As with previous discussions, it’s crucial to specify which HPMA you are referring to. Their chemical properties are vastly different.
I will provide detailed properties for both major types.
1. Chemical Properties of HPMA as a Monomer: N-(2-Hydroxypropyl)methacrylamide
This is a small molecule monomer used to synthesize biomedical polymers.
| Property | Description |
|---|---|
| Chemical Formula | C₇H₁₃NO₂ |
| Molecular Weight | 143.18 g/mol |
| Appearance | Typically a colorless to pale yellow viscous liquid or low-melting solid. |
| Solubility | Highly soluble in water and common polar organic solvents (methanol, ethanol, DMSO, DMF). This is due to its hydrophilic hydroxypropyl amide group. |
| Reactivity | Primary: Free Radical Polymerization. The methacryloyl group (CH₂=C(CH₃)-CO-) contains a reactive carbon-carbon double bond, allowing it to readily copolymerize with other monomers (e.g., for drug conjugation). Secondary: The secondary hydroxyl group (-CH(OH)-CH₃) can be further functionalized (e.g., esterified) to attach targeting ligands or drugs. |
| Stability | Stable under ambient conditions when protected from light and moisture. May polymerize if exposed to heat, light, or radicals. Usually supplied with an inhibitor (e.g., MEHQ). |
| Key Functional Groups | 1. Polymerizable Vinyl Group (C=C). 2. Amide Group (-NH-CO-): Provides stability and biocompatibility. 3. Secondary Hydroxyl Group (-OH): Site for chemical modification. |
| pKa | Not typically relevant for the monomer itself. The amide nitrogen is not basic under physiological conditions. |
Summary for the Monomer: It is a water-soluble, polymerizable, bifunctional molecule designed to create biocompatible, non-immunogenic polymer backbones for drug delivery.
2. Chemical Properties of HPMA as a Water Treatment Polymer: Hydrolyzed Polymaleic Anhydride
This is an industrial oligomer/polymer used as a scale inhibitor.
| Property | Description |
|---|---|
| Chemical Formula | (C₄H₄O₄)ₙ (for the polysuccinimide intermediate); (C₄H₄O₅)ₙ (hydrolyzed form) |
| Molecular Weight | Low, typically 300 – 5,000 Da (oligomeric range). |
| Appearance | Amber to dark brown viscous liquid or solid (often supplied as an aqueous solution ~50% concentration). |
| Solubility | Fully soluble in water (as the sodium/potassium salt). Insoluble in most organic solvents. |
| Acidity | Polyprotic weak acid. Contains multiple carboxylic acid groups (-COOH) per chain. Its aqueous solutions are acidic. |
| Reactivity | 1. Chelation/Sequestration: Carboxylate groups can bind with Ca²⁺, Mg²⁺, Fe²⁺ ions, but this is a weak interaction; its main function is not chelation. 2. Adsorption & Crystal Modification: Reacts with the surface of growing scale crystals (e.g., CaCO₃, CaSO₄) via chemisorption, inhibiting growth. 3. Neutralization: Reacts with bases (NaOH, KOH) to form salts. |
| Stability | Excellent thermal and hydrolytic stability. Can function effectively in boiler water systems up to ~300°C, which is a key advantage over many other polymers (e.g., polyacrylic acid degrades at high T). Stable over a wide pH range. |
| Key Functional Groups | High density of carboxylic acid groups along a short hydrocarbon backbone. This gives it a very high anionic charge density. |
| Biodegradability | Considered inherently biodegradable under appropriate conditions (e.g., in an activated sludge plant), though not readily biodegradable. It is more environmentally friendly than non-biodegradable polyacrylates. |
Summary for the Polymer: It is a thermally stable, water-soluble, low-MW polycarboxylic acid with high anionic charge density, engineered to adsorb onto mineral surfaces and prevent scale formation.
Comparison Table: Key Chemical Property Differences
| Property | HPMA (Monomer) | HPMA (Polymer – Water Treatment) |
|---|---|---|
| State | Liquid / Low-melting solid | Viscous liquid or solid (often in solution) |
| Core Structure | Defined small molecule | Oligomeric mixture |
| Key Groups | C=C bond, amide, hydroxyl | Multiple carboxylic acids |
| Solubility | Water & organics | Water only (as salt) |
| Primary Reactivity | Free-radical polymerization | Surface adsorption, crystal distortion |
| Thermal Stability | Moderate (can polymerize) | Very High (up to ~300°C) |
| pH of Solution | ~ Neutral (if pure) | Acidic |
| Application Driver | Polymerizability, biocompatibility | Scale inhibition, dispersancy, thermal stability |
Conclusion
To get the exact properties you need, always confirm the context:
-
If your work involves drug delivery or polymer synthesis, you need the monomer properties.
-
If your work involves cooling towers, boilers, or industrial water systems, you need the polymer (Hydrolyzed Polymaleic Anhydride) properties.
Please specify the field for even more targeted information.