Reversible melting of high molar mass poly(oxyethylene) |
| |
Authors: | Wulin Qiu Bernhard Wunderlich |
| |
Affiliation: | a Department of Chemistry, The University of Tennessee, Knoxville, TN 37996-1600, United States b Chemical Sciences Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831-6197, United States |
| |
Abstract: | The heat capacity, Cp, of poly(oxyethylene), POE, with a molar mass of 900,000 Da, was analyzed by temperature-modulated differential scanning calorimetry, TMDSC. The high molar mass POE crystals are in a folded-chain macroconformation and show some locally reversible melting, starting already at about 250 K. At 335 K the thermodynamic heat capacity reaches the level of the melt. The end of melting of a high-crystallinity sample was analyzed quasi-isothermally with varying modulation amplitudes from 0.2 to 3.0 K to study the reversible crystallinity. A new internal calibration method was developed which allows to quantitatively assess small fractions of reversibly melting crystals in the presence of the reversible heat capacity and large amounts of irreversible melting. The specific reversibility decreases to small values in the vicinity of the end of melting, but does not seem to go to zero. The reversible melting is close to symmetric with a small fraction crystallizing slower than melting, i.e., under the chosen condition some of the melting and crystallization remains reversing. The collected data behave as one expects for a crystallization governed by molecular nucleation and not as one would expect from the formation of an intermediate mesophase on crystallization. The method developed allows a study of the active surface of melting and crystallization of flexible macromolecules. |
| |
Keywords: | Crystal Glass transition Poly(oxyethylene) Reversible melting Temperature-modulated differential scanning calorimetry (TMDSC) |
本文献已被 ScienceDirect 等数据库收录! |
|