The present invention relates to resins obtained by polymerization of compounds, and more particularly, to high temperature resistant thermoset resins obtained by polymerization of bis-benzocyclobutene compounds.
One form of a cycloaddition reaction is the Diels-Alder reaction in which an unsaturated group, a dienophile, combines with a 1,3-diene to form a six membered ring. Benzocyclobutene functions very well in a Diels-Alder reaction. As taught by W. Oppolzer, Synthesis 793 (1978), under appropriate thermal conditions, the benzocyclobutene unit undergoes an electrocyclic ring opening to form the more reactive o-xylylene functionality. O-xylylene is a powerful diene, and thus, engages in a Diels-Alder reaction in the presence of a suitable dienophile. See Boekelheide, Accounts Chem. Res. 13, 65 (1980).
An example of a suitable dienophile is a bis-maleimide. Bis-maleimides are well-known as possessing strong dienophilicity. The dienophilic site, i.e., the carbon-carbon double bond, is not subjected to the substituent effect imposed by the rest of the structure. Thus, a bis-maleimide engages in a Diels-Alder polymerization in the presence of a suitable bisdiene such as bis (o-xylylene).
In the absence of a suitable dienophile, benzocyclobutene will react with itself. Although the exact cure mechanism for the bis-benzocyclobutene systems is still unclear, the results of studies in F. Jensen, W. Coleman, and A. Berlin, Tet. Lett. 15 (1962) and L. Errede, J. Am. Chem. Soc. 83, 949 (1961) suggest that at least two possible pathways exist: (1) cycloaddition and (2) linear addition. In the cycloaddition mode, an eight member ring is formed and incorporated into the highly aromatic skeleton. However, in the linear addition mode, a polymeric structure with a double strand of poly (o-xylylene) bridged by the aromatic imide groups results. It should be noted, however, that the terms "cycloaddition" and "linear addition" are used to describe the polymeric structures and do not implicate the mechanisms from which they arise.
Bis-benzocyclobutenes and polymers derived therefrom are disclosed in U.S. Pat. No. 4,540,763. The bis-benzocyclobutenes are connected by direct bond or a bridging member such as a cyclic imido group. In general, the polymers are obtained by addition polymerization wherein the fused cyclobutene rings undergo thermal transformation to o-xylylene moieties which can react with one another.