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Paraformaldehyde (PFA) is the smallest polyoxymethylene, the polymerization product of formaldehyde with a typical degree of polymerization of 8–100 units. Paraformaldehyde commonly has a slight odor of formaldehyde due to decomposition.
Depolymerizable polymers or Low-Ceiling Temperature Polymers refer to polymeric materials that can undergo depolymerization to revert the materials to their monomers at relatively low temperatures, such as room temperature. For example, the ceiling temperature T c for formaldehyde is 119 °C, and that for acetaldehyde is -39 °C. [1] [2]
Depolymerization is also related to production of chemicals and fuels from biomass. In this case, reagents are typically required. A simple case is the hydrolysis of celluloses to glucose by the action of water. Generally this process requires an acid catalyst: H(C 6 H 10 O 5) n OH + (n - 1) H 2 O → n C 6 H 12 O 6
In organic synthesis, the Casiraghi formylation is the formation of a salicylaldehyde from a phenol and paraformaldehyde. The reaction requires a strong Brønsted base and a weak Lewis acid, and gives a methanol coproduct: [1] (H 2 CO) 2n + nB + nLA + nHArOH → nHC(=O)ArOH + n[HB][LA:OMe]
Thermal depolymerization (TDP) is the process of converting a polymer into a monomer or a mixture of monomers, [1] by predominantly thermal means. It may be catalyzed or un-catalyzed and is distinct from other forms of depolymerization which may rely on the use of chemicals or biological action.
The direct reaction between phenol and paraformaldehyde is possible via the Casiraghi formylation, [4] but other methods apply masked forms of formaldehyde, in part to limit the formation of phenol formaldehyde resins. Aldehydes are strongly deactivating and as such phenols typically only react once.
At the ceiling temperature, the enthalpy term and the entropy term are equal, so that the rates of polymerization and depolymerization become equal and the net polymerization rate becomes zero. [1] Above the ceiling temperature, the rate of depolymerization is greater than the rate of polymerization, which inhibits the formation of the given ...
In this procedure, a small amount of paraformaldehyde as a fine powder is added to the titrand before the titration. At the endpoint, the first excess of hydroxyl ions catalyzes the depolymerization of paraformaldehyde. The reaction is strongly endothermic and yields a sharp inflection. The titration plot is illustrated in Figure 13.
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