Specific interactions in carbon dioxide + polymer systems

Weak complex formation in ten CO2 + polymer and CO2 + copolymer systems containing C=O groups was quantified using in situ FTIR spectroscopy. The enthalpy of the C=O...CO 2 interaction were found to be approximately - 4 KJ/mole but further decreased to - 6 KJ/mole in the presence of longer alkyl chains in proximity to the C=O group in CO2 + PCL system and to - 8 KJ/mole in systems with greater branching such as CO2 + PtBMA.; The enthalpy of interaction was directly incorporated into a lattice model proposed by Sukhadia et al. [84] and extended by Ozkan and Teja [21]. The limitations of the model with respect to pressure were overcome by the use of modified segment number based on the free volumes. It was possible to correlate phase equilibria in many CO2 + polymer systems using the modified model with parameters that were independent of polymer molecular weight, temperature and pressure. It was also possible to predict phase equilibria of CO2 + PLGA copolymer systems using the modified model with a single parameter obtained by fitting cloud point behavior in a reference system (CO2 + PLA in this case).; It was also shown that CO2 + fluropolymer phase behavior could be correlated within experimental error (AAD of about 2%) using the new model, a task that has been beyond the capability of published models.; New data on sorption equilibria in several CO2 + PLGA systems were obtained using a quartz crystal microbalance (QCM). The data could be predicted using the new model with parameters obtained from cloud point fitting. The new model is therefore capable of fitting data over an extended pressure range.; Glass transition temperatures were predicted by combining the lattice model with the Gibbs DiMarzio criterion. Once again it was possible to predict the glass transition behavior with the model using a single parameter obtained from cloud point fitting. New data on Tg depression in the CO 2 + PLA system were also obtained using a high pressure DSC method. CO2 has a strong plasticization effect on PLA at all pressures and the system was found to exhibit a Tg minimum. The model was also tested on other CO2 + polymer systems with varying strengths of interactions and polymer free volumes. While both specific interactions and higher polymer free-volume contributes to increased plasticization of a polymer by CO2, it was shown that the dominant effect is due to the specific interactions. The model was also used to predict melting point depressions in CO2 + polymer systems. Melting point depressions were shown to be determined primarily by the sorption of the diluent fluid.; In summary, specific interactions between CO2 and C=O and C-F groups have been quantified using FTIR spectroscopy. The results have been directly incorporated into a lattice model that is able to correlate cloud points, sorption equilibria, glass transition temperatures, and melting points using a single parameter. The model is therefore likely to be beneficial in many applications involving CO2 + polymer systems including drug delivery and encapsulation, polymer coating, and membranes for natural gas separations.