Student Oral Presentation #2
Overall Isothermal Crystallization Kinetics of Precision Polyethylenes
with Halogen in a Wide Temperature Range
Xiaoshi Zhang, Rufina G. Alamo
FAMU/FSU College of Engineering, Chemical and Biomedical Engineering Department, 2525 Pottsdamer St.,
Tallahassee, FL 32310-6046, USA.
Abstract
Polyethylenes with halogen substitution at a fixed distance along the methylene backbone are unique models to
study the effect of nanostructured chain-defects on folding and crystallization of polymers. Prior works showed
that the halogen is accommodated in the crystal, yet crystallization and melting are proportional to the halogen's
size and content. Furthermore, precision polyethylenes with chlorine and bromine precisely placed on each and
every 9th, 15th, and 21st backbone carbons were found to develop polymorphs. At low temperatures, the chains
pack in all-trans planar conformation (Form I). The crystals formed at higher temperatures pack in a non-planar
herringbone-like structure (Form II). In this work, we study the independent overall crystallization kinetics of
both forms. Parallel studies via differential scanning calorimetry (DSC) and Fourier transform infrared
spectroscopy (FTIR) indicate an unusual temperature dependence of the overall crystallization rate for Form II.
The overall crystallization rate of Form II displays an inversion with decreasing crystallization temperature in a
range of temperatures where both forms coexist and a second inversion at higher crystallization temperatures near
melting of Form I. The mechanism that leads to this unusual behavior will be discussed.
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