No abstract

2 5 ) J. Mazur and D. McIntyre, Macromolecules, 8,464 (1975).(26) Technical difficulties would be encountered if the lirnk-0 were taken before the evaluation of integrals. To overcome these problems and enable the analytical evaluation of these integrals, recourse is made to the theory of generalized functions.27 The integrals are unchanged if a factor limk-0 exp(-cr) is inserted in them. Then, the orders of limk-0 and lim,,o may safely be interchanged, and the e limit can be evaluated after all integrals have been performed.ABSTRACT: The equilibrium melting of polyethylene is discussed based on new and literature data. Melting temperatures, superheating effects, and heats of fusion are determined on well-crystallized chain folded and extended chain crystals as well as fully extended chain crystals produced by etching. Extrapolation procedures of melting temperatures are critically evaluated. The superheating is shown to he mainly due to effects of the amorphous areas on the crystals, but some superheating remains for sufficiently large crystals after removal of the amorphous material. The heat of fusion is shown to have a surprising temperature dependence which gives a reason for errors in melting temperature extrapolations. The experimental data on volume change on fusion are summarized. The entropy of fusion is discussed in terms of the conformational change which, however, is not approximated by the constant volume entropy of fusion. The following best values have been derived: melting temperature 414.6 f 0.5 K, crystal volume 1.0338 m3/Mg, amorphous volume 1.2765 m3/Mg, heat of fusion 4.1 f 0.2 kJ/mol of CH2, and conformational melt entropy 7.8 f 1.0 J/K/mol of CH2.

No abstract