Time-resolved infrared spectral measurements were made successfully for studying the microscopic mechanism of water-induced solid-state phase transitions of poly(ethylene imine) (PEI) in the hydration process at room temperature. The initial sample, obtained by cooling the melt under a dry atmosphere, showed the infrared spectra characteristic of the anhydrate phase consisting of doubly stranded helices. When this sample was exposed into an atmosphere of 100% relative humidity, the infrared spectra were found to change in a multistage mode from anhydrate to hemihydrate (molar ratio of ethylene imine unit/water ) 1/0.5) to sesquihydrate (1/1.5) and to dihydrate (1/2), where the molecular chains in the latter three phases take the planar-zigzag all-trans conformation and form the complexes with water through the hydrogen bonds. The spectral measurements were made also for heavy water (D 2O) as well as light water (H2O), and the quantitative analysis could be made more successfully for the former case, because the overlap of the polymer bands with water bands could be avoided due to the shift of the broad absorption bands of water molecules. A comparison was made for the strength of hydrogen bonds between PEI and PEI, PEI and water, and water and water. The infrared bands characteristic of the amorphous region could be detected in the frequency region of 1800-2500 cm -1 , the intensities of which were found to decrease in parallel to the crystal phase transition, indicating that some parts of the amorphous region can also crystallize into the hydrates in the hydration process.
The morphological development of crystallizable polymer blends has been investigated using optical microscopy and infrared and Raman spectroscopy. Both binary and ternary blends were studied. In each case, a crystallizable polyester, either poly(hexamethylene adipate) (PHMA) or poly(hexamethylene sebacate) (PHMS), is mixed with noncrystallizable polyether, poly(propylene glycol) (PPG). Although they possess similar chemical structures, PHMA and PHMS exhibit very different miscibility behavior. In ternary blends, an acrylate, poly(methyl methacrylate and n-butyl methacrylate) [P(MMAnBMA)], is also incorporated in the mixture. With the high spatial resolution achievable (∼1 µm 2 ), the composition distribution can be carried out using a micro-Raman instrument. Specific Raman features associated with polyesters have been established. For immiscible PPG/PHMA blends, the composition and distribution within PHMA-rich and PHMA-poor phases are characterized. The exact composition in each phase has been obtained by analyzing Raman data obtained. Additionally, on the basis of the measured intensity for conformation-sensitive Raman peaks, the distribution of crystallites within each phase has been characterized. The third relative immobile acrylate component is extremely effective in changing the overall blend morphology.
The phase separation of ultrahigh molecular weight isotactic polypropylene (it-UHMWPP)
solution in the gelation process was investigated by quenching the solutions to the desired temperature.
When an incident beam of an He−Ne gas laser was directed to the gel, the logarithm of scattered intensity
increased linearly with time in the initial stage and tend to deviate from this linear relationship in the
later stage. The melting endotherm of the differential scanning calorimetry curve showed a clear peak in
the later stage, but no peak could be observed in the initial stage, indicating poor ordering of molecules
in polymer-rich phase. The scattered intensity of laser beam from the gel showed a peak in the scattering
angle direction. The peak became more intense with increasing time, but the peak position did not change.
Accordingly, the phase separation of UHMWPP solution in the initial stage was analyzed within the
framework of the linear theory of spinodal decomposition. In parallel to this small-angle light-scattering
experiment, the time-resolved measurements in the gelation process were carried out for X-ray diffraction
and infrared and Raman spectra. These data could be interpreted reasonably in terms of formation of
crystallites as cross-linkages of the gels. Under optical microscopy, it was confirmed that the gels prepared
by quenching the solution to room temperature compose of periodic honeycomblike structure characterizing
the spinodal decomposition of the solution due to thermodynamic instability. The average size of this
periodic structure is slightly larger than that estimated from the scattering angle to give the maximum
value of growth rate of concentration fluctuation. Periodic honeycomblike structure was also observed
for the dry film under a scanning electron microscopy. The hole size of the honeycomblike structure became
smaller as the quenching temperature decreased, and the size distribution was narrow. The dried films
were stretched up to 60 times, as has been reported already. The possibility of successful elongation up
to λ = 60 became higher with decreasing quenching temperature. Young's modulus, crystallinity, and
molecular orientational degree of the resultant dry gel films became higher with decreasing hole size of
honeycomblike structure. Accordingly, it turns out that the dense network structure created by the spinodal
decomposition of the solution plays an important role in ensuring smooth transmission of inner stress in
the stretching direction and ultradrawing of UHMWPP film can be achieved.
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