Polybenzoxazines are usually considered as high-performance thermosetting resins with high Tg, high strength, high modulus and good thermal stability, though their toughness is not very ideal. Theoretically, ring-opening polymerization of benzoxazine monomer could give N,O-acetal-type (phenoxy-type) linkage, phenolic Mannich-type linkage, and arylamine Mannich-type linkage if aromatic amine was used to synthesize benzoxazine. However, preparation of polybenzoxazine that mainly consists of N,O-acetal-type linkage or arylamine Mannich-type linkage is very hard to achieve. In this work, we have managed to prepare polybenzoxazine that mainly consists of arylamine Mannich-type linkage by employing Lewis acid as catalyst from the usual benzoxazine 2,2-bis(4-phenyl-3,4-dihydro-2H-1,3-benzoxazinyl)-isopropane (BA-a). Its chemical structure was confirmed by FTIR spectra, and distribution of hydrogen bonds was calculated by curve fitting. Compared with phenolic Mannich-type polybenzoxazine, it’s discovered that more -OH---π hydrogen bonds is formed in this type of polybenzoxazine. The increase in weak -OH---π hydrogen bonds and decrease in strong -OH---N hydrogen bonds result in lower Tg but higher flexibility. Tensile experiment shows the maximum elongation at break of 5.17% for polybenzoxazine catalyzed by PCl5 cured at 180 oC with no cost of tensile strength or tensile modulus. The toughing effect is further supported by SEM images, tensiled fractography of arylamine Mannich-type polybenzoxazine shows obvious ductile fracture characteristics. Owing to the different hydrogen bonds distribution and the unique chemical structure, this type of polybenzoxazines also posses shape memory property that the deformation could be rapidly recovered and the recovery ratio is higher than 95% within 2 minutes for polybenzoxazine catalyzed by PCl5. To sum up, we impart polybenzoxazine with different properties by control of chemical structure and hydrogen bonds.

Preparation of flexible shape memory polybenzoxazine through chemical structure manipulation and hydrogen bonds control

255th National Meeting (2018)

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