TIPS is the abbreviation of thermally induced phase separation, which means "thermally induced phase separation" in Chinese. It is a new method for preparing polymer microporous membrane proposed by American A.J.Castro in 198 1, and applied for a patent. Its technological process and principle are that the polymer is dissolved in a solvent with high boiling point and low volatility (also called diluent) higher than the melting point of the polymer to form a homogeneous solution. Then cool down. During the cooling process, phase separation will occur in the system. This process is divided into two categories, one is solid-liquid phase separation (referred to as S-L phase separation) and the other is liquid-liquid phase separation (referred to as L-L phase separation). By controlling the appropriate process conditions, after phase separation, the system forms a two-phase structure with polymer as continuous phase and solvent as dispersed phase. At this time, a suitable volatile reagent (extractant) is selected to extract the solvent, so as to obtain a polymer microporous membrane with a certain structure and shape. The method has simple process and good controllability. Compared with the traditional phase inversion method, it has the following advantages: 1 Pore size and porosity can be controlled. In TIPS process, the type, composition and cooling conditions of solvents are closely related to the final pore structure. The pore size and porosity can be adjusted by changing one or several conditions. 2. The structure and morphology of the holes can be controlled, and the film-making conditions of the tip can be changed to obtain the structural morphology such as honeycomb structure, lace structure and finger holes. , suitable for different purposes. The pores in the membrane can be closed, semi-closed or open, and the pore size distribution can also be very narrow. 3. The types of membrane materials have greatly increased. TIPS can not only make traditional polymer membrane materials into microporous membranes, but also make crystalline polymers with strong hydrogen bonding and solvent-free at room temperature into microporous membranes. In many TIPS studies, some semi-crystalline polyolefins can usually be successfully made into microporous membranes. Such as isotactic polypropylene (iPP), ultra-high molecular weight polyethylene (UHMW-PE) and so on. 4. It is easy to realize continuous production. Due to the TIPS principle, the process is simple, the application range is wide, and the operation controllability is good. Some of them have achieved industrial production or have the conditions for industrial production, such as polypropylene (PP), polyethylene (PE), polysulfone (PSf), polyvinylidene fluoride (PVDF) and so on. Theoretically, as long as the second derivative of Gibbs free energy of polymer-solvent binary mixing system to polymer volume fraction (φ p) is less than zero (constant temperature and constant pressure), that is, there are maxima and minima on the △ GM ~ φ p diagram, microporous membranes can be prepared by TIPS method. However, the current TIPS method is generally only used for UCST phase diagram (there is an upper limit critical solution temperature). For LCST phase diagram, TIPS method has not been reported in the literature. Since the appearance of TIPS method, there is still a lot of scientific research on it, but the industrial products are far less than other methods to manufacture microporous membranes. How to industrialize the microporous membrane prepared by the new method is also a big topic.