PDADMAC

PDADMAC stands for poly(diallyldimethylammonium chloride). It is a synthetic cationic polymer and a quaternary ammonium polyelectrolyte. The polymer consists of repeating units derived from the diallyldimethylammonium chloride monomer, bearing quaternary ammonium groups and chloride counterions. PDADMAC is typically water soluble and exhibits a high charge density; its molecular weight can vary from 10^5 to over 10^6 g/mol depending on polymerization conditions.

Synthesis and properties: PDADMAC is produced by free radical polymerization of DADMAC monomer in aqueous solution, often with initiators such as persulfates or redox systems. The resulting polymer is a polycation that readily interacts with negatively charged surfaces and particles. Its high charge density enables strong electrostatic interactions and bridging between colloidal particles.

Applications: It is widely used as a flocculant and coagulant aid in municipal and industrial wastewater treatment, where it helps destabilize colloids and improve solids removal. In papermaking, PDADMAC acts as a retention and drainage aid and can improve formation, strength, and dewatering. It is also employed in some personal care products as a conditioning polymer, providing antistatic and smoothing effects, though cosmetic use is typically through related polyquaternary compounds.

Mechanism: Flocculation arises from electrostatic attraction between the cationic polymer and negatively charged particles, including clays, organic matter, and colloids. Bridging effects occur when polymer chains span multiple particles, promoting agglomeration into larger flocs.

Safety and environmental considerations: PDADMAC polymers are generally considered irritants to skin and eyes and may cause irritation on contact. They are not readily biodegradable and can pose risks to aquatic life at elevated concentrations, so they are typically used at controlled dosages and disposed of according to regulations.