Synthesis of Wholly Alicyclic Polyimides from N-Silylated Alicyclic Diamines and Alicyclic Dianhydrides

A new synthetic method to give wholly alicyclic polyimides with high molecular weights has been developed. The polymerization of cyclobutanetetracarboxylic dianhydride (<BO>1a</BO>) or bicyclo[2.2.1]heptane-2-methanecarboxylic-3,5,6-tricarboxylic-2,3:5,6-dianhydride (<BO>1b</BO>) with various N-silylated alicyclic diamines (<BO>2</BO>) was carried out in N,N-dimethylacetamide (DMAc) at room temperature, giving poly(amic acid trialkylsilylester)s (<BO>3</BO>) as precursor polymers that were hydrolyzed to poly(amic acid)s (<BO>4</BO>) with inherent viscosities up to 0.99 dL/g. Both polyimide precursors were readily converted to corresponding polyimides (<BO>5</BO>) by thermal treatment. These polyimides are readily soluble in polar aprotic solvents such as 1-methyl-2-pyrrolidone, N,N-dimethylacetamide and dimethyl sulfoxide at room temperature, and showed high thermal stability (T<INF>d10</INF> = 420−445 °C in N<INF>2</INF>) and excellent transparency at wavelengths above 250 nm. The average refractive index of the polyimide <BO>5aa</BO> was 1.498, and the dielectric constant estimated from the refractive index was 2.47.