Chapter 5 - Polyether Plastics

Abstract

This chapter covers polymers in which the most important linking group is the ether moiety, which is –O–, The polymers discussed in this chapter are polyoxymethylene (or acetal homopolymer), polyoxymethylene copolymer (POM-Co or acetal copolymer), and modified polyphenylene ether/polyphenylene oxides. Acetal polymers, also known as POM or polyacetal, are formaldehyde-based thermoplastics. Polyformaldehyde is thermally unstable. It decomposes on heating to yield formaldehyde gas. Two methods of stabilizing polyformaldehyde for use as an engineering polymer were developed and introduced by DuPont. DuPont's method for making polyacetal yields a homopolymer through the condensation reaction of polyformaldehyde and acetic acid. Further, stabilization of acetal polymers also includes the addition of antioxidants and acid scavengers. In addition, the Celanese route for the production of polyacetal yields a more stable copolymer product via the reaction of trioxane, a cyclic trimer of formaldehyde, and a cyclic ether, such as ethylene oxide or 1,3-dioxolane. The improved thermal and chemical stability of the copolymer versus the homopolymer is a result of randomly distributed oxyethylene groups. Further, polyphenylene ether (PPE) plastics are also referred to as polyphenylene oxide (PPO). The PPE materials are always blended or alloyed with other plastics, so they are called modified PPE or PPO. PPE is compatible with polystyrene (PS) and is usually blended with high-impact PS over a wide range of ratios.