Bestimmung von starker neben schwacher säure in polyurethan‐dispersionen mit SO‐ und COO⁻ ‐gruppen

Abstract

ZUSAMMENFASSUNG :Es wurden Dispersionen von Polyetherurethanionomeren mit einem bekannten Gehalt an SO, -und COO--Gruppen hergestellt. Nach Kationenaustausch der Dispersion gegen H + liiBt sich der Gehalt an starker und schwacher Saure durch konduktometrische Titration mit NaOH insbesondere in Gegenwart eines Neutralsalzes (KBr) quantitativ bestimmen. Potentiometrisch wird in Gegenwart von KBr die Summe an starker und schwacher S u r e quantitativ e r f d t , nicht jedoch die Einzelanteile, da sich ein Teil der COOH-Gruppen wie starke Saure verhdt. Der KBr-Zusatz erhoht insbesondere die Sauresttirke der starken Saure und verbessert dadurch die Erkennung der Endpunkte. Nach Kationenaustausch gegen Ag+ 1a8t sich die Summe an starker und schwacher Saure durch konduktometrische Titration mit NaCl bestimmen, da der Ionenaustausch gegen Ag+ quantitativ verlauft. COO--Gruppen lassen sich durch konduktometrische Verdrangungstitration mit HCl erfassen. Die bei der Synthese gebildeten Polyelektrolyte konnen nach Ausfrieren der Dispersion mit den genannten Verfahren im Serum bestimmt werden. Die Abtrennung der Polyelektrolyte mit COO--Gruppen durch Anionenaustausch verlauft im Gegensatz zu Polyelektrolyten mit SO, -Gruppen im allgemeinen nicht quantitativ. SUMMARY:Aqueous dispersions of poly(etherurethanes) with known concentrations of SO; and COO-groups were prepared and analyzed for strong and weak acid groups after cation exchange against H + or Ag+ by conductometric and potentiometric titrations. While the conductometric titration of Ag+ ions with NaCl represents a very reliable method for the determination of the sum of strong and weak acid, the endpoints during neutralization with NaOH are often incorrect or difficult to evaluate. However, the conductometric neutralization in the presence of a salt (KBr) distinguishes quantitatively between strong and weak acid, as the acid strength of the SO,H groups increases by addition of the salt. The replacement of COO-groups in a salt by conductometric titration with a strong acid, such as HC1, represents a method for

Scope and Limitations of Surface Functional Group Quantification Methods: Exploratory Study with Poly(acrylic acid)-Grafted Micro- and Nanoparticles

“…Therein, complete protonation or deprotonation of all surface functional groups is commonly presumed, 22,24 which may, however, occasionally require drastically elongated equilibration times to allow diffusion of titrant ions into the polymer network and avoid a systematic underestimate. 23,25 In our case, base-into-acid titrations in the presence of 0.3 mM KBr as a neutral salt 22 were performed to determine the total number of COOH groups on the particle surface, and a stable conductivity value was reached after 5−10 min. The results indicated PAA surface concentrations in the range of 21−7000 μmol g −1 (see Table S-1, Supporting Information, for details) and were determined with the intention to serve as benchmark values in this report, when compared with results from the other methods.…”

“…Conductometric titrations for quantifying the total number of acidic and basic surface functional groups are frequently used because of their apparent simplicity. Therein, complete protonation or deprotonation of all surface functional groups is commonly presumed, , which may, however, occasionally require drastically elongated equilibration times to allow diffusion of titrant ions into the polymer network and avoid a systematic underestimate. , In our case, base-into-acid titrations in the presence of 0.3 mM KBr as a neutral salt were performed to determine the total number of COOH groups on the particle surface, and a stable conductivity value was reached after 5–10 min. The results indicated PAA surface concentrations in the range of 21–7000 μmol g –1 (see Table S-1, Supporting Information, for details) and were determined with the intention to serve as benchmark values in this report, when compared with results from the other methods.…”

“…Micro- and nanoparticles are of current interest for a range of applications in materials sciences, life sciences, and medicine, including, for example, DNA sequencing, fluorescence-based assays, sensors, in vivo imaging, drug delivery, and optoelectronic devices. − The key to better understand and control their materials properties and interactions with other molecules lies in the precise knowledge of the number, chemical nature, and spatial distribution of their surface functional groups. , Up-to-date methods for quantifying the number of surface functional groups include, for example, attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR), X-ray photoelectron spectroscopy (XPS), solid-state NMR, or isothermal titration calorimetry. − However, for determination of acidic or basic surface functional groups, potentiometry and conductometry are still among the most widely used methods, because they are relatively straightforward to implement and do not require highly sophisticated and specialized instrumentation. − As an alternative, colorimetric or fluorometric assays have been developed, which are faster and more sensitive but may suffer from certain artifacts if not properly validated. − …”

Simple Colorimetric Method for Quantification of Surface Carboxy Groups on Polymer Particles

“…Conductometric titrations were performed as equilibrium titrations according to literature methods . In brief, varying amounts of microparticle stock solution were diluted with 15 mL of 0.3 mM KBr.…”

Multimodal Cleavable Reporters versus Conventional Labels for Optical Quantification of Accessible Amino and Carboxy Groups on Nano- and Microparticles

“…This maximum number typically equals the total number of (de)­protonable surface functionalities, as demonstrated by us in a comparison of conductometry and solid state 13 C NMR for nano- and microparticles surface functionalized with poly­(acrylic acid) . Electrochemical titration methods are inexpensive, but require a relatively large amount of sample and prolonged equilibration times. − Moreover, they are sensitive to ionic contaminations originating, for example, from initiators of radical polymerization reactions, stabilizers, and salts. Optical methods like spectrophotometry and fluorometry require an absorptive or emissive label with a larger size compared to H + and OH – , like organic dyes covalently attached or adsorbed to the FGs of interest. − ,,,− Although this approach yields a smaller amount of FGs with a respective stoichiometry factor depending on label size, it provides important information on the number or density of accessible or derivatizable FGs required for subsequent (bio)­conjugation reactions.…”