Phase separation of chemically crosslinked poly(n-butyl methacrylate-co-methacrylic acid) in mixtures of N,N-dimethyl formamide and water

Abstract

When a copolymer network of chemically crosslinked poly( n -butyl methacrylate- co -methacrylic acid) was immersed into a bath of N,N -dimethylformamide (DMF) and water, the swollen network underwent phase separation depending on the fraction x w of water in the bath. Swelling ratio, light transmittance, thermomechanics, dynamical mechanical spectra, and tensile property of the gels in baths of different x w 's were investigated. A ternary phase diagram of this system was calculated from theory for comparison of the experimental data. A glass line was also provided in the ternary phase diagram from the estimation by the diluent effect on glass temperature. The results indicated that the polymer-rich phase after phase separation became glassy as the bath composition x w was above 0.75. This resulted in a fundamental change in the thermomechanical behavior of the gel from one of a typical rubber to one a typical glassy polymer. Meanwhile a dynamical gel-to-glass transition was observed in the time-temperature superposition (TTS) master curves. The transition temperature T 0 decrease with increasing x w . A weak-to-tough transition was observed at T − T 0 ≈ 0 K, while a tough-to-brittle transition occurs at T − T 0 ≈ −50 K. A conceptual scheme was proposed to clarify the interplay of phase separation, glass transition in the present work. This scheme could also explain some of the previous work. An example of application in shape memory materials was provided. Highlights • Phase separation inside a gel in equilibrium with solvent/nonsolvent is calculated. • Glass transition line and the Berghmans point is added to the phase diagram. • Thermoelasticity of gel swollen in solvent/nonsolvent is eccentric. • The calculated phase diagram explains the window of mechanical toughening.