High-pressure viscosity and density of poly(methyl methacrylate) + acetone and poly(methyl methacrylate) + acetone + CO 2 systems

Abstract

High-pressure viscosity and density of solutions of poly(methyl methacrylate) (PMMA) in acetone and in acetone + CO 2 mixtures have been determined in the temperature range from 50 to 125 °C in steps of 25 °C over the pressure range from 7 to 35 MPa in steps of 7 MPa using a falling cylinder type viscometer. Measurements were conducted with PMMA samples of two different molecular weights ( M w = 15,000, M w/ M n = 1.8 and M w = 540,000, M w/ M n = 2.8) at concentrations of 2, 5, 10 and 20 wt.% with M w=540,000, and at concentrations of 10 and 20 wt.% with M w = 15,000 sample. The effect of adding CO 2 on viscosity was investigated for the 5 wt.% solutions with the high molecular weight polymer sample. The viscosities were observed to be relatively low, with values in the range from 0.2 to 1.6 mPa s for these solutions. The flow activation energies were around 5–10 kJ/mol. Flow activation volumes were in the range from 5 to 40 cm 3/mol. Close-packed volumes determined from density correlations were in the range of 0.76–0.98 cm 3/g. The overlap concentrations, c *, were estimated to be in the range 0.045–0.075 g/cm 3. In the presence of CO 2, densities of the solution show an increase, reflecting the higher density of compressed CO 2 compared to that of acetone, but viscosities were significantly lowered, with a reduction of about 30% at 4 wt.% CO 2 additions. The density dependence of viscosity is used to visually illustrate the need for higher pressures in the presence of CO 2 to sustain a given viscosity level.