ISSN:
0098-1273
Keywords:
Physics
;
Polymer and Materials Science
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
,
Physics
Notes:
The equation of state of a semicrystalline system can be expressed in terms of the corresponding functions for the crystal and the melt, extrapolated into the solid region. This relation may be employed to obtain crystal data by means of information on the semicrystalline material or vice versa. We consider four polymers, namely, polyethylene (LPE), isotactic polypropylene (PP), polyethylene glycol (PEG), and poly(tetrahydrofuran) (PTHF). For LPE, the combination of melt and crystal theories predicts satisfactorily the volume of the semicrystalline polymer at atmospheric and elevated pressures. Good agreement between theory and experiment obtains for PEG and PTHF equilibrium melts. In addition to a PP sample measured and discussed by Zoller, a second PP polymer by Leute et al. is considered. From the corresponding semicrystalline data, the equation of state of the crystal is then derived. The PVT results for the three crystalline polymers obtained in this indirect manner are in satisfactory agreement with the predictions of crystal theory. For purposes of comparison, a polymer melt with a low melting point, viz., cis-1,4-polybutadiene, is also discussed in terms of theory. A consideration of the scaling parameters and derived quantities for both crystal and melt had resulted in certain correlations encompassing LPE, PVF2, and PClF3. These cannot be generalized to the systems considered here, particularly in the crystalline state. PEG stands out in respect to several characteristic quantities in both states, whereas PP can be more nearly grouped with the previous three polymers. The theoretical equation of state for the polymer crystal does not satisfy a principle of corresponding states. However, practically useful and accurate interpolation formulas for the theoretical expressions, polynomials at atmospheric pressure, and Tait equations for the compression ratios are derived. Over certain ranges of reduced temperature and pressure, the theoretical isotherms can be approximated by master curves for the four polymers. At atmospheric pressure, such representations are limited.
Additional Material:
7 Ill.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/pol.1979.180171109
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