Naslov
Size-exclusion chromatography of syntetic polyelectrolytes

Autori
Šegudović, Nikola

Vrsta, podvrsta i kategorija rada
Sažeci sa skupova, sažetak, znanstveni

Izvornik
13th International conference on polymers separation and characterization of macromolecules,Book of Abstracts / Berek, D. - Bratislava : Slovakian Chemical Society, 1999, 88-89

Skup
13th International conference on polymers separation and characterization of macromolecules

Mjesto i datum
Bratislava, Slovačka, 04.07.1999. - 09.07.1999

Vrsta sudjelovanja
Pozvano predavanje

Vrsta recenzije
Međunarodna recenzija

Ključne riječi
size-exclusion chromatography; syntetic polyelectrolytes; molecular mass distribution

Sažetak
Synthetic polyelectrolyte are polymers with anionic or cationic groups located along the polymer chain or on pendant groups attached to the polymer chain backbone. The ionic groups inherently may be part of the chemical structure, or their presence may be induced by the solvent Electrochemically, a polyelectrolyte can be classified as either a polyacid, a polybase or polyampholyte depending upon the nature of its ionization in water solution. From structural point of view polyelectrolyte may also be classified as either linear or crosslinked. Since polyelectrolyte are macromolecular substances, it is quite natural to compare their behaviour in solution with that of neutral polymers. Similarly, the existence of polyionic species in solution suggest the use of solutions of simple electrolyte as a second possible frame of reference. Qualitatively, solution of polyelectrolyte does indeed display some behavioral similarities to both nonionic polymer solutions on one hand, and to simple electrolyte solutions on the other. In contrast to a simple electrolyte like sodium chloride, in which the size of the oppositely charged ions are similar in magnitude. a polyelectrolyte is always composed of a macroion in which the charged group are interconnected by chemical bond, together with an equivalent number of small oppositely charged counterions. Virtually, all of the unique properties of polyelectrolytes result from the interaction of interconnected ionic group of the macroion, and in turn, from the interaction of the charged macroion with its compensating counterion. In aqueous solution all of the synthetic polyelectrolytes mentioned above tend to adopt a randomly coiled configuration, suitably modified by the mutual interaction ( generally repulsive ) of charged groups on the polyion chain. Solution containing charged macroions display a large deviation from thermodynamic ideality. Even in dilute solutions of strong polyelectrolyte, the activity coefficient of small counterion is only about 0.25. These nonidealities are a consequence of the large electrostatic potentials which exist in the vicinity of polyions with multiple charge; counterions become "trapped " in these regions of high potential and essentially lose their identity as independent mobile species. It is instructive to compare the concentration dependence of the reduced viscosity (?sp/c) of polyelectrolyte with that of its parent, nonionic polymer with the same chain length. Dilution of the nonionic polymer results in a linear decrease of reduced viscosity according to the well-known Huggins equation. The effect of dilution on the reduced viscosity for the related polyelectrolyte is remarkably different. In this case, the reduced viscosity increases sharply with dilution and sometimes (?sp/c) approaches the ordinate almost asymptotically. Interpretation of some other solution properties of polyelectrolyte ( osmotic pressure, light scattering ) are also more complicated. Molecular mass is one of the most important parameters for end-use properties of polymers. According to the nature of polymerization reactions it is not a unique feature and it is characterized by one or more molecular mass averages or by molecular mass distribution. High performance size-exclusion chromatography (HPSEC ) is practically the most powerful method for molecular mass distribution determination ( MMDD). HPSEC is a modern separation, liquid chromatography technique which provides a separation of macromolecular species from macromolecular mixtures according to their size (hydrodynamic volume ) in solution and it is used very often in both research and industry. A numbers of homopolymers and copolymers are characterized by HPSEC, but some problems have arisen in molecular mass distribution of polyelectrolytes. The main problem in separating a polyelectrolyte by SEC is that the polymer size in solution is governed not only by molecular mass, but also by the number of the attached ionogenic groups, the type of the counter-ion ( its charge and mobility ), and the polarity and electrical screening properties of the solvent. Abnormal chain expansion occurs when an ionic polymer is dissolved, because the number of electrical charge within the polymer coil generally exceeds that in the bulk solvent. Osmotic forces drive solvent into the coil to expand it and cause the counterion to diffuse out away from the backbone chain into the bulk portions of the solvent.This process leaves a net residue of charged groups ( cationic or anionic ) on the polymer chain. The charge groups remaining on the polymer chain are resposible for large intramolecular repulsive forces and lead to a further chain expansion. The addition of strong electrolyte to the solvent suprresses the loss of counterion from the charged sites on the polymer and permits a return of the polymer to normal physical and thermodynamic solution properties, in which state the polymer can be separated reproducibly. Maleic acid polymers and copolymers as auxiliary agents ( dispersing agents, emulsifier, coatings, adhesives, sizing agent, etc. ) are a typical example of synthetic polyelectrolyte. Due to the presence of two weak carboxylic groups on the maleic acid unit and a strong sulfo group on the alternating sryrene unit, a partially sulfonating copolymers of maleic acid and styrene as an anionic polyelectrolyte are specially interesting to study HPSEC of polyelectrolyte. MMD of partially sulfonated alternating copolymers of maleic acid and styrene with different degree of sulfonation were determined. In pure DMF calculated MM using polystyrene calibration curve have been almost two order in magnitude higher than the expected ones.The increasing concentration of LiBr shifts chromatograms toward the higher elution volume or lower MM. The concentration of LiBr of 0.1 M / L has not been enough to shift chromatograms on the expected MM range for the sample with the highest degree of sulfonation ( 83 mol % S ).

Izvorni jezik
Engleski

Znanstvena područja
Kemija

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