PolyDADMAC (Polydiallyldimethylammonium chloride) is a highly cationic, water-soluble polymer widely used as a flocculant and coagulant aid in water and wastewater treatment. Its strong positive charge makes it especially effective for neutralizing negatively charged colloidal particles (e.g., clays, organic matter, microbes) commonly found in water.
Full name: Poly(diallyldimethylammonium chloride)
Abbreviation: PolyDADMAC or PDADMAC
Charge: Permanent cationic (quaternary ammonium groups — not pH-dependent)
Form: Typically supplied as a viscous aqueous solution (10–50% active polymer)
PolyDADMAC works primarily through charge neutralization, and to a lesser extent, bridging:
Charge Neutralization:
Most suspended particles in water (e.g., clay, bacteria, organic colloids) carry a negative surface charge.
PolyDADMAC’s positively charged quaternary ammonium groups adsorb onto these particles.
This reduces the zeta potential (surface charge), destabilizing the colloidal suspension.
Microflocculation:
After charge neutralization, particles aggregate into small flocs ("microflocs").
Unlike high-MW anionic polymers that form large bridged flocs, PolyDADMAC typically produces dense, compact flocs.
Often Used with Coagulants:
Frequently paired with primary coagulants like alum (Al₂(SO₄)₃) or ferric chloride (FeCl₃).
Acts as a coagulant aid—improving floc formation, settling speed, and dewatering.
| Industry | Use |
|---|---|
| Municipal Water Treatment | Removes turbidity, natural organic matter (NOM), algae |
| Wastewater Treatment | Enhances sludge dewatering, reduces effluent COD/BOD |
| Paper Manufacturing | Retention aid & drainage promoter (binds fibers/fillers) |
| Industrial Process Water | Clarification in food processing, mining, textiles |
Effective over a wide pH range (charge is permanent)
Fast-acting
Reduces sludge volume compared to metal coagulants alone
Improves filterability and settling rates
Less effective for large floc formation alone (often needs anionic flocculant booster)
High doses can restabilize colloids (overdosing reverses charge)
Not biodegradable; residual monomer (DADMAC) is toxic—quality control is essential
Drinking water: 1–10 mg/L (as active polymer)
Wastewater: 5–50 mg/L (depends on solids content and charge demand)
Dosage is often determined by jar testing to optimize performance.
CH3 | [–CH2–CH–]n Cl⁻ | CH2–N⁺(CH3)2
Each repeat unit carries a permanent +1 charge balanced by Cl⁻.
In practice, PolyDADMAC is often followed by a high-molecular-weight anionic polyacrylamide (A-PAM) in a dual-polymer system:
PolyDADMAC → charge neutralization → A-PAM → bridging → large, settleable flocs.
Let me know if you'd like formulation guidelines, compatibility data, or environmental impact details!
