A series of novel copoly(phenyl-s-triazine)s were prepared by solution polycondensation of 2,4-bis(4-fluorophenyl)-6-phenyl-1,3,5-s-triazine (BFPT) with 9,9-bis(4-hydroxyphenyl)fluorine (BHF) and 4-(4-hydroxylphenyl)(2H)-phthalazin-1-one (HHPZ) to investigate the effects of bulky diphenylfluorene units on solubility as well as thermal and mechanical properties. The synthetic procedure was efficiently optimized, resulting in high M (n) up to 4.3 x 10(4) g/mol in GPC. Moreover, the introduction of diphenylfluorene moieties in the main chains leads to the outstanding modification in the solubility of the copolymers in common organic solvents, such as chloroform, chlorobenzene (CB) and N-methylpyrrolidone (NMP). Simultaneously, the copolymers exhibit remarkable dimensional stability as evidenced by DMA, and maintain excellent thermal properties with glass transition temperatures (T (g)s) ranging from 307 to 340 A degrees C, 5 % mass-loss temperatures lying between 525 and 551 A degrees C, and char yields at 800 A degrees C higher than 55 % in N-2. Their solubility increases with the increase of diphenylfluorene content in the polymer backbone, and the thermal properties just decrease slightly. The films obtained via solution casting technology possess commendable mechanical properties, even at elevated temperatures.