Poly(2,6-dimethyl-1,4-phenylene oxide)

Chemical Properties

Poly(2,6-dimethyl-l,4-phenylene oxide) is characterized by high tensile strength, stiffness, impact strength and creep resistance; it also has good dielectric properties. These properties are maintained over a broad temperature range (about -45-120°C). The polymer is self-extinguishing. The polymer has a high glass-transition temperature (Tg = 208°C) which restricts crystallization in normal moulding techniques. Crystalline material may be obtained by heating the amorphous material or from solutions. One notable feature of the polymer is its good dimensional stability; it has a very low coefficient of thermal expansion and low water absorption.
Poly(2,6-dimethyl-l,4-phenylene oxide) is soluble in aromatic hydrocarbons and chlorinated solvents and several aliphatic hydrocarbons cause environmental stress cracking. The polymer is outstandingly resistant to most aqueous reagents, being unaffected by acids, alkalis and detergents.

Chemical Properties

white to off-white powder

Uses

At the present time, most poly(2,6-dimethyl-l,4-phenylene oxide) intended for commercial use is blended with polystyrene (principally in the form of high-impact polystyrene). The two materials are miscible over the complete composition range. The effect of blending is to facilitate melt-processing (by lowering melt viscosity) and to lower cost whilst the desirable properties of the straight polymer are largely retained. In one recent product, the polystyrene is grafted on to the polyether. Polystyrene-modified poly(2,6- dimethyl-l,4-phenylene oxide) (commonly referred to as PPO) has found a variety of uses, which include telecommunication and business equipment housings and components and automotive parts.

Uses

Imidazolium modified PPO with liquid ionic graphene oxide can be used as an anion exchange membrane (AEM) composite with a peak power density of 136 mW cm² for use in the fabrication of high performance fuel cells. It may also be sulfonated to form a long chained polymeric structure with an efficiency of 81.8% at a current density of 120 mA cm² for potentiall use in vanadium redox flow batteries (VRFBs) as effective energy storage systems. It may also be used in the formation of AEMs, which can be used in the development of microbial desalination cell system (MDCS).

Preparation

Oxidative coupling is readily accomplished by passing oxygen into a reaction mixture containing 2,6-xylenol, pyridine and cuprous chloride. (The molar ratio of pyridine to cuprous ion is generally in the range 10: 1 to 100: 1.) External heating is unnecessary; during the course of the reaction the temperature rises to about 70C. The polymer is precipitated with dilute hydrochloric acid and collected by filtration.
It is generally accepted that aryloxy radicals are intermediates in the polymerization reaction since ESR studies have shown the presence of both monomeric and polymeric aryloxy radicals in polymerizing solutions of 2,6- xylenol. The simplest mechanism that can be suggested for the reaction is aromatic substitution:

Definition

ChEBI: 2,6-Dimethylphenol is a hydroxytoluene.

General Description

Poly(2,6-dimethyl-1,4-phenylene oxide) (PPO) is an anion exchange membrane (AEM) material that is mainly used as a cross-linker in which the methyl groups are used to bond with ultraviolet (UV) excited ketones.