Poster Presentation 2
FTIR Spectroscopic Analysis of the Crystallization of Precision
Halogen-substituted Polyethylenes
Xiaoshi Zhang1, Laura Santonja1, Kenneth Wagener2, Emine Boz2, Rufina Alamo1
1
Chemical and Biomedical Engineering, Florida State University, Tallahassee, Florida, United States;
2
Chemistry, University of Florida, Gainesville, Florida, United States
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 has
shown that a crystal structure transition occurs in precision chlorine and bromine substituted polyethylenes
within one degree of undercooling. In the present work we have carried out a complete analysis of the FTIR
progression rocking and stretching modes of series of isothermally crystallized samples using the simple
oscillator model. The effect of halogen size to the periodic oscillation changes the effective number of
oscillators between F and Cl or Br substituted systems. Quantitative analysis of the C-halogen stretching region
and this analysis support the polymorphic transition and documents a C-C all-trans conformation of the
methylenes between halogens. Upon crystallization from the melt below the transition temperature the chains
pack in an all-trans planar conformation (Form I) with layered crystalline chlorines that present some
longitudinal disorder. The crystals formed at higher temperatures pack in a non-planar herringbone-like
structure (Form II) with a TGGT….TG’G’T backbone conformation around the substitution, while conserving
the all-trans packing of the methylene sequence, as shown in the graphical abstract.
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