Sorption of vapors in methanol soaked and in thermally annealed Matrimid® films

Abstract

Matrimid® shows well separated sub‐glass transitions and substantial entrapment of dichloromethane (DCM) in the solution‐cast films. The entrapped DCM was removed by soaking the polymer in the excess of liquid methanol followed either by thermal annealing (vacuum at 200°C) or by the desorption at mild conditions. These physical treatments influenced the sorption kinetics and even the sorption isotherms for vapors of DCM, methanol (MeOH) and acetonitrile (MeCN) at 35.0°C. The sorption isotherms for the thermally annealed Matrimid® were shifted to those for the methanol‐soaked Matrimid® upon its exposure to sufficiently saturated vapors. The physical treatments changed the β sub‐glass transition of the polymer, and did not cause changes in the chemical composition and microstructure as sensed using ATR‐FTIR and SEM, respectively. Relaxation of the annealed Matrimid® was achieved by its soaking in liquid MeOH and by the exposure to vapors, their threshold saturation followed the same order as diffusivity: MeOH > MeCN > DCM. Although methanol appears the least effective agent to induce the relaxation of Matrimid®, it diffuses in and desorbs from the polymer readily. Liquid MeOH and its vapor thus appear the media of choice for causing the relaxation and removal of entrapped solvents from Matrimid®.