Poster Presentation 3
Polymorphism and Crystallization Kinetics of Polyethylenes with
Precise Chlorine Substitution
L. Santonja-Blasco1, X. Zhang1, K.B. Wagener2, E. Boz2, R. G. Alamo1
1
Department of Chemical and Biomedical Engineering, FAMU-FSU College of Engineering, Tallahassee FL, USA, 32310
2
Department of Chemistry, University of Florida, Gainesville FL, USA, 32611-7200
Abstract
Polyethylenes with halogen substitution at a precise distance along the methylene backbone are unique models
to study the effect of nano-structured chain-defects on folding and crystallization of polymers. Prior work
showed that the halogen is accommodated in the crystal; crystallization and melting are proportionally to the
halogen’s size [1, 2]. Furthermore, packing of the chlorine units in the crystallites of a polyethylene with
chlorine substitution on every 15th backbone carbon was found to undergo a transition within one degree of
undercooling [3]. At high undercoolings the chains pack in all-trans planar conformation (Form I) with layered
crystalline chlorines with some longitudinal disorder as demonstrated by FTIR and WAXD. The crystals formed
at higher temperatures pack in a non-planar herringbone-like structure with a TGGT….TG’G’T backbone
conformation around the substitution, while conserving the trans packing of the methylene sequence (Form II).
We have extended the structural analysis to precision samples with chlorine on the 9th, 19th and 21st carbons, and
compared the polymorphic behavior to analogs with random substitution. The unique polymorphic transition is
found in all members of the precision series. Polymorphism is absent when the chlorine is randomly distributed.
The overall crystallization kinetics measured by DSC of Forms I and II showed that with decreasing
crystallization temperature, the rate of Form I follows the usual negative temperature coefficient, while the
overall rate of Form II shows a maximum at crystallization temperatures where both forms coexist. The
polymorphic transition and equilibrium melting temperatures of both forms scale linearly with chlorine content.
References
3. Alamo RG, Jeon K, Smith RL, Boz E, Wagener KB, Bockstaller MR. 2008. Crystallization of polyethylenes containing chlorines:
precise vs random placement Macromolecules 41:7141.
4. Boz E, Nemeth AJ, Wagener KB, Jeon K, Smith R, Nazirov F, Bockstaller MR, Alamo RG. 2008. Well-defined precision
ethylene/vinyl fluoride polymers: synthesis and crystalline properties. Macromolecules 41:1647.
5. Kaner P, Ruiz-Orta C, Boz E, Wagener KB, Tasaki M, Tashiro K, Alamo RG. 2014. Kinetic control of chlorine packing in
crystals of a precisely substituted polyethylene. toward advanced polyolefin materials. Macromolecules 47: 236.
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