Aromatic Groups in Stretched Polyethylene Films
J. Phys. Chem. B, Vol. 107, No. 29, 2003 7025
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The fact that covalently attached aromatic groups are partially
oriented in the stretched films suggests that, while stretching-
induced net translocation of aromatic molecules from amorphous
to interfacial regions takes place when molecules are doped into
the films, it is not necessary for orientation to occur; aromatic
groups such as pyrenyl and anthryl prefer to reside in interfacial
sites even before film stretching. In addition, a long-suspected
dependence of molecular orientation on film morphology has
been verified for the first time by using polyethylene films with
a wide range of crystallinities. The dependence on crystallinity
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must exist for several reasons at higher concentrations.
These data, in toto, demonstrate that the orientation factors
reported for one molecule in different laboratories need not be
the same if the stretched polyethylene matrix is different. We
offer these results as a caveat that orientational factors are most
useful when they are compared for different guest molecules
within one polymer or for one guest molecule within different
polymers. The information that can be gleaned in the two cases
is subtly different, and the additional possibility of investigating
similar species that are covalently attached to the polymer matrix
opens possibilities for detailed investigations of polymer micro-
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Acknowledgment. We are grateful to Ms. Becky Decker
of R. T. Vanderbilt Company (Murray, Kentucky) for supplying
the EPDM materials and to Ms. Nancy Richter of the Baytown
Polymers Center of Exxon (Texas), Mr. Mario Lutterotti of
Dupont of Canada (Ontario, Canada), and Polialden Petro-
quimica of Brazil (through Prof. Teresa Atvars) for the
polyethylene films. We thank Prof. Erik Thulstrup for several
helpful suggestions and discussions, Mr. Jingsong Huang and
Prof. Miklos Kertesz for their help with the calculations, and
Dr. Chuping Luo for assistance with the low-temperature
polarization measurements. The National Science Foundation
is gratefully acknowledged for its support of this work.
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Supporting Information Available: Two tables of fluo-
rescence decay constants and relative preexponential factors for
an Auc-PE46 film and for PyCH2-PE films, UV/vis absorp-
tion spectra showing the course of the 1-pyrenyl attachment
process, excitation and emission spectra of an Auc-PE46 film.
This material is available free of charge via the Internet at http://
pubs.acs.org.
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M
References and Notes
sample showed a smaller (0, 0) emission band than (0, 1) band, due to
radiative energy transfer between the chromophores. While the 10-5
M
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