A computer program has been written which employs an implicit Euler method to solve directly the complete set of coupled differential equations which result from an analysis of polymerization kinetics. The program was written to make full use of the speed and power of modern supercomputers, and is suited to the solution of very large stiff systems of differential equations. The benefit of treating each propagation step as a discrete reaction is that information on the evolution of the molecular weight distribution is obtained directly without the need to make perhaps unjustified assumptions such as the steady-state approximation. For illustrative purposes, the method has been applied in the kinetic simulation of 'quasi-living' radical polymerization to assess the effect of experimental variables on the molecular weight, molecular weight distribution, and rate of polymerization. The calculations show that 'quasi-living' radical polymerization can produce polymers with polydispersities approaching those obtained with anionic 'living' polymerizations. Some necessary conditions for the formation of polymers with narrow molecular weight distribution are defined.' Moad, G., and Solomon, D. H., Aust. J. Chem., 1990, 43, 215.
Pulsed laser photolysis (PLP) has been employed to determine propagation rate constants k, for styrene polymerization in benzene over a wider temperature range (20-80 "C) than previously covered. It is proposed that a small chain length dependence of k, (overall) may, in p a t , be a consequence of a marked chain length dependence of k, for the first few propagation steps [i. e. k,(l) > k,(2) > k, (3) 2 kp( ?4)]. The propagation rate constant for styrene polymerization is given by the expressions: In k, = 16,09-289,,/(RT) (overall) or In k, = 16,47-30084/(RT) (chain length ? 4). Kinetic simulation has been applied both as an aid in data analysis and to demonstrate the reliability of the PLP technique for evaluation of propagation rate constants (k,) in radical polymerization. This has been achieved by examining the sensitivity of the molecular weight distribution of polymers formed in PLP experiments to the values of the kinetic parameters associated with polymerization and their chain length dependence. The termination rate constants (k, = k, + kd) and the ratio of combination to disproportionation (k,:kd) markedly affect the molecular weight distribution of polymer formed in PLP experiments. The prospects for evaluating the values of k,, its chain length dependence and k, : kd by direct analysis of the molecular weight distribution are discussed in the light of these results.
In this paper we give the
results of computing the effect of non-additivity of long range forces on the
fourth virial coefficient of a Lennard-Jones 12-6 gas. We have considered only
dipolar effects but have included all terms up to the fourth order of perturbation
theory. We have also calculated the effect of the fourth-order triple-dipole
term on the third virial coefficient. For the fourth virial coefficient we find
that the dispersion non-additivity, while being positive at low reduced
temperatures, goes through a negative minimum at a reduced temperature of about
1.25 before becoming small and positive at high temperatures. This is in
contradistinction to the behaviour of the third virial co-efficient where the
dispersion non-additivity is always positive.
Certain polydiene rubbers can be doped by iodine to become
electrically conducting. In
particular, the conductivity of trans-1,4-polybutadiene can
be increased by 8 orders of magnitude upon
conjugation and self-doping by iodine at room temperature, whereas
cis-1,4-polybutadiene cannot be made
conducting by reaction with iodine under the same conditions.
cis-1,4-Polybutadiene, however, can be
converted into the trans-isomer by UV irradiation. On the basis of
these previous findings, we have
developed a simple and selective method for the photochemical
generation of conducting patterns in a
nonconducting (iodinated) cis-1,4-polybutadiene matrix.
This was done by microlithographically patterned
photoisomerization of cis-1,4-polybutadiene films followed
by I2-induced conjugation and self-doping of
the UV exposed regions. The conducting patterns thus produced have
remained stable for 10 months to
date. They are colored and show strong fluorescence emission,
which enables visualization of the
conducting polymer regions. This facile method of conducting
pattern generation could make polybutadiene attractive for microelectronic applications.
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