Poly(tetramethylene oxide)-coated silica nanoparticles incorporated into poly(4,4-oxydiphenylene-pyromellitimide) matrix

Telechelic poly(teramethylene oxide) with two isocyanate end groups (OCN-PTMO-NCO) was synthesized by the reaction of polytetrahydrofuran (M-n=1000gmol(-1)) and hexamethylene diisocyanate in 1:2 molar ratio. The resulting macrochains were then covalently grafted to the surface of silica nanoparticles (SNPs). Thus, the inorganic nanoparticles could be thoroughly coated by a thick and soft organic shell. Thermogravimetric measurements showed that up to 85wt.% of the organically modified SNPs (OSNPs) could be formed from the organic part. Different weight ratios of OSNPs were subsequently added to a solution of 4,4-oxydiphenylamine/pyromellitic dianhydride poly(amic acid) (PAA) in dimethylformamide. Chemical cyclodehydration of the PAA in the presence of homogeneously dispersed OSNPs resulted in poly(4,4-oxydiphenylene-pyromellitimide) (POPI) nanocomposites, labeled by POPI/OSNP 5, POPI/OSNP 7.5, and POPI/OSNP 10. The nanocomposites obtained were fully characterized by field emission scanning electron microscopy, Fourier transform infrared spectroscopy, and X-ray diffraction. According to the diffuse reflectance UV spectroscopy, in comparison with neat POPI, the POPI/OSNP series showed an appreciable redshift in the (max) values up to 15-20nm. Moreover, POPI/OSNP series showed significant stability toward heat at temperatures above 540 degrees C. The endothermic phase transitions occurred by the first thermodegradation of the resulting nanocomposites could be obviously seen in the differential thermal analysis.