Synthesis And Properties Of Fluorene-containing Benzoxazine Precursors

A series of fluorene-containing benzoxazine percursours were synthesized usingbisphenol (bisphenol-fluorene, bisphenol-AF, bisphenol-A), formaldehyde anddiamines (ethylenediamine (Eda), hexamethylenediamine (Hda),4,4’-Diamino-diphenylmethane (Mda) and isophoronediamine (Ipda)) as starting materials bysolvent method in this paper. The structure of benzoxazine precurors was identified byFourier transform infrared (FT-IR), Hydrogen nuclear magnetic resonances (1H NMR)and Gel Permeation Chromatography (GPC). The curing reaction of benzoxazineprecuror was monitored by Differential scanning calorimetry (DSC) and FTIR. Thethermal properties of obtained polybenzoxazines were evaluated by DSC and thermogravimetric analyses (TGA).Four benzoxazine precursors were synthesized using bisphenol-fluorene (BHPF),formaldehyde and diamines (Eda, Hda, Mda and Ipda) as starting materials by solventmethod in this paper. The results show that the molar ratio of bisphenol, formaldehydeand diamine was1:4:1.2, chloroform as solvent in the synthesis of benzoxazineprecursor, gained the benzoxazine precursor with around80.0%yield. The molecularweight of benzoxazine precursors was3098~3939. Mw/Mnwas1.46~1.71. Thepolymerization of benzoxazine precursors occured through heterocyclic ring openingat high temperatures， the polybenzoxazine formed Mannich bridge. The glasstransition temperature (Tg) and thermal stability of bisphenol fluoren-basedpolybenzoxazines precursors were highly improved compare with the bisphenolfluoren-based polybenzoxazines monomers. Mda-based polybenzoxazine(BHPF-Mda) had higher Tg(258℃). The temperature of5%loss weight was395℃and10%loss weight was435℃. The char yield was63.0%at800℃(in N2).Two benzoxazine precursors were synthesized using diamine-fluorene (BPF),formaldehyde and bisphenol (bisphenol-AF, bisphenol-A) as starting materials bysolvent method. The molecular weight of diamine-fluorene-AF based benzoxazineprecursor (BPF-AF) was3457, PDI was1.74. The molecular weight ofdiamine-fluorene-A based benzoxazine precursor (BPF-A) was3296, PDI was1.86.The glass transition temperature (Tg) and thermal stability of diamine fluoren-basedpolybenzoxazines were highly improved compare with bisphenol fluoren-based polybenzoxazines. Tgand thermal stability of bisphenol-AF based polybenzoxazineswas higher than bisphenol-A. The temperature of T5was421℃, T10was469℃. Thechar yield at800℃was65.1%.Three copolymer types of fluorene-containing benzoxazine precursors weresynthesized using mixed bisphenol (bisphenol-AF with bisphenol-fluorene orbisphenol-A with bisphenol-fluorene) or diamine (Mda with Hda). The results showthat Tgand thermal stability of polybenzoxazine based on bisphenolfluorene-bisphenol-AF-Hda (BHPF-AF-Hda) was higher than polybenzoxazine basedon bisphenol fluorene-Hda (BHPF-Hda) and polybenzoxazine based onbisphenol-AF-Hda (BAF-Hda). Tgof poly (BHPF-A-Mda) and poly (BHPF-Mda-Hda)was increased, but the thermal stability was decresed a little. The copolymerbenzoxazine precursors had a good processability, can be used as the electronics,aerospace, and other industries.