Bisbenzocyclobutene-bismaleimide

Diels-Alder mechanism. It was found that those polymers which had the least weight loss in the isothermal aging study were derived from those monomers which by DSC polymerized to the greatest extent by a Diels-Alder mechanism. It was inferred therefore that if similar considerations apply to the copolymers of bismaleimides and bisbenzocyclobutenes then these materials too might be the result of predominantly Diels-Alder type polymerizations. To the extent to which these conclusions are correct, the enhanced thermal stability of the bisbenzocyclobutene/bismaleimide copolymers is likely to be due to their being Diels-Alder polymers of some sort. 

Table 14. Preparation of characterization of bisbenzocyclobutene-bismaleimide copolymers...

Novel Cross-Linking Systems Derived from a Bisbenzocyclobutene and Bismaleimides, Dicyanates, and Bisphenylaceiyienes... 

Bisbenzocyclobutenes readily react with molecules which contain sites of reactive unsaturation such as bismaleimides [10,13, 31, 32]. This is in essence, a novel type of Diels-Alder polymerization in which the bis-diene is latently embodied within two benzocyclobutene moieties. The properties of these polymers depends strongly on the mole ratio of the monomers and when it is equimolar, can result in some exceptionally tough high Tg resins [33, 34]. 

Early reports by Kirchhoff, Hahn, Tan and Arnold describe the use of polybenzocyclobutene monomers in Diels-Alder type polymerizations [10,13]. For the most part, these early studies focused on the thermal characterization of mixtures of polybenzocyclobutenes and bismaleimides. Several reports describe the thermal analysis of mixtures of the bisbenzocyclobutene 41 with either the bismaleimide 44 or the diacetylenes 42 and 43 as shown in Fig. 19 [13,79,81, 90-93]. 

The reaction of the bisbenzocyclobutene 41 with the bismaleimide 44 is similar to the reaction of 41 with the activated diacetylene 43. From the DSC thermogram in Fig. 24 it is apparent that there is one major exotherm peak at 258.8 °C associated with this reaction. This could be interpreted as either being the polymerization exotherm peak for a benzocyclobutene-maleimide Diels-Alder reaction or else it is the coincidental overlap of the exotherm peaks associated with each pure component. This latter case is a distinct possibility since both the pure bisbenzocyclobutene 41 and the pure bismaleimide 44 have... 

The advantage of using free radical inhibitors to facilitate the copolymerization of a bisbenzocyclobutene with a bismaleimide was first noted in a patent to Bartmann [78]. Subsequent to this, Corley in a series of patents described some detailed experiments on the copolymerization of bisbenzocyclobutenes with bismaleimides both with and without the addition of a free radical inhibitor [33, 34]. The structures of the bisbenzocyclobutenes used in this study are shown in Fig. 33. The bismaleimide component that was used was a mixture of three different bismaleimides in the molar ratio shown in Fig. 34. The individual bisbenzocyclobutenes were blended at elevated temperature with varying amounts of the bismaleimide composition. In some of the experiments, the free radical inhibitor phenothiazine was added at a 0.5 mole % level. The various monomer mixtures were then copolymerized using one of the cure schedules described in Table 14. The copolymers were then physically characterized using a variety of techniques. Table 14 shows the results obtained from copolymers... 

The monomer compositions were copolymerized using several different cure cycles. All of the cure cycles in this series included an additional post cure at 290 °C for one hour. The exact monomer compositions used, their detailed cure cycles and the physical properties of the resulting copolymers are shown in Table 16. As in the previous examples, here too the glass transition temperature went down as the fracture toughness increased. As before the fracture toughness rose as the mole ratio of bisbenzocyclobutene to bismaleimide approached unity. The presence of phenothiazine appeared to increase the fracture toughness in all of the examples although, its effect appeared most pronounced when... 

Mixtures of bisbenzocyclobutene and bismaleimide such as shown below were also polymerized to form stable polymers. 

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