Surface modification of poly(tetrafluoroethylene) by a low-temperature cascade arc torch and radio-frequency plasmas

Poly(tetrafluoroethylene) (PTFE) films were treated with a low-temperature cascade arc torch (LTCAT) and radio-frequency (RF) plasmas of argon and hydrogen. The plasma-treatment effect on the PTFE surface was studied with contact-angle measurement and scanning electron spectroscopy (SEM). LTCAT argon plasma, which is recognized as a beam of excited argon neutrals, was very efficient at improving the surface hydrophilicity of PTFE. For both the LTCAT and RF operation, argon plasma was more effective at modifying the surface wettability of PTFE films than hydrogen plasma was. Furthermore, the sample positions (inside or beyond the glow region) had a strong impact on the efficiency of the plasma treatment. SEM surface images indicated that no significant morphology change was induced on the PTFE films exposed to a LTCAT and RF argon plasmas. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 4432–4441, 1999     

Characterization of thin polymer‐like films formed by plasma polymerization of methylmethacrylate: A neutron reflectivity study

The microstructure of the plasma‐polymerized methylmethacrylate (ppMMA) films is characterized using neutron reflectivity (NR) as a function of the plasma reaction time or film thickness. Variation in the crosslink density normal to the substrate surface is examined by swelling the film with a solvent, d‐nitrobenzene (dNB). In the presence of dNB, uniform swelling is observed throughout the bulk as well as at the air surface, and silicon oxide interfaces. The results indicate that the MMA film prepared by plasma polymerization (ppMMA) has a uniform crosslink density from air surface to substrate surface. Additionally, the scattering length density of the plasma‐polymerized MMA film (SLD ≈ 0.750 × 10⁻⁶ Å⁻²) is much lower than that of a conventional PMMA film (SLD = 1.177 × 10⁻⁶ Å⁻²). The increase in film thickness following dNB sorption is 7.5% and at least 36% for the ppMMA and PMMA films, respectively. This suggests that the films formed by plasma polymerization are different from conventional polymers in chemical structure. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 2522–2530, 2004     

Selective surface modification of polymers by means of hydrogen and oxygen plasmas

An ESCA investigation has been made of the changes in surface functionalization for a series of polymers effected by means of low-powered inductively coupled rf plasmas excited in hydrogen and oxygen. Reactions in each case are confined to the outermost surfaces of the polymer films and the use of oxygen plasmas leads to extensive oxidative functionalization. Bisphenol-A polycarbonate and polyethylene terephthalate exhibit similar overall reactivities to both oxygen and hydrogen plasmas, while polystyrene is shown to be substantially more reactive than high-density polyethylene to the plasma treatments of interest in this work. Comparison has been made of the effects of straight hydrogen and oxygen plasmas and of sequential hydrogen/oxygen and oxygen/hydrogen plasma treatments.     

Polymérisation de monomères organiques dans des plasmas froids—I. Polymérisation de monomères acryliques déposés en couches minces

One of the applications of cold plasmas in macromolecular chemistry is the polymerization of high molecular weight acrylates in the solid or liquid phase. The reaction is controlled by several parameters (monomer functionality, power of irradiation, nature of the gas used to generate the plasma). The polymerization speed decreases with increasing monomer functionality. The strength of the electric discharge controls the creation of active species and consequently the striking speed. Polymerization speed increases with power but with a maximum depending on the type of the monomer and the nature of the ambient gas. The kinetics are affected by the gas nature (oxygen and carbon dioxide inhibit polymerization). The film surface can be degraded with incorporation of gas atoms. For instance, an argon plasma creates surface sites favourable to later oxidation. In freon 14 plasmas, the formation of C-F bonds can be observed.     

Ring‐opening polymerization of L‐lactide by rare‐earth tris(4‐tert‐butylphenolate) single‐component initiators

The ring‐opening polymerization of L ‐lactide initiated by single‐component rare‐earth tris(4‐tert‐butylphenolate)s was conducted. The influences of the rare‐earth elements, solvents, temperature, monomer and initiator concentrations, and reaction time on the polymerization were investigated in detail. No racemization was found from 70 to 100 °C under the examined conditions. NMR and differential scanning calorimetry measurements further confirmed that the polymerization occurred without epimerization of the monomer or polymer. A kinetic study indicated that the polymerization rate was first‐order with respect to the monomer and initiator concentrations. The overall activation energy of the ring‐opening polymerization was 79.2 kJ mol^?1. ¹H NMR data showed that the L ‐lactide monomer inserted into the growing chains with acyl–oxygen bond cleavage. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 6209–6215, 2004     

Methane plasma polymerization by low‐temperature cascade arc discharge for enhanced adhesion of primer to thermoplastic olefins

Improvement of primer adhesion to thermoplastic olefins (TPOs) by methane plasma polymerization with a low‐temperature cascade arc discharge was investigated. Methane plasma with a low‐temperature cascade arc plasma torch can be used for improving the primer adhesion to TPOs. Tape‐adhesion tests (ASTM 3359‐92a method) demonstrated this improvement, with a rating of 0 for untreated TPOs and 5 for methane plasma‐polymerized TPOs at certain plasma conditions even for aging at 60 °C and 80% relative humidity for 5 days. The adhesion to primer for the soft, flexible TPOs (ETA‐3041c and ETA‐3101) was easily enhanced. The adhesion to primer for the hard and brittle TPOs (ETA‐3183) needs to optimize the plasma conditions to pass the dry‐ and wet‐adhesion test with methane plasmas. To relate the surface characteristics of methane plasma‐polymerized TPOs to adhesion performance with primer, the wettability and polarity of TPOs were evaluated by the contact‐angle measurements of primer and deionized water to TPOs. TPO surface morphology was evaluated with scanning electron microscopy. The surface composition was characterized with electron spectroscopy for chemical analysis. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 2004–2021, 2003     

Free‐radical polymerization of dioxolane and dioxane derivatives: Effect of fluorine substituents on the ring opening polymerization

Partially fluorinated and perfluorinated dioxolane and dioxane derivatives have been prepared to investigate the effect of fluorine substituents on their free‐radical polymerization products. The partially fluorinated monomer 2‐difluoromethylene‐1,3‐dioxolane (I) was readily polymerized with free‐radical initiators azobisisobutyronitrile or tri(n‐butyl)borane–air and yielded a vinyl addition product. However, the hydrocarbon analogue, 2‐methylene‐1,3‐dioxolane (II), produced as much as 50% ring opening product at 60 °C by free‐radical polymerization. 2‐Difluoromethylene‐4‐methyl‐1,3‐dioxolane (III) was synthesized and its free‐radical polymerization yielded ring opening products: 28% at 60 °C, decreasing to 7 and 4% at 0 °C and −78 °C, respectively. All the fluorine‐substituted, perfluoro‐2‐methylene‐4‐methyl‐1,3‐dioxolane (IV) produced only a vinyl addition product with perfluorobenzoylperoxide as an initiator. The six‐membered ring monomer, 2‐methylene‐1,3‐dioxane (V), caused more than 50% ring opening during free‐radical polymerization. However, the partially fluorinated analogue, 2‐difluoromethylene‐1,3‐dioxane (VI), produced only 22% ring opening product with free‐radical polymerization and the perfluorinated compound, perfluoro‐2‐methylene‐1,3‐dioxane (VII), yielded only the vinyl addition polymer. The ring opening reaction and the vinyl addition steps during the free‐radical polymerization of these monomers are competitive reactions. We discuss the reaction mechanism of the ring opening and vinyl addition polymerizations of these partially fluorinated and perfluorinated dioxolane and dioxane derivatives. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 5180–5188, 2004     

Surface characterization of plasma‐modified poly(ethylene terephthalate) film surfaces

Poly(ethylene terephthalate) (PET) film surfaces were modified by argon (Ar), oxygen (O₂), hydrogen (H₂), nitrogen (N₂), and ammonia (NH₃) plasmas, and the plasma‐modified PET surfaces were investigated with scanning probe microscopy, contact‐angle measurements, and X‐ray photoelectron spectroscopy to characterize the surfaces. The exposure of the PET film surfaces to the plasmas led to the etching process on the surfaces and to changes in the topography of the surfaces. The etching rate and surface roughness were closely related to what kind of plasma was used and how high the radio frequency (RF) power was that was input into the plasmas. The etching rate was in the order of O₂ plasma > H₂ plasma > N₂ plasma > Ar plasma > NH₃ plasma, and the surface roughness was in the order of NH₃ plasma > N₂ plasma > H₂ plasma > Ar plasma > O₂ plasma. Heavy etching reactions did not always lead to large increases in the surface roughness. The plasmas also led to changes in the surface properties of the PET surfaces from hydrophobic to hydrophilic; and the contact angle of water on the surfaces decreased. Modification reactions occurring on the PET surfaces depended on what plasma had been used for the modification. The O₂, Ar, H₂, and N₂ plasmas modified mainly CH₂ or phenyl rings rather than ester groups in the PET polymer chains to form C? O groups. On the other hand, the NH₃ plasma modified ester groups to form C? O groups. Aging effects of the plasma‐modified PET film surfaces continued as long as 15 days after the modification was finished. The aging effects were related to the movement of C?O groups in ester residues toward the topmost layer and to the movement of C? O groups away from the topmost layer. Such movement of the C?O groups could occur within at least 3 nm from the surface. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 3727–3740, 2004     

Optical emission diagnostics in cascade arc plasma polymerization and surface modification processes

Optical Emission Spectroscopy (OES) was used to identify reactive species and their excitation states in low-temperature cascade arc plasmas of N₂, CF₄, C₂F₄, CH₄, and CH₃OH. In a cascade arc plasma, the plasma gas (argon or helium) was excited in the cascade arc generator and injected into a reactor in vacuum. A reactive gas was injected into the cascade arc torch (CAT) that was expanding in the reactor. What kind of species of a reactive gas, for example, nitrogen, are created in the reactor is dependent on the electronic energy levels of the plasma gas in the cascade arc plasma jet. OES revealed that no ion of nitrogen was found when argon was used as the plasma gas of which metastable species had energy less than the ionization energy of nitrogen. When helium was used, ions of nitrogen were found. While OES is a powerful tool to identify the products of the cascade arc generation (activation process), it is less useful to identify the reactive species that are responsible for surface modification of polymers and also for plasma polymerization. The plasma surface modification and plasma polymerization are deactivation processes that cannot be identified by photoemission, which is also a deactivation process. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 1583–1592, 1998     

Plasma copolymerization: Hexafluoropropylene and a nonpolymerizable gas

Plasma polymerized (PP) fluoropolymer films have been synthesized by the plasma copolymerization of hexafluoropropylene (HFP) and a nonpolymerizable gas. Plasma etching was inhibited by fluorine scavenging and HF formation on the addition of hydrogen and was accelerated on the addition of oxygen. Nitrogen, oxygen, and hydrogen were incorporated into the deposited polymer molecules when added to the HFP plasma. The polar component of surface tension increased on nitrogen addition and the dispersive component on hydrogen addition. The higher surface tension drove the deposition and coalescence of smaller particles from the gas phase polymerization yielding smooth surfaces. The significant drop in breakdown voltage on the addition of nitrogen was attributed to a different conduction mechanism in the relatively polar PP fluoropolymer film. © 1996 John Wiley & Sons, Inc.     

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     

Preparation of the polymer–clay nanocomposites in exfoliated state by interface stabilization

To suppress the repulsive interfacial energy between hydrophilic clay and a hydrophobic polymer matrix for polymer–clay nanocomposites, a third component of amphiphilic nature such as poly(?‐caprolactone) (PCL) was introduced into the styrene–acrylonitrile copolymers (SAN)/Na‐montmorillonite system. Once ?‐caprolactone was polymerized in the presence of Na‐montmorillonite, the successful ring‐opening polymerization of ?‐caprolactone and the well‐developed exfoliated structure of PCL/Na‐montmorillonite mixture were confirmed. Thereafter, SAN was melt‐mixed with PCL/Na‐montmorillonite nanocomposite, and the SAN matrix and PCL fraction were completely miscible to form a homogeneous mixture with retention of the exfoliated state of Na‐montmorillonite, exhibiting that PCL effectively stabilizes the repulsive polymer–clay interface and contributes to the improvement of the mechanical properties of nanocomposites. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 246–252, 2004     

Nitrogen plasma modification on polyimide films for copper metallization on microelectronic flex substrates

Surface modification of polyimide films Kapton E(N) and Upilex S by nitrogen plasmas were investigated for their enhanced adhesion strength with sputtered coppers. Peel tests demonstrate this improvement, with peel strengths of 7 and 12 N/m for unmodified Kapton E(N) and Upilex S, and 1522 and 1401 N/m for nitrogen plasma‐modified Kapton E(N) and Upilex S at certain plasma conditions. Atomic force microscopy (AFM) and the sessile drop method indicated the surface roughness, and the surface energy of polyimide films were highly increased by nitrogen plasmas. This study shows the enhanced adhesion strengths of polyimide films with sputtered coppers by nitrogen plasmas, and these nitrogen plasmas were strongly affected by the surface characteristics of polyimide films. Electron spectroscopy for chemical analysis (ESCA) observed the increased surface energy on polyimide films by nitrogen plasmas was due to the increased surface composition of O and the increased chemical bond of C? O. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 2023–2038, 2005     

Dimethylketene: Plasma-generated gas-phase precursor of photoluminescence chromophores in plasma polymerized films of methyl methacrylate and tetramethyl-1,3-cyclobutanedione

Gas-phase chemistry of tetramethyl-1,3-cyclobutanedione (TMCB) and formaldehyde plasmas have been studied within situ Fourier Transform Infrared (FTIR) Spectroscopy. Our previous work indicated that methyl methacrylate (MMA) dissociates to intermediate species of dimethylketene (DMK) and formaldehyde in MMA plasmas. This investigation of DMK dimer (TMCB) and formaldehyde plasmas is a continuation of our effort to understand the plasma polymerization chemistry of MMA. FTIR spectra confirmed the presence of DMK in TMCB plasmas and a polymeric thin film was deposited. Formaldehyde plasmas did not deposit any film for our experimental condition. Furthermore, plasma polymerized TMCB (PPTMCB) films exhibit UV photoluminescence similar to that of PPMMA films. Therefore, DMK is proposed to be the gas-phase precursor of photoluminescence chromophores in both PPMMA and PPTMCB films. Paper based on the results presented during the workshop of the Engineering Research Center for Plasma-Aided Manufacturing held in Madison, Wisconsin, in Spring 1996.     

Surface characterization and properties of plasma‐modified cyclic olefin copolymer/layered silicate nanocomposites

In this study, cyclic olefin copolymer (COC)/layered silicate nanocomposites (CLSNs) were prepared by the intercalation of COC polymer into organically‐modified layered silicate through the solution mixing process. Both X‐ray diffraction data and transmission electron microscopy images of CLSNs indicate most of the swellable silicate layers were disorderedly intercalated into the COC matrix. The effect of layered silicate on the mechanical and barrier properties of the fabricated nanocomposites shows significant improvements in the storage modulus and water permeability when compared with that of neat COC matrix. Surfaces of COC and CLSN films were modified by a mixture of oxygen (O₂) and nitrogen (N₂) plasmas with various treated times, system pressures, and radio frequency (RF) powers. The surfaces of plasma‐modified COC and CLSN were investigated using scanning probe microscopy and contact‐angle measurements. The exposure of the COC and CLSN film to the plasmas led to the combination of etching reactions of polymer surface initiated by plasma and the following addition reactions of new functional groups onto polymer surfaces to change the topology of COC film surfaces. The surface roughness was closely related to how high and how long the RF power was input into the system. The plasmas also led to changes in the surface properties of the CLSN surfaces from hydrophobic to hydrophilic; and the contact angle of water on the surface decreases. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 2745–2753, 2005     

Measurement of the dissolved oxygen concentration in acrylate monomers with a novel photochemical method

Because of the well‐known radical‐scavenging behavior, molecular oxygen is capable of inhibiting free‐radical chain polymerizations of unsaturated monomers. The deleterious effects of diffused oxygen in a polymerization system result in both a reduced polymerization rate and the loss of surface properties of a polymer film or coating. However, reliable data for oxygen concentration in organic monomers are relatively scarce because of the experimental and instrumental limitations of the commercially available techniques. In this study, a photochemical method was developed and was used to obtain the dissolved oxygen concentration in seven acrylate monomers. The principle of the method was to convert ground‐state molecular oxygen dissolved in monomer to the excited, singlet‐state oxygen and then react the singlet oxygen with a third compound (singlet oxygen trapper). By monitoring the concentration of this singlet oxygen trapper spectrophotometrically, the concentration of dissolved oxygen can be obtained with the established stoichiometry for the reaction between singlet oxygen and trapper. The singlet oxygen concentrations in the acrylate monomers varied from 0.59 to 2.07 × 10^?3 mol/L, depending on the monomer structure. The strategies and considerations for generalizing the method to other systems, including highly oxygenated organics, are discussed. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 1285–1292, 2004     

Characterization of large molecular weight ester‐functionalized norbornene and hydroxylated norbornane carboxylic acid polymers prepared by ring‐opening metathesis polymerization

5‐Norbornene‐2‐ethyl ester (mixture of endo and exo) is polymerized via ring‐opening metathesis polymerization, yielding polymers with molecular weights ranging from 50,000 to 5,000,000 g/mol. The polymers are hydroxylated and saponified without alteration of the molecular weight. The polymers are analyzed by NMR, gel permeation chromatography, differential scanning calorimetry, and thermogravimetric analysis. Films are cast from the polymers at several molecular weights and their rheological properties are investigated. The results showed greater solid‐like character with increasing molecular weight for all polymers analyzed. Cell viability studies showed that the films possessed minimal cytotoxicity. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Molecular layer‐by‐layer deposition of highly crosslinked polyamide films

A molecular layer‐by‐layer (mLbL) deposition process is demonstrated to synthesize conformal coatings of crosslinked polyamide. This process controls the rapid reaction of trimesoyl chloride and m‐phenylene diamine, unlike interfacial polymerization techniques which produce rough films and poorly defined network structure. Layer‐by‐layer polyamide films appear structurally similar to interfacially polymerized films with a linear film growth rate of ≈0.9 nm per cycle. Films made by mLbL deposition show a 70‐fold decrease in surface roughness as compared to a commercial, interfacially polymerized polyamide. Surface chemistry could be controlled based on which reaction step was performed last, leading to amine or carboxylic acid rich surfaces. With the ability to control chemical structure throughout the crosslinked network, this technique provides new routes to build polyamide films and improve analysis techniques for commercial applications such as reverse osmosis membranes. © 2011 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2012     

Radio-frequency induction plasmas at atmospheric pressure: Mixtures of hydrogen,nitrogen, and oxygen with argon

Numerical calculations are reported which simulate atmospheric-pressure radiofrequency induction plasmas consisting of either pure argon or mixtures of argon with hydrogen, nitrogen, or oxygen. These calculations are compared to observations of laboratory plasmas generated with the same geometry and run conditions. The major features of the laboratory plasmas are predicted well by the calculations: the pure argon plasma is the largest, with the argon-oxygen plasma slightly smaller. The argon-nitrogen plasma is considerably smaller and the argon-hydrogen plasma is the shortest, although somewhat fatter than the argon-nitrogen case. The calculations are not entirely successful in predicting the exact location of the plasmas relative to the coils. A likely explanation is that there is significant uncertainty regarding the actual power coupled to the laboratory plasmas.     

Self‐initiating performance of maleic anhydride on surface photografting polymerization

Maleic anhydride (MAH) was photografted onto low‐density polyethylene (LDPE) films with a grafting efficiency of about 70% in the absence of a photoinitiator. The self‐initiating performance was attributed to a mechanism of abstracting hydrogen atoms from LDPE chains by excited MAH dimers. The supporting experimental results were as follows: (1) the far‐UV radiation (200–300 nm) was indispensable for the graft polymerization and 2) the crosslinking reaction of LDPE inevitably accompanied the grafting of MAH. In addition, the initiation performance of MAH was further confirmed by surface photografting of acrylic acid in the presence of MAH, where MAH was used as the photoinitiator. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 3246–3249, 2001