Synthesis Of Polyamide-amine With Pendant Benzoxazine Groups And Their Thermal Curing Behavior

Benzoxazine is a novel thermosetting resin, it's synthesized by phenols, primary amines and formaldehyde through condensation reaction. It has well molecular-design properties. The modification of polybenzoxazine was focused on synthesizing monofunctional and difunctional benzoxazine monomers. However, the study of trifunctional and multifunctional benzoxazine monomers were few reported. In this paper, benzoxazine resin with low curing temperature was synthesized through the molecular design by using entire generation PAMAM as multiamines.Two novel dendrimer compounds with pendant benzoxazine named 1.0G Benzoxazine(1.0G BZ) and 2.0G Benzoxazine (2.0G BZ), were prepared by 1.0G PAMAM and 2.0G PAMAM, phenol, paraformaldehyde.OG Benzoxazine (0G BZ) was prepared by ethylenediamine, phenol, paraformaldehyde. The structure of 1.0G BZ and 2.0G BZ were characterized by FT-IR and'H NMR. By plentiful solubility tests, we found out good component solvent which could remove impurities of 1.0G BZ and 2.0GBZ.Curing behavior of OG BZ, 1.0G BZ and 2.0G BZ were carried out by differential scanning calorimetry (DSC), the curing peak temperature(Tp) of 1.0G BZ and 2.0G BZ were 203.6℃and 213℃, respectively. Compared with the Tp of OG BZ(225℃), the curing temperature was decreased by the introduction of PAMAM, meanwhile, the curing temperature of PAMAM-based benzoxazine is enhancing with the increase the generations of PAMAM and the amount of oxazines, as a result, the Tp of 2.0G BZ is higher than 1.0G BZ.. Compared with the traditional benzoxazine resins, the curing temperature of 1.0G BZ reduced 22℃. The initial curing temperature(Ti) of 1.0G BZ was lower due to the cavity it contained, phenol as excess reactants was not removed completely and resdued in the cavity. When 1.0G BZ is curing, phenol as catalyst provides active hydrogen to catalyze 1.0G BZ ring-openning, therefore, the initial curing temperature of LOG BZ was lower. The curing kinetics of LOG BZ was explored by non-isothermal DSC. The basic cure process was determined through extrapolation. The Flynn-Wall-Ozawa isoconversional method and Kissinger method were used to evaluate the effective activation energy (Ea). The activation energy values(Ea) were 109.15 and 103.11 kJ·mol-1, respectively. The curing reaction order was one order by Crane method.Thermal properties of cured resin of 1.0G PAMAM. 0G PBZ,1.0G PBZ and 2.0G PBZ were investigated by thermogravimetrical analysis (TGA). The char yields of 1.0G PAMAM,OG PBZ,1.0G PBZ and 2.0G PBZ were 53.30%,37.61% and 26.34%,18.05%, respectively. The results showed that the increasing amount of benzoxazine groups can enhance heat resistance, but importing the higher generation of PAMAM results in descending the thermal performance. The later factor is dominant, so the thermal properties of 2.0G PBZ descend in general. The char yeild of 1.0G PBZ is higher than that of 1.0G PAMAM by 19.56%, which show the outstanding thermal properties of the 1.0G PBZ. Thermal gravimetric analysis of 1.0G PBZ and 2.0G PBZ in different atmosphere indicated that 1.0G PBZ and 2.0G PBZ had excellent thermo-oxidative stability. DSC results showed 1.0G PBZ had high glass transition temperature (Tg=161.4℃), higher than the traditional difunctionality of benzoxazine.