The dynamic mechanical properties of Nafion precursor were determined as a function of the degree of conversion to the sodium ionomer, and those of the acid as a function of the degree of conversion to the cesium salt. A run was also made on the barium neutralized material, as well as on a remolded sample of a partly converted precursor. The precursor shows four dispersions which (in order of decreasing temperature) are identified with the glass transition, motions of the ether side chains, CF2 groups in the backbone, and pendant SO2F groups. Four relaxation regions are also seen in the ionomer, which are identified with the glass transition of the ionic regions and of the matrix, as well as with motions of the ether side chains and the backbone CF2 groups. While the polymers in the acid and the salt forms arc compatible, as seen by the gradual movement of the ionic glass transition peak to higher temperatures with increasing degree of neutralization, the salt and the precursor are not compatible. In the barium salt, the ionic glass transition peak occurs at a temperature close to the melting point of the crystalline regions, and most likely contains a contribution from that process also.
SynopsisSorption phenomena of water and aqueous salt solutions by a perfluorinated polymer containing sulfonic acid groups (Nafion) were investigated. The temperature and concentration dependencies of the sorption by the membranes in the acid and salt forms were studied. The apparent activation energies for the diffusion of water in the H-form membrane and in the K-salt form were obtained as 4.9 and ca. 13.0 kcal/mole, respectively. The sorption kinetics during the neutralization of the membranes were observed in several aqueous solutions. A maximum in the sorption curve during the neutralization process was found and explained as resulting from the differences in the diffusion coefficients of water and of the cations and from the different number of water molecules absorbed by a SO:H+ (acid) site and a neutralized site. The diffusion coefficients D of several cations (K+, Cs+, Ba2+, and Ca2+) were determined and found to be considerably smaller than that of water. For the various cations, log D was related linearly to q/a, where q is the cation charge and a is the separation between centers of charge of the cation and anion. The dependence of water sorption upon the degree of neutralization of the membrane was also studied at room temperature. It was observed that for membranes of a low degree of neutralization a secondary sorption process existed, while no such secondary sorption could be found for the pure acid or the highly neutralized membranes. This secondary sorption was attributed to a structural rearrangement in the polymer. The apparent diffusion coefficient of water and the number of water molecules absorbed at equilibrium by an ionic site, n,, were obtained as a function of the degree of neutralization. The diffusion coefficient of water was dependent strongly on both the degree of neutralization and type of the salt, but no quantitative relation could be established. For all the salts studied in this paper, n, was linearly related to the degree of neutralization, x , supporting the assumption that the value of n, could be divided into those water molecules absorbed by an SO:H+ (acid) site, nh, and those absorbed by a neutralized site, n,. It was found that the value of q X n, had a strong correlation with a characteristic constant of the cations since a plot of q X n, versus log ( q / r ) yielded a straight line (r being the radius of the cation).
The change in thc fraction crystallinity with time and elongation of synthetic cis-1.4polyisoprene is studied through simultaneous measurement of birefringence and stress. Results are compared with values estimatcd from the decrease in stress arising from the crystallization. Various mcthods for calculating the crystallinity from the data arc compared. This method proves to be a sensitive, convenient method for determination of crystallinity of such samples. ZlJSAMM ENFASSIJNG :Die Anderung der Kristallinitiit ids Funktion der Zeit und des Verstreckungsgrades von synthetischem c,is-l,4-Polyisopren wird durch gleichzeitige Messung der Doppelbrechung und der Zugspannung untcrsucht. Die Ergebnisse werden mit Werten vcrplichen. die aus der durch die Kristallisation bedingten Abnahme der Zugspannung abgeschltzt wurden. Verschiedene Methoden zur I3erechnung der Kristallinitiit aus den experimcntellcn Daten wcrdcn verglichcn. Es kann pcrcipt wcrden. dal3 diese Methodc cin cmpfindlichcs. einfach LU handhabendes Vcrkihrcn zur 13estimmunp der Kristallinitlit dieser Prohen darstellt.Professor Mark's studies of the theory of rubber elasticity were among his many noteworthy contributions to the development of polymer science. He was also one of the pioneers in the use of X-ray diffraction in
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