TECHNOLOGY FOCUS - POLYMERS - Preferred Compositions: Episulfide compound is a composite episulfide compound containing formulae (2) and/or (3). Episulfide compound contains 60-97%, preferably 70-95% episulfide compound of formula (1) with respect to whole composite episulfide compound. Episulfide compound contains greater than or equal to 60%, preferably greater than or equal to 70% episulfide compound of formula (2) with respect to whole composite episulfide compound provided that n=1. Episulfide compound can harden independently. Hardenable component contains curable resin which has epoxy resin with fluorene structure.n= greater than or equal to 1.Preferred Conditions: Heat-processing temperature is less than or equal to 180 degrees C. Preferred Definitions:    Z=naphthalene ring.    SPECIFIC COMPOUNDS - 3 Compounds (1) are disclosed, e.g. formulae (1A)-(1C).    EXAMPLE - In a 3 L flask, 200.1 pts. wt. composite epoxy compound containing 9,9-bis(6-glycidyloxy-2-naphthyl) fluorene and 9-(6-glycidyloxy-2-naphthyl)-9-(6-hydroxy-2-naphthyl) fluorene and 1019 pts. wt. tetrahydrofuran (THF) were added. In a 2 L flask, 94.03 pts. wt. thiourea and 943 pts. wt. methanol were added to obtain methanol solution of thiourea. Dropping funnel was attached to the 3 L flask, and methanol solution of thiourea was dripped over 1 hour at room temperature. Reaction solution was heated at 40 degrees C and made to react in completion of dripping for 15 minutes-48 hours. Advancement of reaction was confirmed with thin layer chromatography (TLC) using hexane/ethyl acetate with volume ratio 3:7. After concentrating reaction liquid to 600 ml by rotating evaporator at room temperature and supplying into 1 L distilled water, reaction liquid was extracted using 2 L ethyl acetate extracted and reprecipitated by dripping extracted solution at 2200 pts. wt. methanol in a 5 L beaker. The wet crystal of white product was filtered and dried at 80 degrees C for 40 hours to obtain 131.45 pts. wt. white powder with 62% yield. Analysis of white product showed that it was a composite episulfide compound.