Lubricating oil pour point depressants are products that can reduce the pour point of oils, thus allowing the oil to maintain good fluidity at lower temperatures. According to relevant information, the emergence of lubricating oil pour point depressants can be traced back to the 1930s-1940s. Before that, due to the lack of effective methods to control wax crystallisation in oils, it was quite common for vehicles and equipment to be unable to operate normally in cold winters because the lubricating oil solidified at low temperatures. This prompted the research and development of lubricating oil pour point depressant technology, leading to the development of products such as alkyl naphthalenes, polymethacrylate esters, acrylate esters, fumarate copolymers, and poly-alpha-olefins.

So far, the types of pour point depressants commonly used in the market for lubricating oil are still alkyl naphthalenes, polymethacrylates, polyalphaolefins and fumarate copolymers，etc.Although the types differ, their mechanisms of action are basically the same. The congealing of lubricating oil at low temperatures is mainly due to the gradual crystallisation of the wax components in the oil as the temperature drops, ultimately leading to reduced fluidity or even congealing of the oil. It should be noted that the pour point depression process is not a chemical reaction, but a physical process. From the perspective of the structure of the pour point depressant itself, taking the commonly used PMA-type pour point depressant on the market as an example, the long side chain structure in its molecular chain is similar to the structure of wax, which can absorb and control the formation of wax crystals. The presence of the entire chain structure can interfere with and inhibit the aggregation of wax molecules in the oil and the formation of larger crystals, thus lowering the pour point.

The effectiveness of pour point depressants is generally highly related to their chemical structure, composition, and properties. For easier understanding, it can be explained from two aspects. On the one hand, the ability of the pour point depressant itself to lower the pour point varies. For example, in the same base oil, different pour point depressants achieve different depressant effects, which mainly depends on the structure of the depressant itself and whether its active components match the structure and quantity of wax in the base oil. Simply put, it can be understood as the 'like dissolves like' principle frequently mentioned in chemistry: as long as the structure and quantity are similar, a better effect can be achieved. On the other hand, it depends on the sensitivity of the base oil to the pour point depressant, which is mainly understood from the perspective of the base oil. Based on theoretical and long-term practical experience, pour point depressants have basically no effect on wax-free base oils, while their effect on base oils with very high wax content is also limited. They work better on medium- to low-viscosity base oils and are less effective on high-viscosity base oils. Due to the wide variety of crude oil sources, their composition and content vary greatly. Even crude oils from the same origin may result in differences in the chemical composition of the base oil due to variations in refining and processing methods, which places higher demands on pour point depressants. A depressant that can adapt to a wider range of base oils can be considered to have better sensitivity, practicality, and effectiveness.

Pour point depressants are currently mainly used in engine oils, certain industrial oils, and automotive transmission oils. In addition to base oils, oil formulations may also contain auxiliary additives such as viscosity index improvers, primary functional additives, and detergents/dispersants. Fundamentally, these additives are all derived from crude oil, and the copolymers and some hydrocarbons they contain can negatively affect the low-temperature performance of the oil overall. Therefore, when selecting pour point depressants, it is recommended to conduct low-temperature performance tests on the entire formulated oil, including pour point, low-temperature kinematic viscosity, and low-temperature pumping ability, to ensure the oil meets relevant standards. (Due to the limited expertise of the author, there may inevitably be errors, readers are encouraged to provide corrections)