Reduced viscosity complexes

Polyelectrolyte complexation in aqueous solution between PEI and PMAA has been studied through viscometry, conductometry, potentiometry, and IR spectroscopy [90]. Upon addition of increasing concentrations of PMAA to an aqueous PEI solution, viscosity dropped suddenly around a 1 to 4 ratio of PMAA to PEI because of the complexation and subsequent coiling of the complexed chains. Reduced viscosity then rose past this ratio indicating that the stoichiometry of the complex occurs in a 1 4 (PMAA groups PEI groups) formation. Conductance and titration experiments agreed with this theory. The... 

The suggested rod like structure of the pendant-type FVP-Co(III) complex is supported by the viscosity behavior of the polymer-complex solution (Fig. 3)2 The PVP-Co(III) complexes have higher viscosity than PVP this suggests that the polymer complex has a linear structure and that intra-polymer chelation does not occur. The dependence of the reduced viscosity on dilution and the effect of ionic strength further show that Co(en)2(PVP)Cl] Cl2 is a poly(electrolyte). The polymer complexes with higher x values have a rodlike structure due to electrostatic repulsion or the steric bulkiness of the Co(III) chelate. On the other hand, the solubility and solution behavior of the polymer complex with a lower x value is similar to that of the polymer ligand itself. 

The paste method can also be used with soluble derivatives. Since drying can be problematic with complexes of soluble derivatives, a minimum amount of water (20% maximum) is generally used. In order to reduce viscosity and associated mixing problems, a higher temperature is employed. A glass forms as the complex is removed from the mixer and cools. The glass can be milled and dried if necessary. 

Fig, 12 a, b. Effect of ionic strength on the formation of polyelectrolyte complexes (a) Reduced viscosity, (b) transmittance Poly(methacrylic acid) (PMAA) (degree of neutralization of PMAA a = l)-Ionene-type polycation (2X), O PMAA(a = 0.75)-2X, 3 PMAA(a = 0.5)-2X, Poly(acrylic acid) (tz = 1)-2X, A Poly(sodium styrenesulfonate)-2X... 

Fig. 4. Temperature dependences of reduced viscosities (C of PMAA = 0.1 g/dl) of PMAA-PEG complexes in water Mv of PMAA = 5 x 10s Mv of PEG = 5 X 103 (2), 2 x lO (3) curve 1 denotes PMAA in the absence of PEG33>...

The dilution of solutions33 containing equimolar ratios of monomer units of the complex components results in the dissociation of the complexes of PMAA with low-molecular weight PEG. The reduced viscosity of solutions rapidly increases, which indicates the existence of the equilibrium PMAA + PEG complex. In the case of a relatively high-molecular weight PEG, the PMAA macromolecules are firmly connected with PEG and at the dilution of aqueous solution, an increase of the reduced viscosity typical of polyelectrolytes does not occur, i.e. the complex does not dissociate. The absence of temperature dependence of the relative viscosity in the temperature range 15-40 °C is indicative of the stability of this complex (Fig. 4). 

The formation of polymer-polymer complexes as a rule is observed in aqueous media5,33. The viscosity of complexes in water is about 0.05-0.10 dl/g and close to that of globular proteins. Aqueous solutions have some features low intrinsic viscosity values are independent of the matrix molecular weight, the absence both of the concentration dependence of the reduced viscosity and the polyelectrolyte anomaly, and high values (about 30 s) of the sedimentation constant. 

Fig. 8. Dependences of reduced viscosity (C of PMAA = 0.0516 g/dl) on the degree of ionization a for aqueous solutions of PMAA (1) and of the complex PMAA-PVP (2)57)...

Some papers60-61 have been devoted to phase separation of polyionic complexes from partially furated (PVA-S) and aminoacetylated (PVA-AAC)poly(vinyl alcohol) in aqueous salt solutions. The separation liquid-liquid or complex coacervation occurs at a definite value of the charge density on the macromolecule. From the concentration dependence of the reduced viscosity of the initial components PVA-S, PVA-AAc and their equivalent mixture in water it follows that the viscosity of the components noticeably increases with dilution, and the curve of the equivalent mixture is concentration independent. This fact confirms the formation of the neutral polymer salt, due to electrostatic interactions of PVA-S (strong polyadd) and PVA-AAc (weak polybase). 

The PAA-PVP system in methanol and the PMAA-PVP system in DMF display the typical properties of polycomplexes, namely low values of intrinsic viscosity independent of the matrix molecular weight (for PVP with molecular weight of 50 MO and 560000, the intrinsic viscosity [ /], of PA A-PVP complexes in methanol is equal to 0.07 dl/g), the absence both of the concentration dependence of the reduced viscosity, and of the polyelectrolyte anomaly. 

Fig. 23. Schematic change of complex reduced viscosity t/ /C in a wide range of molecular weights...

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