Poly-(imidesiloxanes) are of particular interest because, like polyimides, they have outstanding thermal and mechanical properties, but are more soluble and more easily processed than polyimides.
Processes for the preparation of poly-(imidesiloxanes) are already known. For example, U.S. Pat. No. 3,274,155 (F. C. Saunders, Midland Silicones Limited) describes the preparation of poly-(imidesiloxanes) from pyromellitic dianhydride, and U.S. Pat. No. 3,325,450 (F. F. Holub, General Electric Company) describes the preparation of poly-(imidesiloxanes) from benzophenonetetracarboxylic dianhydride. Both of these patents describe the preparation of poly-(imidesiloxanes) by polycondensation with fairly long-chain .alpha.,.omega.-bisaminoalkylsiloxanes.
A polycondensation of this type is the most widely used method for preparing poly-(imidesiloxanes). In this connection reference should also be made, for example, to U.S. Pat. No. 4,011,279 (A. Berger, General Electric Company), European Application 54,426 (A. Berger, M&T Chemicals Inc.), U.S. Pat. No. 4,395,527 (A. Berger, M&T Chemicals Inc.) and Japanese Publication 62,227,953 (Yoshida Masatoshi, Hitachi Chemical Co. Ltd.).
In the preparation of poly-(imidesiloxanes) by these processes tetracarboxylic dianhydrides are first condensed with .alpha.,.omega.-bisaminoalkylsiloxanes to form polyamic acids, which are imidized at an elevated temperature.
Another method of preparing poly-(imidesiloxanes) is described in U.S. Pat. No. 4,404,350 (Hong-Son Ryang, General Electric Company), U.S. Pat. No. 4,794,153 (J. D. Rich, General Electric Company) and the corresponding German Offenlegungsschrift 3,618,714, and U.S. Pat. No. 4,795,680 (J. D. Rich, General Electric Company) and the corresponding German Offenlegungsschrift 3,803,088. These processes relate to the condensation of anhydride-siloxanes with organic diamines to give polyamic acids, which then also have to be imidized.
Therefore it is an object of the present invention to provide a process for preparing poly-(imidesiloxanes) in a relatively simple manner and without undesirable side reactions and in which high conversions are achieved in short reaction times.