TECHNOLOGY FOCUS - ORGANIC CHEMISTRY - Preferred Components: Solvent of alkaline solution in the step (i) is tetrahydrofuran, the alkaline polar solvent in the step (ii) is dimethyl sulfoxide or N,N-dimethylformamide, and the strong polar aprotic solvent in the step (iii) is N,N-dimethylacetamide.    TECHNOLOGY FOCUS - POLYMERS - Preparation (Claimed): The preparation of (I), comprises (i) carrying out substitution reaction of 3,4-dicyanophenol with 6-bromohexanol in an alkaline polar solvent in presence of potassium iodide and potassium carbonate under action of anhydrous alchlor catalyst to obtain 4-(6-hydroxy-hexyloxy)phthalonitrile (II), and reacting (II) with methacryloyl chloride monomer in alkaline solution of triethylamine to obtain 6-(3,4-dicyanophenoxy)hexyl methacrylate (III), where molar ratio between 6-bromohexanol and 3,4-dicyanophenol is 0.8-0.9:1, molar ratio between 6-bromohexanol and potassium carbonate is 1:1-2, weight ratio between 3,4-dicyanophenol and alkaline polar solvent is 1:20-30, molar ratio between (II) and methacryloyl chloride is 1:1.1, and molar ratio between triethylamine and methacryloyl chloride is 1:1, (ii) carrying out reversible addition-fragmentation chain transfer polymerization reaction of (III) in alkaline polar solvent under anaerobic condition by using azobisisobutyronitrile as initiator and dithionaphthoic acid isobutyronitrile ester as chain transfer agent to obtain phthalonitrile functional group side chain-containing polymer (IV), where molar ratio between (III), initiator and chain transfer agent is 20-80:1:1.5-5, and weight ratio between (III) and the solvent is 1:6-12, and (iii) carrying out phthalocyanine ring-forming reaction of (IV) with 4-octyloxyphthalonitrile in a strong polar aprotic solvent in presence of a thermo-sensitive catalyst and zinc acetate under argon gas atmosphere to obtain (I), where mass ratio between the thermo-sensitive catalyst and the 4-octyloxyphthalonitrile is 1:3-5, mass ratio between zinc acetate and (IV) is 0.5-3:1, mass ratio between (IV) and 4-octyloxyphthalonitrile is 0.2-0.5:1, mass ratio between 4-octyloxyphthalonitrile and the solvent is 1:10-20, and the thermo-sensitive catalyst is 1,8-diazabicyclo(5,4,0)undec-7-ene. Preferred Method: The step (i): the substituent reaction temperature is 70-80 degrees C and the reaction time is 14-16 hours, and two-step reaction condition is, reacting for 0.8-1 hour under ice bath condition first and then reacting for 22-24 hours at room temperature. The step (ii): the molar ratio between (III), initiator and chain transfer agent is 50:1:2; weight ratio between (III) and the solvent is 1:2; the polymerization reaction temperature is 70-80 degrees C and the reaction time is 1-10 hours. The step (iii): the mass ratio between (IV) and 4-octyloxyphthalonitrile is 0.3:1; the reaction temperature is 130-140 degrees C and the reaction time is 48-72 hours; and the mass ratio between zinc acetate and (IV) is 1.1:1. The products obtained after the steps (i), (ii) and (iii) are respectively subjected to purification before use. The purification process comprises (i) purifying (II) by adding the reaction solution into a beaker placed in ice bath, stirring, allowing to stand and filtering to obtain crude product, and eluting the crude product with petroleum ether/ethyl acetate by column chromatography to obtain pure intermediate, (ii) purifying (III) by extracting the reaction solution with dichloromethane for three times, collecting the organic layer and drying over anhydrous magnesium sulfate overnight, and filtering to obtain crude product, and then eluting the crude product with normal hexane/ethyl acetate by column chromatography to obtain pure monomer, (iii) purifying (IV) by dissolving the reaction product in dimethylformamide to obtain a solution, pouring the solution through a column of neutral alumina, rotary evaporating the solution, adding obtained concentrated liquid into methanol, precipitating and filtering to obtain a precipitate, and vacuum drying the precipitate in an oven at room temperature to obtain green solid product, and (iv) purifying (I) by cooling the reaction solution, adding tetrahydrofuran to the reaction solution, then diluting the reaction solution with methanol, precipitating, allowing to stand for 12-24 hours, filtering, dissolving the filter cake in tetrahydrofuran, allowing to stand and filtering, concentrating the filtrate and dropping into methanol, again precipitating and filtering to obtain crude product, and carrying out Soxhlet extraction of the crude product with diethyl ether to obtain dark green solid product.