SynopsisThe fracture behavior of a piperidinemisphenol A diglycidyl ether (A) resin has been determined in bulk a q l as an adhesive using the linear elastic fracture methods developed by Mostovoy. The effect of adding carboxy-terminated butadiene-acrylonitrile (CTBN) elastomer to resin A was investigated. The opening-mode fracture energy (91~) of resin A was 120 to 150 J/m2, and largely attributable to plastic deformation. Fractographic evidence was obtained for plastic flow a t the crack tip during crack initiation. Propagation was unstable due to the rate dependence of the plasticity. There were no significant differences in the bulk and adhesive fracture behavior. Addition of 5-15% CTBN to resin A produced minute elastomer particles which increased Sic to -4000 J/m2 (at 15%). Further CTBN addition resulted in an elastomerepoxy blend and a decrease in fracture energy. Fractography again indicated that crack initiation involved plastic deformation but that the elastomer had greatly increased the volume in which the deformation occurred. The adhesive fracture of the elaatomer-epoxy was found to be strongly dependent on the crack-tip deformation zone size (ryJ in that 9 1~ was a maximum when bond thickness was equal to 2 rye. At bond thicknesses less than 2 r,, there was a restraint on the development of the plastic zone resulting in lower 91. values.

A statistical-mechanical treatment of a polymer molecule adsorbed on a solid surface is given. The surface coverage by adsorbed molecules is assumed to be sufficiently low that the interactions of the adsorbed polymer molecules with each other may be neglected. The partition function is derived for a polymer molecule with sequences of repeating units adsorbed at an interface and with other sequences (loops) held at the surface only at their ends. The assumption of Gaussian statistics for the loops leads to a formulation equivalent to that used for the helix-coil region in DNA molecules. A broad distribution of loop sizes is found, in contrast to Silberberg's theory in which a sharply peaked distribution is assumed. The latter theory predicts also small loops for all values of the adsorption free energy. In contrast, our theory predicts large loops and few units adsorbed for small adsorption free energies and small loops and more units adsorbed for larger adsorption free energies when the chains are sufficiently flexible. This result is also in partial disagreement with earlier theories that predict large loops, even for relatively large adsorption free energies. On the other hand, for stiff chains our theory predicts only a small number of loops with most units at the surface. A relationship between the initial slope of an adsorption isotherm and the molecular weight of the polymer is presented.

SynopsisThe kinetic parameters of the polymerization of diglycidyl ether of bisphenol A with hexahydrophthalic anhydride and benzyldirnethylamine as catalyst were determined using differential scanning calorimetry. The reaction was found to be first order with some variation with temperature, and the activation energy and natural log of the frequency factor were 25 kcal/mole and -25 sec-', respectively. These results are discussed with respect to a steady-state mechanism of the polymerization and compared with results reported for other epoxide-anhydride reactions.

The conformation of a polyester, poly(ethylene o‐phthalate), of relatively low molecular weight was studied after adsorption. The extension of the adsorbed molecule in a poor solvent on several planar metal surfaces was studied by ellipsometry and the fraction p of attached groups on colloidal silica particles in a good solvent was determined by the shift in the infrared absorption frequency between free and adsorbed carbonyl groups. In contrast to previously reported results for polystyrene, the extension normal to the surface remained constant (∼70 A.) while the concentration of polymer in the adsorbed film increased during the adsorption period. The value of p (0.34 for MW = 5400) is relatively high and was independent of surface population for the range of solution concentrations measured. Differences between these results and those for polystyrene are interpreted as resulting from differences in interaction energy and chain stiffness.

Some data on the adsorption of poly‐4‐vinylpyridine on a glass surface are presented. The results on the un‐ionized polymer are characteristic of the adsorption of organic polymers; the adsorption isotherm has a flat top and the amount adsorbed depends on the solvent used. The adsorption of ionized poly‐4‐vinylpyridine decreases with increasing ionization and increases with increasing ionic strength. The effect of increased ionic strength is presumably associated with the greater tendency of an ionized polymer to coil in the presence of excess salt. These results tend to confirm the general hypothesis that the coiling of a polymer molecule at a liquid–solid interface reflects the tendency of the polymer to coil in solution.