Differential scanning calorimetry glass transition temperature, thermal

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. 

ASTM E 1356-98, ASTM Book of Standards 2002. Standard Test Method for Assignment of the Glass Transition Temperature by Differential Scanning Calorimetry or Differential Thermal Analysis . ASTM International, Conshohocken, PA. 

Thermal Properties. Each of the polyimide film samples was evaluated by differential scanning calorimetry to determine the glass transition temperature (Table I). The general observation is that the BTDA-ODA polyimide films have a higher glass transition temperature than the BDSDA-ODA polyimide films whether they are nonmodifled or are modified with cobalt chloride. This is in agreement with the work of Frye ( ) in which the dianhydride moiety, not the dieunine, was found to control the polyimide glass transition temperature. 

Differential Scanning Calorimetry. Some structural information is provided by the thermal behavior of the polymer. The homopolymer of DPP crystallizes when heated above the glass transition temperature. A crystallization exotherm at the appropriate temperature therefore indicates the presence of DPP blocks, either as the homopolymer or in a block copolymer. 

Most of the physical properties of the polymer (heat capacity, expansion coefficient, storage modulus, gas permeability, refractive index, etc.) undergo a discontinuous variation at the glass transition. The most frequently used methods to determine Tg are differential scanning calorimetry (DSC), thermomechanical analysis (TMA), and dynamic mechanical thermal analysis (DMTA). But several other techniques may be also employed, such as the measurement of the complex dielectric permittivity as a function of temperature. The shape of variation of corresponding properties is shown in Fig. 4.1. 

Glass transition temperatures were measured by differential scanning calorimetry (DSC) using a DuPont 900 Differential Thermal Analyzer. The samples were cooled to -100°C in a closed pan and then scanned to 150°C at a rate of 15°/minute. 

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