SOLUBILITY OF BLOCK-COPOLYMER SURFACTANTS IN COMPRESSED CO2 USING A LATTICE FLUID HYDROGEN-BONDING MODEL

The solubilities of the homopolymers poly(ethylene glycol) (PEG), poly (ethylene glycol) dimethyl ether (PEGDME), and poly(propylene glycol) (PPG) in CO2 were correlated with a lattice fluid hydrogen-bonding (LF HB) model, which was then used to predict solubilities of Pluronic L ( PEG-PPG-PEG) and Pluronic R (PPG-PEG-PPG) triblock copolymers. Simple averaging rules were developed to evaluate the physical properties of the copolymers without introducing any adjustable parameters. For a gi ven average molecular weight, the predictions of the model were quite reasonable and in some cases perhaps more accurate than the data, due to the large polydispersity of the samples. The model predicts the eff ects of total molecular weight, PEG/PPG ratio, terminal functional gro ups, temperature, and density on solubility. The much higher solubilit y of PPG versus PEG is due primarily to steric hindrance fi om the met hyl branch, which weakens segment-segment interactions, and to a lesse r extent to the stronger hydrogen bond donor strength of a primary (in the case of PEG) versus a secondary (in the case of PPG) alcohol term inal group. Consequently, the predicted solubilities of Pluronic L sur factants, which have stronger hydrogen bond donors on the terminal gro ups, are not much smaller than those of Pluronic R surfactants for giv en molecular weights of the blocks.