Versatile Landscape of Low-k Polyimide: Theories, Synthesis, Synergistic Properties, and Industrial Integration

The development of microelectronics and large-scale intelligence nowadays promotes the integration, miniaturization, and multifunctionality of electronic and devices but also leads to the increment of signal transmission delays, crosstalk, and energy consumption. The exploitation of materials with low permittivity (low-k) is crucial for realizing innovations in microelectronics. However, due to the high permittivity of conventional interlayer dielectric material (k ∼ 4.0), it is difficult to meet the demands of current microelectronic technology development (k < 3.0). Organic dielectric materials have attracted much attention because of their relatively low permittivity owing to their low material density and low single bond polarization. Polyimide (PI) exhibits better application potential based on its well permittivity tunability (k = 1.1-3.2), high thermal stability (>500 °C), and mechanical property (modulus of elasticity up to 3.0-4.0 GPa). In this review, based on the synergistic relationship of dielectric parameters of materials, the development of nearly 20 years on low-k PI is thoroughly summarized. Moreover, process strategies for modifying low-k PI at the molecular level, multiphase recombination, and interface engineering are discussed exhaustively. The industrial application, technological challenges, and future development of low-k PI are also analyzed, which will provide meaningful guidance for the design and practical application of multifunctional low-k materials.

An effective strategy for the preparation of intrinsic low-k and ultralow-loss dielectric polysiloxanes at high frequency by introducing trifluoromethyl groups into the polymers

Two new CF₃-containing polysiloxanes with low dielectric constant (D_k) and dielectric loss (D_f ) at a high frequency of 5 GHz were reported. The sample with two −CF₃ groups exhibits better dielectric properties with D_k of 2.53 and ultralow D_f of 1.66 × 10⁻³.

Semi-Interpenetrating Polymer Networks Based on Cyanate Ester and Highly Soluble Thermoplastic Polyimide

Thermoplastic polyimide (TPI) was synthesized via a traditional one-step method using 2,3,3',4'-biphenyltetracarboxylic dianhydride (3,4'-BPDA), 4,4'-oxydianiline (4,4'-ODA), and 2,2'-bis(trifluoromethyl)benzidine (TFMB) as the monomers. A series of semi-interpenetrating polymer networks (semi-IPNs) were produced by dissolving TPI in bisphenol A dicyanate (BADCy), followed by curing at elevated temperatures. The curing reactions of BADCy were accelerated by TPI in the blends, reflected by lower curing temperatures and shorter gelation time determined by differential scanning calorimetry (DSC) and rheological measurements. As evidenced by scanning electron microscopy (SEM) images, phase separation occurred and continuous TPI phases were formed in semi-IPNs with a TPI content of 15% and 20%. The properties of semi-IPNs were systematically investigated according to their glass transition temperatures (T_g), thermo-oxidative stability, and dielectric and mechanical properties. The results revealed that these semi-IPNs possessed improved mechanical and dielectric properties compared with pure polycyanurate. Notably, the impact strength of semi-IPNs was 47%-320% greater than that of polycyanurate. Meanwhile, semi-IPNs maintained comparable or even slightly higher thermal resistance in comparison with polycyanurate. The favorable processability and material properties make TPI/BADCy blends promising matrix resins for high-performance composites and adhesives.

Curing kinetics of phenolphthalein based polyphosphazene towards thermal stability and flame retardancy of polybenzoxazine

Phenolphthalein type polyphosphazene (PZPT) microspheres were synthesized by an ultrasound assisted precipitation polymerization method, and their structures were confirmed by scanning electron microscopy (SEM) and Fourier transform infrared (FTIR) spectroscopy. Benzoxazine/PZPT (Ba/PZPT) hybrid materials were fabricated and cured to prepare polybenzoxazine/PZPT (PBa/PZPT) composites. The effects of PZPT microspheres on the curing kinetics and behaviors of Ba were systematically analyzed and supported by differential scanning calorimetry (DSC) and in situ FTIR. The thermogravimetric (TGA) results demonstrated good thermal stability of the PBa composites incorporating PZPT. The peak of heat release rate and total heat release values of PBa/PZPT-5% composites obviously deceased by 57.8% and 17.3% compared to those of the pristine PBa. Moreover, the smoke released from the PZPT/PBa system significantly reduced with the loading of microspheres. Finally, the dynamical mechanical analysis results demonstrated that the T_g of PBa flame retardant composites was approximately 210 °C, not affecting further applications of PBa composites.

Phenolphthalein type polyphosphazene (PZPT) microspheres were synthesized by an ultrasound assisted precipitation polymerization method, and their structures were confirmed by scanning electron microscopy (SEM) and Fourier transform infrared (FTIR) spectroscopy.

Simultaneous toughening and reinforcing of cyanate ester/benzoxazine resins with improved mechanical and thermal properties by using hyperbranched polyesters

In the present study, the influence of incorporating various amounts of hyperbranched polyester (HBPE) into thermosetting resin blends composed of cyanate ester (CE) and benzoxazine (BOZ) resins was investigated for their structural, morphological, mechanical, and thermal properties. The FTIR spectra revealed that the CE/BOZ resin had reacted with the functional groups of HBPE, and the SEM test confirmed the morphological changes from a smooth surface that was observed for the virgin CE/BOZ resin to a rough surface for the maximum HBPE content. Moreover, the mechanical and thermal properties were found to be pointedly enhanced as we increased the content of HBPE. These remarkable enhancements may be due to the chemical structure of the HBPE which could form a cross-linked structure through a strong hydrogen bonding with the CE/BOZ resin. As a result, a considerable amount of applied mechanical load can be absorbed, and in parallel, the thermal stability can also be improved. We believe that the HBPE can be a good toughener for the CE/BOZ resins that could possibly expand their range of applications in various industrial sectors.

Simultaneously toughening and strengthening cyanate ester resin with better dielectric properties by building nanostructures in its crosslinked network using polyimide-block-polysiloxane rod-coil block copolymers

The fabrication and origin of high performance cyanate ester resins by building nanostructures in its crosslinked network with polyimide-block-polysiloxane block copolymers.

Significantly improving mechanical, thermal and dielectric properties of cyanate ester resin through building a new crosslinked network with unique polysiloxane@polyimide core–shell microsphere

Tough, rigid and thermally resistant resins with outstanding dielectric properties were developed based on polysiloxane@polyimide core–shell microspheres and cyanate ester.

Tough and thermally resistant cyanate ester resin with significantly reduced curing temperature and low dielectric loss based on developing an efficient graphene oxide/Mn ion metal–organic framework hybrid

High performance cyanate ester resins based on a graphene oxide/Mn ion metal–organic framework hybrid with efficient catalysis and toughening effects.