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Polyimides, particularly poly-(pyromellitic dianhydride-4,40-oxydianiline) or PMDA-ODA (Kapton-H®), are ubiquitous in the aircraft and aerospace industries, flexible printed circuits, and many other high-performance applications. For many of these applications, the polymer's stability during and after radiation damage is a serious concern. The effect of electron irradiation on the breaking of inter-molecular bonds and creation of free radicals in Kapton polyimide were studied using reactive molecular dynamics simulation with the polarizable ReaxFF method and experimentally on pristine and electron irradiated polyimide by vibrational spectroscopy, electron paramagnetic resonance, nuclear magnetic resonance, wide angle x-ray diffraction, small angle x-ray scattering, and dynamic mechanical analysis. In our simulations, the electron beam is approximated by a dense column of negatively charged particles, which is inserted at random positions in the polyimide matrix. In order to observe inter-molecular bond breaking during the time frame of the molecular simulations, each electron beam is switched on for 2 fs, causing an average energy of 21 eV per electron trajectory to be transferred to the polyimide through Coulomb interactions during the simulation. Experimentally, polyimide is aged in vacuum with a 90 keV electron beam with a maximum penetration depth greater than the material's thickness. Throughout the simulations, modifications in the chemical structure of the polyimide during and after the electron beam irradiations are monitored. During electron beam irradiation, hydrogen atoms separate from different parts of the polyimide through C–H bond cleavage. After turning off the electron beams and running a microcanonical molecular dynamics simulation for 0.5 ns, several chemical and structural rearrangements are observed in the polyimide structure. The chemical modifications mostly include ring opening and other changes to the imide rings. The computations are compared to infrared spectroscopy, electron paramagnetic resonance, nuclear magnetic resonance, x-ray scattering, and mechanical measurements on aged and pristine polyimide to both guide and validate the conclusions from the computational study. Apart from these changes in chemistry we also evaluate temperature evolution and change in mechanical response of the polyimide slab caused by electron beam exposure. Taken together, the direct measurements of the electronic, chemical, and mechanical properties of the irradiated Kapton films validate the key results of the model.

Recently, shape memory polymers (SMPs) with high optical transmittance have been paid great attentions to endow the flexible optoelectronics with shape memory functions. Herein, a low colored and transparent shape memory copolyimide (SMcoPI) is obtained by suppressing the charge transfer complex interactions. The optical transmittance of the synthesized SMcoPI film could reach at ∼86% at the wavelength of 450 nm, far higher than the nearly zero optical transmittance of yellow and brown Kapton H. The better optical transparency could be attributed to the loose molecular chain arrangements induced by the meta-substituted groups and flexible ether linkages. The glass transition temperature (Tg) range of the synthesized SMcoPI films is from 179 °C to 220 °C, which is higher than that of reported optically transparent SMPs. The effective decomposition temperature at the weight loss of 5 wt% is 517 °C, showing excellent thermal stability. The SMcoPI also demonstrated good shape memory behaviors with high shape recovery ratio (Rr, >96%) and shape fixity ratio (Rf, >97%). In addition, the SMcoPI could maintain high optical transmittance, good thermostability and excellent shape memory behaviors after the ground-stimulated space thermal cycling test for 250 h. The synthesized SMcoPI has application potentials in high temperature areas or optoelectronic devices.

Recently, 3D-graphene infused polyimide (3DC/PI) films have shown to be an effective protection coating for electrostatic discharge in spacecraft. However, these films are not suitable for Low Earth Orbit (LEO) due to atomic oxygen (AO) erosion. Here, we used Polyhedral Oligomeric Silsesquioxane (POSS) to enhance the AO durability of 3D-C/PI films. Three different ways of adding POSS to the composite films were studied with ground-based AO exposure. For all infusion approaches, their electrical conductivity behaviour is well preserved and the presence of POSS results in reduced AO erosion yield. Of all the methods studied here, incorporating POSS directly into PI results in the lowest erosion yield of 4.67 × 10−25 cm3/O-atom (one order of magnitude lower than that of Kapton). Adding POSS to PI, extends the durability of the composite film beyond 10 years, making it an ideal protective material for long term mission in LEO. Accepted version

We have studied the energy shift introduced by surface charging during the course of ion beam analysis of an insulating material (a Kapton thin film) using Rutherford Backscattering Spectrometry (RBS). The potential that develops was found to be proportional to both the incident ion energy and the sample thickness. This correlation suggests a conductance mechanism that is based on the ion beam induced carriers that are generated in the material. A simple relationship between the mobility of the induced carriers and the built-up surface potential has been derived. It provides a semi-quantitative explanation for the observed spectral offset. This relationship also provides important insight into the electrical characteristics of the insulating material being irradiated. In the specific case of Kapton, we observed a split of the high energy edge in the RBS spectra, which we suggest is most likely a reflection of the presence of both amorphous and crystalline forms of Kapton. Some contribution from partial discharge of the surface potential to the surrounding is also considered.

A series of novel fluorinated alicyclic-functionalized polyimides (FPI- x ) were prepared from a new alicyclic-functionalized diamine, 1,3-bis ((4-amino-2-(trifluoromethyl)phenoxylmethylene)-1,2,2-trimethyl cyclopentane (BAFMT), which was derivated from natural-(D)-camphor via multi-step process. The influence of the presence of the alicyclic and fluorinated structure on the general properties of the polymers was systematically investigated in terms of optical, thermal and mechanical properties, solubility and hydrophobicity, rendering the general structure–properties relationships for the FPI- x . Compared with the analogous control aromatic polyimide NPI- x , FPI- x shows better solubility, improved optical transparency, lower moisture absorption and surface energy, owing to the presence of the fluorine-containing group and alicyclic structure in the polymer chain. Although presenting a slight decrease as compared with NPI- x , the good thermal stability of polyimide was retained on the large in the fluorinated alicyclic-functionalized polymer FPI- x , with T g ranging in 197–233 °C and T d5 ranging in 374–420 °C. A particular research emphasis were placed on employing the dielectric relaxation technique to study the dielectric constant (e′), dielectric loss (e″) and electric modulus (M″) of the fluorinated alicyclic-functionalized polyimide film FPI-4 and its control sample NPI-4. The observed dielectric relaxations have been fully studied by integrating the contributions of the specific structure and functional groups. It is revealed that the presence of fluorinated alicyclic-functionalized group endows FPI-4 with lower dielectric constant e′ (2.88 at 1 MHz and 25 °C) and dielectric loss e″ (0.0058 at 1 Hz and 25 °C) than NPI-4 (3.49 and 0.0084) and commercial Kapton HN (3.19 and 0.006) with the same measurement frequency and temperature.

In order to study charge trapping and transport in polyimide, we have submitted samples of Kapton HN to corona charging and measured its surface potential decay with an electrostatic voltmeter. We propose a two terms mobility to explain the experimental data: a non dispersive contribution based on Toomer and Lewis model added to a dispersive process, which is associated with the disordered structure of the material. The non-dispersive model alone did not fit well to the data for short times, but our assumption makes the theoretical expresion fit succesfully to the experimental data. Some important parameters related to the charge transport properties of the material are determined and discussed.

Argon plasma-pretreated polyimide (PI, Kapton ® HN) films were subjected to UV-induced surface graft copolymerization with N , N ′-(dimethylamino)ethyl methacrylate (DMAEMA) and 2-(trimethylammonium)ethyl methacrylate chloride (TMMAC). The DMAEMA graft -copolymerized PI (DMAEMA- g -PI) surfaces were also quaternized and amino-functionalized with 3-bromopropylamine hydrobromide (the Q-DMAEMA- g -PI surfaces). The surface composition and the degree of quaternization of the graft -modified PI films were determined by X-ray photoelectron spectroscopy. The DMAEMA- g -PI, Q-DMAEMA- g -PI and TMMAC graft -copolymerized PI (TMMAC- g -PI) surfaces can be activated directly by PdCl 2 , in the absence of prior sensitization by SnCl 2 (the ‘Sn-free’ activation process), for the subsequent electroless plating of copper. A shorter induction time for the electroless deposition of copper was found for the palladium-activated Q-DMAEMA- g -PI and TMMAC- g -PI surfaces than for the palladium-activated DMAEMA- g -PI surface. The T-peel adhesion strength of the electrolessly deposited copper with the Q-DMAEMA- g -PI surface was enhanced to above 6 N/cm, in comparison to only about 4 N/cm for the DMAEMA- g -PI surface, about 2.5 N/cm for the TMMAC- g -PI surface, or about 0.5 N/cm for the PI surface with argon plasma treatment alone.

A simple technique of thermal graft copolymerization of 1-vinyl imidazole (VIDZ) in the presence of a small amount of a crosslinking agent (XLA) on plasma-pretreated polyimide (PI or Kapton HN®) films with simultaneous lamination of copper foils was demonstrated. The simultaneous thermal grafting and lamination process was carried out in the temperature range of 80–150°C under atmospheric conditions and in the complete absence of a polymerization initiator. Significant improvement in adhesion was achieved by the presence of a XLA, such as 2,4,6-triallyloxy-1,3,5-triazine (TATZ), or 1,3,5-triallyl benzene tricarboxylate (TBTC), in VIDZ during the thermal graft copolymerization and lamination process. T-peel adhesion strength exceeding 17 N/cm can be readily achieved for the polyimide–copper interface for grafting and lamination carried out at the reduced temperature of 100°C. The T-peel adhesion strengths are reported as a function of the cooling rate, the argon plasma pre-treatment time of the polyimide films, the thermal lamination temperature, and the thermal lamination time. The polyimide–copper interface graft copolymerized and laminated in the presence of a XLA also exhibited substantially improved resistance to moisture. The surface compositions of the polyimide films and copper foils from the delaminated interfaces were studied by X-ray photoelectron spectroscopy (XPS). The enhanced interfacial adhesion has resulted in cohesive failure deep inside the PI film as is also revealed by the scanning electron micrograph (SEM).

The effects of gamma irradiation on aromatic polymers, such as polyimides (Kapton, Upilex-R and Upilex-S), poly(aryl ether ether ketone) (PEEK), poly(aryl ether sulphone) (PES), bisphenol A type Udel poly(aryl sulphone) (U-PS) and poly(aryl ester) (U-Polymer), were investigated based on gas evolution. The radiation resistance in terms of gas evolution was in the following order: Upilex-R ⩾ Kapton > PEEK > PES > Upilex-S ⪢ U-PS > U-Polymer. The G values of total gases from these aromatic polymers were 1 100 th to 1 1000 th of the G values from aliphatic polymers. The major component gases were: H 2 and N 2 for polyimides; CO 2 and CO for PEEK; CO 2 , CO and SO 2 for polysulphones; and CO and CO 2 for U-Polymer. The influence of crystallinity on the behaviour and yield of gas evolution was investigated in PEEK. Crystalline PEEK gave lower yield compared to amorphous PEEK. The radiolysis mechanism of gaseous products was discussed based on the structures of the aromatic polymers.

The fluorescence properties of pyromellitic dianhydride-oxydianiline (PDMA-ODA) polyimide are described. The quantum efficiency of fluorescence following excitation at 290 nm is measured to be 10 −6 . The spectroscopically parametrized (complete neglect of differential overlap) CNDO/S3 model is used to provide a quantitative description of the emission spectrum, and to make some preliminary conclusions about the mechanism responsible for laser etching of polyimides.

The ESCA (electron spectroscopy for chemical analysis) spectra of films of Tedlar, tetrafluoroethylene-hexafluoropropylene copolymer (in the form of a Teflon FEP coating on Kapton H, i.e., Kapton F), and polytetrafluoroethylene (Teflon or Teflon TFE), exposed to atomic oxygen O(3P) either in LEO on the STS-8 Space Shuttle or within or downstream from a radio-frequency oxygen plasma, were compared. The major difference in surface chemistry of Tedlar induced by the various exposures to O(3P) was a much larger uptake of oxygen when etched either in or out of the glow of an O2 plasma than when etched in LEO. In contrast, Kapton F exhibited very little surface oxidation during any of the three different exposures to O(3P), while Teflon was scarcely oxidized.

Recent studies of polymer-based pyrolytic amorphous carbon for use in organic electrolyte-lithium batteries and as metal-doped carbon electrodes show considerable promise. Polyimide can be thermally converted to amorphous carbon films. The irreversible evolution of polyimide under progressive heat treatment is characterized by three successive structural changes: pyrolysis, carbonization and graphitization. Four-point contact conductivity and electron spin resonance (e.s.r.) measurements were used to study and correlate electrical conductivity changes with unpaired electrons. From these studies it is concluded that at low pyrolysis temperature ( 700°C) a microcrystalline graphite-like metallic domain starts to appear in the amorphous matrix. The development of this ‘metallic domain’ causes the conductivity of the pyrolysed polyimide to increase sharply.

An exploratory study has been undertaken to determine the effect of simple tensile deformations, applied stepwise, on the permeability and diffusion coefficients (P and D) of gases in glassy polymers. For nitrogen in a polycarbonate film at 73°C, it was found that (1P)dPdϵ ⋍ 13 and (1D)dDdϵ ⋍ 5 to 8, where ϵ is the strain. Also, P and D were found to decrease with time at constant strain and to depend somewhat on strain and thermal histories. A calculation of (1D)dDdϵ, based primarily on considerations of free volume and its strain dependence, gives 11.8 or 8.5, depending on the assumptions made. Progressive stepwise application of strain to a polyimide (Kapton) film at 72° and 125°C caused P and D for carbon dioxide to increase. But above 2% strain at 125°C, they decreased until at 6% strain they became smaller than those for the undeformed specimen, a reflection of a straininduced relaxation process.

Torsional and tensile creep properties of a cellulose acetate butyrate ester and the polyimide Kapton-H were studied in order to reveal physical ageing in these rigid chain polymers. The measured shift rates, μ, were 0.75 and 0.5 for cellulose and polyimide respectively, which indicates that physical ageing also occurs in polymers with stiff chains. These values, compared with those already known for most thermoplastics ( μ ∼ 1), suggest that physical ageing is slowed down by the rigidity of the main chain.

Electron beam irradiation effects of ten kinds of polymers containing various aromatic rings linked by functional groups in the main chain (aromatic polymer) were studied with reference to change in tensile properties. The polymers studied were polyimides ‘Kapton H’, and ‘UPILEX’, polyetherimide ‘ULTEM’, polyamides ‘A-Film’, and ‘APH-50 (nomex type paper)’, poly-ether-ether-ketone ‘PEEK’, polyarylate ‘U-Polymer’, polysulphones ‘Udel-Polysulphone’, and ‘PES’, and modified poly(phenylene oxide) ‘NORYL’. Irradiation was carried out by use of electron beam at a dose rate of 5 × 103 Gy s−1 at room temperature. The elongation at break was the most severely influenced by the irradiation and it decreased with increasing dose. The order of radiation resistivity which was evaluated from the dose required for the elongation to become 50% and 20% of the initial value was as follows: Polyimide>PEEK>polyamide>polyetherimide>polyarylate>polysulphone, poly(phenylene oxide) Based on the above experimental results, the following order was proposed as for the radiation stability of the aromatic repeating units composing the main chain

Electrical conduction in Kapton polyimide film was studied under steady-state conditions in the temperature range 100°–200°C and in electric fields of 50–450 kV cm −1 . An attempt was made to fit the field dependence of current to one of the several possible mechanisms which have been proposed by different workers. Evidence is presented to suggest that even at high fields ionic conduction may be the operative mechanism of conduction. Values of ionic jump distance of 50–60 A show good agreement with values reported by other workers.

The preparation of a series of high molecular weight aromatic polyimides by the reaction of di(4-aminophenyl)ether with 1,3-bis(3,4-dicarboxyphenyl) hexafluoropropane dianhydride, and pyromellitic dianhydride is described. The glass transition temperatures (Tg) of these polymers were measured by differential scanning calorimetry at heating rates of 8–64°K/min on samples of controlled thermal history, and Tgs at a dilatometric heating rate (0.06°K/min) were estimated. The values provide a good fit to a simple molar additive relationship between Tg and copolyimide composition from which the Tg of poly {[5,7-dihydro-1,3,5,7-tetraoxobenzo(1,2,-c:4,5-c′)-dipyrrole-2,6(1H,3H)-diyl]-p-phenyleneoxy-p-phenylene} (Kapton) is estimated to be 598°K. The reason why this predicted Tg is difficult to observe experimentally may be that only limited molecular motion can occur at the Tg because many of the polymer segments are tied into a network by strong intermolecular forces.