TECHNOLOGY FOCUS - POLYMERS - Preferred Components: The proton-conducting membrane comprises 1-15 wt.% component (ii). The cyclic polyether groups are cryptands or crown ethers. The component (ii) is of formula (-(CH2-CH(R1-CPG))n-) (I). The component (ii) is a cyclic oligomer of formula (III) or (IV). The cyclic oligomer is formed by polymerizing 2,11-divinyl-6,7,14,15-tetrahydro-5,8,13,16-tetraoxa-dibenzo(a,g)cyclododecene derivatives of formula (V). The component (i) comprises perfluorosulfonic acid polymers and/or polymers having perfluoro-cyclobutyl groups. The component (i) comprises a copolymer comprising sulfonic acid structural units of formula (CF2=CF-(OCF2CFX1)m1-Or-(CF2)q-SO3H) (VI) and tetrafluoroethylene. The component (i) comprises perfluoro-cyclobutyl groups, preferably perfluorocyclobutane-1,2-diyl or perfluorocyclobutane-1,3-diyl.R1 = 1-20C alkyl, 1-18C polyether, 6-20C alkylaryl or 6-20C aryl, where R1 is optionally present;CPG = cyclic polyether group comprising 24 cyclic polyether groups, preferably e.g. 1,4,7,10,13-pentaoxa-cyclopentadecan-2-yl, 6,7,9,10,17,18-hexahydro-5,8,11,16,19-pentaoxa-dibenzo(a,g)cyclopentadecene moieties of formula (IIa), 1,4,7,10,13,16-hexaoxa-cyclooctadecan-2-yl, 1,4,7,10-tetraoxa-13-aza-cyclopentadecan-13-yl, 6,7,9,10,12,13,15,16,18,19-decahydro-5,8,11,14,17,20-hexaoxa-benzocyclooctadecene moieties of formula (IIb), 6,7,9,10,17,18,20,21-octahydro-5,8,11,16,19,22-hexaoxa-dibenzo(a,j)cyclooctadecene moieties of formula (IIc), 4,11,17,20,25,28-hexaoxa-1,14-diazatricyclo(12.8.8.0(5,10))triaconta-5(10),6,8-trien-7-yl, 4,11,17,20,25-pentaoxa-1,14-diazatricyclo(12.8.5.0(5,10))heptacosa-5(10),6,8-trien-7-yl, 6,7,9,10,12,13,15,16,18,19-decahydro-5,8,11,14,17,20-hexaoxa-benzo-cyclooctadecen-2-yl and 6,7,9,10,12,13,15,16-octahydro-5,8,11,14,17-pentaoxa-benzocyclopentadecene-2-yl;G1 = 6,7,9,10,12,13,15,16,18,19-decahydro-5,8,11,14,17,20-hexaoxa-benzo-cyclooctadecen-2-yl;G2 = 6,7,9,10,12,13,15,16-octahydro-5,8,11,14,17-pentaoxa-benzocyclopentadecene-2-yl;n, m = 1-8;m1 = 0-3;q = 1-12;r = 0 or 1; andX1 = F or CF3. EXAMPLE - No suitable example given.