Surface modification of poly(tetrafluoroethylene) films by plasma polymerization of glycidyl methacrylate and its relevance to the electroless deposition of copper

Surface modification of poly(tetrafluoroethylene) films by plasma polymerization and deposition of glycidyl methacrylate (GMA) was carried out. The effects of glow‐discharge conditions on the chemical structure and composition of the deposited GMA polymer were analyzed by X‐ray photoelectron spectroscopy (XPS) and Fourier transform infrared (FTIR) spectroscopy. XPS and FTIR results revealed that the epoxide groups in the plasma‐polymerized GMA (pp‐GMA) layer had been preserved to various extents, depending on the plasma deposition conditions. The morphology of the modified PTFE surface was investigated by atomic force microscopy (AFM). The pp‐GMA film with well‐preserved epoxide groups was used as an adhesion promotion layer to enhance the adhesion of the electrolessly deposited copper on the PTFE film. The T‐peel adhesion test results showed that the adhesion strength between the electrolessly deposited copper and the pp‐GMA‐modified PTFE (pp‐GMA‐PTFE) film was much higher than that between the electrolessly deposited copper and the pristine or the Ar plasma‐treated PTFE film. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 3498–3509, 2000     

Poly(ether‐imide) and related sepiolite nanocomposites: investigation of physical,thermal, and mechanical properties

Novel poly(ether‐imide) and sepiolite nanocomposites were synthesized based on a unique diamine monomer with the aim of improving physical and mechanical properties of final polyimide films. The diamine was polycondensed with 4,4′‐(hexafluoroisopropylidene) diphthalic anhydride to produce related poly(ether amic acid) prepolymer. Pure poly(ether‐imide) and nanocomposite films were prepared via thermal imidization process of poly(ether amic acid). Coexistence of ether, pyridine, and phenylene functional groups in the diamine chemical structure resulted in flexible polyimide films with significant thermal, physical, and mechanical properties. Thermal stability, glass‐transition temperature, dimensional stability, and tensile properties of polymer and nanocomposites were studied and compared. Morphology of nanocomposites was also investigated using scanning and transmission electron microscopic methods to study the distribution and dispersion behavior of sepiolite nanofibers in the polyimide matrix. By introduction of sepiolite nanoparticles, overall improvement of properties was observed in respect to pure polyimides. Copyright © 2015 John Wiley & Sons, Ltd.     

Kinetic study of low‐temperature imidization of poly(amic acid)s and preparation of colorless,transparent polyimide films

Conventional synthesis of polyimides includes high‐temperature (160–350 °C) imidization of poly(amic acid)s. In the present work, imidization has been carried out at much lower temperatures (40–160 °C). 1,2,4,5,‐cyclohexanetetracarboxylic dianhydride (HPMDA) or pyromellitic dianhydride (PMDA) was polymerized with an aromatic diamine, 4,4′‐diaminodiphenylmethane (DDPM), to give poly(amic acid)s, which were then imidized chemically. Imidization was more than 90% complete even at the very low imidization temperature of 40 °C. It was found that the imidization occurs in two steps: an initial rapid cyclization and a subsequent slower cyclization. The activation energy for the rapid process was determined to be 4.3 kJ/mol, and that of the slower process, 4.8 kJ/mol. As the imidization temperature decreases, the transmittance of the resulting polyimides tends to gradually increase, the cutoff wavelength decreases and the color becomes pale. A partially aliphatic polyimide based on HPMDA and DDPM prepared at 40 °C yielded thin films that were highly transparent and colorless, and had good flexibility, solubility and thermal stability. The polyimide films prepared in this study may be good candidates for flexible, transparent plastic substrates in the display industry. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 1593–1602     

Surface structure of semicrystalline polyimide films

The surface structure of thin films based on poly[4,4′-bis(4″-N-phenoxy)diphenyl]amic acid of 1,3-bis(3′,4-dicarboxyphenoxy)benzene and the product of its thermal imidization—a semicrystalline polyimide—poly[4,4′-bis(4″-N-phenoxy)diphenyl]imide of 1,3-bis(3′,4-dicarboxyphenoxy)benzene—at various stges of thermal imidization and after melting and subsequent annealing has been studied by methods of transmission, scanning electron, and atomic force microscopies. The topological structure of the film surface has been described in terms of the discrete cluster model. Under heating to 200 and 280°C, a continuous network of the infinite cluster appears; subsequent annealing leads to disintegration of the network to discrete fragments that practically correspond to clusters in the starting poly(amic acid) film. The polyimide film heated to 280°C crystallizes in the form of needle crystals stable to the argon plasma. The surface morphology of polyimide films recrystallized from melt is of the spherulite character.     

Thermal imidization of poly(pyromellitic dianhydride-4,4′-oxydianiline) precursors on fluoropolymers modified by surface graft-copolymerization with glycidyl methacrylate

Composite films of polyimide (PI) and poly(tetrafluoroethylene-co-hexafluoropropylene) (FEP) or of PI and poly(tetrafluoroethylene) (PTFE) were prepared by thermal imidization of the poly(amic acid) (PAA) precursors of poly(pyromellitic dianhydride-4,4′-oxydianiline) (PMPA-ODA) on glycidyl methacrylate (GMA) graft-copolymerized FEP and PTFE films. The resulting PI/GMA-g-FEP and PI/GMA-g-PTFE composites exhibited T-peel adhesion strength of approximately 7.0 and 6.5 N/cm, respectively, compared to negligible adhesion strength for the laminates prepared from thermal imidization of the PAA on the pristine and the Ar plasma-treated FEP and PTFE films. X-ray photoelectron spectroscopy (XPS) results revealed that both the PI/GMA-g-FEP and PI/FEP-g-PTFE composite films delaminated by cohesive failure inside the FEP and PTFE films, respectively. The so-delaminated PI films with a covalently tethered FEP or PTFE surface layer were highly hydrophobic, having static water contact angles above 140°. The highly hydrophobic property depends on both the composition and roughness of the delaminated surface.     

In situ infrared spectroscopy study on imidization reaction and imidization-induced refractive index and thickness variations in microscale thin films of a poly(amic ester)

Poly(amic ester) (PAE) is a soluble precursor of polyimide that has attracted interest from both the microelectronic and the flat-panel display industries because of its several important advantages, including excellent solubility, high hydrolytic stability, and solvent-free film formation, over the polyimide precursor, poly(amic acid), for which monomer-polymer equilibration always occurs in solution due to its carboxylic acid groups. In this study, poly(3,4'-oxydiphenylene pyromellitamic diethyl ester) (PMDA-3,4'-ODA PAE) was chosen as a PAE precursor, and its thermal imidization behavior in microscale thin films was investigated quantitatively for the first time using time-resolved infrared (IR) spectroscopy. In addition, the variations of the film refractive index and thickness with temperature and time were determined in detail from the time-resolved IR spectra and are fully interpreted in this paper by considering the imidization kinetics of the precursor.     

Synthesis of novel hyperbranched polyimide for liquid crystal alignment

A novel hyperbranched polyimide (HPPI) was synthesized from a new four‐functional amine and 1,2,3,4‐cyclobutanetetracarboxylic dianhydride. The polyimide with hyperbranched structure exhibited excellent alignment for nematic liquid crystal (LC) compared with traditional linear polyimides. The solution viscosities of the poly(amic acids) (PAAs) and the surface morphology of PI films were investigated using an Ubbelhode‐type viscometer and atomic force microscopy, respectively. The viscosities of the hyperbranched PAAs were much lower than that of the linear PAA solution at any monomer ratio (amine:dianhydride). Pretilt angles of LCs above 2.8° were achieved with HPPI.     

Effect of carbon nanotubes and their dispersion on thermal curing of polyimide precursors

The process of thermal imidization reaction is significant for temperature and time control in the polyimide industry. Here, we report the effect of carbon nanotubes and their states of dispersion on the thermal imidization of the precursor films of polyimide (poly(amic acid)) for the first time. The curing process was followed by measuring Fourier transform-infrared (FT-IR) spectra, fluorescence spectra, thermogravimetric-differential scanning calorimeter (TG-DSC) properties and the refractive indices of films. It was found that by evenly dispersing 1 wt% of carbon nanotubes assisted by a dispersant in the poly(amic acid),the full imidization temperature of the polyimide can be reduced from 300 °C to 250 °C. Different states of distribution of CNTs were observed by light microscopy and scanning electron microscopy, and proved that a better dispersion of carbon nanotubes dramatically enhanced the speed of imidization. Moreover, the DSC results showed that lower decomposition temperature of poly(amic acid) could be obtained with more uniform distribution of carbon nanotubes, which means the process of cyclodehydration of the poly(amic acid) was accelerated.     

聚酰胺酸结构及其亚胺化的红外光谱分析

利用变温透射红外光谱方法,通过跟踪聚酰胺酸（PAA）的亚胺化过程,对由均苯四酸二酐和4,4′-二氨基二苯醚合成的聚酰胺酸及经过加热亚胺化后生成的聚酰亚胺(PI)的红外吸收光谱进行分析,对聚酰胺酸和聚酰亚胺的红外谱峰进行合理的归属,发现聚酰胺酸在亚胺化过程中有-COO-和-NH+2存在,-COO-中羰基的对称与反对称伸缩振动分别位于1607和1406 cm-1,NH+2的伸缩振动则有3200、3133、2938、2880、2820和2610 cm-1等多个精细谱带。 并根据对-COO-和-NH+2谱峰的归属,提出聚酰胺酸生成聚酰亚胺的机理为聚酰胺酸中COOH的H+转移到聚酰胺酸中的NH上,形成NH+2,然后脱水环化生成聚酰亚胺。     

Structure and properties of a photosensitive polyimide: Effect of photosensitive group

The photosensitive poly(p-phenylene biphenylteracarboximide) (BPDA-PDA) precursor was synthesized by attaching photocross-linkable 2-(dimethylamino)ethyl methacrylate (DMAEM) monomer to its poly(amic acid) through acid/base complexation. The polyimide thin films were prepared by a conventional cast/softbake/thermal imidization process from the photosensitive precursors with various concentrations of DMAEM. The structure and properties of the polyimide films were investigated by small-angle and wide-angle x-ray scattering, refractive indices and birefringence analysis, residual stress and relaxation analysis, stress-strain analysis, and dynamic mechanical thermal analysis. In comparison with the polyimide film from the poly(amic acid), the films, which were imidized from the photosensitive precursors, exhibited a better molecular order and microstructure; however, they exhibited less molecular orientation in the film plane. Despite the enhancement in both the molecular order and microstructure, the film properties (i.e., mechanical properties, thermal expansion, residual stress, optical properties, dielectric constant, and water sorption) degraded overall due to both the decrease in molecular in-plane orientation and the formation of microvoids caused by the bulky photosensitive group during thermal imidization. That is, on one hand, the PSPI precursor formation provides an advantageous, direct patternability to the BPDA-PDA precursor, and on the other hand, it results in degraded properties to the resulting polyimide film. © 1995 John Wiley & Sons, Inc.     

Controlled grafting of well-defined epoxide polymers on hydrogen-terminated silicon substrates by surface-initiated ATRP at ambient temperature

Controlled grafting of well-defined epoxide polymer brushes on the hydrogen-terminated Si(100) substrates (Si-H substrates) was carried out via the surface-initiated atom-transfer radical polymerization (ATRP) at room temperature. Thus, glycidyl methacrylate (GMA) polymer brushes were prepared by ATRP from the alpha-bromoester functionalized Si-H surface. Kinetic studies revealed a linear increase in GMA polymer (PGMA) film thickness with reaction time, indicating that chain growth from the surface was a controlled "living" process. The graft polymerization proceeded more rapidly in the dimethylformamide/water (DMF/H(2)O) mixed solvent medium than in DMF, leading to much thicker PGMA growth on the silicon surface in the former medium. The chemical composition of the GMA graft-polymerized silicon (Si-g-PGMA) surfaces were characterized by X-ray photoelectron spectroscopy (XPS). The fact that the epoxide functional groups of the grafted PGMA were preserved quantitatively was revealed in the reaction with ethylenediamine. The "living" character of the PGMA chain end was further ascertained by the subsequent growth of a poly(pentafluorostyrene) (PFS) block from the Si-g-PGMA surface, using the PGMA brushes as the macroinitiators.     

Structure and properties of polyimide films during a far‐infrared‐induced imidization process

The conversion of poly(amic acid) into polyimide (PI) was achieved with far‐infrared radiation (FIR) and conventional thermal treatments. The structure and properties of PI films during different stages of imidization were studied with Fourier transform infrared spectroscopy, weight‐loss analysis during imidization, tensile property measurements, and dynamic mechanical thermal analysis. The effects of the imidization degree, postimidization, and solvent on the thermal and mechanical properties of PI films were quantitatively investigated. The corresponding structural changes were also examined. The experimental results showed that the imidization process proceeded more quickly and more completely in an FIR oven than in a conventional oven. A prolonged FIR treatment at a lower temperature (25–100 °C) accelerated the imidization process. The tensile stress–strain curves had a fanlike distribution with the development of the FIR imidization process and a fishtail distribution with conventional thermal imidization. During FIR imidization, the best tensile properties were obtained at 340 °C, and thermooxidative degradation occurred at about 420 °C. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 2490–2501, 2004     

The effect of film thickness on the depth‐wise chain orientation of rod‐shaped polyimide

Controlling the chain orientation of polyimide is important because it affects the physical and electrical properties of the film. When a polyimide film is thick, the chain orientation has an inhomogeneous distribution along the thickness direction. In this study, poly(amic acids), the precursor of polyimide, with different coating thicknesses are dried, and the distribution of chain orientation in the thickness direction is investigated by measuring the residual solvent content with Raman spectroscopy. The effect of film thickness on the imidization rate is also studied by measuring the depth‐wise degree of imidization at the curing step. With the final cured polyimide film, the depth‐wise chain orientation is quantified by introducing the Fraser distribution function using polarized Raman spectroscopy. The thicker film has a lower degree of in‐plane orientation of polyimide chains, particularly near the substrate. This distribution of polyimide chain orientation in the thickness direction is similar to that of poly(amic acid) after drying. Fast imidization with higher solvent content for thick polyimide retards the formation of a well‐ordered structure with a high degree of in‐plane orientation. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2014 , 52, 848–857     

Surface Modification of Poly(tetrafluoroethylene) Films by Plasma Pre-Activation and Plasma Polymerization of Glycidyl Methacrylate

Surface modification of poly(tetrafuoroethylene) (PTFE) film by plasma polymerzation and deposition of glycidyl methacrylate (GMA), in the presence and absence of Ar or O₂ plasma pre-activation, was carried out to enhance the adhesion with polyimides (PI) film in the presence of an epoxy adhesive. For deposition carried out at low RF power, a high epoxide concentration was preserved in the plasma-polymerized GMA (pp-GMA) layer on PTFE (pp-GMA-PTFE). However, high adhesion strength of the PI/pp-GMA-PTFE laminate was obtained only in the presence of O₂ plasma pre-activation of the PTFE substrates prior to plasma polymerization and deposition of GMA. In the absence of any plasma pre-activation or in the presence of Ar plasma pre-activation, the deposited pp-GMA layer on the PTFE surface could be readily removed by solvent extraction. The adhesion enhancement of the PI/pp-GMA-PTFE laminates in the presence of O₂ plasma pre-activation was attributed to the preservation of the epoxide functional groups in the pp-GMA layer, the curing of the GMA chains into the matrix of the epoxy adhesive, and the covalent bonding of the pp-GMA layer on the PTFE surface.     

Effects of polymer architecture and composition on the adhesion of poly(tetrafluoroethylene).

Poly(glycidyl methacrylate), PGMA, chains in linear and arborescent structures were incorporated onto surfaces of poly(tetrafluoroethylene), PTFE, films by hydrogen plasma and ozone treatment and atom transfer radical polymerization. The epoxide groups of the PGMA chains were further reacted with acetic acid (AAc), oxalic acid (XAc), allyl amine (AA), and ethylenediamine (EDN) to introduce hydroxyl and amine groups to the surfaces of the PTFE films. Surface characterizations performed by Fourier Transform infrared attenuated total reflectance (FTIR-ATR) spectroscopy and X-ray photoelectron spectroscopy (XPS) confirmed the surface modification and the chemical structure. The PGMA chains in arborescent structures show a high effectiveness for the enhancement of the adhesion of PTFE films. The adhesion of PTFE films was also significantly enhanced by ring-opening reactions of the PGMA epoxide groups with acetic acid and amine compounds. A high value of 9.5 N cm(-1) in the optimum 180 degrees peel strength test was observed with PTFE/copper assemblies.     

Highly reflective and conductive double-surface-silvered polyimide films prepared from silver fluoride and BTDA/4,4'-ODA

This work focuses on surface silver metallization on a 3,3',4,4'-benzophenonetetracarboxylic dianhydride/4,4'-oxydianiline (BTDA/ODA)-based polyimide matrix via a direct ion-exchange self-metallization technique using a simple silver salt, silver fluoride, as the silver precursor. The method involves performing an ion-exchange reaction of damp-dry poly(amic acid) films in silver aqueous solution to form silver(I)-containing precursor films. Thermal treatment under tension converts the poly(amic acid) into polyimide and simultaneously reduces the silver(I) to silver(0), yielding silver layers with excellent reflectivity and conductivity on both film sides. However, significant property differences were exhibited on the upside and underside surfaces of the metallized films and this has been discussed in detail. The variation of surface properties and surface morphologies during the thermal curing cycle was also investigated. The mechanical and thermal properties of the metallized polyimide films are essentially similar to those of the host polyimide.     

Partially imidized poly[(amic ester)-alt-imide]: A novel polyimide pregursor

Partial imidization of poly[(amic ester)-alt-(amic acid)], a precursor for the “strictly alternating” copolyimides, was performed via selective chemical imidization of amic acid units in the copolymer precursor. The resulting, poly[(amic ester)-alt-imide], showed superior properties such as an excellent solution stability, good processibility and improved optical transparency, which are essential for the use as a precursor for the polyimide.     

In situ sol–gel fabrication of new poly(amide–ether–imide)/titania (TiO<Subscript>2</Subscript>) nanocomposite thin films containing <Emphasis Type="SmallCaps">l</Emphasis>-leucine moieties

In this study, the synthesis, morphology, and thermal properties of amino acid containing polyimide/titania nanohybrid films are investigated. At first, a chiral diamine containing l-leucine moieties in the structure (synthesized previously) was polymerized with 4,4′-oxydiphthalic anhydride in extremely dry conditions. Resulted poly(amic acid) (PAA) was mixed with a moisture-sensitive titania precursor (tetraethyl orthotitanate [Ti(OEt)₄]) and casted to a dust-free glass plate. The water derived from thermal imidization of PAA hydrolyzed Ti(OEt)₄ to titania nanoparticles with almost spherical shapes. The thermogravimetric analysis of various nanocomposites confirms the improvement in the thermal stability with the increase in the percentage of titania nanoparticle. The transmission electron microscopy of nanohybrid films with 3%, 5%, and 10% w/w of titania contents confirms well dispersion of nanoparticles in the polymer ground. The X-ray diffraction spectra showed that the titania contents have amorphous structure.     

Composite thin films of poly(phenylene oxide)/poly(styrene) and PPO/silver via vapor phase deposition

We report fabrication of thin (100～300 nm) poly(phenylene oxide) (PPO) films and their composites with poly (styrene) (PS) and silver (Ag) nanoparticles using a one‐step electron beam‐assisted vapor phase co‐deposition technique. Surface morphology and the structure of the deposited polymer thin film composites were characterized by FTIR, Raman, X‐ray spectroscopy, and contact angle measurements. As‐deposited PPO films and PPO/Ag composites were of porous nature and contrary to solvent casting techniques were free from nodular growth. In the case of PPO/PS thin film polymer composites, however, film morphology displayed nodular growth of PPO with nodule diameters of about ～200 nm and height of approximately 50 nm. Unique morphological changes on the porous PPO thin film surface were noticed at different Ag filling ratios. Further, the capacitance of PPO/Ag composites (<16 wt%) were measured under radio‐frequency conditions and they were functional up to 100 MHz with an average capacitance density of about 2 nF/cm². The fabricated PPO‐based composite systems are discussed for their potential applications including embedded capacitor technology. Copyright © 2008 John Wiley & Sons, Ltd.     

Controlled formation of optically reflective and electrically conductive silvered surfaces on polyimide film via a direct ion-exchange self-metallization technique using silver ammonia complex cation as the precursor

Double-surface-silvered polyimide films have been successfully fabricated using silver ammonia complex cation ([Ag(NH3)2]+) as the silver precursor and 3,3',4,4'-benzophenonetetracarboxylic dianhydride/4,4'-oxidianile- (BTDA/ODA-) based poly(amic acid) (PAA) as the polyimide precursor via a direct ion-exchange self-metallization technique. The process has been clarified to involve the loading of silver(I) into PAA via ion exchange, the thermally induced reduction of silver(I) to silver(0) and the concomitant imidization of PAA to polyimide upon thermal treatment, the subsequent silver-catalyzed and oxygen-assisted decomposition of the polyimide overlayer, and the self-accelerated aggregation of silver clusters on the film surface to produce well-defined surface silver layers. By employing [Ag(NH3)2]+ solution with a concentration of only 0.01 M and an ion-exchange time of no more than 10 min, the controlled formation of highly reflective and conductive silver surfaces upon thermal treatment at 300 degrees C for less than 4.5 h indicates that the present work provides an efficient route and an effacious silver species for polyimide surface metallization. Although the alkaline characteristics of [Ag(NH3)2]+ have a strong hydrolysis effect on the polyimide precursor chains, the final metallized films retain the key mechanical and thermal properties of the pure polyimide. Films were characterized by ATR-FTIR, XPS, ICP-AES, SEM, TEM, DSC, TGA, reflectivity, conductivity, and mechanical measurements.