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1.
Farida Benmouna Ulrich Maschke Xavier Coqueret Mustapha Benmouna 《Macromolecular theory and simulations》2001,10(1):63-70
Equilibrium phase properties of mixtures of crosslinked polymers and nematic liquid crystals (LCs) are investigated. Effects of the volume fraction of polymer at crosslinking φ0 , the number of monomers between consecutive crosslinks Nc and the Flory‐Huggins interaction parameter χ on these properties are discussed. Two models for the elastic free energy are used to describe the effects of φ0 Three cases are considered depending upon polymer volume fraction at crosslinking. If crosslinking takes place in the bulk, the elastic free energy is the same and the two models are identical. Otherwise, either φ0 is constant or equal to φ2 , the two models may lead to completely different results depending upon crosslinking density. Strong correlations are found between the effects of φ0 and Nc on the phase behavior of crosslinked polymers and nematic liquid crystal mixtures. These diagrams are also strongly dependent upon the Flory‐Huggins interaction parameter for isotropic mixing χ. This dependence is illustrated through three models for the variation of χ with temperature and composition. 相似文献
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Xuebin Ma Fumin Guo Zhen Li Min Wang Wu Zhou 《Journal of Dispersion Science and Technology》2013,34(11):1540-1547
The phase behavior and rheological properties of the concentrated lecithin aqueous solutions were investigated at 37°C. When adding Isopropyl myristate (IPM) to lecithin solutions, besides an anisotropic liquid crystal (LC) phase, an isotropic liquid (L2) region and an isotropic viscous (I) phase are found. By continuously adding Brij 97, the LC region shifts towards higher water content and the L2 region is extended to the area of lower IPM concentration, meanwhile the I phase disappears. By analyzing the shear rate (ηγ=0.1) and yield stress (σ0), adding IPM to lecithin solutions increases the values of ηγ=0.1 and σ0, and after further adding Brij 97, the ηγ=0.1 and σ0 decrease dramatically. Notably, different from the lecithin/DDAB/water system studied by Youssry and Montalvo, in lecithin/Brij 97/IPM/H2O system, at the relatively higher water content area of the LC phase, the water content has little effect on the critical stress. It is also found that the change of dynamic storage modulus (G′) is similar with that of ηγ=0.1 and σ0 parameters when adding IPM and Brij 97. Maxwell model fitting results show that in the LC phase, the relaxation of the water molecule is prolonged by adding IPM and Brij 97 to lecithin solutions. 相似文献
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Polymers containing intact lactone groups are a new class of macromolecules with reactive groups, which are relatively easy to obtain by polymerization, polycondensation and polyaddition, as well as by reactions on existing macromolecules. Polymers with β-lactone Groups in particular can enter into numerous addition reactions, which can be used, for example, to obtain macromolecules containing hydroxy acid or amino acid groupings. The reactions proceed under mild conditions, and can even be carried out in aqueous media, frequently giving water-soluble polymers. The polymers can be cross-linked at low temperatures, even from the aqueous phase, by the addition of bifunctional or oligofunctional reagents. Polymers containing β-lactone groups can also be used as a basis for graft co-polymers; polyester or polyether branches can be grafted on, depending on whether monomeric lactones or monomeric epoxides are used. 相似文献
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Introduction Ternary systemscomprising a rodlike polymer,a random coil polymerand a solventhavereceived much attention in recentyears.The interestin these types of studies is notonly dueto the theoretical understanding of lyotropic liquid crystal but also due to the mixed systemsincluding rigid and flexible polymershaving been taken asa way to produce composite materi-als based on ultrahigh modulus polymer[1 ,2 ]As for the theoretical considerations of the phase behavior for such ternary sy… 相似文献
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Summary: The relaxation behaviour of poly(5-acryloxy-5-methyl-2,3-dioxacyclohexne), poly(2,3-dichlorobenzyl methacrylate) and poly(3-chlorobenzyl methacrylate) was thoroughly studied by broadband dielectric spectroscopy with the aim of investigating how the chemical structure affects the response of polymers to electric perturbation fields over a wide temperature window. Retardation spectra calculated from dielectric isotherms utilizing linear programming regularization parameter techniques were used to deconvolute strongly overlapped absorptions. Special attention is paid to both the splitting region and the fitting of the Williams ansatz to the experimental results. Attempts are made to explain the molecular origin of the relaxations observed in the retardation spectra of the polymers. 相似文献
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Yukiya Kitayama Yasumichi Yazaki Junya Emoto Eiji Yuba Atsushi Harada 《Molecules (Basel, Switzerland)》2022,27(18)
A new programed upper critical solution temperature-type thermoresponsive polymer was developed using water-soluble anionic polymer conjugates derived from polyallylamine and phthalic acid with cleavage-induced phase transition property. Intrinsic charge inversion from anion to cation of the polymer side chain is induced through a side chain cleavage reaction in acidic aqueous media. With the progress of side chain cleavage under fixed external conditions, the polymer conjugates express a thermoresponsive property, followed by shifting a phase boundary due to the change in polymer composition. When the phase transition boundary eventually reached the examined temperature, phase transition occurs under fixed external conditions. Such new insight obtained in this study opens up the new concept of time-programed stimuli-responsive polymer possessing a cleavage-induced phase transition. 相似文献
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A water-soluble monomer N1-(4-vinylbenzyl)-pentane-1,5-diamine dihydrochloride (VBPDA) with cadaverine (1,5-pentanediamine) group was synthesized. pH-responsive polymer with cadaverine group was obtained by free radical polymerization of VBPDA using 4,4-azobis(4-cyanovaleric acid) (ACVA) as the initiator. The structure and molecular weight of the polymer were characterized by FTIR, 1H-NMR and GPC-MALLS. Aggregation behavior of the polymer in aqueous solution was investigated by dynamic light scattering (DLS), UV-Vis and fluorescence measurements. The experimental results show that the fluorescence intensity of the aggregates decreases and the size of the aggregates increases with increasing pH due to the continuous dehydration of the cadaverine side groups. 相似文献
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Endcapping of oligo(oxyethylene) glycols was carried out by transesterification of methyl N,N-dimethylaminobenzoate with sodium methoxide as the catalyst or by the reaction of sodium salicylate with the ditosyl ester of the oligo(oxyethyl-ene) glycols. Several other common reactions were tried for the endcapping of the oligo(oxyethylene) glycols but were found to be either more cumbersome or unsuccessful. All products were obtained in high yield and high purity. The reactions of tetraalkylammonium carboxylates with aliphatic halides were found to be very general and mild reactions for the preparation of esters in high yield and high purity. It was found that these reactions could be utilized for the preparation of esters on polymers even if the carboxylate group was directly attached to the polymer chain. It was also demonstrated that the aliphatic halide group could be on the polymer, as in the case of polyepichlorohydrin. Copolymers of epichlorohydrin and glycidyl N,N-dimethylaminobenzoate with up to 90% glycidyl benzoate as the comonomer were prepared, and poly(tetra-butylammonium methacrylate) was effectively transformed with 4-(2-bromoethoxy)-2-hydroxybenzophenone into the corresponding ester. The products were characterized by the usual spectral means. 相似文献
12.
Herbert Bosshardt Manfred Hesse 《Angewandte Chemie (International ed. in English)》1974,13(4):252-266
The mass spectral decomposition of di- and polyfunctional alkanes is characterized essentially by two, fundamentally different reactions: On the one hand the structures of the fragment ions are determined by separated degradation of each functional group; on the other hand, however, a relatively large number of fragment ions result from the combined action of two or even more functional groups. This special type of fragmentation has become an important topic in today's mass spectral research. In the present progress report an attempt has been made to summarize the results obtained so far. 相似文献
13.
LI Hong-fei JIANG Shi-chun AN Li-jia YU Dong-hong 《高等学校化学研究》2007,23(5):613-621
The calculations presented in this paper are based on the Sanchez-Lacombe(SL)lattice fluid theory.The interaction energy parameter,g12/k,required in this approach was obtained by fitting the cloud points of polystyrene(PS)/methylcyclohexane(MCH)polymer solutions under pressure.The SL lattice fluid theory was used to calculate the spinodals,the binodals,and the Flory-Huggins(FH)interaction parameter of the solutions.The calculated results show that the SL lattice fluid theory can describe the dependences of thermodynamics of PS/MCH solutions on temperature and pressure very well.However,the calculated enthalpy and the excess volume changes indicate that the Clausius-Clapeyron equation cannot be suitable to describe pressure effect on PS/MCH solutions.Further analysis on the thermodynamics of this system under pressure shows that the role of entropy is more important than the excess volume in the present case. 相似文献
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E. Yu. Kramarenko I. Ya. Erukhimovich A. R. Khokhlov 《Macromolecular theory and simulations》2002,11(5):462-471
In this paper we calculate the phase diagrams of polyelectrolyte solutions taking into account the possibility of ion pair formation between counterions and ions on polymer chains with their subsequent aggregation in multiplets. Multiplets play a role of reversible physical crosslinks between different polymer chains. Furthermore, we assume that the dielectric constant, and hence the binding energy of ion pairs and multiplets, depends on the volume fraction of polymer in the solution. We have shown that ion pairing and multiplet formation leads to instability of the homogeneous phase, so that at some conditions the phase separation can proceed even in good solvent. Another qualitatively new feature of the behavior of polyelectrolyte solutions is the emergence of a triple point on the phase diagram. The effect of the solvent polarity and the polarity of the dry polymer on the general form of the phase diagram is studied in detail. 相似文献
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A retention study on perfluorophenyl silica-based stationary phase was undertaken for some organic compounds containing different polar functionalities. The dependence of the retention factor on the content of organic modifier (acetonitrile, or methanol) in mobile phase was fitted by polynomial equations. The only exception was observed for adenine, which showed a sigmoidal dependence for the retention factor versus organic modifier content. The extrapolated values of retention factor for water as mobile phase (log k w) from these dependences were well correlated with octanol–water partition constants (log K ow), excepting the values for hexachlorocyclohexane isomers and adenine. Temperature dependences of the retention factor obeyed the van’t Hoff equation with thermodynamic parameters similar to those obtained in reversed phase on C8 or C18 stationary phases, excepting two statines whose dependences of ln k on the reciprocal value of absolute column temperature were nonlinear. Again, adenine had an atypical behavior with decrease in the retention factor with the increase in column temperature, due to possible tautomeric equilibria of this compound in presence of water, in accordance with theoretical models reported by literature. Charge modeling with MarvinSketch package program revealed charged centers from analyte molecule that could interact differently with charge centers from stationary phase. 相似文献
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金属-超分子聚合物是由金属离子与配体之间的相互作用形成的,是一类具有多样化几何构造和拓扑结构的新型功能高分子,它包括线型、接枝、交联、树枝等多种骨架结构.金属-超分子聚合物具有光、电、磁等特性,因此潜在的应用前景非常广阔,不仅可以在生物医用、分子器件、纳米材料,还可以在催化化学反应及吸附储氢等领域获得应用.由于吡啶基团为常用配体,且近年含吡啶基团的金属-超分子聚合物研究最为广泛,最为代表性,因此,本文以聚合物结构分类对近几年含吡啶基团的金属-超分子聚合物的研究进展作了简要综述. 相似文献
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Thermal stability of samples of polychloral prepared with different initiators and treated with various endcapping agents was studied using differential thermogravimetric analysis (DTG). Four temperature regions at which maxima of DTG curves occur were identified. On the basis of the known mechanism of initiation and the possible mechanism of termination, the structures of both initial and terminal endgroups of individual polychloral samples were elucidated which enabled the identification of the specific temperature region of thermal degradation of polychloral molecules having a specific type of endgroup. These results were confirmed by studies of the DTG curves of chloral-isocyanate copolymers containing stable terminal fragments with a high content of urethane linkages. 相似文献
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Abstract Polyallylamine and polystyrene beads were allowed to react with 3,5-dibutyl-4-hydroxybenzaldehyde (BHB) and t-butylhydroquinone (BHQ), respectively. The polymeric products, poly-Aa(BHB) and polySt(BHQ) beads worked functionally as antioxidants. The antioxidant effect of the polymer beads in the oxidation of linoleic acid suspensions was investigated by both the ferric thiocyanate and thiobarbituric acid methods. The antioxidant activity of poly-St(BHQ) beads was higher than that of poly-Aa(BHB) ones. It was found that the antioxidant activity for 2 mg of 3, 5-dibutyl-4-hydroxytoluene (BHT) corresponded to that for 11.7 g of poly-Aa(BHB) and that of 0.6 g of poly-St(BHQ). The polymer beads are potential antioxidants for foods since their separation from a food oil after their use is easy because of their insolubility. 相似文献
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It was established that linear polymers with quaternary ammonium groups are obtained by the reaction of chloromethylated polystyrene (CMPS) with hydroxyalkylic tertiary amines when the amines contain one or two hydroxyl groups, and that crosslinked polymers are obtained with aminoether groups when the amines have three hydroxyl groups, i.e., tris(2-hydroxyethy1)amine. The aminoether units appear by intramolecular rearrangement of quaternary ammonium structural units. Kinetic studies on the synthesis of polymers with quaternary ammonium groups from CMPS, poly(N,N-dimethylamino-ethylmethacrylate), and poly(N,N-dimethylaminopropylacrylamide), were performed. The main factors which influence the kinetics of reactions are steric hindrance of near neighboring groups, hydrophilic effect for hydroxyalkylamines and polymer-solvent interaction. 相似文献