ABSTRACT:Thermal reactions of N-phenylmaleimide (PMI) and o-allylphenol (AP) or diallylbisphenol-A (DABA) were investigated using 13 C NMR and GPC in order to obtain information on the curing of bismaleimidodiphenylmethane (BMI) with DABA, widely used as thermosetting bismaleimide resins. In the thermal reactions of PMI and AP, I : I and 3: I adducts were generated through ene-reaction and sequential Diels-Alder reactions accompanying the polymer of PMI and AP. The products from PMI and DABA were the ene-adduct and polymer but the Diels-Alder adduct could not be detected, in contrast to PMI/AP system. This difference in reactivity for PMI-AP and PMI-DABA may be due to steric repulsion of DABA and is discussed briefly by AM I molecular orbital calculations.

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ABSTRACT:Analysis of the curing reactions of bismaleimidodiphenylmethane (BMI) with diallylbisphenol-A (DABA) or o-allylphenol (AP) with the high resolution solid-state 13 C NMR technique revealed that while cured products of BMI and AP are formed through ene-reaction and the sequential Diels-Alder reaction, no Diels-Alder reaction occurs in the case of DABA and only ene-reaction and polymerization proceed. This shows that the crosslinking of such widely used curing system proceeds via a different manner suggested previously.KEY WORDS Curing Reaction/ Diels-Alder Reaction/ ene-Reaction / Bismaleimide / Diallylbisphenol-A / Solid-State 13 C Nuclear Magnetic Resonance / The curing system of bismaleimide has been widely used as thermosetting polyimides, which provides excellent thermal stability but brittleness simultaneously because of the high crosslinking density of the network. In order to add toughness to bismaleimide resins, modification has been made by the addition of diallyl compounds such as diallylbisphenol-A (DABA). 1 • 2 The course of this reaction has been investigated and ene-and Diels-Alder reactions were suggested to be involved in this curing system based on the model reaction of Nphenylmaleimide (PMI) and o-allylphenol (AP). 3 -5 The preceding paper showed that the thermal reaction of PMI and AP gave ene-and Diels-Alder adducts but PMI and DABA did not give the Diels-Alder adduct. 6 However, the practical curing reaction remains uncertain because the curing products are generally insoluble toward almost of organic solvents, which prevents to characterize the reaction products.High resolution solid-state NMR with CPMAS (cross polarization magic angle spinning), developed by Schaefer, 7 has been applied to the analysis of insoluble polymer such as cured thermoset resins. 8 Our previous studies showed that the solid-state 13 C NMR is useful to investigate the curing reactions of bismaleimide resins. 9 -12 Although the solid-state 13 C NMR spectrum of the cured product of bismaleimidodiphenylmethane (BMI) with DABA has been illustrated by Carduner et al. 13 • 14 detailed descriptions are not available. On the basis of fundamental data of the model reactions, we report in this paper the direct measurements of the curing reactions of BMI and DABA with a high resolution solid-state 13 C NMR. EXPERIMENTAL MaterialsBMI, purchased from Wako Pure Chemical Industries, was recrystallized from chloroform-methanol. DABA 410 was obtained from Mitsui Toatsu Chemicals Inc. PMI and o-AP were purchased from Wako Pure Chemical Industries. Sample PreparationMono-or di-functional maleimides and mono-or di-functional allylphenols were mixed in a round bottom flask and heated by an oil bath at 150°C for 15 min. Continuous stirring led to a homogenous melt. This mixture was put in a closed aluminous vessel and heated at 175°C for 2 h, at 200°c for 1 h, and at 250°C for 1 h in an air oven. Each stage samples were analyzed by liquid-state and solid-state 13 C NMR. Liquid-State 13 C NMR MeasurementsNMR spectra were obtained...

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...

The reaction of 1,1′-bis(2-chloroethoxy)ferrocene with 1,2-ethanedithiolate in absolute ethanol gave mononuclear 1,10-dioxa-4,7-dithia[10]ferrocenophane and binuclear 1,10,21,30-tetraoxa-4,7,24,27-tetrathia[10,10]ferrocenophane, along with a small amount of unexpected 1,13-dioxa-4,7,10-trithia[13]ferrocenophane and 1,16-dioxa-4,7,10,13-tetrathia[16]ferrocenophane. Extraction of aqueous metal picrates (M; alkali, alkaline earth, Ag+, Tl+, Cd2+, Co2+, Cu2+, Ni2+, and Hg2+) with dioxathia[n]ferrocenophanes was examined and also with the corresponding ring membered polyoxa[n]ferrocenophanes. Dioxathiaferrocenophanes showed a highly selective extraction ability towards bivalent mercury and copper ions.