TECHNOLOGY FOCUS - POLYMERS - Preparation (claimed): 2,6-Diethynyl-benzo(1,2-b;4,5-b')dithiophene derivative of formula (Ia), and thieno(3,4-c)pyrrole-4,6-dione derivative of formula (Ib) or 3,6-di-thiophen-2-yl-2,5-dihydro-pyrrolo(3,4-c)pyrrole-1,4-dione derivative of formula (Ic) in a ratio of 1:0.95-1:1.05 are dissolved in solution of toluene and diisopropylamine, then cuprous iodide and tetrakis(triphenylphosphine)palladium are added and Sonogashira coupling reaction is carried out under protection of inert gas. The reaction liquid is concentrated, methanol is added, obtained crude product is washed with methanol, acetone, n-hexane and chloroform, Soxhlet extraction is then carried out using chloroform, to obtain copolymer (I).X=bromo or iodo.Preferred Processes: Compound (Ia) is prepared by dissolving 2,6-dibromo-4,8-disubstituted-benzo(1,2-b:4,5-b')dithiophene of formula (III) in tetrahydrofuran, adding tetrakis(triphenylphosphine)palladium(0) and cuprous iodide as catalyst, diisopropylamine and trimethylsilylacetylene, reacting at 80 degrees C for 24 hours under protection of inert gas, extracting using dichloromethane, washing with saturated brine several times, drying organic layer to obtain crude product, purified crude product to obtain 2,6-bis(trimethylsilylethynyl)-4,8-disubstituted-benzo(1,2-b:4,5-b')dithiophene of formula (IV), dissolving compound (IV) in tetrahydrofuran, then adding tetrabutylammonium fluoride, stirring at room temperature for 3 hours, carrying out rotary steaming to remove solvent, dissolving residue in dichloromethane, washing using saturated salt solution 3 times, and removing solvent. Compound (Ib) is prepared by dissolving thieno(3,4-c)pyrrolidine-dione in mixed solution of concentrated sulfuric acid and trifluoroacetic acid in a volume ratio of 1:3-1:5, adding N-bromosuccinimide or N- iodosuccinimide, stirring at room temperature until the solution is purple, adding the reaction mixture into ice water, extracting using dichloromethane, washing organic phase with saturated brine and 10% sodium thiosulfate solution, drying and purifying. Compound (Ic) is prepared by dissolving 2,5-di(2-octyldodecyl)thieno-3,6-pyrrolo(3,4- c)pyrrole-4,6-dione and N-bromosuccinimide or N-iodosuccinimide in chloroform, stirring at room temperature for 40 hours in dark under protection of inert gas, adding reaction mixture into methanol, filtering by suction filtration, washing filter cake with hot methanol, drying and purifying. Preferred Composition: The molar ratio of 2,6-dibromo-4,8-disubstituted-benzo(1,2-b:4,5-b')dithiophene, diisopropylamine and trimethylsilylacetylene is 1:35:2.1. The molar ratio of mixture of compound (IV) and tetrahydrofuran, and tetrabutylammonium fluoride is 1:4-1:5.