TECHNOLOGY FOCUS - ORGANIC CHEMISTRY - Preparation (claimed): Alkyl-substituted dibenzothiophene-S,S-dioxide monomer (I) is prepared by brominating dibenzothiophene with liquid bromine into 2-bromo-dibenzothiophene or 2,8-dibromo-dibenzothiophene in presence of argon to obtain a product. 2-Bromo-dibenzothiophene or 2,8-dibromo-dibenzothiophene are dissolved into anhydrous tetrahydrofuran in an ice bath to obtain a solution. Diethyl ether solution of alkyl bromide reagent is treated with the obtained solution at room temperature for 2-10 hours to obtain a mixed solution. Saturated ammonium chloride solution is added to the mixed solution to obtain a crude product. The obtained crude product is filtered by column chromatography to obtain a product. The obtained product is dissolved into acetic acid to obtain a material. The obtained material is oxidized by using sulfur and oxidant i.e. hydrogen peroxide. The oxidized material is crystallized by using methanol to obtain alkyl-substituted dibenzothiophene-S,S-dioxide monomer (I). Alkyl-substituted dibenzothiophene-S,S-dioxide monomer (II) is prepared by oxidizing dibenzothiophene into S,S-dioxo-dibenzothiophene in presence of oxidant i.e. hydrogen peroxide and acetic acid solution. S,S-Dioxo-dibenzothiophene is brominated in sulfuric acid by using bromo-butanimide to obtain 3-bromo-S,S-dioxo-dibenzothiophene or 3,7-dibromo-S,S-dioxo-dibenzothiophene. 3-Bromo-S,S-dioxo-dibenzothiophene or 3,7-dibromo-S,S-dioxo-dibenzothiophene is dissolved into anhydrous diethyl ether to obtain a product. The obtained product is reduced into 3-bromo-dibenzothiophene or 3,7-dibromo- dibenzothiophene by using lithium aluminum hydride at room temperature to obtain a material. 3-Bromo-dibenzothiophene or 3,7-dibromo-dibenzothiophene is dissolved in anhydrous tetrahydrofuran into ice bath to obtain a mixed solution. Diethyl ether solution of alkyl bromide reagent is treated with mixed solution at room temperature for 2-10 hours to obtain crude product. Saturated ammonium chloride solution is added to the obtained crude product. The crude product is filtered by column chromatography to prepare 3-alkyl substituted-dibenzothiophene or 3,7-dialkyl substituted-dibenzothiophene. 3-Alkyl substituted-dibenzothiophene or 3,7-dialkyl substituted-dibenzothiophene is brominated by using liquid bromine to form 3-alkyl substituted-2,8-dibromo-dibenzothiophene or 3,7-dialkly substituted-2,8-dibromo-dibenzothiophene. 3-Alkyl substituted-2,8-dibromo-dibenzothiophene or 3,7-dialkly substituted-2,8-dibromo-dibenzothiophene is oxidized with sulfur in presence of hydrogen peroxide to obtain alkyl-substituted dibenzothiophene-S,S-dioxide monomer (II).