Cloud-point data to temperatures of 270 °C and 3000
bar are presented for CO2 with the family of
poly(acrylates) including methyl, ethyl, propyl, butyl, ethylhexyl, and
octadecyl, with poly(butyl methacrylate),
with poly(vinyl acetate), with statistically random copolymers of
poly(ethylene-co-methyl acrylate) with 41,
31, and 18 mol % acrylate, with
poly(tetrafluoroethylene-co-hexafluoropropylene) and
poly(vinylidene-co-hexafluoropropylene) copolymers, each with ∼20 mol %
hexafluoropropylene, and with Teflon AF. Over
the same range of conditions, CO2 cannot dissolve
polyethylene, poly(acrylic acid), poly(methyl
methacrylate),
poly(ethyl methacrylate), polystyrene, poly(vinyl fluoride),
or poly(vinylidene fluoride). CO2 is a weak
solvent
that exhibits the temperature-sensitive characteristics observed with
polar solvents. The solubility of a nonpolar
hydrocarbon polymer or a copolymer in CO2 can be increased
by at least partially fluorinating the polymer
or by incorporating some polar groups into the backbone architecture of
the polymer. Because it is such a
weak solvent, CO2 can distinguish differences in polymer
architecture even for polymers from the same
chemical family, which means that polymer free volume plays a role in
determining solubility.
ABSTRACT:Cloud point data to 230°C and 2200 bar are presented for poly(acrylate)-ethylene mixtures. When the length of the alkyl tail is increased, the cloud point curve is shifted towards lower pressure, but this trend switches when going from poly(ethyl hexyl) to poly(octadecyl) acrylate. It is apparent that there is an optimum alkyl tail length that balances energetic acrylate-acrylate, ethylene-ethylene, and ethyleneacrylate interactions and free-volume, entropic effects. Both ethylene-poly(acrylate) and CO 2 -poly(acrylate) data are modeled by the Statistical Associating Fluid Theory (SAFT) equation of state. A pseudogroup contribution method is developed for the calculation of the following pure polymer characteristic parameters: m, the number of segments, and v 00 , the volume of a segment. This method cannot be applied for u 0 /k, the attractive energy of a segment, which changes in a nonlinear manner with changes in the structure of the acrylate repeat group. The energy parameter is then calculated from monomer data or fitted directly to one cloud point curve. The experimental data are represented well, even if little predictive power is obtained since a temperatureindependent interaction parameter k ij is needed.
Modification reactions are reported for fully-hydrogenated butadiene-acrylonitle (35.8 mol-% AN) copolymer, ethylene(E)-butyl acrylate (4.7 mol-% BA) copolymer, and ethylene(E)-methyl acrylate (45 mol-% MA) copolymer in dense, near-critical water at 250 "C and 300 "C and at 300 bar and 1 500 bar. Nitrile, amide, and ester moieties can be converted into COOH groups. Kinetic analysis of the ester to acid transformations suggests autocatalytic activity of the acid groups.
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