The Synthesis And Properties Of Polybenzoxazines Based On A Siloxane-containing Diphenol

This paper mainly studies the preparation and the properties of benzoxazines based on a siloxane-containing bisphenol and aniline, methylamine, and allylamine.The siloxane-containing diphenol was synthesized from 1,1,3,3-tetramethyldisiloxane and o-allylphenol, followed by the Mannich condensation with aniline, methylamine, allylamine, and formaldehyde yielding three siloxane-containing benzoxazines. The structrue of the siloxane-containing diphenol was confirmed by ~1H, 13 C, and 29 Si nuclear magnetic resonance(NMR) spectroscopy and Fourier transform infrared(FTIR) spectroscopy.The chemical structures of the benzoxazines based on siloxane-containing diphenol were confirmed by ~1H, 13 C, and 29 Si NMR and FTIR. The thermally activated polymerization behaviors of polybenzoxazines were investigated by FTIR, solid-state 13 C NMR, and differential scanning calorimetry(DSC). Each DSC curve shows only one exothermic peak. The peak temperatures are 237, 212 and 239℃ for TMDSBPDP-a, TMDSBPDP-m, TMDSBPDP-ala, respectively, and the exothermic heats are 64.2, 42.0, and 157.5 J/g, respectively. For poly(TMDSBPDP-a), poly(TMDSBPDP-m) and poly(TMDSBPDP-ala), the dynamic mechanical analyses show that the storage moduli at 0℃ are 2.01, 1.10, and 1.92 GPa, respectively, and the glass transition temperatures are 53, 39, and 86℃, respevtively. The thermogravimetric curves show that the char yields are 35.5%, 34.4%, and 33.5% at 800℃ in nitrogen for poly(TMDSBPDP-a), poly(TMDSBPDP-m), and poly(TMDSBPDP-ala), respectively, and the degradation temperatures corresponding to the 5% weight loss in nitrogen are 237, 233, and 238℃, respectively. The three polybenzoxazines exhibit one-way dual-shape memory behavior in response to changes in temperature. Poly(TMDSBPDP-a) and poly(TMDSBPDP-m) show excellent shape fixity ratios and shape recovery ratios in bending and tensile tests, and their shape fixity ratios and shape recovery ratios can reach 100%. In the tensile stress-strain tests, the fixity ratios of poly(TMDSBPDP-a), poly(TMDSBPDP-m) and poly(TMDSBPDP-ala) are 99.7%, 98.4%, and 95.6%, respectively, and the recovery ratios are 83.6%, 80.7%, and 76.9%, respectively.