Aromatic polyethers with low polydispersities from chain-growth polycondensation [4]

Full text of DOI:10.1021/ja011499f

9902
J. Am. Chem. Soc. 2001, 123, 9902-9903
Scheme 1
Aromatic Polyethers with Low Polydispersities from
Chain-Growth Polycondensation
Tsutomu Yokozawa,* Yukimitsu Suzuki, and Shuichi Hiraoka
Department of Applied Chemistry, Kanagawa UniVersity
Rokkakubashi, Kanagawa-ku, Yokohama 221-8686, Japan
ReceiVed June 19, 2001
The development of living polymerization for the preparation
of polymers with controlled molecular weights and narrow
polydispersities is among the most significant accomplishments
in polymer synthesis.1 However, those well-defined polymers have
not been synthesized by polycondensation, which proceeds in a
step-polymerization manner, except for the cationic polyconden-
sation of phosphoranimines yielding well-defined polyphos-
phazenes.2 We have proposed that the polycondensation, like
living polymerization, would be attained by chain-growth poly-
condensation,3 where the monomer reacts with only the polymer
end group, not with other monomers,4 and we have been
successful in achieving a chain-growth polycondensation by using
phenyl 4-(N-octylamino)benzoate as a monomer and N-octyl-N-
triethylsilylaniline as a base generated by CsF.5 In this polycon-
densation, we took advantage of different substituent effects
between monomer and polymer; the aminyl anion of monomer
strongly deactivates the phenyl ester moiety of monomer, whereas
the amide linkage of polymer activates the polymer end phenyl
ester moiety. Therefore, monomer reacted with only the polymer
end group, and the polycondensation proceeded in a living
polymerization manner.
The acyl group of this monomer is thought to play an important
role in chain-growth polycondensation, because the strong
electron-donating aminyl anion can be changed to the weak
electron-donating amide linkage by bonding to the strong electron-
withdrawing acyl group. Accordingly, monomers having the acyl
group or carbonyl group as an electrophilic site are expected to
undergo chain-growth polycondensation to yield well-defined
condensation polymers such as polyesters, polythioesters, and
polyketones, and so forth. An extension of chain-growth poly-
condensation awoke our interest in whether monomers having
no acyl group as an electrophilic site also undergo chain-growth
polycondensation. It would be more difficult to achieve such a
chain-growth polycondensation, because the substituent effects
on the reactive site are not expected to change much between
monomer and polymer. We now report that the polycondensation
of a potassium 4-fluorophenolate derivative 1, which has no acyl
group as an electrophilic site, also proceeds via chain-growth
polycondensation to yield a polyether having a controlled mo-
lecular weight and low polydispersity (Mw/Mn e 1.1).
The expected course of polymerization of 1 in the presence of
a small amount of reactive initiator 2 bearing an electron-
withdrawing group is shown in Scheme 1. Thus, 1 would react
with 2 to yield ether 3 faster than with the aromatic fluorine of
1 having the strong electron-donating phenoxide group. Monomer
1 would now react with 3 to yield a dimeric ether faster than
with 1 itself, because the ether linkage of 3 is a weaker electron-
donating group than the phenoxide group of 1, and the aromatic
fluorine of 3 would be more reactive than that of the monomer.
Growth would continue in a chain polymerization manner with
the conversion of the strong electron-donating phenoxide group
of 1 to the weak electron-donating ether linkage in polymer.
We also think another polymerization course for the chain-
growth polycondensation of 1, in which phenoxide is the
propagating end group instead of fluorine. If potassium 4-meth-
oxyphenoxide 4 having the electron-donating group is used as
an initiator, 4 would react with 1, and the ether linkage formed
would make the polymer terminal phenoxide more reactive than
the phenoxide of the monomer, because ether linkage has a
stronger electron-donating character than fluorine. With the above
two assumptions, the polymerizations of 1 with 7 mol % of 2
and 4 were carried out at 150 °C in sulfolane, respectively.
Surprisingly, the polymerization of 1 with 4 did not proceed,
whereas the polymerization with 2 took place to yield a polymer
with low polydispersity (Figure 1). This result implies that not
only the reaction of 4 with 1 but also the reaction of monomers
1 with each other did not take place under this condition, and
that the polymerization of 1 in the presence of 2 did not involve
step polymerization but was initiated with 2.
To elucidate whether chain-growth polymerization takes place
in this polycondensation, the polymerization of 1 was carried out
in the presence of 7 mol % of 2, and the Mn values,6 the Mw/Mn
ratios, and the ratios of end group to initiator unit in polymer
were plotted against monomer conversion (Figure 2a). The Mn
values increased in proportion to conversion, and the Mw/Mn ratios
were less than 1.1 over the whole conversion range. The ratios
of end group to initiator unit, which were easily determined by
the 19F NMR spectra of polymer, were constantly about 1.0,
irrespective of conversion. This polymerization behavior agrees
with the features of living polymerizations.1 In general polycon-
densations that proceed in a step polymerization manner, the
molecular weight does not increase much in low conversion of
the monomer and is accelerated in high conversion, and the
Mw/Mn ratios increase up to 2.0. The ratios of end group to initiator
unit would be larger than 1.0 because monomers react with not
only an initiator but also other monomers. Consequently, Figure
2a shows that the polycondensation of 1 proceeds in a chain-
growth polymerization manner. In another series of experiments,
1 was polymerized with varying feed ratio ([1]0/[2]0). As shown
in Figure 2b, the observed Mn values of polymers were in good
(1) For recent reviews of living polymerizations, see: Kobayashi, S.
Catalysis in Precision Polymerization; John Wiley & Sons: New York, 1997.
(2) (a) Honeyman, C. H.; Manners, I.; Morrissey, C. T.; Allcock, H. R. J.
Am. Chem. Soc. 1995, 117, 7035. (b) Allcock, H. R.; Crane, C. A.; Morrissey,
C. T.; Nelson, J. M.; Reeves, S. D.; Honeyman, C. H.; Manners, I.
Macromolecules 1996, 29, 7740. (c) Allcock, H. R.; Nelson, J. M.; Reeves,
S. D.; Honeyman, C. H.; Manners, I. Macromolecules 1997, 30, 50. (d)
Allcock, H. R.; Reeves, S. D.; Denus, C. R.; Crane, C. A. Macromolecules
2001, 34, 748.
(3) (a) Yokozawa, T.; Horio, S. Polym. J. 1996, 26, 633. (b) Yokozawa,
T.; Shimura, H. J. Polym. Sci., Part A: Polym. Chem. 1999, 37, 2607. (c)
Yokozawa, T.; Suzuki, H. J. Am. Chem. Soc. 1999, 121, 11573.
(4) For examples of polycondensation in which the reaction of monomer
with polymer end group is faster than that of monomers with each other,
although the polymerization behavior does not show the character of living
polymerization, see: (a) Lenz, R. W.; Handlovits, C. E.; Smith, H. A. J. Polym.
Sci. 1962, 58, 351. (b) Newton, A. B.; Rose, J. B. Polymer 1972, 13, 465. (c)
Risse, W.; Heitz, W. Makromol. Chem. 1985, 186, 1835. (d) Percec, V.;
Shaffer, T. D. J. Polym. Sci., Part C: Polym. Lett. 1986, 24, 439. (e) Hibbert,
D. B.; Sandall, J. P. B. J. Chem. Soc., Perkin Trans. 2 1988, 1739. (f) Percec,
V.; Wang, J. H. Polym. Bull. 1990, 24, 493. (g) Percec, V.; Wang, J. H. J.
Polym. Sci., Part A: Polym. Chem. 1991, 29, 63. (h) Robello, D. R.; Ulman,
A.; Urankar, E. J. Macromolecules 1993, 26, 6718.
(5) Yokozawa, T.; Asai, T.; Sugi, R.; Ishigooka, S.; Hiraoka, S. J. Am.
Chem. Soc. 2000, 122, 8313.
(6) The Mn values of polymer were estimated by the 1H NMR spectra based
on the ratios of signal intensities of the repeating units to the initiator unit.
10.1021/ja011499f CCC: $20.00 © 2001 American Chemical Society
Published on Web 09/12/2001

Communications to the Editor
J. Am. Chem. Soc., Vol. 123, No. 40, 2001 9903
Figure 3. 19F NMR spectra of 2 and 1 in DMSO-d6 and that of polymer
end group in CDCl3 at 25 °C.
Figure 1. (a) Time-conversion curves for the polymerization of 1 in the
presence of initiator in sulfolane at 150 °C: [1]0 ) 0.17 M; [initiator]0
) 11.7 mM. Initiator: ([) 2; (9) 4. (b) GPC profile of poly1 obtained
in the polymerization of 1 with 2 for 40 min.
Figure 4. XRD pattern: (a) poly1 obtained by ordinary polycondensation
without 2 in sulfolane at 180 °C: [1]0 ) 0.33 M; (b) poly1 obtained in the
presence of 2 at 150 °C in sulfolane: [1]0 ) 0.17 M; [2]0 ) 11.7 mM.
in the lower field in the 19F NMR spectra,8 and the 19F NMR
spectra of 1, 2, and the polymer end group were measured to
estimate their reactivities (Figure 3).9 The signal of 2 appeared
in the lowest field, and the signal of the polymer end group and
that of 1 appeared in the higher field in this order, which is
identical with the order of reactivities that chain-growth poly-
condensation requires.
We found that the polyether having initiator 2 unit with low
polydispersity was less soluble in organic solvent than the
polyether obtained by ordinary polycondensation without 2.
Furthermore the powder X-ray diffraction (XRD) pattern of both
polymers showed that the crystallinity of the polymer obtained
by chain-growth polycondensation was higher than that of the
polymer obtained by ordinary polycondensation, even though the
molecular weight of the former polymer was lower than that of
the latter polymer (Figure 4). This implies that the crystallinity
of condensation polymers could be controlled by polydispersity.
Our present results demonstrate that not only monomers having
the acyl group but also monomers without the acyl group undergo
chain-growth polycondensation like living polymerization to yield
condensation polymers with low polydispersities. We anticipate
that many kinds of condensation polymers with low polydisper-
sities could be produced by chain-growth polycondensation, and
that novel physical properties of well-defined condensation
polymers could be discovered. Experiments along these lines are
in progress.
Figure 2. (a) Mn and Mw/Mn values of poly1 and the ratios of end group
to initiator unit in poly1, obtained in the presence of 2 in sulfolane at
150 °C, as a function of monomer conversion: [1]0 ) 0.17 M; [2]0 )
11.7 mM. (b) Mn and Mw/Mn values of poly1, obtained in the presence 2
in sulfolane at 150 °C, as a function of the feed ratio of 1 to 2: [1]0 )
0.17 M; [2]0 ) 8.3-167 mM; conversion ) 100%.
Acknowledgment. This work was supported in part by a Grant-in-
Aid (10650873) for Scientific Research from the Ministry of Education,
Science, and Culture, Japan.
Supporting Information Available: Synthesis of monomer 1,
polymerization procedure, and measurements (PDF). This material is
available free of charge via the Internet at http://pubs.acs.org.
agreement with those calculated with the assumption that one
initiator molecule forms one polymer chain. The Mw/Mn ratios
were less than 1.1 when the [1]0/[2]0 ratios were more than 1.0.7
This also agrees with the features of chain-growth polymerization.
This successful chain-growth polycondensation would be based
on the different reactivity of aromatic fluorines between the
polymer end group and monomer 1 as we expected; initiator 2
and the polymer end group are more reactive than 1. It has been
reported that more reactive aromatic fluorines show the signals
JA011499F
(7) When the [1]0/[2]0 ratios were 25 or above, the polymer was precipitated
during polymerization.
(8) Lozano, A. E.; Jimeno, M. L.; Abajo, J.; Camp, J. G. Macromolecules
1994, 27, 7164.
(9) The 19F NMR spectrum of polymer was measured in CDCl3, because
the polymer was not soluble in DMSO. However, it was confirmed that there
was little difference of the chemical shift of the signal b of 2 between in
DMSO-d6 and in CDCl3.