Kinetics and Mechanisms of Elementary Reactive Processes in Polymer Pyrolysis.
Kinetics and Mechanisms of Elementary Reactive Processes
in Polymer Pyrolysis.
Knyazev, V. D.
NIST GCR 09-923; 14 p. March 2009.
Sponsor:National Institute of Standards and Technology,
polymers; pyrolysis; kinetics; polyethylenes;
dissociation rates; prototypes; molecular dynamics;
Polymer backbone scission reactions were studied
computationally using polyethylene macromolecules as
prototypes. Classical RRKM modeling, molecular dynamics,
transition state theory, and molecular mechanics were
used as research tools. The results demonstrate
significant effects of polymer chain length and
conformation on backbone dissociation rates. The results
of molecular dynamics modeling performed for single
molecules in vacuum show that per-bond rates of C-C bond
dissociation increase with the increasing alkane chain
length. Moreover, per-bond rates of C-C bond
dissociation further increase (by orders of magnitude)
in the cases where the motion of polymer chain ends is
restricted. Effects of macromolecular surroundings under
the conditions of polymer melt on the rates of
carbon-carbon bond scission reactions were observed:
rate constants obtained under the condensed phase
conditions are approximately an order of magnitude lower
than those of single molecules in the gas phase. The
condensed phase rate constants display a strong
dependence on the polymer melt density, with lower
density resulting in larger rate constant values.
Research was started on the kinetics of the reactions of
H atom transfer: chain radical isomerization and
inter-chain H atom transfer. An experimental study of
the initial stages of polyethylene pyrolysis was started
using 1H NMR and GC/MS as analytical tools applied to
the condensed phase and the gas phase products,