Degradation and stabilization of polyacetal copolymers

Abstract

synopsisAcetal copolymers prepared from trioxane and ethylene oxide consist of polyoxymethylene segments with oxyethylene units distributed in the chain. These oxyethylene units profoundly affect the thermal and chemical behavior of the polymer. The presence of the oxyethylene units renders the copolymer amenable to thermal or base hydrolytic treatment which results in a final product with stable endgroups. The copolymers so obtained are significantly more stable, thermally and chemically, than acetylated polyoxymethylene homopolymer.

Data on Specific Polymers

“…In spite of this, POM 203,205,367,369,[617][618][619][620][621][622][623][624][625][626][627][628][629][630][631][632][633] degrades when exposed outdoors from which it can be inferred that chromophore-containing impurities are present. The copolymer containing a small amount of oxyethylene was found to be more stable.…”

Study on the Thermal Stabilization Effect of Polyamide on Polyoxymethylene

“…The degradation mechanism of POM is complicated, including several processes: stepwise thermal depolymerization from the chain ends [6] , oxidative attack leading to chain scission and depolymerization, acidolytic cleavage of the acetal linkages of the polymer chain, and thermal chain scission at elevated temperatures (280-350 C) [9] . The degradation reaction products such as formaldehyde or the polymer are cleavaged to low molecular weight compounds and gasified, leading to the weight loss of the polymer.…”

The Thermostabilization of Polyoxymethylene Through Amine Treatment

“…The Thermostabilization Mechanism of Amine Treatment of POM Due to its chemical properties, amine can deactivate Lewis acid arising from the residual initiator and formic acid formed in situ when the trace quantities of formaldehyde generated in processing are oxidized [9,11] . Amine used in this work contains hydroxy group in its molecule and is weakly alkaline, displaying the following four functions during melt treatment of POM:…”

“…During the polymerization, cationic initiators like Lewis acids are often used to copolymerize trioxides with cyclic ethers and acetals, which may be still active in the crude polymer after polymerization, and do a negative part in initiating POM and result in chain breaking [7] . Besides, the crude POM copolymers downstream of the polymerization step still contain unstable end groups (hemiformal acetals), which prohibit direct use or processing of polymers [8,9] . Therefore, the study on the postprocessing unit is substantially important for the application of POM.…”