Structure and Properties of Novel Asymmetric Biphenyl Type Polyimides

1996 Journal of Photopolymer Science and Technology (Fotoporima Konwakai shi)  
Asymmetric biphenyl type polyimides (PI) were prepared by thermal imidization of polyamic acids (PAA) derived from 2,3,3',4'biphenyltetracarboxylic dianhydride (a-BPDA) and p-phenylenediamine (PDA) or 4,4'-oxydianiline (ODA). The degrees of molecular orientation, film densities, and dynamic mechanical properties of these PIs were compared with those of familiar PIs based on symmetric 3,4,3',4'biphenyltetracazboxylic dianhydride (s-BPDA). PI(a-BPDA/PDA) cured at 350°C showed a Tg close to that
more » ... PI(s-BPDA/PDA) prepared under the same condition in spite of the bent chain structure of the former. Comparison of the PIs cured at 400°C manifested that PI(a-BPDA/PDA) has a Tg at 410°C (abrupt decrease in E') whereas PI(s-BPDA/PDA) show no distinct Tg. Similar result was also observed for the ODA systems. The unexpectedly high Tgs of a-BPDA-based PIs were explained in terms of the restricted conformational change around the phenyl-phenyl bond in the a-BPDA unit. The difference of the E' decrement at the Tg for both type of PIs are probably attributed to the difference of the intensity of intermolecular interactions. In PI(a-BPDA/ PDA) thin film cured on a substrate, the segments unexpectedly align slightly to the film plane. Introduction Polyimides have been utilized as electrical insulators, flexible printed circuits, passivation layers, intrinsic photo-patternable materials, and alignment film for liquid crystal, owing to their outstanding thermal, mechanical, and dielectric properties. To understand how the PI physical properties are influenced by manufacturing conditions is indispensable to control precisely the properties necessary for practical applications. So far, we have studied local ordered structure[1-S] and spontaneous molecular orientation behavior induced by thermal imidization [6-lo] especially for PI(s-BPDAIPDA) which possesses some excellent physical properties (e.g., lower thermal expansion coefficient (TEC) and higher modulus) better than the most familiar polyimide, Kapton® and concluded that the higher order structure strongly affects the physical properties. The present paper describes the chemical and physical structures-properties relationships for symmetric and asymmetric biphenyl type polyimides. [11, 12] A large number of systematic studies revealed that the chain structure of PI is one of the most
doi:10.2494/photopolymer.9.367 fatcat:a4kd4bh3snaojpfl22k5pakfli