Early stages of crystallization in Isotactic Polypropylene

Heeley, E.L.; Maidens, A.V.; Olmsted, P.D.; Bras, W.; Dolbyna, I.P.; Fairclough, J.P.A.; Terrill, N.J. and Ryan, A.J. (2003). Early stages of crystallization in Isotactic Polypropylene. Macromolecules, 36(10) pp. 3656–3665.

DOI: https://doi.org/10.1021/ma021373i

Abstract

An experimental study of the early stages of crystallization in iPP has shown a qualitative
difference between the behavior at low supercooling with that observed with a deep quench. To address
previous misgivings in the limits of resolution of crystallites by wide-angle scattering, a new detector
has been used that has many orders of magnitude improvements in count rate. At low degrees of
undercooling there is a substantial gap between the appearance of a peak in the small-angle scattering,
associated with electron density modulations, and the resolution of crystallites. This early growth in
electron density has been analyzed in terms of a spinodal decomposition process and the stability limit
of isotactic polypropylene determined for three different samples of varying molecular weight. The
underlying physics of the early stages of crystallization are discussed and a number of scenarios eliminated;
at high temperature Avrami kinetics are not observed whereas at low temperatures the structure in
both the small-angle and wide-angle regimes grow contemporaneously following secondary nucleation.