Polymethacrylate (PMA) Viscosity Modifier, how it is produced and how it performs?

The production method of polymethacrylate (PMA)

 

Methacrylic acid is esterified with higher carbon alcohol under acidic conditions to form methacrylate, and the generated water is continuously absorbed by sulfuric acid to make the reaction continue. Remove the unreacted substances and by-products from the crude methacrylate, after refining, carry out free radical polymerization under the trigger of benzoyl peroxide or azobisisobutyronitrile, etc., and also use dodecanethiol to control the molecular weight (in During the polymerization process, a certain amount of diluent oil should be added), the reaction formula is:

 

 

Reaction Formula of polymethacrylate (PMA)

 

Typical polymethacrylate viscosity index improvers (PMA VII) are linear polymers consisting of three segments or three hydrocarbon side chains of different lengths.

Simple statistics show that a PMA molecule is composed of a short chain of 1 to 7 carbon atoms. The short-chain material mainly affects the curl size of the polymer at low temperatures and the viscosity index of the polymer oil solution; the slightly longer chain It contains 8-13 carbons, which can improve the solubility of polymers in hydrocarbon solutions; the long-chain contains 14 or more carbons, which can interact with wax crystals to improve low-temperature performance.

There are also reports: when the average alkyl chain of the monomers selected for PMA polymerization is 9, the resulting polymer has good oil solubility (branched or straight chain is fine), and the 1-4 carbon alcohols have good viscosity-temperature Performance, 10-20 carbon alcohols can improve low-temperature performance; especially 14-carbon alcohols will combine with wax to change the crystal structure of wax, thereby changing the low-temperature performance.

 

The carbon number of the alkyl side chain R of PMA has a great influence on the performance of the product. By changing the average carbon number of R, the carbon number distribution, and the relative molecular weight of the polymer, a series of products with different properties and different uses can be obtained.

 

For a single VII that only has a viscosity improvement, the average carbon number of R is C8~C10 (the average alkyl chain should be C9), and it is formed by mixing low-carbon alcohols and high-carbon alcohols. The polymer obtained in this way has good oil solubility and is stable. It can provide good viscosity-temperature performance;

 

For VII with dual effects of viscosity improving and pour point reduction, the average carbon number of R is 12~14, and C14 is the best.

If it has viscosity increasing, pour point depressing and dispersing functions at the same time, it is necessary to introduce a third component of nitrogen-containing polar compounds for copolymerization, such as dimethyl (or diethyl) amino ethyl methacrylate, hydroxymethacrylate Ethyl ester, 2-methyl-5-vinylpyridine. The relative molecular mass of PMA used for internal combustion engine oil is about 150,000, and the relative molecular mass of PMA used as a pour point depressant is less than 100,000. If it is used in hydraulic oil and gear oil that require particularly good shear stability, the relative molecular mass of PMA is between 20,000 and 30,000.

 

The low-temperature performance of PMA is particularly good, the effect of improving the viscosity index of the oil is good, and the oxidation stability is good, but the thickening ability, thermal stability, and mechanical shear resistance (SSI) are not so good. PMAs of high molecular weight, in particular, are susceptible to mechanically induced permanent viscosity loss as a function of the molecular weight (size) of the solution for a given shear stress. The relative molecular mass distribution plays a secondary role, if the relative molecular mass distribution favors high relative molecular mass polymers, the viscosity loss is greater than for polymers with similar average relative molecular masses. Different applications have very different stresses, so the viscosity loss of any given molecular weight polymer will vary from application to application. To be sure, the viscosity loss is directly related to the relative molecular weight and the stress of the application.

 

Dispersive PMA can be used not only as a dispersant but also as a dispersive viscosity index improver. Therefore, dispersive viscosity index improvers are often used in engine oils, to replace some traditional ashless dispersants, or only to improve their dispersibility.