Aliphatic polyketones via cross-metathesis polymerization: Synthesis and post-polymerization modification

Article abstract of DOI:10.1016/j.polymer.2019.121936

Polyolefins attract considerable attention due to their vast consumption and wide application. In this study, cross-metathesis polymerization (CMP) is demonstrated to be an efficient and feasible method for the synthesis of aliphatic polyketones. The synt

Full text of DOI:10.1016/j.polymer.2019.121936

Journal Pre-proof
Aliphatic polyketones via cross-metathesis polymerization: Synthesis and post-
polymerization modification
Fu-Rong Zeng, Jing Xu, Qi Xiong, Kai-Xuan Qin, Wei-Jun Xu, Yue-Xin Wang, Zan-
Jiao Liu, Zi-Long Li, Zi-Chen Li
PII:
S0032-3861(19)30942-5
DOI:
https://doi.org/10.1016/j.polymer.2019.121936
JPOL 121936
Reference:
To appear in: Polymer
Received Date: 22 August 2019
Revised Date: 20 October 2019
Accepted Date: 21 October 2019
Please cite this article as: Zeng F-R, Xu J, Xiong Q, Qin K-X, Xu W-J, Wang Y-X, Liu Z-J, Li Z-L, Li
Z-C, Aliphatic polyketones via cross-metathesis polymerization: Synthesis and post-polymerization
modification, Polymer (2019), doi: https://doi.org/10.1016/j.polymer.2019.121936.
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Graphical Abstract

Manuscript submitted to Polymer as an article
Aliphatic Polyketones via Cross-Metathesis Polymerization: Synthesis and
Post-Polymerization Modification
Fu-Rong Zenga, Jing Xub, Qi Xionga, Kai-Xuan Qina, Wei-Jun Xua, Yue-Xin Wanga,
Zan-Jiao Liua, Zi-Long Lia,*, Zi-Chen Lic
a Department of Chemistry, College of Science, Huazhong Agricultural University,
Wuhan 430070, Hubei, China
b College of Materials Science and Engineering, Key Laboratory of Textile Fiber and
Products (Ministry of Education), Wuhan Textile University, Wuhan 430200, Hubei,
China
c Beijing National Laboratory for Molecular Sciences (BNLMS), Key Laboratory of
Polymer Chemistry & Physics of Ministry of Education, Department of Polymer
Science & Engineering, College of Chemistry and Molecular Engineering, Peking
University, Beijing 100871, China
* Corresponding author:
E-mail address: lizilong@mail.hzau.edu.cn (Z.-L. Li)

Abstract
Polyolefins attract considerable attention due to their vast consumption and wide
application. In this study, cross-metathesis polymerization (CMP) is demonstrated to
be an efficient and feasible method for the synthesis of aliphatic polyketones. The
synthetic route features good yield, mild condition and easy operation. The success
of CMP relies on the high cross-metathesis tendency between α-olefin and vinyl
ketone units of monomer 2. Optimization of polymerization condition was conducted
to generate unsaturated polyketone P0 (Mn,GPC = 14 kDa), and the results of kinetic
study verified high efficiency and structural integrity of this system. Furthermore,
post-polymerization modification of P0 by using thiol-Michael chemistry furnished
functional polyketones P1-P6, and full conversion of the internal vinyl ketone groups
of P0 was observed in each case. The pristine and functional polyketones P0-P6 were
virtually soluble in most common organic solvents. In particular, hydrophobic and
fluorescent polyketones (P5 and P6) were also obtained by this means. Therefore,
this synthetic strategy shows promising future and exemplifies huge potential for the
synthesis of a diverse range of functional polyketones.

Keywords
Aliphatic polyketones
Cross-metathesis polymerization
Thiol-Michael chemistry

1. Introduction
Copolymers of ethylene and polar monomers attract considerable attention due
to their broad range of applications [1-3]. Even low incorporation of polar groups will
significantly influence the performance of polyolefins [4]. In particular, aliphatic
polyketones have become a research focus recently due to their unique properties
such as crystallinity, thermal stability, high stiffness, corrosion resistance and photo
degradability [5]. Meanwhile, a number of preparative approaches have been
developed over the last decades. For example, free radical copolymerization of
ethylene and CO generally leads to low content of CO and a high degree of branching
[6]. Linear polyketones can be synthesized by using insertion copolymerization in the
presence of palladium catalysts [7-14]. It is noteworthy that this method is by far the
most reliable one for the synthesis alternating polyketones [15-17]. However, this
technique still faces challenges such as generation of homopolyolefins and methyl
branches [18]. Therefore, control over microstructure is still an urgent demand for
the synthesis of aliphatic polyketones.
The above issue has been partially addressed with the advent of metathesis
polymerization [19,20]. For example, defect-free model polyketones were obtained
through acyclic diene metathesis (ADMET) polymerization although vacuum, high
temperature and rather long reaction time were basically required [21,22]. Later on,
precision polyketone with regular spacing was generated by ring-opening metathesis
polymerization (ROMP) [23,24]. In this case, low conversion was observed as a result
of chain transfer. It is notable that ADMET and ROMP systems suffer from insolubility

of saturated polyketones in most common organic solvents. Moreover, main chain
functionalization of aliphatic polyketone is scarcely reported probably due to the lack
of reactive sites [25].
In this work, we propose cross-metathesis polymerization (CMP) as an efficient
and feasible technique for the synthesis of linear polyketones with definite structures.
Biobased monomer 2 bearing α-olefin and vinyl ketone terminuses were synthesized
in two steps. Following CMP of monomer 2, the resulting unsaturated polyketone P0
underwent post-polymerization modification to furnish functional polyketones P1-P6.
Thiol-Michael addition under proper condition enabled full conversion of the internal
alkene units of P0 in each case. Ultimately, soluble polyketones with diverse pendent
groups such as fluorophore and perfluorocarbon were readily obtained.
2. Experimental
2.1. Materials
10-Undecenal (97%, Adamas-beta), vinylmagnesium bromide (1 mol L-1 in dry
tetrahydrofuran, Aladdin), 2-iodoxybenzoic acid (IBX, 95%+, Adamas-beta),
3-octen-2-one (>96%, TCI), 1-butanethiol (97%, Aladdin), benzyl mercaptan (98%,
Aladdin), methyl thioglycolate (>98%, TCI), 4-methylthiophenol (98%, Aladdin),
1H,1H,2H,2H-perfluorodecanethiol (97%, Aladdin), 8-mercaptoquinoline
hydrochloride (95%, TCI), dimethylphenylphosphine (DMPP, 97%, Alfa Aesar),
Hoveyda-Grubbs second generation catalyst (HG-II, 97%, Sigma-Aldrich),
1,4-benzoquinone (BQ, 99%, Innochem), ethyl vinyl ether (EVE, 98%, stabilized with

0.1% KOH, Aladdin), tetrahydrofuran (THF, 99.0%, Sinopharm), dimethyl sulfoxide
(DMSO, ≥99%, Sinopharm), N,N-dimethylformamide (DMF, ≥99.5%, Sinopharm),
toluene (TOL, 99.5%, Sinopharm), dichloromethane (DCM, 99.5%, Sinopharm),
chloroform (TCM, 99.5%, Sinopharm), petroleum ether (petrol, 60-90 oC, 99.7%,
Sinopharm), ethyl acetate (EtOAc, ≥99.6%, Sinopharm), diethyl ether (≥99.7%,
Sinopharm), methanol (≥99.5%, Sinopharm), magnesium sulfate anhydrous (MgSO4,
≥98.0%, Chinasun), sodium chloride (≥99.5%, Sinopharm), silica gel (reagent grade,
200-300 mesh, Qingdao Haiyang Chemical Co., Ltd), calcium chloride anhydrous
(CaCl2, ≥98.0%, Sinopharm), calcium hydride (CaH2, ≥97.0%, Tianjin Chemical Reagent
Research Institute Co., Ltd) and deuterated chloroform (CDCl3, 99.8% deuteration,
0.03 % v/v tetramethylsilane (TMS) and silver foil, Cambridge Isotope Laboratories,
Inc) were used as received unless otherwise noted. Argon gas (99.9%) was obtained
from Wuhan Minghui Gas Technology Co., Ltd. THF was refluxed with sodium for 8 h
and distilled. DMF was vigorously stirred with CaH2 for 6 h and distilled in vacuo. TOL,
DCM and TCM were all degassed by sonication for 5 min prior to polymerization.
2.2. Characterization
Bruker Avance 600 spectrometer was used to measure the 1H (600 MHz) and 13C
(150 MHz) NMR spectra. All the samples were dissolved in CDCl3 with TMS as the
internal reference for chemical shifts. Number-average molecular weights (Mn,GPC
)
and polydispersity indices (Ð) were measured by gel permeation chromatography
(GPC). The measurements were conducted in THF (flow rate: 1 ml min-1) at 35 oC with

Waters 1525 binary HPLC pump equipped with a Waters 2414 refractive index
detector and three Waters Styragel columns (1 × 104, 1 × 103, and 500 Å pore sizes). A
series of narrowly dispersed polystyrenes were used as the standards, and Breeze
3.30 SPA software was used to calculate the Mn,GPC and Ð values. Electrospray
ionization mass spectroscopy (ESI-MS) characterization was conducted by using a
Bruker APEX-IV Fourier transform mass spectrometer in positive ion mode. Thermal
gravimetric analysis (TGA) was carried out by using a Q600-SDT thermo-gravimetric
analyzer (TA Co., Ltd.) with nitrogen purging rate of 100 ml min-1. Measurement was
conducted from ambient temperature to 600 oC at a heating rate of 10 oC min-1.
Differential scanning calorimetry (DSC) characterizations were carried out by using a
Q100 differential scanning calorimeter (TA Co., Ltd.) with nitrogen purging rate of 50
ml min-1. The program was set to finish two cycles within temperature range from -80
oC to 80/120 oC. The heating or cooling rate was 10 oC min-1. 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. Wide angle
powder X-ray diffraction (WAXD) data were obtained by using a Bruker D8 ADVANCE
diffractomer at 40 kV and 50 mA (copper Kα radiation with λ = 1.54 Å). All the
measurements were conducted at room temperature with a scanning rate of 10o
min-1 over 2θ ranges from 5o to 85o. Polymer solutions of P0 and P5 (10 mg mL-1 in
TCM) were spin coated at 1500 rpm for 20 s onto glass wafers. The static contact
angle of a 2 µL water droplet deposited on a spin-coated surface was measured. The
results are the average of ten measurements. UV-Vis spectra were recorded by using

a UV-Vis spectrophotometer UV-2601 (Shimadzu) at ambient temperature within
wavelength (λ) range from 280 nm to 400 nm. Fluorescence spectra were recorded
by using a Hitachi F-7000 fluorescence spectrometer at room temperature within
wavelength (λ) range from 360 nm to 600 nm. The scanning rate was 240 nm min-1,
and the excitation and emission slit widths were both 5.0 nm.
2.3. Synthesis of monomer precursor 1
10-Undecenal (5.05 g, 30 mmol) and dry THF (40 mL) were added to a 250 mL
round bottom flask and cooled to -20 oC under Ar. Vinylmagnesium bromide (45 mL,
1 mol L-1 in dry THF) was added, and the mixture was stirred at 0 oC for 1 h. At this
time, the light yellow solution was warmed to ambient temperature. Afterward,
saturated ammonium chloride solution (50 mL) was added, and the mixture was
vigorously stirred for 5 min. The mixture was extracted by EtOAc (twice), and the
combined organic phase was washed with brine, dried over MgSO4 followed by
filtration and removal of solvent to furnish viscous colorless oil. The crude product
was purified by silica gel column chromatography (petrol/EtOAc = 30/1) to generate
monomer precursor 1 as a viscous colorless oil (3.83 g, 19.5 mmol). Production yield:
65%. 1H NMR (600 MHz, CDCl3), δ (TMS, ppm): 5.78-5.90 (m, 2H), 5.20-5.24 (dt, J =
17.2, 1.3 Hz, 1H), 5.09-5.11 (m, 1H), 4.97-5.01 (ddd, J = 17.1, 3.4, 1.6 Hz, 1H),
4.92-4.94 (m, 1H), 4.06-4.13 (dd, J = 14.5, 9.9 Hz, 1H), 2.02-2.06 (m, 2H), 1.50-1.57
(tdt, J = 11.4, 7.8, 3.9 Hz, 2H), 1.47-1.59 (d, J = 4.1 Hz, 1H), 1.34-1.42 (m, 2H),
1.25-1.34 (m, 10H). 13C NMR (150 MHz, CDCl3): δ 141.35, 139.23, 114.53, 114.12,

73.29, 37.05, 33.81, 29.54, 29.52, 29.42, 29.12, 28.92, 25.33. ESI-MS: [M + H+] =
C13H25O, calcd: 197.190545, found: 197.190600.
2.4. Synthesis of monomer 2
IBX (6.72 g, 24 mmol) and DMSO (30 mL) were added to a 150 mL round bottom
flask to generate solution 1. Precursor 1 (3.92 g, 20 mmol) was dissolved in THF (30
mL) to obtain solution 2, which was dropwise added to solution 1. The mixture was
stirred at room temperature for 2 h. At this time, water (20 mL) was added under
stirring, and white solid was observed. After filtration, the mixture was extracted by
EtOAc (twice), and the combined organic phase was washed with brine, dried over
MgSO4 followed by filtration and removal of solvent to furnish viscous colorless oil.
The crude product was purified by silica gel column chromatography (petrol/EtOAc =
50/1) to give monomer 2 as a viscous colorless oil (2.85 g, 14.7 mmol). Production
yield: 74%. 1H NMR (600 MHz, CDCl3), δ (TMS, ppm): 6.33-6.38 (dd, J = 17.7, 10.6 Hz,
1H), 6.20-6.23 (d, J = 17.6 Hz, 1H), 5.77-5.84 (m, 2H), 4.97-5.01 (dd, J = 17.1, 1.1 Hz,
1H), 4.92-4.94 (d, J = 10.1 Hz, 1H), 2.56-2.59 (t, J = 7.4 Hz, 2H), 2.02-2.05 (q, J = 7.1 Hz,
2H), 1.59-1.64 (m, 2H), 1.34-1.39 (dd, J = 13.5, 6.7 Hz, 2H), 1.23-1.34 (s, 8H). 13C NMR
(150 MHz, CDCl3): δ 201.13, 139.20, 136.62, 127.86, 114.15, 39.66, 33.79, 29.37,
29.31, 29.25, 29.07, 28.90, 24.01. ESI-MS: [M + H+] = C13H23O, calcd: 195.174342,
found: 195.174227.
2.5. Model reactions

Take the synthesis of 4-(benzylthio)octan-2-one as an example.
3-octen-2-one (126 mg, 1 mmol) was dissolved in DMF (5 mL) in a 10 mL round
bottom flask. At this time, benzyl mercaptan (234 µL, 2 mmol) and DMPP (1.5 µL, 10
µmol) were added, and the mixture was stirred at room temperature for 24 h, at
which time TLC showed that 3-octen-2-one was fully converted. EtOAc was added to
the system, and the organic phase was washed by water and brine, dried over MgSO4
followed by filtration and removal of solvent to give viscous colorless oil. The crude
product was purified by silica gel column chromatography (petrol/EtOAc = 30/1) to
give the desired product as a viscous colorless oil in nearly quantitative yield. 1H NMR
(600 MHz, CDCl3), δ (TMS, ppm): 7.29-7.33 (m, 4H), 7.22-7.24 (t, J = 6.9 Hz, 1H),
3.71-3.76 (m, 2H), 3.01-3.06 (p, J = 6.8 Hz, 1H), 2.57-2.68 (ddd, J = 39.2, 16.8, 6.9 Hz,
2H), 2.08 (s, 3H), 1.47-1.53 (m, 2H), 1.21-1.39 (m, 4H), 0.85-0.87 (t, J = 7.2 Hz, 3H).
13C NMR (150 MHz, CDCl3): δ 206.98, 138.53, 128.92, 128.48, 126.99, 49.65, 40.43,
35.77, 34.84, 30.54, 28.81, 22.45, 13.98. ESI-MS: [M + H+] = C15H23OS, calcd:
+
251.146413, found: 251.145803; [M + NH4 ] = C15H26ONS, calcd: 268.172962, found:
268.172258.
Likewise, the synthesis of thiol-Michael adducts 4-(butylthio)octan-2-one, methyl
2-((2-oxooctan-4-yl)thio)acetate and 4-(p-tolylthio)octan-2-one was carried out
similarly. Notably, the amount of methyl thioglycolate was 120 mol% with respect to
substrate 3-octen-2-one. Meanwhile, 4-(p-tolylthio)octan-2-one was obtained in
about 40% yield, and only partial consumption of 3-octen-2-one was observed as
reflected by TLC. Fortunately, full conversion of 3-octen-2-one could be achieved if a

large excess of 4-methylthiophenol (600 mol% with respect to 3-octen-2-one) was
used. These compounds were all viscous colorless oils.
NMR and ESI-MS data of 4-(butylthio)octan-2-one:
1H NMR (600 MHz, CDCl3), δ (TMS, ppm): 3.06-3.11 (m, 1H), 2.62-2.73 (m, 2H),
2.47-2.54 (m, 2H), 2.18 (s, 3H), 1.51-1.57 (m, 4H), 1.22-1.47 (m, 6H), 0.89-0.92 (m,
6H). 13C NMR (150 MHz, CDCl3): δ 207.17, 49.74, 40.60, 35.08, 31.84, 30.82, 30.63,
28.98, 22.55, 22.08, 14.00, 13.68. ESI-MS: [M + H+] = C12H25OS, calcd: 217.162063,
found: 217.161955.
NMR and ESI-MS data of methyl 2-((2-oxooctan-4-yl)thio)acetate:
1H NMR (600 MHz, CDCl3), δ (TMS, ppm): 3.74 (s, 3H), 3.22-3.32 (m, 3H),
2.65-2.81 (ddd, J = 23.5, 17.2, 6.8 Hz, 2H), 2.17 (s, 3H), 1.51-1.61 (m, 2H), 1.25-1.47
(m, 4H), 0.89-0.91 (t, J = 7.2 Hz, 3H). 13C NMR (150 MHz, CDCl3): δ 206.55, 171.14,
52.40, 49.41, 41.38, 34.60, 32.86, 30.54, 28.83, 22.44, 13.95. ESI-MS: [M + H+] =
+
C11H21O3S, calcd: 233.120592, found: 233.120575; [M + NH4 ] = C11H24O3NS, calcd:
250.147141, found: 250.147081; [M + Na+] = C11H20O3SNa, calcd: 255.102536, found:
255.102615; [M + K+] = C11H20O3SK, calcd: 271.076474, found: 271.076551.
NMR and ESI-MS data of 4-(p-tolylthio)octan-2-one:
1H NMR (600 MHz, CDCl3), δ (TMS, ppm): 7.30-7.32 (d, J = 8.1 Hz, 2H), 7.10-7.11
(d, J = 7.9 Hz, 2H), 3.47-3.51 (m, 1H), 2.58-2.71 (ddd, J = 24.4, 17.0, 6.8 Hz, 2H), 2.33
(s, 3H), 2.12 (s, 3H), 1.38-1.58 (m, 4H), 1.23-1.36 (m, 2H), 0.87-0.90 (t, J = 7.3 Hz, 3H).
13C NMR (150 MHz, CDCl3): δ 207.00, 137.46, 133.20, 130.45, 129.71, 49.11, 44.11,
34.39, 30.64, 29.03, 22.47, 21.11, 13.98. ESI-MS: [M + H+] = C15H23OS, calcd:

+
251.146413, found: 251.145914; [M + NH4 ] = C15H26ONS, calcd: 268.172962, found:
268.172419.
2.6. Optimization of CMP condition
Take the procedure of run 1 as an example.
Monomer 2 (97 mg, 0.5 mmol) and BQ (0.5 mg, 5 µmol) were weighed in a 25 mL
Schlenk flask equipped with a Teflon valve. TOL (0.5 mL) was added to form solution
1, which was placed in 80 oC oil bath. HG-II catalyst (1.6 mg, 2.5 μmol) was dissolved
in TOL (0.5 mL) to furnish green solution 2. At this time, solution 2 was rapidly mixed
with solution 1 under argon ([2] = 0.5 mol L-1). The flask was connected to a reflux
condenser which was equipped with an anhydrous CaCl2 loaded drying tube. The
polymerization solution was stirred at 80 oC for 12 h. Argon was supplied through the
Teflon valve. No precipitation of polyketone or apparent evaporation of TOL was
observed throughout the polymerization process. EVE (0.5 mL) was added under
argon to terminate the polymerization, and the solution was stirred for an additional
5 min. The polymer solution was poured into ice-cold methanol (100 mL) to generate
brownish precipitate. After centrifugation and vacuum dryness, polymer was
obtained as a brownish solid in 88% yield.
Samples for run 2-7 were synthesized similarly.
2.7. Polymerization kinetics
The synthetic procedure was similar to that of optimization of CMP condition

(run 7). Specifically, an aliquot solution of P0 was taken at 0.5 h, 1 h, 2 h, 3 h, 4 h, 6 h,
8 h, 12 h and 24 h followed by termination and removal of volatiles prior to 1H NMR
characterization.
2.8. Post-polymerization modification
Take the synthesis of polymer P2 as an example.
Polymer P0 (194 mg, 1 mmol vinyl ketone), TCM (5 mL) and DMF (5 mL) were
mixed in a 25 mL round bottom flask to form a brownish solution. Afterward, benzyl
mercaptan (725 μL, 6 mmol) and DMPP (1.5 μL, 10 μmol) were added. The mixture
was stirred at 50 oC for 48 h. At this time, the solution was poured into cold methanol
(100 mL) and stored at 4 oC overnight to give brownish semi-solid. Precipitation was
conducted for three times to completely remove excessive thiol and DMF. After
centrifugation and vacuum dryness, polymer P2 was obtained as a viscous semi-solid
in about 90% yield.
Polymers P1 and P3-P6 were synthesized similarly. These samples were viscous
semi-solids.
3. Results and discussions
3.1. Monomer synthesis
A two-step synthetic route of monomer 2 was depicted in Scheme 1, and a
natural product derivative 10-undecenal was selected as the starting material. This
compound is derived by pyrolysis and reduction from castor oil [26,27], which has

been used for the synthesis of poly-α,β-unsaturated aldehydes [28] and bifunctional
aldehyde derivatives [29]. According to olefin categorization proposed by Grubbs [30],
terminal alkene and vinyl ketone are type I and II olefins, respectively. Consequently,
compound 2 is an AB-type monomer featuring head-to-tail polycondensation. At first,
intermediate 1 was obtained through Grignard reaction between 10-undecenal and
vinylmagnesium bromide in dry THF. Subsequently, monomer 2 was synthesized via
oxidation of precursor 1 in mixed solvent by using IBX as the oxidant [31]. These two
reactions enjoy the unique merits of mild condition, facile operation and good yields.
The chemical structure and purity of compounds 1 and 2 were confirmed by 1H and
13C NMR (Fig. S1-S4) and ESI-MS spectra.
Scheme 1. Monomer synthesis. Reagents and conditions: a) 1.5 equiv. vinylmagnesium bromide
(1 mol L-1 in THF), dry THF, -20 oC to 0 oC, 1 h; b) 1.2 equiv. IBX (0.8 mol L-1 in DMSO), THF, rt, 2 h.
3.2. Thiol-Michael model reactions
Vinyl ketone and α-olefin groups are anticipated to undergo cross-metathesis
reaction to generate α,β-unsaturated ketones. In order to examine the feasibility of
post-polymerization modification of unsaturated polyketone, as shown in Scheme 2,
model reactions were conducted by using four types of thiols as nucleophiles. The
occurrence of thiol-Michael addition between 3-octen-2-one and 1-butanethiol,
benzyl mercaptan, methyl thioglycolate and 4-methylthiophenol indicates the

feasibility of post-polymerization modification. Specifically, methyl thioglycolate
showed the strongest nucleophilicity since only a slight excess of thiol (120 mol%
with respect to 3-octen-2-one) enabled full conversion of the substrate. Meanwhile,
1-butanethiol and benzyl mercaptan both allowed full conversion of 3-octen-2-one
although excessive thiols (200 mol% with respect to the substrate) were basically
required. Owing to the moderate nucleophilicity of 4-methylthiophenol, only 40%
conversion of 3-octen-2-one was observed under the same condition. In spite of this,
quantitative conversion of 3-octen-2-one could be realized if a large excess of
4-methylthiophenol (600 mol% with respect to the substrate) was used. In this study,
DMF was selected as the solvent to promote Michael addition [32]. Moreover, DMPP
instead of amine was selected as the catalyst in order to prevent imine formation
[33]. The structures and purity of model compounds were verified by 1H and 13C NMR
spectra as shown in Fig. S5-S12. Notably, thioketal was not detected in any case.
Scheme 2. Model reaction. Reagents and condition: a) thiol (see Experimental section for detail),
1 mol% DMPP, DMF, rt, 24 h.
3.3. Optimization of CMP condition
Inspired by CMP systems involving monomers containing α-olefin and acrylate as
metathetically polymerizable groups [34-69], as shown in Scheme 3, we envision that

generation of unsaturated polyketone P0 via CMP of AB-type monomer 2 is feasible.
Likewise, the occurrence of CMP is motivated by the high cross-metathesis tendency
between vinyl ketone and α-olefin groups. In this way, internal vinyl ketone units are
periodically incorporated on polymer main chain. As depicted in Table 1, a variety of
experimental parameters were examined to optimize the CMP condition with an aim
to increase the Mn,NMR of P0. HG-II catalyst was selected due to its wide application in
cross-metathesis reaction [70]. BQ was used in order to suppress olefin isomerization
although this inhibitor generally showed negative effect on Mn [71,72]. The solvent
for polymerization should be screened so as to meet the requirements of polymer
solubility and high catalyst activity. Finally, a suitable polymerization temperature
ought to be determined depending on the compromise among reaction rate, solvent
evaporation rate and polymer viscosity.
Scheme 3. Synthesis of P0 via CMP of monomer 2.
Table 1
Optimization of CMP condition for the synthesis of P0.
d
run
1
cat a [mol%]
BQb
yes
yes
solvent
TOL
T c [oC]
80
time [h]
Mn,NMR
3600
0.5
0.5
12
6
2
DCM
40
2000

3
4
5
6
7
0.5
0.5
0.5
0.5
1.0
yes
no
DCM
DCM
TCM
TCM
TCM
40
40
60
60
60
12
12
12
24
24
2400
3600
6200
7800
8600
yes
no
no
a Feed ratio of HG-II with respect to monomer 2.
b 1.0 mol% BQ with respect to monomer 2.
c Polymerization temperature.
d Calculated based on terminus analysis. See Fig. S13 for detail.
The conductance of CMP in toluene (which evaporated rather slowly) at 80 oC (at
which polymer was soluble and catalyst decomposition was negligible) resulted in
moderate Mn,NMR of P0 (run 1), which was due to the relatively low activity of HG-II in
toluene [73]. Indeed, HG-II generally exhibited high activity in DCM. Run 2-4 jointly
showed that prolonged reaction time and no addition of BQ were beneficial for the
increase of Mn,NMR. However, rapid evaporation of DCM led to polymer precipitation,
so that the formation of high molecular weight polymer was inaccessible. Notably,
proton signals of olefin isomerization were not detected even if no BQ was used. A
significant increase of Mn,NMR was observed if TCM was selected as the solvent (run 5),
which might be best explained as the relatively high activity of HG-II and high
concentration of CMP system as a solution. Small amount of TCM was intermittently
added to prevent polymer precipitation. Encouraged by this, we conducted further

optimization. A final Mn,NMR of 8600 was achieved by increasing the amount of HG-II
and prolonging polymerization time. Hence, run 7 was determined as the standard
condition. Once again, the system was confirmed to be free from olefin isomerization.
Mn,NMR values of run 1-7 were calculated based on terminus analysis of each relevant
1H NMR spectrum (Fig. S13).
3.4. Polymerization kinetics
Chemical structure and molar mass of P0 (run 7 in Table 1) was monitored by
NMR and GPC, respectively. Data of kinetic analysis is collected in Table 2. Samples
were taken at certain time interval followed by termination and removal of volatiles
prior to characterization. Relative amounts of proton signals denoting α-olefins and
vinyl ketones were equally defined as 100%. As shown in Table 2, the polymerization
reached almost completion after 24 h, which was slower than the systems employing
monomers bearing α-olefin and acrylate terminuses [74-76]. As expected, signals of
cross-metathesis (CM) prevail in the CMP process, while those of residual terminuses
are marginal. In a mechanistic point of view, kinetically favored self-metathesis (SM)
of α-olefins rapidly yields SM dimer. Subsequently, CM between internal alkenes and
terminal vinyl ketones gives rise to intermediates bearing internal vinyl ketone units.
Notably, relative amount of CM proton signals was 86.2% when the polymerization
proceeded for just 0.5 h and finally reached 92.0% when the reaction was terminated
at 24 h. This observation indicates that CM overwhelms SM of α-olefins in a rather
short time and then proceeds sluggishly to almost completion. Signals of residual

terminuses decreased over time, reflecting a gradual increase of molecular weight. It
is notable that proton signal of SM indicates the existence of side reaction during
polymerization procedure and structural defect within polymer. Incomplete CM
between vinyl ketone and 1,2-disubstituted alkene groups along with marginal SM of
vinyl ketones (generally considered as SM inactive groups) are responsible for such
undesired signals. Unreacted vinyl ketones and SM of α-olefins prevail in terminus
structures and structural defects, respectively. These results can be attributed to the
priority of SM of α-olefins although SM and CM occur simultaneously throughout the
polymerization. Thus, CM indeed dominates in microstructure of P0 but by no means
precludes side reaction such as SM, and alternation index P should never reach 100%.
The internal vinyl ketone moieties of P0 predominantly adopted trans configuration.
NMR spectra associated with kinetic analysis were collected in Fig. S14, and chemical
structure of P0 was evidenced by 1H and 13C NMR spectra (Fig. S15 and S16).
Table 2
Kinetic analysis of P0.
α-olefina
SM
vinyl ketonea
time
[h]
c
d
Pb
Mn,NMR Mn,GPC
Đd
residue
6.0%
CM
residue
SM
CM
0.5
1.0
2.0
3.0
7.8% 86.2% 11.6% 2.2% 86.2% 94.2%
3300
4000
5000
5200
4700
5700
7100
7400
1.60
1.81
2.03
2.11
4.0%
7.5% 88.5%
7.5% 89.3%
7.6% 89.5%
9.4%
8.0%
7.8%
2.1% 88.5% 94.3%
2.7% 89.3% 94.2%
2.7% 89.5% 94.5%
3.2%
2.9%

4.0
6.0
2.6%
2.5%
2.1%
1.9%
1.4%
1.1%
7.2% 90.2%
7.3% 90.2%
7.1% 90.8%
7.1% 91.0%
6.7% 91.9%
6.9% 92.0%
7.8%
7.2%
6.7%
6.6%
5.4%
5.1%
2.0% 90.2% 94.2%
2.6% 90.2% 94.2%
2.5% 90.8% 94.5%
2.4% 91.0% 94.5%
2.7% 91.9% 94.3%
2.9% 92.0% 94.4%
5700
6000
6400
7100
8600
9800
8100
8600
9100
2.15
2.25
2.36
8.0
12.0
24.0
24.0e
10100 2.44
12300 2.49
14000 2.47
a Relative molar fraction of olefins calculated based on proton signal integration ratios.
b Alternation index, calculated based on integration ratio between signals of CM and SM.
c Calculated based on terminus analysis.
d Measured by GPC (1 mL min-1 in THF at 35 oC) using polystyrene calibration.
e After precipitation.
Mn,NMR is calculated based on integration ratio among proton signals of residual
terminus, SM and CM. A final Mn,NMR value of 9800 is reached after precipitation.
Meanwhile, GPC results show that Mn,GPC value increased over time (Fig. S17 and
S18), and the trend coincide well with that of Mn,NMR. Finally, high value of
polydispersity (Đ) is in consistent with step-growth mechanism.
3.5. Post-polymerization modification
As shown in Scheme 4, post-polymerization modification of P0 was conducted via
thiol-Michael chemistry [77] to afford functional polymers P1-P6. Full conversion of
the internal vinyl ketone groups of P0 was achieved by using thiols T1-T6 although

excessive thiol, elevated temperature and prolonged reaction time were basically
required in each case. First of all, polymers P1-P4 were synthesized to examine the
efficacy of post-polymerization modification by employing thiols T1-T4, which were
previously investigated in model reaction study. Chemical structures of P1-P4 were
confirmed by 1H (Fig. 1) and 13C (Fig. S19) NMR spectra. Complete disappearance of
the proton signals of terminal and internal vinyl ketone groups verifies full conversion
of these Michael acceptors. Internal, terminal and SM vinyl ketone moieties were
apparently identical in chemical reactivity whereas terminal and SM α-olefin groups
were inert to post-polymerization modification. Moreover, proton signal of thioketal
unit cannot be detected. The integration ratios among all the characteristic proton
signals are highly consistent with predicted values. The 1H, 13C and 19F NMR spectra
of polymers P5 and P6 are shown in Fig. S20-S22.
Scheme 4. Synthesis of P1-P6 via post-polymerization modification of P0. Reagents and
condition: a) 6 equiv. thiol, 1 mol% DMPP, TCM/DMF, 50 oC, 48 h.

Fig. 1. 1H NMR spectra of P1-P4 in CDCl3 (structures of side chains shown and characteristic
peaks designated only).
We moved on to investigate the molecular weights and thermal properties of
polymers P0-P4. As shown in Table 3, polymers P0-P4 show similar Mn,GPC, indicating
that hydrodynamic radiuses of these polymers are very close. Moreover, this system
is free from chain scission or cross-linking. The relatively low Đ values of polymers
P1-P4 are due to repetitive precipitation, during which the fractions of low molecular
weight components are reduced.
Table 3
Molecular weight and thermal data of P0-P4.

a
b
c
entry
P0
Mn,GPC
Đa
Tg [oC]
Tm b [oC]
86.3
n.d.d
n.d.
Td [oC]
12300
12200
13000
14500
13800
2.49
1.96
1.91
1.94
1.93
-1.5
394
e
P1
-57.7
-57.1
-57.2
-57.6
-
P2
-
-
-
P3
n.d.
P4
n.d.
a Determined by GPC (1 ml min-1 in THF at 35 oC) using polystyrene calibration.
b Determined by DSC, 10 °C min-1 scan rate. Values were recorded from second scan data.
c Determined by TGA, 10 °C min-1 scan rate. Td is defined as the temperature at 5% weight loss.
d Not detected.
e Not measured.
As for thermal properties, polymer P0 shows relatively high Tg due to the rigidity
of vinyl ketone groups. On the contrary, the Tgs of polymers P1-P4 significantly
decrease after thiol-Michael addition, which is due to the flexibility of polymer chain
induced by saturation. To our interest, polymers P1-P4 exhibit nearly identical Tgs,
suggesting that the Tg of the functional polyketone is irrelevant to the type of side
group for this system. Meanwhile, the crystallinity of P0 is evidenced by DSC and
WAXD results (Fig. S23 and S24), and this polymer shows a unique melting peak at
86.3 oC. On the contrary, the absence of melting peak for polymers P1-P4 might be
best explained as the irregular packing of polymer chain caused by bulky side groups.
In addition, polymer P0 exhibits high thermal stability, whereas the Tds of polymers

P1-P4 are not measured in this contribution so as to prevent the release of odorous
sulfur-containing substances. The TGA curve of P0 is shown in Fig. S25.
In order to expand the potential application areas of this synthetic methodology,
post-polymerization modification of polymer P0 was conducted by using thiols T5
and T6 to yield hydrophobic (P5) and fluorescent (P6) polyketones, respectively. First
of all, water contact angles of P0 and P5 were measured to examine the wettability
of surfaces that coated with these polymers. Fig. 2A shows that the hydrophobicity
of polymer P5 is more pronounced due to the existence of perfluorocarbon pendent
groups. The data of different measurements shows consistent result. It is anticipated
that the wettability of polyketone can be altered by using different thiols. Moreover,
superhydrophobic surface can also be fabricated if the roughness is increased [78].
UV-Vis absorption and fluorescence emission spectra of polymer P6 are recorded
to establish correlation between concentration and spectroscopic property. As shown
in Fig. 2B and 2C, the UV-Vis absorbance at 340 nm displays linear relationship with
concentration of P6 in the range from 77.2 µmol L-1 to 3.67 mmol L-1. On the other
hand, polymer P6 shows concentration-dependent fluorescence intensity as revealed
by Fig. 2D-2F. Specifically, the fluorescence intensity enhances while increasing the
concentration of polymer P6 from 77.2 µmol L-1 to 1.84 mmol L-1 but decreases if the
concentration is higher than 1.84 mmol L-1. As expected, the increase of fluorophore
concentration should increase the fluorescence intensity. Nevertheless, fluorescence
quenching may occur if the concentration exceeds some critical value [79,80]. In this
study, the critical value appears to be 1.84 mmol L-1. Noteworthy, the fluorescence

intensity of polymer P6 shows plausible linear relationship with concentration in the
range from 77.2 µmol L-1 to 617.6 µmol L-1. Moreover, blue emission was observed
under UV light (365 nm irradiation by handheld UV lamp, concentration of P6 being
1.84 mmol L-1), indicating that polymer P6 is a practical fluorescent probe.
Fig. 2. (A) Contact angle images and data for droplets of water on P0 and P5 surfaces. (B) UV-Vis
spectra of P6 in TCM at room temperature. (C) Linear plots of absorbance versus different
concentrations of P6 at 340 nm. [P6] is calculated based on its monomer unit. (D) and (E)
Fluorescence spectra of P6 in TCM at room temperature. Optical images are inserted (under
daylight and irradiation by UV lamp, Ex = 365 nm, respectively). (F) Plots of fluorescence intensity
versus different concentrations of P6 at 412 nm.
4. Conclusions
In this study, we report the synthesis of aliphatic polyketones via sequential CMP
and thiol-Michael chemistry. First of all, bio-based monomer 2 was synthesized in

two steps by using natural product derivative 10-undecenal as the starting material.
The results of model reaction verified the feasibility of Michael addition between
3-octen-2-one and thiol compounds. Optimization of CMP condition was carried out
to afford high molecular weight P0 (Mn,GPC = 14 kDa). Moreover, the results of kinetic
study demonstrated high efficiency and structural fidelity of this system. Finally,
post-polymerization modification of pristine polyketone P0 by using thiol-Michael
addition readily yielded functional polyketones P1-P6. Full conversion of the internal
vinyl ketone groups of P0 was observed in each case. In particular, the fabrication of
hydrophobic and fluorescent polyketones P5 and P6 indicated the huge potential of
this synthetic protocol for the synthesis of a diverse range of functional polyketones.
Acknowledgements
F.-R.Z. and J.X. contributed equally to this work. The authors appreciate financial
support from the Open Project Program of Beijing National Laboratory for Molecular
Sciences (BNLMS201808) and the National Natural Science Foundation of China (No.
21504027).
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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