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 (1a) or bicyclo[2.2.1]-heptane-2-methanecarboxylic-3,5,6-tricarboxylic-2,3:5,6-dianhydride (1b) with various N-silylated alicyclic diamines (2) was carried out in N,N-dimethylacetamide (DUAc) at room temperature, giving poly(amic acid trialkylsilylester)s (3) as precursor polymers that were hydrolyzed to poly (amic acid)s (4) with inherent viscosities up to 0.99 dL/g. Both polyimide precursors were readily converted to corresponding polyimides (5) 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-d10 = 420-445 degreesC in N-2) and excellent transparency at wavelengths above 250 nm. The average refractive index of the polyimide 5aa was 1.498, and the dielectric constant estimated from the refractive index was 2.47.