Swelling properties of polystyrene crosslinked by high energy radiation

Abstract

Polystyrene has been crosslinked by atomic pile radiation, the degree of crosslinking being proportional to the radiation dose. The swelling properties of the crosslinked polymer have been studied as a function of degree of crosslinking γ. There is found a relationship of the form required by theory: V^5/3 ∝︁ 1/γ, V being the volume swelling ratio. This formula fails at low degrees of crosslinking. A fuller investigation shows that a number of corrections must be applied, taking into account gel fraction, distribution of molecular weight, and crosslinking index in the gel, etc. On the assumption that the initial molecular weight follows a Poisson distribution, good agreement is obtained between the fuller theory and observed data. The number‐average molecular weight is between 1.53 × 10⁵ and 2.14 × 10⁵. The relationship between γ and radiation dose R is also obtained, and is identical with that deduced previously by entirely different means from solubility data. Pile radiation provides a means of producing polymers with accurately known crosslinking index. The energy required to produce a crosslink in polystyrene by high energy radiation is much greater than in many other linear polymers.