Nano-network with dual temperature and pH responsiveness based on copolymers of 2-hydroxyethyl methacrylate with 3,9-divinyl-2,4,8,10-tetraoxaspiro[5.5]-undecane

Abstract  

This study refers to the synthesis of a nano-network with dual temperature and pH responsiveness based on the 2-hydroxyethyl methacrylate (HEMA) copolymers with a comonomer with spiroacetal moiety and crosslinking capacity, namely 3,9-divinyl-2,4,8,10-tetraoxaspiro[5.5]-undecane (U). The copolymers were synthesized by radical emulsion polymerization, using 4,4′-azobis(cyanopentanoic acid) as initiator, in the presence of sodium lauryl sulfate as tensioactive agent and poly(vinyl alcohol) as protective colloid. Three copolymer variants were taken into study resulted from the different ratio between the comonomers (HEMA/U), which was about 98/2, 95/5, and 90/10, respectively. The copolymers were characterized by FTIR and thermal analysis. The copolymers sensitivity was evidenced by studying the evolution of the hydrodynamic radius and zeta potential of the polymeric particles as a function of pH. Thus, the particles size increases with the comonomer amount, from 193 nm in case of the homopolymer up to 253 nm for the copolymer with maximum content of the comonomer (10%). The increase of the particle hydrodynamic radius with the growth of temperature was also put into evidence.     

Thermal studies on ethylene–vinylcyclohexane copolymers prepared with bis-indenyl type metallocene catalyst systems

Ethylene–vinylcyclohexane copolymers (EVCH) were synthesized with unsubstituted and substituted bis-indenyl type metallocene catalysts and their thermal and dynamic mechanical behavior was studied and compared to a series of metallocene catalyzed ethylene-1-hexene (EH) and ethylene-1-hexadecene (EHD) copolymers. Increasing comonomer incorporation in the chain decreased the melting point, the level of crystallinity, and the density of all copolymers, but the bulky size of the vinylcyclohexane (VCH) group made this decrease very insignificant for the EVCH copolymers. The influence of the VCH group was also noticed in the loss tangent curves by dynamic mechanical analysis as a very insignificant shift of the β-transition to lower temperatures at increasing comonomer content, a behavior quite opposite to the behavior of the EH and EHD copolymers. The storage modulus curves explained that the stiffness properties of the EVCH copolymers are as good or better than those of the EH and EHD copolymers at the same comonomer level. The intensities of the maximum in the loss tangent curves indicate that EVCH copolymers may have good impact properties. Fractionation studies by differential scanning calorimetry (DSC) using a self-nucleation/annealing (SSA) procedure confirmed a broadening of the lamellar thickness distribution as the amount of comonomer increased. Self-nucleation/annealing curves of highly branched EVCH and EH copolymers exhibited big similarities suggesting similar random comonomer distributions.     

Hypercoiled structures in aqueous solutions of 2-hydroxyethyl methacrylate-methacrylic acid copolymers at low metnacrylic acid content

The behavior of solutions of 2-hydroxyethyl methacrylate-methacrylic acid copolymers in aqueous 2–8M urea was investigated at temperatures ranging from 10 to 50°C at pH from 3 to 8. The molar fraction of methacrylic acid in the copolymer was 0.045 at most. The values of the intrinsic viscosity and Huggins coefficient were determined. Under these conditions, the poly-(2-hydroxyethyl methacrylate) molecules are in a hypercoiled state. In copolymers at a low degree of dissociation, the methacrylic acid units make the degree of coiling even higher, but in the dissociated state this degree is much lower. Hypercoiling is interpreted as a consequence of the association of hydrophobic groups in the molecule of copolymers.     

The polymorphism of poly(vinylidene fluoride) V. The effect of hydrostatic pressure on the melting behavior of copolymers of vinylidene fluoride

The high-pressure melting behavior of samples of vinylidene fluoride copolymerized with vinyl fluoride, trifluoroethylene, or tetrafluoroethylene indicate that the copolymers have a lower entropy of melting than the poly(vinylidene fluoride) homopolymers in the same phase. As the comonomer size increases, the entropy of melting decreases. High-pressure crystallization of copolymers of 91-9 mole% vinylidene fluoride-trifluoroethylene and 93-7 mole% vinylidene fluoride-tetrafluoroethylene results in a high-melting form of phase I (planar zig-zag).     

EFFICIENCY OF β-NUCLEATING AGENTS IN PROPYLENE/α-OLEFIN COPOLYMERS

Crystallization and melting behavior of β-nucleated propylene/1-pentene random copolymers were studied. Samples with different comonomer content were nucleated with the calcium salt of suberic acid. The WAXS, differential scanning calorimetry (DSC), and polarized light microscopy (PLM) measurements showed that morphological behavior of the β-nucleated copolymers is similar to that of the homopolymer, but the rate of crystallization and the characteristic temperatures decrease with increasing pentene content. Crystallization at low temperatures and lower chain regularity lead to the formation of imperfect crystal structures with high instability, which enables the study of structural perfection processes like ββ′- or βα-recrystallization during partial melting. The PLM studies proved that the critical crossover temperature T(βα) decreases with increasing pentene content. The effect of comonomer content on the critical recooling temperature ( T _R ^* ), as well as on the equilibrium melting point of the β-form ( T _m ⁰) was also investigated. However, in our case, the linear Hoffman–Weeks method proved to be unsuitable for the accurate determination of T _m ⁰.     

Polarized Raman study of random copolymers of propylene with olefins

The polarized Raman spectroscopy is employed in the study of structural modifications in the films of isotactic polypropylene (PP) whose chain contains ethylene, 1-butene, 1-hexene, 1-octene, and 4-metyl-pentene-1, which represents an isomer of 1-hexene. It is demonstrated that the phase and conformational compositions of copolymer molecules depend on the comonomer content and the side-chain length of the second monomer. The content of the PP molecules in the helical conformation in the crystalline and amorphous phases of the copolymers monotonically decreases with increasing content of the second monomer. The decrease in the content of helical macromolecules in the crystalline phase is faster than the decrease in the amorphous phase. At a certain content of comonomers, the total content of the helical fragments decreases with increasing length of the side chain of the second monomer. The structures and Raman spectra of the copolymers of propylene with 1-hexene and 4-methyl-1-pentene are similar.     

PHASE SEPARATION IN THE MELT OF POLYPROPYLENE–1-DECENE COPOLYMERS

A propylene homopolymer and three copolymers with 1-decene containing 1.82, 3.55, and 7.83 mol% of comonomer units, respectively, were prepared with metallocene catalyst and the phase behavior in the melt of these polymers was studied using simultaneous synchrotron small-angle x-ray scattering and differential scanning calorimetry. The results show that the phase behavior of the melt varies with comonomer content and the copolymers tend to be phase-separated with increasing comonomer content. The phase separation in the melt of the propylene–1-decene copolymers was further confirmed by the fitting of the experimental data with Teubner–Strey micro-emulsion model and a transition from the phase-separated melt to the disordered melt was observed. We tentatively attribute this phenomenon to the inhomogeneous intra-molecular composition distribution at high levels of comonomer and the incompatibility of propylene sequences with different lengths. Such a finding is consistent with the facts of multiple melting peaks and mixed γ and α crystal phases in the polymer solids. Since the phase behavior depends on temperature, the effect of annealing temperature, from which the copolymers were cooled, on the nonisothermal crystallization of the copolymers was also investigated. It is found that higher degree of phase separation accelerates the crystallization but reduces the crystallization enthalpy.     

Theoretical study of the smiles rearrangement in the activation mechanism of proton pump inhibitors

This work describes the conformational behavior and the activation mechanism of timoprazole and substituted prazoles from the most stable conformation to the sulphenic acid. The stability of the conformers can be explained by the presence of hydrogen bonds, stereoelectronic effect because of the lone pair of sulfur atom and the N^…C and N^…S interactions. The first step of the Smile rearrangement is a nucleophilic addition to benzimidazole by pyridine moiety, which depends on the difference of the electron population of the atoms involved in the attack. The second step produces sulphenic acid by a concerted reaction where breaking of the S–C bond goes along with a proton migration, and is determined by the electron population of the sulfur atom. Copyright © 2011 John Wiley & Sons, Ltd.     

Photoelectron spectroscopy of irontricarbonyl complexes of vinylnaphthalenes: Quantum-chemical calculations by the density functional method

The HeI photoelectron spectra of the complexes η⁴-1-vinylnaphthalene-Fe(CO)₃ and η ⁴-2-vinylnaphthalene-Fe(CO)₃ and the free organic ligands 1-vinylnaphthalene and 2-vinylnaphthalene are measured. The spectra are interpreted on the basis of quantum-chemical calculations by the density functional method in the SVWN/6-31G(d) local density approximation and with the B3LYP/6-31G(d) hybrid exchange-correlation functional. The Kohn-Sham orbital energies with calibration corrections are shown to reproduce well the vertical ionization potentials of both the irontricarbonyl π complexes under study and their ligands. The relative ionization cross sections σ_i of the valence orbitals of the complexes are calculated in terms of the Gelius model. These quantities prove to agree perfectly with the relative ionization cross sections σ _i ^exp determined experimentally from direct estimation of the band areas of the photoelectron spectra.     

Intensities of DNA ion-phosphate modes in the low-frequency Raman spectra

The Raman intensities of counterion vibrations with respect to the phosphate groups of the double-helix backbone (ion-phosphate modes) in the low-frequency spectra (< 200 cm^-1) of B -DNA with different alkali metal counterions have been calculated using the model for DNA conformational vibrations and the valence-optic approach. The results have showed that the spectra of DNA with heavy counterions ( Rb⁺ and Cs⁺ differ from the spectra of DNA with light counterions ( Na⁺ and K⁺ . The calculated spectra of DNA with heavy counterions are characterized by intensive modes of ion-phosphate vibrations that form one united band near 115cm^-1. Ion-phosphate modes in the spectra of DNA with light counterions are characterized by higher frequencies (near 180cm^-1) and much lower intensity. Our calculations explain why the modes of ion-phosphate vibrations are observed in Cs-DNA spectra rather than in Na-DNA. The determined sensitivity of the intensities of DNA low-frequency spectra to the counterion type proves the existence of the ion-phosphate modes.     

CORRELATION AMONG MORPHOLOGY,INTERFACE, AND MECHANICAL PROPERTIES: EXPERIMENTAL STUDY

The effect of the disperse phase and the diffuse interface between phases on the tensile and impact strengths of polypropylene (PP)/poly(ethylene terephthalate) (PET) (75/20 by weight) blends compatibilized with maleic anhydride–grafted PP derivatives and on the tensile modulus of poly(vinyl chloride)/polystyrene (PVC/PS) nanoparticle blends compatibilized with polystyrene/poly(vinyl acetate) (PS/PVAc) block copolymers were investigated experimentally. The weight fraction of the diffuse interface between the PP and PET phases in the PP/PET blends was determined by modulated differential scanning calorimetry (MDSC). A correlation between the diffuse interface content and mechanical properties was found. With increasing diffuse interface weight fraction, the impact and tensile strengths of the PP/PET blends increased. There is a brittle-tough type transition in these PP/PET blends. With increasing diffuse interface content in the PVC/PS nanoparticle blends in which the particle size was fixed at about 100 nm, the tensile modulus also clearly increased.     

超短强激光脉冲与H2＋相互作用研究：经典与量子计算的比较

用经典动力学和量子力学方法分别研究了Ｈ２＋在超短强激光场中的电离、离解和残存行为，得到了相似的结果：即在超短强激光脉冲作用下，Ｈ２＋的电离占优，但有限的量子计算低估了Ｈ２＋的离解几率；而经典处理则没有显示Ｈ２＋在超强场中的稳定化。另外，经典计算表明当核间距Ｒ伸展到一定范围时，Ｈ２＋的电离率最大。这符合量子计算中发现的电荷谐振增强电离（ＣＲＥＩ）现象。     

The importance of the ortho effect in the solvolyses of 2,6‐difluorobenzoyl chloride

The ortho effect of the chloro substituents in 2,6‐dichlorobenzoyl chloride sufficiently hindered attack on the acyl carbon such that an ionization mechanism was observed over the full range of solvents studied. We now compare this behavior with that of 2,6‐difluorobenzoyl chloride. The smaller fluoro substituents allow the dominant pathway to be addition–elimination (association–dissociation) in all solvents except those rich in fluoroalcohol, where ionization is dominant. Ranges of operation for both mechanisms had previously been observed for the parent benzoyl chloride but with a wider ionization range than for the 2,6‐difluoro derivative. This indicates that, relative to the parent, the electronic destabilizing influence of the fluorines on acyl cation formation outweighs the steric retardation to attack because of the presence of the two ortho‐fluorine atoms. An extended (two‐term) Grunwald–Winstein equation treatment of the solvolyses of 2,6‐difluorobenzoyl chloride is reported. Copyright © 2011 John Wiley & Sons, Ltd.     

Morphology and infrared spectroscopy of strongly interacting polymer blends: EVOH/copolyamide-6/6.9

The presence of aliphatic hydroxyl groups in poly(ethylene-co-vinylaleohol) (EVOH) suggests that these copolymers have the potential of forming miscible blends, within certain composition ranges, with a variety of polymers containing complementary functional groups. Hydrogen bonding in EVOH involves a wide variety of inter- and intramolecular species and plays an important role in the phase behavior of EVOH blends. Polymer blends of two random copolymers, EVOH with different ethylene contents and copolyamide-6/6.9 (COPA) at an approximately 1:1 comonomer ratio, were investigated using Fourier transform infrared (FTIR), near-IR, transmission electron microscopy (TEM), and scanning electron microscopy (SEM) methods. The blends were found to be partially miscible due to intermolecular hydrogen bonding between the OH group of the EVOH and the amide group of the copolyamide. The EVOH-rich blends exhibit much lower miscibility compared with the copolyamide-rich blends.     

Chemical Profiling of an Indian Herbal Formula Using Liquid Chromatography Coupled with Electro Spray Ionization Mass Spectrometry

Amruthotharam kashayam is an important Ayurvedic formulation prepared using specified plant parts of Tinospora cordifolia, Terminalia chebula, and Zingiber officinale. The current study developed a rapid liquid chromatographic method coupled with electro spray ionization mass spectrometry for the identification of major phytoconstituents present in the formulation. Reverse phase high-pressure liquid chromatogram was developed as chemical fingerprint. The mass spectrum along with the MS/MS fragmentation on collision-induced dissociation led to the structural identification of separated compounds. Phenolic acids such as quinic acid, protocatechuic acid, gallic acid, and chebulic acid were identified in the formulation along with some flavonoids.     

Impact of the Vibrationally Excited States on the Macroscopic Behaviour of the Band-like Electron Beam Discharge Plasma in H/H2-Mixture

The investigation of the impact of the vibrationally excited molecules in the electronic ground state was performed by simultaneously solving a balance equation system for the main charge carriers, the H atoms, the metastable H atoms, the H₂ molecules in the different vibrational states and for the power transfer of the electrons in the beam discharge mixture plasma. The balance equations for the vibrational states include in particular one-quantum step excitation and deexcitation, electronic excitation, dissociation and ionization from each vibrational level in electron collisions as well as the finite life time of these states because of the gas transfer through the band-like plasma. A main finding is that due to the additional impact of vibrationally excited molecules there is a marked enhancement of the resulting dissociation and ionization degree in the beam discharge plasma at medium power input from the turbulent electric field. For discharge parameters of practical interest the ionization and dissociation budget, the population of the vibrational states, the different energy dissipation processes and the energy pumping into the ladder of the vibrational states were calculated and discussed in detail.     

Solution conformational preferences of glutaric, 3‐hydroxyglutaric, 3‐methylglutaric acid,and their mono‐ and dianions

Conformational preferences of glutaric, 3‐hydroxyglutaric and 3‐methylglutaric acid, and their mono‐ and dianions have been investigated with the aid of NMR spectroscopy. In contrast to succinic acid, glutaric acid displays essentially statistical conformational equilibria in polar and non‐polar solutions of high and low hydrogen‐bonding ability with no clear evidence for intramolecular hydrogen‐bonding interactions. The acid ionization constant ratios, K ₁/K₂, in D₂O and DMSO of glutaric, 3‐hydroxyglutaric, and 3‐methylglutaric acids also indicate that intramolecular interactions are much less important than, or indeed insignificant, for shorter‐chain acids. FTIR studies on 3‐methylglutaric acid indicate some preference for either association with solvent or dimerization, depending on the solvent, rather than intramolecular hydrogen bonding. Copyright © 2008 John Wiley & Sons, Ltd.     

Structure and morphology of vinylidene chloride—methyl acrylate copolymers

The structure and morphology of vinylidene chloridemethyl acrylate copolymers were studied using small-angle and wide-angle x-ray scattering. Long period increased with comonomer concentration for compressionmolded films crystallized at the same temperature. An increase in the “a” dimension of the unit cell was noted for the “as polymerized” powder as comonomer content increased. Sequence distribution information obtained from the instantaneous copolymer composition equation agreed well with the observed powder data. No such trend was observed for melt-crystallized films, possibly because of a greater restriction on crystallization and a lower level of crystallinity within these samples.     

Chirping-dependent ionization and dissociation of methane in an intense femtosecond laser field

We studied the ionization and dissociation of polyatomic molecule methane in an intense femtosecond laserfield with wavelength of 810 nm and intensities ranging from 1.4×10~(14)to 2.6×10~(15) W/cm~2 by massspeetroscopy.Abundant fragment inos were observed in addition to the strong parent ion.The effect offrequency chirp was investigated and it was found that the negatively chirped pulses dramatically enhancedthe dissociation probability,which might be used to control the dissociation pathways.     

NMR and INDO study of the Ni(II) complexes of maleic and succinic acids

A new approach to investigate the conformational properties of the Ni(II) complexes of maleic and succinic acids is reported. The use of C-13 and H-1 paramagnetic shifts and relaxation rates together with an INDO analysis on suitable radical models of the ligands proved a powerful tool in elucidating the conformation of the Ni(II) complex with the partially rigid maleic acid.