Chain statistics in polyethylene crystallization

The molecular mechanism of polyethylene crystallization in solution is revisited within the framework of the bundle model [Allegra G, Meille SV. Adv Polym Sci 2005;191:87]. Previous SANS/IANS results [Sadler DM, Keller A. Science 1979;203:263; Spells SJ, Sadler DM. Polymer 1984;25:739; Stamm M, Fischer EW, Dettenmaier M, Convert P. Faraday Disc Chem Soc 1979;68:263] from partially deuterated samples are used. It is proposed that the chain deposits on the growing lamella under the form of compact crystalline domains, their size being sqrt(Mw). The radius of gyration of the crystallized chain agrees with a model consisting of a linear sequence of crystalline domains connected by chain segments with random orientations. It is suggested that the whole chain is in a bundle meta-stable equilibrium and collapses in the vicinity of the growing lamellar edge, then crystallizing around secondary nuclei. Compactness of the crystalline domains is correlated to prior chain collapse in the liquid state. The observed proportionality to sqrt(Mw) of the crystalline domain size is approximately explained.