Glass transitions high pressures

Keywords Gas sorption Glass transition High pressure Self-assembling Solubility Transitiometry Vibrating-wire technique... 

Figure 8 Illustration of the scanning transitiometry technique for low-temperature, high-pressure investigation of polymers glass transition. The pressure coefficient of the glass transition temperature is given in the inset...

Two resin systems based on this chemical concept are commercially available from Shell Chemical Company/Technochemie under the COMPIMIDE trademark COMPIMIDE 183 (34) [98723-11-2], for use in printed circuit boards, and COMPIMIDE 796 [106856-59-1], as a resin for low pressure autoclave mol ding (35). Typical properties of COMPIMIDE 183 glass fabric—PCB laminates are provided in Table 8. COMPIMIDE 183 offers a combination of advantageous properties, such as a high glass transition temperature, low expansion coefficient, and flame resistance without bromine compound additives. 

Polymer-Fluid Equilibria and the Glass Transition Most polymer systems fall in the Class HI or Class V phase diagrams, and the same system can often change from one class into the other as the polymer s molecular weight changes. Most polymers are insoluble in CO9 below 100°C, yet CO9 can be quite sohible in the polymer. For example, the sorption of CO9 into silicone rubber is highly dependent upon temperature and pressure, since these properties have a large influence on the density and activity of CO9. 

Figure 10. LCT configurational entropy ScT as a function of the reduced temperature 5T = (T — To)/To for low and high molar mass F-F and F-S polymer fluids at constant pressure of P = 1 atm (0.101325 MPa). The product ScT is normalized by the thermal energy k To at the ideal glass transition temperature To- (Used with permission from J. Dudowicz, K. F. Freed, and J. F. Douglas, Journal of Physical Chemistry B 109, 21350 (2005). Copyright 2005 American Chemical Society.)...

Figure 17. Specific volume Vt and isothermal compressibility (at the glass transition temperature Tg) calculated from the LCT as a function of the inverse number l/M of united atom groups in single chains for constant pressure (P = I atm 0.101325 MPa) F-F and F-S polymer fluids. Both quantities are normahzed by the corresponding high molar mass limits (i.e., by...

Figure 22. The configurational entropy Sc per lattice site as calculated from the LCT for a constant pressure, high molar mass (M = 40001) F-S polymer melt as a function of the reduced temperature ST = (T — To)/Tq, defined relative to the ideal glass transition temperature To at which Sc extrapolates to zero. The specific entropy is normalized by its maximum value i = Sc T = Ta), as in Fig. 6. Solid and dashed curves refer to pressures of F = 1 atm (0.101325 MPa) and P = 240 atm (24.3 MPa), respectively. The characteristic temperatures of glass formation, the ideal glass transition temperature To, the glass transition temperature Tg, the crossover temperature Tj, and the Arrhenius temperature Ta are indicated in the figure. The inset presents the LCT estimates for the size z = 1/of the CRR in the same system as a function of the reduced temperature 5Ta = T — TaI/Ta. Solid and dashed curves in the inset correspond to pressures of P = 1 atm (0.101325 MPa) and F = 240 atm (24.3 MPa), respectively. (Used with permission from J. Dudowicz, K. F. Freed, and J. F. Douglas, Journal of Physical Chemistry B 109, 21350 (2005). Copyright 2005, American Chemical Society.)...

Measurements of glass transition temperatures at high pressure were made indirectly using, in particular, creep compliance [95, 96] or directly using differential scanning calorimetric techniques [97, 98]. The measured depression reaches values as high as 60°C for poly(methyl methacrylate) and polystyrene. 

One of the most important variables which affects the glass transition in addition to temperature is pressure. Light scattering experiments at high pressure are far from routine, but both polystyrene44, and PEA30,52) have now been extensively studied. The shape of the relaxation function for polystyrene was independent of pressure as well as... 

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