Polymeric films thermal analysis

Packaging Materials. As in the case of fibers, thermal analysis can easily distinguish between most polymeric films on the basis of the glass transition and the thermal history dependence of the melt and recrystallization (20, 21). From the analysis of thin films--as, for example, used in plastic bags recovered with drugs—it should be possible to identify by comparison the bag manufacturer and possibly the manufacturing lot. 

In this section the broad spectrum of melting of one-component macromolecular systems is described by means of several specific polymers. The description starts with polyethylene, the most analyzed polymer. It continues with two sections that present several special effects seen in the thermal analysis of polymers including some examples of detailed analyses by TMDSC, documenting the locally reversible melting and crystallization equilibrium within a globally metastable structure. Then illustrations of poly(oxymethylene) and PEEK are given as typical common polymeric materials. This is followed in the last section with the discussion of special effects seen in drawn polymers, as are commonly found in fibers and films. 

Polymeric films are used primarily as substrates for a variety of media (e.g., recording tapes), and as packaging materials. Similar to fibers, the thermal analysis of films may give information about orientation and thermal and mechanical history of the sample. A detailed description of thermal analysis of polymeric films can be found in Menczel et al. (1997b). Fiber and film preparation is also briefly described in Section 5.5 (of Chapter 5). 

The desired polyimide derivatives were prepared by condensation polymerization as shown in Scheme 1. The initial polyamic acids (PAA 1-4) could be spun onto a substrate and cured by ramping the temperature to 260 C. For those examples where X=(CF3)2C, the polyimide derivatives were soluble in organic solvents. These materials were usually spun in the preimidized form. The improved thermal stability of the arylamino substituted chromophores tethered to the polyimide backbone is obvious from the DSC analysis. The onset decomposition temperature measured by DSC of the aryl substituted polymer PI-2b is almost 40°C hi er than that of Pl-lb (Td = 376 vs 338T). Likewise, this stabilizing effect is apparent variable temperature, UV-visible spectroscopic studies of the polymer films. In this case, the absorbance at the max of the chromophore was monitored versus time at a variety of temperatures (18), While the absorbance of PI-2b (Amax 498 nm) was little changed after one hour at 275°C, that of Pl-lb (Amax 474 nm) decreased by almost 30%. In each case, the heating was conducted under an inert atmosphere. Studies such as these are the origin of the data shown in the last column of Table I. 

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