Thermal Imidization Research Articles

Low Dielectric Properties and Transmission Loss of Polyimide/Organically Modified Hollow Silica Nanofiber Composites.

In this study, a series of low dielectric constant and transmission loss of polyimide (PI)/organically modified hollow silica nanofiber (m-HSNF) nanocomposites were synthesized via two-step polymerization. Two different PIs were fabricated using two types of diamine monomers with or without fluorine-containing groups and biphenylene structure of dianhydride. The chemical structure and morphology of the fabricated composites were characterized using Nuclear magnetic resonance (NMR), Fourier transform infrared (FTIR) and field-emission scanning electron microscopy (FESEM). The two-step polymerization process successfully manufactured and converted from polyamic acid to polyimide after thermal imidization was proved by the NMR and FTIR results. The FESEM and their related energy-dispersive X-ray spectroscopy (EDS) images of nanocomposites indicate that the m-HSNF is extremely dispersed into the polyimide matrix. The high-frequency dielectric constants of the nanocomposite materials decrease as the presence of fluorine-containing groups in diamine monomers and the loadings of the m-HSNF increase. These findings are probably attributed to the presence of the steric hindrance effect brought by trifluoromethyl groups, and the m-HSNF can disrupt the chain packing and increase the free volume, thus reducing the dielectric properties of polyimides. The transmission loss and its related uncertainty of fabricated composite materials contain excellent performance, suggesting that the fabricated materials could be used as substrate materials for 5G printed circuit board.

Controlled Thermal Imidization of Thermoplastic Polyimide for Temporary Bonding and Debonding in Advanced Packages

Temporary bonding and debonding (TBDB) is a key technology in the semiconductor field to enable 2.5D/3D integration of devices. However, the conventional polyimides, which serve as the laser-response material in TBDB, exhibit extremely poor solubility in aprotic polar solvents due to high-temperature imidization, limiting the cleaning process for wafers after debonding. Herein, a feasible method of controlling the curing temperature to enhance the solubility of thermoplastic polyimide (TPI) has been developed. The results proved that the ultimate solubility of TPI cured at 200 °C (TPI-200 °C) could be as high as 28.4 wt %. Besides, TPI-200 °C exhibits excellent heat resistance, outstanding mechanical properties, and ultrahigh absorptivity (99.96%) at a 355 nm UV wavelength. Meanwhile, we demonstrate the feasibility of the as-prepared TPI material for application in the TBDB process, showing excellent efficiency and low cost, and the follow-up elemental analysis of the cleaned wafer surfaces proved that TPI-200 °C can be completely removed after debonding. All these results demonstrate that TPI materials that can be used for TBDB are promising for ultrathin chip packaging and wafer level packaging (WLP) in the field of advanced electronic packaging.

Ultralight and flexible silver nanoparticle-wrapped “scorpion pectine-like” polyimide hybrid aerogels as sensitive pressor sensors with wide temperature range and consistent conductivity response

The demand for sensitive pressure sensors is increasing due to the rapid development of intelligent electronic equipment in high-tech fields such as aerospace and transportation. However, the high-temperature conditions encountered in aerospace applications pose challenges to the performance of flexible sensing materials used in related equipment. In this context, silver nanoparticles (AgNPs)-wrapped polyimide (PI) hybrid aerogels (PI/AgNPs aerogels) with scorpion pectine-like microstructures (SPM) were fabricated by freeze-drying the precursor solution, followed by a thermal imidization reaction and a dipping process with a AgNPs solution. The SPM grew vertically on the layered structure with a height between 20 and 40 μm. These PI/AgNPs provided sufficient structural strength as a support while providing recovery and contact points. The AgNPs were uniformly dispersed on the SPM (with a thickness of 78–120 nm on PI/AgNPs-1). The SPM-interface secondary response structure was used to realize an electrical response in a broad tension (the PI/AgNPs-2 aerogel has changed from −15.63 kPa under 30 % tensile stress to 69.25 kPa under 70 % compression stress). The hybrid aerogels had excellent sensing performance, including good resistance change (89 %), ultra-high sensitivity (6.9 kPa−1), the ability to detect different deformations (compression, tension, and bending), and low fatigue after 3000 load-unload cycles. In addition, these aerogels were able to withstand high temperatures up to 250 °C, and they showed good conductivity response consistency at high and room temperatures. These PI/AgNPs aerogels can be used as sensors in extreme conditions such as in aeroengine peripheral electronics for sensing and detecting external loads.

Electrospun Benzimidazole-Based Polyimide Membrane for Supercapacitor Applications.

A benzimidazole-containing diamine monomer was prepared via a simple one-step synthesis process. A two-step procedure involving polycondensation in the presence of aromatic dianhydrides (4,4′-oxydiphthalic anhydride, ODPA) followed by thermal imidization was then performed to prepare a benzimidazole-based polyimide (BI-PI). BI-PI membranes were fabricated using an electrospinning technique and were hot pressed for 30 min at 200 °C under a pressure of 50 kgf /cm2. Finally, the hot-pressed membranes were assembled into supercapacitors, utilizing high-porosity-activated water chestnut shell biochar as the active material. The TGA results showed that the BI-PI polymer produced in the two-step synthesis process had a high thermal stability (Td5% = 527 °C). Moreover, the hot-press process reduced the pore size in the BI-PI membrane and improved the pore-size uniformity. The hot-press procedure additionally improved the mechanical properties of the BI-PI membrane, resulting in a high tensile modulus of 783 MPa and a tensile strength of 34.8 MPa. The cyclic voltammetry test results showed that the membrane had a specific capacitance of 121 F/g and a capacitance retention of 77%. By contrast, a commercial cellulose separator showed a specific capacitance value of 107 F/g and a capacitance retention of 49% under the same scanning conditions. Finally, the membrane showed both a small equivalent series resistance (Rs) and a small interfacial resistance (Rct). Overall, the results showed that the BI-PI membrane has significant potential as a separator for high-performance supercapacitor applications.

Anisotropic and Lightweight Carbon/Graphene Composite Aerogels for Efficient Thermal Insulation and Electromagnetic Interference Shielding.

High-performance and lightweight carbon aerogels (CAs) have attracted considerable attention in various fields such as electrochemistry, catalysis, adsorption, energy storage, and so on. However, finding an environmentally friendly and efficient preparation method and achieving a controllable performance of CAs are still a challenge. Herein, a series of anisotropic carbon/graphene composite aerogels were synthesized by unidirectional freezing of polyamic acid ammonium salt/graphene oxide (PAS/GO) suspension followed by lyophilization, thermal imidization, and carbonization. The prepared aerogels presented a tubular pore structure oriented along the freezing direction. The GO dispersed in the polymer matrix reinforced the skeleton of aerogels, which significantly inhibited the volume shrinkage during the preparation process, thus giving low densities of 0.074-0.185 g cm-3. In addition, the oriented pore structure endowed the composite aerogels with obviously anisotropic heat insulation performance. The radial thermal conductivity was as low as 0.038 W m-1 K-1 at the density of 0.074 g cm-3. When the initial content of GO rose to 20 phr, the resultant aerogels exhibited a high electrical conductivity of about 0.77 S cm-1 in the radial direction and the electromagnetic interference shielding effectiveness (EMI SE) reached 54.6 dB at the same time. Therefore, this study provided a facile and environmentally friendly method to prepare lightweight and anisotropic carbon aerogels.

Thermotolerant separator of cross-linked polyimide fibers with narrowed pore size for lithium-ion batteries

Separators are of significance in the thermal safety and energy-storage performance of lithium-ion batteries (LIBs). Thermotolerant separators of electrospun polyimide (PI) fibers hold great promise as candidate to commercial polyolefin-based separators due to their high thermal and electrochemical stability. However, their applications in LIBs are limited by the undesirably large pore size (∼2 μm) that will induce dendrite growth and thermal runaway of batteries. Here, we demonstrate a facile and scalable strategy to prepare thermotolerant separators of cross-linked PI fibers (c-PI) with a narrowed pore size (0.78 μm) via a blended electrospinning of polyamic acid and polystyrene followed by a thermal imidization. The electrospun fibers in the c-PI separator are ribborn-like and feature adhesion structure between adjacent fibers, while no such structures are observed for PI separator obtained without adding polystyrene. In comparison with the PI separators, the c-PI separator exhibits higher porosity, better electrolyte adsorption and higher ionic conductivity. In Comparison to the batteries with PI and Celgard separators, the battery with c-PI separator shows greatly enhanced electrochemical performance with a high capacity of 100.1 mAh/g at 10 C after 1600 cycles. This work offers a feasible and effective route to develop advanced membranes of electrospun fibers for safe LIBs.

Cetyltrimethylammonium bromide decorated MXene/polyimide nanocomposites with enhanced dielectric properties, thermostability, and moisture resistance

AbstractUnder extreme conditions, the polymer dielectric materials are expected to have good dielectric properties and heat resistance. Polyimide (PI) has high service temperature (>250°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 Bénard‐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.

Synthesis and characterization of poly(amide-imide)s with high Tg and low CTE derived from isomeric amide-containing diamines

Two series of poly(amide imide)s (PAIs) based on two novel isomeric amide-containing diamine monomers and different commercial aromatic dianhydrides were synthesized via thermal imidization. These PAIs exhibited excellent Tgs ranging from 368 to 431 °C, low coefficients of thermal expansion (CTE) of 6.7–47.2 ppm/K, and good 5% weight loss temperatures (Td5%s) in N2 of 494–540 °C, which was attributed to the introduction of rigid backbone and strong intermolecular hydrogen bonding resulted from amide bond. In particular, PAI-1a and PAI-1b displayed well-balanced performance with Tgs in the range of 419–431 °C, CTE in the range of 6.7–9.0 ppm/K, and mechanical properties with tensile strengths of 116–125 MPa, tensile moduli of 8.4–8.7 GPa, which could be probably used in flexible displays. In addition, the effects of two isomeric monomers on the properties of films were compared, and it was found that PAI-(1–3)a showed higher Tg,Td5% and CTE, but lower tensile strength and transparency than PAI-(1–3)b.

Preparation, characterizations and investigation of properties of new poly(ether-imide) nanocomposite films reinforced with zinc oxide nanoparticles

This research deals with fabrication and evaluation of properties of poly(ether-imide)/functionalized zinc oxide nanocomposites (PEI/f-ZnO NCs) via an in-situ polymerization method. The process involves the dispersion of pre-functionalized zinc oxide nanoparticles (f-ZnO NPs) in N,N-dimethylacetamide, polycondensation of 5-(2-benzoxazole)-1,3-bis(4-aminophenoxy)benzene (DABO) and pyromellitic dianhydride (PMDA) in the presence of f-ZnO NPs suspension to form poly(amic acid) (PAA), and followed by the thermal imidization of PAA/f-ZnO nanocomposites. For increasing reactivity and compatibility between the nano-fillers and polymer matrix, the periphery of ZnO NPs was amine-functionalized with 3‐aminopropyltriethoxysilane (APS) to form f-ZnO NPs. The structure, morphology, and thermal properties of nanocomposite films with various f-ZnO NPs loadings were systematically characterized using FTIR spectroscopy, X-ray diffraction (XRD) analysis, scanning electron microscopy (SEM), and thermogravimetric analysis (TGA). The results indicated that f-ZnO NPs were dispersed uniformly at a nanometer scale in PEI matrix. Owing to such nanodispersion of nanoparticles, the PEI/f-ZnO nanocomposite films exhibit dramatic improvements on thermal stability as compared with the neat polymer.

Anti-oxidation polyimide-based hybrid foams assembled with bilayer coatings for efficient electromagnetic interference shielding

High-performance electromagnetic interference (EMI) shielding materials are highly desirable in high-tech fields, particularly in high temperature conditions, whereas long term effectiveness of the EMI shielding performance still remains a challenge. Herein, polyimide-based PI@MXene@ANFs/PI hybrid foams assembled with MXene and polyimide bilayer coatings were fabricated via a facile strategy of freeze-drying plus thermal imidization followed by two-step dip-coating. More specifically, MXene coating acted as conducting layer to ensure the electrical conductivity of hybrid foams and polyimide coating served as protecting layer to enhance the long-term effectiveness of the hybrid foams by protecting MXene coating from oxidation during use. Benefiting from the conductive MXene coating and porous structure of the as-prepared hybrid foams, massive EMWs were converted into heat energy via ohmic losses, resulting in excellent EMI shielding performance of MXene@ANFs/PI and PI@MXene@ANFs/PI hybrid foams with an absorption-dominant EMI shielding mechanism in terms of EMI SE. After heat-treated at 250 °C for 100 h, the average EMI SET of PI@MXene@ANFs/PI-35 foam was slightly decreased by 4.97% from 46.3 to 44.0 dB, yet 65.85% from 48.9 to 16.7 dB for MXene@ANFs/PI-35 foam. The results indicated that the special bilayer coatings endowed the polyimide-based foams with lightweight, outstanding EMI shielding and anti-oxidation performance, presenting great prospects for the long-term application in extreme conditions.

Investigation of the structure–dielectric relationship of polyimides with ultralow dielectric constant and dissipation factors using density functional theory

Polyimides (PIs) possessing both low dielectric constant (Dk) and dissipation factor (Df) remain an intriguing study for the ever-increasing demand for the high frequency transmission of signals. In this study, the relationship between the chemical structures and the dielectric properties of PIs were comprehensively investigated. 35 kinds of PIs with different types of functional groups such as ester, fluorine and ether were prepared via the polyaddition and the subsequent thermal imidization. Their chemical structures and physical properties including the mechanical and dielectric properties were systematically studied. We found that the additive group contribution method failed to provide an effective correlation on the PIs with low Dk and Df values, and it is incapable of distinguishing geometry isomers of PIs. Herein, by utilizing the density functional theory simulation, we successfully remedied those issues. The Dk and Df values of PIs provided strong correlations with volumetric polarizability and volumetric dipole moment. The results elaborated the effect of the interchain behavior to the Dk values and the impact of the chain rigidity on the Df values of PIs. Combining with the molar volume derived from the film density, and a correction factor expressing the polymer rigidity, we eventually established a confident correlation of Dk and Df values with the structure parameters of PIs, respectively. In the meantime, this study interprets the guidelines for the design on PIs molecular structure which sheds light on the development of the insulating materials at high frequencies.

Polyimide composite aerogels towards highly efficient microwave absorption and thermal insulation

The development of lightweight microwave absorbing materials with thermal insulation is critical to the aerospace industry. In this work, polyimide (PI) composite aerogels with efficient microwave absorption and thermal insulation performance were fabricated with the addition of amino-functionalized core–shell structure ferroferric oxide (NH2-SiO2@Fe3O4) via an eco-friendly freeze-drying method followed by a thermal imidization process. PI works as the skeleton, where NH2-SiO2@Fe3O4 nanoparticles not only serve as microwave absorbers but also can induce interfacial thermal resistance, resulting in improved thermal insulation performance. Herein, the strong reflection loss (RL) reaches −49.7 dB at 14.0 GHz and an effective absorption bandwidth (EAB) of 10.0 GHz (7.2–16.4 GHz, 17.2–18.0 GHz) is achieved. Additionally, the PI composite aerogel shows superior thermal insulation with a thermal conductivity of 44.7 mW/(m·k). This study may offer a promising approach to develop PI composite aerogels with integrated microwave absorption and thermal insulation functions.

Preparation of semi-alicyclic homo- and blended polyimide membranes using alicyclic dianhydrides with kink structures and their gas separation properties

Aromatic polyimides are promising membrane materials for gas separation due to their excellent gas separation properties. Herein, two soluble semi-alicyclic polyimides were synthesized via a one-step thermal imidization process with two semi-alicyclic dianhydrides possessing kink structures: bicyclo[2,2,2] oct-7ene-2,3,5,6-tetracarboxylic dianhydride (BCDA) and 5-(2,5-dioxotetrahydrofuryl)-3-methyl-3-cyclohexene-1,2-dicarboxylic anhydride (DOCDA), and a flexible aromatic diamine: 4,4′-Oxydianiline (ODA). Their homo- and blended membranes were prepared in various mixing ratios (100/0, 75/25, 50/50, 25/75, and 0/100) and their gas permeation properties were investigated for five gases (H2, CO2, O2, N2, and CH4) and selectivity for five gas pairs (H2/CH4, H2/N2, CO2/CH4, CO2/N2, and O2/N2). The homopolyimides (BCDA-ODA, DOCDA-ODA) exhibited amorphous structure without crystallinity and good solubilities in the casting solvents. BCDA-ODA showed larger d-spacing/FFV values, higher gas diffusivities/gas solubilities than DOCDA-ODA, resulted in higher gas permeabilities and lower gas selectivity, which were remarkably affected by feed temperature. Also, the gas permeability and selectivity of the blended membranes were dependent upon the BCDA/DOCDA mole ratio. The good gas separation performances of homo- and blended membranes were observed for H2/CH4, H2/N2, CO2/CH4, and O2/N2, which are comparable to those of commercial membrane materials such as P84®, PSF, CA, Matrimid®, etc.

Preparation of polyimide aerogels by freeze‐extraction and chemical imidization for 3D printing

AbstractPolyimide (PI) aerogels with excellent mechanical and thermal stability, low density, and flexibility have attracted extensive attention in recent years. However, the existing preparation method usually requires chemical pre‐crosslinking followed by supercritical drying or freeze drying, and then thermal imidization, which has the weakness of a complicated preparation method and high cost. In this study, PI aerogels were prepared by a simple method that involved freeze extraction and chemical imidization, which exhibited low density (0.14 g cm−3), high porosity (85.61%), excellent thermal stability (T5% and Tg were 418.12 and 230.60°C, respectively), shape fidelity, and compressibility. Furthermore, this method regulated the pore size, such as the macro/microstructure, and then used the PI aerogel ink to build complex architectures by 3D printing. As a proof of concept, pyramids, multilayer grids, ring‐hole disks, Chinese knots and cuboids were printed, and all of them exhibited the shape fidelity property after freeze‐extraction and chemical imidization. Therefore, we believe this novel preparation method enables significant promotion of the application potential of PI aerogels and 3D printing.

Ultra‐lightweight 3D woven spacer integrated composites with stabilization of dielectric and robust mechanical properties at room and elevated temperatures

AbstractPolymer matrix composites with lightweight, low dielectric constant (ε) and dielectric loss tangent (tan δ), high‐temperature resistance, and excellent mechanical properties are urgently needed in the fields of aviation, aerospace, transportation, and wireless communication services. In this work, 3D woven spacer Kevlar/polyimide composites (3DKPC) with excellent dielectric properties and robust mechanical properties were designed and obtained by combining 3D weaving technology and thermal imidization process. Results show that the volume density of the prepared composites is as low as 0.24 g·cm−3, but its compressive strength can be up to 6.24 MPa. The dielectric constant and loss tangent of 3DKPC at room temperature are extremely low, with the value of ~1.32 and 6.9 × 10−3, respectively. Moreover, the compressive strength retention rate is more than 96% and the dielectric constant can be consistently lower than 1.36 when the temperature increases from 25 to 300°C, demonstrating the outstanding mechanical and dielectric stability of 3DKPC. In addition, as an application example of resulting composites, a microstrip antenna with 3DKPC as the substrate material was designed, followed by the simulation of its electromagnetic properties via High Frequency Structural Simulator. The results display that the gain of the microstrip antenna is 6.2 dB, which is superior to those of many other reported microstrip antennas, indicating that the 3DKPC proposed here has great application potential in aerospace, wireless communication, and other fields.

Synthesis of Sulfonated Copolyimides by Thermal Imidization for Efficient Lead Ion Adsorption from Aqueous Media

Synthesis of Sulfonated Copolyimides by Thermal Imidization for Efficient Lead Ion Adsorption from Aqueous Media

Laser Shock Fabrication of Nitrogen Doped Inverse Spinel Fe3O4/Carbon Nanosheet Film Electrodes towards Hydrogen Evolution Reactions in Alkaline Media

The reliable and cost-effective production of high-performance film electrodes for hydrogen evolution reactions remains a challenge for the laser surface modification community. In this study, prior to a thermal imidization reaction, a small number of Fe3O4 nanoparticles were vortexed into a poly(amic acid) (PAA) prepolymer, and the achieved flat composite film was then ablated by a 1064 nm fiber laser. After laser irradiation, the hierarchical architectures of carbon nanosheets decorated with Fe3O4 nanoparticles were generated. Although pure polyimide (PI) film and laser carbonized PI film, as well as bare Fe3O4, showcase poor intrinsic catalytic activity toward alkaline hydrogen evolution reactions, our laser-derived Fe3O4/carbon nanosheet hybrid film demonstrated enhanced electrocatalytic activity and stability in 1 M KOH electrolyte; the overpotential(η10) reached 247 mV when the current density was 10 mA cm−2 with a slight current decay in the chronoamperometric examination of 12 h. Finally, we proposed that the substitution of N to O in Fe−O sites of trans spinel structured magnetite would be able to modulate the free energy of hydrogen adsorption (ΔGH*) and accelerate water dissociation.

Synthesis, Characterization and Dynamic Mechanical Properties of Polyimide-Polyurea-Polysilsesquioxane Block Terpolymers

A novel type of polyurea-b-polyimide(PUI)-LPS terpolymer containing ladder like polysilsesquioxane (LPS) hybrid thin film was successfully prepared by coupling ladder-like polysilsesquioxane (LPS) with polyurea-b-poly(amide acid), followed solution film casting and thermal imidization. The LPS composed of mercapto and fluoride side groups was synthesized by sol–gel and monomer self-assembly methods. The structure and properties of the resulting PUI-LPS thin films were affected by the reaction conditions. Dynamic contact angles (DCA) and dynamic mechanical analysis (DMA) were used to study the surface energy and mechanical properties of PUI-LPS thin films. The presence of LPS containing fluoride and mercapto side groups significantly increased the extent of cyclodehydration (imidization) process at a relatively low temperature of about 150°C. The surface energy of the hybrid thin films was remarkably decreased as LPS concentration increased. The dynamic mechanical properties of the hybrid thin films were determined by dynamic mechanical analysis (DMA). Fourier transform infrared spectroscopy (FTIR) and Wide-angle X-ray diffraction (WAXRD) methods were used to study the composition and structure of the hybrid thin films

Comparison of Properties of Colorless and Transparent Polyimide Nanocomposites Containing Chemically Modified Nanofillers: Functionalized-Graphene and Organoclay.

Poly(amic acid) (PAA) was synthesized from dianhydride 4,4-(4,4-isopropylidenediphenoxy)bis(phthalic anhydride) and diamine bis [4-(3-aminophenoxy) phenyl] sulfone. Colorless and transparent polyimide (CPI) hybrid films were synthesized through thermal imidization after dispersing nanofillers using an intercalation method in a PAA solution. C16-GS and C16-MMT, in which hexadecylamine (C16) was substituted on graphene sheet (GS) and montmorillonite (MMT), respectively, were used as nanofillers to reinforce the CPI hybrid films. These two nanofillers were admixed in varying loadings of 0.25 to 1.00 wt%, and the morphology, thermal properties, and optical transparency of the hybrid films were investigated and compared. The results suggest that the thermal properties of the CPI hybrid films can be improved by adding only a small amount of nanofiller. Transmission electron microscopy results of the CPI hybrid film containing two types of fillers suggested that the fillers were well dispersed in the nano-size in the matrix polymer; however, some of the fillers were observed as agglomerated particles above the critical concentration of 0.50 wt%.

Potential of hydrophobic paper-based sorptive phase prepared by in-situ thermal imidization for the extraction of methadone from oral fluid samples

Paper-based sorptive phases (PSPs) are functional planar materials with a demonstrated potential in analytical sample preparation. This article describes the synthesis of a polyimide coated paper by an in-situ imidization at a high temperature. Polyimides (PI) are synthesized in two subsequent steps where a hydrophilic polymer, in this case, poly(amic acid) (PAA), is formed as an intermediate product. PAA is finally transformed into hydrophobic PI by thermal curing at 180 °C. The synthesis of PI-paper takes advantage of this two-step procedure. In the first stage, a segment of filter paper is immersed into an aqueous PAA solution. After the solvent evaporation, the paper is heated at 180 °C for 1 h inducing the formation of the hydrophobic PI over the cellulose fibers. Infrared spectroscopy has been used to characterize the synthesized materials by defining a coverage factor F. The hydrophobicity of the materials has been studied using an aqueous methylene blue solution as a marker. To fully demonstrate the usefulness of the material in the sample preparation field, the extraction of methadone from oral fluid (OF) samples has been considered as a model analytical problem. The main variables affecting the synthesis (PAA concentration on the precursor solution and number of dips) and the extraction (elution and extraction times) have been fully evaluated. Working under the optimum conditions, a limit of quantification of 9 µg/L, intraday and interday precision better than 14.6%, and accuracy in the range of 87–108% were obtained.