethylene to modify its properties. Here, the silane graft- ing reactions of low density (LDPE), linear low density (LLDPE) and high density polyethylene (HDPE) were compared, all with a fixed amount of silane (vinyltrimethoxysilane) and peroxide (dicumylperoxide). Processing for silane grafting was carried out in an internal mixer, and FTIR spectra were used for comparing the silane grafting efficiencies. The effect of polymer physical form and pre-mixing the components was also determined. Molecular structure parameters were ana- lyzed to investigate their effect on silane grafting efficiency. In case of LDPE and LLDPE, the probable interfering effect of two types of antioxidants on silane grafting reactions was studied. Ethylene propylene diene monomer (EPDM) was added to LDPE to evaluate its effect on silane grafting efficiency. Amongst different grades of polyethylene, LLDPE had a better efficiency in silane grafting. Branchings, PDI, Mw, and MFI are all determining factors and should be considered in comparing the silane grafting efficiency between different grades of polyethylene. In case of incorporating antioxidant, dif- ferent results were observed when the polymer under study was different. EPDM as an additive would enhance silane graft- ing efficiency.