Preparation of Nanoporous Polyimide Films from Poly(urethane‐imide) by Thermal Treatment

Nanoporous polyimide films were prepared in two steps. The first step is the preparation of poly(urethane‐imide) films by casting blend solutions containing various weight percentages of poly(amic acid) and phenol blocked polyurethane prepolymer (from 1,6‐hexamethylene diisocyanate and poly(ethylene glycol)). Three poly(amic acid)s were obtained from biphenyltetracarboxylic dianhydride (or) 2,2‐bis(3,4‐dicarboxyphenyl)hexafluoropropane dianhydride with 1,4‐phenylenediamine (or) 2,5‐dimethyl‐1,4‐phenylenediamine. Poly(urethane‐imide) films were characterized by density and surface energy measurements, AFM, DSC, TMA, mechanical properties and TGA. In the second step, these films were thermally treated above 300 °C to give nanoporous polyimide films. During thermal treatment, less thermally stable urethane domains decomposed, leaving porous polyimide films. The presence of pores was confirmed by scanning electron microscopy (SEM). The dielectric constant of the polyimide film was found to decrease with increasing amounts of urethane content.

A nanoporous polyimide film.     

Interpenetrating polymer network from castor oil-based polyurethanes and poly(methyl acrylate). XIV

Castor oil containing hydroxyl functionality was reacted with 4,4′-diphenylmethanediisocyanate under different stoichiometric ratios of NCO/OH to obtain liquid polyurethanes. These polyurethanes were subsequently interpenetrated with methyl acrylate monomer using ethylene glycol dimethacrylate as a crosslinker by radical polymerization using benzoyl peroxide as an activator. The polyurethane/poly(methyl acrylate) interpenetrating polymer networks (PU/PMA IPNs) were obtained as tough films by transfer molding techniques. All IPNs were characterized by their resistance to chemical reagents, optical properties, thermal behavior, and mechanical properties: tensile strength, Young's modulus, elongation at break (%) and hardness Shore A. The morphology of the IPNs was studied by scanning electron microscopy and dielectric properties: electrical conductivity (σ), dielectric constant (?′), dielectric loss (?″), and loss tangent (tan δ) at different temperatures.     

Synthesis and characterization of poly(urethane‐co‐imidine)s having pendent phenyl and benzylidene groups using bisphthalides,bislactones and blocked polyurethane prepolymers

Poly(urethane‐co‐imidine)s were prepared using amine blocked polyurethane (PU) prepolymer. The PU prepolymer was prepared by the reaction of poly(propylene glycol) (PPG₂₀₀₀) and 2,4‐tolylene diisocyanate (TDI) and end capped with N‐methyl aniline. The PU prepolymer was then reacted with bisphthalides and bislactones, until the evolution of carbon dioxide ceased. Polymerization reactions with bispthalides and bislactone took more time than with dianhydrides. Polymers were characterized by FTIR, GPC, TG and DSC analyses. Molecular weights of the poly(urethane‐co‐imidine)s were found to be lower than that of poly(urethane‐co‐imide)s. Compared to poly(urethane‐co‐imide)s all poly(urethane‐co‐imidine)s showed high glass transition temperature and crystallization peak in DSC. The thermal stability of the polyurethanes was found to increase with the introduction of imidine component. © 2001 Society of Chemical Industry     

Synthesis and characterization of polyimide/oligomeric methylsilsesquioxane hybrid films

In this study, polyimide/silsesquioxane hybrid materials were synthesized from aminoalkoxysilane‐capped poly(pyromellitic dianhydride‐co‐4,4′‐oxydianiline) (PMDA‐ODA) and oligomeric methylsilsesquioxane (O‐MSSQ) precursors. The O‐MSSQ moiety was used to obtain well characterized nano‐inorganic cage and network structures in the hybrid materials. The effects of molecular structures and composition on the morphologies and properties of the prepared hybrid materials were studied. The phase separation of the prepared hybrid materials could be controlled by varying the molecular weight of the polyimide moiety, the Si? OH end group content of the O‐MSSQ or the coupling agent. Homogeneous and transparent hybrid thin films were obtained from the low molecular weight polyimide moiety with a coupling agent, 3‐aminopropyltrimethoxysilane (APrTMS). However, microphase separation occurred if the molecular weight of the polyimide moiety was enhanced or was prepared without a coupling agent, as evidenced by atomic force microscopy (AFM), field emission scanning electron microscopy (FE‐SEM), and electron spectroscopy for chemical analysis (ESCA). The high Si? OH content of the O‐MSSQ could enhance the bonding density between the organic and inorganic moiety and thus retard phase separation. The thermal and mechanical properties of the prepared hybrid materials were largely improved compared with the parent polyimide, PMDA‐ODA, and were demonstrated by thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), and thermal‐stress analysis. The hybrid materials showed adjustable refractive index and dielectric constant by varying the O‐MSSQ content. The birefringence of the PMDA‐ODA was reduced by incorporating the O‐MSSQ moiety. This work revealed that the polyimide/O‐MSSQ hybrid materials could have potential applications as optical films or low dielectric constant materials. Copyright © 2004 Society of Chemical Industry     

Characteristics of the degradation and improvement of the thermal stability of poly(siloxane urethane) copolymers

This work investigates the characteristics of the thermal degradation of poly(ether urethane) (E‐PU) and poly(siloxane urethane) (S‐PU) copolymers by thermogravimetric analysis (TGA) and thermogravimetric analysis/Fourier transform infrared spectroscopy (TG–FTIR). The stage of initial degradation for E‐PU was demonstrated as a urethane‐B segment consisting of 4,4′‐diphenylmethane diisocyanate (MDI) and 1,4‐butanediol. Moreover, the urethane‐B segment in the copolymers had the lowest temperature of degradation (ca. 200°C). The degradation of E‐PU was determined by TGA and TG–FTIR analyses and had three stages including seven steps. Although the soft segment of S‐PU possessed the thermal stability of polydimethylsiloxane (PDMS), the unstable urethane‐B segment existed in S‐PU. Therefore, the initial degradation of S‐PU appeared around 210°C. The four stages of degradation of S‐PU involved eight steps, as revealed by TG–FTIR, which identified the main decomposition products: CO₂, tetrahydrofuran, and siloxane decomposition products. The imide group with high thermal stability was to replace the urethane‐B segment of S‐PU, which had the lowest thermal stability herein. The poly(siloxane urethane imide) (I‐PU) copolymer around 285°C exhibited a high initial temperature of degradation, and the initial degradation occurred at the urethane‐S segment consisting of MDI and PDMS. The degradation of I‐PU was similar to that of S‐PU and had four stages including six steps. Moreover, the degradation region of the imide group between 468 and 625°C was merged into the degradation stage of the siloxane decomposed products. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Correlation of residual stress and adhesion on copper by the effect of chemical structure of polyimides for copper‐clad laminates

BACKROUND: Polyimide films coated on copper are a potential new substrate for fabricating printed circuit boards; however, adhesion between the copper and polyimide films is often poor. The relations between residual stress and adhesion strength according to the development of molecular orientation of polyimide films with different chemical backbone structure coated on copper were studied. RESULTS: The effect of chemical structures on properties including the residual stress and the adhesion strength were widely investigated for four different polyimides. Diamine 4,4′‐oxydianiline (ODA) and dianhydrides 1,2,4,5‐benzenetetracarboxylic dianhydride (PMDA), 4′‐(hexafluoroisopropylidene)diphthalic anhydride (6FDA), 4,4′‐oxydiphthalic anhydride (ODPA) and 3,3′,4,4′‐benzophenone tetracarboxylic dianhydride (BTDA) were used to synthesize polyimide. In an attempt to quantify the interaction of thermal mismatch with the polyimide films depending on various structures, residual stress experiments between polyimide film and Cu? Si wafer were carried out over a range of 25–400 °C using in situ thin film stress analysis. A universal test machine was used to conduct 180° peel test (ASTM D903‐98) of polyimide film from cooper foil. The residual stress on Cu? Si (100) wafer decreased in the order 6FDA‐ODA > BTDA‐ODA > ODPA‐ODA > PMDA‐ODA, and the interfacial adhesion strength decreased in the order BTDA‐ODA (5 N mm^?2) > ODPA‐ODA > PMDA‐ODA > 6FDA‐ODA. The results may suggest that the morphological structure, degree of crystallinity of chain orientation and packing significantly relate to the residual stress and adhesion strength in polyimide films. Wide‐angle X‐ray diffraction was used for characterizing the molecular order and orientation and X‐ray photoelectron spectroscopy was used for the analysis of components on copper after polyimide films were detached to confirm the existence of copper oxide chemical bonding and to measure the binding energy of elements on the copper surface. CONCLUSION: In this research, it is demonstrated that BTDA‐ODA polyimide has a low residual stress to copper, good adhesion property, good thermal property and low dielectric constant. Therefore, BTDA‐ODA would be expected to be a promising candidate for a two‐layer copper‐clad laminate. Copyright © 2007 Society of Chemical Industry     

Synthesis and properties of novel poly(urethane‐imide) dispersions based on 2,2‐bis[N‐(3‐hydroxyphenyl)phthalimidyl]hexafluoropropane

Imide units are incorporated into thermoplastic and solvent‐based polyurethane (PU) chains to improve the thermal stability of PU. However, these poly(urethane‐imide) (PUI) materials have poor processablity and suffer from solvent emission. To prepare easily processable and environmentally friendly PUI products, some waterborne PUIs are synthesized using a prepolymer process. A series of PUI dispersions with 25 wt % solid content, viscosities of 7.5–11.5 cps, and particle sizes of 63–207 nm was prepared. The composition–property relationship of PUIs, including the solubility behavior of PUI cast films, and their thermal and mechanical properties were established. The solvent resistance and tensile strength of PUI film increased with the number of imide groups. All PUIs exhibited improved thermal stability but not char yield as the temperature increased. The inclusion of a little imide increased the decomposition temperature of PUI while maintaining the elasticity of the polymer, revealing successful translation of PUI into the water‐based form. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Thermal and mechanical properties of poly(urethane‐imide)/epoxy/silica hybrids

Improving properties of polyurethane (PU) elastomers have drawn much attention. To extend the properties of the modified PU composite, here a new method via the reaction of poly(urethane‐imide) diacid (PUI) and silane‐modified epoxy resin (diglycidyl ether of bisphenol A) was developed to prepare crosslinked poly (urethane‐ imide)/epoxy/silica (PUI/epoxy/SiO₂) hybrids with enhanced thermal stability. PUI was synthesized from the reaction of trimellitic anhydride with isocyanate‐terminated PU prepolymer, which was prepared from reaction of polytetramethylene ether glycol and 4,4′‐diphenylmethane diisocyanate. Thermal and mechanical properties of the PUI/epoxy/SiO₂ hybrids were investigated to study the effect of incorporating in situ SiO₂ from silane‐modified epoxy resin. All experimental data indicated that the properties of PUI/epoxy/SiO₂ hybrids, such as thermal stability, mechanical properties, were improved due to the existence of epoxy resin and SiO₂. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Mechanical,thermal, and electric properties of polyurethaneimide elastomers

Linear polyurethaneimide elastomers (PUI) were obtained from polyether- or polyester-diols, diphenylmethane diisocyanate or bitolylene diisocyanate and pyromellitic acid dianhydride. It was found that these polymers have considerably better mechanical properties than typical linear polyurethanes (PU). The elastic modulus and stress at break increase with contents of the hard polyimide segments. The softening temperatures and thermal stability of the PUI at 500°C were higher than the ones of PU with similar hard segment contents. Electric properties of PUI were close to the ones of conventional PU. It was shown that cellular PUI had considerably lower dielectric constant. T_g's of the soft segments PUI were less than T_g's corresponding to PU. It is connected with greater phase separation of the hard imide segments from the soft polyether– or polyester–urethane matrix.     

Hydroxyl‐terminated poly(urethane acrylate) as a soft liner in dental applications: Synthesis and characterization

Hydroxyl‐terminated poly(urethane acrylate)s were synthesized for use in biomedical applications. Acrylate end capping via an interesterification reaction was successfully achieved with methacryloyl chloride addition to the hydroxyl ends of the polyurethane at low temperatures. 2,4‐Toluene diisocyanate, 1,6‐hexane diisocyanate, and methylene diphenyl diisocyanate were used as diisocyanates for urethane synthesis, and they were end‐capped with methyl methacrylate and hydroxyethyl methacrylate. The nature of the monomers that we used had an effect on the thermal and morphological properties that were interpreted in terms of the level of hydrogen bonding and the degree of phase separation. The synthesized polymers were characterized by NMR, Fourier transform infrared/attenuated total reflectance spectroscopy, differential scanning calorimetry, thermogravimetric analysis, and gel permeation chromatography. The number‐average molecular weights of the poly(urethane acrylate)s were 2500–6000 g/mol. To use the polymer as a soft‐liner material in denture applications, the residual isocyanate should not exist. In this study, we showed that a prepolymer without residual isocyanate could be synthesized. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Silicon‐containing heterocyclic polymers and thin films made therefrom

Thin films, in the range of tens of micrometers thickness, have been prepared by casting onto glass plates the chloroform or N‐methylpyrrolidone solutions of polyimides or poly(imide‐amide)s containing silicon and phenylquinoxaline units in the main chain. The polymers have been synthesized by solution polycondensation reaction of aromatic diamines having preformed phenylquinoxaline rings with bis(3,4‐dicarboxyphenyl)dimethylsilane dianhydride or with a diacid chloride resulting from the reaction of this dianhydride with p‐aminobenzoic acid. The polymers were easily soluble in polar aprotic solvents and showed high thermal stability. The free‐standing films exhibited good mechanical properties with tensile strengths in the range of 48–86 MPa, tensile modulus in the range of 1.25–2.22 GPa and elongation at break in the range of 3–37%. Electrical insulating properties of some polymer films were evaluated on the basis of dielectric constant and dielectric loss and their variation with frequency and temperature. The values of the dielectric constant at 10 kHz were in the range of 2.94–3.08 for polyimides and 3.89–4.49 for poly(imide‐amide)s. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 3062–3068, 2006     

The effect of curing history on the residual stress behavior of polyimide thin films

The effect of curing history on the residual stress behaviors in semiflexible structure poly(4,4′‐oxydiphenylene pyromellitimide) (PMDA–ODA) and rigid structure poly(p‐phenylene biphenyltetracarboximide) (BPDA–PDA) polyimide was investigated. Depending upon the curing history and different structures of polyimide, the residual stress behaviors and the morphology of polyimide thin films were detected in situ by using a wafer bending technique and wide angle X‐ray diffraction (WAXD), respectively. For the rigid structure BPDA–PDA polyimide, the residual stress and the slope decreased from 11.7 MPa and 0.058 MPa/°C to 4.2 MPa and 0.007 MPa/°C as the curing temperature increased, and the annealing process is done. However, for the semiflexible structure PMDA–ODA, the change of the residual stress and the slope was relatively not significant. In addition, it was found that the cured polyimide prepared at a higher temperature with a multistep curing process showed a higher order of chain in‐plain orientation and packing order than does the polyimide film prepared at a lower temperature with a one‐step curing process. These residual stress behaviors of polyimide thin films show good agreement with WAXD results, such as polyimide chain order, orientation, and intermolecular packing order, due to curing history. Specifically, it shows that the effect of curing history on residual stress as well as morphological change was significant in rigid BPDA–PDA polyimide but, not in semiflexible PMDA–ODA polyimide. Therefore, it suggests that the morphological structure depends upon curing history, and the polyimide backbone structure might be one of important factors to lead the low residual stress in polyimide thin films. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 3287–3298, 1999     

Morphology and properties of poly(benzoxazine‐co‐urethane)s based on bisphenol‐S/aniline benzoxazine

Poly(benzoxazine‐co‐urethane) was prepared by melt‐blending bisphenol‐S/aniline‐type benzoxazine (BS‐a) with isocyanate‐terminated polyurethane (PU) prepolymer based on 2,4‐toluene diisocyanate and poly(ethylene glycol), followed by thermally activated polymerization of the blend. The copolymerization reaction between BS‐a and PU prepolymer was monitored using Fourier transform infrared spectroscopy. The morphology, dynamic mechanical properties, and thermal stability of the poly(benzoxazine‐co‐urethane) were studied using scanning electron microscopy, dynamic mechanical analysis, and thermogravimetry. Homogeneous morphology is shown in scanning electron micrographs of the fracture surfaces of poly(benzoxazine‐co‐urethane)s with different urethane weight fractions, and the roughness of the surface increases with urethane content increasing. Correspondingly, a single glass transition temperature (T_g) is shown on the dynamic mechanical analysis curves of the poly(benzoxazine‐co‐urethane)s, and the T_g is higher than that of the polybenzoxazine. With increase in the urethane content, the T_g and water absorption of poly(benzoxazine‐co‐urethane) increase, whereas the storage modulus and thermal stability decrease. POLYM. ENG. SCI., 53:2633–2639, 2013. © 2013 Society of Plastics Engineers     

Facile modifications of polyimide via chloromethylation: II. Synthesis and characterization of thermocurable transparent polyimide having methylene acrylate side groups

From chloromethylated polyimide, a useful starting material for modification of aromatic polyimides, a thermocurable transparent polyimide having acrylate side groups was prepared. In the presence of 1,8‐diazabicyclo[5,4,0]undec‐7‐ene, chloromethylated polyimide was esterified with acrylic acid to synthesize poly(imide methylene acrylate). The polymer was soluble in organic solvent, which makes it possible to prepare a planar film by spin coating. The polymer film became insoluble after thermal treatment at 230 °C for 30 min. Optical transparency of the film at 400 nm (for 1 µm thickness) was higher than 98 % and not affected by further heating at 230 °C for 250 min. Adhesion properties measured by the ASTM D3359‐B method ranged from 4B to 5B. Preliminary results of planarization testing showed a high degree of planarization (DOP) value (>0.53). These properties demonstrate that poly(imide methylene acrylate) could be utilized as a thermocurable transparent material in fabricating display devices such as TFT‐LCD. Copyright © 2004 Society of Chemical Industry     

Residual stress and mechanical properties of polyimide thin films

Four different structure polyimide thin films based on 1,4‐phenylene diamine (PDA) and 4,4′‐oxydianiline (ODA) were synthesized by using two different dianhydrides, pyromellitic dianhydride (PMDA) and 3,3′,4,4′‐biphenyltetracarboxylic dianhydride (BPDA), and their residual stress behavior and mechanical properties were investigated by using a thin film stress analyzer and nanoindentation method. The residual stress behavior and mechanical properties were correlated to the morphological structure in polyimide films. The morphological structure of polyimide thin films was characterized by X‐ray diffraction patterns and refractive indices. The residual stress was in the range of ?5 to 38 MPa and increased in the following order: PMDA‐PDA < BPDA‐PDA < PMDA‐ODA < BPDA‐ODA. The hardness of the polyimide films increased in the following order: PMDA‐ODA < BPDA‐ODA < PMDA‐PDA < BPDA‐PDA. The PDA‐based polyimide films showed relatively lower residual stress and higher hardness than the corresponding ODA‐based polyimide films. The in‐plane orientation and molecularly ordered phase were enhanced with the increasing order as follows: PMDA‐ODA < BPDA‐ODA < BPDA‐PDA ～ PMDA‐PDA. The PDA‐based polyimides, having a rigid structure, showed relatively better‐developed morphological structure than the corresponding ODA‐based polyimides. The residual stress behavior and mechanical properties were correlated to the morphological structure in polyimide films. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Synthesis and characterization of polyurethane urea acrylates: Effects of the hard segments structure

A series of poly(ester‐urethane‐urea) acrylates were synthesized using poly(ethylene adipate) diol (PEA), 4,4′‐diphenyl methane diisocyanate (MDI), different diamines and acrylic acid. On the basis of IR, stress–strain, thermogravimetric, and differential scanning calorimetry measurements of their cured materials, relations between their structure and physical properties were investigated systematically. The properties were compared with a polyurethane acrylate (PUA) elastomer in which the variable was the diamine modification. The mechanical analysis indicated that, when the short chain of diamine was used, the strength and strain at break of the polymer was enhanced. The thermal stability and the glass transition of PUA increased with increased of diamine chain. The crosslinking process depresses crystallization of the soft segments and can be used to obtain protective films and finishing materials for the leather industry. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007     

Phthalonitrile‐containing poly(amide imide)s with nanoactuation properties

A series of aromatic poly(amide imide)s containing pendant phthalonitrile groups was prepared by solution polycondensation reaction of 4,4′‐diamino‐4″‐(3,4‐dicyanophenoxy)triphenylmethane, 1, or of different amounts of 1 and 1,3‐bis(4‐aminophenoxy)benzene, with a fluorinated imide diacid chloride, 2,2‐bis[N‐(4‐chloroformylphenyl)phthalimidyl]hexafluoroisopropane. The polymers were easily soluble in polar organic solvents, such as N‐methyl‐2‐pyrrolidone, N,N‐dimethylacetamide, N,N‐dimethylformamide, and dimethylsulfoxide. They can be cast from solutions into thin flexible films showing nanoactuation properties in the range of 120–450 nm, depending on the nitrile group content, when an electric voltage is applied on their surface. Electrical insulating properties of the polymer films were evaluated on the basis of dielectric permittivity and dielectric loss and their variation with the frequency and temperature. The values of the dielectric permittivity at 10 kHz and 20°C were in the range of 3.01–3.43. All polymers exhibited high thermal stability, decomposition temperature being above 420°C. POLYM. ENG. SCI., 2013. © 2012 Society of Plastics Engineers     

High performance poly(urethane-imide) prepared by introducing imide blocks into the polyurethane backbone

A series of novel linear poly(urethane-imide)s were synthesized by the reaction between isocyanate-terminated polyurethane (PU) prepolymer and amine- or anhydride-terminated oligoimide. PU prepolymer was synthesized by reacting polyethylene adipatediol of molecular weight 1000 with tolylene-2,4-diisocyanate at the molar ratio of 2:3 or 1:2. Oligoimide was synthesized from the reaction of 4,4′-(hexafluoroisopropylidene)diphthalic acid with 4,4′-oxydianiline at various molar ratios. Equimolar amounts of PU prepolymer and oligoimide were reacted in N-methyl-2-pyrrolidone, followed by casting on glass plates and heat treatment at 100 and 150 °C for 1 h each to give linear poly(urethane-imide)s as transparent yellowish brown films. Poly(urethane-imide) films with less of 30% of imide component became elastomer, and films with more than 36% imide component became plastic. The effects of end-groups of oligoimide, molecular weight of oligoimide, and molecular weight of PU prepolymer on the solvent resistance, the tensile properties, viscoelastic properties, and thermogravimetric properties of poly(urethane-imide) films were systematically examined. Solvent resistance and tensile modulus of poly(urethane-imide) films from amine-terminated oligoimides were better than those from anhydride-terminated oligoimides. On the other hand, thermal stability and elongation at break for the poly(urethane-imide) films from anhydride-terminated oligoimides were higher than those from amine-terminated oligoimides.     

Preparation and properties of poly(siloxane‐ether‐urethane)‐acrylic hybrid emulsions

Poly(siloxane‐ether‐urethane)‐acrylic (PU‐AC) hybrid emulsions were prepared by introducing different hydroxyethoxypropyl‐terminated polydimethylsiloxane (PDMS) content into the acrylic‐terminated poly(ether‐urethane) backbone and then in situ copolymerizing with methyl methacrylate and butyl acrylate via emulsion process. The effects of PDMS on the particle size and viscoelastic behavior of the hybrid emulsions were investigated. Meanwhile, the hydrogen bonding, mechanical and thermal mechanical properties, water resistance, the surface gloss, and wettability of the resultant hybrid films were also studied. The results showed that all the hybrid emulsions showed shear‐thinning behaviors, and the introduction of PDMS resulted in the formation of the hybrid emulsions with increased average particle size and decreased viscosity. The chemical bonds built between PU and AC yielded higher than 73% crosslinking fraction in all the hybrid materials, but this value decreased with increasing PDMS content because PDMS reduced the hydrogen bonding interactions and enhanced the phase separation. As a result, an increase in the PDMS content led to an increase in the elongation, water resistance, surface roughness, and water hydrophobic of the films, but the tensile strength, hardness, storage modulus, and glass transitions temperature decreased. It is suggested that introduction of PDMS can provide the hybrid materials with the improved flexibility, water resistance, and surface hydrophobicity, which has potential application value in the fouling‐release coatings, biomaterials, and surface fishing. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44927.     

Synthesis and characterization of polyimide–silica nanocomposites using novel fluorine‐modified silica nanoparticles

Polyimide–silica nanocomposites were synthesized with 4,4′‐oxydianiline, 4,4′‐(4,4′‐isopropylidenediphenoxy)bis(phthalic anhydride), and fluorine‐modified silica nanoparticles. Fluorinated precursors such as 4″,4?‐(hexafluoroisopropylidene)bis(4‐phenoxyaniline) (6FBPA) and 4,4′‐(hexafluoroisopropylindene)diphenol (BISAF) were employed to modify the surface of the silica nanoparticles. The microstructures and thermal, mechanical, and dielectric properties of the polyimide–silica nanocomposites were investigated. An improvement in the thermal stability and storage modulus of the polyimide nanocomposites due to the addition of the modified silica nanoparticles was observed. The microstructures of the polyimide–silica nanocomposites containing 6FBPA‐modified silica exhibited more uniformity than those of the nanocomposites containing BISAF‐modified silica. The dielectric constants of the polyimide were considerably reduced by the incorporation of pristine silica or 6FBPA‐modified silica but not BISAF‐modified silica. The addition of a modifier with higher fluorine contents did not ensure a lower dielectric constant. The uniformity of the silica distribution, manipulated by the reactivity of the modifier, played an important role in the reduction of the dielectric constant. Using 6FBPA‐modified silica nanoparticles demonstrated an effective way of synthesizing low‐dielectric‐constant polyimide–silica nanocomposites. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 882–890, 2007