Study on the Ring-Opening Polymerization of Benzoxazine through Multisubstituted Polybenzoxazine Precursors

To discuss the mechanism of ring-opening polymerization (ROP) of benzoxazine, a bisphenol A/diaminodiphenylmethane-based polybenzoxazine precursor (PBz-0M), <i>o</i>-dimethylbisphenol A/diaminodiphenylmethane-based polybenzoxazine precursor (PBz-2M), and <i>o</i>-dimethylbisphenol A/<i>o</i>-tetramethyldiaminodiphenylmethane-based polybenzoxazine precursor (PBz-6M) were prepared. Among the polybenzoxazine precursors, free ortho positions to the O of oxazine are available for PBz-0M. No free ortho or para position to the O of oxazine is available for PBz-2M, but free ortho position to the N of oxazine is available. No free ortho positions to the O or N of oxazine are available for PBz-6M. According to DSC, IR, and thermal analysis, we found that the ROP of PBz-2M can be carried out even though no free ortho or para position to the O of oxazine is available. We conclude that the ROP is carried out through the ortho position to the N of oxazine and propose a reaction mechanism to explain the polymerization

Origin of the Rapid Trimerization of Cyanate Ester in a Benzoxazine/Cyanate Ester Blend

Blends of cyanate ester and benzoxazine have been independently studied by several researchers, and different reaction mechanisms were reported. Recently, we unexpectedly observe that gelation occurred in a 50 wt % methyl ethyl ketone solution of P-oda/BACY (1/1 mol/mol) blend after 24 h at 30 °C, in which P-oda is a 4,4′-oxyaniline/phenol-based benzoxazine and BACY is a dicyanate ester of bisphenol A. Previous studies suggest that the rapid trimerization of cyanate ester in the blend is related to the ring-opened structure of benzoxazine. However, the possibility of ring-opening polymerization for benzoxazine at 30 °C is rare. Therefore, it is highly likely that the catalytic effect results from the benzoxazine itself, not from the ring-opened structure of benzoxazine. Through IR and DSC analyses, we conclude that the tertiary amine of benzoxazine catalyzes the trimerization of cyanate ester, and we propose a three-step catalytic mechanism of benzoxazine for the trimerization of cyanate ester

Low Dielectric Polyetherimides Derived from Bis[4-(4-(4-aminophenoxy)-2-<i>tert</i>-butylphenoxy)phenyl] Sulfone and 4,4′-Bis[4-(4-aminophenoxy)-2-<i>tert</i>-butylphenoxy]perfluorobiphenyl

Two diamines, bis­[4-(4-(4-aminophenoxy)-2-<i>tert</i>-butylphenoxy)­phenyl] sulfone (PSNH₂) and 4,4′-bis­[4-(4-aminophenoxy)-2-<i>tert</i>-butylphenoxy)­perfluorobiphenyl (PFNH₂), were prepared from 3-<i>tert</i>-butyl-4-hydroxyanisole using a four-step procedure, including two nucleophilic substitutions, demethylation, and catalytic reduction. On the basis of PSNH₂ and PFNH₂, two series of low dielectric polyetherimides (PEIs) were prepared. Both series of PEIs exhibit moderate-to-high thermal properties, including a glass transition temperature (<i>T</i>_g) > 259 °C (depending on the rigidity of dianhydride), a 5 wt % decomposition temperature (<i>T</i>_d5%) > 496 °C, and a coefficient of thermal expansion < 66 ppm/°C. Because of the hydrophobic <i>tert</i>-butyl phenylene oxide structure, both series of PEIs show excellent dielectric properties, with a dielectric constant as low as 2.4–2.7. The structure–property relationship of both series of PEIs is discussed in this work

Miscibility, Microstructure, and Thermal and Dielectric Properties of Reactive Blends of Dicyanate Ester and Diamine-Based Benzoxazine

This study discusses the miscibility, microstructure, and the thermal and dielectric properties of the reactive blends of dicyanate ester of bisphenol A and diamine-based benzoxazine. DSC and IR were applied to monitor the curing reactions of the reactive blends. Three reactions were observed in the curing reactions: the first is the cyclotrimerization of cyanate ester, producing the triazine structure; the second is the coreaction between the triazine structure and benzoxazine, forming alkyl isocyanurate and diphenyl ether linkages, followed by the further reaction of the isocyanurate linkage; and the third is the ring-opening of benzoxazine. The coreaction decomposes the polycyanurate structures and brings parts of the polycyanurate structures into the polybenzoxazine matrix. Thus, a miscible blend can be achieved in all compositions, as judged by the single composition-dependent <i>T</i>_g in the dynamic mechanical and thermal mechanical analyses. The experimental data also show that the dimensional stability and dielectric properties are enhanced via the reactive blends

Synthesis of a Bisbenzylideneacetone-Containing Benzoxazine and Its Photo- and Thermally Cured Thermoset

A bis­(4-hydroxybenzylidene)­acetone/aniline-based benzoxazine (<b>BHBA-a</b>) was prepared from a bisbenzylidene-containing bisphenol, bis­(4-hydroxybenzylidene)­acetone (<b>BHBA</b>), aniline, and paraformaldehyde through Mannich condensation in a cosolvent of toluene/ethanol (2:1, v/v). The structure of <b>BHBA-a</b> was successfully confirmed by Fourier transform infrared and ¹H and ¹³C NMR spectra. According to the differential scanning calorimetry (DSC) thermogram of <b>BHBA</b>, an immediate exothermic peak after the melting peak was observed, suggesting that <b>BHBA</b> is thermally active. NMR data of thermally treated <b>BHBA</b> confirm that the immediate exothermic peak after melting of <b>BHBA</b> in the DSC thermogram is resulted from the curing of a double bond. UV and ¹H NMR spectra of <b>BHBA-a</b> show that the bisbenzylideneacetone moiety underwent dimerization through the [2π + 2π] cycloaddition. Therefore, two procedures were applied to cure <b>BHBA-a</b>. The first one was thermal curing of the double bond of bisbenzylideneacetone and oxazine moieties. The second one was photocuring of the bisbenzylideneacetone moiety, followed by thermal curing of the oxazine moiety. The thermal properties of thermosets were evaluated based on these two procedures. Thermosets of <b>BHBA-a</b> exhibit <i>T</i>_g as high as 318 °C for curing procedure 1 and 342 °C for curing procedure 2. These values are much higher than that of a traditional bisphenol/aniline-based benzoxazine thermoset. We conclude that the thermal curing of the double bond of bisbenzylideneacetone and photodimerization of bisbenzylideneacetone contributes to the good thermal properties