Polycarboxylates : properties, uses

Polycarboxylates are polymers of high molecular weight and are generally used in neutral form, pH between 6 and 8 as sodium salts. They have two types of polymers: acrylic acid AA-P homopolymers and copolymers of acrylic maleic acid P-AA / MA (HERA ref.) and are used as additives to remove dirt and to prevent dirt particles from depositing on the washed object again.

The name defines the structure of the molecule:

• Poly comes from the Greek word "many", and in the context of chemistry, refers to polymers, which are large molecules composed of repeated subunits.
• Carboxylates refers to the form of salt or ester of a carboxylic acid. Carboxylic acids are organic compounds that contain a carboxyl group (-COOH), which consists of a carbon atom double-bound to an oxygen atom and single-bound to a hydroxyl group (-OH).

The synthesis process takes place in several stages:

• Monomer preparation. The first step concerns the preparation of common monomers used in the production of polycarboxylates which include acrylic acid and a polyether monomer, such as methoxy polyethylene glycol methacrylate.
• Polymerization. The monomers are inserted into a reaction vessel and a radical initiator is added. The mixture is heated, which initiates the polymerization reaction that causes the formation of the polycarboxylate polymer.
• Neutralization. The resulting polymer is acid due to the presence of carboxylated groups. It is neutralized by adding a base, such as sodium hydroxide, to form the sodium salt of polycarboxylate.
• Purification. Polycarboxylate is purified to remove any unreacted monomers and other impurities with a series of washing and filtration steps.
• Drying. In the last step the purified polycarboxylate is dried and ground into a fine powder ready for use.

Safety

Their use in detergents avoids the use of polyphosphates that had the characteristic to remain in the soil.

Detergents

Polycarboxylates are polymers that contain many carboxylated groups. In the context of detergents, they are often used as to improve the cleaning efficiency of the detergent. In concrete, they are used as superplasticizers, to reduce the water content while maintaining the workability of concrete. In personal care products, they can work as thickeners or emulsion stabilizers.

Commercial applications   

Concrete Additives. They act as superplasticizers in concrete to improve workability and reduce water content.

Water Treatment. Used as antiscalants and dispersants to prevent the formation of mineral deposits.

Agriculture. Used as chelating agents to enhance mineral uptake in plants.

Studies

• The properties of stimuli-responsive polymers change significantly with changes to their environment, such as temperature and pH. This behavior can be utilized for the preparation of stimuli-responsive carriers for efficient cytosolic delivery of active drugs (1). Titratable polyanions, and more particularly polymers bearing carboxylate groups, have been used in recent years to produce a variety of pH-sensitive colloids. These polymers undergo a coil-to-globule conformational change upon a variation in pH of the surrounding environment. This conformational change can be exploited to trigger the release of a drug from a drug delivery system in a pH-dependent fashion (2).
• The performance of many contemporary detergent products critically depends on polymers. Water-soluble polycarboxylates represent an important class of detergent polymers, and their quantitative assessment in detergent matrices stands as a considerable challenge (3).
• Antifreeze proteins (AFPs) lower the noncolligative freezing point of water in the presence of ice below the ice melting point. The temperature difference between the melting point and the noncolligative freezing point is termed thermal hysteresis (TH). The magnitude of the TH depends on the specific activity and the concentration of AFP, and the concentration of enhancers in the solution. Known enhancers are certain low molecular mass molecules and proteins. Here, we investigated a series of polycarboxylates that enhance the TH activity of an AFP from the beetle Dendroides canadensis (4).

References_________________________________________________________________________

(1) Harada A, Teranishi R, Yuba E, Kono K. Effect of the side chain spacer structure on the pH-responsive properties of polycarboxylates. J Biomater Sci Polym Ed. 2017 Jul - Aug;28(10-12):1025-1035. doi: 10.1080/09205063.2017.1324551. 

(2) Felber AE, Dufresne MH, Leroux JC. pH-sensitive vesicles, polymeric micelles, and nanospheres prepared with polycarboxylates.  Adv Drug Deliv Rev. 2012 Aug;64(11):979-92. doi: 10.1016/j.addr.2011.09.006. 

(3) Visser I, Klinkenberg M, Hoos P, Janssen HG, van Duynhoven J. Identification and quantification of polycarboxylates in detergent products using off-line size exclusion chromatography-nuclear magnetic resonance.  Anal Chim Acta. 2009 Nov 3;654(1):40-4. doi: 10.1016/j.aca.2009.06.017. 

(4) Amornwittawat N, Wang S, Duman JG, Wen X.  Polycarboxylates enhance beetle antifreeze protein activity.  Biochim Biophys Acta. 2008 Dec;1784(12):1942-8. doi: 10.1016/j.bbapap.2008.06.003.