A novel nanocomposite composed of polybenzoxazine (PBZ) and multiwalled carbon nanotubes (MWNT) was prepared successfully. The surface modification of MWNT, including nitric acid modification followed by toluene-2,4-diisocyanate (TDI) treatment, introduced hydroxyl, carboxyl, and isocyanate groups on the MWNT surface. The surface carboxyl groups catalyzed the ring-opening reaction of benzoxazine and thus decreased the curing temperature of the system. The isocyanate groups reacted with the phenolic hydroxyl groups generated by the ring opening of benzoxazine resulting in the significant improvement of the adhesion between PBZ and MWNT. Dynamic mechanical analyses indicated the increase of storage modulus as well as Tg by the addition of MWNT into PBZ. A well dispersed modified-MWNT on nanoscale level inside PBZ matrix was observed by TEM and SEM.

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Phenolphthalein (3,3-bis(4-hydroxyphenyl)-1(3H)-isobenzofuranone, B-hpi), reacted with paraformaldehyde and allylamine by the Mannich reaction, was investigated as the acid ingredient for the first time, and a novel benzoxazine was synthesized. In order to confirm the structure of benzoxazine, benzyl-terminated B-hpi (3,3-bis(4-benzyloxyphenyl)-1(3H)-isobenzofuranone, B-bpi) was prepared. The chemical structures of B-hpi, B-bpi and benzoxazine were compared by FT-IR, 1H-NMR and 13C-NMR; it was demonstrated that the lactone structure remains in the molecular structure of benzoxazine (3,3-bis(3-allyl-3,4-dihydro-2H-1,3-benzoxazine)-1(3H)-isobenzofuranone, B-adi). B-adi transformed into a quinoid structure in basic medium similar to that of B-hpi. Software of Accelrys' materials studio (DMol3), FT-IR and UV-Vis spectrophotometry were employed to investigate the properties of the quinoid structure of B-adi and B-hpi. In situ FT-IR spectra showed the thermal curing behavior of B-adi. The char yield of poly B-adi was about 40% by weight at 800◦C in nitrogen atmosphere, as determined by TGA. Tg values for this poly B-adi were as high as 273◦C and 295◦C from the maximum of loss modulus and tan δ by DMTA, respectively.

The thermosetting resin from 2,2'-(1,3-phenylene) bis(4,5-dihydro-oxazoles) (PBO) and bis(3-pheny-l3,4-dihydro-2H-1,3-benzoxazine)isopropane (BZ) was prepared, and it was found that the thermal property of the final resin was affected greatly by the content of PBO. The nanocomposite from the thermosetting resin from BZ and PBO (molar ratio of PBO to BZ, 0.8 : 1) (PBZ–PBO) and organically modified montmorillonite (OMMT) was prepared by melt method. Differential scanning calorimetry showed that on the introduction of OMMT, the onset curing temperature of the copolymerization of BZ and PBO decreased. The X-ray diffractometer and transmission electron micrograph characterization of the dispersion of OMMT in the PBZ–PBO matrix suggested that exfoliation structure of OMMT was achieved. Dynamic mechanical analyses indicated that the nanocomposites exhibited much higher Tg values than the PBZ–PBO resin and pristine polybenzoxazine, and storage modulus of the nanocomposites was maintained up to higher temperature with the increasing OMMT content. Dynamic thermogravimetric analysis showed that the dispersion of clay nanolayers in the PBZ–PBO copolymer gave better thermal stability.