Study Of POSS Grafted Polybenzimidazole Copolymer

Polybenzimidazoles (PBI) are a kind of engineering plastics which have excellent comprehensive performances such as mechanical properties, thermal properties and chemical resistance. These excellent performances make PBIs have extensive application prospect in many fields. However, PBIs exhibit poor solubility due to the rigid backbones and strong intermolecular hydrogen bond, resulting in the limit of their use and development. Polyhedral oligomeric silsesquioxane (POSS) is a class of nanosized cage-like molecules. POSSs are suitable candidate to prepare organic-inorganic composites due to the both characteristics of inorganic core and organic groups, POSSs have been widely used in polymer modification to gain good comprehensive performances.In the present work, a mono-functional phenyl-POSS was prepared. A novel phenyl-POSS grafted PBI copolymers which have good comprehensive performances such as mechanical properties, thermal properties and chemical resistance were synthesized.A mono-functional 3-chloropropylheptaphenyl POSS(Cl-POSS) was synthesized through corner-capping reaction. A 3-iodopropylheptaphenyl POSS (I-POSS) was synthesized through iodization of Cl-POSS. The results of FT-IR, NMR, EA showed that the two kinds of POSSs had been successfully synthesized. The results of XRD and SEM indicated that I-POSS is a crystalline substance. Both that Cl-POSS and I-POSS showed good thermal stabilities.A series of novel POSS grafted PBI copolymer (PPBI) containing different amounts of POSSs were prepared by N-substituted reaction. The graft copolymers were prepared through substitution of the hydrogens in the parent PBI polymer with POSS groups. Meanwhile, physical blend PBI and POSS (PBIB) blends which had same ratio of POSS in PPBI were also prepared.The degree of substitution and weight of POSS in the PPBI which were calculated from the element alanalysis results were 11.26～27.13% and 31.70～57.76% respectively. The intrinsic viscosities of PPBIs were decreased with the increasing of POSS amount. Solubilities of PPBIs were better than that of PBI polymer, PPBI could be soluble in some organic solvenst at room temperature.The effect of POSS on PBI aggregated structure and dispersivity of POSS in PPBI were studied through XRD and SEM. The results showed that molecular chains of PPBI were less tightly packed, there were no POSS aggregation domains in the PPBI, POSS was dispersed well in the PPBI, there were no obviously POSS aggregation areas can be observed in SEM images. However, the dispersivity of POSS was not good for PBIB composites. There were lots of POSS crystals in PBIB, showed obviously two-phase structure in SEM images. Mechanical property test declared the maximal Young’s modulus of PPBI was 4.72 Gpa, increased at first and then decreased with the increasing of POSS amount, but all of them had higher Young’s modulus than that of PBI. The maximal breaking strength of PPBI was 85.00 Mpa, also increased at first and then decreased with the increasing of POSS amount. The elongation at break of PPBI decreased with the increasing of POSS amount. However, Young’s modulus of PBIB was 0.60 Gpa, less than 1.36 Gpa of PBI, the breaking strength of PBIB decreased from 70.83 Mpa of PBI to 6.14 Mpa, the elongation at break of PBIB decreased from 6.32% of PBI to 2.6%. All three above decresed with the increasing of POSS amout. Contact angle tests showed the introduction of POSS in the PBI chains was able to change the surface properties of PBI, the surface of PPBI exhibits form hydrophilie properties to hydrophobic properties with the increasing of POSS amout. Thermogravimetric analysis indicated that PPBI had good thermal stability,5% weight loss temperatures were over 400℃, the 800℃ residual weight were over 55%.In conclusion, the novel POSS grafted PBI copolymer had good comprehensive properties.