DOPO-HCA (CAS 35948-25-5)

DOPO-HCA (CAS 35948-25-5)

Chemical Identification

Common Name: DOPO-HCA

IUPAC Name: (6-Oxido-6H-dibenz[c,e][1,2]oxaphosphorin-6-yl)methyl butanedioate

CAS Number: 35948-25-5

Molecular Formula: C17H15O5P

EC Number: 252-808-9

Structural Information

DOPO-HCA is a derivative of DOPO (9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide). Its structure features two critical components:

1. The phosphaphenanthrene group from the DOPO core, which is responsible for its flame-retardant efficacy.

2. A terminal carboxylic acid group (-COOH).

The molecule is formed by reacting DOPO with itaconic acid, resulting in a structure that can be simplified as: DOPO–P–CH₂–C(O)O–CH₂–CH₂–C(O)OH. The presence of the carboxylic acid group is its key functional feature, enabling it to act as a reactive flame retardant.

Key Characteristics

Appearance: White to off-white crystalline powder.

Molecular Weight: 330.27 g/mol.

Melting Point: Typically in the range of 118 - 126 °C.

Phosphorus Content: Approximately 9.4%.

Key Functional Group: Carboxylic acid (-COOH), which allows for covalent bonding into polymer chains.

Primary Applications and Use

DOPO-HCA is predominantly used as a high-performance, reactive flame retardant in polymer systems, with its main application being:

Flame-Retardant Epoxy Resins for Electronics: It is extensively used to manufacture halogen-free epoxy formulations for Printed Circuit Boards (PCBs) and other electronic encapsulation materials. During the curing process of the epoxy resin, the carboxylic acid group of DOPO-HCA reacts with epoxy groups, chemically incorporating the flame retardant moiety directly into the polymer network.

Mechanism of Flame Retardancy

DOPO-HCA operates through a highly efficient combined mechanism:

1. Gas Phase Action: Upon exposure to fire, the compound decomposes and releases PO· radicals. These active radicals scavenge and neutralize the highly energetic H· and OH· radicals in the flame front, effectively quenching the combustion process.

2. Condensed Phase Action: It promotes the formation of a stable, insulating char layer on the polymer's surface. This char acts as a protective barrier, shielding the underlying material from heat and oxygen and reducing the release of flammable gases.

Significance and Advantages

DOPO-HCA represents a leading halogen-free flame retardant solution, developed to replace traditional brominated compounds like Tetrabromobisphenol A (TBBPA). Its primary advantages stem from its reactive nature:

Permanence: By chemically bonding to the polymer backbone, it prevents issues like migration, blooming, or leaching, ensuring long-term durability and flame retardancy.

Minimal Impact on Properties: It does not act as a plasticizer, thus it does not significantly depress the glass transition temperature (Tg) or compromise the thermal and mechanical properties of the cured resin.

High Efficiency and Environmental Profile: It enables epoxy systems to achieve high safety standards such as the UL-94 V-0 rating without the environmental and toxicological concerns associated with halogenated flame retardants.

In summary, DOPO-HCA is a crucial reactive, halogen-free flame retardant, primarily valued for creating high-performance, durable, and environmentally safer epoxy resins for the electronics industry.