The effect of substituent position on the liquid crystalline properties of dodecyl-D-xylitols

Recently we have been concerned with a systematic and fundamental investigation into the effects of the linking group on the lyotropic and thermotropic properties of aliphatic substituted acyclic carbohydrate systems. For this purpose, we chose to study the selfassembling behaviour of alkyl substituted xylitols where the aliphatic chain was attached to the xylitol moiety via ether, ester and thioether linkages. We have extended this work and, in this current study, we report the effects on the self-assembling properties of sequentially moving the position of a dodecyl chain in acyclic x-O-dodecyl-D-xylitols. This work was used for a direct comparison with results reported on cyclic systems such as the dodecyl x-O-beta-Dglucopyranosides.     

The substituent effect in the fragmentation of phenylcyclohexanols

All the main fragmentation pathways undergone by trans-4- and trans-2-p-substituted phenylcyclohexanols have been studied, and the ionic abundances have been correlated with the σ constants. This analysis shows that electron withdrawing substituents, increasing the fraction of molecular ions having sufficient energy to decompose, favour all fragmentations. However, along with this ‘non-specific’ substituent effect, there is a ‘specific’ effect, in the opposite sense, increasing the formation of the [M—59]⁺ and [M—85]⁺ ions with increasing electron releasing power of the substituents. The loss of water, although it is almost exclusively a 1,4 elimination in the case of trans phenyl cyclohexanols, is not specifically influenced by the substituents.     

Synthesis and characterization of a new benzobisoxazole/thiophene derivative polymer and the effect of the substituent on the push/pull properties

Conducting polymer synthesis of a new benzobisoxazole/thiophene derivative is reported. The conjugated co-polymer presents the lowest bandgap (1.78 eV) reported for a neutral benzobisoxazole/thiophene polymer. Electrochemical polymerization is carried out by cyclic voltammetry, and the new conducting polymer is characterized by Raman spectroscopy and X-ray photoelectron spectroscopy. The results indicate that the coupling of the monomer unit occurs at the 2,2′ positions of the thiophene ring. Theoretical studies in derivatives of this family of compounds are conducted to validate the effect on the bandgap modulation due to the change in the substituent on the phenyl moiety of the monomer. The comparison between experimental and theoretical properties shows the substituents impact on the optical properties of the system, and its viability to be used in sensors.     

The effect of the amido substituent on polymer molecular weight in propene homopolymerisation by titanium cyclopentadienyl‐amide catalysts

In the homopolymerisation of propene by the cyclopentadienyl‐amide titanium catalyst systems [η⁵,η¹‐C₅H₄(CH₂)₂NR]TiCl₂/MAO and [η⁵,η¹‐C₅H₄(CH₂)₂NR]Ti(CH₂Ph)₂/B(C₆F₅)₃ (R = ^tBu, ⁱPr, Me), the catalyst with the smallest substituent (Me) on the amido moiety consistently gives the highest polymer molecular weight. This differs from the trend usually observed in related catalysts with tetramethylcyclopentadienyl‐amide ancillary ligands, where larger amide substituents result in higher molecular weights. Based on the present information a hypothesis is formulated in which an increased cation‐anion interaction for the less sterically hindered catalyst is responsible for disfavouring chain transfer relative to chain growth.     

The t-butyl group as sensor group of the ortho effect

The ¹³C chemical shift difference between the Me group C atoms and the quaternary C atom of the t-Bu group in 58 p-, m- and o-substituted t-butyl-benzenes has been measured and analysed in terms of inductive. mesomeric and proximity effects. It is shown that the ortho effect is too complex to justify a unified explanation by a correlation treatment.     

Swelling and shrinking of polymer chains in homopolymer blends

The radius of gyration, R, of polymer chains in homopolymer blends is studied in the framework of a self-consistent one-loop approximation. We show that the polymer chains can shrink or swell in comparison to the Gaussian chain. Swelling of the polymer chains in a region far away from the critical point is caused by the steric repulsive forces that were included in the model as the constraint of incompressibility. The chains shrink progressively, as we approach the critical region passing through the Gaussian limit, $ R_0 = \sqrt{\frac{N}{6}}l $, far away from the critical point (N − degree of polymerization, l − length of monomer). The correction responsible for the swelling and the shrinking is small when the concentrations of components ϕ are comparable ($ N = 1000,\bar\phi = 0.5,\frac{{R_0^2 - R^2}}{{R_0^2}} = \pm 0.02\%$). This effect, although small, leads to a local demixing, a sharp shrinking of chains in both components accompanied by a strong change of the global inter-monomer distance, which should be observable experimentally. When the local demixing occurs there is a sudden increase in the scattering intensity (of the order of 30% for N = 1000, and ϕ _A = 0.2). The increase of the degree of polymerization of the same type of chains leads to an increase of the swelling-shrinking effects. In addition, the critical concentration of the shorter chains component is smaller in comparison to the value obtained in the Flory-Huggins theory. The self-consistent determination of the radius of gyration and the upper wave-vector cutoff make our model free from any divergences. In the limit of N → ∞ this theory reduces to the random phase approximation (RPA) of de Gennes.     

The mechanism of the distant substituent effect on molecule reactivity

The effect of distant polar substituents on the reaction mechanism of some chemical reactions is considered. It has been shown that the traditional approach, based on transferring the substituent action to the reaction centre along the chain of bonds connecting them and leading to a significant change in electronic density at the reaction centre, is wrong. The role of a polar substituent consists of changing, sometimes dramatically, the electrostatic potential character around the molecule, particularly in the space near the reaction centre.     

Liquid crystalline properties of dissymmetric molecules IV. The substituent effect on thermal properties of nematic and smectic A phases in three aromatic ring systems with ester linkages

This paper describes the effect of substituent and ester linkage on smectic properties for some derivatives of 4-R -phenyl 4-(4-octyloxybenzoyloxy)benzoates (1 ), 4-octyloxyphenyl 4-(4-R-benzyloxy)benzoates (2), 4-(4-octyloxybenzoyloxy)phenyl 4- R -benzoates (3), and 4-R-phenyl 4-octyloxyphenyl terephthalates (4) where R = OCH₃, CH₃, OC₈H₁₇, C8H17, halogens, CF₃, OCF₃, CN, NO2, etc. The thermal properties are discussed in terms of the electrostatic nature of the substituents and the relative orientation of the ester groups with respect to both terminal substituents. The substituent effect on the layer structure of the smectic A phase is also examined by means of a small angle X-ray analysis.     

Liquid crystalline properties of dissymmetric molecules IV. The substituent effect on thermal properties of nematic and smectic A phases in three aromatic ring systems with ester linkages

This paper describes the effect of substituent and ester linkage on smectic properties for some derivatives of 4-R -phenyl 4-(4-octyloxybenzoyloxy)benzoates (1), 4-octyloxyphenyl 4-(4-R-benzyloxy)benzoates (2), 4-(4-octyloxybenzoyloxy)phenyl 4- R -benzoates (3), and 4-R-phenyl 4-octyloxyphenyl terephthalates (4) where R = OCH₃, CH₃, OC₈H₁₇, C8H17, halogens, CF₃, OCF₃, CN, NO2, etc. The thermal properties are discussed in terms of the electrostatic nature of the substituents and the relative orientation of the ester groups with respect to both terminal substituents. The substituent effect on the layer structure of the smectic A phase is also examined by means of a small angle X-ray analysis.     

The effect of electric discharges on electrophysical properties of polymer blends

The electric aging of HDPE-PP blends obtained from melt and PS-PVC blends prepared from solution is studied in the range of low (0.1–10 wt %) concentrations of the second component. It is found that the addition of a minor amount of PE (1–2 wt %) to PP significantly intensifies changes in the electric properties and erosion of PP. For a PS-PVC blend, the addition of small (up to 1 wt %) amounts of PVC leads to an abnormally rapid degradation of PS.     

The effect of polymer adsorption on the wetting properties of partially hydrophobized magnetite

Upon reverse flotation of iron ore, the surface of the iron ore concentrate may become partially hydrophobized due to adsorption of flotation collector, which is facilitated by the calcium ions present in the process water. Hydrophobic areas on the concentrate surface may introduce problems in subsequent pelletization of the concentrate. A possible way to restore the wettability of the surface could be by modifying the surface with a hydrophilic polymer. The effect of hydrophilic polymers of different types, viz. cationic, anionic, and non-ionic, on the wettability of the magnetite surface after adsorption of a surfactant was investigated. Although all the polymers could adsorb on magnetite at pH 8.5, the contact angle measurements revealed that only anionic ammonium polyacrylate could decrease the contact angle of synthetic magnetite after surfactant adsorption to a level close to that of as-synthesized magnetite. Such effect was probably achieved due to shielding of the hydrophobic surfactant chains from the aqueous phase by hydrophilic polyacrylate molecules. The fact that polyacrylate adsorption on magnetite occurred via calcium ions makes polyacrylate suitable for application in calcium-rich process water. The results presented in this work illustrate that ammonium polyacrylate could be successfully used to improve the wettability of magnetite after adsorption of surfactants.     

The effect of copolymer composition on the dynamics of random copolymers in a homopolymer matrix

The effect of copolymer composition on the dynamics of random copolymers in a homopolymer matrix is studied using computer simulations within the framework of the bond-fluctuation model on blends containing low concentrations (10%) of A-B copolymers, where A and B are two different types of monomers, dispersed in a homopolymer matrix of chains with only A-type monomers. Four copolymer compositions were studied, phi(A)=0.33, phi(A)=0.5, phi(A)=0.66, and phi(A)=0.82, while maintaining a statistically random sequence distribution. For this study, we have only included intermolecular interactions between A and B monomers. Our results indicate, in agreement with experimental data, that copolymer composition has an impact on system dynamics. Analysis of the structure reveals that copolymers with majority A content are expanded in the homopolymer matrix, have fewer interchain copolymer-copolymer contacts, and are well dispersed in the homopolymer matrix. On the other hand, copolymers with lower A content form a more compact structure, have more interchain contacts, and form aggregates that are short lived. This in turn leads to slower system dynamics. Both the radius of gyration (Rg) and copolymer end-to-end vectors (Re) increase with increasing A content until phi(A)=0.66 and then decrease. Copolymers with lower A content form more compact structures as the repulsive interactions between unlike species are minimized by the copolymers folding back on themselves and forming aggregates of copolymer chains. Thus, these results provide insight into the variation of copolymer dynamics with composition in the system by documenting the correlation between the thermodynamics of this mixture, the conformation of a copolymer chain in a homopolymer matrix, and the dynamics of both components in this blend.     

Chain confinement in polymer nanocomposites and its effect on polymer bulk properties

The issue of chain confinement in nanocomposites remains largely unanswered because experimental systems are plagued by additional complicating variables such as particle–polymer interactions and free volume increases brought upon by the addition of the particles. Using computer simulation of high length chain polymers, we show that simple excluded volume interactions between polymer and nanoparticles lead to a wealth of changes in the diffusion coefficient and entanglement density of the chains. This opens up the possibility of using nanoparticles for tuning polymer properties, such as toughness, melt viscosity, and transient rubberlike behavior. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 687–692, 2010     

Pyridiniumchlorochromate oxidations: Studies on the kinetics and substituent effect in the oxidation of aniline in nonaqueous systems

Pyridiniumchlorochromate (PCC) oxidizes aniline and substituted anilines except nitro anilines smoothly in chlorobenzene–nitrobenzene mixtures in the presence of dichloroacetic acid. The reaction has unit dependence on each of the aniline, PCC, and dichloroacetic acid concentrations. Electron-releasing substituents accelerate the reaction, whereas electronwithdrawing groups retard the reaction, and the rate data obey Hammett's relationship. The reaction constant ρ is -3.75. Azobenzene and p-benzoquinone have been obtained as products. The observed experimental data have been rationalized in terms of the formation of an intermediate complex involving PCC–amine undergoing a rapid decomposition to products.     

Emulsifying effect of graft copolymer for the homopolymer

Precipitation of poly(methyl methacrylate) (PMMA) from dimethyl sulfoxide solution by addition of water as a precipitant was studied in the presence of a well-characterized graft copolymer of poly(vinyl alcohol) (PVA). The graft copolymer which had been prepared by a radiation method and freed from PMMA and PVA homopolymers had one PMMA branch whose length was nearly equal to that of the PVA backbone. Even when such an amount of water was added to PMMA solution as to cause all the PMMA to precipitate from the solution, the precipitation was prevented by the presence of relatively small amounts of the graft copolymer. With decreasing molecular weight of PMMA, the effect of protection became more pronounced. When the precipitation was prevented, the solution was transformed into a stable emulsion. The mechanism of protection against precipitation was discussed on the basis of the results obtained and electron microscopic photographs of the emulsion particles. It was concluded that the particles of the precipitated homopolymer were covered by a monolayer of the graft copolymer, resulting in prevention of coagulation.     

Solvent properties governing protein partitioning in polymer/polymer aqueous two-phase systems

Distribution coefficients of various proteins were measured in aqueous Dextran-Ficoll, Dextran-PES, and Ficoll-PES two-phase systems, containing 0.15M NaCl in 0.01 M phosphate buffer, pH 7.4. The acquired data were combined with data for the same proteins in different systems reported previously and known solvatochromic solvent properties of the systems to characterize the protein-solvent interactions. The relative susceptibilities of proteins to solvent dipolarity/polarizability, solvent hydrogen bond acidity, solvent hydrogen bond basicity, and solvent ability to participate in ion-ion and ion-dipole interactions were characterized. These parameters, which are representative of solute-solvent interactions, adequately described the partitioning of the proteins in each system. It was found that the relative susceptibilities of proteins to solvent dipolarity/polarizability are interrelated with their relative susceptibilities to solvent hydrogen bond acidity and solvent hydrogen bond basicity similarly to those established previously for small nonionic organic compounds.     

The effect of counterion in polymer sulfonates on the synthesis and properties of poly-3,4-ethylenedioxythiophene

The electrochemical polymerization of 3,4-ethylenedioxythiophene (EDOT) in the presence of the salt and acid forms of polymer sulfonates with different polymer-chain flexibility is studied. The dependence of the rate of synthesis of poly(3,4-ethylenedioxythiophene) (PEDOT) on the nature of polysulfonate counterion that determines the type and distribution density of the charge in the polyelectrolyte chain is demonstrated. For the Н⁺ form of a rigid-chain polysulfonate, it is found that the specific interactions between parts of its macromolecules lead to destabilization of EDOT?⁺ radical cations, hinder the growth of PEDOT chains, and favor the formation of structures with the high degree of charge localization.     

Remote substituent effects in the Baeyer-Villiger oxidation. I. through-bond γ substituent effect on the regioselectivity

Regioselectivity of the Baeyer-Villiger oxidation of 8-oxabicyclo[3.2.1] octan-3-one derivatives is markedly affected by the electronic nature of substituents at position γ to the carbonyl function.