Abstract
A mathematical model for the anionic polymerization of isoprene using n-butyl lithium (n-BuLi) as initiator and N,N,N′,N′-tetramethylethylenediamine (TMEDA) as microstructure modifier, considering a system similar to a tetrapolymerization and a scheme of reaction that considers that the active sites are different in configuration, has been developed. Experimental data of conversion versus time and structure development (1,4-cis, 1,4-trans, vinyl or isopropenyl units) were taken from the literature. Since 1,4-cis structural units are difficult to measure, directly, we used reports based on indirect measurements for natural polyisoprene. The cis structural unit fraction was varied from 0.1 to 0.9 (referred to cis+trans content) in order to provide enough data for parameter estimation purposes. Rate expressions for monomer consumption as well as microstructure and dyad development were obtained from the proposed scheme of reaction. The fraction of active sites and dyad distribution were calculated using Markov chains theory, based on conditional probabilities. The kinetic model correctly describes the performance anionic polymerizations with and without TMEDA.
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Abbreviations
- (C):
-
Cis active sites
- (T):
-
Trans active sites
- (D):
-
Isopropenyl active sites
- (V):
-
Vinyl active sites
- FC :
-
Cis isomer formation
- FT :
-
Trans isomer formation
- FD :
-
Isopropenyl isomer formation
- FV :
-
Vinyl isomer formation
- FCC :
-
Cis-cis dyad formation
- FCT :
-
Cis-trans dyad formation
- FCD :
-
Cis-isopropenyl dyad formation
- FCV :
-
Cis-vinyl dyad formation
- FTC :
-
Trans-cis dyad formation
- FTT :
-
Trans-trans dyad formation
- FTD :
-
Trans-isopropenyl dyad formation
- FTV :
-
Trans-vinyl dyad formation
- FDC :
-
Isopropenyl-cis dyad formation
- FDT :
-
Isopropenyl-trans dyad formation
- FDD :
-
Isopropenyl-isopropenyl dyad formation
- FDV :
-
Isopropenyl-vinyl dyad formation
- FVC :
-
Vinyl-cis dyad formation
- FVT :
-
Vinyl-trans dyad formation
- FVD :
-
Vinyl-isopropenyl dyad formation
- FVV :
-
Vinyl-vinyl dyad formation
- Fij:
-
Total quantity of the ij dyad
- i:
-
Active site that reacts with a isoprene molecule
- [I]:
-
Initiator concentration
- j:
-
Terminal living isomer resulting from the propagation reaction
- kij :
-
Propagation rate constant
- kC, kT, kD, kV :
-
Initiation rate constants
- [M]:
-
Isoprene concentration
- MR:
-
[TMEDA]/[I]o ratio
- Р:
-
\( {\text{matrix = }}\left[ {\matrix{ {{{\text{P}}_{\text{CC}}}} \hfill &{{{\text{P}}_{\text{CT}}}} \hfill &{{{\text{P}}_{\text{CD}}}} \hfill &{{{\text{P}}_{\text{CV}}}} \hfill \\ {{{\text{P}}_{\text{TC}}}} \hfill &{{{\text{P}}_{\text{TT}}}} \hfill &{{{\text{P}}_{\text{TD}}}} \hfill &{{{\text{P}}_{\text{TV}}}} \hfill \\ {{{\text{P}}_{\text{DC}}}} \hfill &{{{\text{P}}_{\text{DT}}}} \hfill &{{{\text{P}}_{\text{DD}}}} \hfill &{{{\text{P}}_{\text{DV}}}} \hfill \\ {{{\text{P}}_{\text{VC}}}} \hfill &{{{\text{P}}_{\text{VT}}}} \hfill &{{{\text{P}}_{\text{VD}}}} \hfill &{{{\text{P}}_{\text{VV}}}} \hfill \\ }<!end array> } \right] \)
- Pij :
-
Conditional probability
- [Pc], [PT] [PD], [PV]:
-
Concentration of active sites
- Pc 1,0,0,0, PT 0,1,0,0, PD 0,0,1,0 :
-
Active sites with one monomeric unit with the negative
- PV 0,0,0,1 :
-
Charge located on the cis, trans, isopropenyl and vinyl isomer units, respectively
- PX a,b,f,m :
-
Living polymer with the negative charge located on the isomer X, (X = C, T, D or V) with a, b, f and m units of cis, trans, isopropenyl and vinyl, respectively
- val:
-
Valvassori equality: (rCT)(rTD)(rDC) = (rCD)(rDT)(rTC)
- R:
-
Cis/(cis+trans) ratio
- rij :
-
Reactivity ratio
- Wi :
-
Fraction of active sites
- W :
-
Vector (Wc, WT, WD, WV)
- XCj, XTj, XDj, XVj :
-
Isoprene conversion converted to the dyad Cj, Tj, Dj, Vj
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Tenorio-López, J.A., Benvenuta-Tapia, J.J., Vivaldo-Lima, E. et al. Modeling of polymerization rate and microstructure in the anionic polymerization of isoprene using n-butyl lithium and N,N,N′,N′-tetramethylethylenediamine considering different reactivities of the structural units. J Polym Res 19, 9909 (2012). https://doi.org/10.1007/s10965-012-9909-2
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DOI: https://doi.org/10.1007/s10965-012-9909-2