Four main-chain type polybenzoxazine precursors were synthesized from the Mannich-type polycondensation of biphenol A, paraformaldehyde, and four typical aromatic diamines: 1,4-phenylenediamine, 4,4'-diaminodiphenyl methane, 4,4'-diaminodiphenyl ether, and 2,2-bis[4-(4-aminophenoxy)phenyl] propane. The solvent effect on the polycondensation was examined. We found that polybenzoxazine precursors prepared in toluene/ethanol exhibit higher purity, higher molecular weight, and lead to better thermal properties after curing than those prepared in chloroform, as recommended by Takeichi's group (T. Takeichi et al., Polymer, 2005, 46, 12172). The cured polybenzoxazine films prepared by these polybenzoxazine precursors display unusual flexibility, extremely high T-g, and low surface energy. They show T-g values as high as 272-353 degrees C (DMA data), coefficients of thermal expansion as low as 39-49 ppm/degrees C, contact angles as high as 100-102 degrees, and surface energy as low as 17.7-24.5 mJ m(-2)

A main-chain type polybenzoxazine, PBz (1), with pyridinyl moieties was prepared. When the THF dilute solution of PBz (1) was protonated with HCl, a new absorption signal at 458 nm was observed in the UV-vis spectrum. After being excited at 458 nm, a strong emission at 570 nm was observed in the fluorescence spectrum. This result suggests that the pyridinyl-containing PBz (1) can be used as a proton sensor.

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