Molecular thermodynamic model for solvent-induced glass transitions in polymer—supercritical fluid systems

Raman spectroscopic study of CO2 sorption process in poly methyl methacrylate

“…Figure 6 shows the Raman spectra in the energy region of the skeletal vibration modes at 273 K. The solid, broken, and dotted lines represent the spectra of glassy PMMA before the pressurization (i.e., at 0 min), the rubbery PMMA in its equilibrium state under the CO 2 pressurization to 4.5 MPa (i.e., at 240 min), and the foamed glassy PMMA, respectively. The peaks observed at 811.8 and 1124.7 cm −1 in the spectrum at 0 min are assigned to the CC 4 symmetric‐stretching mode and the CO stretching mode, respectively 20, 21. The vibration energies of the modes depend on the lengths of the CC and CO bonds, respectively.…”

“…The excitation energy for Raman emission was produced by a Yag laser using single mode operation of 532 nm with an output of 100 mW. The spectra were measured over the energy range between 100 and 4000 cm −1 , which includes the peaks of the Fermi resonance of the symmetric stretching mode and the overtone of the bending mode of CO 2 ,18 the CH stretching modes (2800–3800 cm −1 ),19 and the skeletal vibration modes of PMMA (200–1300 cm −1 ) 20, 21. The intensities of all spectra were normalized by the peak intensity of the CC 4 symmetric stretching mode of PMMA at ∼813 cm −1 .…”

A new technique for measuring retrograde vitrification in polymer-gas systems and for making ultramicrocellular foams from the retrograde phase

“…18,19 This enhanced solubility is, in fact, responsible for the existence of the rubbery state at low temperatures as shown in Figure 5, or conversely, the rapid decrease in solubility on heating the low temperature phase is responsible for the rubber-to-glass transition identified as T g,l in Figure 4. The existence of the rubbery state at low temperatures is further supported by the sorption kinetics results shown in Figure 8; gas sorption occurs more rapidly at Ϫ0.2°C than at 24°C because of the much faster diffusion of CO 2 at the lower temperature.…”

“…This observation was later on accounted for by the theoretical models, 18,19 which predicted that at a certain constant gas pressure or solubility, the polymer existed in the liquid (i.e., rubbery) state at temperatures below T g,l and above T g,h , and in the glassy state at temperatures in between T g,l and T g,h . The existence of T g,l is attributed to enhanced solubility of the gas at lower temperatures.…”

Phase behavior of semicrystalline polyester resin in supercritical fluid solvents and solvent mixtures: Implications for supercritical fluid processing

“…Although it can take significant pressures to dissolve a polymer in a low molecular weight SCF solvent,1 it does not take much pressure to dissolve an SCF solvent into a molten polymer. Significant polymer plasticization occurs as the polymer absorbs the SCF solvent, which lowers the viscosity, depresses the glass‐transition temperature ( T g ), reduces surface tension, and modifies the ultimate pore structure 2–6. The SCF processing of crystalline resins capitalizes on the decreased resin viscosity at temperatures well below the melt point, which means that high intensity mixing can be used to efficiently disperse materials such as inorganic or crosslinking agents into the polymer matrix.…”