Synthesis and properties of polyethers containing 1,3-butadiene skeleton in the backbone

Article abstract of DOI:10.1246/cl.190381

Polyethers containing 1,3-butadiene skeletons in the backbone were prepared from the polycondensation of 2,3-diiode-methyl-1,3-butadiene (2b) and bisphenols (3). Although the polymerization conditions were limited due to the low reactivity of 2b, a series of polyethers was obtained under the optimized conditions. These polymers exhibited glass transition temperatures (T_gs) around 130 °C, while curing points (T_cures) were observed around 245 °C. In addition, P2b/3a afforded a network polymer by the copolymerization with styrene.

Full text of DOI:10.1246/cl.190381

CL-190381
Received: May 10, 2019 | Accepted: May 27, 2019 | Web Released: June 5, 2019
Synthesis and Properties of Polyethers Containing 1,3-Butadiene Skeleton in the Backbone
Yasuhiro Kohsaka*1,2 and Akira Hiramatsu2
Research Initiative for Supra-Materials (RISM), Shinshu University, 3-15-1 Tokida, Ueda, Nagano 386-8567, Japan
Faculty of Textile Science and Technology, Shinshu University, 3-15-1 Tokida, Ueda, Nagano 386-8567, Japan
1
2
E-mail: kohsaka@shinshu-u.ac.jp
Polyethers containing 1,3-butadiene skeletons in the back-
bone were prepared from the polycondensation of 2,3-diiode-
methyl-1,3-butadiene (2b) and bisphenols (3). Although the
polymerization conditions were limited due to the low reactivity
of 2b, a series of polyethers was obtained under the optimized
conditions. These polymers exhibited glass transition temper-
atures (Tgs) around 130 °C, while curing points (Tcures) were
observed around 245 °C. In addition, P2b/3a afforded a network
polymer by the copolymerization with styrene.
(2b) as a monomer. 2b was prepared from 2,3-dimethyl-1,3-
butadiene according to the literature with slight modifica-
1
6­18
tions.
2b has halogen atoms at the allylic positions of the
conjugate system. This structural feature is similar to 1, which
undergoes polycondensation with bisphenols through conjugate
11
substitution. Therefore, the polymerization of 2b and bisphenol
A (3a) was conducted under similar conditions, although the
solvent was changed from CHCl to 1,4-dioxane due to low
3
1
9
solubility of 2b (Scheme 1, Table 1, Entry 1). However, no
reaction proceeded. In the case of 1, the electron-withdrawing
carbonyl group decreases the electron density on the vinylidene
bond, resulting in the high reactivity toward nucleophiles in
addition-elimination (SN2¤) mechanisms. On the other hand, 2b
does not have an electron-withdrawing group and thus exhibits
low reactivity. In other words, the major path might be not SN2¤
but rather an SN2 mechanism similar to allyl iodide. In order to
Keywords: Polycondensation
| Bisphenol | Curing
Polymers carrying vinyl groups (PCVGs) have gained
1
­5
chemists’ attention as thermosetting resins and curing agents,
while they are also attractive as reactive polymers for further
6­11
functionalization.
Ring-opening polymerization (ROP) of
α-exomethylene lactones is a typical synthetic route to PCVGs
with acrylate skeletons in the backbones.2 Despite the low
reactivity of α-exomethylene lactones in ROP, the recent
developments of catalysts have achieved the preparation of
,4,5
5
polyesters with acrylate skeletons in the backbones. Step-
growth polymerization of α-functionalized acrylic acids and
their derivatives also provides effective route to prepare PCVGs.
Peng and Joy reported the polyaddition of an acrylate monomer
1
0
bearing two hydroxy groups in the α- and ester-substituents.
On the other hand, Morita-Baylis-Hillman reaction of diacrylate
and dialdehyde results in polyaddition to afford a PCVG of
poly(ester ether), although the molecular weight is not high
4
(
Mn <10 ) due to the low efficiency of the Morita-Baylis-
8
Hillman reaction. In contrast, conjugate substitution reaction
of α-(chloromethyl)acrylates, prepared from acrylates through
Morita-Baylis-Hillman reaction and chlorination, proceeds
quantitatively even under ambient condition.1
1­13
Recently, we
applied this reaction to prepare PCVGs; polycondensation
of bis[α-(chloromethyl)acrylate] (1) and various nucleophilic
monomers such as dithiols, dicarboxylic acids and bisphenols
1
1
afforded a series of PCVG with the corresponding backbones.
,3-Butadine is a radically polymerizable monomer with
1
higher stability against acids, bases and other chemicals than
acrylates. However, as far as we know, PCVGs with 1,3-
butadiene skeletons have not been reported except for a few
9
,14
examples.
Ottenbrite reported the polyaddition of 2,3-
dibromomethyl-1,3-butadiene (2a) and bifunctional tertiary
1
4
amines. It is also reported that the condensation reactions of
1
5
2
a with hydroxide, sulfide, and carboxylate anions. These
examples suggest that 2a have a potential as an electrophilic
monomer to afford PCVGs. In this paper, we describe the
polycondensation of 2 with bisphenols and other nucleophilic
monomers as well as the properties of the resulting PCVGs.
Since the preparation of 2a required the use of heavy
metals,15 we chose the analogue, 2,3-diiodemethyl-1,3-butadiene
Scheme 1. Polycondensation of 2 with various bisphenols and
structures of relative monomers.
894 | Chem. Lett. 2019, 48, 894–897 | doi:10.1246/cl.190381
© 2019 The Chemical Society of Japan

f
Table 1. Polymerization of 2b and 3a at 25 °C for 24 h.
Solvent
*
CH2
d
e
c
Me
f
O
O
Entrya
Base
Mnb
Đb
Me
n
(
Volume [mL])
H
a
H
b
c
1
2
3
Et3N
DBU
DBU
K2CO3
tBuOK
Dioxane
Dioxane
Dioxane
Dioxane
DMSO
(1.5)
(1.5) 1300
(1.5) 1300
(1.5) Insoluble product
(2.5) 3900
No polymer
1.04
1.03
d
e
c
d
a,b
4
5
6
7
8
9
2.00
3.35
1.38
1.85
2.14
tBuOK DMSO/THFe (2.5) 7300
tBuOK
tBuOK
tBuOK
DMF
DMAc
NMP
(2.5) 2600
(2.5) 5900
(2.5) 10500
7
6
5
4
3
2
1
0
a[2b]0/[3a]0/[base]0 = 1/1.00/2.20, 2b: 0.500 mmol. Deter-
b
Figure 1. 1H NMR spectrum of P2b/3a obtained in Run8
(400 MHz, CDCl , 26 °C). : NMP, ©: Me Si, and *: CHCl .
c
mined by SEC (THF, 40 °C, polystyrene standards). At 60 °C.
At 80 °C. DMSO/THF = 2/1 (v/v). DMSO: Dimethylsulf-
d
e
3
4
3
oxide, THF: Tetrahydrofuran. DMF: N,N-Dimethylformamide,
DMAc: N,N-Dimethylacetamide, NMP: N-methyl-2-pyrrori-
done.
Figure 2a shows the thermogravimetric and differential
thermal analysis (TG-DTA) profiles of P2b/3a. An exothermic
peak (Tcure) corresponding to the curing at 1,3-butadiene
skeletons was observed at 245 °C. However, the 10% weight-
loss temperature (Td10 = 267 °C) was close to Tcure. As a thermo-
setting resin, this is a critical problem. In order to improve
thermal stability, polymerizations with various bisphenols were
employed (Table 2, Entries 10­13). As the molecular weights of
the resulting polymers were significantly different, their thermal
properties could not be simply attributed to their monomer
structures. Nevertheless, the results allowed the following
qualitative discussions. All resulting polymers exhibited Tcures
around 245 °C, while Td10s were dependent on the monomer
structures (Figure 2b­e). Consequently, the incorporation of a
cyclic linker between the two phenol moieties seems effective
to improve Td10s. For example, P2b/3e resulted in the highest
Td10 (= 322 °C). Differential scanning calorimetry (DSC) was
conducted for P2b/3c, P2b/3d, P2b/3e, as their Tcures were
increase the reaction rate, a stronger base, 1,8-diazabicylco-
[
5.4.0]undec-7-ene (DBU) was used (Entry 2), resulting in an
1
oligomeric product. Although the H NMR spectrum of the
product indicated the proceeding reaction (Figure S2), the large
signals from the end structure indicated a low conversion.
A similar result was obtained by the polymerization at 60 °C
(
(
Entry 3), while insoluble precipitate appeared at 80 °C
Entry 4), probably thermal polymerization of 1,3-butadiene
skeletons. Therefore, the polymerization should be employed at
room temperature. To promote the polymerization, the reaction
was conducted in the presence of tBuOK, a much stronger base.
In DMSO, the polymerization proceeded in a homogeneous
system at the initial stage, but precipitate gradually appeared
(
Entry 5). As the isolated polymer exhibited incomplete sol-
ubility in DMSO, the precipitate might be the resulting polymer.
Although the molecular weight of the polymer was highest
among the above experiments, the precipitation would prevent
the chain-growth. Consequently, polar solvent is effective both to
dissolve tBuOK (and monomers) and to promote the nucleophilic
reaction by solvation, although it is not effective to dissolve the
product. Therefore, various solvents were investigated to increase
the resulting molecular weight (Entries 6­9). Among them, the
polymerization in N-methyl-2-pyrrolidone (NMP) maintained a
homogeneous system and the resulting polymer had the highest
sufficiently lower than T s (Figure 2f­h). The polymers ex-
d
hibited Tgs around 130 °C, while exothermic peaks were
observed at similar temperature to Tcures determined by DTA.
In the second scans, peaks corresponding to Tg and Tcure were not
observed, suggesting the formation of crosslinked structure
during the first heating.
Polymerizations with other nucleophilic monomers were
also investigated (Table 2). In contrast to the polymerization of 1
11
reported previously, 2b did not polymerize with isophthalic
acid (4, Entry 14) and adipic acid (5, Entry 15). This could
be attributed to the low electrophilicity of 2b. On the other
hand, 1,10-decandithiol (6) yielded a polymeric product. In this
polymerization, precipitate appeared during the polymerization.
molecular weight (M = 10500, Đ = 2.14). The structure of
n
1
the resulting polymer, P2b/3a was characterized by H NMR
spectrum (Figure 1) together with C NMR and IR spectra.
In the H NMR spectrum, signals a and b, assignable to the
vinylidene group, were clearly observed at 5.43 and 5.39 ppm,
respectively, while signal c for allylic protons were found at
13
20
1
The isolated precipitate was insoluble in CHCl and THF but
3
swollen. In addition, the THF-soluble fraction of the products
showed wide molecular weight distribution (Mn = 4200, Đ =
3.57). These results suggested that the thiol chain end might
react with the 1,3-butadiene backbone leading to branching and
crosslinking.
4.70 ppm. On the other hand, signals for an alkylene group
formed by radical polymerization of 1,3-butadiene skeletons
were not observed. These results confirmed that the obtained
polymer has linear structure without any crosslinking or branch-
The obtained PCVGs were expected as a macro-crosslinker
in radical polymerization. Then, P2b/3a (5 mol %) was copoly-
merized with styrene (95 mol %) in bulk at 65 °C for 24 h with
1
3
ing. C NMR spectra indicated similar structure. The linear
structure was also confirmed by unimodal size exclusion
chromatography (SEC) and the degree of molecular weight
dispersity (Đ = 2.14) close to the ideal value by Flory-Carothers
theory (Đ = 2).
2
1
AIBN as an initiator (Scheme 2). A film insoluble in hexane
2
2
and CHCl , i.e. good solvents for polystyrene, was obtained.
3
Therefore, P2b/3a functioned as macromolecular crosslinker.
Chem. Lett. 2019, 48, 894–897 | doi:10.1246/cl.190381
© 2019 The Chemical Society of Japan | 895

(a)
(b)
1
00
100
80
60
40
20
4
2
0
0
40
20
0
8
0
0
0
0
Tcure
6
4
2
Tcure
0
0
0
1
50
350
550
150
350
550
Temperature [°C]
Temperature [°C]
(c)
(d)
1
00
100
80
60
40
20
4
0
0
40
20
0
8
0
0
0
0
Tcure
6
4
2
Tcure
2
0
Scheme 2. Crosslinking of polystyrene with P2b/3a.
0
0
1
50
350
550
150
350
550
Temperature [°C]
Temperature [°C]
Despite our initial expectation, 2b did not show high
reactivity comparable to 1 but similar to allyl iodide. Therefore,
polymerization was very sensitive to the nucleophilic mono-
mers, solvents, and bases. Nevertheless, 2b afforded a series
of polyethers with 1,3-butadiene skeletons in the backbone. As
the polyethers are composed of hydrocarbon and ether bond,
they are expected to be thermosetting resins stable against acids
and bases.
(
e)
(f)
0
1
00
4
0
0
Tcure
8
0
0
0
0
Tg
–
1
6
4
2
Tcure
2
–2
0
0
1
50
350
500
100
200
280
Temperature [°C]
Temperature [°C]
This research was financially supported by Eno Science
Foundation for Y.K. 9,9-bis(4-hydroxyphenyl)fluorene (3d) and
(g)
(h)
Tcure
0
0
9
,9-bis(4-hydroxy-3-methylphenyl)fluorene (3e) were supplied
Tg
Tcure
Tg
by Osaka Gas Chemicals Co., Ltd. The authors appreciate Prof.
Yasuo Goto and Ms. Natsuko Tsukada for TG-DTA and DSC
measurements.
–
1
–1
Supporting Information is available on https://doi.org/
0.1246/cl.190381.
1
00
200
270
100
200
270
1
Temperature [°C]
Temperature [°C]
References and Notes
Figure 2. TG-DTA curves of (a) P2b/3a, (b) P2b/3b, (c)
P2b/3c, (d) P2b/3d, and (e) P2b/3e under N2 atmosphere
1
2
3
S. S. Satav, R. N. Karmalkar, M. G. Kulkarni, N. Mulpuri,
G. N. Sastry, J. Am. Chem. Soc. 2006, 128, 7752.
J. Zhou, A. M. Schmidt, H. Ritter, Macromolecules 2010,
43, 939.
Y. Murali Mohan, V. Raghunadh, S. Sivaram, D. Baskaran,
Macromolecules 2012, 45, 3387.
(heating rate: 10 °C/min, red solid line: TG, blue dashed line:
DTA). DSC curves of (f) P2b/3c, (g) P2b/3d, and (h) P2b/3e
under N2 atmosphere (heating rate: 10 °C/min, green solid line:
1st scan, orange dashed line: 2nd scan).
Table 2. Polymerization of 2b and various nucleophilic
monomers in NMP at 25 °C for 24 h.
4
5
M. Hong, E. Y.-X. Chen, Macromolecules 2014, 47, 3614.
X. Tang, M. Hong, L. Falivene, L. Caporaso, L. Cavallo,
E. Y.-X. Chen, J. Am. Chem. Soc. 2016, 138, 14326.
H. Zhang, E. Ruckenstein, Macromolecules 1998, 31, 746.
K. Sugiyama, K. Watanabe, A. Hirao, M. Hayashi, Macro-
molecules 2008, 41, 4235.
Td10c
[°C]
Tcurec
[°C] [°C]
Tgd
Yield
%]
Entrya
M
Mnb
Đb
6
7
[
9
0
3a
3b
3c
3d
3e
4
>99 10500 2.14 267
245
254
230
241
249
1
>99
88.9
>99
2800 1.61 310
2900 1.35 321
3900 1.71 288
8
9
1
S. Ji, B. Bruchmann, H.-A. Klok, Macromolecules 2011, 44,
5
1
1
126
133
137
218.
N. Nishioka, S. Hayashi, T. Koizumi, Angew. Chem., Int. Ed.
012, 51, 3682.
0 C. Peng, A. Joy, Macromolecules 2014, 47, 1258.
1 Y. Kohsaka, T. Miyazaki, K. Hagiwara, Polym. Chem. 2018,
, 1610.
1
1
1
1
1
2
3
4
5
6
78.1 10200 2.45 322
No polymer
2
5
6
No polymer
1
89.4
4200 3.57
9
a[2b]0/[M]0/[base]0 = 1/1.00/2.20, 2b: 0.500 mmol, NMP:
12 Y. Kohsaka, K. Hagiwara, K. Ito, Polym. Chem. 2017, 8,
976.
13 Y. Kohsaka, T. Kurata, K. Yamamoto, S. Ishihara, T.
Kitayama, Polym. Chem. 2015, 6, 1078.
b
1
.5 mL. Determined by SEC (THF, 40 °C, polystyrene
c
standards). Determined by TG/DTA under N2 atmosphere.
Determined by DSC under N2 atmosphere.
d
896 | Chem. Lett. 2019, 48, 894–897 | doi:10.1246/cl.190381
© 2019 The Chemical Society of Japan

1
4 R. M. Ottenbrite, G. R. Myers, J. Polym. Sci., Polym. Phys.
Ed. 1973, 11, 1443.
solution (0.122 M) in a freezer. 2b: Yield 89.7%; pale
yellow solid; mp: 86.6­87.5 °C; H NMR (400 MHz, 26 °C,
1
1
1
5 Y. Gaoni, S. Sadeh, J. Org. Chem. 1980, 45, 870.
6 S. Kotha, E. Brahmachary, N. Sreenivasachary, Tetrahedron
Lett. 1998, 39, 4095.
CD3CN) δ/ppm 5.63 (s, 2H, CHH=), 5.40 (s, 2H, CHH=),
¹
1
4.20 (s, 4H, CH I); IR (ATR) ¯max/cm 3093 (C-H), 1584
2
(C=C), 904 (C-I).
1
7 J.-T. Huang, S.-H. Zheng, J.-Q. Zhang, Polymer 2004, 45,
19 A typical polymerization procedure (Entry 9): Bisphenol A
(114 mg, 0.500 mmol) and tBuOK (124 mg, 1.10 mmol) were
weighed in a brown test tube and dissolved in N-methyl-
2-pyrrolidone (NMP, 0.40 mL). A solution of 2b (167 mg,
0.500 mmol) in NMP (1.1 mL) was added. The reaction
mixture was stirred for 24 h and added to methanol (20 mL)
dropwise. The precipitate was collected by centrifugation
4
349.
8 2b was prepared within two steps as follows: Synthesis of
,4-dibromo-2,3-bis(bromomethyl)-2-butene (7): A solution
1
1
of bromine (25.2 g, 0.158 mmol) was added dropwise to a
solution of 2,3-dimethyl-1,3-butadiene (12.9 g, 0.157 mol) in
CCl4 (120 mL) over 4 h. N-Bromosuccinimide (NBS, 55.9 g,
0
.314 mol), 2,2¤-azoisobutyronitrile (AIBN, 0.832 g, 5.07
and dried in vacuo to afford P2b/3a (167 mg, M = 10500,
n
mmol) and CCl4 (6.0 mL) were added. The reaction mixture
was refluxed for 2 h. The hot mixture was filtrated, and the
filtrate was cooled to 0 °C. The precipitated yellow crystals
were collected by filtration. The obtained crude 7 (29.5 g) was
used in the next reaction without further purification. 7: Yield:
Đ = 2.14).
20 See Supporting Information.
21 P2b/3a (62 mg, 0.20 mmol), styrene (400 mg, 3.80 mmol)
and AIBN (13 mg, 0.080 mmol) were mixed and heated at
65 °C for 24 h. The reaction mixture was soaked in CHCl3
(15 mL). The supernatant was removed by decantation, and
the precipitated film was soaked in hexane (15 mL) for 19 h.
The supernatant was removed, and the remained precipitate
was dried in vacuo to yield a yellow film (183 mg, yield:
38.9%).
4
7.3%; yellow solid; mp 151.3­156.1 °C; 1H NMR (400
13
MHz, 30 °C, CDCl ) δ/ppm: 6.51 (s, 8H, CH Br). C NMR
3
2
(
100 MHz, 30 °C, CDCl3) δ/ppm: 137.5, 28.2.
Synthesis of 2b: A suspension of crude 7 (15.1 g) and
acetone (55 mL) was stirred, and Na S O (17.8 g, 113
2
2
3
mmol) and KI (18.7 g, 113 mmol) was added. The reaction
mixture was vigorously stirred at 45 °C for 2 h and then
poured into crushed ice (85 g). After warming, the products
22 As a control experiment, the polymerization of styrene
(420 mg, 4.0 mmol) with AIBN (13 mg, 0.080 mmol) was
conducted. The products were soluble in CHCl3 (3.0 mL),
and reprecipitation to hexane (20 mL) yielded polystyrene
(155 mg, yield: 36.2%, Mn = 20700, Đ = 1.77).
were extracted with Et O (120 mL © 3). The combined
2
organic layer was washed with brine (120 mL © 3) and dried
over MgSO4. The obtained 2b (11.2 g) was stored as Et2O
Chem. Lett. 2019, 48, 894–897 | doi:10.1246/cl.190381
© 2019 The Chemical Society of Japan | 897