Abstract
An alicyclic tetracarboxylic dianhydride having cyclopentanone bis-spironorbornane structure (CpODA) was polycondensated with aromatic dianhydrides to form the corresponding poly(amic acid)s which possessed logarithmic viscosities in the range 1.47–0.54 dL/g. The poly(amic acid) was imidized by three methods: a chemical, a thermal, and a combined chemical and thermal process. In a thermal method, imidization temperature markedly influenced the film quality and molecular weight of the polyimide. When the poly(amic acid) was cured over the Tg of the corresponding polyimide, the flexible polyimide films were obtained and the molecular weights increased several times, which means that the post-polymerization took place. In spite of low-temperature cure below Tg flexible films with the imidization ratio of 100% were fabricated by a combined chemical and thermal imidization technique. The films possessed the decomposition temperatures in a range of 475–501 °C and Tgs over 330 °C. The high Tg results from a dipole–dipole interaction between the keto groups of the polymer chains as well as development of the rigid polyalicyclic unit. The polyimide films exhibited CTE between 17 and 57 ppm/K. All the films fabricated were entirely colorless and possessed the λcut-offs shorter than 337 nm. Notably, the films prepared by a chemical method exhibited outstanding optical properties.
Highlights
The earliest of the thermally stable polymers, and still one of the most common commercial materials, is an aromatic polyimide that was synthesized by DuPont in 1964 and marketed under the name H-Film and later Kapton® (E.I. du Pont Co.) [1]
We investigated the origin of discoloration of Kapton®-type polyimide from the viewpoint of quantum chemistry using the model compound, and reported that the light absorption is attributable to intramolecular CT from diamine moiety to dianhydride one [7]
Polyimides were synthesized by a two-step method where the first step includes the poly(amic acid) (PAA) formation at room temperature in DMAc (Scheme 1)
Summary
The earliest of the thermally stable polymers, and still one of the most common commercial materials, is an aromatic polyimide that was synthesized by DuPont in 1964 and marketed under the name H-Film and later Kapton® (E.I. du Pont Co.) [1] It exhibits excellent electrical and high-temperature mechanical properties and cosmic ray resistance [2]. As one of our continuous studies developing high-performance colorless polyimide films for advanced optical applications, the enhancement of thermal and optical properties was endeavored by introducing a cyclopentanone bisspironorbornane unit into the molecular structure and by adopting a low temperature film-fabrication method. The effects of the introduced unit and the fabrication method on the optical and thermal properties of the derived colorless polyimide films will be described in detail
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