A facile synthetic route to functional poly(phenylacetylene)s with tunable structures and properties

Article abstract of DOI:10.1021/ma2014657

Pentafluorophenyl (PFP) ester-functionalized poly(phenylacetylene)s (PPAs, P1, P2, and P3) were designed and synthesized in desirable yields and molecular weight by using organorhodium complexes as catalysts. Furthermore, these PFP-containing PPAs were us

Full text of DOI:10.1021/ma2014657

ARTICLE
pubs.acs.org/Macromolecules
A Facile Synthetic Route to Functional Poly(phenylacetylene)s with
Tunable Structures and Properties
Xiao A Zhang,† Min Rui Chen,†,§ Hui Zhao,†,§ Yuan Gao,† Qiang Wei,† Shuang Zhang,† Anjun Qin,†
Jing Zhi Sun,*,† and Ben Zhong Tang*,†,‡
†Department of Polymer Science and Engineering, MOE Key Laboratory of Macromolecular Synthesis and Functionalization,
Zhejiang University, Hangzhou 310027, China
‡Department of Chemistry, The Hong Kong University of Science & Technology, Clear Water Bay, Kowloon, Hong Kong, China
S Supporting Information
b
ABSTRACT: Pentafluorophenyl (PFP) ester-functionalized poly-
(phenylacetylene)s (PPAs, P1, P2, and P3) were designed and synthe-
sized in desirable yields and molecular weight by using organorhodium
complexes as catalysts. Furthermore, these PFP-containing PPAs were
used as precursors to prepare a series of mono- and dual-functionalized
PPAs by the substitution of the activated ester moieties with functional
amines. The structures of the PFP-containing PPAs and the derived
functional PPAs were characterized by using multiple spectroscopic
techniques including GPC, FTIR, 1H NMR, 13C NMR, and 19F NMR.
The experimental details and the characterization data demonstrate
that activated ester synthetic route to functional PPAs is facile (just
stirring the precursor polymer with proper amine(s) at room tempera-
ture for hours), efficient (complete transition from ester to amide has
been confirmed), and quantitative (the relative content of a specific functionality can be precisely preset by controlling the feed ratio
of the functional amines). By reacting three PFP-containing PPAs with chiral amines or with chiral and nonchiral alkyl amines in a
step-by-step way, a series of seven different PPAs with asymmetric carbon in the side chains were obtained. CD measurements
indicated that the incorporation of chiral amine into polymer side chains induced helicity formation of P1 backbone. P1-C*Ph(L)
and P1-C*Ph(D) backbones adopt predominantly right-handed and left-handed helical conformation, respectively. While the
flexible spacer between the chiral center and the rigid PPA backbone blocked the induction of main-chain helicity by chiral pendants,
thus no CD signals were recorded for P2-C*Ph(L) and P3-C*Ph(L). Substitution of PFP ester with amine-functionalized PEGs
transited the hydrophobic PPAs to hydrophilic. All of the PEG-containing PPAs can be dissolved in water and form clear solutions.
Meanwhile, all of the aqueous solutions exhibit LCST behavior and the hydrophilic PEG chains and hydrophobic alkyl spacers have
positive and negative impact on the cloud point, respectively. Contact angles measurements showed that the length and content of
the PEG chains contribute greatly to the hydrophilic property, and the length of the alkyl spacers and the content of the alkyl amine
component played a contrary role. By controlling the ratio of the PEGylated and alkyl amines, the amphiphilic property of the PPAs
can be well tailored.
’ INTRODUCTION
and stereoregularities. Consequently, the systematic and explicit
investigation on structureꢀproperty relationship of functional
PAs is restricted. Therefore, it is practically demanding and
fundamentally significant to develop a platform-like synthetic
route toward various functional PAs.
In previous studies, postpolymerization reactions have been
utilized to prepare functional PAs to avoid the defects of direct
polymerization of acetylenic monomers.1e However, to the best
of our knowledge, only several reactions are involved in this field
such as ionization of amine and carboxyl pendants,7 deprotection
of the protected hydroxyl6 and carboxyl groups,9a click reaction
Functional poly(acetylene)s (PAs) have attracted much re-
search effort1 due to their versatile properties such as electrical
and photoconductivity,2 chain helicity,3 liquid crystalline property,4
gas permeability,5 and biocompatibility.6 Generally, an expected
functional PA is attained by polymerization of the specially
designed monomer, to which a corresponding functional moiety
is chemically attached. Sometimes, the functional groups, espe-
cially those used for hydrogen-bonding formation, can poison
the catalyst system.1e,7 Thus, rigid conditions and complex group-
protection strategies have to be employed.1e,8 In addition, to
obtain the expected resultants, the polymerization of acetylenic
monomers with different functionalities needs different reaction
conditions, which usually result in functional PAs with different
molecular weights and polydispersity indices, chain configurations,
Received: June 28, 2011
Revised:
July 25, 2011
Published: August 17, 2011
r
2011 American Chemical Society
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of triple bond and azide,9d hydrazinolysis of imide to amine
group,9b,c and nucleophilic substitution of halogen by imidazole.9eꢀg
Since the pioneer work of reactive polymers based on activated
esters reported by Ringsdorf and co-workers and Ferruti et al.,10
the conversion of activated esters with amines to amides has
received much attention in such diverse fields as polymer chemistry,
orthogonal reaction of bioconjugated macromolecules, and sur-
face modification of nanostructures.11 It has been proved that the
conversion of polymeric activated esters with amines is usually
quantitative and proceeds without any side reactions under mild
conditions.11a Recently, Theato’s group successfully synthesized
pentafluorophenyl (PFP) ester-functionalized PAs with a W-based
catalyst for the first time and conducted their polymer reaction
with basic aliphatic or aromatic amines.12
These key features of activated ester triggered us to explore its
application in modifying the side chain of PAs in order to obtain
elaborately designed structure and various functions. In this
work, we report our studies on the synthesis and postmodification
of PFP ester-functionalized PAs. Rh-based catalysts have been used
to prepare three PFP ester-functionalized poly(phenylacetylenes)
(PPAs). Normally, Rh complexes are more widely used than
W-based catalysts in the polymerization of phenylacetylene
derivatives because they are tolerable to variety of functionalities.
The predesigned PFP ester-functionalized PPAs (Chart 1, P1,
P2, and P3) have been obtained in high yield and acceptable
molecular weight. Furthermore, P1, P2, and P3 reacted with
functional amines, chiral amines, and PEGylated amines, giving
rise to PPA deriveatives with high molecular weight in high yield.
Besides, we have tried to tune the side-chain ratio through
controlling the feed ratio of two reacting amines. The chain
helicity, water solubility and LCST property, and amphilicity of
obtained PPAs are demonstrated.
’ RESULTS AND DISCUSSION
Polymerization. The synthetic routes to PPAs containing
activated ester pendant are shown in Schemes 1 and 2 (the
experiment details and characterization data are included in the
Experimental Section). Phenylacetylene derivatives with a penta-
fluorophenyl activated ester (monomers 1ꢀ3) were obtained by
condensation between pentafluorophenol and carboxyl-containing
phenylacetylenes (compounds 5ꢀ7) in the presence of DCC,
DMAP, and TsOH. All of the three monomers were characterized
by standard spectroscopic methods, from which satisfactory analysis
data were obtained (see Experimental Section for details).
To conduct polymerization of monomer 1, we first tried orga-
norhodium complexes [Rh(diene)Cl]2, which are widely used as
effective catalysts to polymerize phenylacetylene derivatives.1
We first attempted to use [Rh(cod)Cl]2 and [Rh(nbd)Cl]2 to
polymerize monomer 1 in THF without Et3N, and polymer P1
with moderate molecular weight was obtained (Mw ∼ 23 800,
Table 1, nos. 1 and 3). However, the yield of P1 was only 47.2%
and 65.0%, which were lower than the average level of polymeriza-
tions of phenylacetylene-based monomers. Higher yield (∼75.4%)
was obtained when Et3N was used as cosolvent (Table 1, nos. 2 and
4). Even higher yield (∼96.9%) was achieved when different
solvents such as dioxane and toluene were used (Table 1, nos. 6
and 7). Furthermore, as an excellent catalyst for the alkyne
polymerization, the zwitterionic complex Rh+(nbd)[C6H5Bꢀ-
(C6H5)3] could also transform monomer 1 into P1 in THF
(without using Et3N) in high yield of 80.1% (Table 1, no. 8).
Again, higher yield was obtained when different solvents were
used (Table 1, nos. 9 and 10).
Similarly, monomers 2 and 3 were polymerized in THF with
organorhodium complexes [Rh(diene)Cl]2. In these cases, Et3N
was found to play a more important role in achieving high yield
(Table 1, nos. 9 and 10). The zwitterionic complex Rh+(nbd)-
[C6H5Bꢀ(C6H5)3] was also an effective catalyst in the polymeri-
zation of monomers 2 and 3 (Table 1, nos. 15 and 21). Noteworthy,
both of the obtained P2 and P3 showed higher Mw value than P1,
especially when [Rh(nbd)Cl]2 was used, regardless of whether
Et3N was utilized or not.
Chart 1
Structural Characterization. The structures of the obtained
polymers P1, P2, and P3 were well-characterized by spectro-
scopic methods such as FTIR and NMR. The analysis data were
quite satisfactory corresponding to the expected molecular
structures (see Experimental Section for details). An example
of the IR spectra of polymer P2 and its monomer 2 are shown in
Figure 1. The monomer shows absorption bands at 3311 and
Scheme 1
Scheme 2
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Table 1. Polymerizations of PFP Ester-Functionalized
Phenylacetylenes (Monomers 1ꢀ3)a
yield
Mw/
no.
catalyst
solventb
(%)
Mw
Mn
c
c
Monomer 1
1
2
3
4
5
6
7
8
9
[Rh(cod)Cl]2
THF
47.2
23 800 1.71
31 800 1.85
23 100 1.54
41 300 1.92
7 800 1.93
9 500 2.54
19 300 4.52
7 000 1.90
12 500 2.40
[Rh(cod)Cl]2
[Rh(nbd)Cl]2
[Rh(nbd)Cl]2
[Rh(cod)Cl]2
[Rh(cod)Cl]2
[Rh(cod)Cl]2
THF/Et3N
THF
75.0
65.0
75.4
68.9
83.3
96.9
80.1
88.5
THF/Et3N
DCM/Et3N
toluene/Et3N
dioxane/Et3N
Rh+(nbd)[C6H5Bꢀ(C6H5)3] THF
Rh+(nbd)[C6H5Bꢀ(C6H5)3] DCM
10 Rh+(nbd)[C6H5Bꢀ(C6H5)3] toluene
91.5 16 300d 3.22
Monomer 2
11 [Rh(cod)Cl]2
12 [Rh(cod)Cl]2
13 [Rh(nbd)Cl]2
14 [Rh(nbd)Cl]2
THF
trace
86.4
THF/Et3N
THF
70 600 2.22
11.2 296 400 2.15
89.1 305 400 2.28
THF/Et3N
15 Rh+(nbd)[C6H5Bꢀ(C6H5)3] THF
74.6
83 900 2.41
Figure 1. IR spectra of (A) monomer 2, (B) P2 (sample from Table 1,
no. 12), and (C) P2-C*Ph (L) (sample from Table 2, no. 7).
Monomer 3
16 [Rh(cod)Cl]2
17 [Rh(cod)Cl]2
18 [Rh(nbd)Cl]2
19 [Rh(nbd)Cl]2
20 [Rh(cod)Cl]2
THF
trace
78.4
84.0 and 75.9, which completely disappear in the spectrum of P2.
Instead, two new peaks appear at δ 134.1 and 114.7, which are
assignable to the polyene carbons of the polymer.2b This result,
like the IR spectra, once again confirms that the triple bond of the
monomer has been consumed by the polymerization reaction.
Accordingly, the resonance of the phenyl carbons directly attached
to the double bond is downfield shifted to δ 125.3 from δ 114.7,
for the phenyl groups now have linked in conjugation with
polyene backbone after polymerization.
THF/Et3N
THF
97 300 1.94
6.8 267 800 2.18
82.8 288 000 2.61
95.2 104 800 2.25
82.2 92 100d 2.42
THF/Et3N
toluene/Et3N
21 Rh+(nbd)[C6H5Bꢀ(C6H5)3] toluene
a Carried out at room temperature under nitrogen for 24 h in THF or
THF/Et3N, [M]0 = 0.2 mol/L, [cat.] = 4 mmol/L; Abbreviations: THF =
tetrahydrofuran, DCM = dichloromethane, Et3N = triethylamine, PPh3 =
triphenylphosphine, cod =1,5-cyclooctadiene, nbd =2,5-norborndiene, Mw
= weight-average molecular weight, Mn = number-average molecular
weight. b In the case of the THF/Et3N mixture, one drop of Et3N
was used. c Estimated by gel permeation chromatograph (GPC) in THF
on the basis of polystyrene calibration. d Data for the soluble fraction; for
the polymerization product was only partially soluble in THF.
Since polymers and their monomers contains PFP activated
ester moiety, 19F NMR spectroscopy has been utilized to analyze
their structures. Exemplary 19FNMRspectraofP2and its monomer
2 are shown in Figure 4. Both spectra show three signals with a
2:1:2 integral ratio, which can be ascribed to three chemically
1
different fluorine atoms of the PFP ester. Like H signals,
19F signals of P2 are broader than those of its monomer 2.
Identical results are obtained, as monomers 1, 3 and their
polymers P1, P3 are concerned.
2106 cmꢀ1, which are ascribed to the stretching vibrations of
ꢁCH and CtC, respectively. Both of the two bands are absent
in the spectrum of P2, indicating that the acetylene triple bond of
monomer 2 has been fully consumed during the rhodium-
catalyzed polymerization. On the other hand, like that of mono-
mer 2, the spectrum of polymer P2 exhibits a strong band at
1780 cmꢀ1 associated with CdO stretching vibration, which
indicates that the activated ester functionality remains intact after
the polymerization.
Polymer Reaction and Resultant Characterization. The
pentafluorophenol group can be easily substituted by strong
nucleophilic reagents such as amines and alcohols.11 Therefore,
various amines were separately chosen to react with P1, P2, or P3
(see Scheme 3). After simple stirring the solution of polymer and
amine in THF (one drop of Et3N added) at room temperature
for 12 h ([polymer]:[amine] = 1:1.1), the target polymers were
synthesized in high yields (see Table 2). Compared with other
polymers, PPAs with PEG side chain were obtained in a lower
yield. The main reason is that the pure polymer could be obtained
over three times precipitations, which caused the washing away
of the resultant.
A significant feature of the experimental data in Table 2 is the
small differences in Mw and Mw/Mn (PDI) between the analo-
gous resultants. For example, through reaction of P1 (Table 1,
no. 2) with L-1-phenylethylamine and D-1-phenylethylamine,
P1-C*Ph(L) and P1-C*Ph(D) have been obtained in high yield
with similar values of Mw and PDI. The differences in Mw and
To further characterize the polymers, NMR spectroscopy is an
effective method. 1H NMR spectra of polymer P2 and its monomer
2 are shown in Figure 2. For the polymer, there is no resonance
peak around δ∼3.00, which is associated with the acetylene proton,
and a new peak due to the resonance of olefinic protons appears
at δ ∼ 5.76, indicating that the polymerization has transformed
the acetylenic triple bond in monomer 2 to olefinic double bond
in P2. Meanwhile, the polymerization has also upfield shifted the
resonance of the phenyl protons to δ ∼ 6.62 and 6.44 from δ ∼
7.41 and 6.82, respectively (Figure 2, peaks b and c).
The 13C NMR spectra of polymer P2 and its monomer 2 are
shown in Figure 3. The acetylene carbon atoms of 2 resonate at δ
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Figure 2. 1H NMR spectra of (A) monomer 2 and (B) P2 (sample from
Table 1, no. 12) in chloroform-d. The solvent peaks are marked with
asterisks.
Figure 4. 19F NMR spectra of (A) monomer 2, (B) P2 (sample from
Table 1, no. 12), and (C) P2-C*Ph (L) (sample from Table 2, no. 7) in
chloroform-d. The solvent peaks are marked with asterisks.
of their properties and the systematic investigation on structureꢀprop-
erty relationship for the synthesized functional PPAs.
Even better results can be extracted from Table 2. P1-C*Ph(L)
and P1-C*Ph(D) have been derived from the postreaction of P1
(Table 1, no. 2) with L-1-phenylethylamine and D-1-phenylethy-
lamine, and the parameters of Mw and Mw/Mn are quite similar to
each other. The differences in Mw and Mw/Mn are 1.7% and
13.1%, respectively (see Table 2, nos. 5 and 6). It is of great
importance to obtain polymers in a controllable way. By means of
living polymerization such as atom transfer radical polymerization
(ATRP) and reversible additionꢀfragmentation chain transfer
(RAFT) polymerization, polymers from olefinic monomers are
easy to achieve this goal. But for functional PPAs, it is very
difficult to perform living polymerization.1e,15 Consequently, Mw
and Mw/Mn of expected PPAs cannot be controlled in the
polymerization of different reaction batches, functionalities, and
conditions. Combining the data in Table 2 with the mild reaction
conditions, we have presented a facile route to the synthesis of
functional PPAs with unique characteristic of controllable Mw
and Mw/Mn values, which may pave a way to more precisely
compare and systematically investigate on structureꢀproperty
relationship of PPA derivatives.
The data in table indicate that, as for PPAs with PEG side
chains, GPC measurement gave much lower Mw values (Table 2,
nos. 3, 4, 8, 9, 11, and 12). This observation is probably caused by
the fact that the hydrodynamic volumes of the brush-type PPAs
probably differ substantially from those of the linear polystyrene
standards.16 Besides, degradation of the PFP ester-functionalized
PPAs and/or the PEG-functionalized PPAs may be another possible
mechanism of the low Mw values. In our experiments, all the
polymer reactions were performed under same conditions: under
nitrogen at room temperature. It is unreasonable to conclude that
the degradation of the PFP ester-functionalized PPAs happened
only in the case of reacting with amino-functionalized PEGs.
Therefore, the degradation of PFP ester-functionalized PPAs is
Figure 3. 13C NMR spectra of (A) monomer 2 and (B) P2 (sample
from Table 1, no. 12) in chloroform-d. The solvent peaks are marked
with asterisks.
PDI are 15.7% and 5.2%, respectively. In our previous works, we
found for several times that the polymerization of different
phenylacetylenic monomers at same condition gave rise to
polymers with drastically different values of Mw and PDI. As
revealed by the data in Chart 2 (the differences in structure are
highlighted in red), the polymers derived from reference mono-
mers 1 and 2 (RM1 and RM2) have evidently discrete Mw and PDI
values. The differences in Mw and PDI are 40.2% and 44.4%,
respectively, indicating that a small change in the flexible spacer
between the PPA backbone and pyrene moiety may lead to huge
fluctuated variations in the resultants.8 The polymerization data
of RM3 and RM4 demonstrate that the change in functional
moieties (from pyrene to ferrocene) in the PPAs’ side chains can
also result in pronounced changes in Mw and PDI values.13 When
both the functional moiety and the linkage to PPA backbone are
changed, the polymerization should be frequently carried out in
different conditions.14 As reflected by the polymerization data of
RM5 and RM6, in this case the parameters of Mw and PDI for the
resulted polymers are not comparable. The existence of evident
differences in Mw and PDI has heavily hampered the precise evaluation
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Scheme 3
of P2-C*Ph(L), indicating the full consumption of PFP ester in
P2 during the polymer reaction. Meanwhile, there emerges a new
band at ∼1640 cmꢀ1, corresponding to the stretching vibrations
of the carbonyl group in amide group and a broad band at
∼3292 cmꢀ1, which is assignable to the stretching vibrations
of NꢀH. The IR spectra confirm that the PFP ester has been
substituted completely by amines. Furthermore, it is known that
polyacetylenes undergo thermal degradation in the presence of
oxygen, and the degradation product shows strong absorption
bands at ∼1800 cmꢀ1, which is ascribed to CdO formed during
the degradation.15 Therefore, we can further conclude from the
IR result that the polymers have not degraded during the polymer
reaction.
Table 2. Polymer Reactions between PFP Ester-Functional-
ized PPAs and Aminesa
resultant
b
b
no.
amine
polymer
yield (%) Mw Mw/Mn
P1
1
2
3
4
5
6
L-1-phenylethylamine
D-1-phenylethylamine
MePEG350-NH2
P1-C*Ph(L)
P1-C*Ph(D)
P1-PEG350
P1-PEG750
86.2
91.2
88.5
78.4
90.6
92.3
27 300 2.40
32 400 2.28
5 400 1.43
3 950 1.23
28 800 1.98
28 300 1.72
MePEG750-NH2
1-tetradecylamine (TDA) P1-C14
1-butylamine (BA)
P1-C4
1H NMR spectra of polymer P2-PEG750 in deuterated chloro-
form and water are shown in Figure 5. Compared with the
spectrum of P2 in CDCl3 (see Figure 2), new peaks at δ 7.90 and
3.33 appear in the spectrum of P2-PEG750, which are ascribed to
the resonance of amide and terminal methyl protons, respec-
tively. Meanwhile, the integration value of peaks round δ 3.62
increases from 2 to 62, indicating the attachment of PEG chain to
the polymer. However, in the spectrum of P2-PEG750 in D2O,
there are only two peaks at δ 3.43 and 3.10 due to the resonance
of protons of water-soluble PEG chain. Hydrophobic backbones
and alkyl chains cannot be dissolved in water; therefore, no peaks
are observed. 19F NMR spectrum spectroscopy is also useful
to ascertain whether the PFP ester is completely substituted by
amine or not. As shown in Figure 4C, in comparison with P2, in
the 19F NMR spectrum of P2-C*Ph(L), the resonance peaks
corresponding to F atoms disappeared completely. Like IR and
1H NMR spectral characteristics, 19F NMR spectrum indicates
that the reaction of PFP ester and amines is completely conducted.
Tuning Side-Chain Ratios. Since the polymer reactions of
PFP ester-functionalized PPAs with amines are facile, complete,
and controllable, we designed to prepare dual-functionalized PPAs
by attach two kinds of amines to one maternal PPA by using a
step-by-step strategy (Scheme 4). One attempt was to synthesize
PPAs with different ratios of L-2-phenylethylamine [C*Ph(L)]
and 1-butylamine (C4) in the side chains. The expected polymers
were obtained in desirable yields by direct reaction of P1 with
L-2-phenylethylamine and 1-butylamine, and the resultants were
named as follows: P1-C*Ph(L)75%-C425%, P1-C*Ph(L)50%-
C450%, and P1-C*Ph(L)25%-C475%. The other attempt was to
prepare functional PPAs with different amphiphilicity by reaction
P2
7
8
9
L-1-phenylethylamine
MePEG350-NH2
P2-C*Ph (L)
P2-PEG350
P2-PEG750
92.4
82.8
84.8
58 800 1.99
6 930 1.38
7 260 1.51
MePEG750-NH2
P3
10 L-1-phenylethylamine
11 MePEG350-NH2
12 MePEG750-NH2
P3-C*Ph (L)
P3-PEG350
P3-PEG750
93.8
78.6
85.2
78 500 2.03
5 240 1.41
8 140 2.22
a Carried out at room temperature under nitrogen for 12 h in THF/
Et3N, [polymer]:[amine] = 1:1.1. P1 P2, and P3 were taken from
Table 1, no. 2, no. 12, and no. 17, respectively. b Estimated by gel
permeation chromatograph in THF on the basis of polystyrene calibration.
impossible through polymer reaction. To rule out the degrada-
tion of PEG functionalized PPAs, thermal gravimetric analysis
(TGA) was conducted on the obtained polymers. Similar to the
observation for PFP ester-functionalized PPAs, PPAs with PEG
side chain also show typical polymer’s TGA curves (see Figure S6),
indicating that the substitution process of amino-functionalized
PEG chain to PFP moieties did not degrade the polymers.
The transformation from PFP ester-functionalized PPAs to
expected functional PPAs. Spectroscopic analyses (such as NMR
and FTIR) were conducted on the characterization of the poly-
mers’ structure (see Experimental Section for details). A repre-
sentative example of the IR spectrum of P2-C*Ph(L) is shown in
Figure 1C. As described above, P2 shows an absorption band
at ∼1780 cmꢀ1, which is ascribed to the stretching vibration of
carbonyl group in ester moiety. This band is absent in the spectrum
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Chart 2
Scheme 4
Figure 5. 1H NMR spectra of P2-PEG750 in chloroform-d (A) and D2O
(B). The solvent peaks are marked with asterisks.
of P1 with methyl-capped amino-functionalized poly(ethylene
glycol) (MePEG350-NH2) and 1-tetradecylamine (C14), and
the resultants were as follows: P1-PEG35075%-C1425%, P1-
PEG35050%-C1450%, and P1-PEG35025%-C1475%.
available copolymerization rate and other kinetic parameters, the
copolymerization of different phenylacetylenic monomers can-
not definitely result in copolymers with expected composition of
functionalities. Hopefully, the data summarized in Table 3 indicate
that the synthetic strategy of postpolymerization reaction of PFP-
ester functionalized PPAs with different amines can lead to PPA-
based copolymers with quantitatively controllable content of
specific functionalities. Moreover, the dual functionalized PPAs
have similar values of Mw and Mw/Mn (Table 3). These results
make it possible to study the structureꢀproperty relationship of
functional PPAs in a more systematic and explicit way.
Chain Helicity. Polymerization of monosubstituted acetylenes
catalyzed by Rh complexes usually gives polyacetylenes with
highly stereoregular head-to-tail cis-transoidal conformations,18,19
which are believed to be advantageous, even if not indispensable,
for helix induction.20ꢀ22 Therefore, the backbone of our chiral
pendant-containing polyacetylenes may take helical conformation.
To check this idea, we have measured the circular dichromism (CD)
1
Figure 6 shows the H NMR spectra of PPAs with different
ratio of C*Ph(L) and C4. Typically, in the case of Rf = 50%/50%
(P1-C*Ph(L)50%-C450%), the resonance peaks around δ ∼
5.04 and 3.42 are ascribed to the chiral carbon protons and CH2
ortho to amino groups, respectively. Besides, terminal alkyl
protons resonate at δ ∼ 0.79 and others between δ ∼1 and 2.
Every resonance peak is ascertained so well that the Ra value
(the actual molar ratio of C*Ph(L) to C4 alkyl chain) can be
estimated from the spectrum, which is 0.52/0.48 (Table 3), very
close to the ideal Rf value (the feed ratio of C*Ph(L) and C4).
PPAs with different ratio of PEG and C14 alkyl chains were
characterized by 1H NMR as well (Figure S7), and the Ra values
were also calculated and are summarized in Table 3. These results
indicate that we can readily control the degree of functionalities
in the side chains of functional PPAs by varying the feed ratio of
two reacting amines. Unlike the vinyl-based monomers that have
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Figure 6. 1H NMR spectra of (A) P1-C*Ph(L)75%-C425%, (B) P1-
C*Ph(L)50%-C450% in DMSO-d6, and (C) P1-C*Ph(L)25%-C475% in
chloroform-d. The integrated areas for peaks are shown as numerals and
the solvent peaks are marked with asterisks.
Figure 7. UV (upper panel) and CD (lower panel) spectra of P1-
C*Ph(L), P1-C*Ph(D), P2-C*Ph(L), and P3-C*Ph(L) in DMF at room
temperature. The UV spectrum of monomer 1 in DMF is shown for
comparison. Concentration: 0.15 mM.
Table 3. Preparation of Functional PPAs with Different Ratio
of Two Side Chainsa
absorption shoulder and hillside, respectively. In addition, P1-
C*Ph(L) exhibits positive Cotton effect at the 376 nm, the sign of
which is coincident with that of L-2-phenylethylamine. These data
indicate that the chiral pendant of P1-C*Ph(L) successfully induces
backbone helicity through chirality transfer from the pendant to the
backbone. Similar to its twin brother, P1-C*Ph(D) exhibits identi-
cally intense CD signals in the region where the backbone absorbs,
but as a minus-to-plus pattern. In contrast, P2-C*Ph(L) and P3-
C*Ph(L) exhibit no CD signals at expected wavelengths, mainly
because the chirality transfer is blocked by the flexible spacer
between the chiral pendant and the backbone of P2 and P3, and
the chiral pendant fails to induce backbone helicity.
Activated ester strategy provides an effective way of quantita-
tive controlling the content of chiral moiety or chiral content.
By using a step-by-step method, we designed and synthesized a
series of PPAs with different chiral contents, which are named
by P1-C*Ph(L)75%-C425%, P1-C*Ph(L)50%-C450%, and P1-
C*Ph(L)25%-C475%. Figure 8 shows the UV (upper panel) and
CD (the lower panel) spectra of these polymers in DMF. The
absorption feature of the three polymers is identical to that of P1-
C*Ph(L), While the CD spectra show that the intensity of the
CD signals depends on the chiral content. It is clearly seen that
weaker intensity of CD signals centered at 376 nm corresponds
with lower chiral content. To examine whether the chiral
amplification behavior exists, the Kuhn dissymmetry factor g,
defined as Δε/ε (ε: molar absorbance) at 376 nm, is plotted
against the chiral content of the polymers (Figure 9). The plot of
|g376| value shows a good linear relationship with the chiral
content, indicative of no or a very weak cooperativity between
repeat units. Thus, there is no chiral amplification behavior between
the backbone and chiral pendant of polyacetylenes with different
c
d
d
Rfb
Ra
yield (%) Mw
Mw/Mn
P1-C*Ph(L)75%-C425% 0.75/0.25 0.76/0.24
P1-C*Ph(L)50%-C450% 0.50/0.50 0.52/0.48
P1-C*Ph(L)25%-C475% 0.25/0.75 0.28/0.72
P1-PEG35075%-C1425% 0.75/0.25 0.79/0.21
P1-PEG35050%-C1450% 0.50/0.50 0.54/0.46
P1-PEG35025%-C1475% 0.25/0.75 0.24/0.76
91.3
88.5
90.6
72.8
75.3
81.9
26 800
25 900
25 300
5270
2.53
2.46
2.51
1.38
1.24
1.35
5050
4860
a Carried out at room temperature under nitrogen for 12 h in THF/
Et3N. P1 was taken from Table 1, no. 2. b The feed molar ratio of Rf =
PEG/TDA or C*Ph/BA. c The actual molar ratio of Ra = PEG/C14 or
C*Ph/C4 obtained from the H NMR spectrum. d Estimated by gel
1
permeation chromatograph (GPC) in THF on the basis of polystyrene
calibration.
spectra of the obtained polymers in DMF solution, and the
recorded CD spectra of P1-C*Ph(L), P1-C*Ph(D), P2-C*Ph(L),
and P3-C*Ph(L) are displayed in the lower panel of Figure 7. UV
measurements were taken to make sure where the backbone
absorbs and the UV spectra of these polymers as well as monomer 1
in DMF are also given for comparison. It is obvious that the
monomer does not absorb at wavelength longer than 310 nm.
Therefore, the absorption feature of all polymers in the
310ꢀ500 nm region (a hillside at 323 nm and a shoulder at
376 nm) is ascribed to the πꢀπ* transition of the polyene backbone.
If these polymers own helical backbones, CD signals are
supposed to appear at wavelength where the backbones absorb.
Delightfully, viewing from longer wavelength in the CD spec-
trum of P1-C*Ph(L), an intense (ca. 60 < Δε < 100) plus-to-
minus pattern appear in the same wavelength region, and the
positions of the peak and valley roughly correspond to the
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Figure 10. Light transmission spectra of the aqueous solution of P1-
PEG750, P2-PEG750, P3-PEG750, P1-PEG350, and P1-PEG35075%-
C1425%. Polymer concentration: 0.04 mg/mL.
systems to prepare materials with functions such as water solubility,25
amphiphilicity,26 biocompatibility,27 thermal responsiveness,28
and hydrogel formability.29 In the results and discussion men-
tioned above, we have shown that the activated ester strategy
provides an effective way to quantitatively control the ratio of
different functionalities in the side chains of PPAs. Thus, it is
reasonable to design and synthesize PEG functionalized PPAs by
the substitution of PFP moieties with amine-terminated PEG
chains, and the content of PEG chains can be precisely preset to
tune the water solubility and amphiphilicity. As illustrated in
Scheme 4, six PEG functionalized PPAs have been successfully
derived from the reaction of PFP ester-functionalized PPAs
(P1, P2, and P3) with two PEGs (MePEG350 and MePEG750).
The MePEGy (y = 350 and 750) functionalized P1, P2, and P3
are defined as P1-PEGy, P2-PEGy, and P3-PEGy, respectively.
Accordingly, the copolymers bearing both MePEGy and C14
alkyl side chains are abbreviated as P1-PEGyx-C14(1 ꢀ x) (x =
Figure 8. UV (upper panel) and CD (lower panel) spectra of P1-
C*Ph(L)75%-C425%, P1-C*Ph(L)50%-C450%, and P1-C*Ph(L)25%-
C475% in DMF at room temperature. Concentration: 0.15 mM.
75%, 50%, and 25%, respectively). We found that P1-PEG750
,
P2-PEG750, and P3-PEG750 had good solubility in water at room
temperature due to the solvating power of the long PEG750
chains. When shorter PEG350 segments were introduced into the
PPAs side chains, P1-PEG350 showed desirable solubility, but P2-
PEG350, and P3-PEG350 exhibited lower solubility in water. The
hydrophobic alkyl spacers played an important role in the
determination of polymers’ water solubility. Without the alkyl
spacer, even the copolymer of P1-PEG35075%-C1425% showed
acceptable water solubility. To demonstrate the water solubility
of the polymers, light transmission spectra of selected polymers
in aqueous solution were recorded at room temperature. As
depicted in Figure 10, it is obvious that the transmittances of
polymer aqueous solutions are 100% at wavelength longer than
520 nm, even when the polymer concentration is as high as
1 mg/mL (see Figure S8). In the region where the wavelength is
shorter than 520 nm, the transmittances of polymer aqueous
solutions decrease, and the declination is associated with the
electronic absorption of the PPA backbone. These phenomena
suggest that PPAs containing PEG350 and PEG750 side chains can
be dissolved in water to form clear aqueous solution.
Figure 9. Plot of Kuhn dissymmetry factor (g = Δε/ε) at 376 nm of P1-
C*Ph(L), P1-C*Ph(L)75%-C425%, P1-C*Ph(L)50%-C450%, and P1-
C*Ph(L)25%-C475% in DMF against chiral content. The dotted line is
shown simply to guide the eye.
chiral ratios. This observation may imply that the PFP moieties of
P1 are randomly substituted by L-2-phenylethylamine [C*Ph(L)]
and 1-butylamine (C4), and the resulting polymers of P1-C*Ph-
(L)x-C4(1-x) (x = 0.25, 0.5, and 0.75) are random copoly-
(phenylacetylene)s. It is noteworthy that the |g376| value of
P1-C*Ph(L) is 0.0238, 10 times greater than that of other heli-
cal polymers reported (0.002 83),23 which was probably caused
by two factors: excellent ability of the stiff backbone to form helix
and effective chiral induction of the chiral pendant. Indeed, we
have already prepared helical poly(diphenylacetylene)s with Δε
The attachment of PEG segments onto PPA backbone
bestowed the resultant polymers with a brushlike structure,
which has a hydrophobic main chain and hydrophilic side chains.
In aqueous solution, the hydrophobic part is encapsulated by the
hydrophilic surrounding PEG segments. As a result, a single
polymer chain takes a micelle-like configuration, and PPA back-
bone of P1-PEG750 or the PPA backbone and hydrophobic alkyl
as high as 100 L molꢀ1 cmꢀ1 24
.
Water Solubility and Amphiphilic Property. As widely used
building blocks, PEG chains have been incorporated into polymer
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Figure 11. Contact angle data of different polymer surfaces.
Figure 12. Impact of PEG chain content on water contact angle of
polymer surfaces.
spacers of P2-PEG750 and P3-PEG750 are insoluble in water,
although clear aqueous solutions have been observed. This
1
deduction was validated by the measurements of the H NMR
1
spectra of the polymers in D2O at room temperature. The H
NMR spectra of P2-PEG750 in D2O and CDCl3 are shown in
Figure 5 as an example. In CDCl3, the resonance peaks for the
protons on phenyl groups and alkyl spacers can be found, and the
resonance peaks for the protons on PEG segments are also
clearly recognized (Figure 5A). This indicates the good solubi-
lities of both the hydrophobic (PPA main chain and alkyl spacer)
and hydrophilic (PEG segment) parts are soluble. While in D2O,
there exist only two peaks at δ 3.43 and 3.10, which can be
assigned to the resonance of protons of water-soluble PEG chain
(Figure 5B); but no other peaks are observed, indicating that
hydrophobic backbones and alkyl chains cannot be dissolved
in water.
Figure 13. Variation of cloud point (Tcp) with polymer concentration
of the obtained PEG functionalized PPAs.
Incorporating PEG chains into PPA derivatives, the hydro-
philic or hydrophobic properties of resultant polymers were
supposed to change dramatically. To evaluate the effect of PEG
substitution on the variation of the hydrophilic properties of the
polymers, the water contact angles of all the obtained polymers
have been detected. The polymers were fabricated into films by
casting their THF solution (5 mg/mL) on glass slides, and the
results are shown as diagrams in Figure 11. The contact angles
of P1, P2, and P3 are between 90° and 100°, indicative of the
hydrophobic surfaces of PFP ester-functionalized PPAs. Mean-
while, all the P1- and P2-based PEG functionalized PPAs show
contact angles smaller than 10°, indicating that the substitution
of PFP groups with PEG chains has turned the polymers from
hydrophobic to hydrophilic property. The results depicted in
Figure 11 disclose another message: the length of the alkyl spacer
has evident influence on the hydrophilic property of the PEG-
functionalized PPAs. Taking P3-PEG350 and P2-PEG350 as
examples, the alkyl spacer with 10 methyl units (P3) made the
water contact angle to be 48°, while in the case of the alkyl spacer
with 5 methyl units, the water contact angle is only 7.5°. A similar
The water contact angles of these polymer films are shown in
Figure 12. As expected, the contact angle is increased by the
introduction of higher content of C14 component into the
copolymer. When the content of C14 component is 25%, the
water contact angle is 48°; when the content of C14 compo-
nent is 75%, this value increases to 100°, which approximates
that of pure P1, indicating that the tetradecyl side chain plays a
dominant role even in the presence of 25% PEG side chains.
Considering that the ratio of PEG and alkyl chains can be
precisely controlled through the activated ester strategy, it is
possible to fine-tune the hydrophilic/hydrophobic property of
the film surface. Such a tunable surface with specific PEG
content and hydrophilicity may find important applications in
biomaterials.
LCST Behavior. Owing to the existence of PEG side chain, the
water-soluble PPAs may have a lower critical solution tempera-
ture (LCST, a characteristic temperature above which the clear
solution would become turbid) in aqueous solution because PEG
is a typical thermal responsive polymer. To confirm this, the
thermal responsive behaviors were monitored for a series of
PEG-functionalized PPAs in their aqueous solutions. The re-
spective cloud points (Tcp) for these polymers were recorded and
displayed in Figure 13. It is obvious that, for all samples, a lower
polymer concentration corresponds to a higher Tcp. This trend is
in good agreement with the results observed for other thermal
responsive polymers.30,31
trend is also observed for P3-PEG750 and P2-PEG750
.
Since the hydrophilic/hydrophobic property of the polymer
films are sensitive to the alkyl spacer between PPA backbone
and PEG segment, incorporation of alkyl segments into PEG-
functionalized PPAs is expected to evoke prominent change in
hydrophilic/hydrophobic property. By using the step-by-step
synthetic scheme, amino-functionalized PEG350/PEG750 and
n-tetradecylamine (C14) were used to substitute the PFP groups
Further analysis of the experiment data reveals more details.
P1-PEG750 aqueous solution (1 mg/mL) became turbid above
145 °C; the transition temperature decreased to 129 °C when the
hydrophilic side chain changed from PEG750 to PEG350. This
indicates that the length of hydrophilic PEG chain has a positive
of P1, and a series of copoly(phenylacetylene)s, i.e., P1-PEG350
-
75%-C1425%, P1-PEG35050%-C1450%, and P1-PEG35025%-C1475%,
were prepared. Their structure characterization data are summar-
ized in the Experimental Section and Supporting Information.
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effect on the cloud point. In comparison, the Tcp of P1-PEG350
aqueous solution with that of P1-PEG750, although both of them
show the identical dependency of Tcp on polymer concentration,
P1-PEG350 aqueous solution has evident lower Tcp values. It is a
consensus that introducing hydrophobic moieties into an LCST-
active polymer can decrease its Tcp.32 Thus, the observed decrease in
Tcp can be explained by the fact that the content of hydrophobic
component in P1-PEG350 is higher than that in P1-PEG750
due to the shorter PEG chain length. Reasonably, the Tcp value
decreases in an order of P1-PEG750 > P2-PEG750 > P3-PEG750
because the hydrophobic property takes a reverse order. It should
be pointed out that Mn and PDI are also relevant parameters to
determine the Tcp of a polymer. The activated-ester synthetic
strategy led to PEG-functionalized PPAs with similar Mn and
PDI because they sprang from the same parent polymer. There-
fore, the evaluation of the effect of the length of PEG chain or
PEG content on the LCST behavior can be more precise and
more approximating to the true situations.
pendant fails to induce backbone helicity of P2-C*Ph(L) and
P3-C*Ph(L). The PEG-functionalized PPAs [P1-PEG350, P1-
PEG750, P2-PEG350, P2-PEG750, P3-PEG350, and P3-PEG750
]
can dissolve in water to form clear aqueous solutions. Contact
angle measurement results indicate the surface property of their
casting films are hydrophilic, and the length of the PEG segment
and the alkyl spacer contribute to the hydrophilic property in
positive and negative moods, respectively. At the same time, the
PEG-functionalized PPAs exhibited the LCST behavior of PEG
component. The cloud point (Tcp) of P1-PEG350 is lower than
that of P1-PEG750, and an order of Tcp(P1-PEG750) > Tcp(P2-
PEG750) > Tcp(P3-PEG750) has been observed. The hydrophilic
PEG chain and hydrophobic alkyl spacer have positive and
negative impacts on the cloud point of the corresponding PPA
derivatives.
Moreover, the quantitative substitution of PFP moieties with
different amines enabled us to design prepare a series of dual-
functionalized PPAs [e.g., P1-C*Ph(L)75%-C425%, P1-C*Ph-
(L)50%-C450%, P1-C*Ph(L)25%-C475%, P1-PEG35075%-C1425%,
P1-PEG35050%-C1450%, and P1-PEG35025%-C1475%]. It is
noticeable that the specific content of the functional moieties
(i.e., C* center and PEG segments) can be simply determined by
the feed ratio of functional amines. As a result, the derived PPAs
possess the structure of copoly(phenylacetylene)s, which cannot
be directly synthesized in a controllable way by copolymerization
of different phenylacetylene monomers. In the present work, we
found that lower content of chiral pendant resulted in lower
intensity of CD signal, and the plot of |g376| value against the
content of chiral pendant showed a linear relationship (no chirality
amplification effect), indicating that the cooperativity between
the chiral pendants was weak and the substitution of PFP moieties
by the two kinds of amines took place in a random mood. Mean-
while, the water contact angle detection of the polymer films
revealed that the amphiphilic property can also be fine tailored by
controlling the structural factors such as the content of PEG
component, the chain length of the PEG segment, and the alkyl
spacer. Promisingly, such a controllable synthetic strategy to prepare
dual or even multiple functionalized PPAs (as well as other
conjugated polymers) may find applications in such diverse fields
as multifunctional polymers, orthogonal reaction of bioconjugated
macromolecules, and selective modification of materials surface.
’ CONCLUDING REMARKS
We have designed and synthesized three PFP ester-function-
alized PPAs (P1, P2, and P3). In comparison with the pioneer’s
work by Theato and colleagues, who had used WCl6 as catalyst,
the Rh-based catalysts used in our research can afford the
expected polymers with high molecular weight in high yield.
In addition, the catalysts worked well either in the polymerization
of the monomer with PFP ester direct linking to phenylacetylene
(P1) or in the polymerization of the monomers with alkyl spacers
between the PFP ester and phenylacetylene (P2 and P3). Thus,
the present work has extended the species of catalysts and
monomers for the preparation of activated-ester functionalized PPAs.
We have also shown that P1, P2, and P3 are ideal precursors to
functional PPAs by postpolymerization reaction route. A series of
functionalities including different chiral amines and amino-con-
taining PEGs have been successfully integrated in the target
functional PPAs, and total of 18 PPA derivatives were prepared.
Their structures were carefully characterized by different spectro-
1
scopic techniques such as FTIR, H NMR, 13C NMR, and 19F
NMR. The characterization data not only confirmed the ex-
pected macromolecular structure but also demonstrated that the
conversion of PPA-based activated esters with amines was quan-
titative and proceeded without side reactions under mild condi-
tions. Specifically, 1H NMR was used to determine the relative
contents of the incorporated functional moieties when two
different kinds of functionalized amines were attached to the
PPA backbone. The results showed that the relative content of
the different functionalities can be well controlled by presetting
the feed ratio of two reacting amines.
’ EXPERIMENTAL SECTION
Materials. Dichloromethane (DCM) was distilled under normal
pressure over calcium hydride under nitrogen before use. Tetrahydrofuran
(THF), toluene, and dioxane were distilled under normal pressure from
sodium benzophenone ketyl under nitrogen immediately prior to use.
Triethylamine (Et3N) was distilled and dried over potassium hydroxide.
p-Toluenesulfonic acid monohydrate (TsOH), N,N0-dicyclohexylcarbo-
diimide (DCC), and 4-(dimethylamino)pyridine (DMAP) were purchased
from Acros. Pentafuorophenol was purchased from Aldrich. Organor-
hodium complexes [Rh(nbd)Cl]2 (nbd = 2,5-norbornadiene), [Rh(cod)Cl]2
(cod = 1,8-cyclooctadiene), and Rh+(nbd)[C6H5Bꢀ(C6H5)3] were
prepared in our laboratories by literature methods.33 4-Ethynylbenzonic
acid (5), 6-(4-ethynylphenoxy)hexanoic acid (6), and 11-(4-ethynyl-
phenoxy)undecanoic acid (7) were synthesized according to our pre-
viously published procedures.8,18 L-(ꢀ)-1-methylbenzylamine and
D-(+)-1-methylbenzylamine were purchased from Acros. Poly(ethylene
glycol) monomethyl ether (MePEG350-OH and MePEG750-OH) were
obtained from Alfa. Pentafluorophenol, 1-tetradecylamine (TDA), and
1-butylamine (BA) were purchased from Aladdin.
The complete substitution of PFP moieties with amines
allowed us to derive a series of functional PPAs [e.g., P1-C*
Ph(L), P2-C*Ph(L), P3-C*Ph(L), P1-C*Ph(D), P2-C*Ph(D),
P3-C*Ph(D), P1-PEG350, P1-PEG750, P2-PEG350, P2-PEG750
,
P3-PEG350, and P3-PEG750] in high purity. CD measurements
indicate that the incorporation of chiral amine into polymer side
chains endows the polymers with backbone helicity. The CD
spectra of P1-C*Ph(L) and P1-C*Ph(D) show an intense (ca. 60
< Δε < 100) plus-to-minus and minus-to-plus pattern in the
310ꢀ500 nm region, respectively, indicating that the PPA back-
bone of P1-C*Ph(L) and P1-C*Ph(D) adopt a predominantly
right-handed and left-handed helical conformation, respectively.
However, owing to the flexible spacer’s blocking, the chiral
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Instrumentation. 1H, 13C, and 19F NMR spectra were measured
on a Bruker ARX 500 NMR spectrometer using tetramethylsilane
(TMS; δ = 0 ppm) as internal standard. FTIR spectra were measured
on a Perkin-Elmer 16 PC FT-IR spectrophotometer. Molecular weights
(Mw and Mn) and polydispersity indexes (PDI, Mw/Mn) of the polymers
were estimated in THF by a Waters gel permeation chromatography
(GPC) system. A set of monodisperse polystyrene standards covering
molecular weight range of 103ꢀ107 was used for molecular weight
calibration. High-resolution mass spectra (HRMS) were recorded on a
Finnigan TSQ 7000 operating in a MALDI-TOF mode. UVꢀvis
absorption spectra were measured on a Varian CARY 100 Bio UVꢀvis
spectrophotometer. Circular dichroism (CD) spectra were recorded on
an Jasco J-720 spectropolarimeter. The thermogravimetric analysis
(TGA) was conducted on a Pyris 6 thermogravimetric analyzer (Perkin-
Elmer), in which a sample of ∼3 mg was heated to 600 °C at a rate of
20 °C/min and under a flow of nitrogen stream.
Preparation of Amino-Functionalized PEGs. Amino-func-
tionalized PEGs were synthesized according to Scheme S1. PEG
monomethyl ethers were first reacted with tosyl chloride, followed by
reaction with potassium phthalimide and treatment with hydrazine
(Gabriel method). Spectroscopic data ascertained that two kinds of
MePEG-NH2 were prepared successfully (see Supporting Information
for details).
Perfluorophenyl 11-(4-Ethynylphenoxy)undecanoate (3). Mono-
mer 3 was synthesized from 11-(4-ethynylphenoxy)undecanoic acid
(7) by a procedure similar to that used for preparation of monomer 1.
A white solid was obtained in yield 76.8%. 1H NMR (500 MHz, CDCl3),
δ (TMS, ppm): 7.41 (d, 2H), 6.82 (d, 2H), 3.95 (t, 2H), 2.99 (s, 1H),
2.65 (t, 2H), 1.72ꢀ1.80 (m, 4H), 1.20ꢀ1.50 (m, 12H). 13C NMR (125
MHz, CDCl3), δ (TMS, ppm): 169.8, 159.8, 142.4, 140.3, 139.2, 138.6,
137.0, 133.8, 114.7, 114.1, 84.0, 75.9, 68.3, 33.6, 29.7, 29.5, 29.4, 29.0,
25.0. 19F NMR (125 MHz, CDCl3), δ (TMS, ppm): ꢀ152.9, ꢀ158.2,
ꢀ162.4. FTIR, ν (cmꢀ1, in KBr pellet): 3311 (HꢀCtC), 2932, 2852,
2106 (HCtC), 1788 (OCdO), 1607, 1519, 1470, 1292, 1248, 1174,
1095, 1000, 890, 832, 723, 667, 630, 537. HRMS (MALDI-TOF): m/z
469.1804 [(M + 1)+, calcd 469.1724; see Figure S5].
Polymer Synthesis. All the polymerization reactions were carried
out under nitrogen using Schlenk technique (see Schemes 1 and 2) in a
vacuum-line system except for the purification of the polymers, which
was done in air. Typical experimental procedures for preparation of P2
are given below as an example.
Into a 10 mL baked Schlenk tube with a side arm was added 199 mg
(0.50 mmol) of monomer 2. The tube was evacuated under vacuum and
flushed with dry nitrogen three times through the side arm. Then 1.5 mL
of THF was injected into the tube to dissolve the monomer. The catalyst
solution was prepared in another tube by dissolving 4.9 mg (0.01 mmol)
of [Rh(cod)Cl]2 in 1 mL of THF with one drop of TEA added. After
aging for 15 min, the catalyst solution was transferred to the monomer
solution using a hypodermic syringe. The reaction solution became
brown from light yellow immediately. After being stirred at room
temperature under nitrogen for 24 h, the resultant solution was diluted
with 7 mL of THF and added dropwise to 300 mL of methanol through a
cotton filter under vigorous stirring. The precipitate was allowed to stand
for 24 h and then filtered with a Gooch crucible. The obtained polymer
was washed with methanol for three times and then kept in an ambient
atmosphere at room temperature.
Characterization data for P2: brown solid; yield 86.4%. Mw: 70 600;
Mw/Mn: 2.22 (GPC, polystyrene calibration; Table 1, no. 12). 1H NMR
(500 MHz, CDCl3), δ (TMS, ppm): 6.62, 6.44, 5.76, 3.58ꢀ4.06, 2.63,
1.59ꢀ1.90, 1.40ꢀ1.60. 13C NMR (125 MHz, CDCl3), δ (TMS, ppm):
169.5, 158.3, 142.4, 140.4, 138.8, 137.1, 136.0, 134.1, 130.4, 128.9, 125.3,
113.8, 67.6, 33.2, 29.1, 25.7, 24.7. 19F NMR (125 MHz, CDCl3), δ
(TMS, ppm): ꢀ152.9, ꢀ158.2, ꢀ162.5. FTIR, ν (cmꢀ1, in KBr pellet):
2932, 2852, 1788, and 1740 (OCdO), 1607, 1519, 1470, 1292, 1248,
1174, 1095, 1000, 890, 832, 723.
Monomer Preparation. PFP ester-containing monomers (1, 2,
and 3) were synthesized according to the synthetic routes shown in
Schemes 1 and 2. Typical experimental procedures for their syntheses
are given below.
Perfluorophenyl 4-Ethynylbenzoate (1). 4-Ethynylbenzonic acid
(5, 1.46 g, 10 mmol), pentafluorophenol (1.84 g, 10 mmol), DCC
(3.09 g, 15 mmol), DMAP (0.073 g, 0.6 mmol), TsOH (0.114 g, 0.6
mmol), and 150 mL of dry dichloromethane were added into a 250 mL
flask. The mixture was stirring at room temperature for 8 h, and white
precipitate was formed. Then the solid was filtrated and washed with dry
ether. After being concentrated by a rotary evaporator, the crude product
was purified by silica-gel column chromatography using petroleum
(60ꢀ90 °C) as eluent. After evaporation of the solvents by a rotary
evaporator, white solid was collected in a yield 79%. 1H NMR (500 MHz,
DMSO-d6), δ (TMS, ppm): 8.14 (d, 2H), 7.71 (d, 2H), 4.59 (s, 1H).
13C NMR (125 MHz, DMSO-d6), δ (TMS, ppm): 162.2, 142.5, 141.5,
139.7, 138.0, 136.6, 132.1, 130.5, 128.7, 126.8, 82.3, 81.4. 19F NMR (125
MHz, DMSO-d6), δ (TMS, ppm): ꢀ152.3, ꢀ157.6, ꢀ162.1. FTIR, ν
(cmꢀ1, in KBr pellet): 3270 (HꢀCtC), 1762 (OCdO), 1522, 1257,
1064, 993. HRMS (MALDI-TOF): m/z 313.0287 [(M + 1)+, calcd
313.0210; see Figure S3].
Perfluorophenyl 6-(4-Ethynylphenoxy)hexanoate (2). 6-(4-Ethynyl-
phenoxy)hexanoic acid (6, 2.32 g, 10 mmol), pentafluorophenol (1.84 g,
10 mmol), DCC (3.09 g, 15 mmol), DMAP (0.073 g, 0.6 mmol), TsOH
(0.114 g, 0.6 mmol), and 150 mL of dried DCM were added into a
250 mL flask. The mixture was stirring at room temperature for 12 h, and
white precipitate was formed. Then the solid was filtrated and washed
with absolute ether. After being concentrated by a rotary evaporator,
the crude product was purified by a silica gel column using petroleum
ether (60ꢀ90 °C) as eluent. After evaporation of solvents by a rotary
evaporator, a white solid was obtained in yield 82.5%. 1H NMR (500
MHz, CDCl3), δ (TMS, ppm): 7.41 (d, 2H), 6.82 (d, 2H), 3.98
(t, 2H), 2.99 (s, 1H), 2.70 (t, 2H), 1.82ꢀ1.89 (m, 4H), 1.30ꢀ1.32
(m, 2H). 13C NMR (125 MHz, CDCl3), δ (TMS, ppm): 169.6, 159.6,
142.3, 140.7, 140.3, 139.8, 139.0, 138.6, 137.1, 133.8, 114.6, 114.3,
83.9, 76.0, 67.7, 33.5, 29.0, 25.7, 24.7. 19F NMR (125 MHz, CDCl3),
δ (TMS, ppm): ꢀ152.9, ꢀ158.1, ꢀ162.4. FTIR, ν (cmꢀ1, in KBr
pellet): 3311 (HꢀCtC), 2932, 2852, 2106 (HCtC), 1788 (OCdO),
1607, 1519, 1470, 1292, 1248, 1174, 1095, 1000, 890, 832, 723, 667, 630,
537. HRMS (MALDI-TOF): m/z 399.1009 [(M + 1)+, calcd 399.0941;
see Figure S4].
Characterization data for P1: orange-yellow powder; yield 75.0%.
Mw: 31 800; Mw/Mn: 1.85 (GPC, polystyrene calibration; Table 1,
no. 2). 1H NMR (500 MHz, CDCl3), δ (TMS, ppm): 7.80, 6.79, 5.97.
13C NMR (125 MHz, DMSO-d6), δ (TMS, ppm): 141.7, 139.2, 138.6,
137.0, 136.0, 134.0, 132.5, 129.6, 128.1, 124.5. 19F NMR (125 MHz,
DMSO-d6), δ (TMS, ppm): ꢀ153.0, ꢀ157.1, ꢀ162.1. FTIR, ν (cmꢀ1
,
in KBr pellet): 1764 (OCdO), 1521, 1249, 1051, 1009.
Characterization data for P3: dark brown solid; yield 78.4%. Mw:
97 300; Mw/Mn: 1.94 (GPC, polystyrene calibration; Table 1, no. 17).
1H NMR (500 MHz, CDCl3), δ (TMS, ppm): 6.62, 6.44, 5.65ꢀ5.80,
3.63ꢀ3.67, 2.60ꢀ2.66, 1.65ꢀ1.85, 1.31. 13C NMR (125 MHz, CDCl3),
δ (TMS, ppm): 169.7, 159.6, 142.4, 140.5, 139.1, 138.5, 137.1, 130.4,
128.9, 125.3, 114.9, 113.9, 68.1, 34.3, 33.5, 29.1, 26.5, 25.2, 25.0. 19F
NMR (125 MHz, CDCl3), δ (TMS, ppm): ꢀ152.9, ꢀ158.3, ꢀ162.5.
FTIR, ν (cmꢀ1, in KBr pellet): 2932, 2852, 1788, and 1740 (OCdO),
1607, 1519, 1470, 1292, 1248, 1174, 1095, 1000, 882, 832, 723.
Polymer Reaction. Poly(phenylacetylene) derivatives with PFP
ester (P1, P2, and P3) were reacted with various amines under nitrogen
according to the synthetic routes shown in Scheme 3. Typical experimental
procedures for preparation of P1-amide are given below as an example.
Into a 10 mL reaction tube with magnetic stirring bar were added 250 mg
(0.8 mmol) P1, 106.7 mg (0.88 mmol) of L (or D)-1-phenylethylamine,
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and 8 mL of dry THF with a drop of Et3N under nitrogen. The reaction
solution was kept stirring for 12 h at room temperature. After that, the
mixture solution was added dropwise to 300 mL of methanol through a
cotton filter under vigilant stirring. The precipitate was kept still for 24 h
and then filtered with a Gooch crucible. The obtained polymer was
washed with methanol for several times and dried at room temperature.
Characterization data for P1-C*Ph: red-orange powder; yield 86.2%
for P1-C*Ph(L), Mw: 27 300; Mw/Mn: 2.40 (GPC, polystyrene
calibration), and yield 91.2% for P1-C*Ph(D), Mw: 32 400; Mw/Mn:
2.28 (GPC, polystyrene calibration). 1H NMR (500 MHz, DMSO-d6),
δ (TMS, ppm): 8.40 (s, 1H, NH), 7.17ꢀ6.62 (m, aromatic protons),
5.77 (olefinic protons), 5.04(s, 1H, NHCH), 1.21ꢀ1.33(m, 3H, CH3).
13C NMR (125 MHz, DMSO-d6), δ (TMS, ppm): 165.0, 144.2, 127.9,
126.2, 125.6, 125.4, 66.8. 19F NMR (125 MHz, DMSO-d6), δ (TMS,
ppm): nothing. FTIR, ν (cmꢀ1, in KBr pellet): 3423 and 3300 (NꢀH),
2966 and 2927 (CꢀH); 1720 and 1645 (CdONH), 1604, 1534, 1493,
1449, 1260, 1089, 1017, 851, 802, 761, 699.
Characterization data for P1-PEG350: brown sticky semisolid sub-
stance; yield 88.5%. Mw: 5400; Mw/Mn: 1.43 (GPC, polystyrene
calibration). 1H NMR (500 MHz, CDCl3), δ (TMS, ppm): 3.75,
3.63, 3.54, 3.37 (s, 3H). 13C NMR (125 MHz, CDCl3), δ (TMS, ppm):
71.9, 70.5, 70.7, 70.1, 70.0, 69.9, 69.8, 58.9. FTIR, ν (cmꢀ1, in KBr
pellet): 3442 (NꢀH), 2866, 1735 and 1660 (CdONH), 1606, 1514,
1465, 1355, 1290, 1246, 1110, 947, 842, 539.
Characterization data for P3-PEG750: red-orange sticky semisolid
substance; yield 85.2%. Mw: 8140; Mw/Mn: 2.22 (GPC, polystyrene
calibration). 1H NMR (500 MHz, CDCl3), δ (TMS, ppm): 7.87, 6.25ꢀ
7.00, 3.87, 3.63, 3.50, 3.34, 2.61, 1.57, 1.25. 1H NMR (500 MHz, D2O),
δ (DSS, ppm): 3.42, 3.10.
P1 was reacted with two amines step by step under nitrogen according to
the synthetic routes shown in Scheme 4. Typical experimental proce-
dures for preparation of P1-C*Ph(L)50%-C450% are given below as an
example. Into a 20 mL reaction tube with magnetic stirring bar were
added 250 mg (0.8 mmol) of P1, 48.5 mg (0.4 mmol) of L-1-pheny-
lethylamine, and 8 mL of dry THF with a drop of Et3N under nitrogen.
The reaction solution was kept stirring for 12 h at room temperature.
Then, the reaction solution was added 32.2 mg (0.44 mmol) of 1-
butylamine and reacted for another 12 h at room temperature. After that,
the mixture solution was added dropwise to 300 mL of methanol through a
cotton filter under vigilant stirring. The precipitate was kept still for 24 h
and then filtered with a Gooch crucible. The obtained polymer was
washed with methanol for several times and dried at room temperature.
Characterization data for P1-C*Ph(L)75%-C425%: brown powder;
yield 91.3%. Mw: 26 800; Mw/Mn: 2.53 (GPC, polystyrene calibration).
1H NMR (500 MHz, CDCl3), δ (TMS, ppm): 8.55, 7.50, 7.20, 6.62,
5.77, 5.03, 3.41, 1.37, 0.79.
Characterization data for P1-C*Ph(L)50%-C450%: brown powder;
yield 88.5%. Mw: 25 900; Mw/Mn: 2.46 (GPC, polystyrene calibration).
1H NMR (500 MHz, CDCl3), δ (TMS, ppm): 8.55, 7.50, 7.20, 6.62,
5.77, 5.03, 3.41, 1.37, 0.79.
Characterization data for P1-C*Ph(L)25%-C475%: yellow powder;
yield 90.6%. Mw: 25 300; Mw/Mn: 2.51 (GPC, polystyrene calibration).
1H NMR (500 MHz, CDCl3), δ (TMS, ppm): 8.55, 7.50, 7.20, 6.62,
5.77, 5.03, 3.41, 1.37, 0.79.
Characterization data for P1-PEG750: brown sticky semisolid sub-
stance; yield 78.4%. Mw: 3950; Mw/Mn: 1.23 (GPC, polystyrene
1
calibration). H NMR (500 MHz, CDCl3), δ (TMS, ppm): 7.90, 3.77,
3.63, 3.59, 3.51, 3.33 (s, 3H). 1H NMR (500 MHz, D2O), δ (DSS, ppm):
3.68ꢀ3.73 (t, 2H), 3.53ꢀ3.69 (s, 60H), 3.51 (t, 2H), 3.33 (s, 3H).
Characterization data for P1-C14: red solid; yield 90.6%. Mw: 28 800;
1
Characterization data for P1-PEG35075%-C1425%: brown sticky
semisolid substance; yield 78.5%. Mw: 5720; Mw/Mn: 1.38 (GPC,
polystyrene calibration). 1H NMR (500 MHz, CDCl3), δ (TMS, ppm):
3.63, 3.36, 1.25, 0.86.
Characterization data for P1-PEG35050%-C1450%: brown sticky
semisolid substance; yield 80.6%. Mw: 5050; Mw/Mn: 1.24 (GPC,
polystyrene calibration). 1H NMR (500 MHz, CDCl3), δ (TMS, ppm):
3.63, 3.36, 1.25, 0.86.
Mw/Mn: 1.98 (GPC, polystyrene calibration). H NMR (500 MHz,
CDCl3), δ (TMS, ppm): 3.43, 1.68, 1.26, 0.88. 19F NMR (125 MHz,
CDCl3), δ (TMS, ppm): nothing.
Characterization data for P1-C4: red solid; yield 92.3%. Mw: 28 300;
1
Mw/Mn: 1.72 (GPC, polystyrene calibration). H NMR (500 MHz,
CDCl3), δ (TMS, ppm): 6.57, 5.86, 3.43, 1.64, 1.40, 0.82ꢀ1.00.
Characterization data for P2-C*Ph(L): brown solid; yield 92.4%. Mw:
1
58 800; Mw/Mn: 1.99 (GPC, polystyrene calibration). H NMR (500
Characterization data for P1-PEG35025%-C1475%: brown sticky
semisolid substance; yield 85.3%. Mw: 4860; Mw/Mn: 1.35 (GPC,
polystyrene calibration). 1H NMR (500 MHz, CDCl3), δ (TMS, ppm):
3.63, 3.36, 1.25, 0.86.
MHz, CDCl3), δ (TMS, ppm): 7.51, 7.22, 6.60, 6.38, 5.74, 5.01, 3.58,
2.15, 1.61, 1.37. FTIR, ν (cmꢀ1, in KBr pellet): 3272 (NꢀH), 3030,
2929, 2860, 1736 and 1640 (CdONH), 1604, 1543, 1505, 1450, 1376,
1284, 1242, 1172, 1047, 827, 760, 698, 612, 537.
Contact Angle Measurements. Contact angles were measured
on a JY-82 goniometer. The polymer solutions in THF (5 mg/mL) were
cast onto glass slides to form polymer films, after which the samples were
stayed at room temperature under vacuum for 24 h. The sessile drop
method was performed. Deionized water drops (e0.5 μL) were
positioned onto the polymer surfaces by means of the syringe. All the
contact angle data were read from the scale on the microscope lens at the
15th second after the water dropping.
LCST Measurements. Polymers are first dissolved in deionized
water, and then the aqueous solution was diluted to different concentra-
tions. The cloud points of polymers in this work are too high to be tested
by UV. Therefore, the solutions were heated slowly in an oil bath to
certain temperature. The temperature at which the solution begins to
change from clear to turbid was recorded.
Characterization data for P2-PEG350: red-orange sticky semisolid
substance; yield 82.8%. Mw: 6930; Mw/Mn: 1.38 (GPC, polystyrene
calibration). 1H NMR (500 MHz, CDCl3), δ (TMS, ppm): 7.90,
6.00ꢀ7.00, 3.85, 3.62, 3.50, 3.33, 2.70, 1.20ꢀ1.90.
Characterization data for P2-PEG750: red-orange sticky semisolid
substance; yield 84.8%. Mw: 7260; Mw/Mn: 1.51 (GPC, polystyrene
calibration). 1H NMR (500 MHz, CDCl3), δ (TMS, ppm): 7.90, 6.00ꢀ
7.00, 3.86, 3.63, 3.50, 3.33, 2.70, 1.20ꢀ1.90. 1H NMR (500 MHz, D2O),
δ (DSS, ppm): 3.43, 3.10. 13C NMR (125 MHz, CDCl3), δ (ppm): 85.9,
71.8, 70.5, 70.1, 70.0, 69.8, 69.3, 59.0. FTIR, ν (cmꢀ1, in KBr pellet):
3442 (NꢀH), 2866, 1735 and 1660 (NHCdO), 1606, 1514, 1465,
1355, 1290, 1246, 1110, 947, 842, 539.
Characterization data for P3-C*Ph(L): brown solid; yield 93.8%. Mw:
1
78 500; Mw/Mn: 2.03 (GPC, polystyrene calibration). H NMR (500
MHz, CDCl3), δ (TMS, ppm): 7.51, 7.22, 6.60, 6.38, 5.74, 5.01, 3.58,
2.15, 1.61, 1.37. FTIR, ν (cmꢀ1, in KBr pellet): 3292 (NꢀH), 3062,
2925, 2852, 1739, and 1640 (CdONH), 1604, 1543, 1506, 1467, 1375,
1284, 1245, 1175, 1021, 829, 760, 699, 612, 538.
Characterization data for P3-PEG350: red-orange sticky semisolid
substance; yield 78.6%. Mw: 5240; Mw/Mn: 1.41 (GPC, polystyrene
calibration). 1H NMR (500 MHz, CDCl3), δ (TMS, ppm): 6.10ꢀ7.00,
3.58ꢀ3.76, 3.51, 3.35, 2.63, 1.50ꢀ1.58, 1.00ꢀ1.50.
’ ASSOCIATED CONTENT
S
Supporting Information. Synthetic scheme and proce-
b
dures for the preparation of amino-functionalized PEGs; 1H and
13C NMR spectra of amino-functionalized PEGs; mass spectrum
of monomers 1ꢀ3; TGA thermograms of P1, P2, and P3 and
their PEG750 derivatives P1-PEG750, P2-PEG750, and P3-PEG750
;
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ARTICLE
1H NMR spectra of P1-PEG35075%-C1425%, P1-PEG35050%-
C1450%, and P1-PEG35025%-C1475%; light transmission spectra
of P1-PEG750 in water. This material is available free of charge via
the Internet at http://pubs.acs.org.
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’ AUTHOR INFORMATION
Corresponding Author
*E-mail: sunjz@zju.edu.cn (J.Z.S.); tangbenz@ust.hk (B.Z.T.).
Author Contributions
§M. R. Chen and H. Zhao contributed equally to this work.
’ ACKNOWLEDGMENT
This work was partially supported by the National Science
Foundation of China (21074113, 50873086, 20634020, and
20974028); the key project of the Ministry of Science and
Technology of China (2009CB623605), the Research Grants
Council of Hong Kong (603509 and HKUST2/CRF/10), and
the University Grants Committee of Hong Kong (AoE/P-03/
08). B.Z.T. thanks the support from the Cao Guangbiao Founda-
tion of Zhejiang University.
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49, 211.
(13) Yuan, W. Z.; Mao, Y.; Zhao, H.; Sun, J. Z.; Xu, H. P.; Jin, J. K.;
Zheng, Q.; Tang, B. Z. Macromolecules 2008, 41, 701.
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