The main objective of this work has been to develop some rational hypothesis for the toughness of rubber‐modified glassy polymers as defined by the energy to rupture in a tensile measurement. It is shown that the rigid phase yields and that the toughness is a result of the large energy absorption involved in the cold drawing of the matrix. The rubber phase acts principally to induce a yielding in the matrix. A triaxial stress field in the environment of the dispersed particles results in local increases in free volume which aid in the initiation of cold drawing and provides the rubber with sufficient breaking stress to prevent premature crack propagation.

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SynopsisMelt crystallization of isotactic polypropylene (iPP), poly(ethy1ene oxide), poly(butene-l), and polycaprolactone in contact with various substrates (mostly polymeric) has been studied by hot stage polarizing microscopy. Nucleating abilities of surfaces have been characterized qualitatively by examining the substrate-induced morphologies of the crystallizing polymer. These morphologies have been classified into three groups, depending on whether the substrate is very active (transcrystallinity), moderately active, or inactive as a nucleating agent. The morphologies observed are temperature-dependent, changing from transcrystalline to spherulitic upon increase of the crystallization temperature. A t intermediate temperatures, mixed surface morphologies (transcrystalline plus spherulitic) are observed.The concentration of titanium and aluminum catalytic residues in isotactic polystyrene (ips) samples can be reduced by two methods, i.e., (a) fractionating the polymer and (b) chelating Ti and A1 with acetylacetone. The high nucleating ability of IPS samples in the crystallization of iPP has been shown to be due to the polymer (ips) itself, and not to Ti and A1 residues. Apart from ips, other polymers (low energy surfaces) have also been found to induce transcrystallinity.From a, survey of 43 substrate-crystallizing polymer pairs, conclusions have been drawn which are relevant to the following potential factors in heterogeneous nucleation processes: (a) chemical structure, (b) crystallographic unit cell type, (c) lattice parameters, (d) crystallinity of substrate, and (e) surface energy of substrate.Summit, New Jersey 07901. chusetts, Amherst, Massachusetts.

Root‐mean‐square end‐to‐end dimensions (r2)1/2 and molecular weights M have been determined from light scattering studies carried out on a series of fractions of poly‐(acrylic acid) in dioxane (θ point, 30°C.), on two polyisobutylene fractions in cyclohexane and in ethyl n‐caprylate (θ point, 22°C.), and on a single poly‐(methyl methacrylate) fraction in acetone. Intrinsic viscosities of the various polymers measured in these same solvents at the same temperature (30°C.) support the relationship [η] = Φ(r2)3/2/M, where Φ is a constant independent of molecular weight and solvent type and (according to the data herein reported) has the approximate value 2.2 × 1021. The θ points, representing the temperatures at which ideal behavior prevails, were determined for the two poor solvent–polymer systems by extrapolation of critical consolute temperatures to M = ∞. The intrinsic viscosity of poly‐(acrylic acid) in dioxane at 30°C. (the θ point) is given by [η] = 0.85 × 10−3M1/2; the value of the constant approximates those for nonpolar polymers. The influence of molecular weight heterogeneity on the fundamental relationship of the intrinsic viscosity to (r23/2/M) is analyzed, and it is shown that the true value of the universal parameter Φ will be greater than the apparent value deduced in the foregoing manner without correction for the heterogeneity of the polymer fraction. For a fraction possessing a relatively sharp distribution as denoted by 〈M〉w/〈M〉n = 1.15. the magnitude of this correction may be as high as 20%.