摘要:

AbstractMost theoretical and experimental efforts in polyelectrolyte science have been aimed at understanding equilibrium properties. The purpose of this chapter is to call attention to the wide array of kinetic phenomena which occur in polyelectrolyte solutions on their way to equilibrium. Such time‐dependent processes include dissolution of dry powders, phase separation, aggregation, gelation, and degradation. Because equilibration times in polyelectrolyte solutions can be quite long, polyelectrolyte solutions may often be used and studied, wittingly or not, in non‐equilibrium states. After a brief review of some of the equilibrium properties of polyelectrolyte solutions, a few simple ideas and examples are given to illustrate non‐equilibrium processes. A larger emphasis is given to the degradation problem, simply because it is the area of time‐dependent phenomena where the author and co‐workers have so far made the most quantitativ

ISSN:0005-9021    

DOI:10.1002/bbpc.19961000602

出版商:Wiley‐VCH Verlag GmbH&Co. KGaA    

年代:1996

数据来源: WILEY

摘要:

AbstractViscoelastic properties of polyelectrolyte solutions were studied in the absence and presence of added salt over a wide range of polymer concentration in comparison with those of non‐ionic polymers in good solvents.In the semidilute region where the polymer concentrationCis higher than the overlap concentration for viscosityC*v, but lower thanC**(ca. 0.3 kg/dm3), the polymer concentration dependence of specific viscosity at zero‐shear rateη 0spincreases with increasing added‐salt concentrationCsand at highCsit almost agrees with that of non‐ionic polymers in good solvents. In the concentrated and entangled region whereC>C *JandC>C**,η 0spmore steeply increases withCeven in salt‐free solutions, implying the screening of electrostatic interaction and the increase of local frictional coefficients as considered in concentrated non‐ionic polymer solutions.In the dilute region whereCis lower than the overlap concentration for steady‐state complianceC *J, the steady‐state complianceJemore strongly depends on molecular weight andCthan in non‐ionic polymer solutions. In the semidilute region whereC>C *J, butCC**, the polymer concentration dependence becomes similar to that of non‐ionic polymer solutions. In the concentrated and non‐entangled region whereCC**, the frequency dependences of storage and loss moduli are well explained by the modified Rouse model like non‐ionic polymer systems in the same region.The experimental results in the semidilute region are well explained by our theory of viscoelastic properties of polyelectrolyte solutions based on the reptat

ISSN:0005-9021    

DOI:10.1002/bbpc.19961000603

出版商:Wiley‐VCH Verlag GmbH&Co. KGaA    

年代:1996

数据来源: WILEY

摘要:

AbstractThis paper deals with the investigation of the electroviscous effects on sodium hyaluronate aqueous solutions. Dilution of a polyelectrolyte in water or low salt concentration solvent gives a reduced viscosity passing through a maximum whose position corresponds to a polymer concentration directly related to the ionic concentration. Independently of the molecular weight when isoionic dilution is performed, the conformation is preserved and the intrinsic viscosity corresponding to the adopted ionic concentration is obtained as soon as the concentration range corresponds to the dilute domain.At end the model previously proposed to take into account the role of the electrostatic interactions on the conformation is adopted to interpret, with a good agreement, the data of intrinsic viscosity versus ionic concentration.

ISSN:0005-9021    

DOI:10.1002/bbpc.19961000604

出版商:Wiley‐VCH Verlag GmbH&Co. KGaA    

年代:1996

数据来源: WILEY

摘要:

AbstractThe synthesis and characterization of polyelectrolytes, composed of a shape persistent poly(p‐phenylene) backbone with regularly attached sulfonic acid‐ and n‐alkyl residues, is described. Polymers were obtained by Pd‐catalyzed coupling of substituted p‐phenylene‐bis‐boronic acid esters with 2,5‐dibromobenzenesulfonates or 4,4′‐dibromodiphenyl‐2,2′‐disulfonates, followed by saponification of the sulfonates. The polymers were found to have number average contour lengths (Ln) betwen 23 and 155 nm. The polymer sulfonic acids behave as strong acids and are soluble in water as their tetramethylammonium salts. The concentration dependence of the viscosity of aqueous solutions of the salts does not follow the behavior seen for conventional polyelectrolytes. The polymers show lyotropic behavior at low to moderate concentrations. Polymers with long alkyl substituents, if spread as monolayers on a Langmuir trough and subject to the Langmuir‐Blodgett technique, give LB‐multi‐layers, which have been characterized by X‐ray reflectometry. As a model compound, sodium 4,4″‐dimethyl‐1,1′:4′,1″‐terphenyl‐2′‐sulfonate was obtained a

ISSN:0005-9021    

DOI:10.1002/bbpc.19961000605

出版商:Wiley‐VCH Verlag GmbH&Co. KGaA    

年代:1996

数据来源: WILEY

摘要:

AbstractAccording to some statements in the literature, it is very hard or virtually impossible to get meaningful relaxation data for macromolecular systems by methods involving electric field pulses (electric field jump and Joule temperature jump), mainly because of perturbations resulting from field induced orientation effects. These statements have been presented until recently, in spite of the fact that the magic angle technique for suppression of such effects has been described in the literature quite some time ago. Apparently there is not sufficient knowledge on the existence/validity/practicability of this technique. More than 20 years experience with magic angle detection is summarized, including a recent detailed comparison of magic angle fluorescence T‐jump data with corresponding stopped flow data for the case of ethidium intercalation into DNA double helices. The results demonstrate that chemical relaxation induced by application of electric field pulses to macromolecular solutions can be measured without perturbations, provided that appropriate procedures are used. Moreover, techniques using electric field pulses proved to be the only practicable approach to analysis of many macromolecular reactions.It is not always necessary to suppress orientation effects; on the contrary, orientation effects can be very useful to follow reactions which cannot be detected by other procedures. A special case is demonstrated where reaction and orientation effects appear as a convolution produc

ISSN:0005-9021    

DOI:10.1002/bbpc.19961000606

出版商:Wiley‐VCH Verlag GmbH&Co. KGaA    

年代:1996

数据来源: WILEY

摘要:

AbstractRecently the controversial discussion on the reliability of electrooptical relaxation data of polyelectrolyte systems has been revived. It can be shown that chemical‐conformational contributions, for instance, to the dichroitic absorbance changes are exactly given by ΔACH=(ΔA∥+2·ΔA⊥)/3, where ΔA∥and ΔA⊥are the measured at the light polarization modes σ = 0° (∥) and σ = 90° (⊥), respectively. Alternatively, ΔACH=ΔAσ*, where σ*= 54.7° is the magic angle (for small absorbance changes). If ΔA∥is measured at the various σ‐polarization modes according to ΔAσcos2σ+ΔA⊥sin2σ, the exact value of ΔACHis readily obtained. On the other hand, the linear dichroism ΔA= ΔA OR∥‐ΔA ⊥OR=ΔA∥‐ΔA∥+(ΔA ∥CH‐ΔA ⊥CHcan only be determined as an approximation of the

ISSN:0005-9021    

DOI:10.1002/bbpc.19961000607

出版商:Wiley‐VCH Verlag GmbH&Co. KGaA    

年代:1996

数据来源: WILEY

摘要:

AbstractCopolymers of acrylamide with quaternary ammonium cationic monomers (dimethylaminoethylacrylate‐methyl chloride, DMAEA and dimethylaminoethylmethacrylate‐methyl chloride, DMAEM) have been synthesized by inverse‐emulsion copolymerization using both sorbitan monoleate (SMO) and a block copolymeric surfactant (HB246) whose hydrophilic moiety is polyethylene oxide and whose hydrophobic moiety is poly‐12 hydroxy stearic acid. Residual monomer concentrations were determined by means of an optimized HPLC method using a CN coated column. The optimized conditions consist of an acetonitrile‐water mobile phase with a ratio of 50:50 vol% with dibutylamine used as an additive to reduce the adsorption of the cationic monomer at a concentration of 0.01 M and phosphoric acid to adjust the pH. The results indicate that the choice of surfactant influences strongly the quality of the copolymers produced. For example, more uniform copolymers of acrylamide and DMAEA can be synthesized using the block copolymeric surfactant (HB246) at faster production rates in comparison with sorbitan monoleate (SMO). However, a composition drift is observed in the inverse‐emulsion copolymerization of acrylamide and DMAEM using HB246. It is shown that uniform water soluble copolymers of acrylamide and DMAEM can be produced by implementing semi‐batch policies with non time‐var

ISSN:0005-9021    

DOI:10.1002/bbpc.19961000608

出版商:Wiley‐VCH Verlag GmbH&Co. KGaA    

年代:1996

数据来源: WILEY

摘要:

AbstractIn relation to recent results of regioselective reactions in cellulose chemistry, the synthesis and properties of important cellulose polyelectrolytes, namely of carboxymethyl cellulose and cellulose sulfate are described. Synthesis paths leading to such cellulose polyelectrolytes with an unusual pattern of the distribution of functional groups were developed using protecting group technique, activation effects, as well as phase separation phenomena. The regioselective distribution of functional groups within the anhydroglucose repeating unit at fixed degree of substitution and along the polymer chain is shown to be especially relevant, e.g., to solubility, salt tolerance, and interaction with human blood.

ISSN:0005-9021    

DOI:10.1002/bbpc.19961000609

出版商:Wiley‐VCH Verlag GmbH&Co. KGaA    

年代:1996

数据来源: WILEY

摘要:

AbstractRadical polymerization is the most commonly employed polymerization technique for the preparation of water‐soluble polymers. Unfortunately, not all water‐soluble monomers readily undergo radical homopolymerization in water. Here we report on a new redox‐initiator system for starting radical polymerizations in aqueous media. The initiator system consists of at least two components. One component (A) must contain an organic sulfonate or sulfonic acid, the other one is tetravalent Cerium. Results are presented for the following cases, which differ with respect to the properties of the componentA:I)I) IfAis saturated it acts only as a reducing agent of the initiator system which is capable of starting radical polymerizations in the water phase. In this case the rate of polymerization is higher the higher the water solubility of the monomers.II)However, ifAis an unsaturated sulfonic compound (M) the reaction leads to hyperbranched products. This is due to the fact thatM, which is for ordinary radical polymerizations a monofunctional monomer, becomes bifunctional in this special case of initiation.III)On the other hand, ifAis the water‐soluble polymer derived fromM, one or more other monomers can be grafted onto the backbone of this polymer leading to graft‐blockc

ISSN:0005-9021    

DOI:10.1002/bbpc.19961000610

出版商:Wiley‐VCH Verlag GmbH&Co. KGaA    

年代:1996

数据来源: WILEY

摘要:

AbstractThe concept of apparent charge is a convenient tool for the description of electrical effects on polyelectrolytes in solution. The apparent charge can be significantly lower than the structural charge. The difference between these two parameters provides information on the interactions between the particle and the surrounding medium. Assessment of the physical contribution to the apparent charge can be made with the use of modern electrolyte theories; chemical speciation processes can be described by suitable chemical models.

ISSN:0005-9021    

DOI:10.1002/bbpc.19961000611

出版商:Wiley‐VCH Verlag GmbH&Co. KGaA    

年代:1996

数据来源: WILEY