234 A.K.Mishra et al.Progress in Organic Coatings 55 (2006)231-243 -torr.A thin possible differences in the chemical composition between the funct appl to th stage,causing two energy transitions.It promotes transitions At e=09 the sample was nernendicular to the detector lead ina between rotational and vibrational energy ing to the maximum sampling depth.The effective sampling When transitions between rotational and tonal energy le de ved by 2=3 where is the ef molecule will absorb I Therefore an IR a set to th unique to a specific molecular vibration frequency.When IR ,=1.94nm [13].The accurate binding energies of ed by the 一Te identification of func onal groups is a major application of IR of the lens from a filament located directly atop the sample spectrome etry [42] pectra were edusing Sun Solarisbase data manin mode.Therefore.the elucidation of structure-property relations ulation,a linear background subtraction was performed prior to in P -urea-imide copolymers are composed or tv Lore to fit th tzian sum ed the hard can be realized from FT-IR spectroscopy by properly analyz algorithm.This is a time domain procedure,which fits a fourth rogen izable number of polyme ckgr an h ring imide copol ymer where multiple peaks overlap strongly. The and quantification of the functional groups present on the sam ple surface [43] The bind ding energy(BE)scale was calibrate eves of the pure metals plicated not a)s by m叫 eaks but also by other band distortionseffects,(b)aproper 3.Results and discussion etc. 3.1.FT-IR analysis Now let us confine e our racterist Fourier transform of the PU-ure imide thin films on KBr dise in the zone 400-4000 cm- viour in polymers,since m 3500cm ps.2795m mer or macromolecules possess bonds and functional groups (O-CH stretching)600-10cm(amide:C stretch. characteristics of their identity.These functional groups vibrate c)[46 of each oth ing vibrations),1540cm and weakly s we group ina macromolecule arises from the contribution ofuransla tional,rotational,vibrational,and electronic energies.Therefore scissoring and CH3 deformation.The band at 1780cm-is an inter with ra EM)spec 山he stret ing vibra the cai functional group involved in the Without an 7731780Cm8201380cm120amd720cm-ae EM radiation effect,these bonds or functional groups vibrate attributed to imide I,imide Il,imide Ill and imide IV,respec 33 cr conming that imide 234 A.K. Mishra et al. / Progress in Organic Coatings 55 (2006) 231–243 pressure in the analyzer chamber was kept at ∼10−8 torr. A thin film of thickness 0.15 mm was used for XPS analysis. To detect possible differences in the chemical composition between the surface and bulk, samples were measured at two different take￾off angles. The sample was tilted in such a way as to change the angle θ between the normal to the sample and the analyzer. At θ = 0◦, the sample was perpendicular to the detector, lead￾ing to the maximum sampling depth. The effective sampling depth, z, was derived by z = 3λcosθ, where λ is the effective mean free path for electrons to escape the surface and was set to the value of 2.5 nm. Therefore, at θ = 0◦, z = 7.5 nm and at θ = 75◦, z = 1.94 nm [13]. The accurate binding energies of the component peaks in each spectrum were determined after charge correction by referencing to the aromatic carbon bonded to another carbon at 284.6 eV. Charge neutralization was imple￾mented by low energy electrons injected into the magnetic field of the lens from a filament located directly atop the sample. Spectra were deconvoluted using Sun Solaris based Vision 2 curve resolver. Data acquisition and processing were performed with the Kratos Vision 2 data system. Concerning data manip￾ulation, a linear background subtraction was performed prior to any peak-fitting procedure. A Gaussian–Lorentzian sum func￾tion in 70:30 ratios was used to fit the individual peak. Before deconvolution, each peak was smoothed using Savitzky–Golay algorithm. This is a time domain procedure, which fits a fourth order polynomial in a moving window of a sizable number of data points. Shirley background was chosen during data fitting. The percentage of the overall area contributed by each individ￾ual peak can then be determined. This enabled the identification and quantification of the functional groups present on the sam￾ple surface [43]. The binding energy (BE) scale was calibrated by setting the Au 4f7/2 or Pt 4f7/2 core levels of the pure metals to values 84.0 or 71.2 eV, respectively. 3. Results and discussion 3.1. FT-IR analysis Fourier transform-infrared spectroscopy (FT-IR) is well established as an analytical technique for functional group anal￾ysis and to study the hydrogen bonding and phase separation behaviour in polymers, since mid-infrared spectral changes in band intensity and frequency shifts are known criteria for the presence and strength of hydrogen bonds [44]. In general poly￾mer or macromolecules possess bonds and functional groups characteristics of their identity. These functional groups vibrate independently of each other and weakly interact. It is well￾known that the total energy of a particular bond or functional group in a macromolecule arises from the contribution of transla￾tional, rotational, vibrational, and electronic energies. Therefore, an interaction with radiation of the electromagnetic (EM) spec￾trum will result in different energy transitions of the bond or functional group involved in the macromolecule. Without any EM radiation effect, these bonds or functional groups vibrate independently at their equilibrium position. Sometimes the local vibration depends on the intermolecular interactions such as weak London forces or hydrogen bonding phenomenon if any. Therefore, the equilibrium vibration of a bond or functional group depends on the local geometry involved. However, when IR radiation (which is part of the EM spectrum) is applied to a functional group, it breaks down the equilibrium (position) stage, causing two energy transitions. It promotes transitions in a macromolecule between rotational and vibrational energy. When transitions between rotational and vibrational energy lev￾els occur and cause a net change in the dipole moment, the molecule will absorb IR. Therefore, an IR absorption profile is unique to a specific molecular vibration frequency. When IR radiation passes through a sample, some of it is absorbed by the sample and some of it is passed through (transmitted). The result￾ing spectrum represents the molecular absorption/transmission, which creates a fingerprint of the analyzed sample. Therefore, identification of functional groups is a major application of IR spectrometry [45]. Thus, it should be realized that any change in a peak position or shape means a change has occurred in the distribution of frequencies included in that particular vibration mode. Therefore, the elucidation of structure–property relations in PU-urea-imide copolymers, which are composed of two seg￾ments, namely the soft segment derived from the macrodiol and the hard segment that consists of urethane/urea-imide linkages can be realized from FT-IR spectroscopy by properly analyz￾ing the amount and type of hydrogen bonding present in a particular polymer. While this may seem to be a trivial fact, it can be important for interpretation of segmented PU-urea￾imide copolymer where multiple peaks overlap strongly. The complicacy of projecting the structure–property correlation in a polymer with spectral deconvolution arises great scientific chal￾lenges due to: (a) spectral investigation of hydrogen bonding is complicated not only by multiple overlapping peaks but also by other band distortions effects; (b) a proper baseline correction is needed; (c) the time during the scanning should be high, so that the effect of noise can be minimized; (d) care should be taken not to force fit the bands, which may generate erroneous results, etc. Now let us confine our attention to the spectral changes appeared or the characteristic bands observed in the synthesized PU-urea-imide copolymers. Fig. 1 shows the infrared spectra of the synthesized PU-urea-imide thin films on KBr disc in the zone 400–4000 cm−1. The spectra are mainly character￾ized by bands at 3150–3500 cm−1 (NH stretching vibrations), 2800–3000 cm−1 (CH stretching vibrations: anti-symmetric and symmetric stretching modes of methylene groups), 2795 cm−1 (O CH2 stretching), 1600–1800 cm−1 (amide I: C O stretch￾ing vibrations), 1540 cm−1 (amide II, δN H + νC N + νC C) [46], 1376–1388 cm−1 (νC N), 1226–1292 cm−1 (amide III, νC N), 1110 cm−1 (C O C stretching vibration, ether group) and 766 cm−1 (amide IV). Band at 1455 cm−1 is attributed to CH2 scissoring and CH3 deformation. The band at 1780 cm−1 is assigned to the asymmetric stretching vibration of the car￾bonyl of the imide groups. Characteristic spectral absorbance at 1730–1780 cm−1, 1320–1380 cm−1, 1120 and 720 cm−1 are attributed to imide I, imide II, imide III and imide IV, respec￾tively. The absorption bands at about 1780 and 720–733 cm−1 are characteristic bands of imide bonds, confirming that imide