Effective click construction of bridged-and spiro-multicyclic polymer topologies with tailored cyclic prepolymers (kyklo-telechelics)

Article abstract of DOI:10.1021/ja103402c

An alkyne-azide addition, i.e., click, reaction in conjunction with an electrostatic self-assembly and covalent fixation (ESA-CF) process has been demonstrated to effectively construct a variety of unprecedented multicyclic polymer topologies. A series of single cyclic poly(telrahydrofuran), poly (THF), precursors having an alkyne group (Ia), an azide group (Ib), two alkyne groups at the opposite positions (Ic), and an alkyne group and an azide group at the opposite positions (Id) have been prepared by the ESA-CF process. Moreover, a bicyclic 8-shaped precursor having two alkyne groups at the opposite positions (Ie) was synthesized. The subsequent click reaction of Ia with linear (IIa) and three-armed star (IIb) telechelic precursors having azide groups has been performed to construct bridged-type two-way (IIIa) and three-way (IIIb) paddle-shaped polymer topologies, respectively. Likewise, spiro-type tandem tricyclic (IVa) and tetracyclic (IVb) topologies resulted from Ib/Ic and Ib/Ie, respectively. Furthermore, three types of multicyclic topologies that are composed of repeating ring (Va), alternating ring/linear (Vb), and alternating ring/star (Vc) units have been synthesized from Id, Ic/IIa, and Ic/IIb, respectively.

Full text of DOI:10.1021/ja103402c

Published on Web 07/02/2010
Effective Click Construction of Bridged- and Spiro-Multicyclic
Polymer Topologies with Tailored Cyclic Prepolymers
(kyklo-Telechelics)
Naoto Sugai, Hiroyuki Heguri, Kengo Ohta, Qingyuan Meng, Takuya Yamamoto,
and Yasuyuki Tezuka*
Department of Organic and Polymeric Materials, Tokyo Institute of Technology, O-okayama,
Meguro-ku, Tokyo 152-8552, Japan
Received April 21, 2010; E-mail: ytezuka@o.cc.titech.ac.jp
Abstract: An alkyne-azide addition, i.e., click, reaction in conjunction with an electrostatic self-assembly
and covalent fixation (ESA-CF) process has been demonstrated to effectively construct a variety of
unprecedented multicyclic polymer topologies. A series of single cyclic poly(tetrahydrofuran), poly(THF),
precursors having an alkyne group (Ia), an azide group (Ib), two alkyne groups at the opposite positions
(Ic), and an alkyne group and an azide group at the opposite positions (Id) have been prepared by the
ESA-CF process. Moreover, a bicyclic 8-shaped precursor having two alkyne groups at the opposite positions
(Ie) was synthesized. The subsequent click reaction of Ia with linear (IIa) and three-armed star (IIb) telechelic
precursors having azide groups has been performed to construct bridged-type two-way (IIIa) and three-
way (IIIb) paddle-shaped polymer topologies, respectively. Likewise, spiro-type tandem tricyclic (IVa) and
tetracyclic (IVb) topologies resulted from Ib/Ic and Ib/Ie, respectively. Furthermore, three types of multicyclic
topologies that are composed of repeating ring (Va), alternating ring/linear (Vb), and alternating ring/star
(Vc) units have been synthesized from Id, Ic/IIa, and Ic/IIb, respectively.
Introduction
Remarkable progress has been made in the effective and
controlled synthesis of single cyclic polymers by employing
Topologically intriguing polymer architectures have been an
enduring synthetic challenge.1-4 Notably, the flexible confor-
mational motion of skeletal polymer segments between junctions
is relevant to the characteristic features of the topological
geometry.1 Cyclic and multicyclic polymers are particularly
unique from the topological viewpoint because of their absence
of chain termini in contrast to linear and branched counterparts.4
ring-expansion polymerization5 and end-to-end prepolymer
cyclization processes.6 By making use of novel cyclic polymers
having prescribed chemical structures, remarkable topology
effects have been revealed.7 Moreover, cyclic and other
topologically unique polymers have been demonstrated to be
versatile scaffolds to fabricate nano-objects of unusual shapes,
extending the scope of nanoscience and nanotechnologies
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10.1021/ja103402c  2010 American Chemical Society

Click Construction of Multicyclic Polymer Topologies
A R T I C L E S
Scheme 1. Click Construction of a Variety of Bridged- and Spiro-Type Multicyclic Polymer Topologies
remarkable achievements have been made in the construction
of simple and complex topologies, even Borromean rings.11
Moreover, various innovative methods have been developed
for the formation of catenanes comprised of large synthetic
polymer ring units.12
col13 with polymeric self-assemblies comprised of linear and star
telechelic precursors having cyclic ammonium salt groups carrying
plurifunctional carboxylate counteranions, the three forms of
bicyclic constructions, θ (fused), 8 (spiro), and two-way paddle
(bridged), as well as a trefoil (spiro tricyclic) topology have thus
Conversely, in bonded multicyclic topologies, there are three
subtypes, fused, spiro and bridged structures, according to the
covalent linking mode of the ring units.1e By employing an
electrostatic self-assembly and coValent fixation (ESA-CF) proto-
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Scheme 2. Synthesis of Single Cyclic and Bicyclic Poly(THF)s Having Alkyne and/or Azide Groups via the ESA-CF Process
far been produced.13a,14 Moreover, the ESA-CF process can
produce kyklo-telechelics, cyclic and multicyclic polymers having
predetermined functional groups at the designated positions,15
which have been further utilized to construct complex multicyclic
polymer topologies. Thus, a δ-graph (doubly-fused tricycle) topol-
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topologically significant constructions such as R-graph (fused
tricyclic) and K3,3 graph (tetracyclic) architechtures17 as well as a
variety of spiro and bridged structures of lower geometrical
symmetries have still been elusive, limiting the current scope of
synthetic polymer chemistry.
In the present study, we show an effective means to construct a
variety of unprecedented multicyclic polymer topologies by taking
advantage of an alkyne-azide cross-coupling, i.e., click, reaction
by employing tailored single cyclic and bicyclic polymer precursors
(kyklo-telechelics) as large as 300-membered rings obtained by the
ESA-CF protocol (Scheme 1). Click chemistry has now been
employed to prepare a wide variety of functional polymers as well
as block and graft copolymers.18,19 Recently, this reaction has also
been applied for the synthesis of simple rings and multicyclic
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A R T I C L E S
Figure 1. 300 MHz 1H NMR spectra of single cyclic and bicyclic poly(THF)s. [A] Ia, [B] Ib, [C] Ic, [D] Id, and [E] Ie (CDCl3, 40 °C, see Scheme 2 for
detailed structures).
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Scheme 3. Structures of the Linear and Star Poly(THF)s Having
Azide End Groups
reactions, generally require a base additive, which in turn could
cause the chain decomposition of polymer precursors.23
We have prepared a series of single cyclic and bicyclic
poly(THF)s having alkyne and/or azide groups (Ia-Ie) as key
polymer precursors for the click process. N-Phenylpyrroli-
-
dinium-terminated telechelic precursors with (1b/CF3SO3 ) and
without (1a/CF3SO3-) an alkyne group at the center position,
carrying an alkyne-(2a) or azide-functionalized (2b) dicarboxy-
late counteranion, have been employed (Scheme 2). Addition-
ally, linear (IIa) and three-armed star (IIb) poly(THF)s having
azide end groups have been prepared by the end-capping
reactions of the respective linear and star living poly(THF)s
with tetrabutylammonium azide (Scheme 3). The subsequent
click reaction of Ia/IIa and Ia/IIb selectively afforded, for the
first time, poly(THF)s having bridged-type two-way (IIIa) and
three-way (IIIb) paddle-shaped topologies, respectively (Scheme
1). Analogously, those having spiro-type tandem tricyclic (IVa)
and tetracyclic (IVb) topologies were constructed from Ib/Ic
and Ib/Ie, respectively (Scheme 1). Moreover, three new
multicyclic polymers consisting of repeating ring (Va), alternat-
polymers20 due to its extremely high efficiency even under high
dilution.21 It is also notable that the cross-coupling process offers
a rational design to selectively combine polymer precursors having
different topologies, producing complex constructions of lower
geometrical symmetries that are not accessible by one-step
processes. In contrast, a metathesis condensation proceeds through
the concurrent homo- and cross-coupling of prepolymers, resulting
in a mixture of topological isomers.22 Finally, condensation cross-
coupling processes, such as Pd-mediated Suzuki and Sonogashira
Figure 2. MALDI-TOF mass spectra of single cyclic and bicyclic poly(THF)s. [A] Ia, [B] Ib, [C] Ic, [D] Id, and [E] Ie. (Linear mode, matrix: dithranol
with sodium trifluoroacetate. DPn denotes the number of monomer units in the product.) The series of side peaks observed in the spectra were assignable as
the H+ adducts (Ia-Ie) and Na+ adducts that lost a N2 molecule from the azide group for Id.
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A R T I C L E S
Table 1. Mass/Charge Values Calculated for Ia-Ie, IIa, IIb, IIIa, IIIb, IVa, and IVb and Those for the Corresponding Peaks Observed in the
MALDI-TOF Mass Spectra
sample
formula
calculated mass/charge
observed mass/charge
Ia
Ib
Ic
Id
(C4H8O) × 35 + C35H40N2O5 plus Na+
(C4H8O) × 30 + C34H41N5O5 plus Na+
(C4H8O) × 40 + C50H58N2O8 plus Na+
(C4H8O) × 20 + C49H59N5O8 plus Na+
(C4H8O) × 60 + C103H112N4O16 plus Na+
(C4H8O) × 30 + C4H8N6 plus Na+
3115.459
2785.940
3722.303
2311.174
6011.471
2326.356
4625.516
8511.295
13902.924
9248.203
11537.372
3115.0
2786.5
3722.2
2311.1
6012.0
2326.3
4625.2
8511.8
13902.5
9248.8
11538.4
Ie
IIa
IIb
IIIa
IIIb
IVa
IVb
(C4H8O) × 55 + C24H36N12O9 plus Na+
(C4H8O) × 100 + C74H88N10O10 plus Na+
(C4H8O) × 160 + C129H156N18O24 plus Na+
(C4H8O) × 100 + C118H140N12O18 plus Na+
(C4H8O) × 120 + C171H194N14O26 plus Na+
ing ring/linear (Vb), and alternating ring/star (Vc) units were
fabricated from Id, Ic/IIa, and Ic/IIb, respectively (Scheme 1).
at the center position (1b) carrying dicarboxylate counteranions
having an alkyne (2a) or azide (2b) group. Moreover, a bicyclic
8-shaped precursor having two alkyne groups at the opposite
positions (Ie) was also synthesized (Scheme 2).
Results and Discussion
1. Synthesis of Single Cyclic and Bicyclic Poly(THF) Pre-
cursors Having Alkyne and/or Azide Groups. A series of single
cyclic poly(tetrahydrofuran), poly(THF), precursors having an
alkyne group (Ia),24 an azide group (Ib), two alkyne groups at
the opposite positions (Ic), and an alkyne group and an azide
group at the opposite positions (Id) were prepared by the
electrostatic self-assembly and coValent fixation (ESA-CF)
process using an N-phenylpyrrolidinium-terminated poly(THF)
precursor (1a) and the relevant analogue having an alkyne group
Therefore, 1a/2a and 1a/2b were first prepared through ion-
exchange by precipitating the poly(THF) precursor carrying
-
trifluoromethanesulfonate (triflate) counteranions (1a/CF3SO3 ,
1
see Figure S1A for the H NMR spectrum in the Supporting
Information (SI)) in ice-cooled aqueous solutions containing
large excesses of 2a and 2b, respectively. The extent of the
1
ion-exchange was determined by H NMR (Figures S1B and
S1C in the SI). The ionically linked polymer precursors, 1a/2a
and 1a/2b, were subjected to heat treatment by refluxing for
Figure 3. SEC traces of the precursors and products for the construction of bridged-type topologies. [A] (a) Ia, (b) IIa, (c) crude IIIa, and (d) purified IIIa.
[B] (a) Ia, (b) IIb, (c) crude IIIb, and (d) purified IIIb. (TSK G3000HXL, eluent: THF 1.0 mL/min. IIIa and IIIb were purified by preparative SEC
fractionation.)
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Figure 4. 300 MHz 1H NMR spectra of (top) IIIa and (bottom) IIIb. (CDCl3, 40 °C. The measurements were carried out after fractionation by preparative
SEC.)
1
Table 2. SEC and H NMR Analyses of the 3D Sizes of the
spectrum of Ic showed signals of the two distinctive propynyl
Bridged-Type (IIIa and IIIb) and Spiro-Type (IVa and IVb)
groups from the initiator and the counteranion, i.e., the ethynyl
Multicyclic Polymers
protons at 2.53 and 2.54 ppm and the propynyl methylene
protons at 4.69 and 4.76 ppm, respectively (Figure 1C). The
signals for the ethynyl (2.54 ppm) and azidomethylene (3.63
sample
Mp(SEC)a [kDa]
Mn(NMR)b [kDa]
Mp(SEC)/Mn(NMR)
IIIa
IIIb
IVa
IVb
7.8
10.7
8.0
11
16
12
15
0.68
0.68
0.67
0.66
(20) (a) Sumerlin, B. S.; Vogt, A. P. Macromolecules 2010, 43, 1–13. (b)
Van Camp, W.; Germonpre´, V.; Mespouille, L.; Dubois, P.; Goethals,
E. J.; Du Prez, F. E. React. Funct. Polym. 2007, 67, 1168–1180. (c)
Sumerlin, B. S.; Tsarevsky, N. V.; Louche, G.; Lee, R. Y.; Matyjas-
zewski, K. Macromolecules 2005, 38, 7540–7545. (d) Helms, B.;
Mynar, J. L.; Hawker, C. J.; Fre´chet, J. M. J. J. Am. Chem. Soc. 2004,
126, 15020–15021. (e) Malkoch, M.; Schleicher, K.; Drockenmuller,
E.; Hawker, C. J.; Russell, T. P.; Wu, P.; Fokin, V. V. Macromolecules
2005, 38, 3663–3678. (f) Li, Z.; Wu, W.; Li, Q.; Yu, G.; Xiao, L.;
Liu, Y.; Ye, C.; Qin, J.; Li, Z. Angew. Chem., Int. Ed. 2010, 49, 2763–
2767. (g) Lammens, M.; Fournier, D.; Fijten, M. W. M.; Hoogenboom,
R.; Du Prez, F. Macromol. Rapid Commun. 2009, 30, 2049–2055. (h)
Engler, A. C.; Lee, H.-i.; Hammond, P. T. Angew. Chem., Int. Ed.
2009, 48, 9334–9338.
10.2
a Peak molecular weight determined by SEC calibrated with linear
polystyrene standards. Mp determined as a polystyrene equivalent was
converted into that for poly(THF) by
Number-average molecular weight determined by H NMR.
a
factor of 0.556.30
b
1
3 h at a concentration of 0.2 g/L to promote ring-opening of
the pyrrolidinium salt groups through attack by the dicarboxylate
counteranions, leading to the formation of Ia and Ib, respec-
1
tively. The completion of the reaction was confirmed by H
NMR spectroscopic analysis (Figures 1A and 1B, Figures S1B
and S1C in the SI), where the signals for the N-phenyl-adjacent
methylene groups in 1a (3.7-4.4 ppm) were replaced with that
for the ester-adjacent methylene group, a triplet in Ia and Ib
(4.37 ppm), and the multiplet N-phenyl signals in 1a (7.4-7.6
ppm) were split into two sets in Ia and Ib (6.6-6.7 and 7.18
ppm). The signals for the ethynyl (2.54 ppm) and propynyl
methylene (4.76 ppm) groups in Ia, as well as that for the
azidomethylene group (3.62 ppm) in Ib, were visible.
(21) Polymer cyclization by a click chemistry. See: refs 6c-l. The reaction
between one unit of an eight-armed star precursor and four units of a
bifunctional end-linking reagent reportedly produced a quatrefoil
(spiro-tetracyclic) polymer product. If this could happen, the star
precursor should react with exactly four end-linking reagents in the
course of the reaction. See: Ge, Z.; Wang, D.; Zhou, Y.; Liu, H.; Liu,
S. Macromolecules 2009, 42, 2903–2910.
(22) (a) Tezuka, Y.; Komiya, R. Macromolecules 2002, 35, 8667–8669.
(b) Tezuka, Y.; Komiya, R.; Washizuka, M. Macromolecules 2003,
36, 12–17. (c) Adachi, K.; Honda, S.; Hayashi, S.; Tezuka, Y.
Macromolecules 2008, 41, 7898–7903. (d) Trnka, T. M.; Grubbs, R. H.
Acc. Chem. Res. 2001, 34, 18–29. For the application of metathesis
condensation to construct complex looped topologies, see: (e) Bogdan,
A.; Vysotsky, M. O.; Ikai, T.; Okamoto, Y.; Bo¨hmer, V. Chem.sEur.
J. 2004, 10, 3324–3330. (f) Badjic´, J. D.; Cantrill, S. J.; Grubbs, R. H.;
Guidry, E. N.; Orenes, R.; Stoddart, J. F. Angew. Chem., Int. Ed. 2004,
43, 3273–3278.
-
Likewise, the counterion-exchange of 1b/CF3SO3 (Figure
S1D in the SI) prepared through the living polymerization of
THF using an alkyne-functionalized initiator gave 1b/2a and
1b/2b (Figures S1E and S1F in the SI), which were then
1
covalently converted to Ic and Id, respectively. The H NMR
(23) Tezuka, Y.; Komiya, R.; Ido, Y.; Adachi, K. React. Funct. Polym.
2007, 67, 1233–1242.
(18) Kolb, H. C.; Finn, M. G.; Sharpless, K. B. Angew. Chem., Int. Ed.
2001, 40, 2004–2021.
(24) A cyclic poly(THF) having an alkyne group was previously synthesized
by the post-functionalization of a ring polymer (ref 23), while in the
present study, a dicarboxylate counteranion having an alkyne group
(2a) was employed for an ESA-CF process to form Ia.
(19) (a) Binder, W. H.; Sachsenhofer, R. Macromol. Rapid Commun. 2007, 28,
15–54. (b) Lutz, J.-F. Angew. Chem., Int. Ed. 2007, 46, 1018–1025.
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Click Construction of Multicyclic Polymer Topologies
A R T I C L E S
Figure 5. MALDI-TOF mass spectra of (top) IIIa and (bottom) IIIb. (Linear mode, matrix: dithranol with sodium trifluoroacetate. DPn denotes the number
of monomer units in the product. The measurements were carried out after fractionation by preparative SEC.)
ppm) protons were also visible in Id (Figure 1D). Furthermore,
8-shaped bifunctional Ie was prepared by the ESA-CF process
using a tetracarboxylate counteranion (2c) accompanied by 2
as the H+ adducts (Ia-Ie), and in addition, Na+ adducts that
lost a N2 molecule from the azide group were noticeable in Id
(Figure 2).
equiv of 1b (1b/2c, Figure S1G in the SI).25 The H NMR
SEC (Figures S2A, S2B, and S2C in the SI) shows that Ia-Id
possessed narrow size distributions (PDI ) 1.12-1.26) and
notably smaller hydrodynamic volumes compared to their linear
1
spectroscopic analysis of Ie (Figure 1E) showed the character-
istic signals for the propynyl groups at 2.54 and 4.69 ppm,
together with those for the tetracarboxylate group.
-
counterparts that were obtained by the reaction of 1a/CF3SO3
-
The MALDI-TOF mass spectra of (Ia-Ie) are collected in
Figure 2. Uniform series of peaks with an interval of 72 mass
units for the repeating THF units were observed, and each peak
exactly matched the total molar mass of the initiator fragment,
poly(THF) units, and linking group. Thus, in Figure 2A, the
peak at m/z ) 3115.0, which was assumed to be the adduct
with Na+, corresponds to Ia possessing the expected chemical
structure with a DPn of 35; (C4H8O) × 35 + C35H40N2O5 plus
Na+ equals 3115.459. Likewise, representative peaks that match
the calculated molecular weights were found for Ib-Ie (Table
1). Side peaks observed in the series of spectra were assignable
and 1b/CF3SO3 with tetrabutylammonium benzoate. The
hydrodynamic volume ratios of Ia-Id compared to their
corresponding linear counterparts, estimated by the SEC peak
molecular weights, were 0.68-0.86, in agreement with those
previously reported.13a,26 SEC of Ie (Figure S2D bottom in the
SI) showed a narrow size distribution (PDI ) 1.15) and apparent
molecular weight (Mp ) 5.9 kDa) significantly higher than that
of 1b after reaction with tetrabutylammonium benzoate (Mp )
3.7 kDa) but lower than twice that (2 × 3.7 kDa ) 7.4 kDa).
The contraction of the 3D size was estimated to be 0.80, in
good agreement with previous studies.25
In addition, linear (IIa) and three-armed star (IIb) telechelic
poly(THF)s having azide end groups were prepared by the end-
(25) The synthesis of 8-shaped polymers by an ESA-CF process has been
demonstrated before. See refs 13a and 16, as well as Oike, H.; Hamada,
M.; Eguchi, S.; Danda, Y.; Tezuka, Y. Macromolecules 2001, 34,
2776–2782.
(26) Oike, H.; Mouri, T.; Tezuka, Y. Macromolecules 2001, 34, 6592–
6600.
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Sugai et al.
Figure 6. SEC traces of the precursors and products for the construction of spiro-type topologies. [A] (a) Ic, (b) Ib, (c) crude IVa, and (d) purified IVa.
[B] (a) Ie, (b) Ib, (c) crude IVb, and (d) purified IVb. (TSK G3000HXL, eluent: THF 1.0 mL/min. IVa and IVb were purified by preparative SEC fractionation.)
capping reaction of bifunctional and trifunctional living poly-
(THF)s, respectively (Scheme 3). The 1H NMR analyses of the
products (Figure S3 in the SI) confirmed a quantitative end-
capping reaction. The signal for the azidomethylene groups was
visible at 3.30 ppm as a triplet. IR spectroscopic analysis showed
the absorption of the azide groups at 2094 cm-1 (Figures S4A
middle and S4B middle in the SI). MALDI-TOF mass spectra
of IIa and IIb (Figure S5 in the SI) showed uniform series of
peaks with an interval of 72 mass units for the repeating THF
units, and each peak exactly corresponded to the total molar
mass of the main chains and the end groups, along with the
initiator fragment in the case of IIb (Table 1).
2. Selective Construction of Bridged-Type Two-Way and
Three-Way Paddle-Shaped Polymer Topologies by the Click
Process. A single cyclic precursor having an alkyne group (Ia)
was subjected to the click reaction with linear (IIa) and three-
armed star (IIb) telechelic precursors having azide end groups
to selectively produce bicyclic (IIIa) and tricyclic (IIIb) paddle-
shaped polymers, respectively (Scheme 1).27 To ensure complete
reaction, a slight excess of Ia was charged relative to IIa and
IIb. Products IIIa and IIIb were analyzed by SEC and exhibited
a noticeable peak shift toward the higher molecular weight
region (Figure 3). The peak molecular weight for IIIa (Mp )
6.7 kDa) was nearly equal to the sum of those of the precursors,
i.e., two units of Ia and one unit of IIa (2 × 2.5 kDa + 2.1
kDa ) 7.1 kDa). Also, Mp for IIIb (11.1 kDa) was close to the
total of the corresponding telechelics, three units of Ia, and one
unit of IIb (3 × 2.4 kDa + 4.6 kDa ) 11.8 kDa).28 The yields
of IIIa and IIIb were estimated to be 48% and 57%,
respectively, based on the weights and SEC peak area ratios of
the crude products. The subsequent isolation of IIIa and IIIb
was performed by means of a preparative SEC fractionation
technique (Figures 3A-d and 3B-d).
Furthermore, the extent of the contraction in the 3D sizes of
IIIa and IIIb was estimated by the ratio of the peak molecular
weight by SEC to the number-average molecular weight by 1H
NMR (Mp(SEC)/Mn(NMR)) after the fractionation (Table 2).
The obtained value, 0.68 for both IIIa and IIIb, was comparable
with those of previously reported various multicyclic topologies
such as 8-shaped (0.69-0.80),13a,25 trefoil-shaped (0.65),13a
θ-shaped (0.63),13a,29 and δ-graph (0.61)16 constructions.
1
By comparing the H NMR spectra of product IIIa (Figure
4 top) with precursors Ia (Figure 1A) and IIa (Figure S3 top in
the SI), as well as those of IIIb (Figure 4 bottom) with Ia
(Figure 1A) and IIb (Figure S3 bottom in the SI), the selective
reaction between the alkyne and azide groups of the prepolymers
(27) A two-way paddle-shaped polymer has been obtained concomitant
with a θ-shaped topological isomer. The selective synthesis has not
been achieved before. See ref 13a as well as: (a) Tezuka, Y.;
Tsuchitani, A.; Oike, H. Polym. Int. 2003, 52, 1579–1583. (b) Tezuka,
Y.; Tsuchitani, A.; Oike, H. Macromol. Rapid Commun. 2004, 25,
1531–1535.
(28) The molecular weight of Ia used for the click reaction with IIa is
slightly different from that of Ia reacted with IIb.
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Click Construction of Multicyclic Polymer Topologies
A R T I C L E S
Figure 7. 300 MHz 1H NMR spectra of (top) IVa and (bottom) IVb. (CDCl3, 40 °C. The measurements were carried out after fractionation by preparative
SEC.)
was confirmed. Thus, the signal for the ethynyl proton (2.54
ppm) in Ia and that for the azidomethylene protons (3.30 ppm)
in IIa and IIb completely disappeared, and a triazole proton
signal emerged at 7.65 ppm in IIIa and IIIb. Moreover, the
signal for the propynyl methylene protons (4.76 ppm) observed
in Ia was replaced with that for the methylene protons adjacent
to the 4-position of the triazole ring (5.26 ppm) in IIIa and
IIIb. The IR absorbance of the azide groups at 2094 cm-1
observed in precursors IIa and IIb was scarcely visible in the
products, IIIa and IIIb, indicating that the reaction proceeded
effectively (Figure S4 in the SI). The MALDI-TOF mass spectra
of IIIa and IIIb showed a uniform series of peaks with an
interval of 72 mass units corresponding to repeating THF units,
and each peak exactly matched the total molar mass of the
complementary precursors (Figure 5). Thus, in Figure 5 (top),
the peak at m/z ) 8511.8, which was assumed to be the adduct
with Na+, corresponds to IIIa possessing the expected chemical
structure with a DPn (n + m in the chemical formula in Figure
4) of 100; (C4H8O) × 100 + C74H88N10O10 plus Na+ equals
8511.295. Furthermore, the sum of twice the molar mass of Ia
with a DPn of 35 (Figure 2A, 2 × (3115.0 - [Na+]) ) 6184.0)
and the molar mass of IIa with a DPn of 30 (Figure S5 top in
the SI, (2326.3 - [Na+]) ) 2303.3) is 8487.3, in agreement
with the molar mass of IIIa with a DPn of 100 (8511.8 - [Na+])
) 8488.8) given above. Analogously, in Figure 5 (bottom), the
peak at m/z ) 13 902.5, which was also assumed to be the
adduct with Na+, corresponds to IIIb possessing the expected
chemical structure with a DPn (n + m in the chemical formula
in Figure 4 bottom) of 160; (C4H8O) × 160 + C129H156N18O24
plus Na+ equals 13 902.924. The sum of 3-fold the molar mass
of Ia with a DPn of 35 (Figure 2A, 3 × (3115.0 - [Na+]) )
9276.0) and the molar mass of IIb with a DPn of 55 (Figure S5
bottom in the SI, 4625.2 - [Na+] ) 4602.2) is 13 878.2, in
agreement with the molar mass of IIIa with a DPn of 160
(13 902.5 - [Na+] ) 13 879.5) given above. From these results,
it was concluded that IIIa and IIIb had bridged-type multicyclic
topologies. Of note, the polymer-polymer cross-coupling
proceeded under ambient conditions, even at the low concentra-
tion of the reactive groups (10-3 M).
3. Selective Construction of Spiro-Type Tandem Tricyclic
and Tetracyclic Polymer Topologies by the Click Process. A
single cyclic precursor having two alkyne groups at the opposite
positions (Ic) and a bicyclic 8-shaped analogue (Ie) were
subjected to a click reaction with a single cyclic precursor having
an azide group (Ib) to selectively produce spiro-type tandem
tricyclic (IVa) and tetracyclic (IVb) topologies, respectively
(29) Tezuka, Y.; Tsuchitani, A.; Yoshioka, Y.; Oike, H. Macromolecules
2003, 36, 65–70.
(30) Burgess, F. J.; Cunliffe, A. V.; Dawkins, J. V.; Richards, D. H. Polymer
1977, 18, 733–740.
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A R T I C L E S
Sugai et al.
Figure 8. MALDI-TOF mass spectra of (top) IVa and (bottom) IVb. (Linear mode, matrix: dithranol with sodium trifluoroacetate. DPn denotes the number
of monomer units in the product. The measurements were carried out after fractionation by preparative SEC.)
(Scheme 1). As in the synthesis of the bridged-type multicyclic
polymers, slightly excess amounts of Ib were charged relative
to Ic and Ie to ensure complete cross-coupling.
By comparing the 1H NMR spectra of product IVa (Figure
7 top) with precursors Ic (Figure 1C) and Ib (Figure 1B), as
well as those of IVb (Figure 7 bottom) with Ie (Figure 1E)
and Ib (Figure 1B), selective reaction between the alkyne
and azide groups of the prepolymers was confirmed. Thus,
the signals for the ethynyl protons (2.53 and 2.54 ppm in Ic
and 2.54 ppm in Ie) completely disappeared with that of the
azidomethylene protons (3.62 ppm) in Ib. On the other hand,
triazole proton signals emerged at 7.81 ppm in both IVa and
IVb. Moreover, the signals for the propynyl methylene
protons (4.69 and 4.76 ppm in Ic and 4.69 ppm in Ie) were
replaced with those for the methylene protons adjacent to
the 4-position of the triazole rings (5.24 and 5.26 ppm in
IVa and 5.21 ppm in IVb). The IR absorbance of the azide
groups at 2104 cm-1 observed in precursor Ib was scarcely
visible in the products, IVa and IVb (Figure S6 in the SI),
indicating that the reaction proceeded effectively. The
MALDI-TOF mass spectra of IVa and IVb showed uniform
series of peaks with an interval of 72 mass units correspond-
ing to the repeating THF units, and each peak exactly
matched the total molar mass of the complementary precur-
sors (Figure 8). Thus, in Figure 8 (top), the peak at m/z )
9248.8, which was assumed to be the adduct with Na+,
corresponds to IVa possessing the expected chemical struc-
ture with a DPn (n + m in the chemical formula in Figure 7)
The progress of the reaction was monitored by means of a
SEC technique, where the peak was shifted toward the higher
molecular weight region (Figure 6). The observed Mp for IVa
(7.4 kDa) was almost identical to the sum of those for the
precursors; two units of Ib and one unit of Ic (2 × 2.1 kDa +
3.1 kDa ) 7.3 kDa). On the other hand, the Mp observed for
tetracyclic IVb (9.2 kDa) was marginally lower (86%) than the
individually added Mp values of the prepolymers, two units of
Ib and one unit of Ie (2 × 2.4 kDa + 5.9 kDa ) 10.7 kDa).13a,31
The yields of IVa and IVb were estimated to be 76% and 71%,
respectively, based on the weights and SEC peak area ratios of
the crude products. The subsequent isolation of IVa and IVb
was performed by means of a preparative SEC fractionation
technique (Figures 6A-d and 6B-d).
The Mp(SEC)/Mn(NMR) values were calculated to be 0.67
and 0.66 for fractionated IVa and IVb, respectively, which were
almost identical to those of IIIa (0.68) and IIIb (0.68) (Table
2).25 This suggests that an increase of the number of ring units
in bridged- and spiro-multicyclic polymer constructions causes
comparative contractions in their 3D sizes.
(31) The smaller Mp value of crude IVb could be due to the peak overlap
to excess Ib.
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Click Construction of Multicyclic Polymer Topologies
A R T I C L E S
1
Figure 9. 300 MHz H NMR spectra of (top) Va, (middle) Vb, and (bottom) Vc (CDCl3, 40 °C).
of 100; (C4H8O) × 100 + C118H140N12O18 plus Na+ equals
9248.203. Furthermore, the sum of twice the molar mass of
Ib with a DPn of 30 (Figure 2B, 2 × (2786.5 - [Na+])
)5527.0) and the molar mass of Ic with a DPn of 40 (Figure
2C, (3722.2 - [Na+]) ) 3699.2) was 9226.2, in agreement
with the molar mass of IVa with a DPn of 100 (9248.8 -
[Na+]) ) 9225.8) given above. Analogously, in Figure 8
(bottom), the peak at m/z ) 11 538.4, which was also
assumed to be the adduct with Na+, corresponds to IVb
possessing the expected chemical structure with a DPn (n +
m in the chemical formula in Figure 7 bottom) of 120;
(C4H8O) × 120 + C171H194N14O26 plus Na+ equals 11 537.372.
The sum of twice the molar mass of Ib with a DPn of 30 (2
× (2786.5 - [Na+]) ) 5527.0) and the molar mass of Ie
with a DPn of 60 (Figure 2E, (6012.0 - [Na+]) ) 5989.0)
was 11 516.0, in agreement with the molar mass of IVb with
DPn of 120 (11 538.4 - [Na+]) ) 11 515.4) given above.
On the basis of these results, we concluded that IVa and
IVb had spiro-type multicyclic topologies.
group at the opposite positions (Id) to produce a linearly
connected spiro-type multicyclic polymer (Va) (Scheme 1).
Moreover, the copolyaddition between a single cyclic precur-
sor having two alkyne groups (Ic) and linear (IIa) or three-
armed star-shaped (IIb) precursors having azide end groups
was performed to produce multicyclic polymers having
alternating ring/linear (Vb) or ring/star-branched (Vc) poly-
mer units, respectively (Scheme 1). In the case of reaction
between bifunctional Ic and trifunctional IIb, expected to
form a network polymer, the conditions were chosen to avoid
uncontrolled gelation. Products Va, Vb, and Vc, consisting
of various multicyclic polymer units, were obtained in 82%,
67%, and 72% yields, respectively.
The reaction between the alkyne and azide units was
1
confirmed by the H NMR spectra of the products, Va, Vb,
and Vc (Figure 9), compared with the precursors, Id (Figure
1D), Ic (Figure 1C), IIa, and IIb (Figure S3 in the SI). Thus,
the signals for the ethynyl (2.54 ppm), propynyl methylene
(4.69 ppm), and azidomethylene (3.63 ppm) groups in Id
were replaced with those for a triazole proton (7.81 ppm)
and the methylene group adjacent to the 4-position of the
triazole ring (5.21 ppm) in Va. Similarly, the two distin-
guishable signals each for the ethynyl (2.53 and 2.54 ppm)
and propynyl methylene (4.69 and 4.76 ppm) groups in Ic,
4. Construction of Multicyclic Polymer Topologies
Composed of Repeating Ring, Alternating Ring/Linear
and Alternating Ring/Star Units by the Click Process. The
click reaction was further applied to the polyaddition of a
single cyclic precursor having an alkyne group and an azide
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A R T I C L E S
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Figure 10. SEC traces of the precursors and products for the construction of multicyclic polymers with repeating ring-containing units. [A] (a) Id and (b)
Va. [B] (a) IIa, (b) Ic, and (c) Vb. [C] (a) IIb, (b) Ic, and (c) Vc. (For [A], TSK G3000HXL, eluent: THF 1.0 mL/min. For [B] and [C], a combination of
three columns, TSK G5000HXL, TSK G4000HXL, and TSK G3000HXL, eluent: THF 1.0 mL/min.)
as well as that for the azidomethylene groups (3.30 ppm) in
IIa and IIb, completely disappeared. Instead, the signals for
triazole protons (7.62 and 7.65 ppm) and the methylene
groups adjacent to the 4-position of the triazole rings (5.20
and 5.26 ppm) emerged in Vb and Vc. The IR absorbance
of the azide groups observed in the precursors (2104 cm-1
in Id and 2094 cm-1 in IIa and IIb) was scarcely visible in
the products, indicating that the reaction proceeded effectively
(Figure S7 in the SI).
Finally, SEC showed, upon reaction, notable peak shifts
toward the higher molecular weight region with multimodal
distributions (Figure 10). The Mp(SEC) of Va reached as high
as 10.5 kDa, suggesting the formation of a linearly arranged
spiro-type hexacyclic construction on average. Likewise, the
highest Mp(SEC) value observed for Vb was 12.8 kDa,
presumably multicyclic polymers roughly consisting of four
rings connected with three chains in an alternating fashion.
On the other hand, the Mp(SEC) of the soluble fraction of
Vc was 20.1 kDa, corresponding to oligomeric structures
consisting of approximately four Ic and three IIb units.32 In
addition, the SEC traces indicated that concurrent intramo-
lecular reactions took place. Thus, an 8-shaped product was
formed by the unimolecular reaction of Id, and a θ-shaped
polymer resulted from the bimolecular reaction of Ic and IIa
(Scheme 1, marked with * in Figure 10).
constructions, as well as tandem tricyclic and tetracyclic
constructions, were designed and successfully formed. Fur-
thermore, three multicyclic polymers with repeating ring,
alternating ring/linear, and alternating ring/star units were
produced. This novel synthetic protocol is applicable for the
construction of a wide variety of complex polymer topologies
including spiro- and bridged-multicyclic constructions, of-
fering unique opportunities for polymer material designs from
the topological point of view. The future developments of
topological polymer chemistry include combination of the
click process with an effective homocoupling process such
as a metathesis condensation for the construction of fused
polymer topologies with higher complexities, which are not
attainable solely via the present click process. This challenge
is currently being investigated in our laboratory.
Acknowledgment. This paper is dedicated to Professor Shohei
Inoue in honor of his 75th birthday. The authors are grateful to
Prof. M. Kakimoto for our access to the NMR apparatus. Financial
support from The Mitsubishi Foundation and Tokyo Tech Innova-
tive Research Engineering Award is gratefully acknowledged. T.Y.
thanks the KAKENHI (21850013), the Mizuho Foundation for the
Promotion of Sciences, The Ogasawara Foundation for the Promo-
tion of Science & Engineering, and the Tokuyama Science
Foundation for partial support of this work.
Conclusions
Supporting Information Available: Experimental details for
the synthesis of cyclic (Ia-Id), bicyclic (Ie), linear (IIa), and
star (IIb) polymer precursors, H NMR spectra (1a/2a, 1a/2b,
1b/2a, 1b/2b, and 1b/2c), SEC traces (Ia-Ie and the linear
counterparts), MALDI-TOF MS spectra (IIa and IIb), and IR
spectra (Ia-Ie, IIa, IIb, IIIa, IIIb, IVa, IVb, and Va-Vc).
This material is available free of charge via the Internet at http://
pubs.acs.org.
An alkyne-azide addition, i.e., click, reaction in conjunc-
tion with an electrostatic self-assembly and coValent fixation
(ESA-CF) process has been demonstrated as an effective
means to combine kyklo-telechelics along with linear and
branched prepolymers. Accordingly, complex multicyclic
polymer topologies such as two- and three-way paddle-shaped
1
(32) A gelated material also formed and is expected to be arising from a
higher degree of copolyaddition.
JA103402C
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14802 J. AM. CHEM. SOC. VOL. 132, NO. 42, 2010