PAA/PEG complexes

The temperature stability of the complexes seems to be dependent on the molecular weight of the PEG chain, i.e., the larger the PEG the lower the temperature at which the complex dissociates. An important observation was that the complexation/decomplexation phenomenon was reversible by changing the temperature of the system. The positive values of the thermodynamic parameters as well as the experimental observations clearly indicate the important role of hydrophobic interactions in the stabilization of the PMAA/PEG complexes. Since PAA is considerably more hydrophilic than PMAA, hydrophobic interactions do not play an important role in stabilizing the PAA/PEG complexes. This is represented by the much... 

Enthalpy Values Associated with the Formation of PMAA/PEG and PAA/PEG Complexes in Water and Water/Methanol Mixtures... 

PEG, PAA-PEG complexes is much higher than that of the initial high molecular weight components. Sedimentation coefficients of PMAA-PEG complexes in water are 20-25 s/g, indicating a high compactness of the particles. Two types of distribution are possible ... 

PEG). Note that even though the PAA-PEG complex is known to form a stoichiometric complex, ( 1,2 ) there is no discontinuity at the stoichiometric ratio the Ip/Ijj continues to drop even in the presence of excess PAA. However, acetic acid does not cause any change over the whole composition range. 

Third, the addition of PAA induced a decrease of intramolecular excimer formation for PEG. Even though the PAA-PEG complex is found to have an equal mole of each repeating unit by past studies, d. 2) Ip/lM isolated chain decreases continuously with an... 

The biphasic association kinetics of the PAA/PEG complexes at pH 2.7 and 20°C were also followed by fluorescence spectroscopy by Bednar et al. [69]. The complexation rate constants in PAA/PEG were found to be surprisingly insensitive to chain length. In general, chain interchange rates decreased with increasing salt concentrations and PAA/PNVP interchange rates were much slower than those of PAA/PEG. These rates were also inversely related to PEG molecular weight. 

Papisov et al. (1974) performed calorimetric and potentiometric experiments to determine the thermodynamic parameters of the complex formation of PMAA and PAA with PEG. They investigated how temperature and the nature of the solvent affected the complex stability. They found that in aqueous media the enthalpy and entropy associated with the formation of the PMAA/PEG complex are positive while in an aqueous mixture of methanol both of the thermodynamic quantities become negative. The exact values are shown in Table II. The viscosities of aqueous solutions containing complexes of PMAA and PEG increase with decreasing temperature as a result of a breakdown of the complexes. 

Figure 9. The two kinds of polymer complex structure, (a) compact complex (b) gel-like complex. (----) PAA ( ) PEG ...

Osada and Takeuchi [132] have done pioneering work based on interpolymer complexation and specifically with PMAA-PEG and PAA-PEG systems. In some interesting work, they looked at the effects of PEG treatment on a PMAA membrane. Drastic dilations and contractions because of complexation were seen as a function of pH when a PMAA membrane was treated with PEG. Upon treatment with a small amount of PEG, a PMAA membrane could lift and lower a weight by contraction and dilation to 90% of its length. Based... 

The complex formation in PMAA-PEG and PAA-PEG systems was investigated for various molecular weights of PEG by means of potentiometric titration91. The degree of the complex formation 6 and the stability constant K were determined. PEG with M = 2000 forms complexes at elevated temperatures (K = 500, 6 = 0.6 at 55 °C) however, a further increase in temperature causes the complex to dissociate. PEG with M = MOO forms a more stable complex which does not dissociate in the investigated temperature range (K = 100, 0 - 0.7). PEG s with M = 7.5 x 103 and 20 x 103 produce a stable complex, the stability of which does not change with temperature. 

It has been shown that much more stable complexes are formed from shorter PEG chains in the PMAA-PEG system as compared with the PAA-PEG system91. This confirms the essential role of the hydrophobic interactions in the formation of interpolymer complexes. 

G. Baeras et al.124 have studied the complex formation in the systems PAA-PEG, PMAA-PEG and PMAA-block copolymer of ethylene and propylene oxides by spectrometry when PMAA is added to the PAA complexes in the presence of a dye (bromocresol green). It is shown that PMAA is more susceptible to complex formation than PAA in the reaction with oligomers. 

Second, the longer chain of PAA showed a stronger interaction with PEG. The present observation of the molecular weight dependence of PAA on complexation is similar to the results of the molecular weight dependence of PEG, where Antipina observed that longer chains of PEG reduced the viscosity a greater amount for molecular weights between 6000 and 40,000 because of complexation. (12)... 

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