Transparent polyimides (PI) films with outstanding overall performance are attractive for
next generation optoelectronic and microelectronic applications. Semi-alicyclic PIs derived from
alicyclic dianhydrides and aromatic diamines have proved e ective to prepare transparent PIs with
high transmittance. To optimize the combined properties of semi-alicyclic PIs, incorporating bulky
trifluoromethyl groups into the backbones is regarded as a powerful tool. However, the lack of
fundamental understanding of structure–property relationships of fluorinated semi-alicyclic PIs
constrains the design and engineering of advanced films for such challenging applications. Herein,
a series of semi-alicyclic PIs derived from alicyclic dianhydrides and trifluoromethyl-containing
aromatic diamines was synthesized by solution polycondensation at high temperature. The e ects of
alicyclic structures and bulky trifluoromethyl groups on thermal, dielectric and optical properties of
PIs were investigated systematically. These PI films had excellent solubility, low water absorption
and good mechanical property. They showed high heat resistance with Tg in the range of 294–390 C.
It is noted that tensile strength and thermal stability were greatly a ected by the rigid linkages
and alicyclic moieties, respectively. These films exhibited obviously low refractive indices and
significantly reduced dielectric constants from 2.61 to 2.76, together with low optical birefringence
and dielectric anisotropy. Highly transparent films exhibited cuto wavelength even as low as 298 nm
and transmittance at 500 nm over 85%, displaying almost colorless appearance with yellowness
index (b*) below 4.2. The remarkable optical improvement should be mainly ascribed to both weak
electron-accepting alicyclic units and bulky electron-withdrawing trifluoromethyl or sulfone groups.
The present work provides an e ective strategy to design molecular structures of optically transparent
PIs for a trade-o between solution-processability, low water uptake, good toughness, high heat
resistance, low dielectric constant and excellent optical transparency.