EFFECT OF MOLECULAR WEIGHT ON CHANGES PRODUCED IN SURFACE LAYER OF POLYSTYRENE FILM IN A NITROGEN ATMOSPHERE BY ULTRAVIOLET IRRADIATION

The effect of molecular weight on the changes in the surface layer of polystyrene films on near‐ultraviolet irradiation has been studied in a nitrogen atmosphere at 25°C. Changes produced by irradiation were followed by determining the amount of solvent‐insoluble portions, the molecular weight changes, and the intrinsic viscosity changes. Most crosslinking took place in the range of the transmissible depth of 2537 Å light. Low molecular weight samples formed a small amount of solvent‐insoluble material. High molecular weight samples formed a large amount of solvent‐insoluble material. In the range above a certain molecular weight, the amount of solvent‐insoluble material approached an asymptotic value with increasing molecular weight, because of the limited penetration of 2537 Å light. Since most crosslinking took place in the range of the transmissible depth of 2537 Å light, the average number of crosslinks in the solvent‐soluble portions was influenced by the amount of solvent‐insoluble material. Low molecular weight samples produced many crosslinks. High molecular weight samples produced a few crosslinks. In the range above a certain molecular weight, the average number of crosslinks in the solvent soluble portions approached an asymptote with increasing molecular weight. Chain scission seems to have occurred in every sample. Copyright © 1969 John Wiley & Sons, Inc.