POLYMER-CHAIN RUPTURE AND THE FRACTURE-BEHAVIOR OF GLASSY POLYSTYRENE

Uniform latexes of anionically polymerized polystyrene, M(n) = 180 000, M(n) = 250 000, and M(n) = 420 000, were prepared by direct miniemulsification. The 1200-angstrom-diameter particles were cleaned, dried, and sintered, and the resulting films were annealed for various periods of time at 144-degrees-C. The films were fractured with fine dental burr instrumentation at a depth of 4000 angstrom/pass. The number of chain ruptures and consumed energy per unit area were measured, as well as tensile strength. Plots of chain scissions and energy consumed vs 0.5 power of annealing time showed three regimes: mixed, peak, and recovery. Data in the mixed regime confirm portions of the de Gennes and Tirrell theory which predicts a 0.5 power dependence on annealing time and portions of the Wool theory. Using the Lake-Thomas theory, rubber elasticity theory, and bond dissociation energy, the contribution of the several mechanisms consuming energy were estimated on the basis of an energy balance approach. A mechanism involving the scissor-action opening of the 109-degrees carbon-carbon bond and concomitant bond stretching of the about 300 bonds trapped between entanglements is consistent with the consumption of most of the energy in the later annealing stages and/or fast fracture processes. Tensile strength and the fracture energy per unit area of the films increase linearly with the number of chain scissions per unit fracture area in the first regime, as predicted by Peppas.