Copolymerization of Isoprene with <i>p</i>‑Alkylstyrene Monomers: Disparate Reactivity Ratios and the
Shape of the Gradient
Philipp von Tiedemann
Jan Blankenburg
Kamil Maciol
Tobias Johann
Axel H. E. Müller
Holger Frey
10.1021/acs.macromol.8b02280.s001
https://acs.figshare.com/articles/journal_contribution/Copolymerization_of_Isoprene_with_i_p_i_Alkylstyrene_Monomers_Disparate_Reactivity_Ratios_and_the_Shape_of_the_Gradient/7578707
The statistical copolymerization
of isoprene with <i>p</i>-ethyl- (<i>p</i>-ES), <i>p-</i>isopropyl- (<i>p-i</i>PS), and <i>p-tert-</i>butylstyrene (<i>p-t</i>BS) initiated by <i>sec</i>-butyllithium in
cyclohexane was investigated with respect to kinetics, reactivity
ratios, and formation of tapered block copolymers with pronounced
monomer gradient. An efficient synthetic route to the monomers was
developed on a multigram scale, relying on the precipitation of the
side-product triphenylphosphine oxide at low temperature. The copolymerization
kinetics and resulting molecular weight distributions were analyzed.
The dispersity, <i>Đ</i>, of the copolymers depends
on the <i>p</i>-alkyl substituent, the the degree of polymerization <i>P</i><sub>n</sub> and the comonomer mole fraction, <i>X</i>. <i>In situ</i> <sup>1</sup>H NMR kinetics characterization
revealed a strong gradient structure for all three copolymer systems
(<i>r</i><sub>I</sub> = 21.9, <i>r</i><sub><i>p‑</i>ES</sub> = 0.022; <i>r</i><sub>I</sub> = 19.7, <i>r</i><sub><i>p‑i</i>PS</sub> = 0.027; <i>r</i><sub>I</sub> = 19.8, <i>r</i><sub><i>p‑t</i>BS</sub> = 0.022). The rate of crossover
from a polyisoprenyllithium chain end (I) to a <i>p</i>-alkylstyrene (S) unit relative to the alkylstyrene homopolymerization, <i>k</i><sub>IS</sub>/<i>k</i><sub>SS</sub> (in 10<sup>–3</sup> (L mol<sup>–1</sup>)<sup>−1/4</sup>), decreases in the order <i>p</i>-MS (19.1) > <i>p</i>-ES (11.3) > <i>p-i</i>PS (5.71) ≈ <i>p-t</i>BS (5.63), supporting the observed, increasingly bimodal
character of the molecular weight distributions and the higher dispersity.
Thermogravimetric analysis revealed that all poly(<i>p</i>-alkylstyrene) homopolymers are stable up to 300 °C.
2019-01-11 17:52:54
alkylstyrene
BS
p-t
Disparate Reactivity Ratios
PS
gradient
copolymers
ES
MS
copolymerization
comonomer mole fraction
1 H NMR kinetics characterization
SS
polymerization P n
side-product triphenylphosphine oxide
weight distributions
dispersity
p-i