Abstract: Disclosed is a copolymer represented by the following general formula (1): ##STR1## wherein R.sub.1 represents a group based on a polymer or a copolymer possessing electroconductivity and inducing coloration or discoloration on being oxidized or reduced, R.sub.2 and R.sub.3 represent independently a hydrogen atom or an alkyl group having 1 to 1,000 carbon atoms, A represents a group possessing polarity and exhibiting affinity for ions, and L and M are independently an integer of at least 1, providing that the total degree of polymerization is an integer in the range of 10 to 12,000. The copolymer may be a block copolymer or a random copolymer. This copolymer exhibits electrochromism and, therefore, is useful as a coloring-discoloring material which induces coloration or discoloration on being oxidized or reduced, particularly as an electrochromic substance used in an electrochromic display device.

Abstract: An electroluminescent element includes an organic compound layer formed of a thiophene polymer as a light emitting layer or a hole injection transport layer. The element emits light at high luminance and is reliable.

Abstract: A sulfuric acid concentration sensor including a sensor body comprising a high molecular compound having a property to react with sulfuric acid and a property to change an electric conductivity in such a way as one-valued function with a change in sulfuric acid concentration, in which an electric current is flown through the sensor body impregnated in sulfuric acid solution to obtain the electric conductivity of sensor body so as to know the sulfuric acid concentration. Since the electric conductivity of high molecular compound changes corresponding to the sulfuric acid concentration, the sulfuric acid concentration can be known when the electric conductivity of the sensor body i.e. the high molecular compound is obtained, so that the concentration of sulfuric acid can be measured easily.