NOVELTY - A hydroquinone compounds (I) or their salts are new.    USE - For the preparation of aromatic polyether polymers or copolymers selected from block copolymers, random copolymers, periodic copolymers, or alternating polymers (claimed) useful as electrolytes in high temperature proton exchange membrane fuel cells.    ADVANTAGE - The compounds provide aromatic polyether polymers having good mechanical properties, high oxidative and thermal stability, and high conductivity.    DETAILED DESCRIPTION - A hydroquinone compounds of formula (I) or their salts, are new.R=pyridine-2-yl, pyridine-3-yl, pyridine-4-yl, pyrimidin-2-yl or pyrimidin-5-yl.    INDEPENDENT CLAIMS are included for the following:    (1) preparation of (I);    (2) new aromatic polyether copolymer of formula (II) and aromatic polyether of formula (III), or their salts;    (3) preparing (M1) the copolymer (II) or polymer (III) involving reacting monomers comprising aromatic difluoride and the compound (I) at high temperature;    (4) a blend (B1) of copolymers or homopolymers, prepared by mixing a dimethylacetamide solution of the copolymer (II) and a dimethylacetamide solution of the polymer (III) in a predetermined ratio;    (5) a composition (C1) comprising a slurry mixture of the polymer (III), copolymer (II), or the blend (B1), and a polar aprotic solvent;    (6) preparing a catalyst involving: (a) depositing a layer of a mixture of the composition (C1) and a Pt-catalyst by calendaring, screen printing or spraying on a hydrophobic layer; and (b) drying and sintering the layer deposited in step (a), to obtain the catalyst; and    (7) a layered membrane electrode assembly comprising: a substrate layer; two gas diffusion layers; and the polymer electrolyte (II) or (III).    X1 and Y1=-(1,4-phenylene)-SO2-(1,4-phenylene)-, -(1,4-phenylene)-C(O)-(1,4-phenylene)-, -(1,4-phenylene)-P(O)(C6H5)-(1,4-phenylene)-, or -(1,4-tetrafluorophenylene)-(1,4- tetrafluorophenylene)-;    A=absent, -CH2-, -CF2-, or phenyl;    n=0.5-99.5%;    m=99.5-0.5%.    Provided that: n+m is 100%.