The homogeneous nucleation of the solid from the melt is studied in low molecular weight (MW) polyethylene samples with a narrow MW distribution and average carbon numbers in the range 38 ≤ n ≤ 144. The measurements employ scanning calorimetry on both emulsified and non-emulsified samples, and low- and high-angle X-ray diffraction. The shortest polyethylenes show undercoolings agreeing well with those of monodisperse n-alkanes of similar chain lengths. The longer samples extrapolate smoothly between the undercoolings measured for monodisperse alkanes and high-MW polyethylenes with n ≥ 654. The results support the earlier conclusions that any transition from a full-molecule nucleation to a 'bundle' nucleation must occur well below n ∼ 25. The absence of significant features around n = 120 where chain folding is expected to set in, implies that it may not occur at the nucleation stage, or may have no significant contribution to the nucleation energetics.
|Number of pages||9|
|State||Published - 18 Jun 2001|
Bibliographical noteFunding Information:
An important discussion with Sam Safran (Weizmann Institute) which nucleated this, and a preceding study is gratefully acknowledged. We thank Exxon Research and Engineering Co. for financial support of the work at Bar-Ilan University, NSLS and Exxon for beamtime at and use of X10A, and the MINERVA Foundation for a fellowship to H.K.