Conformations and Structures of Poly(oxyethylene) Melts from Molecular Dynamics Simulations and Small-Angle Neutron Scattering Experiments
Received October 30, 1995 Revised Manuscript Received February 1, 1996 Abstract: An ensemble of
H(CH2OCH2)12H chains has been
studied by molecular dynamics simulations
as both melt chains and unperturbed phantom chains as a model system to
investigate condensed phase
effects on chain conformations of poly(oxyethylene) (POE). In
addition, conformations of high molecular
weight POE chains in the melt have been determined by small-angle
neutron scattering (SANS)
experiments over a temperature range of 347-459 K. Our
simulations show that POE chains in the
melt are more extended than the phantom chains which represent the
unperturbed chains in Download the full text:
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solution.
Moreover, the melt chains exhibit a negative temperature
coefficient of chain dimensions in contrast to
a positive value for the phantom chains. The difference in chain
dimensions and the difference in the
temperature dependence of chain dimensions between melt and phantom
chains are corroborated by the
results of our SANS measurements when they are compared with
experimental results for POE chains
in solution. We attribute these significant deviations in
conformational properties of POE chains in
the melt from those of unperturbed ideal chains to condensed phase
effects, similar to those found in
1,2-dimethoxyethane (DME), a dimer molecule of POE, from both
experiments and simulations. That is,
simulations show that the population of the C-C-O gt
conformation is greater in melt chains than in
the phantom chains, while the C-C-O
g±g
populations are
much smaller in the melt, the latter effect
largely accounting for the more extended dimensions of the melt chains.
As in DME, the conformation-dependent intermolecular polar attractions (O···H interactions,
for example) account for these condensed
phase effects, which become more pronounced at lower temperatures.
Such intermolecular polar
attractions in POE melts also result in increased interatomic packing
order, but do not appear to enhance
the intermolecular orientational order when compared to simulation
results for polymethylene melts.
