A.K.Mishra et al.Progress in Organic Coatings 55 (2006)231-243 tral band we have not tried to force fit the bands since this e IV may result erroneous results.The curve-fitting simulations were software version 6.The (N-H)and and N-H zone was used to find out the number of Gaussian zone o 3.1.1.The C=o stretching region The hydrogen bonding interaction makes the carbonyl bond length elongate avenumber (cm )b The hydrogen bonded C)band appears at a lower wave ber region in comparison to that of the free v(CO)band 61m hvdrogen bonded C-0)wher tuo ha at Tie copdo n a compariso n poly e de 17172 cm (free( from urethane)and at assigned to the bonded urethane andu are ce tered at -and164 1655cm-1 728 b Wavenumber(cm1) Fig.2.FT-IRspe mof(a)PUI-16and(b)PUL-3inth line was chosen in between 1600 and 1800cm and the spectra the ba HS X—C—Hs a HS 。ss type l:produce phase separation type ll:produce phase mixin here,XisCfor imide bone,or urethaneand NH for urea bond 236 A.K. Mishra et al. / Progress in Organic Coatings 55 (2006) 231–243 Fig. 2. FT-IR spectrum of (a) PUI-16 and (b) PUI-3 in the range 400–2000 cm−1. tral band. We have not tried to force fit the bands since this may result erroneous results. The curve-fitting simulations were performed using Origin software version 6. The ν(N H) and ν(C O) band were deconvoluted considering peaks as Gaussian with a number of iteration to get the best fit Gaussian peaks. For deconvolution study, the second derivatives of spectra in νC O and νN H zone was used to find out the number of Gaussian peaks. The maximum error associated with the fit was estimated to be less than 5%. The main purpose of this study is to identify the relative degree of order of the hard segments and to show how the local order is influenced by the specified formulation variables. Fig. 3(a) and (b) shows the amide I region and N H zone of different PU-urea-imide copolymers, respectively. 3.1.1. The C O stretching region The hydrogen bonding interaction makes the carbonyl bond length elongated and results in a decrease in the bonding force constant as well as the bond order of C O bond, leading to the reduction of the stretching vibration frequency. Therefore, the hydrogen bonded ν(C O) band appears at a lower wavenum￾ber region in comparison to that of the free ν(C O) band [51]. During ν(C O) spectral deconvolution, we were able to deconvolute polyester based PU-urea-imide copolymers into only two bands appearing at approximately 1737 cm−1 (free C O) and 1685–1700 cm−1 (hydrogen bonded C O), whereas PPG based PU-urea-imide copolymers show four deconvoluted bands (see Fig. 3(a) for a comparison between polyester and PPG based systems). The representative C O peak decon￾volution of PUI-16 is shown in Fig. 3(c) and confirms the bands assignable to the urethane group are centered at approx￾imately 1725–1740 cm−1 (free C O from urethane) and at 1710–1725 cm−1 (free C O from urea groups), whereas those assigned to the bonded urethane and urea groups are centered at approximately 1670–1685 cm−1 and 1644–1655 cm−1, respec￾tively. Free and hydrogen bonded imide C O components could not be deconvoluted separately as they were overlapping with the urethane functions during the deconvolution curve-fitting process. Before deconvolution of the ν(C O) band, a flat base￾line was chosen in between 1600 and 1800 cm−1 and the spectra was corrected by subtracting the baseline. The correlation coeffi- cients of the fitting process were more than 0.999. The analyzed Scheme 2. Two hydrogen bonded structure responsible for phase separation and phase mixing characteristics in the PU-urea-imide copolymer prepared from PPG: (a) type I hydrogen bonding between the hard segment (HS) and hard segment (HS), and (b) type II hydrogen bonding between hard (HS) and soft segment (SS)