Thermal glasses

The thermal glass-transition temperatures of poly(vinyl acetal)s can be determined by dynamic mechanical analysis, differential scanning calorimetry, and nmr techniques (31). The thermal glass-transition temperature of poly(vinyl acetal) resins prepared from aliphatic aldehydes can be estimated from empirical relationships such as equation 1 where OH and OAc are the weight percent of vinyl alcohol and vinyl acetate units and C is the number of carbons in the chain derived from the aldehyde. The symbols with subscripts are the corresponding values for a standard (s) resin with known parameters (32). The formula accurately predicts that resin T increases as vinyl alcohol content increases, and decreases as vinyl acetate content and aldehyde carbon chain length increases. 

Dynamics Simulations of the Thermal Glass Transition in Polymer Melts a-Relaxation Behavior. 

As an independent experiment to verify the findings of the TDBS we also performed quasi adiabatic measurements of the specific heat capacity Cp (74) using modulated differential scanning calorimetry (N SC) (20-22). Usually the glass transition is characterized by a step like behavior of Cp(T). The thermal glass transition... 

The equation is set up for a typical PVB with 19% residual vinyl alcohol and 1.5% residual vinyl acetate. For this typical PVB (C = 4, VOH = 19.0, and VAC = 1.5) the equation reduces to a predicted thermal glass transition of 65°C. Vinyl acetal polymers of any glass-transition temperature between roughly 20 and 120°C can be obtained by formulating with mixed aldehydes. Glass-transition temperatures for mixed aldehyde polymers can be estimated using equation 1 by... 

Figure 7 Scheme of the dynamics taking place at the glass transition for amorphous polymers, (a) Imaginary part e" of the complex dielectric function vs. frequency for two temperatures Ti and T2- The different processes are indicated, (b) Relaxation map (relaxation rate vs. inverse temperature) for the different processes, (c) Thermal glass transition where the specific heat capacity is plotted vs. inverse temperature. 

The thermal glass transition temperature (Tot) of polyvinylacetals of aliphatic aldehydes can be estimated from... 

OH and OAC are weight per cent hydroxyl and acetate. C is the number of carbons in the original aldehyde. The equation is centered for a typical polyvinyl butyral of 19 weight percent hydroxyl and 1.5 weight per cent acetate. For this typical butyral (C = 4, OH = 19.0, and OAC = 1.5) the equation reduces to a predicted thermal glass transition of 65 C. The standard error of the estimate is 3 C based on data from the general references and Ref. 21. 

Journal of Polymer Science Polymer Physics Edition 36, No.12, 15th Sept. 1998, p.2165-75 DESCRIPTION OF THERMAL RELAXATION OF POLYSTYRENE CLOSE TO THE THERMAL GLASS TRANSITION Schawe J E K Ulm,University... 

The first study reporting on the thermal glass transition of polymers under confinement is that of Keddie et al. [82]. They studied the temperature dependent thickness of thin PS films supported on silicon wafers by means of ellipsometry. They found negative deviations in the Tg for PS bulk for thicknesses below 30-40 nm. The study of Keddie et al. [82] represented an important impulse for the study of the thermal glass transition in confinement and, since then, a huge number of works have been presented in file topic. 

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