Polyimide (PI) is widely used in high-frequency communication technology due to its exceptional comprehensive properties. However, traditional PI has a relatively elevated dielectric constant and dielectric loss. Herein, the different cross-linked structures were introduced in PI matrix and conducted a detailed discussion on the influence of cross-linking agent content and cross-linking structure type on the overall performance of PI films. In comparison to the dielectric constant of 2.9 of neat PI, PI with an interchain cross-linking structure containing 2 wt% 1,3,5-tris(4-aminophenyl)benzene (TAPB) (interchain-PI-2) exhibited the reduced dielectric constant of 2.55 at 1 MHz. The PI films with intrachain cross-linking structure containing 2 wt% TAPB (intrachain-PI-2) exhibited the lowest dielectric constant of 2.35 and the minimum dielectric loss of 0.0075 at 1 MHz. It was due to the more entanglement junctions of intrachain-PI resulting in decreased carrier transport. The thermal expansion coefficients of both interchain-PI and intrachain-PI films were effectively reduced. Moreover, in contrast to interchain-PI films, the intrachain-PI films maintained colorlessness and transparency as the cross-linking agent content increased. This work compared the effects of two different cross-linked structures on the performance of PI films and provided a feasible way to obtain low-k PI films with excellent comprehensive performance for 5G applications.

Polyimide (PI) is considered one of the most promising candidate materials for the microelectronics and wireless communication industries. Nevertheless, the relatively high dielectric constant of PI has become a significant obstacle, constraining its utilization in the realm of microelectronics. Herein, novel PI nanocomposite films were fabricated by incorporating covalent organic frameworks (COFs) and their functionalized counterparts (COF@POSS and COF@DTF) through post-synthetic modification. Among all PI nanocomposites films, PI/ COF@POSS nanocomposite film including 2 wt% COF@POSS achieved the lowest dielectric constant (2.41) and dielectric loss (0.0076). These values represented a reduction of 22.5 % and 24 % compared to pure PI, respectively. The decrease in dielectric constant is ascribed to the combined influence of the porous structure of COF and the augmentation in free volume fraction caused by the steric hindrance of POSS. Additionally, the tensile strength of the PI/COF@POSS and PI/COF@DTF nanocomposite films increased up to 121.1 MPa and 112.0 MPa, representing a 95% and 80% improvement over pure PI, respectively. Furthermore, the introduction of COFs functionalized with POSS and DTF significantly enhanced the hydrophobicity of PI nanocomposite films. The combination of porous organic nanofillers with surface functionalization offers a feasible route to create lowk PI nanocomposite films with improved mechanical properties and hydrophobicity.

To enhance the flame retardancy and mechanical performance of PLA, a polyelectrolyte complex predicated on lignin was obtained by electrostatic mutual adsorption of ammonium polyphosphate (APP), polyethyleneimine (PEI), and copper ions as raw materials. The FT-IR spectra and EDX analysis confirmed the successful synthesis of a lignin -based flame retardant hybrid (APL-Cu2+) containing copper, phosphorus, and nitrogen elements. The combustion test results showed that the peak heat release rate and total heat release of the PLA composite containing 12 wt% APL-Cu2+ were decreased by 15.1 % and 18.2 %, respectively, as compared to those of pure PLA. The char residue morphology observation revealed that the addition of APL-Cu2+ could promote the formation of a highly dense and stable graphitized char layer, while TG -MS detected the emission of refractory gases such as ammonia gas, carbon dioxide, and water during combustion. The strong hydrogen bonding between APLCu2+ and the PLA matrix kept the composite maintaining good strength and toughness. The tensile strength and impact strength of PLA/6APL-Cu2+ increased by 4.73 % and 65.71 %, respectively, due to its high crystallinity and good interfacial compatibility. This work provides a feasible method to develop biobased flame retardant hybrids for PLA composites with better fire safety and improved mechanical properties.

Polydopamine (PDA) has been extensively investigated due to its excellent adhesion ability and versatile chemical potential for secondary reactions. However, the potential application of hollow polydopamine micro spheres (H-PDA) in the field of low-dielectric electronic packaging remains an unexplored area. Here, H-PDA microspheres with adjustable size were synthesized by a template-assisted approach, and the influence of size and content of H-PDA on the comprehensive performance of PI/H-PDA composites was explored in detail. The morphology observation revealed that the presence of H-PDA could be homogeneously dispersed in the PI matrix, and the PI/H-PDA composite containing 2 wt% H-PDA-800 achieved the lowest dielectric constant of 1.96 with a dielectric loss of 0.0123 at 1 MHz. It was attributed to the synergistic effects of nano-sized air bubbles from H-PDA and the dielectric confinement effect. Meanwhile, PI/H-PDA composites maintained high thermal stability (T5 > 517 C). In addition, the incorporation of H-PDA had a strengthening and toughening effect on PI composites, which can be explained by the sliding theory of macromolecular chains. This work offers a feasible strategy to obtain ultra-low dielectric constant of porous PI composites while maintaining good mechanical properties and thermal stability.

Biodegradable polylactide/poly(butylene adipate-co-terephthalate) (PLA/PBAT) blends have been widely uti-lized as packaging materials. However, it is urgent to develop a biocompatibilizer to improve the interfacial interaction of the biodegradable immiscible polymer blends in practice. In this paper, a novel type of hyper-branched polysiloxane (HBPSi) with terminal methoxy groups was synthesized and then utilized to functionalize lignin through a hydrosilation reaction. The HBPSi modified lignin (lignin@HBPSi) was incorporated into immiscible PLA/PBAT blends to serve as a biocompatibilizer. The lignin@HBPSi was uniformly dispersed in the PLA/PBAT matrix with improved interfacial compatibility. Dynamic rheological results revealed that the addi-tion of lignin@HBPSi reduced the complex viscosity, improving the processing ability of the PLA/PBAT com-posite. The PLA/PBAT composite containing 5 wt% lignin@HBPSi had a superior toughness with an elongation at break of 300.2 % and a slight enhancement in tensile stress (34.47 MPa). In addition, the presence of lig-nin@HBPSi contributed to blocking ultraviolet rays in the full ultraviolet band. This work provides a feasible way to develop highly ductile PLA/PBAT/lignin composites with good UV-shielding properties for the packaging applications.

The inherent shortcomings such as flammability, brittleness, and low crystallinity limit the broad applications of poly(lactic acid) (PLA). To improve the fire resistance and mechanical properties of PLA, a chitosan-based core-shell flame retardant additive (APBA@PA@CS) was prepared for PLA via the self-assembly of interionic interactions among chitosan (CS), phytic acid (PA), and 3-aminophenyl boronic acid (APBA). The peak heat release rate (pHRR) and total heat release rate (THR) of PLA composite containing 3 wt% APBA@PA@CS decreased from 460.1 kW/m2 and 75.8 MJ/m2 to 419.0 kW/m2 and 53.1 MJ/m2, respectively. The presence of APBA@PA@CS contributed to the formation of a high-quality char layer rich in phosphorus and boron in the condensed phase and released non-flammable gases in the gas phase to hinder the exchange of heat and O2, thereby having a synergistic flame retardant effect. Meanwhile, the tensile strength, elongation at break, impact strength, and crystallinity of PLA/APBA@PA@CS were increased by 3.7 %, 17.4 %, 5.3 %, and 55.2 %, respectively. This study provides a feasible route to construct a chitosan-based N/B/P tri-element hybrid to improve the fire safety performance and mechanical properties of PLA biocomposites.

Polyimide（PI） is a promising electronic packaging material, but it remains challenging to obtain an all-organic PI hybrid film with decreased dielectric constant and loss without modifying the monomer. Herein, a series of allorganic PI hybrid films were successfully prepared by introducing the covalent organic framework（COF）, which could induce the formation of the cross-linking structure in the PI matrix. Due to the synergistic effects of the COF fillers and the cross-linking structure, the PI/COF hybrid film containing 2 wt% COF exhibited the lowest dielectric constant of 2.72 and the lowest dielectric loss（tan δ） of 0.0077 at 1 MHz. It is attributed to the intrinsic low dielectric constant of COF and a large number of mesopores within the PI. Besides, the cross-linking network of PI prevents the molecular chains from stacking and improves the fraction of free volume（FFV）. The molecular dynamics simulation results are well consistent with the dielectric properties data. Furthermore, the PI/COF hybrid film with 5 wt% COF showed a significant enhancement in breakdown strength, which increased to 412.8kV/mm as compared with pure PI. In addition, the PI/COF hybrid film achieve to reduce the dielectric constant and thermal expansion coefficient（CTE）. It also exhibited excellent thermal, hydrophobicity, and mechanical performance. The all-organic PI/COF hybrid films have great commercial potential as next-generation electronic packaging materials.

Halloysite nanotubes (HNTs) have been considered as a promising flame retardant fillers for polymers. In this work, the polyhedral oligomericsilsesquioxane (POSS) containing amino group was covalently grafted on the surface of HNTs with 3-(2,3-epoxypropoxy)propytrimethoxysilane as a chemical bridge. The POSS modified HNTs (HNTs-POSS) dispersed uniformly in the thermoplastic polyurethane (TPU) matrix and endowed TPU nanocomposites with enhanced tensile properties and fire safety. Cone calorimeter tests revealed that the introduction of 2 wt% HNTs-POSS to TPU matrix remarkably reduced the peak of heat release rate (PHRR) and total heat release (THR) by 60.0% and 18.3%, respectively. In addition, the peak CO production rate and total smoke release (TSR) could be significantly suppressed by the addition of HNTs-POSS. The well dispersed HNTs in combination with the ceramified silicon network from the thermal decomposition of POSS contributed to the formation of a continuous and compact char layer, exhibiting a tortuous effect by inhibiting heat diffusion and evaporation of volatile gaseous. In addition, the released crystal water from HNTs could dilute the combustible volatiles and then decline the combustion intensity. The tensile tests demonstrated that introduction of 2 wt% HNTs-POSS would enhance the maximum stress of TPU nanocomposite with a slight decrease of elongation at break. The combination of HNTs and POSS through the construction of effective interfacial interactions provides a feasible way to effectively enhance the fire safety of TPU nanocomposites without scarifying ductility.

Thermoplastic polyurethane (TPU) is widely used in daily life due to its characteristics of light weight, high impact strength, and compression resistance. However, TPU products are extremely flammable and will generate toxic fumes under fire attack, threatening human life and safety. In this article, a nanohybrid flame retardant was designed for the fire safety of TPU. Herein, Co3O4 was anchored on the surface of exfoliated ultra-thin boron nitride nanosheets (BNNO@Co3O4) via coprecipitation and subsequent calcination. Then, a polyphosphazene (PPZ) layer was coated onto BNNO@Co3O4 by high temperature polymerization to generate a nanohybrid flame retardant named BNNO@Co3O4@PPZ. The cone calorimeter results exhibited that the heat release and smoke production during TPU combustion were remarkably restrained after the incorporation of the nanohybrid flame retardant. Compared with pure TPU, the peak heat release rate (PHRR) decreased by 44.1%, the peak smoke production rate (PSPR) decreased by 51.2%, and the peak CO production rate (PCOPR) decreased by 72.5%. Based on the analysis of carbon residues after combustion, the significant improvement in fire resistance of TPU by BNNO@Co3O4@PPZ was attributed to the combination of quenching effect, catalytic carbonization effect, and barrier effect. In addition, the intrinsic mechanical properties of TPU were well maintained due to the existence of the PPZ organic layer.

AbstractThe advancement of the microelectronics industry necessitates the use of interlayer insulation materials with low dielectric constants and high mechanical properties. In this paper, a new type of copolymerized fluorinated polyimide (PI) is synthesized, and mixed with polyhedral oligomeric silsesquioxane (POSS) functionalized mesoporous silica (MCM‐41@POSS). The PI/MCM‐41@POSS composites exhibit good hydrophobicity. With the addition of 3 wt% MCM‐41@POSS, the PI composite attained an ultralow dielectric constant (k = 1.88) and low dielectric loss (0.01) at 1 MHz, which is attributed to the mesoporous structure of MCM‐41 and the restriction of polarization in the bonded region. The decorated POSS effectively prevents the penetration of PI molecular chains into the mesopores of MCM‐41. In addition, the PI composites containing 3 wt% of MCM‐41@POSS obtain the highest maximum stress of 104.03 MPa with an elongation at break of 13.73%. The hydrophobic PI composites with ultralow‐k are expected to be good candidates as interlayer materials in microelectronics devices.

Under extreme conditions, the polymer dielectric materials are expected to have good dielectric properties and heat resistance. Polyimide (PI) has high service temperature (>250 degrees C) and low dielectric loss, but its low dielectric constant limits its further application. The addition of MXene can significantly improve the dielectric constant of PI, but the poor compatibility between MXene and weak polar matrix leads to Benard-Marangoni (BM) instability in the process of thermal imidization. This issue can be solved by the surface modification of MXene. Therefore, in this work, a new cetyltrimethylammonium bromide (CTAB) decorated MXene/PI nanocomposite film was prepared by in-situ polymerization. With the addition of 7 wt% MXene@CTAB, the PI nanocomposite shows improved dielectric constant (k = 7.8 at 100 Hz), which is 2.4 times that of pure PI due to the formation of micro-capacitors structure and Maxwell-Wagner-Sillars (MWS) interfacial polarization. Its dielectric loss keeps at an ultra-low level (0.027 at 100 Hz) while that of 7 wt% MXene/PI nanocomposite is 3.027. It is owing that CTAB inhibits the agglomeration of MXene. In addition, MXene@CTAB/PI composites have excellent thermal stability, good hydrophobicity, and low water absorption. The above properties ensure MXene@CTAB/PI composites wide application in various extreme situations.

There is a great demand for low dielectric materials as insulating interlayers in large-scale integrated circuit development.However, it is still a huge challenge to reduce the dielectric permittivity of polymers while maintaining excellent thermal stability and mechanical properties.In this work, the fluorinated polyimides (PIs) in combination with a micro-branched crosslinking structure were prepared successfully by introducing different amounts of 1,3,5-tris(4-aminophenyl) benzene (TAPB) to obtain ultra-low dielectric permittivity.The results revealed that PI film containing 2 mmol TAPB had the lowest dielectric permittivity (2.47) and dielectric loss (0.008) at 1 MHz due to the fluorine atoms and the micro-branched crosslink structure, which not only decreased the molecular polarizability but also increased the free fractional volume.In addition, PI film containing 2 mmol TAPB had the highest tensile strength of 106.02 MPa with an elongation at a break of 15.1% because the presence of TAPB effectively promoted the connection between PI molecular chains, resulting in the inhibition of the molecular mobility.The incorporation of TAPB also enhanced the thermal stability and ultraviolet light-shielding performance of PI films.This method paves the way for the development of PIs with ultra-low dielectric permittivity for the electronic industry.

Dielectric polymer composites with high dielectric constant and low dielectric loss are highly demanded for various types of devices. In this work, the core-shell structured polydopamine functionalized silicon carbide whiskers (SiC@PDA) were successfully synthesized. The presence of PDA effectively suppressed the dielectric loss of PVDF/SiC@PDA composites because it could inhibit the connection between fillers and reduce the interfacial polarity. Moreover, the thicker PDA layer contributed to improving dielectric breakdown strength and reducing AC conductivity of PVDF composites. The insulating PVDF/SiC@PDA-a-30 composite containing 30 wt % of SiC@PDA-a had a dielectric constant of 35.1 while the dielectric loss still maintained as low as 0.037 at 1 KHz. Meanwhile, PVDF/SiC@PDA-a-30 achieved the maximum stress of 58.8 MPa with elongation at break of 17.3% due to PDA layer improved the compatibility between SiC@PDA and PVDF. This simple coated PDA shell strategy could be extended to inorganic fillers to develop high performance dielectric polymer composites.

The incorporation of high-dielectric permittivity ceramic or conductive fillers into the polymer is an effective method to obtain flexible high-performance dielectric materials, but it is still a huge challenge to achieve a balance between dielectric and mechanical properties. In this paper, we report a polyvinylidene fluoride (PVDF) nanocomposite based on a novel crab leg-like filler, in which Ag nanoparticles (AgNPs) were decorated on the surface of polydopamine (PDA)-coated silicon carbide (SiC) nanowhiskers (NWs). Compared with the nanocomposites with as-received SiC, this PVDF/SiC@PDA@Ag nanocomposites exhibited significantly suppressed dielectric loss (0.03 at 1 kHz) and leakage current. The Argant plot ( $${\varepsilon }^{^{\prime}}$$ - $${\varepsilon }^{\prime\prime}$$ curve) and electric modulus analysis demonstrated that the inhibition of the organic layer of PDA to interface polarization and the coulomb-blockade effect of AgNPs hindered carrier transport, which resulted in the largely suppressed dielectric loss. Furthermore, while the dielectric properties were improved, the PVDF/SiC@PDA@Ag nanocomposites also exhibited excellent mechanical and thermal conductivity. Ultimately, the nanocomposites prepared via this method are promising for applications in microelectronic devices.

The high flammability and generation of toxic volatiles during combustion are big obstacles for thermoplastic polyurethane (TPU). In this work, a 10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) derivate containing phosphorus and nitrogen was synthesized and then grafted onto the surface of graphene oxide (GODOPO) by using a silane agent [(3-glycidyloxypropyl)trimethoxysilane] as the chemical bridge. Then the GODOPO was mixed with TPU by melt compounding to improve its flame retardancy. Tensile tests exhibited that the TPU/GO-DOPO nanocomposite maintained high ductility with a slight increase in tensile stress. The cone calorimeter tests exhibited that the incorporation of 2 wt% GO-DOPO into TPU presented a significant reduction in peak heat release rate (35.8%) and peak smoke production rate (50%), respectively, as compared with those of pure TPU. Meanwhile, the peak of CO production rate and the peak of CO2 production rate decreased by 57.1% and 35.9%, respectively. The investigation of the flame retardant mechanism for TPU nanocomposites revealed that the presence of GO-DOPO in TPU contributed to generating the compact, continuous and higher graphitized char layer exerted barrier effect in condensed phase, protecting the underlying TPU matrix. This work provides a feasible functionalization approach of GO to enhance the fire safety of TPU nanocomposites without sacrificing the superior mechanical properties, which facilitates the promising applications of TPU in various fields.

Dielectric polymer nanocomposites with high dielectric permittivity and low dielectric loss have great applications in energy storage field. In this study, a series of PVDF/MXene nanocomposites was prepared by solution method. The surface of MXene was functionalized with cetyltrimethylammonium bromide (MXene@CTAB) to achieve better dispersion in poly(vinylidene fluoride) (PVDF) matrix. The results revealed that the MXene@CTAB dispersed uniformly and had a good compatibility with PVDF matrix. In addition, the dynamical rheological test revealed that the viscosity and storage modulus of PVDF nanocomposites increased with the increasing of MXene@CTAB loading. The PVDF/MXene@CTAB nanocomposite containing 7 wt% MXene@CTAB exhibited a dielectric permittivity of 82.1 and a loss factor as low as 0.2 at 1 kHz. The presence of CTAB could serve as an insulating layer to suppress dielectric loss and AC conductivity of PVDF nanocomposites simultaneously. The PVDF/MXene@CTAB nanocomposite with high dielectric permittivity may find potential applications in energy storage capacitors for electronics. Moreover, the addition of MXene@CTAB contributed to the formation of Beta phase of PVDF.