Since 1869, Thomas Andrews discovered the existence of the critical point, and it has been more than 100 years, but the development of supercritical fluid technology has been relatively slow. The potential application prospects have been able to develop rapidly.

At present, supercritical fluids have been widely used in various related fields such as food, medicine, energy, environment and chemical reaction engineering, and will gradually penetrate and develop into a broader field.

In all application fields, chemical reactions under supercritical conditions will be a hot spot and frontier in the research and application of supercritical fluid technology in the future. The reason is mainly due to the increasingly serious resource and environmental problems. Supercritical fluids are used to replace traditional Organic solvents are equal to the elimination of substances harmful to the environment from the source, and are an important part of "green chemistry"; the properties of supercritical fluids are adjustable, that is, the reaction rate and reaction selectivity can be adjusted only by changing the temperature or pressure. , And this is difficult to achieve with conventional organic solvents; when supercritical fluid is used as the reaction medium, reaction and separation can be combined into one, simplifying the operation process, and realizing the economic efficiency of the process.

Based on the above reasons, this thesis selects the polymer polymerization reaction in supercritical fluid as the research content, focusing on the study of the effect of co-solvents on the reaction. Around this center, before studying the polymerization reaction, the properties and density inhomogeneities of the supercritical fluid (including its long-range density unevenness and local density unevenness) were first studied, and it was revealed that the solvent molecules in the high compression zone The phenomenon of aggregation around the solute can occur at high density, and this is precisely the key to the difference between the properties of supercritical fluids and the properties of general solvents. The paper uses the apparent density of the solvent and the partial molar volume of the solute to study the binary mixed system of supercritical carbon dioxide-tetrahydrofuran. The negative partial molar volume of the solute under infinite dilution conditions indicates that a solvated structure is formed in the solution, that is, the solvent Aggregation occurs around the solute, which indicates the non-uniformity of the long-range density of the solvent.

The paper also used FT-IR to study the hydrogen bond association between tetrahydrofuran and acetic acid in the supercritical carbon dioxide-tetrahydrofuran-acetic acid ternary mixed system, and for the first time observed different driving forces for the formation of hydrogen bonds in different compression ranges, namely The enthalpy and entropy of the high compression zone are positive values, that is, entropy driven, and the enthalpy and entropy of low compression zone are negative values, that is, enthalpy driven. .