A recently developed technique, i.e., two-dimensional infrared (2D IR) correlation spectroscopy, is used to study the thermal behavior of poly(ethylene-co-vinyl alcohol)-graft-poly(-caprolactone), a new synthesized highly grafted copolymer. The use of the 2D IR approach to analyze temperature-dependent spectra collected in situ during the temperature elevation process effectively enhanced the spectral resolution and revealed details on the hydrogen bonding and conformational change which are not easily detected in the traditional one-dimensional spectra. The sequence of the spectral changes of different OH and CH2 fundamental vibrations during heating the polymer was inferred from the signs of the asynchronous peaks. Evidence that the conformational changes of the methylene groups precede the loosening of hydrogen bonds is provided.

In the present contribution, two-dimensional ATR-FTIR spectroscopy was used to study the diffusion of water in poly(-caprolactone) (PCL). In the spectral region of the

In this study, the diffusion process of water molecules in poly(є-caprolactone) (PCL) has been investigated using in-situ attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopy. In our system, the original broad water OH bands in 1D IR spectra can be effectively differentiated into four bands, located at 3641, 3593, 3410, and 3203cm-1, respectively, using 2D correlation analysis. The bands at 3641cm-1 (antisymmetric) and 3593cm-1 (symmetric) are assigned to the OH stretching vibration of water partially hydrogen bonded with hydrophilic carbonyl group (CvO) of PCL, while the other band pair at 3410cm-1 (antisymmetric) and 3203cm-1 (symmetric) could be attributed to the stretching vibration of water fully hydrogen bonded with another water molecule. According to the result of the asynchronous correlation, it was concluded that the water molecules at first diffuse into free volume (microvoids) or are molecularly dispersed into the PCL matrix and then form hydrogen bond with the CvO group of the polymer during the process of water diffusion. In addition, the diffusion coefficient was estimated using nonlinear curve fitting of OH band areas in the range of 3800-3000cm-1.

Two-dimensional (2D) correlation ATR-FTIR spectroscopy was used to study the dynamic diffusion behavior and state of water in syndiotactic polypropylene (S-PP). The 2D asynchronous spectra of water bending band clearly reveal that there are three separate bands in the 1800-1500cm-1 region. These three bands at 1676, 1645, and 1592cm-1 are assigned, respectively, to the aggregated water with strong hydrogen bond, the aggregated water with moderate strong hydrogen bond, and the "free water". On the basis of this approach, the following mechanism for the diffusion process of water in S-PP has been proposed: the aggregated water molecules first diffuse into the polymer during the diffusion process. The water molecules with strong hydrogen bond will diffuse slower than water with moderate strong hydrogen bond because of their large size. In the late stage of the diffusion process, some aggregated water molecules in the PP matrix are forced to dissolve into the "free water" form.

A novel experimental approach, based on time-resolved two-dimensional (2D) ATR-FTIR spectroscopy has been used to study water diffusion behavior of novolac epoxy resins cured with novolac resin and novolac acetate resin named as EP and EPA, respectively. The diffusion coefficients calculated by a nonlinear curve fitting are quite consistent with the results of gravimetric analysis. In 2D-IR spectra, the splitting of the water OH vibration band at 2800-3700 and 1500-1800cm-1 shows that there are two different states of water in epoxy networks, in which one could be confined into free volume (microvoids) or molecularly dispersed with less hydrogen-bonding (bulk dissolved), while the other could be attributed to bound water forming strong hydrogen-bonding with hydrophilic groups of epoxy networks. The sequential order of intensity changes of the two water bands elucidates that, in the process of water diffusion into epoxy networks, water molecules first bind with specific hydrophilic groups as bound water and then diffuse into free volume (microvoids) or molecularly dispersed with less hydrogen-bonding (bulk dissolved). The wavenumber difference of OH vibration band appearing from bound water between EP and EPA indicates that water molecules form much stronger hydrogen-bonding with EP networks than with EPA networks.