Curing Reactions of Bismaleimide Resins Catalyzed by Triphenylphosphine. High Resolution Solid-State 13C NMR Study

Abstract

ABSTRACT:The curing reactions of bismaleimide resins consisted of N,N' -4,4' -diphenylmethanebismaleimide (BMI) and o,o' -diallylbisphenol-A (DABA) in the presence of triphenylphosphine (TPP) as a catalyst were investigated. DSC measurements showed that the catalytic effect of TPP on the curing reaction of BMI was more in the presence of DABA than in its absence. In order to explore this curing reaction, N-phenylmaleimide (PMI) and o-allylphenol (AP) were selected as model compounds. The products of the PMI/TPP system were oligomers and polymers of PMI, whereas the main product of the PMI/AP/TPP system was the PMI trimer which had the five-membered ring formed via the phosphonium ylide intermediate. In these model reactions, 13 C NMR was found to be useful to distinguish between trimerization and polymerization of PMI. On the basis of the results of the model reactions, the curing reactions of bismaleimide resins were investigated by high resolution solid state 13 C NMR techniques. In the BMI/TPP system, maleimides polymerize above l 75°C, but the polymerization does not proceed at I20°C. On the other hand, maleimides trimerize above 120°C in the presence of DABA and TPP. The mechanism of the trimerization is briefly discussed.KEY WORDS Solid-State Nuclear Magnetic Resonance / Curing Reaction / Bismaleimide Triphenylphosphine / Ally! Phenols / Model Reactions / Differential Scanning Calorimetry / Bismaleimide resins are widely applied in multilayer print circuit boards and advanced composite materials because of their good heat-resistance. However, the main disadvantage is their brittleness due to high crosslinking density. In order to reduce brittleness, modification has been made by an aromatic diamine such as diaminodiphenylmethane or a diallyl compound such as diallylbisphenol-A. 1 Another disadvantage is poor curability. Thus, the resins are cured at a temperature higher than 200°C. The use of catalysts such as imidazoles, organic peroxides and tricoordinate phosphines has been studied to lower the curing temperature. 2 · 3 However, detailed descriptions are not available as to the structures of the cured resins and the reaction mechanism. This would be due to the insolubility of the cured resins in various organic solvents, preventing the study of the reactions and analysis of the structures of the products.Recently, solid state NMR with CP/MAS (cross polarization/magic angle spinning) technique, developed by Schaefer,4 has been applied to the analysis of insoluble polymers such as cured thermoset resins. 5 According to this technique, we studied a series of the curing reaction of bismaleimide resins and reported the curing reactions of amine-modified bismaleimide 6 and the effects of imidazole catalyst on bismaleimide/epoxy resin blend system 7 • 8 based on the model reactions. 9 -12 We also found that the trimer of N-phenylmaleimide (PMI) was a chief product in the reaction of PMI and o-allylphenol (AP) in the presence of tripheylphosphine (TPP). The cured maleimide resin containing partly 752 trimeriz...

Preparation of Microporous Organic Polymers via UV-Initiated Radical Copolymerization

“…In the solid-state 13 C CP/MAS NMR spectra (Figure c and Figure d), all the products show four resonance peaks around 176, 139, 128, and 43 ppm, which are ascribed to the carbonyl carbon, the substituted aromatic carbon, the nonsubstituted aromatic carbon, and the methyne and methylene carbon, respectively. While the peak at 17 ppm, appearing in the spectrum of B-MOP-2 (Figure c), is assigned to the methyl carbon . In the spectra of P-MOPs (Figure d), the peak near 63 ppm belongs to the methylene carbon adjacent to the O–CO, originating from the PET4A .…”

“…While the peak at 17 ppm, appearing in the spectrum of B-MOP-2 (Figure 1c), is assigned to the methyl carbon. 30 In the spectra of P-MOPs (Figure 1d), the peak near 63 ppm belongs to the methylene carbon adjacent to the O−CO, originating from the PET4A. 31 Additionally, the element contents of all the MOPs were measured and filed in Table S1.…”

Morphology transition of bismaleimide‐modified novolac resin

“…The curing mechanism has been exploited by many researchers, and it varies with different feeding ratio of allyl : BMI, preparation process, and the cure schedule. Although an unambiguous mechanism has not been proposed, the generally accepted mechanism is allyl group and BMI's “Ene” reactions and “Diels‐Alder” reactions, plus the condensation of phenol OH groups 11–21…”

Versatile One-Pot Construction Strategy for the Preparation of Porous Organic Polymers via Domino Polymerization

“…After polymerization, solid 13 C-CPMAS NMR spectra of M-POPs exhibit the same characteristic bands. Comparing with the spectra of monomers (Figure S4), the peaks at 176 and 143 ppm are assigned to carbonyl carbon and the N-substituted phenyl carbon of five-membered imide rings, respectively, 41,42 indicating the occurrence of the imidization reaction. The signal at 43 ppm in 13 C-CPMAS can be easily observed under a high rotating speed, attributed to the aliphatic methyne carbons (−CH−) on the imide ring.…”