Experimental study of the equation of state and the surface tension of water-soluble polymers: poly(ethylene glycol)-b-poly(propylene glycol)-b-poly(ethylene glycol) plus water at 298.15 K

The equation of state of poly(ethylene glycol)-b-poly(propylene glycol)-b-p oly(ethylene glycol) (PEG-PPG-PEG)+water has been measured in the sol phase at 298.15 K and up to 40 MPa. For the sake of comparison two mixtures of ( PEG+PPG)+water, with the same PEG:PPG ratio as the copolymer, have been mea sured. The differences found between the data of the copolymer and the blen d solutions are well beyond the experimental precision, the compressibility for the copolymer mixtures being larger than for the blend one. Contrary t o previous non-aqueous mixtures, the aqueous ones present deviations with r espect to the corresponding states equation proposed by the group of Sanche z (I. C. Sanchez, J. Cho and W. J. Chen, Macromolecules, 1993, 26, 4234). T he surface tension gamma results show that both PEG-PPG-PEG and PPG are sur face active, leading to a strong decrease of gamma with respect to that of water even for very low polymer concentrations. The behaviour of the spinod al pressure of the system is discussed in terms of the compressibility and the surface tension data.