Effect of Self-Poisoning on Crystallization Kinetics of Dimorphic Precision Polyethylenes with Bromine

• DOI: 10.1021/acs.macromol.7b02745
• Publication Date: 2018-02-09T19:39:16Z
• Authors: Xiaoshi Zhang; Wei Zhang; Kenneth B. Wagener; Emine Boz; Rufina G. Alamo
• Keywords: 01 natural sciences; 0104 chemical sciences

High molar mass polyethylenes with bromine atoms placed on each and every 21st, 19th, 15th, or 9th backbone carbon crystallize into two distinctive layered polymorphs by changing undercooling. Crystallization at low temperatures produces Form I, a planar all-trans conformation, while at higher temperatures gauche conformers set for backbone bonds adjacent to the methine due to a close intermolecular staggering of bromines resulting in a herringbone Form II structure. In this work, the sharp range of isothermal crystallization temperatures for the transition between Form I and Form II is first identified via WAXD and melting behaviors for all members of the series. Furthermore, the temperature dependence of the isothermal linear spherulitic growth rates of Form II has been studied for a wide range of crystallization temperatures. The linear growth rates display a discrete minimum with decreasing temperature at a crystallization temperature near the melting point of Form I, a feature which is reminiscent of...