Synthesis of polyacetal resins

Formaldehyde is a strong electrophile, allowing acetal to polymerize by nucleophilic, anionic, or cationic addition of an alcohol to ketene carbonyl groups. Relatively weak bases such as pyridine initiate anionic addition polymerization cationic addition polymerization is catalyzed by strong acids. When the cyclic trimer trioxane is used as a copolymer to polymerize acetal copolymers, Lewis acids such as boron tiifluoride promote copolymerization. A more fundamental description is polymerization of an aldehyde or ketone -l- alcohol -i- an acid or base catalyst to form hemiac-etal, which further converts to acetal. The hemiacetal reaction is reversible to aldehyde and alcohol. 

Chain growth polymerization produces linear polyacetal macromolecules. Polyacetal resin is a clear, flammable, volatile, highly crystalline liquid with the repeating units 

Acetal homopolymer has a T oi about 175°C (347°F) and specific gravity of 1.41 g/cc acetal copolymer has a T oi about 165°C (329°F) and specific gravity of 1.42 [5]. Acetal polymers are synthesized entirely from formaldehyde directly, as noted earlier, or by copolymerization of the formaldehyde cyclic trimer (cyclic oligomer) trioxane and cyclic ethers. 

Commercial polymerization of acetal homopolymer starts with anhydrous formaldehyde monomer from formaldehyde solution. Water is evaporated from the aqueous solution, forming paraformaldehyde, poly-oxymethylene, and hemiformal, which are purified and thermally decomposed to form anhydrous formaldehyde [6]. Methanol and formic acid are removed, either by freeze-trapping at a temperature just above the boiling temperature of formaldehyde or by washing with a nonvolatile polyol [6]. The anhydrous formaldehyde is fed into a reactor containing the inert hydrocarbon solvent, initiator, and dispersant, where the 

Cyclic ether comonomer — Additives, stabilizers Reinforcements — Acetal copolymer 

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