Synthesis and Characterization of Thermoset (Epoxy-Benzoxazine)

Abstract

A main chain benzoxazine oligomer MCBOs(PH-p.APH) containing phenolic hydroxyl end group based on phenol, 4-aminophenol and paraformaldehyde was synthesized using a solvent-free method. Epichlorohydrine was used for the epoxidation of the benzoxazine oligomer in the presence of tetra-butyl ammonium chloride (TBAC). The benzoxazine oligomer and its epoxidized product were then step cured in a stainless steel mold in an air-circulating oven according to a heating cycle from 140 to 250 °C. The benzoxazine oligomer MCBOs(PH-p.APH) was characterized by FT-IR, ¹H-NMR and ¹³C-NMR spectroscopy, and number average molecular weight was measured using the cryscopic technique. The epoxy derivative of benzoxazine oligomer [E-MCBOs(PH-p.APH)] was characterized by FT-IR spectroscopy and ¹H-NMR. The polymerization process and the curing behavior were verified with DSC and FT-IR. The thermal stability of the cured product was investigated with TGA. The DSC analysis showed that the presence of phenolic hydroxyl in benzoxazine oligomer resulted in lowering the curing temperature compared to epoxy derivative of benzoxazine oligomer due to catalytic effect of phenolic hydroxyl and the retardation effect of epoxy group. The TGA analysis of the thermosets showed that the cross-linked structure of polybenzoxazine(PH-p.APH) has higher thermal stability than that of poly[E-MCBOs(PH-p.APH)].