A comparative evaluation between the FTIR spectra of CO and MCO reveals a broad, intense and strong absorption band at 3400 cm-1 for MCO. This is attributed to the increase in the number of hydroxyl (OH) groups in MCO after transesterification reaction [17]. Further, the results depicted in table 2 validates the above observation. Both the materials exhibited peak at 1734 cm-1 indicating the presence of the ester carbonyl group. Meanwhile, the band visualized at 1100 cm-1 in CO can be assigned to the secondary OH group. However, MCO revealed an absorption band at 1051 cm-1 which might be due to the introduction of primary OH groups (Scheme 2) after thetransesterification process which was absent in the case of CO.
The FTIR spectra of the UBPU 1.4 and MBPU 1.4 films are represented in Fig 2. It is noticeable that the –NH peak for MBPU 1.4 appears at a lower wavenumber as compared with UBPU 1.4. Coleman et.al. [36] have reported that in case of H-bonded polyurethane the –NH bond appears at lower wavenumber as compared with the PUs devoid of H-bonding. Usually the hydrogen bonding (H-bonding) is formed between two types of proton donors i.e. (urethane N-H and urea N-H) and four types of proton acceptors (urethane C=O, urea C=O, ester carbonyl and ether oxygen group) [37]. Generally the N-H stretching bands are responsible for the formation of H-bonds and the magnitude of frequency shifts in their peak positions from 3200-3400 cm-1 region is often analyzed to study the H-bonding and phase separation behavior [37]. It has been reported that a linear relationship exists between the length of H-bonding (R) and frequency shift (Δʋ) of the N-H absorption band [38] which can be calculated by using the following equation, In general, the shorter the H-bond the stonger is the bonding [38]. …show more content…
As revealed from table 7, MBPU 1.4 exhibits shorter H-bond length, which, confirms its higher H-bonding as compared with UBPU 1.4. This result was predictable by taking into account the difference in reactivity of OH groups and the number of dangling chains in CO and MCO respectively. It is to be noted that the presence of the primary hydroxyl (OH) groups in terminal position of MCO renders higher reactivity towards the NCO groups in Tolonate TM X FLO 100 resulting in the formation of H-bonded N-H of relatively higher intensity. Moreover, the presence of less dangling chains [39] in MBPU inhibits the steric hindrance effect resulting in the formation of stronger H- bonds and enhanced intermolecular interaction. Besides, the band in the range 1742-1710 cm-1 corresponding to the stretching vibration of the C=O urethane group is also monitored to access the H-bonding environment. Yong –He et.al. [37] has reported that the shifting of –C=O peak dictates the nature of H-bonding formed between the NH groups of hard segments with the C=O group of the soft segment. The spectra for UBPU shows peak at 1741 cm-1 (free H bond) and 1710 cm-1 (H-bond in amorphous domains), whereas MBPU revealed a single peak at 1710 cm-1 [40]. The successful synthesis of UBPU and MBPU is confirmed through the presence of this peak in the FTIR spectra. This shift in MBPU suggests that with transesterification the OH functionality in MCO increases as a result more interurethane H- linkages between the hard and soft segments is formed inducing prominent H-bonded (NH-C=O) peaks at 1710 cm-1 . Moreover, the observed arrangement can also be explained on
The FTIR spectra of the UBPU 1.4 and MBPU 1.4 films are represented in Fig 2. It is noticeable that the –NH peak for MBPU 1.4 appears at a lower wavenumber as compared with UBPU 1.4. Coleman et.al. [36] have reported that in case of H-bonded polyurethane the –NH bond appears at lower wavenumber as compared with the PUs devoid of H-bonding. Usually the hydrogen bonding (H-bonding) is formed between two types of proton donors i.e. (urethane N-H and urea N-H) and four types of proton acceptors (urethane C=O, urea C=O, ester carbonyl and ether oxygen group) [37]. Generally the N-H stretching bands are responsible for the formation of H-bonds and the magnitude of frequency shifts in their peak positions from 3200-3400 cm-1 region is often analyzed to study the H-bonding and phase separation behavior [37]. It has been reported that a linear relationship exists between the length of H-bonding (R) and frequency shift (Δʋ) of the N-H absorption band [38] which can be calculated by using the following equation, In general, the shorter the H-bond the stonger is the bonding [38]. …show more content…
As revealed from table 7, MBPU 1.4 exhibits shorter H-bond length, which, confirms its higher H-bonding as compared with UBPU 1.4. This result was predictable by taking into account the difference in reactivity of OH groups and the number of dangling chains in CO and MCO respectively. It is to be noted that the presence of the primary hydroxyl (OH) groups in terminal position of MCO renders higher reactivity towards the NCO groups in Tolonate TM X FLO 100 resulting in the formation of H-bonded N-H of relatively higher intensity. Moreover, the presence of less dangling chains [39] in MBPU inhibits the steric hindrance effect resulting in the formation of stronger H- bonds and enhanced intermolecular interaction. Besides, the band in the range 1742-1710 cm-1 corresponding to the stretching vibration of the C=O urethane group is also monitored to access the H-bonding environment. Yong –He et.al. [37] has reported that the shifting of –C=O peak dictates the nature of H-bonding formed between the NH groups of hard segments with the C=O group of the soft segment. The spectra for UBPU shows peak at 1741 cm-1 (free H bond) and 1710 cm-1 (H-bond in amorphous domains), whereas MBPU revealed a single peak at 1710 cm-1 [40]. The successful synthesis of UBPU and MBPU is confirmed through the presence of this peak in the FTIR spectra. This shift in MBPU suggests that with transesterification the OH functionality in MCO increases as a result more interurethane H- linkages between the hard and soft segments is formed inducing prominent H-bonded (NH-C=O) peaks at 1710 cm-1 . Moreover, the observed arrangement can also be explained on