Phosphinated Benzoxazines and Their High-Performance Thermosets

Autor: Hung-Tse Lin, 林宏澤
Rok vydání: 2011
Druh dokumentu: 學位論文 ; thesis
Popis: 99
In this research, we synthesized many phosphorus-containing benzoxazines derived from some typical aromatic amines, such as p-Toluidine, 4-aminophenol, 4-aminobenzoic acid, 4, 4’-diamino diphenyl methane, 4,4’-diaminodiphenyl sulfone, and 4,4’-diaminodiphenyl ether. The thermal properties and the structure-property relationship of the resulting copolymers were studied as follows. First of all, three benzoxazines (I7-I9) with a tolyl, p-hydroxyphenyl or p-carboxyphenyl structure, respectively, were successfully synthesized by a three-pot or two-pot procedure. In the three-pot approach, the first step is the condensation of 2-hydroxybenzaldehyde with p-toluidine, 4-aminophenol and 4-aminobenzoic acid, respectively, forming intermediates (I1-I3) with an imine linkage. The second step is the addition of 9, 10-dihydro-9-oxa-10-phosphaphenanthrene 10-oxide (DOPO) on the imine linkage, resulting in intermediates (I4-I6) with a secondary amine linkage. The last step is the ring closure condensation of (I4-I6), leading to benzoxazines (I7-I9). In the simplified two-pot approach, the first two steps-the condensation and imine reduction were carried out in one reactor, so the yield of (I4-I6) was increased. The structures of monomers (I1-I9) were characterized and confirmed by 1D and 2D NMR spectra. The synthesized benzoxazines were thermally self-cured or copolymerized with a commercial benzoxazine, bis(3-phenyl-3,4-dihydro-2H-benzo[e][1,3]oxazin-6- yl)methane (F-a). IR analysis was utilized to monitor the ring-opening reaction of (I7-I9) and to propose the structures of P(I7-I9). The microstructure and the structure-property relationship of the resulting homopolymers and copolymers are studied. Secondly, a series of advanced epoxy resins (II2) were prepared by the nucleophilic addition of cresol novolac epoxy (CNE) with a benzoxazine monomer (II1), which is prepared by a one-pot procedure using 2-hydroxybenzaldehyde, 4-aminophenol and 9, 10-dihydro-9-oxa-10-phosphaphenanthrene 10-oxide (DOPO) as starting materials. The nucleophilic addition was monitored by epoxy equivalent weight titration and NMR analysis. Based on this approach, the overall number of functionality of the resulting epoxy resins was retained because a curable benzoxazine linkage was also incorporated after the nucleophilic addition. As a result, high-Tg thermosets qualified for the UL-94 V-0 rating can be achieved after curing. When an UL-94 V-0 rating was achieved, Tg as high as 245 oC (DMA data) was obtained for 4, 4’-diaminediphenyl sulfone (DDS)-cured systems. The corresponding phosphorus content for the UL-94 V-0 rating was as low as 0.61 wt%. The flame retardant nature of oxazine linkage and nitrogen-phosphorus synergistic effect might be responsible for the low phosphorus content required for flame retardancy. Thirdly, three aromatic diamine-based, phosphinated benzoxazines (III7-III9) were prepared from three typical aromatic diamines – 4,4’-diamino diphenyl methane (III1), 4,4’-diamino diphenyl sulfone (III2), and 4,4’-diamino diphenyl ether (III3) by a one-pot procedure. To clarify the reaction mechanism, a two-pot procedure was applied, in which the reaction intermediates (III4-III6) were isolated for characterization. The structures of intermediates and benzoxazines were confirmed by high resolution mass, IR, and 1D and 2D-NMR spectra. In addition to self-polymerization, (III7-III9) were copolymerized with cresol novolac epoxy (CNE). After curing, the homopolymers of P(III7-III9) are brittle while the copolymers of (III7-III9)/CNE are tough. Dynamic mechanical analysis DMA shows the Tgs of (III7-III9)/CNE copolymers are 187, 190 and 171 oC, respectively. Thermal mechanical analysis TMA shows the CTEs of (III7-III9)/CNE copolymers are 46, 38 and 46 ppm, respectively. All the (III7-III9)/CNE copolymers belong to an UL-94 V-0 grade, demonstrating good flame reatardancy. Fourthly, we revealed a facile, one-pot procedure to prepare phosphinated biphenols (IV4-IV6) from the nucleophilic addition of DOPO and aromatic diamine-based benzoxazines. Then, phosphinated biphenols (IV4-IV5) were chosen to prepare two series of advanced epoxy resins (IV7-IV8). After curing (IV7-IV8) with diaminodiphenyl sulfone and phenol novolac, the properties such as glass transition temperature, coefficient of thermal expansion, thermal decomposition temperature, water absorption and flame retardancy of the resulting thermosets were evaluated. The structure-property relationship was also discussed. The resulting epoxy thermosets display moderate to high Tg, good flame retardancy, high modulus, and very low water absorption. Fifthly, we revealed a propargyl ether-containing benzoxazines (V2) from the nucleophilic substitution of a phenolic OH containing benzoxazine (V1) and propargyl bromide in the catalysis of potassium carbonate. The structure of (V2) was characterized and confirmed by high resolution mass spectrum, 1H, 13C, 1H-1H, 1H-13C NMR spectra, and X-ray single crystal diffratogram. IR and DSC were utilized to monitor the ring-opening of oxazine and crosslinking of propargyl ether. The microstructure and the structure-property relationship of the resulting homopolymers and copolymers are discussed. Tg of (V2)-based thermoset, P(V2), is 208 oC by DMA, Coefficient of thermal expansion is 44 ppm/oC, Td 5% is 370 oC. These values are higher than those of (V1)-based thermoset, demonstrating the beneficial effect of crosslinking afforded by the incorporation of propargyl ether group is higher than phenolic OH group. In summary, new mono-functional benzoxazines with a p-hydroxyphenyl, p-carboxyphenyl and propargyl ether linkage, and diamine-based phosphinated benzoxazines or biphenols with electron-withdrawing/donating character, respectively, were successfully prepared by extending Ulrich and Franck’s approach. According to DSC thermograms and IR analysis, the phosphinated benzoxazines can be thermally polymerized. Depending on the structure, moderate to high Tgs can be achieved. In addition to self-curing, phosphinated benzoxazines were also applied as curing agents of cresol novolac epoxy, and the reaction sequence can be monitored by IR analysis. After curing, homogeneous and tough copolymers with good flame retardancy can be achieved.
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