Novel Interpolymers (1961)
U.S. Patent No. 3,010,946, granted on November 28, 1961, to Albert Y. Garner, describes a new class of phosphorus-containing linear polyphosphines and the methods for their preparation. Albert Garner, a researcher for the Monsanto Chemical Company in St. Louis, Missouri, developed these specialized materials to expand the frontier of organophosphorus polymer technology.
This specific invention solved a persistent problem in material sciences: the lack of flame-resistant, highly stable polymers capable of performing in demanding industrial and structural environments without supporting combustion.
The Innovation: Free-Radical Linear Chain Building
Previously, phosphorus-based polymer technology remained relatively undeveloped. Garner discovered that by copolymerizing a diene monomer (lacking aliphatic conjugation) with a mono-substituted phosphine in a strictly oxygen-free environment, the molecules would link together into highly uniform linear chains.
Because the reaction proceeds via a free-radical mechanism, it can be initiated cleanly through heat, ultraviolet (UV) light, radiation, or conventional chemical catalysts like benzoyl peroxide or azo-bis-isobutyronitrile.
Why These Polyphosphines?
- Inherent Flame Retardancy: The presence of structural phosphorus natively represses combustion.
- Self-Extinguishing Nature: When exposed to a direct flame, the polymers will not fuel the fire and will completely stop burning once the external heat source is removed.
- Versatile Physical States: By manipulating molecular weights (ranging from 500 to 500,000), the resulting materials can be engineered as viscous liquids or as solids that vary from soft and flexible to tough and rigid.
Key Chemical Components
The polymer matrix is a strictly proportioned copolymer where the properties are dictated by the starting monomers:
| Component | Function / Feature |
| Mono-Substituted Phosphine | Hydrocarbon phosphines (such as phenylphosphine or cyclohexylphosphine) that introduce the fire-resistant phosphorus backbone into the chain. |
| Diene Monomer | Non-conjugated compounds (such as diallyl, diallyl ether, or p-divinylbenzene) that form the structural organic linkages. |
| Inert Atmosphere (e.g., Nitrogen) | A protective gas shield required during synthesis to prevent the premature oxidation of the highly reactive phosphine groups. |
| Free-Radical Initiator | A catalyst (like dibenzoyl peroxide) or energy source (like UV light) used to activate the chemical bonding mechanism. |
| Inert Solvent (Optional) | Organic liquids like benzene or dioxane added to guarantee the fluidity and homogeneity of dense reaction mixtures. |
Performance: Defeating Flame and Combustion
Garner’s patent demonstrates the dramatic fireproofing capabilities of these interpolymers when applied to both raw plastics and organic matter using a standard Meeker burner test.
Test Results on Treated Materials:
- Pure Polyphosphine Slabs: Slabs formed from diallyl, diallyl ether, or divinylbenzene variants were placed directly into a burner flame. All variations proved entirely self-extinguishing upon removal from the fire.
- Treated Wood (Ponderosa Pine Chip): A raw pine chip was soaked in a 75% polyphosphine-benzene solution and dried. When subjected to flammability testing, the treated wood was rendered completely incapable of supporting combustion.
The Manufacturing Process
Garner outlined multiple precise pathways to trigger the free-radical polymerization depending on the choice of initiator:
- Charge a reflux-condenser equipped vessel with substantially equimolar proportions (40% to 60% ratios) of the diene monomer and mono-substituted phosphine.
- Purge the reaction system thoroughly to establish a completely oxygen-free nitrogen atmosphere.
- Activate the free-radical mechanism. This can be done at a room temperature of 20°C using continuous UV light irradiation for 30 hours, or by adding a peroxide catalyst and heating to 70°C for 90 hours.
- Precipitate or Strip the final product. Unreacted monomers are removed via tight vacuum distillation (down to 0.1 mm of mercury), or the polymer solids are precipitated cleanly by pouring the mixture into an excess of methanol or ether.
About the Inventor: Albert Y. Garner
Albert Y. Garner was an influential mid-century American research chemist whose prolific output at the Monsanto Chemical Company helped define early industrial organophosphorus chemistry.
As the post-WWII era demanded increasingly advanced synthetic materials for aerospace, military, and commercial architecture, Garner focused heavily on engineering polymers that could withstand hazardous environments. His pioneering design of linear polyphosphines contributed directly to modern methods for fire-retarding structural plastics, developing non-flammable industrial adhesives, and manufacturing highly stable aircraft hydraulic fluids that prevent catastrophic electrical and thermal fires.
Summary of Claims
The patent explicitly claims:
- A linear polyphosphine composition consisting of 40 to 60 mol percent of a specific diene monomer interpolymerized with 60 to 40 mol percent of a mono-substituted hydrocarbon phosphine.
- The specific use of divinylbenzene, diallyl, or diallyl ether interpolymerized with phenylphosphine.
- A preparation process characterized by copolymerizing these components under an inert atmosphere specifically in the presence of free radicals.
