Synthesis and post-polymerization modification of polynorbornene bearing dibromomaleimide side groups

Article abstract of DOI:10.1016/j.polymer.2016.01.020

We demonstrate that polynorbornene containing dibromomaleimide side group is a novel polymer platform for post-polymerization modification. Polymer P0 was obtained through ring-opening metathesis polymerization of monomer 2 by using Grubbs third generation catalyst. Subsequently, P0 was chemically modified with 1-butanethiol and benzyl mercaptan to generate P1 and P2, respectively. In this way, the dibromomaleimide units on polymer side chain were quantitatively converted to dithiolmaleimide moieties. All the polymer samples exhibited good thermal stability and relatively high glass transition temperature. Meanwhile, the effects of substituent and solvent on fluorescent properties of the polymers were elucidated.

Full text of DOI:10.1016/j.polymer.2016.01.020

Accepted Manuscript
Synthesis and post-polymerization modification of polynorbornene bearing
dibromomaleimide side groups
Zi-Long Li, Linhao Sun, Jimei Ma, Zhen Zeng, Hong Jiang
PII:
S0032-3861(16)30020-9
10.1016/j.polymer.2016.01.020
JPOL 18372
DOI:
Reference:
To appear in: Polymer
Received Date: 14 October 2015
Revised Date: 5 January 2016
Accepted Date: 6 January 2016
Please cite this article as: Li Z-L, Sun L, Ma J, Zeng Z, Jiang H, Synthesis and post-polymerization
modification of polynorbornene bearing dibromomaleimide side groups, Polymer (2016), doi: 10.1016/
j.polymer.2016.01.020.
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Graphical Abstract

ACCEPTED MANUSCRIPT
Manuscript submitted to Polymer as an article
Synthesis and post-polymerization modification of polynorbornene bearing
dibromomaleimide side groups
Zi-Long Li*, Linhao Sun, Jimei Ma, Zhen Zeng, Hong Jiang*
Department of Chemistry, College of Science, Huazhong Agricultural University,
Wuhan 430070, Hubei, China
*
Corresponding author:
Tel.: +86 27 8728 4018.
E-mail address: lizilong@mail.hzau.edu.cn (Z.-L. Li), jianghong@mail.hzau.edu.cn (H.
Jiang)

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Abstract
We demonstrate that polynorbornene containing dibromomaleimide side group
is a novel polymer platform for post-polymerization modification. Polymer P0 was
obtained through ring-opening metathesis polymerization of monomer 2 by using
Grubbs third generation catalyst. Subsequently, P0 was chemically modified with
1
-butanethiol and benzyl mercaptan to generate P1 and P2, respectively. In this way,
the dibromomaleimide units on polymer side chain were quantitatively converted to
dithiolmaleimide moieties. All the polymer samples exhibited good thermal stability
and relatively high glass transition temperature. Meanwhile, the effects of
substituent and solvent on fluorescent properties of the polymers were elucidated.
Keywords
Polynorbornene; Dibromomaleimide; Post-polymerization modification

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1
. Introduction
Functional polymeric materials have attracted much attention from both
academic and industrial communities. In particular, the diversity of functionality
expands rapidly in recent years due to the wide applications of highly efficient
organic reactions in polymer chemistry [1]. In general, functional polymers can be
synthesized via polymerization of monomers that bearing functional moieties, so
that the functionality of the corresponding polymers are highly predicted. However,
the scope of functional groups that could be selected was usually narrowed due to
the intolerance of highly reactive species such as cations, anions and transition metal
catalysts to polar moieties. Moreover, monomer synthesis is the very first and
indispensable step to meet the requirements of developing a specific sort of
polymeric material with novel functions. On the other hand, post-polymerization
modification represents another synthetic methodology to afford functional
polymers always in an efficient and powerful manner [2-7]. In this way, the
as-prepared polymer serves as a platform ready to be chemically modified with
functional groups of a broad range. At the same time, a large number of functional
polymers can be obtained simply by choosing different modification reactions. A
unique chain length and molecular weight distribution of the final polymers is
anticipated, which provides convenience to make a point-to-point comparison of the
structure-property relationships. After modification, the microstructure of the
functional polymer is highly predicted as long as the reactive sites are quantitatively
converted.

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Ring-opening metathesis polymerization (ROMP) is an exceptional synthetic
method to obtain polymers with controlled chain length and low polydispersity index
[
8]. The release of monomer ring strain is the driving force of chain propagation,
therefore norbornene and cyclooctene derivatives both become ideal choices for
ROMP monomers. The ruthenium-based catalysts (best known as Grubbs catalysts)
are not only commercially available but also highly tolerant to a variety of polar
groups. In this way, functionality of a polymer chain can be well controlled and the
concentration of functional groups in local environment can be facially adjusted by
using ROMP. Indeed, in the last decade, tremendous research efforts have been
dedicated to this chain-growth polymerization protocol, and the diversity of
functional polymers that derived from ROMP was greatly enriched. Among the
reported contributions, post-polymerization modification of ROMP polymer
represents an increasingly appealing research field. For example, functional groups
including azido [9-11], alkyne [12-14], activated ester [15-18], activated bromide [19]
and pentafluorophenyl [20] have been induced to the ROMP polymer side chains for
further modification. Very recently, multiple “click” reactions (e.g. activated ester
nucleophilic substitution, Diels-Alder reaction, atom transfer nitroxide radical
coupling, maleimide-thiol coupling, hydrazone formation, thiol-ene reaction and
copper-catalyzed azido-alkyne 1,3-dipolar cycloaddition, etc) are used for orthogonal
modification of ROMP polymer side chains [21-26]. At the same time, quantitative
conversion of the internal alkene moieties of ROMP polymers to other functional
groups was also realized upon several approaches [27-30]. However, only a single

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functional moiety is induced to each repeating unit of the polymer. Moreover,
although the induction of functional groups along with the construction of polymer
topology such as grafted polymer and polymer brush both become successful,
research on the property of the resultant polymer is rather limited.
Dibromomaleimide (DBM) is capable of modifying cysteine in a selective and
reversible way as reported by Baker [31]. From then on, this sort of native disulfide
bridging protocol was widely used in biomedical field such as protein modification
including PEGylation [32] and fluorescent labeling [33] as well as bioconjugation [34].
The carbon-bromide bond can be efficiently substituted by thiols under mild
condition and in a quantitative manner, and this novel sort of “click” reaction have
already found wide applications in polymer chemistry. For example, O’Reilly group
demonstrated that polymer chain end [35] and side chain [36] functionality could be
tuned in a broad range by DBM-thiol reaction, and functional polymers were also
obtained by polymerization of pre-functionalized monomers [37]. At the same time,
cyclic [38] and star [39] polymers were successfully generated with the assistance of
DBM-thiol reaction to control polymer topology, and even sequence-regulated
polymers [40] were obtained due to the “click” nature of this reaction. Very recently,
functional materials such as gene delivery vehicle [41], nanomedicine [42] and
biomolecule-modified surface [43] have been fabricated to exemplify the huge
potential and impact of this novel “click” reaction in materials science. Inspired by
the previous works, we speculated that the marriage of ROMP and DBM will certainly
provide new opportunity for post-polymerization modification. A new sort of

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chemically modifiable polymer platform could be generated through the ROMP of
norbornene monomer bearing DBM moiety, which contains two reactive sites in each
repeating unit. After the DBM-thiol reaction, different kinds of densely functionalized
polynorbornene could be obtained simply by changing the type of thiols. Importantly,
the thiol-substituted maleimide has been reported to be a fluorophore, so that
fluorescent polymers are anticipated. Therefore, the effect of thiols as well as
environmental factors such as solvent on fluorescent properties of the polymers
could be investigated, which is surely helpful for the development of polymeric
fluorescent probe of next generation.
In this contribution, we provide the first example of polynorbornene bearing
DBM units as side groups via ROMP and the subsequent post-polymerization
modification. Monomer bearing DBM moiety was synthesized in a two-step manner
and was obtained in high yield. ROMP of the monomer was catalyzed by Grubbs third
generation (G-III) catalyst, and the resultant polymer was obtained with predicted
chain length and narrow molecular weight distribution. Subsequently,
post-polymerization modification was performed by using DBM-thiol reaction to
quantitatively convert the DBM units to dithiolmaleimide (DTM) moieties. All the
polymer samples exhibited good thermal stability and relatively high glass transition
temperature (T ). Fluorescent polymers were generated after the modification, and
g
the fluorescence intensity and the maximum emission wavelength were found to be
correlated with the type of thiol and solvent.

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2
. Experimental
2
.1. Materials
3
,4-Dibromo-1H-pyrrole-2,5-dione (DBM, Ark Pharm, Inc.), methylchloroformate
MCF, ≥99%, Xiya Reagent Co., Ltd.), N-methylmorpholine (NMM, ≥99.8%, Aladdin),
-norbornene-2-methylamine (NMA, mixture of isomers, >98.0%, TCI), G-III catalyst
Sigma-Aldrich), ethyl vinyl ether (EVE, stabilized with 0.1% N,N-diethylaniline, Alfa
(
5
(
Aesar), 1-butanethiol (98%, Alfa Aesar) and benzyl mercaptan (99%, Alfa Aesar) were
all used as received without further purification. Tetrahydrofuran (THF), chloroform
(CHCl3), dichloromethane (DCM), N,N-dimethylformamide (DMF), anhydrous
methanol (MeOH), petroleum ether (petrol), ethyl acetate (EtOAc), anhydrous
magnesium sulfate (MgSO ) and anhydrous ammonium chloride (NH Cl) were all
4
4
purchased from Sinopharm Chem. Reagent Co., Ltd. Calcium hydride (CaH ) was
2
bought from Tianjin Xuan’ang Trade and Industry Co., Ltd. THF, CHCl and DCM were
3
refluxed with CaH for 8 h and then redistilled. DMF was vigorously stirred with CaH
2
2
for 6 h and then distilled under reduced pressure. CDCl was obtained from J&K
3
Chemical Co., Ltd.
2
.2. Characterization
Bruker ARX-400 spectrometer was utilized to measure the H (400 MHz) and
100 MHz) NMR spectra. ROMP monomer and polymer samples were all dissolved in
1
13
C
(
CDCl with tetramethylsilane (TMS) as the internal reference for chemical shifts.
3
Number- and weight-average molecular weights (M and M ) and polydispersity
n
w

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indices (Ð = M /M ) were determined by gel permeation chromatograph (GPC). The
w
n
o
measurements were conducted in THF (flow rate: 1 mL/min) at 35 C with a Waters
1
525 binary HPLC pump equipped with a Waters 2414 refractive index detector and
4
3
three Waters Styragel columns (1 × 10 , 1 × 10 and 500 Å pore sizes). A family of
narrowly dispersed polystyrenes was used as the standards, and Breeze 3.30 SPA
software was applied to calculate the M and Ð values. Electrospray ionization mass
n
spectroscopy (ESI-MS) characterization was conducted using a Bruker APEX-IV
Fourier transform mass spectrometer in a positive ion mode. Thermal gravimetric
analysis (TGA) was carried out using a Q600-SDT thermogravimetric analyzer (TA Co.,
Ltd.) with nitrogen purging rate set at 100 mL/min. Measurements were conducted
o
o
from room temperature to 600 C at a heating rate of 10 C/min. Calorimetric
measurement was performed using a Q100 differential scanning calorimeter (TA Co.,
Ltd.) with nitrogen purging rate set at 50 mL/min. The program was set to finish two
o
o
cycles in the temperature range from 0 C to 180 C. The heating/cooling rate was set
o
to 10 C/min. Data of the endothermic curve was acquired from the second scan. TA
Universal Analysis software was used for data acquisition and processing in TGA and
DSC measurements. Fluorescence spectra of polymers were recorded on a Hitachi
F-7000 fluorescence spectrometer at room temperature. The scanning rate was 240
nm/min and both excitation and emission slit widths were 5.0 nm.
2
.3. Synthesis of intermediate 1
To a solution of DBM (3.00 g, 11.7 mmol) and NMM (1.30 mL, 11.7 mmol) in THF

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(135 mL), MCF (0.90 mL, 11.7 mmol) was added and the mixture was stirred for 1 h
at room temperature. The solvent was removed in vacuo, and then DCM (100 mL)
was added. The organic phase was sequentially washed with water and brine, and
then dried over anhydrous MgSO . After filtration, the solvent was removed in vacuo
4
to generate the intermediate 1 as a pink powder in quantitative yield. The compound
1
2
1
was directly subjected to the next synthetic step without further purification.
.4. Synthesis of ROMP monomer 2
NMA (1.42 mL, 11.2 mmol) was added dropwise to a stirred solution of 1 (3.66 g,
1.7 mmol) in DCM (120 mL). After 10 h, the solvent was removed in vacuo, and
EtOAc (100 mL) was added to dissolve the crude product. The organic phase was
sequentially washed with saturated NH Cl solution, water and brine, and then dried
4
over anhydrous MgSO . After filtration, the organic filtrate was concentrated to
4
dryness, and the yellowish crude residue was purified by column chromatography
1
(
petrol/EtOAc = 50/1) to generate 2 as white solid. Yield: 79%. H NMR (400 MHz,
CDCl ), δ (TMS, ppm): 6.50-5.83 (m, 2H), 3.83-3.14 (dddd, J = 39.3, 23.1, 13.8, 8.2 Hz,
3
1
3
2
1
1
5
H), 2.98-2.30 (m, 3H), 2.10-0.40 (m, 4H). C NMR (100MHz, CDCl ): δ 163.93 (d, J =
3
4.7 Hz), 137.89, 137.06, 135.97, 132.34, 129.27 (d, J = 5.0 Hz), 49.45, 44.85 (d, J =
3.4 Hz), 44.22 (d, J = 8.8 Hz), 43.62, 42.45, 41.78, 38.04 (d, J = 4.7 Hz), 30.37 (d, J =
+
3.4 Hz). ESI-MS: [M + Na ] = C H O NBr Na, calcd: 383.9034, found: 383.9090.
1
2
11
2
2
2
.5. ROMP

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To a 25 mL Schlenk tube 2 (36.1 mg, 0.1 mmol) and DCM (1 mL) was added to
generate solution 1. G-III catalyst (2.9 mg, 3.3 μmol) was dissolved in DCM (1 mL) to
form solution 2. Subsequently, solution 2 (1 mL) was added to solution 1 under
nitrogen atmosphere by using pipette ([2] = 0.05 mol/L), and the resulting solution
was vigorously stirred at room temperature for 0.5 h. Afterwards, an excess of EVE
was added under nitrogen atmosphere, and the polymer solution was vigorously
stirred for an additional 5 min with the Schlenk tube sealed. The as-prepared
polymer solution was directly subjected to GPC characterization. Meanwhile, the
solution was poured into cold methanol (100 mL) to rapidly generate P0 as a white
solid for NMR characterization, thermal analysis and fluorescent property
investigation. At the same time, the as-prepared polymer solution was concentrated
to dryness, and P0 was obtained as brownish semi-solid in this case for the
subsequent DBM-thiol reaction. The overall yield was over 95%.
2
.6. DBM-thiol reaction
Take the synthesis of P1 as an example.
To a solution of P0 (36.1 mg) in DMF (2 mL), 1-butanethiol (21.4 μL, 0.2 mmol)
was added by using pipette, and the resulting solution was vigorously stirred at room
temperature for 10 h. The as-prepared P1 solution was directly subjected to GPC
characterization. Meanwhile, the solution was poured into cold methanol (100 mL)
to rapidly generate P1 as a yellowish solid for NMR characterization, thermal analysis
and fluorescent property investigation.

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Polymer P2 was synthesized similarly with benzyl mercaptan (23.5 μL, 0.2 mmol)
as the added thiol compound. The overall yields were over 95% in both cases.
3
. Results and discussions
3
.1. Monomer synthesis
The synthesis of ROMP monomer 2 was conducted in two consecutive steps as
shown in Scheme 1. It is reported that DBM derivatives could be obtained by treating
dibromomaleic anhydride with amine. Nevertheless, a large amount of acetic acid is
used as solvent and high reflux temperature is required, making the reaction
condition extremely harsh and the purification rather tedious. As a result, we
adopted a two-step synthetic procedure to get ROMP monomer 2 referring to the
recently reported mild synthesis of N-functionalized DBM [44]. As a first step, DBM
was treated with MCF and NMM to obtain the highly reactive intermediate 1 in THF
at room temperature for 1 h and in quantitative yield. Subsequently, ROMP
monomer 2 was generated through mixing compound 1 with 0.95 equivalent amount
of NMA in DCM at room temperature for 10 h, and the overall yield of two steps
reached 79% after purification. Intermediate 1 was one sort of reactive conjugate
acceptor, so that no more than a stoichiometric amount of NMA was used, otherwise
unwanted byproduct would be generated. The chemical structure and purity of 2
1
13
were confirmed by H and C NMR (Figs. 1 and S1) and ESI-MS spectra.

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Scheme 1. Monomer Synthesis. Reagents and Conditions: (a) 1 equiv. MCF, 1 equiv. NMM, THF, rt,
1
h (b) 0.95 equiv. NMA, DCM, rt, 10 h.
1
Fig. 1. H NMR spectrum of ROMP monomer 2 in CDCl3
3
.2. ROMP and DBM-thiol reaction
Polymer P0 was obtained in nearly quantitative yield through ROMP of monomer
with the assistance of G-III catalyst in DCM at room temperature for 0.5 h. The dose
2
of catalyst was 3.3 mol% relative to monomer 2, corresponding to degree of
polymerization being 30, so that the theoretical molecular weights of P0-P2 could be
calculated, and the results were shown in Table 1. Gels were observed during the

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ROMP process if the monomer concentration was higher than 0.1 mol/L. Hence, the
monomer concentration was kept 0.05 mol/L in this study.
Subsequently, as shown in Scheme 2, DBM-thiol reaction was carried out by
mixing polymer P0 with theoretical amounts of 1-butanethiol or benzyl mercaptan in
DMF at room temperature for 10 h to afford DTM units functionalized
polynorbornene P1 and P2, respectively. The color of the solution turned bright
yellow rapidly, suggesting the occurrence of nucleophilic substitution of thiols to
DBM moieties.
Scheme 2. ROMP and DBM-thiol reaction. Reagents and Conditions: (a) G-III catalyst (3.3 mol%),
DCM ([2] = 0.05 mol/L), rt, 0.5 h (b) stoichiometric 1-butanethiol or benzyl mercaptan, DMF, rt, 10
h.
All the GPC traces are unimodel as shown in Fig. 2, and the molecular weight
values are summarized in Table 1. Each of the polymer samples exhibited M value
n
exceeding 10,300 with narrow molecular weight distribution (Ð values lower than
1
.24 even after DBM-thiol reaction), so that efficient ROMP and post-polymerization
modification was confirmed. Since GPC traces of P1 and P2 exhibited very similar
shape to that of P0 without the appearance of shoulder peak or significant

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broadening, side reactions such as cross-linking or chain scission could be ruled out
in this study. The elevated M values of P1 and P2 compared to that of P0 could be
n
attributed to the inherent increase of molecular weight. Meanwhile, the molecular
weights of polymers measured by GPC were in high accordance with the theoretically
calculated values.
Fig. 2. GPC traces of P0-P2 using THF as the eluent.
NMR characterization was carried out to manifest the chemical structures of
polymer samples. Polymers P0-P2 all exhibited good solubility in CDCl , and the
3
1
related H NMR spectra were shown in Fig. 3. Signals of internal alkene (5.1-5.5 ppm),
methylene spacer (3.3-3.7 ppm) and cyclopentane of polymer backbone (1.0-3.2
ppm) protons were clearly distinguished for P0, respectively. At the same time,
signals corresponding to internal alkenes could be seen for polymer samples of P1
and P2 as well, suggesting the absence of side reaction between thiols and those
moieties. Meanwhile, signals of n-butyl protons (for P1) and benzyl protons (for P2)
were clearly observed and depicted in Fig. 3, confirming the successful DBM-thiol
reaction. Importantly, the integration ratios between the signals of n-butyl or benzyl

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groups and those of the internal alkene moieties matched well with the theoretical
values, which solidly confirm the quantitative manner of DBM-thiol reaction for
post-polymerization modification.
1
Fig. 3. H NMR spectra of P0-P2 in CDCl .
3
Table 1
Molecular weights and thermal data of polymer samples.
a
b
b
c
o
d o
Polymer
P0
Mn, thero
Mn, GPC
Ð
T ( C)
Td ( C)
g
10 900
11 500
13 500
10 300
10 800
12 700
1.17
1.23
1.24
153
126
174
241
P1
207
P2
231
a
Calculated according to the feed ratio [2]/[G-III] = 100/3.3 (degree of polymerization being 30).
Then Mn, thero = (theoretical repeating unit mass) × 30 + terminuses.

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b
c
o
Determined by GPC (1 mL/min in THF at 35 C) using polystyrene calibration.
o
Determined by DSC (10 C/min scan rate, nitrogen purging rate at 50 mL/min), the values
recorded from the second scan data.
d
o
Determined by TGA (10 C/min scan rate, nitrogen purging rate at 100 mL/min). T is defined as
d
the temperature at 5 % weight loss.
3
.3. Thermal properties
Thermal stability of all the polymer samples was examined by TGA, and the
photograph of solid P0-P2 could be seen in Fig. S2. All the data are collected in Table
. T is defined as the temperature at 5% weight loss. Fig. 4A depicts the TGA curves
1
d
o
o
of P0-P2 with the onset T values ranging from 207 C to 241 C, indicating the
d
thermal stability of these polymers is suitable for common use. Multi-step
o
catastrophic decomposition was detected above 200 C, suggesting the complicated
mechanism of thermal degradation. Although polynorbornene was commonly
regarded as thermal resistant polymeric material [45], induction of DBM or DTM
moieties as side groups severely diminished the thermal stability. Finally, all the
o
polymer samples decomposed completely at about 600 C.
Thermal transition behaviors of all the polymer samples were measured by DSC.
Polymers P0-P2 only exhibited typical glass transition stages in the DSC thermograms
of Fig. 4B, and no melting peaks or other transition was observed even when heated
o
to 180 C. The polymers decompose before they melt owing to the moderate thermal
stability, resulting in the absence of melting peaks. The as-prepared polymer P0

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o
exhibited glass transition stage at 153 C, and this result could be explained as the
stiffness of polymer main chain and the structural rigidity of DBM moieties. P1
o
showed lower T value (126 C) compared with P0 due to the flexibility of butyl
g
o
chains. Meanwhile, the glass transition stage of P2 appeared at 174 C since the
aromatic phenyl ring elevated the rigidity of polymer side chain. These results
indicate that the thermal transition behaviors of this family of functional polymers
can be potentially adjusted over a broad temperature range simply by altering the
type of thiol compound for substitution.
Fig. 4. (A) TGA curves of P0-P2. (B) Endothermic DSC thermograms of P0-P2.
3
.4. Fluorescent properties
The fluorescent properties of all the polymer samples were evaluated by
fluorescence spectra. We selected CHCl , DMF and MeOH as three representative
3
organic solvents to carry out the experiment. All the polymer samples exhibited
solvent-dependent fluorescent properties. As shown in Fig. 5A-C, the fluorescence
intensity as well as the maximum emission wavelength of polymer P0-P2 is a
function of the type of organic solvent. For example, the fluorescence emission of P0

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was not only obviously bathochromic-shifted but also drastically diminished as
increasing the polarity of organic solvent. Polymers P1 and P2 exhibited the similar
trend but differed in maximum emission wavelength. This phenomenon can be
explained as the sensitivity of intra-molecular electron transfer to environmental
factor such as solvent. The electron shifted away from the sulfur or bromide atom
(electron donor) in the excited state to carbonyl group (electron acceptor) [46]. The
significant decrease of fluorescence intensity and the phenomenon of
bathochromic-shift in protic solvent such as methanol could be ascribed to the
hydrogen bond between organic solvent and imide moiety of maleimide group [47].
On the other hand, due to the difference in fluorescence emission energy resulting
from the alteration of substitution, the maximum emission wavelengths of P1 and P2
are bathochromic-shifted compared to that of P0. For a specific sort of organic
solvent, as summarized in Fig. 5D, polymers bearing DTM moieties (P1 and P2)
exhibit relatively strong fluorescence while the as-prepared polymer P0 shows much
weaker emission. This result coincided well with the previously reported ON-OFF
switch between DTM and DBM units [48]. Meanwhile, the weaker fluorescence
intensity of P2 compared to that of P1 is due to the negative effect of aromatic
moieties such as benzyl group on fluorescence emission [49].
Overall, the fluorescent properties of P0-P2 are determined by organic solvent
and substituent. The maximum emission wavelength is bathochromic-shifted and the
fluorescence intensity is diminished as increasing the polarity of organic solvent.
Converting DBM to DTM group has a significant effect on bathochromic-shift of

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maximum emission wavelength and enhancement of fluorescence intensity of the
polymer. The variation of fluorescent property is the synergistic outcome of chemical
structure and organic solvent. It is worth mentioning that polymer concentration of 2
μM was sufficient for fluorescent property characterization, and the homogeneous
sample solutions were generated in this case. However, increasing the concentration
of polymer solution (e.g. 5 μM) may result in opaque suspension especially when
protic solvent such as methanol was selected. The maximum excitation (λ ) and
ex
emission (λ ) wavelengths of all the polymer samples were collected in Table S1.
em
Fig. 5. (A)-(C) Fluorescence emission spectra of P0, P1 and P2 in different solvents, respectively.
All the spectra were recorded at polymer concentration of 2 μM. (D) Comparison of the relative
fluorescence intensity of P0-P2 in different solvents.

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4
. Conclusions
The first example of polynorbornene containing DBM side groups via ROMP was
provided in this study. Monomer 2 was obtained in high yield by means of two
consecutive synthetic steps. Subsequently, ROMP of monomer 2 was successfully
conducted by using G-III catalyst to generate polymer P0 with predicted chain length
and narrow molecular weight distribution. Thiol-DBM reaction was utilized for
post-polymerization modification to quantitatively convert DBM units to DTM
moieties, and polymers P1 and P2 were generated after treatment of P0 with
stoichiometric amount of 1-butanethiol and benzyl mercaptan, respectively.
o
o
Polymers P0-P2 were stable up to 200 C and exhibited T s higher than 125 C, and all
g
the solid samples were re-dissolvable in common organic solvents even after
selective precipitation. The fluorescence intensity and the maximum emission
wavelength of the polymers were determined by substituent and solvent. Specifically,
the fluorescence intensity of the polymer was greatly enhanced after the thiol-DBM
reaction but significantly diminished as increasing the polarity of organic solvent. The
present work not only provides an alternative of chemically modifiable polymer
platform but also sheds light on the exploration of novel polymeric fluorescent
probe.
Acknowledgements
The authors are grateful for the helpful discussions with Prof. Zi-Chen Li from Peking
University and Dr. Jing Xu from Wuhan Textile University. The authors also appreciate

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financial support from the National Natural Science Foundation of China (No.
2
2
1504027) and the Fundamental Research Funds for the Central Universities (No.
015BQ043).
Appendix A. Supplementary data
Supplementary data related to this article can be found at
http://dx.doi.org/10.1016/j.polymer.201X.XX.XXX.
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Highlights
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Polynorbornene containing DBM side groups was synthesized by means of ROMP.
Thiols were used for quantitative conversion of DBM units to DTM moieties.
Fluorescent properties of the polymers were governed by substituent and solvent.