Backbone polymers flammability

Reduction of polymer flammability is of broad interest for applications ranging from plastics to textiles. For polyesters, given their inherent instability towards water at elevated temperatures, and the high temperatures of manufacture, many classes of flame-retardant (FR) agents, including most halogen-containing materials, are impractical. Phosphate esters, capable of incorporation into the polymer backbone, were pioneered by Hoechst AG, and continue to be the materials of choice [84, 85],... 

It is known that increased char yield is usually associated with improved flammability behavior ( 1). This can be understood if one considers that the volatile flammable products can only diffuse with difficulty through the char, and that the thermal conductivity of a porous char layer is relatively poor (2). The structure of the polymer can contribute to the amount of char formed based on the character of the functional groups present and the nature of the backbone (2,3). Ritchie ( ) found that for a series of unsaturated polyesters and their copolymers, the temperatures at which carbon dioxide is eliminated was in the range of 280 to 345°C depending on the structure of the polyester. Aliphatic polyesters and their copolymers have less thermal... 

The monomer that we have used as a backbone for our work toward flame retardant polymers is commonly called bisphenol C (BPC) or l,l-dichloro-2,2-bis(4-hydroxyphenyl) ethylene. As has been shown by many research groups, BPC can be used as a blendable additive in a commercial plastic or as part of a polymer backbone to effectively impart flame resistance to certain polymeric materials.When thermally decomposed, BPC exothermically produces volatile products such as HCl and CO2, and the unique structure formed upon thermal degradation leads to a very stable carbon structure (char). It is this pyrolysis byproduct and the high char forming nature of BPC that give inherently low flammability and flame retardancy (Fig. 3) in these polymers and blends. 

Fire retardant polyesters contain a blend of chlorine, bromine, phosphorus or antimony based chemical groups and offer reduced flammability but with somewhat reduced mechanical properties and wet durability. The smoke emissions are reduced but the fumes may still be unhealthy. Additives may be particulate or the fire retardant groups embedded into the polymer backbone by using substituted acids. HET acid polyesters (hexachloromethylene-tetra-hydrophthalic acid) are an example of the latter. 

The key to developing a truly melt-processable polyimide was to build more flexible hnkages into the polymer backbone. This had to be done in such a way that the polyimide stiU retained other desirable features (e.g., heat resistance, strength, high use temperatiure, and low flammability). Scientists at the General Electric Corporate Research and... 

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