Table 1 Evolution in mechanical properties of the dynamic acylhydrazone polymer films F1–F7 as a function of the incorporation of monomers
M2 and M4 into polymer P1a
Ratio of M2 and M4 to P1 (mol%)b
Thickness/mm
Mn
Mw/Mn
Tg (DSC)/uCd
Tg (E0)/uCe
E9/GPaf
c
c
Film
F1
F2
F8
F6
F7
F9
a
0
100
25
50
75
50
0.057
—
0.049
0.049
0.055
0.039
41 000
14 000
47 000
59 000
75 000
34 000
1.6
1.8
1.5
1.5
1.5
2.1
b
1
100
10
—
32
56
88
30
0.015
—
0.48
1.1
1.3
0.59
g
g
g
g
—
46
g
—
19
In presence of 2.5 mol% acid per acylhydrazone unit for F6–F8; no acid added for F9. Total molar ratio of M2 and M4 in the resulting
c
polymers on the basis of monomer units. Molecular weight Mn and distribution Mw/Mn determined by GPC with polystyrene calibration.
d
e
Glass transition temperature determined by DSC. Glass transition temperature determined by the profile of the loss elastic modulus E0.
Storage elastic modulus E9 at 25 uC. Not determined.
f
g
The degree of evolution in mechanical properties was correlated
responding-to external stimuli. Such behavior by dynamers is thus
a result of the application of the principles of constitutional
dynamic chemistry1,3 to polymer science.
with the ratio of M2 and M4 incorporated into the resulting
polymers (Table 1). Three molar equivalents of M2 and M4, on
the basis of P1 units, led to a film F7 (harder than F6), whereas
one third of both M2 and M4 gave film F8 (softer than F6) (Fig. 5).
We thank Mr. Sokei Sekine, Mr. Takumi Yamanoue and
Dr. Tomoyoshi Sasakawa for viscoelasticity measurements and
DSC analyses, and Dr. Masaki Okazaki for GPC measurements.
1
The H NMR spectra of F7 and F8 showed that both were also
random copolymers P7 and P8, respectively, consisting of M1,
M2, M3 and M4 in approximately the expected ratios. In the case
of P7, for instance, the ratio of the peak areas assigned to the
connections between M1 and M3, M1 and M4, M2 and M3, and
M2 and M4 was about 1 : 3 : 3 : 9, whereas P7 was a random
copolymer made of M1, M2, M3 and M4 in about a 1 : 3 : 1 : 3
molar ratio, as expected. Tg and viscoelasticity values were in
accordance with the proportion of M2 and M4 in the polymers.
The mechanical properties of these resulting polymers were thus
markedly different from those of the parent homopolymer P1 or
P2, implying that the mechanical properties of the acylhydrazone
polymers are adjustable via the nature and/or the proportion of the
different components incorporated.
Notes and references
{ The bis-hydrazide(s) and dialdehyde(s) at concentrations of around 0.1 M
were each dissolved in a 1 : 1 stoichiometry in CHCl3 and heated to 60 uC
for 3 h. The solution was poured into a 50 mm diameter Petri dish made of
fluoroplastic, followed by evaporation at 60 uC at normal pressure until
most of the solvent had disappeared, and then kept at 60 uC in vacuo for
24 h. About 200 mg of the total amounts of the monomers were used to
obtain the polymer film of around 0.04–0.06 mm thickness. The films thus
obtained were used as such for the study of their mechanical properties and
usually contained trace amounts of CHCl3, as determined by 1H NMR.
§ Equimolar amounts of polymer P1, on the basis of its repeating unit, bis-
hydrazide M2 and dialdehyde M4 were dissolved in CHCl3 (the
concentration was around 0.05 M), followed by the addition of
pentadecafluorooctanoic acid in 0.025 molar ratio with respect to the
resulting total acylhydrazone bonds. The solution was heated to 60 uC for
24 h and then poured into a Petri dish, followed by evaporation at 60 uC at
normal pressure until most of the solvent had disappeared, and then
in vacuo for 24 h at the same temperature.
In contrast, lack of incorporation did not bring evolution in
mechanical properties, leading only to the behavior expected for a
blend of the parent polymers P1 and P2. Thus, a slightly cloudy
film, F9, was obtained from an equimolar ratio mixture of P1 and
P2 heated in CHCl3 solution for 24 h in the absence of acid,
1 J.-M. Lehn, Prog. Polym. Sci., 2005, 30, 814.
2 J.-M. Lehn, Polym. Int., 2002, 51, 825.
1
followed by solvent evaporation. The H NMR spectrum of F9
showed that it was just a polymer blend, P9, of P1 and P2 with
only a very small amount of exchange (,5%). The film F9 seemed
to be softer than F6, although both F9 and F6 consisted originally
of the same segments. Single glass transition temperatures for P9
were observed based on both DSC and the loss elastic modulus E0,
respectively, and were about 20 uC higher than those of P1. The
profile of the storage elastic modulus, E9, showed that P9
possessed a glass state up to around 30 uC, and that E9 itself
decreased with relative moderation above Tg as the temperature
increased. These observations implied that P2 was microdispersed
in a P1 matrix at a nanometer scale in the polymer blend P9.
In conclusion, the present results show that the mechanical
properties of polyacylhydrazone dynamers can be varied through
incorporation of other components into the main chain of the
original polymer, making use of the reversible nature of the
3 J.-M. Lehn, Proc. Natl. Acad. Sci. U. S. A., 2002, 99, 4763; J.-M. Lehn,
Science, 2002, 295, 2400.
4 S. J. Rowan, S. J. Cantrill, G. R. L. Cousins, J. K. M. Sanders and
J. F. Stoddart, Angew. Chem., Int. Ed., 2002, 41, 898.
5 J.-M. Lehn, Chem.–Eur. J., 1999, 5, 2455.
6 G. R. L. Cousins, S.-A. Poulsen and J. K. M. Sanders, Curr. Opin.
Chem. Biol., 2000, 4, 270.
7 O. Ramstro¨m and J.-M. Lehn, Nat. Rev. Drug Discovery, 2001, 1, 26.
8 J.-M. Lehn, in Supramolecular Science: Where It Is and Where It Is
Going, ed. R. Ungaro and E. Dalcanale, Kluwer, Dordrecht, The
Netherlands, 1999, pp. 287.
9 J.-M. Lehn, in Supramolecular Polymers, ed. A. Cifrri, Taylor Francis,
New York, 2nd edn, 2005, ch. 1, pp. 3.
10 W. G. Skene and J.-M. Lehn, Proc. Natl. Acad. Sci. U. S. A., 2004, 101,
8270.
11 T. Ono, T. Nobori and J.-M. Lehn, Chem. Commun., 2005, 1522.
12 H. Otsuka, K. Aotani, Y. Higaki and A. Takahara, Chem. Commun.,
2002, 2838; H. Otsuka, K. Aotani, Y. Higaki and A. Takahara, J. Am.
Chem. Soc., 2003, 125, 4064; G. Yamaguchi, Y. Higaki, H. Otsuka and
A. Takahara, Macromolecules, 2005, 38, 6316.
acylhydrazone bond. This feature provides
a very useful
methodology for modifying the mechanical properties of polymers,
giving access to smart and adaptive dynamic materials1,8 such
as self-strengthening polymeric materials controlled-by and
13 T. Nishinaga, A. Tanatani, K. Oh and J. S. Moore, J. Am. Chem. Soc.,
2002, 124, 5934.
14 R. Nguyen and I. Huc, Chem. Commun., 2003, 942.
48 | Chem. Commun., 2007, 46–48
This journal is ß The Royal Society of Chemistry 2007