Polymer crystallization by chemical nucleation

Abstract

Several attempts^1–5 have been made to control the rate of crystallization and the morphology by the addition of very finely-divided substances which promote abundant nucleation. However, these studies have mostly been carried out on an empirical basis and, except in a few cases (self-seeding⁶, epitaxy^2–5), the mechanism of action of these nucleating agents is poorly understood despite several attempts at modelling^1,2. This is particularly so in the case of most technical nucleating agents such as mica, talc and organic salts. We report here that the mechanism of action of organic nucleating agents such as sodium benzoate and its derived salts completely differs from the generally accepted model, at least in the case of polyesters. The nucleating agent reacts as a true chemical reagent with the molten macromolecules and produces ionic end groups which constitute the true nucleating species.