NOVELTY - An electroactive polymer has, in its oxidized state, one or more conductive and non-conductive polymer segments, at least one of which is bonded to polysulfide chains. The polysulfide chains comprise at least one moiety selected from -(Sm)-, -(Sm)- and (Sm)2-. m = an integer of 3-200 and is the same or different at each occurrence    USE - For a cathode for a secondary electrochemical cell (claimed).    ADVANTAGE - High utilization of electrochemical energy is obtained, with good retention over many charge/discharge cycles. The cathode has high surface area, high charge and discharge rates and sulfur content. The cell has improved discharge characteristics, long shelf life, improved capacity and manufacturing reliability.    DETAILED DESCRIPTION - INDEPENDENT CLAIMS are also included for:    (I) a method of preparing an electroactive grafted organic polymer as above, which comprises:    (i) providing a dispersion of elemental sulfur in a liquid medium containing a non-conductive polymer;    (ii) a adding precursor of a polymer repeat unit and a polymerization initiator comprising an oxidant, to the dispersion;    (iii) stirring to form the electroactive grafted organic polymer; and    (iv) separating the polymer from the reaction medium;    (II) a composite cathode for an electrochemical cell comprising the above polymer and one or more conductive fillers e.g. conductive carbon, graphite, activated carbon fibers, nonactivated carbon nanofibers, metal flakes, metal fibers, carbon fabric, metal mesh, conductive polymers and conductive metal chalcogenides;    (III) a method of forming the above cathode, which comprises:    (i) dispersing or suspending the electroactive organic polymer in a liquid;    (ii) optionally adding a conductive filler;    (iii) mixing to disperse the polymer;    (iv) casting the mixture on a substrate; and    (v) removing some or all of the liquid; and    (IV) an electrochemical cell comprising a cathode as above, an anode and an electrolyte between them.