MECHANICAL DEGRADATION OF POLYSTYRENE

This paper is concerned with the mechanism of the stress-induced fracture of polymers, particulary with a number of complex events occurring on the molecular level which takes place before the failure. In recent years, stress-induced bond cleavage in polymers has received increased attention, many authors noting the presence of free radicals and/or volatile products released upon fracture; a free-radical decomposition mechanism involving up to 10**3 molecules per chain rupture also has been postulated. A special tensile stress-strain and shear apparatus was developed and located inside the ion-source housing of a time-of-flight mass spectrometer to characterize the volatile products released during mechanical degradation of PS. The PS was purified by two methods: vacuum outgassing and fractional reprecipitation. Large amounts of styrene evolved from both the as-received and outgassed samples; however, essentially none was observed from the reprecipitated samples. Previous reports on monomer evolution during mechanical stress of PS may be the result of residual monomer and not mechanical degradation products. The product of the surface density of primary radicals and the chain length for unzipping is less than 3 multiplied by 10**1**0 radicals/mm**2 indicating a maximum radical concentration of approximately 10**1**0 radicals/mm**2.