It can be observed that the pulse is stretched and the spectrum is compressed in the initial propagation step
. Afterwards, the width of central peak of the spectrum decreases and the main part of the pulse energy goes to the spectral satellites.
The specimen was meshed into uniform 80 x 80 structured bilinear quadrilateral elements, with the propagation step
set at a constant value of 0.01 m.
After one propagation step
, the whole graph is monitored so [[gamma].sub.P,k](G/e) [greater than or equal to] a - k - 1.
The reaction mechanism includes an activation reversible step that transforms inactive specie (I) into active one ([I.sup.*]), followed by a propagation step
, in which the addition of an epoxy/anhydride couple (M) to the growing chain takes place.
Therefore some initiative has to be introduced the enable the propagation step
to be interrupted and able to separate the wavelength eventually (Figure 4 (b).
In the propagation step
, peroxyl radical is able to abstract H from another fatty acid, resulting lipid hydroperoxide or peroxide (LOOH).
The propagation step
involves H: shift and :CH3 group shift to form tertiary carbenium ion which is more stable and abundantly available during propagation.
Once the [T.sub.c] is reached, the propagation step
is no longer favoured, and the reverse reaction dominates.
Once the free radical process is initiated, abstraction of the most labile hydrogen atom in the polymer by alkylperoxy radical predominates in the propagation step
Almost all thermal oxidations of vinyl polymers at moderate temperatures are postulated to involve the hydroperoxide radical in the propagation step
of the degradation.
As the kinetic model will be applied in the conversion range previous to vitrification, the specific rate constant for the propagation step
will be considered independent of conversion.