Influence of the alkyl tail on the solubility of poly(alkyl acrylates) in ethylene and CO2 at high pressures: Experiments and modeling

Cloud point data to 230 degrees C and 2200 bar are presented for poly(acryl ate)ethylene mixtures. When the length of the alkyl tail is increased, the cloud point curve is shifted towards lower pressure, but this trend switche s when going from poly(ethyl hexyl) to poly(octadecyl) acrylate. it is appa rent that there is an optimum alkyl tail length that balances energetic acr ylate-acrylate, ethylene-ethylene, and ethylene-acrylate interactions and f ree-volume, entropic effects. Both ethylene-poly(acrylate) and CO2-poly(acr ylate) data are modeled by the Statistical Associating Fluid Theory (SAFT) equation of state. A pseudogroup contribution method is developed for the c alculation of the following pure polymer characteristic parameters: m, the number of segments, and v(oo), the volume of a segment. This method cannot be applied for u(o)/k, the attractive energy of a segment, which changes in a nonlinear manner with changes in the structure of the acrylate repeat gr oup. The energy parameter is then calculated from monomer data or fitted di rectly to one cloud point curve. The experimental data are represented well , even if little predictive power is obtained since a temperature-independe nt interaction parameter k(ij) is needed. (C) 1999 John Wiley & Sons, Inc.