ChemComm
Cite this: Chem. Commun., 2011, 47, 11092–11094
COMMUNICATION
Poly(oxyalkylene) synthesis in Brønsted Acid Ionic Liquidsw
Shaodong Zhang,ab Aurelie Feret,ab Herve Lefebvre,ab Martine Tessierab and Alain Fradet*ab
Received 11th July 2011, Accepted 2nd September 2011
DOI: 10.1039/c1cc14162g
The polyetherification of diols with 4–12 methylene units was
studied in Brønsted Acid Ionic Liquids (BAILs). High molar
mass poly(oxyalkylene)s were obtained at relatively low
temperatures (130 8C), except in the cases of 1,4-butanediol
and 1,6-hexanediol where cyclic ether formation was observed.
Scheme 1 Synthesis of linear polyether in 4-(30-butyl-10-imidazolio)-
1-butanesulfonic acid bis(trifluoromethylsulfonyl)imidide ([RBSIm]Tf2N),
Poly(oxyalkylene)s are generally synthesized by the ring-opening
m 4 6.
polymerization of the corresponding cyclic ethers, such as
oxiranes,1,2 oxetanes,3 THF4 and oxepane.5 However, tetrahydro-
1-butane-sulfonic acid bis(trifluoromethylsulfonyl)imidide,
[BBSIm]Tf2N and [OBSIm]Tf2N, respectively. High molar
mass polyethers were produced according to Scheme 1 in these
two BAILs, which served as both reaction medium and catalyst.
A preliminary study on the direct polyetherification of
1,12-dodecanediol was conducted in the two BAILs, under
various experimental conditions (Table 1). The influence of
temperature was first studied and, as expected for a kinetically
controlled polymerization, reactions were slower at lower
temperatures, as the molar masses of final products were
only about 7000–8000 at 110 1C (entries 1 and 2). However,
when the reaction was carried out at 130 1C, high molar mass
polyethers were produced, as molar mass increased to
ca. 23 000 (entries 3 and 4). It seems that the length of the
alkyl substituent of imidazolium-based ionic liquids does not
necessarily have an impact on 1,12-dodecanediol polyetherifi-
cation. For example, when polyetherification was carried out
in the two BAILs at 110 1C, no significant difference was
observed between the molar masses or polydispersities of
resulting polyethers (entries 1 and 2). The same tendency
was observed at 130 1C (entries 3 and 4).
The influence of initial diol concentration on polyetherification
was also examined. No significant molar mass variation was
observed when the monomer/BAIL molar ratio increased from
2 : 1 to 3 : 1 (entries 4 and 5), though it was found that the
viscosity of the reaction media increased. On the other hand,
when the molar ratio decreased to 1 : 1 (entries 6 and 7), even
though the reactions were maintained for a longer time (70 to 96
hours), the molar masses of resulting poly(oxydodecamethylene)s
were only 12 000 and 14 000, which shows that the reaction is less
effective in a diluted medium. The polydispersity index (PDI) of
the polyethers obtained with 2 : 1 molar ratio was close to 2,
which is the theoretical PDI value for polycondensation polymers
with the most probable distribution of molar masses. Whatever
the experimental conditions, the molar mass was limited to
23 000, which may be due to diffusion control of the kinetics
when reaction medium viscosity increases with chain growth or to
the existence of side reactions during the polymerization.
pyran (cyclic ether with 5 methylene units) does not homo-
polymerize6 and the polymerization of cyclic ethers with 7 or
more methylene units still remains largely unknown. Another
polyether synthetic method is based on the Williamson reaction
between activated diols and dihalides or involving monomers
with both hydroxy and halide groups.7–9 However, this method is
rather ineffective when dealing with aliphatic diols.10 It is also
reported that Williamson polyetherifications can be carried out
under heterogeneous conditions with phase-transfer catalysts,11–15
but polyethers precipitate during the reactions, which inevitably
limits the formation of high molar mass polyethers.
In the early 1950s, Rhoad and Flory16 reported the self-
condensation of 1,10-decanediol and of benzylic diols. In their
pioneering work, polyethers were synthesized in bulk, in the
presence of sulfamic or sulfuric acids at elevated temperature
(200–300 1C). Later on, Kobayashi et al.17 also conducted the
synthesis of linear poly(oxyalkylenes) with the same method in
the presence of H2SO4 and (C2H5)2OꢀBF3. No polymer molar
mass was reported in their works. These results encouraged our
research on direct polyetherification of different dialcohols carried
out in Brønsted Acid Ionic Liquids (BAILs), as to the latter a
burgeoning attention has been paid in recent years. BAILs are
non-volatile, easily recyclable reaction media of high thermal and
chemical stabilities,18–21 which can be used as both an alternative
of organic solvent and catalyst for acid-catalyzed reactions.22–25
In this communication, we report, to the best of our knowledge,
the first direct polyetherification of different aliphatic diols in
BAILs, namely 4-(30-butyl-10-imidazolio)-1-butanesulfonic acid
bis(trifluoromethylsulfonyl)imidide and 4-(30-octyl-10-imidazolio)-
a UPMC Univ. Paris 06, UMR 7610, Laboratoire de Chimie des
Polyme`res, Courrier 184, 94200 Ivry sur Seine, France.
E-mail: alain.fradet@upmv.fr
b
`
CNRS, UMR 7610, Laboratoire de Chimie des Polymeres, Courrier
184, 4 Place Jussieu, 75005 Paris, France
w Electronic supplementary information (ESI) available: Experimental
part, 1H–1H COSY-45 2D-NMR and 19F NMR spectra, DSC thermo-
grams. See DOI: 10.1039/c1cc14162g
c
11092 Chem. Commun., 2011, 47, 11092–11094
This journal is The Royal Society of Chemistry 2011