This invention relates to polyimidesiloxane extended block copolymers and methods of preparing them. In particular, it relates to such extended block copolymers wherein the siloxane-anhydride containing block is prepared using a controlled excess of dianhydride.
Polyimidesiloxanes are polymers made by reacting a dianhydride with a diamine, where either a mixture of siloxane-containing dianhydride and non-siloxane containing dianhydride, or a mixture of siloxane-containing diamine and non-siloxane containing diamine, is used. Polyimidesiloxanes are used in a variety of different applications, but are particularly useful as coatings and adhesives in the microelectronics industry Two properties of polyimidesiloxanes that are particularly important are glass transition temperature, T.sub.g, and solubility. A high T.sub.g means that the polymer will not lose its physical or mechanical properties readily at higher temperatures. Good solubility is required in order to form a solution of the polymer so that coatings can be formed from it.
It is a general.rule in polymer chemistry that block copolymers have a higher T.sub.g than do the corresponding random copolymers. However, normally increasing the block size will decrease the solubility. A polyimidesiloxane block copolymer is a polyimidesiloxane having two or more T.sub.g 's. A polyimidesiloxane can display two T.sub.g 's whenever the siloxane-containing diamine or dianhydride is large, even though the siloxane-containing monomer is randomly dispersed throughout the polymer.