Functional oligomers titrations

As to Eq. (7), it is to be remembered that AG, in a general case is a function of p. Therefore, the experimental dependencies of p on concentration, chain length of oligomer and temperature may be employed to find thermodynamic parameters only for a fixed value of p, e.g., for p = 0.5 using Eqs. (8 a- b). These equations have been taken by various authors to calculate the enthalpy and entropy of complex formation between simple synthetic oligomers and polymers 28). In a number of cases the correspondence between the values of complex formation enthalpy thus obtained and determined, either by calorimetry or by potentiometric titration 26), has been found satisfactory although it is obvious that in a general case these values do not necessarily coincide. 

The titration-determined molecular weights of the individual samples were used to calculate the amount of benzophenone required to completely derivatize the amine functionalities. A 10 mol % excess of benzophenone was used to ensure complete derivatization. The reaction was done in bulk at 80 °C by heating the siloxane oligomer and benzophenone for 24 h in the presence of 3-A molecular sieves. GPC analysis was then carried out at 30 °C with a Waters 590 GPC apparatus equipped with ultrastyragel columns with particle sizes of 500, 10, 10", and 10" A. A Waters 490 programmable wavelength detector set at 218 nm was used with THE (tetrahydro-fiiran) as the solvent. 

The GPC traces for the parent oligomer and several of the fractions derived from it are reproduced in Figure 10. The efficiency of this technique at producing difunctionalized fractions of narrow polydispersity is evident from Table III and Figure 10. The presence of two functional groups in these fractions was confirmed by comparing the determined by titration... 

MALDI analysis of hyperbranched polyesteramides showed rapid dissociation of higher oligomers into lower oligomers, and PSD/CID of mass selected ions was used to discriminate between fragment ions and the iso-baric cyclic oligomers. " The results, as well those obtained by NMR, titration, and FD-MS, indicated that simple MALDI-TOF spectra yielded wrong conclusions about the chemical composition and functionality type distribution for the hyperbranched samples. " ... 

The determination of accurate molecular mass values of the copolymers and their distribution, as well as of the functionality of difunctional oligomers remains a difficult problem. It is necessary to compare the results of, at least, two different techniques, for instance SEC and titration of the end-groups but, unfortunately, the latter is inapplicable when the chain length is high. NMR is probably one of the most efficient tools in the determination of the end-group... 

The surface characterization of a polymer particle involves investigating the adsorption of ions and amphiphilic molecules (emulsifiers, oligomers), determining the number of covalently bonded functional groups and acquiring information on the structure of the interfadal layer (swollen state or hairy layers ). Presently this task can not be solved satisfactorily. The main methods used are titrimetric analyses on purified dispersions, soap titration and electrokinetics. 

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