Stable char forming polymers

The same method is applicable to control critical temperature where the reaction between polyphosphates and polyols takes place. For example, melamine polyphosphate-polyol system, which is stable at the degradation temperature of PP, has been activated for application in polyolefins [47], An activating effect is ascribed also to the char-forming polymers in intumescent nanocomposites, according to the blending approach [48],... 

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. 

Although elimination reactions are clearly degradation, leading to color and char formation, they can have advantages. Conjugated sequences and ladder structures confer thermal stability on the polymers, forming stable chars. This is the basis of the preparation of carbon fibers by pyrolysis of polyacrylonitrile. It is also one reason for the use of plasticized PVC in electrical insulation in a... 

Within polymer solids, volatile, reactive fragments are trapped and often rereact, forming rearranged structures. If the rearranged structures exhibit markedly better stability, excessive char results. Thus solid ldpe decomposes with little char, whereas polyacrylonitrile (PAN) gives excessive char because of the formation of thermally stable rearranged products. 

Since the majority of research carried out on flame retardancy of nanocomposite has dealt with OMLS, the most investigated combinations have concerned the corresponding class of nanocomposites of polymers, particularly EVA copolymer, PP, and polystyrene. The great interest taken in the development of IFR systems has also entailed the development of various and complex compositions in which OMLS have been associated with different intumescent systems containing APP and co-synergists able to promote the formation of a stable and expanded char layer reinforced by aluminophosphate species formed by reaction between APP and OMLS. 

Aliphatic linkage is completely eliminated in ladder polymers such as polybenzimidazopyrrolones, commonly called pyrrones (Figure 1.38). Such polymers are highly stable in air. They do not bum or melt when heated but form carbon char without much weight loss. They are potentially the ultimate in heat- and flame-resistant materials. 

Condensed-phase systems decompose upon heating to form a large amount of thermally stable residue, or char. This char acts as a thermal shield for radiant heat transfer from the flame to the polymer and as a physical barrier to limit diffusion of flammable gases from the polymer to the combustion zone. 

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