Metal-free alkyne polyhydrothiolation: synthesis of functional poly(vinylenesulfide)s with high stereoregularity by regioselective thioclick polymerization

Article abstract of DOI:10.1002/adfm.200901943

A new synthetic route to sulfur-rich polymers has been developed. The alkyne polyhydrothiolations of 4,4'-thiodibenzenethiol (1) and arylene dipropiolates (2-5) mediated by amines proceed at room temperature in a regioselective fashion, furnishing sole an

Full text of DOI:10.1002/adfm.200901943

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Metal-Free Alkyne Polyhydrothiolation: Synthesis of
Functional Poly(vinylenesulfide)s with High
Stereoregularity by Regioselective Thioclick Polymerization
By Cathy K. W. Jim, Anjun Qin, Jacky W. Y. Lam,* Faisal Mahtab, Yong Yu, and
Ben Zhong Tang*
carbon single bonds. Because of electronic
saturationofthesinglebonds,theolefinicor
vinyl polymers are electrically inactive and
have thus been commonly used as com-
modity materials in contemporary society.
A new synthetic route to sulfur-rich polymers has been developed. The alkyne
polyhydrothiolations of 4,4(-thiodibenzenethiol (1) and arylene dipropiolates
(2–5) mediated by amines proceed at room temperature in a regioselective
fashion, furnishing sole anti-Markovnikov products of poly(vinylenesulfide)s
(P1/2–P1/5) with high molecular weights (Mw up to 32 300) and high
stereoregularities (Z content up to 81.4%) in high yields (up to 98.2%).
Polymers P1/2–P1/4 are soluble in common organic solvents. They are
optically transparent, allowing almost all visible and IR light to transmit
through. Thanks to the high sulfur contents of the polymers, their films show
high refractive indices (n ¼ 1.73–1.70) in the wavelength region of 500–
Polymerizationsofacetylenicmonomers
can generate polymers with p-conjugated
carbon–carbon double bonds that are
expected to be electronically active.
Indeed, polyacetylene has been found to
show metallic conductivity upon doping—
this seminal discovery has triggered much
research activity in the utilization of alkynes
as building blocks to construct functional
polymers.[1] As a result of the enthusiastic
efforts of polymer chemists, a large number
of acetylenic polymers have been synthe-
sized.[2] In almost all the acetylenic poly-
mers, their monomer repeating units are
strung together by carbon–carbon linkages.
The polymerizations of acetylene mono-
´
1700 nm as well as high Abbe numbers (nD’ up to 539) and low optical
dispersions (D’ down to 0.002) at wavelengths important for
telecommunications. Their refractivities can be further enhanced (n up to
2.06) by metal complexation and their films can be crosslinked by UV
irradiation, which enables ready fabrication of fluorescent photopatterns.
mers through carbon–heteroatom hookups are of great interest
because the resultant heteroatom-containing acetylenic polymers
may exhibit properties that are difficult, if not impossible, to access
by the polymers with pure carbon-based skeletons.
1. Introduction
The exploration of effective polymerization reactions for the
synthesis of new polymers with novel structures and unique
properties is an important area of research in macromolecular
science. Addition polymerizations of olefinic monomers have been
one of the main routes to synthetic polymers. In the olefinic
polymerizations, the monomers are knitted together by carbon–
Alkyne hydrothiolation is a reaction that is potentially useful for
the synthesis of heteroatom-containing acetylenic polymers. The
reaction was first reported by Truce and Simms in the 1950s:
admixing alkynes with sodium thiolates resulted in the formation
of vinyl sulfides.[3] The extensive studies on alkyne hydrothiola-
tions in the past half century have revealed that the reactions
proceed through Markovnikov and anti-Markovnikov addition
routes to produce regio- and stereoisomers with branched and
linear structures (Scheme 1).[4,5] One recent development in the
area is the report by Yorimitsu and coworkers that certain cesium
saltsinitiatehydrothiolationsofarylalkyneswithalkylthiols.[6] The
inorganic bases, however, was not applicable to aryl thiols, while
organic bases such as triethylamine completely failed to work as
catalysts when the reactions were attempted at room temperature.
It is envisioned that alkyne hydrothiolation of alkyne and thiol
with two triple bonds (diyne) and mercapto groups (dithiol) may
produce a poly(vinylenesulfide) (PVS) with linear and branched
conformations. The sulfur-containing polymer may exhibit
properties uniquely associated with its high sulfur content, such
as high light refractivity and excellent optical transparency, and
[*] Prof. B. Z. Tang, Dr. J. W. Y. Lam, C. K. W. Jim, Dr. A. Qin, F. Mahtab,
Y. Yu
Department of Chemistry, Institute of Molecular Functional Materials
The Hong Kong University of Science & Technology (HKUST)
Clear Water Bay, Kowloon (Hong Kong, PR China)
E-mail: tangbenz@ust.hk, chjacky@ust.hk
Prof. B. Z. Tang, Dr. J. W. Y. Lam, C. K. W. Jim, Dr. A. Qin, F. Mahtab,
Y. Yu
HKUST Fok Ying Tung Research Institute
Nansha, Guangzhou (PR China)
Prof. B. Z. Tang, Dr. A. Qin
Department of Polymer Science and Engineering
Key Laboratory of Macromolecular Synthesis and Functionalization of
the Ministry of Education of China
Zhejiang University, Hangzhou 310027 (PR China)
DOI: 10.1002/adfm.200901943
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transparent and are readily metallized by
complexation with cobalt carbonyls to furnish
organometallic polymers with high refractive
indexes (n ¼ 2.106–1.708) and low chromatic
aberrations (D’ down to 0.002).
2. Results and Discussion
2.1. Monomer Preparation
Scheme 1. Formation of 1,1- and 1,2-disubstituted olefins with branched and linear structures by
Markovnikov and anti-Markovnikov routes of alkyne hydrothiolation, respectively.
To explore the possibility of utilizing alkyne
thus find high-tech applications as a promising photonic
material.[7] ThePVS mayreadily react orcoordinate with transition
metals and the resultant macromolecular complexes may work
as recyclable and reusable polymer catalysts[8] and serve as pro-
cessable precursors to non-oxide ceramics upon pyrolysis.[9] Such
possibilities, although attractive, have been virtually unexplored.
Our groups have been working on the development of alkyne
polymerization reactions. Employing monoynes, diynes, and
triynes as monomers, we have successfully synthesized a large
variety of polyacetylenes, polyarylenes, polydiynes, and polytria-
zoles with linear and hyperbranched structures and regio- and
stereoregularities bymetathesis, cyclotrimerization, coupling, and
click polymerizations.[10] In our previously investigated click
polymerization systems, azide–alkyne cycloaddition (or ‘azido-
click’) reactions were utilized. Thiol–alkene addition is another
well-known click reaction and has been used by several research
groups to synthesize saturated macromolecules such as dendri-
mers and star polymers.[11,12] In contrast, thiol–alkyne addition or
alkyne hydrothiolation remains unexploited, although it has the
potential to be developed into a new ‘‘thioclick’’ polymerization
technique for the synthesis of sulfur-containing unsaturated
polymers.
In this work, wehave extendedouracetylene-based researchto a
heteroatom-mediated system and have developed alkyne hydro-
thiolation into a versatile polymerization technique for the
preparation of sulfur-rich acetylenic polymers. In this paper, we
show that alkyne polyhydrothiolations of 4,40-thiodibenzenethiol
(1) and arylene dipropiolates (2–5) are mediated by organobases
such as secondary amines at room temperature to afford
regioregularlinearPVSs(P1/2–P1/5)withhighmolecularweights
and high stereoregularities in high yields (Scheme 2). This
represents the first example of a metal-free, organobase-mediated,
thioclick polymerization reaction. The PVSs are optically
hydrothiolation to construct sulfur-containing macromolecules,
we adopted an A2 þ B2 approach and used dithiol 1 and
dipropiolates 2–5 as building blocks for the synthesis of linear
PVSs. The advantage of this strategy is that the monomers can be
synthesized with ease and can be kept for a long time on the shelf
under ambient conditions, which circumvents the self-oligomer-
ization problem met by the AB2 approach.
Arylene dipropiolates 2–5 were prepared by esterifications of
theircorresponding diolswithpropiolicacidinthepresenceof 1,3-
dicyclohexylcarbodiimide (DCC), 4-(dimethylamino)pyridine
(DMAP), and p-toluenesulfonic acid (TsOH). All the monomers
were characterized by spectroscopic techniques, from which
satisfactory analysis data corresponding to their expected
molecular structures were obtained (see Experimental section
for details).
2.2. Polymer Synthesis
The development of non-metallic and metal-free polymerization
reactions has attracted much interest among polymer chemists in
recent years because of their remarkable advantages, such as
environmental benignity, economic benefit, and ease in polymer
purification.[13] The reactions are free of the detrimental effects of
metallicionsinthecatalystresiduesonpolymerproperties,suchas
light emission and optical non-linearity. In addition, functional
groups that are toxic to transition metals can be used, which helps
widen the variety of polymers that can be synthesized by the
reactions.
In our previous investigations, we found that bis(aroylacety-
lene)s and dipropiolates could be polycyclotrimerized in the
presence of secondary amines or in refluxing N,N-dimethylform-
amide (DMF).[10] We thus tried to synthesize
PVS from 1 and 3 under metal-free conditions.
After stirring in DMF at room temperature for
24 h, a PVS with an Mw of 5200 was isolated in a
yield of ꢀ92% (Supporting Information, Table
S1, run 1). Changing the solvent to tetrahy-
drofuran (THF), toluene, and dioxane had little
effect on the yield of the PVS but decreased its
molecular weight. Both yield and Mw dropped
whenthepolymerizationwaspreformedin1,2-
dichlorobenzene.
In the presence of organobase, the nucleo-
philicity of the thiol group will be increased,
which may enhance the efficiency of its
Scheme 2. Synthesis of PVSs P1/2–P1/5 by polyhydrothiolation of dithiol 1 and diynes 2–5.
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Table 1. Effect of organobase on polyhydrothiolation of 1 and 3.
Run [a]
Base
Yield [%]
Mw [b]
Mw/Mn [b]
1
2
3
4
5
6
7
8
piperidine
methylpiperazine
diethylamine
triethylamine
diphenylamine
triphenylamine
morpholine
Gel
Gel
37.0
71.7
97.1
97.1
81.8
97.8
17 100
6300
3.2
1.7
1.9
1.7
1.7
2.1
32 300
6800
3900
diphenylamine
30 100
[a] Carried out at room temperature in DMF under nitrogen for 24 h;
[1] ¼ [3] ¼ 0.06 M; [base] ¼ 0.6 M (except for run 8, where [base] ¼ 1.2 M).
[b] Estimated by gel permeation chromatography (GPC) in THF on the
basis of a polystyrene calibration.
addition reaction. With this consideration in mind, we tested the
effects of different amines on the alkyne polyhydrothiolation.
Insoluble gels are formed when the polymerizations are initiated
bypiperidineandmethylpiperazine(Table1,runs1and2). Soluble
polymers, however, are obtained in moderate to high yields when
other amines are used. Among them, diphenylamine works
efficiently for the reaction, producing a PVS with a high molecular
weight (Mw 32 300) in a nearly quantitative yield (97%). Doubling
the amount of diphenylamine to 1.2 M gives similar results,
because the thiol group of 1 is already converted into thiolate in the
reaction mixture containing 0.6 M diphenylamine.
Wethentriedtodeterminetheoptimalmonomerconcentration
[M] in the polymerization of 1 and 3 in the diphenylamine/DMF
mixture. In all the runs, an equimolar ratio of 1 and 3 was used.
With an increase in [M], the Mw of the polymer is enhanced and
reaches its maximum value of ꢀ32 000 at [M] ¼ 0.06 M (Fig. 1).
Further increasing [M] has an adverse effect on the molecular
weight. The polymer yield remains high at all [M]s studied, which
demonstrates of thehigh efficiency of the polymerization reaction.
Figure 2. Effect of temperature on the polyhydrothiolation of 1 and 3 in
DMF under nitrogen in the presence of 1.2 M of diphenylamine for 24 h;
[1] ¼ [3] ¼ 0.06 M.
Temperature strongly influences the polymerization reaction.
Both the yield and Mw of the PVSs are decreased when the
temperature is raised from 23 to 150 8C (Fig. 2). As mentioned
above, dipropiolates can undergo polycyclotrimerization in
refluxing DMF.[10] Some portion of monomer 3 may self-
polymerize at high temperatures to form low-molecular-weight
hyperbranched oligomers that may have been removed during the
purificationprocessofthereactionproduct. Theconcentrationof3
in the solution is thus lowered, which leads to the formation of
polymers with lower molecular weights in lower yields. Figure 3
shows the time course of the alkyne polyhydrothiolation. After
12 h, a polymer with a Mw of 25 000 is obtained, which is high
enough for practical applications. Prolonging the reaction time to
Figure 1. Effect of monomer concentration on the polyhydrothiolation of 1
and 3 at room temperature in DMF under nitrogen for 24 h in the presence
of 1.2 M of diphenylamine.
Figure 3. Time course of polyhydrothiolation of 1 and 3 at room tempera-
ture in DMF under nitrogen in the presence of 1.2 M of diphenylamine;
[1] ¼ [3] ¼ 0.06 M.
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Table 2. Polyhydrothiolation of 1 with 2–5.
Run [a]
Monomers
Yield [%]
S [b]
Mw [c]
Mw/Mn [c]
Z [d] [%]
1
1 þ 2
1 þ 3
1 þ 3
1 þ 4
1 þ 5
73.5
97.2
97.1
87.2
98.2
H
H
H
H
ꢂ
21 000
29 000
32 300
7500
2.9
1.7
1.9
2.1
78.1
80.2
81.4
68.9
2 [e]
3
4
5
[a] Carried outatroomtemperatureinDMF inthepresenceof1.2 M diphenyl-
amine under nitrogen for 24 h unless stated otherwise; [monomer]¼ 0.06 M.
[b] Solubility (S) tested in common organic solvents such as toluene, DCM,
chloroform, and THF: H ¼ completely soluble, ꢂ ¼ insoluble. [c] Estimated
by GPC in THF on the basis of a polystyrene calibration. [d] Determined by
1H NMR spectroscopy. [a] Conducted in air.
24 h slightly lowers the yield of the PVS but increases its Mw to
33 000.
The above systematic studies enable us to polymerize 1 with 2–5
under optimal conditions. Table 2 summarizes the polymerization
results. All the polymerizations proceed smoothly, giving P1/2–
P1/5ingoodyields.Comparingthepolymerizationresultsof1and
3 obtained under nitrogen and in air, it is clear that oxygen and
moisture exert little effect on the alkyne polyhydrothiolation
reaction (Table 2, runs 2 and 3). The oxygen and moisture
tolerances greatly help simplify the reaction procedures.
Figure 4. IR spectra of monomers a) 1, b) 3, and c) their polymer P1/3.
respectively. No such peaks are observed in the spectrum of
P1/3. Instead, new peaks associated with C¼C stretching and
bending vibrations are observed at 1580 and 940 cmꢁ1, and reveal
that all the mercapto groups and triple bonds of 1 and 3 have been
transformed by the polymerization reaction into vinyl sulfide units
in P1/3.
2.3. Structural Characterization
The model reaction suggests that the alkyne polyhydrothiola-
tion is regioselective. To prove whether this is the real case, we
analyzed the NMR spectra of the polymers. Figure 5 shows the
1H NMR spectra of P1/3 and its monomers 1 and 3 in chloroform-
d; for better peak assignment, the spectrum of model compound 8
isalsogiveninthefigure. Thethiolandacetyleneprotonsof 1and3
resonate at d 3.46 and 3.06, respectively, which completely
disappear after the monomers have been subjected to alkyne
polyhydrothiolation reaction. By comparison with the spectra of
monomers1and3andmodelcompound8, theresonancepeaksin
the spectrum of P1/3 can be readily assigned. The resonances of
the phenyl protons in P1/3 are located at similar chemical shifts to
those in 1 and 3.
New peaks assigned to the proton resonances of the linear vinyl
groups newly formed by the alkyne polyhydrothiolation are
observed at d 5.86, 6.15, and 7.92. While the first and third
peaks stem from the resonances of the PVS segments with an
E-conformation, the second one originates from the resonance of
the chain segments that comprise Z-isomeric units. Thanks to the
large difference in the chemical shifts of the stereoisomers, the
To verify that dithiol 1 and dipropiolates 2ꢁ5 have indeed been
polymerized in an alkyne polyhydrothiolation mechanism, we
conducted a model reaction using thiophenol (6) and phenyl
propiolate (7) as reactants (Scheme 3). While a thiol can undergo
Markovnikov addition to an alkyne to give a branched vinyl sulfide,
the reaction can also proceed in an anti-Markovnikov fashion to
yield linear adducts with E and Z conformations (cf., Scheme 1).
When6and7arereactedunderconditionssimilartothosegivenin
Table 2, run 2, product 8 is isolated in a high yield (94%).
Spectroscopic analysis reveals that 8 is a linear anti-Markovnikov
product with a predominant Z conformation (Z : E ¼ 4 : 1). No
branched product is obtained at all, which indicates that the
reaction proceeds in a regioselective fashion.
To collect direct structural information, we characterized the
polymers by spectroscopic methods. Examples of the IR spectra of
P1/3 and its monomers 1 and 3 are given in Figure 4. The SꢁH
stretchingvibrationof1isobservedat2600 cmꢁ1,whilethe CꢁH
–
–
ꢁ1
–
and C C stretchings of 3 occur at 3266 and 2124 cm
,
–
Scheme 3. Synthesis of model compound 8 with high stereoselectivity (Z : E ¼ 4 : 1) through organobase-catalyzed regioselective alkyne hydrothiolation.
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Table 3. Thermal properties of P1/2–P1/5 determined by thermogravi-
.
metric analysis under nitrogen at a heating rate of 10 8C minꢁ1
Polymer
FS [a] [wt %]
Td [b] [8C]
Wr [c] [%]
P1/2
P1/3
P1/4
P1/5
13.38
16.51
21.21
22.39
345
335
324
333
45.6
42.0
14.1
32.9
[a] Sulfur content of PVS calculated from its repeat unit. [b] Temperature for
5% weight loss. [c] Wr ¼ weight residue at 600 8C.
chloroform, THF, and dioxane, and can be readily fabricated into
tough solid films by spin-coating and static-casting processes.
Among the PVSs, P1/5 has the highest sulfur content (FS > 22 wt %;
Table 3). Its intractability may thus be caused by the strong
interaction between the sulfur atoms in different polymer chains,
which leads to the formation of physical crosslink networks. This
hypothesis is further supported by the good solubility of its
sulfonylated counterpart of P1/4. The oxidation of the thio group
between the phenyl rings reduces the likelihood of the formation
of a disulfur bridge between the polymer chains, thus making P1/
4 soluble in common organic solvents.
All the polymers are thermally stable. As can be seen from
Fig. S2 in the Supporting Information, the temperatures for 5%
weight loss or the degradation temperatures (Td) of the polymers
are all higher than 320 8C under nitrogen, which is indicative of
theirstrongresistancetothermolysis(Table3). ExceptforP1/4, the
residues of the polymers after pyrolysis at 600 8C are higher than
30%. The exceptionally low weight residue for P1/4 (ꢀ14 wt %) is
probably a result of the ready evaporation of the sulfur dioxide gas
formed in the pyrolysis process of the sulfonylated polymer at the
high temperature.
Figure 5. 1H NMR spectra of a) model compound 8, b) monomer 3,
c) monomer 1, and d) polymer P1/3 in CDCl3. The solvent peaks are
marked with asterisks.
2.5. Metal Complexation
The polymers contain p-electron-rich aromatic rings and vinyl
double bonds as well as metal-affinitive or metallophilic thio
groups that are expected to form organometallic complexes with
cobalt carbonyls.[14] Indeed, when the soluble PVSs (P1/2, P1/3,
and P1/4) are admixed with Co2(CO)8 in THF, their solutions are
darkened, which is accompanied by gas evolution. The solutions
remain homogeneous throughout the whole process of the cobalt-
complexation reaction. However, the isolated macromolecular
complexes P1/2(Co)–P1/4(Co) are insoluble, possibly because of
the formation of supramolecular aggregates during the product
purification processes (precipitation into poor solvent and drying
under vacuum).
We used elemental analysis (EA) and energy-dispersion X-ray
analysis (EDX) to estimate the compositions of the PVS(Co)
complexes. The cobalt contents of P1/2(Co), P1/3(Co), and P1/
4(Co) determined by EA are 0.09, 6.25, and 1.86%, respectively
(Table 4). The severe steric effect of the bulky, non-planar
tetraphenylethene (TPE) units in P1/2 may have greatly shielded
the vinyl sulfide groups and hampered them from reacting with
Co2(CO)8. Ontheotherhand, thehigher Mw valueof P1/3together
E and Z contents of the polymer can be calculated using their
integrals and the Z/E ratio is found to be 81.4%. Other polymers
are also Z-rich. Evidently, the alkyne polyhydrothiolation produces
polymers with high stereoregularity.
The 13C spectrum of P1/3 shows no resonance peaks of the
acetylenic carbons of monomer 3 at d 76.6 and 74.3 (Supporting
Information, Fig. S1). New peaks that correspond to the
resonances of the olefinic carbons are observed at d 164.8,
163.5, 115.0, and 112.8, because of the conversion of the acetylene
triple bonds in 3 into the double bonds in P1/3.
2.4. Solubility and Stability
Except for P1/5, all other polymers are completely soluble in
common organic solvents, such as toluene, dichloromethane,
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Table 4. Chemical compositions of PSV(Co)s in units of at%.
Polymer
complex
EA
H
EDX
O
XPS
O
C
Co
C
Co
C
Co
P1/2(Co) 72.95 3.92 0.09 85.85 2.72 0.16 83.99
8.59 0.12
P1/3(Co) 67.46 4.41 6.25 71.97 7.55 8.33 80.88 10.76 2.02
P1/4(Co) 59.18 3.33 1.86 65.78 3.93 1.62 73.70 15.73 0.87
with its less sterically hindered bisphenol-A moieties may have
enabled more efficient metal complexations, which leads to the
higher cobalt content in its complex. Similar results are obtained
from the EDX measurements.
The analysis by X-ray photoelectron spectroscopy (XPS) offers
information about chemical compositions on the surfaces of
PVS(Co) powders. The cobalt contents estimated by the XPS
analysis are generally lower than those obtained from the EA and
EDX analyses, which suggests that the cobalt species are
aggregated in the bulk rather than on the surface. The ceramic
materials obtained from the pyrolyses of the PVS(Co) complexes
are practically non-magnetic, in sharp contrast to the very high
magnetizabilities of the ceramics obtained from the cobalt
complexes of the hyperbranched polymers in our previous
studies.[9] This is probably because of the formation of cobalt
sulfides CoxSy by the pyrolysis of the PSV(Co) complexes, which
are known to be magnetically insusceptible.[15]
Figure 6. Light transmission spectra of THF solutions of P1/2ꢁP1/4 and
thin solid films of P1/2(Co)ꢁP1/4(Co). Solution concentration (mg mLꢁ1):
7.2 (for P1/2), 5.7 (for P1/3), 6.0 (for P1/4).
2.6. Optical Transparency
Polymers with high optical clarity are promising candidate
materials for advanced photonic applications.[16] The PVSs absorb
little light in the visible spectroscopic region and allows almost all
the light at wavelengths longer than 400 nm to transmit through
(Fig. 6). Forexample, thelighttransmittanceofP1/3isalready99%
at a wavelength as short as 370 nm. Although the optical
transparencies of the polymers are decreased after complexation
withcobaltmetal,thelighttransmittancesarestillhigherthan90%
beyond 400 nm. For example, the light transmittance of P1/3(Co)
at 370 nm is 98%, just 1% lower than that of its parent form (P1/3).
The excellent transparencies of the PVSs and PVS(Co)s may be
attributed to the existence of two ester groups in every one of their
repeat units, which weaken the electronic communications
between the neighboring aromatic and vinyl groups, thereby
decreasing their absorptivities in the long wavelength region.
2.7. Light Refractivity
The PVSs are comprised of polarizable aromatic rings, ester
groups, and sulfur atoms and may show high refractive indices.[17]
This is indeed the case: as shown in Figure 7a, P1/2 displays high
refractivities (n ¼ 1.7300–1.6569) over a wide spectroscopic region
(500–1700 nm). Polymers P1/3 and P1/4 display similarly high
refractive indexes of 1.7148–1.6611 and 1.7345–1.7003, respec-
tively, in the same spectroscopic region. It is noted that the n value
Figure 7. Wavelength dependence of refractive indexes of thin films of
a) P1/2 and P1/2(Co), b) P1/3 and P1/3(Co), and c) P1/4 and P1/4(Co); Dn
values given in the figures are the differences in the refractive indexes at
1550 nm.
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Table 5. Refractive indices and chromatic dispersions of PVSs and
PSV(Co)s.
material, using its n values at the non-absorbing wavelengths
of 1064, 1319, and 1550 nm.[19] The first two wavelengths are
chosen in view of the practical interest of a commercial laser
wavelength (Nd:YAG), while the last one is the wavelength of
0
Film [a]
n632.8
n1550
nD
nD
D
D0
P1/2
1.7004
1.6918
1.7317
1.7728
2.0593
1.9166
1.6583
1.6640
1.7004
1.7097
1.9962
1.9002
18.4
22.8
26.3
13.6
18.6
156.5
70.4
69.6
0.054
0.044
0.038
0.074
0.054
0.006
0.014
0.014
0.002
0.020
0.014
0.002
´
telecommunication importance. The modified Abbe number is
defined as
P1/3
P1/4
539.0
50.7
P1/2(Co)
P1/3(Co)
P1/4(Co)
n1319 ꢁ 1
nD0
¼
(2)
80.0
n1064 ꢁ n1559
643.0
where n1319, n1064, and n1550 are the refractive indexes at 1319,
1064, and 1550 nm, respectively. The chromatic dispersion (D0) is
´
[a] Abbreviations: n ¼ refractive index, nD ¼ Abbe number (calculated from
´
equation 1), nD’ ¼ modified Abbe number (calculated from equation 2),
the constringence of the Abbe number (nD0):
D ¼ chromatic dispersion in the visible region, and D’ ¼ chromatic dis-
´
persion in the IR region.
1
nD0
D0 ¼
(3)
increases with the sulfur content (FS) in the polymer (cf., Table 3).
When the FS valueis increased fromꢀ13%inP1/2to ꢀ21%in P1/
4, the n value at 1550 nm is increased from 1.6583 to 1.7004. The
refractivity of the PVS can thus be tuned through molecular
engineeringendeavors.P1/5hasthehighestsulfurcontentamong
the polymers but unfortunately its refractivity cannot be measured
because of its insolubility in common organic solvents.
The n values of P1/2, P1/3, and P1/4 are around 1.7 at 632.8 nm
and larger than 1.65 even at 1550 nm (Table 5), which are much
higher than those of the commercially important optical plastics
[e.g., n ꢀ 1.49 for poly(methyl methacrylate) (PMMA) and n ꢀ 1.59
for poly(ethylene terephthalate) (PET) and polycarbonate (PC)].
The PVSs are thus highly refractive polymers. No or little
birefringence is detected, which is indicative of the amorphous
nature of their thin solid films.
0
The nD and nD values of P1/4 are 26.3 and 643, which
correspond to D and D0 values of 0.038 and 0.002, respectively
(Table 5). After metal complexation, the D and D0 values of P1/
4(Co) drop to 0.006 and 0.002, respectively, which are lower than
those of PC (D ¼ 0.0297) and PMMA (D ¼ 0.0175),[20] and are
comparable to our recently synthesized poly(triazole)s by the
metal-free azido-click polymerizations (D0 ¼ 0.006–0.004).[10]
Other PVS(Co)s also show small chromatic dispersions. The
low spectroscopic aberrations of the polymers, coupled with their
high optical transparencies and light refractivities, may enable
them to find technological applications as coating materials in
advanced optical display systems, such as microlens components
for charge-coupled devices and high-performance complementary
metal-oxide semiconductor image sensors.[7]
Interestingly, after metal complexation, the n values of the
polymers are further enhanced (up to 2.0593). Inorganic and
organometallic materials often show higher refractive indexes
than pure organic materials.[17,18] The high refractive indexes of
PSV(Co)sarethuslikelybecauseoftheirmetalliccomponents.The
differences in the refractivity (Dn) between PVSs and PVS(Co)s at
the telecommunication important wavelength of 1550 nm can be
as large as 0.3322 (Fig. 7b). The Dn value of the P1/2 and P1/2(Co)
pairisrelativelysmall(0.0514),whichisunderstandablebecauseof
the low cobalt content in P1/2(Co).
2.9. Photoresponsive Patterning
The PVSs contain a large number of photosensitive vinyl and ester
groups. The polymers maybe readily photo-crosslinked because of
the formation of free radicals by UV irradiation and can thus be
used as negative photoresist materials for pattern generation.[21]
When a thin solid film of P1/2 spin-coated on a silicon wafer is
irradiated in air through a copper photomask, the exposed region
of the thin film is readily photo-crosslinked and a negative
photoresist pattern with clear-cut edges is generated after the
development of the irradiated polymer film by 1,2-dichloroethane
(Fig. 8).
2.8. Chromatic Dispersion
For a material to be useful for practical applications, its optical
´
The TPE moieties in the backbone of P1/2 are well-known
luminogenic units that exhibit an unusual phenomenon of
aggregation-induced emission (AIE).[22,23] Although light emis-
sion of a ‘conventional’ luminophore is often quenched when its
molecules are aggregated in the solid state and fabricated into a
thin film, the film of P1/2 is still luminescent, thanks to its unique
AIE feature. The photopattern generated by the photolysis of P1/2
emits a yellow light upon illumination with a handheld UV lamp,
as evidenced by the luminescence image taken under a
fluorescence microscope shown in Figure 8. Clearly, the polymer
can be used as a photoresist material for the creation of fluorescent
images.
aberrations should be small. The Abbe number (vD) of a material is
a measure of the variation or dispersion in its refractive index with
wavelength, which is defined as
nD ꢁ 1
nD
¼
(1)
nF ꢁ nC
where nD, nF, and nC are the refractive indexes at wavelengths of
the Fraunhofer D, F, and C spectroscopic lines of 589.2, 486.1,
and 656.3 nm, respectively. A modified Abbe number (nD0) has
been proposed to evaluate the application potential of an optical
´
Adv. Funct. Mater. 2010, 20, 1319–1328
ß 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
1325

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4. Experimental
Materials: THF (Labscan), toluene (BDH), and dioxane (Aldrich) were
distilled under nitrogen from sodium benzophenone ketyl immediately
prior to use. Dichloromethane was distilled under nitrogen over calcium
hydride. DMF was stirred with calcium hydride overnight, distilled under
reduced pressure, and kept under nitrogen. Other solvents, such as
triethylamine and dimethyl sulfoxide (DMSO), were purified using
standard procedures. All the chemicals used in this work, such as 4,40-
thiodibenzenethiol (1), were purchased from Aldrich and used as received
without further purification. 1,2-Bis(4-hydroxyphenyl)-1,2-diphenylethene
was prepared according to our previously published procedures [23b].
Instrumentation: IR spectra were recorded on a Perkin–Elmer 16 PC
FTIR spectrophotometer. 1H and 13C NMR spectra were measured on
Bruker ARX 300 NMR spectrometers using CDCl3 or DMSO-d6 as solvents.
Light transmission spectra were measured on a Milton Roy Spectronic
3000 array spectrophotometer. MALDI-TOF spectra were recorded on a
GCT Premier CAB048 mass spectrometer operating in a chemical
ionization (CI) mode with methane as carrier gas. Mw, Mn, and Mw/Mn
values of the polymers were estimated by a Waters Associates GPC system
equipped with refractive index (RI) and UV detectors. THF was used as
eluent at a flow rate of 1.0 mL minꢁ1. A set of monodisperse linear
polystyrenes were used as standards for the molecular weight calibration.
EA experiments were conducted on an Elementary Vario EL analyzer. XPS
measurements were conducted on a PHI 5600 spectrometer (Physical
Electronics), and the core level spectra were measured using a monochro-
matic Al Ka X-ray source (hn ¼ 1486.6 eV). The analyzer was operated at
23.5eV pass energy and the analyzed area was 800 mm in diameter. EDX
analyses were preformed on a JEOL-6300 SEM system with quantitative
elemental mapping and line scan capacities operating at an accelerating
voltage of 15kV. Thermogravimetric analyses (TGA) were carried out under
nitrogen on a Perkin–Elmer TGA 7 analyzer at a heating rate of 108C minꢁ1
.
Refractive indices of the polymers were determined on a J. A. Woollam
variable angle ellipsometry system with a wavelength tunable from 300 to
1700 nm. To fit the acquired C and D curves with the data obtained from
the three-layer optical model that consisted of a crystalline silicon
substrate, a 2 nm silicon dioxide layer, and a uniform polymer film, the
Levenberg–Marquardt regression algorithm was employed. The Cauchy
dispersion law was applied to describe the polymer layer from the visible to
the IR spectroscopic region.
Figure 8. Negative photoresist pattern generated by photolithography of
P1/2; photographs taken under a) room lighting and b) UV illumination.
Monomer Preparation: Dipropiolates 2–4 were prepared by the
esterification reactions of propiolic acid with 1,2-bis(4-hydroxyphenyl)-
1,2-diphenylethene, bisphenol A, 4,40-sulfonyl diphenol, and 4,40-thiodi-
phenol, respectively. The synthetic procedures were similar to those
described in our previous publications [10c].
3. Conclusions
In this work, we have developed a thioclick polymerization
technique for the synthesis of heteroatom-containing acetylenic
polymers. The alkyne polyhydrothiolations of dithiol 1 and
dipropiolates 2–5 proceed smoothly in the presence of diphenyl-
amine at room temperature, producing sulfur-rich polymers P1/
2–P1/5 with high molecular weights in high yields. The
organobase-mediated alkyne hydrothiolation reaction is strictly
regioselective and furnishes polymers with high stereoregula-
rities. The polymerization reaction is tolerant to functional groups
as well as air and moisture. All these advantageous attributes make
the alkyne polyhydrothiolation a true click reaction.[11]
Polymers P1/2–P1/4 are completely soluble, film-forming,
thermallystable, andopticallytransparent. Theirfilmsexhibithigh
refractive indices and low chromatic aberrations. Their refractiv-
ities can be tuned by their sulfur contents and greatly enhanced by
complexation with transition-metal compounds such as cobalt
carbonyls. The PVSs are photoresponsive and their films can be
readily photo-crosslinked to create negative photoresist patterns
that emit strong visible light upon photoexcitation. These unique
features make the polymers promising photonic materials for
high-tech applications.
Characterization Data for 4,4(-(1,2-Diphenylethenylene)diphenyl
Dipropiolate (2): White solid; yield 63.5%. IR (thin film) n ¼ 3276, 3054,
2934, 2856, 2124, 1732, 1650, 1502 cmꢁ1 1H NMR (300 MHz, CDCl3,
.
TMS, d): 8.04 (s, 1H), 8.05 (s, 1H), 6.91 (t, 4H), 7.02 (m, 8H), 7.11 (m, 6H).
13C NMR (75 MHz, CDCl3, TMS, d): 150.71, 148.25, 142.89, 141.77, 140.46,
132.23, 131.21, 129.45, 128.47, 127.76, 126.77, 120.39, 94.08, 76.83, 76.65,
74.15. HRMS (MALDI-TOF, m/z): [M þ H]þ calcd for C32H21O4, 469.4988;
found, 469.1034. Anal. calcd for C32H20O4: C 82.04, H 4.30; found: C 82.00,
H 4.50.
Characterization Data for 4,4(-Isopropylidenediphenyl Dipropiolate
(3): White solid; yield 53.2%. IR (thin film), n ¼ 3266, 2934, 2124, 1730,
1634cmꢁ1. 1H NMR (300MHz, CDCl3, TMS, d): 7.26 (d, 2H), 7.05 (d, 2H),
3.06 (s, 1H), 1.67 (s, 3H). 13C NMR (75 MHz, CDCl3, TMS, d): 151.0, 148.5,
147.7, 127.9, 120.6, 76.6, 74.3, 42.6, 30.8. HRMS (MALDI-TOF, m/z):
[Mþ H]þ calcd for C21H17O4, 333.3493; found, 333.1080. Anal. calcd for
C21H16O4: C 75.89, H 4.85; found: C 75.17, H 5.01.
Characterization Data for 4,4(-Sulfonyldiphenyl Dipropiolate (4): White
solid; yield 62.3%. IR (thin film) n ¼ 3268, 2126, 1734, 1656, 1588, 1490,
1
1410, 1324, 1294 cmꢁ1. H NMR (300 MHz, DMSO-d6, TMS, d): 8.20 (d,
2H), 7.66 (d, 2H), 5.03 (s, 1H). 13C NMR (75 MHz, DMSO-d6, TMS, d):
153.2, 150.0, 139.0, 129.7, 123.4, 82.3, 74.0. HRMS (MALDI-TOF, m/z):
[M þ H]þ calcd for C18H11O6 S, 355.6681; found, 355.3334. Anal. calcd for
C18H10O6S: C 61.01, H 2.84; found: C 61.62, H 3.05.
Adv. Funct. Mater. 2010, 20, 1319–1328
1326
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Characterization Data for 4,4(-Thiodiphenyl Dipropiolate (5): Pale yellow
solid; yield 57.3%. IR (thin film) n ¼ 3273, 2934, 2126, 1732, 1585,
1487 cmꢁ1. 1H NMR (300 MHz, CDCl3, TMS, d): 7.37 (d, 2H), 7.13 (d, 2H),
3.90 (s, 1H). 13C NMR (75 MHz, CDCl3, TMS, d): 150.6, 149.0, 135.8,
132.3, 122.8, 77.1, 74.0. HRMS (MALDI-TOF, m/z): [M þ H]þ calcd for
C18H11O4S, 323.3346; found, 323.0307. Anal. calcd for C18H10O4S:
C 67.07, H 3.13; found: C 67.07, H 3.65.
Polymer Synthesis: All the polymerization reactions were carried out
under dry nitrogen using a standard Schlenk technique, unless otherwise
specified. A typical procedure for the polymerization of 1 and 2 is given
below as an example. In a 15 mL Schlenk tube with a three-way stopcock on
the sidearm was placed 40 mg of 1 (0.15 mmol) and 70 mg of 2
(0.15 mmol) under nitrogen in a glovebox. Diphenylamine (0.5 g, 3 mmol)
and DMF (2.5 mL) were added to dissolve the monomers using a
hypodermic syringe. After stirring at room temperature for 24 h, the
mixture was added dropwise to about 300 mL of a hexane/diethyl ether
(v/v, 1 : 1) mixture through a cotton filter under stirring. The precipitate was
allowed to stand overnight and then collected by filtration. The product was
washed with the hexane/diethyl ether mixture and dried under vacuum at
room temperature to a constant weight.
obtained from a Spectroline ENF-280C/F UV lamp as light source at a
distance of 1 cm. The incident light intensity was ꢀ18.5 mW cmꢁ2. The film
was prepared by spin-coating the polymer solution (10% w/w in 1,2-
dichloroethane) at 2000 rpm for 1 min on a silicon wafer. The polymer film
was dried in a vacuum oven at room temperature overnight. The
photoresist patterns were generated by irradiating the polymer films for
3 min through a copper photomask. The films were developed in 1,2-
dichloroethane for 40 s and dried at room temperature overnight under
reduced pressure. The three-dimensional patterns were images on an
optical microscope (Olympus B202) using a normal light and a fluorescent
optical microscope (Olympus BX41) with a 330–385 wideband UV
excitation.
Acknowledgements
This work was partially supported by the Research Grants Council of Hong
Kong (603509, 601608 and 602707), the National Natural Science
Foundation of China (20634020 and 20974028), and the University Grants
Committee of Hong Kong (AoE/P–03/08). B.Z.T. acknowledges the
support from the Cao Guangbiao Foundation of Zhejiang University.
Supporting Information is available online from Wiley InterScience or from
the author.
Characterization Data for P1/2: White powder; yield 73.5%. Mw 21 000,
Mw/Mn 2.9 (GPC, polystyrene calibration). IR (KBr), n ¼ 3050, 2936, 2860,
1714, 1672, 1524, 1502, 1478, 1386, 1358, 1204, 1142, 1096, 1012, 960,
814, 788, 700 cmꢁ1. 1H NMR (300 MHz, CDCl3, TMS, d): 7.89, 7.41, 7.34,
7.26, 7.09, 7.03, 6.09, 5.81. 13C NMR (75 MHz, CDCl3, TMS, d): 168.1,
164.5, 163.2, 151.9, 149.0, 143.5, 141.0, 140.3, 135.9, 135.0, 134.1, 133.7,
132.2, 131.3, 128.3, 127.8, 127.7, 120.7, 114.8, 112.8.
Received: October 15, 2009
Revised: January 17, 2010
Published online: March 15, 2010
Characterization Data for P1/3: White powder; yield 97.2%. Mw 29 000,
Mw/Mn 1.7 (GPC, polystyrene calibration). IR (thin film), n ¼ 3061, 2965,
2926, 2866, 1714, 1574, 1505, 1475, 1392, 1359, 1205, 1169, 1144, 1100,
1080, 1012, 961, 818, 734 cmꢁ1. 1H NMR (300 MHz, CDCl3, TMS, d): 8.02,
7.96, 7.91, 7.45, 7.43, 7.40, 7.32, 7.26, 7.23, 7.08, 7.05, 6.99, 6.96, 6.16,
6.12, 5.83, 5.81, 1.78. 13C NMR (75 MHz, CDCl3, TMS, d): 164.8, 151.6,
148.5, 148.4, 146.9, 135.9, 135.2, 133.7, 132.5, 132.1, 132.0, 131.8, 131.8,
131.3, 128.4, 120.9, 114.9, 122.8, 42.5, 31.0.
Characterization Data for P1/4: White powder; yield 87.2%. Mw 7500;
Mw/Mn 2.1 (GPC, polystyrene calibration). IR (thin film), n ¼ 3062, 2092,
1724, 1568, 1474, 1388, 1356, 1324, 1296, 1210, 1134, 1102, 1012, 958,
818, 734 cmꢁ1. 1H NMR (300 MHz, CDCl3, TMS, d): 8.00, 7.98, 7.95, 7.77,
7.74, 7.52, 7.49, 7.44, 7.41, 7.38, 7.35, 7.32, 7.26, 6.25, 7.23, 7.08, 7.05,
6.90, 6.87, 6.14, 6.11, 5.81, 5.77. 13C NMR (75 MHz, CDCl3, TMS, d): 167.5,
163.1, 162.5, 161.2, 154.4, 154.2, 153.7, 153.5, 150.6, 138.4, 136.1, 135.1,
134.9, 134.6, 134.1, 133.8, 133.5, 132.6, 131.8, 131.3, 130.4, 129.9, 129.3,
128.9, 128.3, 122.5, 122.3, 116.2, 113.6, 111.8.
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Model Reaction: Phenyl 3-(phenylthio)acrylate (8) was designed and
prepared as a model compound by alkyne hydrothiolation of thiophenol (6)
and phenyl propiolate (7; Scheme 2). The experimental procedures were
similar to those described above for the synthesis of P1/2. A white solid of 8
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precipitate was washed with hexane several times to remove the unreacted
octacarbonyldicobalt and then dried under vacuum to a constant weight. A
pale purple powder of P1/2(Co) was obtained.
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