Synthesis and characterization of poly(N-propargylurea)s with helical conformation, optical activity and fluorescence properties

Article abstract of DOI:10.1016/j.reactfunctpolym.2009.11.001

This article presents novel N-propargylurea-based copolymers that contain both carbazole and urea moieties in their side chains. The homopolymer of monomer 1 with a carbazole group exhibited interesting fluorescence properties, while the homopolymer of monomer 2 with a chiral center formed helical structures. The copolymerizations of monomers 1 and 2 provided optically active helical copolymers, which had fluorescence properties, even for the copolymer that contained as low as 20 mol% of monomer unit 1. Fluorescent and optically active composite films were further prepared based on the copolymers and with poly(vinyl butyl) as the supporting material. This study contributes to the intriguing research field of optically active helical polymers and their practical applications.

Full text of DOI:10.1016/j.reactfunctpolym.2009.11.001

Reactive & Functional Polymers 70 (2010) 116–121
Contents lists available at ScienceDirect
Reactive & Functional Polymers
journal homepage: www.elsevier.com/locate/react
Synthesis and characterization of poly(N-propargylurea)s with helical
conformation, optical activity and fluorescence properties
a,b,
Xiaofeng Luo a,b, Jie Chang b, Jianping Deng a,b, , Wantai Yang
*
*
a State Key Laboratory of Chemical Resource Engineering, Beijing University of Chemical Technology, Beijing 100029, China
b College of Materials Science and Engineering, Beijing University of Chemical Technology, Beijing 100029, China
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 2 August 2009
Received in revised form 6 November 2009
Accepted 7 November 2009
Available online 13 November 2009
This article presents novel N-propargylurea-based copolymers that contain both carbazole and urea moi-
eties in their side chains. The homopolymer of monomer 1 with a carbazole group exhibited interesting
fluorescence properties, while the homopolymer of monomer 2 with a chiral center formed helical struc-
tures. The copolymerizations of monomers 1 and 2 provided optically active helical copolymers, which
had fluorescence properties, even for the copolymer that contained as low as 20 mol% of monomer unit
1. Fluorescent and optically active composite films were further prepared based on the copolymers and
with poly(vinyl butyl) as the supporting material. This study contributes to the intriguing research field
of optically active helical polymers and their practical applications.
Keywords:
Copolymerization
Fluorescence
Helical structure
Polyacetylenes
Thin films
Ó 2009 Elsevier Ltd. All rights reserved.
1. Introduction
backbones for instance polyacetylenes would provide polymers
with some novel and interesting properties.
Urea functional groups are very important in organic chemistry.
As a well-known denaturant of proteins, urea compounds are fre-
quently used to investigate the folding and unfolding mechanisms
of proteins [1]. Cyclic urea derivatives have drawn increasing inter-
est [2] and possess interesting pharmacological properties [3]. Urea
derivatives exhibit chirality [4] and organocatalytic functions [5].
They can be used as soft engineering materials [6], habit modifiers
[7], optical sensors for anions [8] and gene carriers [9]. With high
reactivity and the ability to form stable hydrogen bonds, urea is
also frequently used as a linking molecule in the synthesis of func-
tional polymers [10] or segmented copolymers [11].
Carbazole is a hole-transporting and electroluminescent unit.
Therefore, it has many unique properties such as light emission
[12] and luminescence properties [13]. Polymers containing carba-
zole moieties in their side chains can be used as photoconductive,
electroluminescent, and/or photorefractive materials [14–17],
which have numerous potential technological applications, e.g.,
in high-density optical data storage, multiple image processing,
and phase conjugated mirrors [18–20]. Therefore, simultaneous
introduction of urea and carbazole moieties to certain polymer
Substituted polyacetylenes possess various intriguing proper-
ties such as semiconductivity, nonlinear optical properties, and
high gas permeability. In particular, some polyacetylenes can
adopt helical conformations [21]. To date, a variety of substituted
polyacetylenes such as poly(phenylacetylene)s [22] and poly(N-
propargylamide)s [23] have been synthesized. We have synthe-
sized a number of helical substituted polyacetylenes including
poly(N-propargylamide)s [24], poly(N-propargylsulfamide)s [25]
and poly(N-propargylurea) [26–28], either in organic solvents or
in aqueous medium [29,30]. Poly(N-propargylurea)-containing
suitable pendent groups were also found to adopt helical confor-
mations under appropriate conditions [26–28].
In this study, carbazole groups were introduced onto poly(N-
propargylurea) side chains for the preparation of highly func-
tional polymers which combine the unique properties of helical
polymer backbones with the fluorescence properties from carba-
zole moieties. Such polymers were prepared via copolymeriza-
tions of two monomers: achiral monomer 1, providing the
carbazole moiety, and chiral monomer 2, providing the helical
structure. Fluorescent and optically active composite films were
further prepared based on the obtained copolymers and with
poly(vinyl butyl) as the supporting material. It should be noted
that polyacetylenes containing carbazole moieties in their side
chains have been synthesized by Tang [31], Masuda [32], and
Tabata [33]. However, polyacetylenes that simultaneously contain
carbazole and urea groups and the capacity to form ordered
* Corresponding authors. Address: State Key Laboratory of Chemical Resource
Engineering, Beijing University of Chemical Technology, Beijing 100029, China. Tel./
fax: +86 10 6443 5128.
E-mail addresses: dengjp@mail.buct.edu.cn (J. Deng), yangwt@mail.buct.edu.cn
(W. Yang).
1381-5148/$ - see front matter Ó 2009 Elsevier Ltd. All rights reserved.
doi:10.1016/j.reactfunctpolym.2009.11.001

X. Luo et al. / Reactive & Functional Polymers 70 (2010) 116–121
117
helical structures have not yet been reported. Such a class of no-
2.4. Polymerization and copolymerization
vel polymers undoubtedly integrates the intriguing helical struc-
tures and the desirable properties of urea and carbazole
functional groups and would be of great interest, especially for
practical applications.
(Co)Polymerizations were carried out in a glass tube equipped
with a three-way stopcock that contained a dry solvent under nitro-
gen atmosphere. A catalyst (nbd)Rh+BÀ(C6H5)4 (5 mM) was added to
a solution of monomers (0.5 M) in THF (2 ml) under nitrogen atmo-
sphere, and the resulting solution was kept at 30 °C for 2 h. After
(co)polymerization, the solution was poured into a large amount
of hexane to precipitate the polymer out. The solid product was fil-
tered and then dried under reduced pressure. Spectroscopic data of
poly(1) were as follows: IR (KBr): 3420 (HÀN), 2337 (HÀC@), 1697
2. Experimental section
2.1. Measurements
(C@O), 1600, 1447, 1326, 1238, 725, and 564 cmÀ1 1H NMR
.
Melting point (m.p.) was measured by an X-4 micro-melting
point apparatus. 1H nuclear magnetic resonance (NMR) spectra
were recorded on a Bruker AV600 spectrometer (Bruker, Germany).
Fourier transform spectroscopy (FT-IR) spectra were recorded with
a Nicolet NEXUS 670 spectrophotometer (Nicolet, USA). Number-
average molecular weights (Mn) and molecular weight distribu-
tions (Mw/Mn) of the (co)polymers were determined by Gel perme-
ation chromatography (GPC) (Waters 515-2410 system) (Waters,
USA) calibrated by using polystyrenes as standards and THF as
the eluent (unless otherwise pointed out). Circular dichroism
(CD) and ultraviolet–visible (UV–vis) spectra were recorded on a
JASCO J-810 spectropolarimeter (Jasco, Japan). Fluorescence spec-
tra were measured on a Varian Cary Eclip sE spectrophotometer
(Varian, USA). The thickness of the film was determined with a
thickness gauge (Q/DBEF-2-91) (Shanghai Liuling Instrument Plant,
China).
(DMSO-d6, 600 MHz, 25 °C): d 3.31 (2H, C@CCH2), 6.45 (1H, HÀC@),
7.14–7.16 (4H, Ar), 7.36–7.39 (2H, Ar), 7.47–7.48 (2H, Ar), and 8.10–
8.11 (1H, NÀH).
The Spectroscopic data of copolymers were as follows (taking
Poly(10.2-co-20.8) as an example): IR (KBr): 3385 (HÀN), 2341
(HÀC@), 1645 (C@O), and 1523.
2.5. Preparation of composite films
The copolymers synthesized above were applied to prepare
composite films with PVB as supporting material. Copolymers
(0.05 g) were dissolved in 20 ml PVB (1 g) CHCl3 solution and cast
onto a glass dish. The CHCl3 was then evaporated under ambient
conditions and films with a uniform thickness of 55
obtained.
5 lm were
3. Results and discussion
2.2. Materials
3.1. Synthesis and polymerization of N-propargylurea monomers
Propargylamine, bis(trichloromethyl)-carbonate (BTC), poly(vi-
nyl butyral) (PVB) and carbazole were purchased from Aldrich
and used as received without further purification. (nbd)Rh+BÀ
(C6H5)4 was prepared as reported elsewhere [34]. Solvents were
distilled under reduced pressure [22–28].
Monomers 1 and 2 were synthesized according to the strategy
outlined in Scheme 1. The major synthetic procedure was as fol-
lows. A secondary amine was first reacted with bis(trichloro-
methyl)-carbonate (BTC) to form carbamoyl chloride, which was
then directly reacted with propargylamine to yield the target
monomer. The details for the synthesis and purification procedure
and the spectroscopic data of monomer 1 are described in the
experimental section. Monomers 1 and 2 were polymerized with
(nbd)Rh+BÀ(C6H5)4 as the catalyst in THF at 30 °C for 3 h. The rele-
vant details are also presented in the experimental section. Poly-
merization results for monomer 1 are summarized in Table 1.
The results of monomer 2 and poly(2) were introduced in our pre-
vious article [27]. Poly(1) was obtained as an 86% yield and its
number-average molecular weight (Mn) was 3700. It was assumed
that the low molecular weight resulted from the low coordination
ability of the ethynyl group of monomer 1 to Rh catalyst, due to the
low electron density [35], and thus the polymerizability of mono-
2.3. Monomer synthesis
The typical monomer synthesis procedure is as follows. To
synthesize monomer 1, carbazole (2 g, 12 mmol) was dissolved
in THF (50 ml), and the solution was added dropwise to a solution
of BTC (2 g, 6 mmol) in ethyl acetate (150 ml) while stirring at
0 °C for approximately 2 h. Afterwards, the mixture was further
stirred at room temperature for another 30 min and then refluxed
at 80 °C for about 3 h. Then, ethyl acetate and THF were removed
under reduced pressure, producing the corresponding carbamoyl
chloride, which was directly used for the next reaction. The car-
bamoyl chloride was dissolved in ethyl ether (150 ml), into which
triethyl amine (1.3 ml, 18 mmol) and propargylamine (0.5 ml,
12 mmol) were subsequently added at room temperature, and
the mixture was stirred at room temperature for about 2 h. The
solution was washed three times with 2 N HCl and then neutral-
ized by washing with saturated NaHCO3. The resulting solution
was dried over anhydrous MgSO4, filtered, and concentrated, pro-
ducing the target monomer. The crude monomer was further
purified by recrystallization with THF and hexane. The data for
monomer 1 were as follows: yield-40%, colorless crystal, m.p.
256–258 °C; IR (KBr): 3419 (H–N), 2163 (HC„), 1697 (C@O),
3048, 1598, 1495, 1447, 1330, 1240, 1138, 997, 925, 853, 725,
and 572 cmÀ1 1H NMR (DMSO-d6, 600 MHz, 25 °C): d 2.25 (1H,
.
HC„), 3.33 (2H, C„CCH2), 7.14–7.16 (4H, Ar), 7.37–7.39 (2H,
Ar), 7.48–7.49 (2H, Ar), and 8.10–8.11 (1H, NÀH). Calculation
for (C16H12N2O): C, 77.42; H, 4.84; N, 11.29. The real values were:
C, 77.53; H, 4.79; N, 11.21. Monomer 2 was synthesized according
to our previous study [27].
Scheme 1. Monomer synthesis and polymerization. Reagents: (a) bis(trichloro-
methyl)carbonate (BTC), ethyl acetate and THF; (b) propargylamine, ethyl acetate;
(c) (nbd)Rh+BÀ(C6H5)4 (nbd, norbornadiene), THF.

118
X. Luo et al. / Reactive & Functional Polymers 70 (2010) 116–121
Table 1
(Co)Polymerization results of monomers 1 and 2.a
Yield (%)b
Mn
Mw/Mn
[a
]
(°)
D
c
c
d
Entry
Monomer (1/2) (mol/mol)
Poly(1)
100/0
95/5
86
92
99
91
97
90
92
100
3700
3200
2800
2400
6400
6700
8900
12,700
1.36
2.11
1.82
1.21
1.94
2.01
2.07
1.59
0
Poly(10.95-co-20.05
Poly(10.90-co-20.10
Poly(10.80-co-20.20
Poly(10.60-co-20.40
Poly(10.40-co-20.60
Poly(10.20-co-20.80
Poly(2)
)
)
)
)
)
)
611
646
982
1107
1230
1341
1398
90/10
80/20
60/40
40/60
20/80
0/100
a
b
c
With (nbd)Rh+BÀ(C6H5)4 catalyst in THF, [M]0 = 0.5 M; [M]0/[Rh] = 100, 30 °C, 3 h.
Hexane-insoluble part.
Measured by GPC (polystyrenes as standards; THF as eluent).
Measured by polarimeter at room temperature, c = 0.080–0.1 g/dL in CHCl3.
d
mer 1 was low. The cis content of poly(1) was 98%, according to 1H
NMR measurement [24–28], i.e., by the integration ratio between
the vinyl proton of the polymer main chain and the other signals.
The high cis content was consistent with the preceding studies
[24–28], indicating that the Rh catalyst was efficient for synthesiz-
ing the polymers with high cis content.
The solubility of poly(1) was examined. It was completely solu-
ble in commonly used organic solvents, such as CHCl3, CH2Cl2, THF,
toluene, DMF, DMSO, and methanol.
Fig. 1 shows the UV–vis spectra of poly(1) and monomer 1 mea-
sured in CHCl3. Poly(1) and monomer 1 show little difference in
UV–vis absorption at the wavelength of 290–350 nm. This result
suggests that the polyacetylene backbones are not well conjugated,
possibly because of the irregular bending and crumpling of the
polymer chains [36].
of poly(1). In addition, the compositions of the copolymers were in
accordance with the monomer feed ratios. Taking poly(10.20-co-
20.80) as an example, according to the 1H NMR measurement and
the integration ratio between the amine and the methyl protons
in the copolymer side chains (in the units of monomer 2), the pro-
portion of monomer 2 units in the copolymer was found to be 76%.
Furthermore, the copolymers were considered to have random
structures, supported by our earlier studies [24–28] and the similar
investigations from other research groups [37–39]. For example, in
the work of Masuda, copolymers of N-propargylamides were con-
sidered adopting random structures. CD and UV–vis spectra of
the poly(1-co-2)s measured in CHCl3 at room temperature are
illustrated in Fig. 2.
In Fig. 2a, the copolymers produced UV–vis absorption peaks at
290 nm, 320 nm, and 332 nm, due to the carbazole groups. In addi-
tion, UV–vis absorption peaks at 360 nm originated in the poly-
acetylene main chains. By increasing the content of monomer 1
unit in the copolymers, the intensity of UV–vis absorption peaks
at 360 nm decreased. Fig. 2b presents CD spectra of the copoly-
mers. The CD signals of the copolymers at 360 nm demonstrate
that the copolymers have large optical activities. Referring to our
preceding investigations on poly(N-propargylamide)s [24],
poly(N-propargylsulfamide)s [25] and poly(N-propargylurea)s
[26–28], we concluded that the copolymers exhibited helical con-
formations under the examined conditions. Moreover, the CD sig-
nals weakened gradually as the content of monomer unit 1 in
the copolymers increased, as observed in Fig. 2b. This further indi-
cated that the helical content in the copolymers increased with the
content of monomer 2. Fig. 2b also demonstrates that the forma-
tion of helical structures conformed to the widely-known ‘‘Ser-
geants and Soldiers rule” [40]. The specific rotations of
copolymers in Table 1 showed the same trend as the CD signals,
which also demonstrated that the copolymers possessed very high
optical activities.
3.2. Preparation and properties of poly(1-co-2)s
(Co)polymerizations of monomers 1 and 2 were carried out for
the preparation of helical polymer backbones with carbazole
groups in their side chains. The (co)polymerization results are
listed in Table 1. The yields of all the copolymers are 90% and
above. The molecular weights of the copolymers show a general
tendency, i.e., increasing from approximately 3000 to approxi-
mately 13,000 with the content of monomer 2 unit. The molecular
weights and yields of the copolymers were both higher than those
Fig. 3 shows Kuhn’s dissymmetry ratios [41] (gabs
= De/e, in
which = [h]/3298) in a series of (co)polymers at approximate
D
e
360 nm, as a function of monomer 2 unit composition, in order
to quantitatively evaluate the chiral molar composition response
of the Cotton effects. It appears that only 5 mol% of monomer 2
unit in the copolymers completely determines the overall screw
sense, as shown in Fig. 2. With the composition of monomer 2 unit
increasing, the g value rises, indicating that the preferences of heli-
cal screw sense of the copolymer were increased. When the com-
position of monomer 2 unit is more than 10 mol%, the g value
was almost constant. It can be concluded that the copolymers
maintain their preferential helical screw sense in the region of
monomer 2 units above 10 mol%.
Fig. 4 shows the fluorescence spectra of monomer 1 and poly(1).
Monomer 1 and poly(1) exhibit fluorescence at 360 nm upon exci-
tation at 332 and 324 nm, respectively. The fluorescence properties
Fig. 1. UV–vis spectra of monomer 1 and poly(1) measured in CHCl3 (c = 0.1 mM) at
20 °C.

X. Luo et al. / Reactive & Functional Polymers 70 (2010) 116–121
119
Fig. 3. Plots of the g values of (co)polymers versus monomer 2 unit composition
(calculated from data of Fig. 2).
Fig. 2. UV–vis (a) and CD (b) spectra of poly(1-co-2)s measured in CHCl3
(c = 0.1 mM) at 20 °C.
of monomer 1 and poly(1) were due to the carbazole groups in
their side chains.
Fig. 4. Fluorescence spectra of monomer 1 and poly(1) measured in THF, excited at
332 and 324 nm, respectively.
Having helical (co)polymers with carbazole groups in their side
chains available, we further characterized the (co)polymers by
fluorescence spectroscopy. Copolymers have fluorescence proper-
ties, even for the copolymer containing monomer unit 1 as low
film from poly(10.20-co-20.80) (as a representative) and the pure
PVB film were characterized with both UV–vis and CD spectrosco-
pies, as presented in Fig. 6. Compared to the pure PVB film with
minor UV–vis absorption and no CD signal at 250–450 nm, the
composite film showed substantial UV–vis absorption peaks at
290, 320, and 332 nm, originating from the carbazole groups. The
composite film also showed a peak at 375 nm that was the copoly-
mer’s main chains. The CD spectra showed a bi-signal Cotton effect
and similar shapes, as presented in Fig. 6b. The CD signal at around
325 nm and 375 nm strongly demonstrated that the composite
film possessed very high optical activity. The bi-signal Cotton effect
assumed the formation of helical supramolecular structure in the
composite films of the copolymers, similar to polymer aggregates
[42].
as 20 mol% [poly(10.20-co-20.80)], as presented in Fig. 5. Poly(10.20
-
co-20.80 exhibits fluorescence at 430 nm upon excitation at
)
390 nm. A red shift can be observed in poly(10.20-co-20.80) (Fig. 5)
when compared to poly(1) (Fig. 4). Three are some factors leading
to the shift, for instance the intramolecular hydrogen bonds and
the synergic effects between the pendent groups especially in the
copolymers. Accordingly, poly(10.20-co-20.80) not only adopted a
helical conformation, but also exhibited fluorescence properties.
3.3. Optical activity and fluorescence properties of composite films
To attest to the practical uses of the fluorescent poly(N-propa-
rgylurea)s with chiroptical property, composite films consisting
of copolymers and PVB were prepared. PVB acts as a supporting
material for the optically active helical polymers. The composite
The prepared composite films were also subjected to fluores-
cence spectroscopy measurements, and the result is illustrated in
Fig. 7. The composite film exhibited fluorescence at 420 nm upon

120
X. Luo et al. / Reactive & Functional Polymers 70 (2010) 116–121
Fig. 7. Fluorescence spectrum of composite film containing poly(10.20-co-20.80),
Fig. 5. Fluorescence spectrum of poly(10.20-co-20.80) measured in THF, excited at
excited at 370 nm.
390 nm.
excitation at 370 nm; this wavelength was similar to that of the
corresponding copolymer. The results of CD and fluorescence spec-
troscopy measurements demonstrated that the composite films
exhibited both optical activity and fluorescence property. The no-
vel (co)polymers and composite films reported here are thus con-
sidered having potential applications for instance as optically
active luminescent materials emitting circular polarized light.
The relevant investigations are in progress.
4. Conclusions
A
poly(N-propargylurea) compound with carbazole groups
(poly(1)) in its side chains was successfully prepared by polymer-
izing the monomer in the presence of (nbd)Rh+B–(C6H5)4 as the cat-
alyst. Poly(1) had fluorescence properties. The copolymers of
monomers 1 and a chiral monomer 2 showed strong CD signals,
indicating that the copolymers had large optical activities and
adopted helical conformations with a predominantly one-handed
screw sense. The copolymers had considerable fluorescence prop-
erties. Composite films consisting of the copolymers and PVB
exhibited optical activities and fluorescence properties. These
investigations allow further design and development of multifunc-
tional polymers and facilitate the use of substituted polyacetylenes
in practical applications.
Acknowledgements
We gratefully thank the National Science Foundation of
China (20574004, 20974007), the ‘‘Program for New Century
Excellent Talents in University” (NCET-06-0096), the ‘‘Specialized
Research Fund for the Doctoral Program of Higher Education”
(20060010001), and the ‘‘Program for Changjiang Scholars and
Innovative Research Team in University” (PCSIRT, IRT0706) for
financial support of this work.
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