Alkyl-substituted cyclobutanetetracarboxylic dianhydrides (CBDAs) were synthesized by photo-dimerization of alkylsubstituted maleic anhydrides to obtain novel colorless polyimides (PIs). Dimethyl-substituted CBDA (DM-CBDA) showed much higher polymerizability with various diamines than conventional cycloaliphatic tetracarboxylic dianhydrides and led to high molecular weights of PI precursors. Polyaddition of non-substituted CBDA and trans-1,4-cyclohexanediamine (t-CHDA) was completely inhibited by salt formation in the initial reaction stage. The use of DM-CBDA allowed the formation of a homogeneous/viscous PI precursor solution by overcoming the salt formation problem. The prominent substituent effect probably reflects how the methyl substituents of DM-CBDA contributed to increasing the salt solubility. Some of the thermally imidized DM-CBDA-based systems simultaneously possessed non-coloration, low coefficient of thermal expansion (CTE), very high T g exceeding 300 • C and very low dielectric constant. Copolymerization was very effective for improving the solubility of DM-CBDA-based PIs. The copolyimide cast films prepared via chemical imidization displayed a further decreased CTE without sacrificing other target properties, suggesting that the present materials can be useful as plastic substrates in display devices. The mechanism of self-chain orientation behavior during solution casting is also discussed. A potential application of the copolyimide systems as optical compensation film materials in liquid crystal displays is proposed.

Polyimide precursors were successfully polymerized from trans-1,4-cyclohexanediamine (CHDA) with pyromellitic dianhydride (PMDA) and 1,2,3,4-cyclobutanetetracarboxylic dianhydride (CBDA) under very limited conditions: at controlled extents of silylation for CHDA in a mixed solvent containing hexamethylphosphoramide (HMPA). Flexible and transparent polyimide films were obtained upon thermal imidization of the precursor films on a substrate after residual solvent extraction from the precursor films by using adequate alcohols. Semi-aromatic PMDA/CHDA polyimide film displayed a considerably lower linear coefficient of thermal expansion (CTE = 9.6 ppm K—1) and a relatively low dielectric constant (2.92). On the other hand, wholly cycloaliphatic CBDA/CHDA film attained a low CTE (26 ppm K—1) and a considerably lower dielectric constant (2.66), simultaneously. Factors influencing the imidization-induced in-plane orientation, namely, effect of the steric structures of cycloaliphatic units are discussed in comparison with polyimides from hydrogenated PMDA (1,2,4,5-cyclohexanetetracarboxylic dianhydride).

Crystals of Pbi 2 (pyd) 2 and Pbi 2 (enu) 2 (pyd=2pyrrolidone; enu=ethyleneurea) were obtained by cooling their saturated N-methylformamide solution. The compoQ~ds crystallize in space group ~c2 1 n with a=l3.423(l), b=l5.662(l), c=6.6898(6) A and Z=4, and with a=l3.287(l), b=l5.458(2), c=