Cohesional Entanglement of Amorphous Polymer in Glass State as Probed by Equilibrium Swelling in a "Non-Solvent

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Cohesional Entanglement of Amorphous Polymer in Glass State as Probed by Equilibrium Swelling in a "Non-Solvent

The equilibrium swelling of the system Polystyrene (PS) (M = 1.7 × 10^s, monodisperse)/diethyl ether at 30 °C and 35 °C has been studied in detail in quiescent state for a time span over 150 d. Arguments are given to show that the swelling process in a “non‐solvent” is a network swelling rather than a phase separation process. It is different from the cloud point curve (CPC) experiment studied in literature, where the experiment starts from a one‐phase solution, so that the cohesional entanglement present in the solid polymer is disrupted by dissolution. The cohesional entanglement structure of the solid polymer, on the contrary, is retained in the concentrated phase on swelling, at least in the initial stage. The course of swelling as presented by the curve V_a(t) was found to proceed in three stages, where V_a is the volume of the concentrated phase. In the first and third stages of V_a(t), the curve goes up smoothly, while in the second stage the curve V_a(t) shows large up and down jumps, indicating probably a readjustment in the network structure. Some results on a monodisperse PS sample of M = 5.8 × 10⁵ and a polydisperse sample of M = 2.0 × 10⁵ are also given. The values of V_a observed at swelling equilibrium are not in accord with the expected cloud point temperature. The cloud point curve represents a phase separation process occurring in local regions (space limited to μm) and in time scale of the order of minute, while the process V_a(t) occurred in the whole space of the concentrated phase, in time scale of days. For quantitative characterization of the network present in the concentrated phase, a precise value of the polymer‐solvent interaction parameter x is needed.