u00d7 10 3 s cm after being doped with sulfuric anhydride this pyrolyzed film had an electroconductivity of 1 1 u00d7 10 4 s cm the film of polyelectrolyte of sulfonium salt obtained in example 5 was cut into a size of 30 u00d7 30 mm both ends of the film cut out were fixed after which the film cut out was uniaxially stretched at 100 u00b0 to 120 u00b0 c in a nitrogen gas atmosphere to a size 5 times or 8 times as large as the original size before the stretching the temperature was further raised to 250 u00b0 c each stretched film was heat treated at 250 u00b0 c for 30 minutes the uniaxially stretched poly p phenylenevinylene films thus obtained were preliminarily pyrolyzed at 950 u00b0 c in a nitrogen gas atmosphere for 2 hours and then pyrolyzed at 3 000 u00b0 c in an argon gas atmosphere the pyrolyzed products retained film form and had an electroconductivity of 1 15 u00d7 10 3 s cm or 1 20 u00d7 10 3 s cm respectively after being doped with sulfuric anhydride the pyrolyzed products had a maximum electroconductivity of 1 8 u00d7 10 4 s cm or 2 1 u00d7 10 4 s cm respectively a 3 000 u00b0 c pyrolyzed film of a poly p phenylenevinylene film obtained by fixing both ends of the film cut out under the same conditions except that no stretching treatment was carried out had an electroconductivity of 1 10 u00d7 10 3 s cm after being doped with sulfuric anhydride this pyrolyzed film had an electroconductivity of 2 u00d7 10 4 s cm.