Synthesis and crosslinking reaction of polyacetylenes substituted with benzoxazine rings: Thermally highly stable benzoxazine resins

Article abstract of DOI:10.1002/pola.29076

Novel polyacetylenes, poly(1) and poly(2) substituted with benzoxazine rings were synthesized by the polymerization of the corresponding acetylene monomers 1 and 2 using Rh catalysts, [(nbd)RhCl]₂, and (nbd)Rh⁺B^–Ph₄

Full text of DOI:10.1002/pola.29076

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POLYMER SCIENCE
POLYMER SCIENCE
Synthesis and Crosslinking Reaction of Polyacetylenes Substituted with
Benzoxazine Rings: Thermally Highly Stable Benzoxazine Resins
1
1
2
1
Masahide Goto, Yu Miyagi , Masaki Minami, Fumio Sanda
1
Department of Chemistry and Materials Engineering, Faculty of Chemistry, Materials and Bioengineering, Kansai University,
3
-3-35 Yamate-cho, Suita, Osaka 564-8680, Japan
2
Chemicals R and D Group, HPM Research and Development Department, High Performance Materials Company, JXTG Nippon
Oil and Energy Corporation, 8 Chidori-cho, Naka-ku, Yokohama, Kanagawa 231-0815, Japan
Correspondence to: F. Sanda (E-mail: sanda@kansai-u.ac.jp)
Received 18 March 2018; accepted 25 May 2018; published online in Wiley Online Library
DOI: 10.1002/pola.29076
ABSTRACT: Novel polyacetylenes, poly(1) and poly(2) substituted
with benzoxazine rings were synthesized by the polymerization
of the corresponding acetylene monomers 1 and 2 using Rh cat-
differential scanning calorimetry and thermogravimetric analy-
0
sis. The surface of poly(1) film became hydrophilic compared to
0
that of poly(1), while the surfaces of poly(2) and poly(2) films
1
–
alysts, [(nbd)RhCl]
2
,
and (nbd)Rh B Ph
4
(nbd5 2,5-norborna-
to obtain
showed almost the same hydrophilicity judging from the water
0
0
diene). The polymers were heated at 250 8C under N
2
contact angle measurement. Poly(1) and poly(2) exhibited
refractive indices smaller than those of poly(1) and poly(2).
0
0
the corresponding polybenzoxazine resins, poly(1) and poly(2)
V
2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym.
C
possessing polyacetylene main chains via the ring-opening
polymerization of the benzoxazine moieties. The polyacetylene
backbones were maintained after crosslinking reaction at 250 8C,
which were confirmed by Raman spectroscopy. The benzoxa-
zine resins were thermally highly stable as evidenced by
Chem. 2018, 56, 1884–1893
KEYWORDS: phenol resin; polyacetylene; polybenzoxazine; ring-
opening polymerization; thermosetting resin
4
INTRODUCTION Benzoxazines are easily synthesized by dehy-
dration of phenolic compounds, amines, and formaldehyde.
Benzoxazines undergo ring-opening polymerization/cross-
linking without catalyst to afford polybenzoxazine resins, in
which the crosslinked networks are constructed by phenolic
moieties linked with Mannich bridges (–CH –NR–CH –) and
metal catalysts such as Mo and W, late transition metal cata-
5
lysts such as Rh and Ir, and recently with Ru and Pd. Rh cat-
alysts are most widely used for the polymerization of
monosubstituted acetylene monomers such as phenylacety-
lenes. It is possible to synthesize cis-stereoregulated acetylene
polymers by Rh catalysts because the polymerization takes
place via the coordination–insertion mechanism, which is
satisfactorily supported by the DFT calculations. It is also
possible to control the molecular weights of the formed
monosubstituted acetylene polymers by employing well-
defined Rh catalysts such as [(nbd)Rh(CBCPh)(PPh
[(nbd)Rh{C(Ph)@CPh }(PPh )]. Substituted linear polyacety-
2 3
lenes prepared with Rh catalysts are transformed into cross-
linked polymers by the postpolymerization reactions of pendant
functional groups, including crosslinking by subsequent UV
irradiation to poly(pentafluorophenyl ethynylbenzoate)s modified
with mono o-nitrobenzyl-protected diamine, salicylaldimine-
metal ionic crosslinking reactions of salicylidene Schiff-base-
and interchain crosslinking of
poly(4-ethynyl)phenylacetylne by heating. o-Diethynylbenzene
6
7
2
2
six-membered intramolecular OH–N hydrogen bonding. Poly-
benzoxazines are focused as promising thermosetting resins,
which show fine heat resistance, dimensional stability due to
the near-zero volumetric properties and low electric con-
8
1
9
stant, and so forth. On the other hand, p-conjugated poly-
3
)] and
1
0
mers are extensively investigated as photonics, nonlinear
optical materials, electrical semiconductors, and organic light-
2
emitting diodes. Substituted polyacetylenes, representative
11
p-conjugated polymers, possess carbon–carbon alternating
double bonds at the main chain, in which the extent of the
conjugation depends on the number, type, and bulkiness of
substituents. Substituted polyacetylenes feature high gas
permeability/separation ability, stimuli response, and chiral
12
13
containing polyacetylenes,
3
14
recognition as well as photoelectric functions. Substituted
polyacetylenes are commonly synthesized by the polymeriza-
tion of the corresponding monomers with early transition
gives crosslinked polymers, whose network structures are
dependent on polymerization catalysts (Rh, Ta). On the other
15
Additional Supporting Information may be found in the online version of this article.
2018 Wiley Periodicals, Inc.
V
C
1
81 88 48 4
JJ OO UU RR NN AA LL OO FF PP OO LL YY MM EE RR SS CC II EE NN C EE ,, PP AA RR TT AA :: PP OO LL YY MM EE RR CC HH EE MM I ISS TT RR YY 2 20 01 18 8, ,5 56 6, ,1 18 88 84 4– –1 18 89 93 3

JJ OO UU RR NN AA LL OO FF
PP OO LL YY MM EE RR SS CC II EE NN CC EE
WW WW WW .. PP OO LL YY MM EE RR CC HH EE MM II SS TT RR YY .. OO RR GG
AA RR TT II CC LL EE
SCHEME 1 Synthesis of monomers 1 and 2.
hand, 1-ethynyl-2-phenylethynylbenzene gives a linear poly
phenylacetylene) derivative bearing phenylethynyl groups by
polystyrene standards. Melting points (mp) were measured on
a Yanaco micro melting point apparatus. Elemental analysis
was done at the Analytical Center, Faculty of Engineering,
(
the selective polymerization of the terminal ethynyl group
with Rh catalysts, while gives a polymer mainly consisting of
trisubstituted benzene rings by the polymerization with W
Osaka University. ESI-MS spectra were recorded on
a
THERMO FISHER Q mass spectrometer. IR spectra were mea-
sured on a JASCO FT/IR-4100 spectrophotometer. IR spectra
(ATR method) were measured on a Thermoscientific iS-50 FT-
IR equipped with a Specac Golden Gate ATR unit. Raman
spectra were recorded on a TOKYO INSTRUMENTS 3D Laser
Raman Microspectroscopy System Nanofinder 30 and a JASCO
NRS-5100 series of Raman spectrometer. UV–vis absorption
spectra were recorded on a JASCO V-550 spectrophotometer.
Diffuse reflectance UV–vis spectra were recorded on an Ocean
Optics USB4000 UV-VIS-NIR equipped with a DH-2000-BAL as
a light source. Thermogravimetric analysis (TGA) was per-
formed on an SHIMADZU TGA-50 thermogravimetric analyzer.
Differential scanning calorimetry (DSC) was performed on a
Seiko Instruments DSC7020. Static water contact angles were
measured on a Kyowa Interface Science DropMaster 100 and
AUTO DISPENSER AD-31. Refractive indices were measured
on a HORIBA smart SE Spectroscopic Ellipsometer.
15
and Mo catalysts.
p-Conjugated poly(high internal phase
emulsion) foams are synthesized using poly(1,3-diethynyl ben-
16
zene) skeleton as a crosslinker. Poly(propargyl ether) deriva-
tives bearing benzoxazine groups undergo irreversible cis–trans
17
isomerization and thermally activated curing without catalyst.
We have designed novel acetylene monomers substituted with
a benzoxazine ring in the course of our study on substituted
polyacetylenes, aiming at the development of highly thermally
stable resins based on the synergistic effect by the rigid polya-
cetylene backbone and high performance of bezoxazine. In this
article, we disclose the synthesis and crosslinking reaction of
novel poly(phenylacetylene) derivatives substituted with ben-
zoxazine rings, which have no spacers between the poly(pheny-
lacetylene) backbone and benzoxazine moieties.
EXPERIMENTAL
Measurements
H (400 MHz) and 13C (100 MHz) NMR spectra were
recorded on JEOL ECA-400 and ECS-400 spectrometers.
Number-average molecular weight (M ) and dispersity ( D- )
Monomer Synthesis
The monomers 1 and 2 were synthesized according to
Scheme 1. The synthetic procedures are described below.
1
n
values of polymers were determined by SEC eluted with THF
4-(Trimethylsilylethynyl)Phenol (1a)
(columns: Shodex KF-805L 3 3, JASCO RI-4030, UV-4075, PU-
Into a reaction vessel, 4-iodophenol (5.50 g, 24.0 mmol), CuI
4
180, DG-980-50, CO-4060, LC-NetII/ADC, AS-2055 Plus)
(0.182 g, 0.96 mmol), and Pd(PPh
were charged. THF (60 mL), trimethylsilylacetylene (3.38 mL,
24.0 mmol), and Et N (8.0 mL, 108 mmol) were fed to the
3 4
) (0.554 g, 0.48 mmol)
and SEC eluted with LiBr solution (10 mM) in N,N-dimethyl-
formamide (DMF) (columns: TSK gel a-M, GMHXL, JASCO RI-
3
930, UV-2075 Plus, PU-980, DG-980-50, CO-965) calibrated by
vessel, and the resulting mixture was stirred in the dark at
J OJ OU UR RN NA AL LO OF FP PO OL LY YMM E ER RS SC CI EI ENN C CE E, ,P PAA RR TT AA :: PP OO LL YY MM EE RR CC HH EE MM II SS TT RR YY 22 00 11 88 ,, 55 66 ,, 11 88 44 –– 11 88 99 33
1 18 88 85 5

JJ OO UU RR NN AA LL OO FF
PP OO LL YY MM EE RR SS CC II EE NN CC EE
AA RR TT II CC LL EE
WW WW WW . .PP OO LL YY MM EE RR CC HH EE MM II SS TT RR YY .. OO RR GG
a
TABLE 1 Polymerization of 1 and 2
b
Run
Monomer
Rh cat.
[M]
0
/[Rh]
Solvent
THF
Yield (%)
M
n
D-
c
c
c
c
c
c
c
c
c
1
2
3
4
5
6
7
8
9
1
1
1
1
2
2
2
2
2
2
2
2
[(nbd)RhCl]
[(nbd)RhCl]
2
2
100
100
100
100
100
100
50
46
12,000
19,000
10,000
14,900
2.4
2.7
2.9
2.3
1.7
CHCl
3
3
3
33
1
–
(nbd)Rh B Ph
4
THF
71
1
–
(nbd)Rh B Ph
4
CHCl
THF
60
c
[(nbd)RhCl]
[(nbd)RhCl]
[(nbd)RhCl]
[(nbd)RhCl]
2
2
2
2
87
7,100
e
e
CHCl
DMF
DMF
THF
90
–
–
d
d
Quant.
Quant.
Quant.
80
25,000
1.8
e
e
100
100
100
50
–
–
1
–
e
e
(nbd)Rh B Ph
4
4
4
4
–
–
1
–
e
e
1
1
1
0
1
2
(nbd)Rh B Ph
CHCl
DMF
DMF
3
–
–
1
–
e
e
(nbd)Rh B Ph
83
–
–
1
–
e
e
(nbd)Rh B Ph
100
Quant.
–
–
a
c
Conditions: [1]
h under Ar. Ten equivalents of Et
0
5 [2]
0
5 0.05 mol/L in THF, CHCl
3
, or DMF at 30 8C for
Determined by SEC eluted with THF calibrated by polystyrene standards.
Determined by SEC eluted with DMF calibrated by polystyrene stand-
d
1
3
N was added in the polymerization
with [(nbd)RhCl]
2
.
3
ards. The polymer was insoluble in THF and CHCl .
b
e
MeOH-Insoluble part.
3
Could not be determined due to insolubility in THF, CHCl , and DMF.
room temperature under Ar for 24 h. The solvent was dis-
tilled off on a rotary evaporator, and diethyl ether was added
to the residue. The resulting solution was washed with water,
and the organic layer was separated and dried over anhy-
(15 mL) was stirred at 90 8C for 5 h. The solvent was dis-
tilled off, and diethyl ether was added to the residue. The
resulting solution was washed with 0.5 M NaOH aqueous
solution. The organic layer was separated, dried over anhy-
4
drous MgSO . It was concentrated on a rotary evaporator, and
4
drous MgSO , and concentrated on a rotary evaporator to
benzene (15 mL) and ethylenediamine (3 mL) were added to
the residue. The resulting mixture was stirred at 60 8C for 20
min, and diethyl ether was added to the mixture. The result-
ing solution was washed with 0.5 M HCl, and the organic
obtain 1b as a brown solid (1.19 g, 3.8 mmol). Yield 5 77%.
1
H NMR (400 MHz, CDCl ): d 0.23 (s, 9H, TMS), 4.56 (s, 2H,
3
Ar–CH –N), 5.36 (s, 2H, O–CH –N), 6.70–7.25 (m, 8H, Ar).
2
2
13C NMR (100 MHz, CDCl ): d 0.16, 50.2, 80.1, 92.6, 105.0,
3
layer was separated and dried over anhydrous MgSO , and
115.4, 117.0, 118.6, 120.8, 121.9, 129.4, 130.7, 131.9, 148.1,
154.8.
4
concentrated on a rotary evaporator to obtain a brown vis-
cous liquid. It was purified by silica gel column chromatogra-
phy eluted with ethyl acetate/hexane5 1/1 (v/v) to give 1a
6-Ethynyl-3-Phenyl-3,4-Dihydro-1,3-Benzoxazine (1)
as a brownish white solid (2.50 g, 13.1 mmol). Yield 5 54%.
Compound 1b (0.40 g, 1.30 mmol) was dissolved in THF
(5 mL), and then 1 M tetrabutylammonium fluoride solution
in THF (15.6 mL, 15.6 mmol) was added dropwise to the
solution. The resulting mixture was stirred at room tempera-
ture for 1 h. Diethyl ether was added to the mixture, and the
resulting mixture was washed with water. The organic layer
1
H NMR (400 MHz, CDCl ): d 0.21 (s, 9H, TMS), 4.90 (s, 1H, –
3
OH), 6.74 (d, J 5 8.8 Hz, 2H, Ar), 7.35 (d, J 5 12.0 Hz, 2H, Ar).
6
-(Trimethylsilyl)Ethynyl-3-Phenyl-3,4-Dihydro-1,3-
Benzoxazine (1b)
A mixture of 1a (0.95 g, 5.0 mmol), 1,3,5-trioxane (0.30 g,
was separated and dried over anhydrous MgSO , and concen-
4
3.33 mmol), aniline (0.46 mL, 5.0 mmol), and toluene
trated on a rotary evaporator to obtain a yellowish brown
a
TABLE 2 Copolymerization of 2 with Phenylacetylene (PA)
b
c
D- c
[
2]
0
/[Rh]
[PA]
0
/[Rh]
Yield (%)
M
n
0
5
2
5
1
100
95
75
50
0
Quant.
Quant.
Quant.
78
12,300
16,700
5.2
4.5
d
d
5
0
6,100
6.3
d
d
10,000
1.6
e
e
00
Quant.
–
–
a
c
Conditions: [2]
N]/[Rh] 5 10.
Insoluble part in MeOH.
0
1 [PA]
0
5 0.2 mol/L in THF at 30 8C for 1 h under Ar.
Determined by SEC eluted with THF calibrated by polystyrene
standards.
[
Et
3
b
d
THF-soluble part.
e
3
Could not be determined due to insolubility in THF, CHCl and DMF.
1
81 88 68 6
JJ OO UU RR NN AA LL OO FF PP OO LL YY MM EE RR SS CC II EE NN C EE ,, PP AA RR TT AA :: PP OO LL YY MM EE RR CC HH EE MM I ISS TT RR YY 2 20 01 18 8, ,5 56 6, ,1 18 88 84 4– –1 18 89 93 3

JJ OO UU RR NN AA LL OO FF
PP OO LL YY MM EE RR SS CC II EE NN CC EE
WW WW WW .. PP OO LL YY MM EE RR CC HH EE MM II SS TT RR YY .. OO RR GG
AA RR TT II CC LL EE
22
0
TABLE 3 Static Water Contact Angles of Poly(1), Poly(1) ,
Polymerization
0
Poly(2), and Poly(2)
Typical procedure: [(nbd)RhCl]
(4.58 mg, 0.99 3 10
2
mmol) was dissolved in CHCl (9.8 mL) in a 50 mL Schlenk
tube under Ar. Then a solution of 1 (234 mg, 0.99 mmol) in
3
Spin Speed upon
Preparing the
Static Water
Contact
CHCl3 (10 mL) and Et N (0.01 mL) were fed into the tube,
3
Sample
Sample (rpm)
Angle h (8)
and the resulting solution was stirred at 30 8C for 1 h ([1]0/
[
Rh] 5 100, [1] 5 0.05 mol/L, [Et N]/[Rh] 5 10). The poly-
Poly(1)
Poly(1)
Poly(1)
800
81.6 6 0.6
78.5 6 0.7
87.2 6 1.6
33.2 6 0.1
27.2 6 0.3
32.8 6 1.9
81.0 6 0.3
80.5 6 0.6
71.7 6 1.4
0 3
merization mixture was poured into CH OH (200 mL) to pre-
900
3
cipitate a solid mass. It was separated from the solution
with a membrane filter (ADVANTEC H100A047A), and dried
in vacuo to obtain a polymer [poly(1)] as a brownish solid
1000
800
0
Poly(1)
0
Poly(1)
900
(
79.1 mg, yield 5 33%).
0
Poly(1)
1000
a
Poly(2)
–
Thermal Curing
A powdery sample of poly(1) was fed in a glass tube. It was
placed on a glass petri dish, and heated in a Nitto black
0
a
Poly(2)
–
Glass plate
–
2
MINI SH-OMT oven at 250 8C for 2 h under N to obtain
a
Prepared by drop cast method.
0
0
poly(1) . Poly(2) was obtained by thermal curing of poly(1)
in the same fashion. Film samples of poly(1) and poly(2)
were prepared by casting solutions in THF (4 or 10 mM) on
a glass plate or a silicon wafer. The samples were submitted
to thermal curing as described later. The polymer films on a
glass plate and a silicon wafer were used for water contact
angle and refractive index measurements, respectively.
viscous liquid. It was purified by silica gel column chroma-
tography eluted with CHCl to obtain 1 as a brownish white
solid (0.20 g, 0.85 mmol). Yield 5 65%, mp 5 92–94 8C. IR
(
1
5
4
3
KBr disk): 3269, 3036, 2913, 2101, 1671, 1599, 1576,
494, 1416, 1368, 1323, 1233, 939, 758, 694, 669, 603,
21 1
72 cm . H NMR (400 MHz, CDCl ): d 2.96 (s, 1H, CHBC),
3
.58 (s, 2H, Ar–CH
2
–N), 5.36 (O–CH
2
–N), 6.73–7.30 (m, 8H,
Spectroscopic Data of the Polymers
Ar). 13C NMR (100 MHz, CDCl ): d 50.3, 76.0, 80.0, 83.5,
Poly(1) IR (KBr disk): 3393, 3026, 2892, 1600, 1559, 1554,
1494, 1452, 1415, 1375, 1321, 1301, 1230, 1152, 1029, 997,
3
1
1
2
14.3, 117.2, 118.6, 121.0, 121.9, 129.4, 130.8, 132.0, 148.1,
1
21
1
55.0. ESI-MS (m/z): [M 1 H]
calcd for C H NO,
970, 943, 754, 693, 616, 520 cm
CDCl ): d 4.07 (s, Ar–CH –N), 4.84–5.01 (s, O–CH
s, CH@CH), 6.32–7.20 (m, Ar). Poly(2) IR (KBr disk): 3398,
.
H NMR (400 MHz,
1
6 13
36.1031; found, 236.1070.
3
2
2
–N), 5.71
(
3
1
8
027, 2957, 2918, 2835, 1605, 1583, 1559, 1507, 1488,
3
-(4-Ethynyl)Phenyl-3,4-Dihydro-1,3-Benzoxazine (2)
455, 1375, 1336, 1251, 1226, 1189, 1159, 1111, 1034, 970,
The title compound was synthesized from 4-ethynylaniline
2.25 g, 19.1 mmol), 1,3,5-trioxane (1.20 g, 12.8 mmol) and
2
1 1
20, 751, 586 cm . H NMR (400 MHz, CDCl ): d 4.08–4.14
3
(
(
s, Ar–CH –N), 4.86 (s, O–CH –N), 5.71 (s, CH@CH), 6.32–
2 2
phenol (1.80 g, 19.1 mmol) in a manner similar to 1b. The
product was purified by recrystallization with CH Cl2 to
obtain 2 as a brown solid (2.10 g, 8.9 mmol). Yield 5 46%,
mp 5 96–99 8C. IR (KBr disk) 5 3262, 2100, 1606, 1511,
0
.22 (m, Ar). Poly(1) IR (KBr disk): 3393, 2958, 2919,
7
2
1
6
2
368, 1773, 1734, 1718, 1700, 1696, 1685, 1653, 1647,
617, 1559, 1554, 1534, 1522, 1507, 1490, 1165, 820, 750,
2
1
0
92 cm . Poly(2) IR (KBr disk): 3393, 2918, 2368, 1617,
1455, 1373, 1297, 1252, 1225, 1183, 1159, 1086, 1033, 948,
2
1
21
1
1559, 1554, 1507, 1458, 1169, 818, 751, 515 cm
.
8
CDCl
(
58, 832, 767, 744, 678, 626, 547 cm . H NMR (400 MHz,
): d 2.98 (s, 1H, CHBC), 4.63 (s, 2H, Ar–CH –N), 5.35
O–CH –N), 6.80–7.39 (m, 8H, Ar). 13C NMR (100 MHz,
CDCl ): d 50.1, 76.1, 78.6, 83.9, 114.3, 117.1, 120.7, 121.1,
3
2
Preparation of Samples for Water Contact Angle
Measurement
The samples were prepared by drop cast or spin-coating from
a polymer solution in THF (4 mol/L) on a glass plate at 800,
2
3
1
126.8, 128.1, 133.4, 148.5, 154.3. ESI-MS (m/z): [M 1 H]
calcd for C H NO, 236.1031; found, 236.1070.
1
6 13
9
00, or 1000 rpm for 30 s. The samples after thermal curing
were prepared by heating the aforementioned samples in a
Nitto black MINI SH-OMT oven at 250 8C for 2 h under N2.
0
TABLE 4 Thickness and Refractive Indices of Poly(1), Poly(1) ,
0
a
Poly(2), and Poly(2)
Samples Used for Spectroscopic Measurement, TGA, and
DSC
Sample
Thickness (nm)
Refractive Index
Poly(1)
31.2 6 0.17
23.3 6 0.07
41.3 6 0.12
28.3 6 0.11
1.68
1.72
1.80
1.79
The samples obtained by runs 1 and 5 in Table 1 were used
for the measurements depicted in Figures 5–10 and Tables 3
0
Poly(1)
0
0
Poly(2)
and 4. Poly(1) and poly(2) samples in Figure 7 and Tables 3
and 4 were prepared by drop cast or spin-coating from a poly-
mer solution in THF (10 mM) on a glass plate at 1000 rpm
for 30 s followed by heating at 250 8C for 2 h under N2.
0
Poly(2)
a
Measured by ellipsometry.
J OJ OU UR RN NA AL LO OF FP PO OL LY YMM E ER RS SC CI EI ENN C CE E, ,P PAA RR TT AA :: PP OO LL YY MM EE RR CC HH EE MM II SS TT RR YY 22 00 11 88 ,, 55 66 ,, 11 88 44 –– 11 88 99 33
1 18 88 87 7

JJ OO UU RR NN AA LL OO FF
PP OO LL YY MM EE RR SS CC II EE NN CC EE
AA RR TT II CC LL EE
WW WW WW . .PP OO LL YY MM EE RR CC HH EE MM II SS TT RR YY .. OO RR GG
SCHEME 2 Polymerization of 1 and 2 followed by crosslinking reaction.
RESULTS AND DISCUSSION
with phenylacetylene (PA) was also carried out with various
feed ratios using [(nbd)RhCl] –Et N] catalyst in THF to obtain
2
3
Polymerization
the corresponding copolymers with Mn and D- values of
6,100–16,700 and 1.6–6.3 in good yields as listed in Table 2.
The copolymer was completely soluble in THF when the feed
ratio of 2 was 5%. On the other hand, the copolymers were
partly insoluble in THF when the feed ratios of 2 were 25%
and 50%.
The polymerization of 1 and 2 was carried out using
1
–
2 3 4
[
(nbd)RhCl] –Et N and (nbd)Rh B BPh as catalysts in THF,
CHCl , and DMF as solvents at 30 8C for 1 h under Ar
3
(
Scheme 2). The corresponding polymers [poly(1) and
poly(2)] with M and D- values of 7,100–25,000 and 1.7–2.9
n
were obtained in 33%–quantitative yields as listed in Table
1
. All the samples of poly(1) obtained by the polymerization
Thermal Curing of the Polymers
Poly(1) and poly(2) were heated at 250 8C under N for 2 h
of 1 were soluble in THF, CHCl3 and DMF. The polymeriza-
tion of 1 in CHCl afforded poly(1) with an M higher than
that in THF both with [(nbd)RhCl]2 and (nbd)Rh B BPh .
The polymer yields by the polymerization in CHCl were
lower than those in THF (runs 1–4). Poly(2) samples
2
3
n
1
–
to obtain polymers with ring-opened benzoxazine moieties.
Brownish poly(1) turned into black after heating as shown
in Figure 1, while poly(2) exhibited no apparent color
change. Figure 2 shows the IR spectra of monomers 1, 2 and
the polymers before and after heating. Monomers 1 and 2
exhibited a stretching vibration peak of CBC of the ethynyl
4
3
1
8
obtained by the polymerization with [(nbd)RhCl]2 in THF
(run 5, [M] /[Rh] 5 100) and that in DMF (run 7, [M] /
0
0
[Rh] 5 50) were soluble in THF, CHCl3 and DMF just after
2
1
group around 2100 cm , while poly(1) and poly(2) did not,
indicating the successful acetylene polymerization. The
monomers and polymers exhibited stretching vibration peaks
assignable to the trisubstituted benzene ring around 1490–
isolation, while the polymers became insoluble in the
solvents during storing. The other samples of poly(2) were
insoluble in the solvents even just after isolation. All the poly-
merization took place homogenously, and no precipitation or
gelation was observed during the polymerization. It is there-
fore likely that the crosslinking by the ring-opening of the
benzoxazine moieties partly took place during acetylene poly-
merization and/or after isolation. The copolymerization of 2
2
1
21
1510 cm
and 940–970 cm , and that of C–O–C around
2
1
1230 cm . These peaks almost disappeared after thermal
curing, indicating that the ring-opening reaction of the ben-
0
0
zoxazine moieties took place to give poly(1) and poly(2) as
SCHEME 3 Copolymerization of 2 with phenylacetylene (PA).
1
81 88 88 8
JJ OO UU RR NN AA LL OO FF PP OO LL YY MM EE RR SS CC II EE NN C EE ,, PP AA RR TT AA :: PP OO LL YY MM EE RR CC HH EE MM I ISS TT RR YY 2 20 01 18 8, ,5 56 6, ,1 18 88 84 4– –1 18 89 93 3

JJ OO UU RR NN AA LL OO FF
PP OO LL YY MM EE RR SS CC II EE NN CC EE
WW WW WW .. PP OO LL YY MM EE RR CC HH EE MM II SS TT RR YY .. OO RR GG
AA RR TT II CC LL EE
absorption, which also confirmed that the acetylene polymer-
ization of 1 successfully took place. The UV–vis absorption
spectra of poly(2) could not be measured because the sam-
ples of poly(2) became insoluble in organic solvents during
storing after isolation as mentioned above. The UV–vis
absorption spectra of the monomers and polymers were
therefore measured by the KBr pellet method (Supporting
Information, Fig. S15), and diffuse reflectance UV–vis spectra
of the polymers as well (Supporting Information, Fig. S16).
0
0
Poly(1) and poly(2) exhibited UV–vis absorption/reflection
peaks at longer wavelength regions compared with poly(1)
and poly(2), respectively, suggesting the extension of conju-
gation by thermal treatment presumably accompanying the
isomerization of the polyacetylene backbone from cis to
trans.
Figure 6 shows the DSC thermograms of the monomers and
polymers. Monomer 1 exhibited the first endothermic peak
at 93 8C corresponding to the mp, and exothermic peak at
1
45–245 8C corresponding to the ring-opening reaction of
FIGURE 1 Appearance of the polymer samples before and after
the benzoxazine moieties [Fig. 6(a)]. Monomer 2 exhibited
0
heating at 250 8C for 2 h under N
2
: (a) Poly(1), (b) Poly(1) , (c)
0
Poly(2), (d) Poly(2) . The samples were obtained by runs 4 and
5
in Table 1. [Color figure can be viewed at wileyonlinelibrary.
com]
shown in Scheme 2. Rh catalysts commonly polymerize
monosubstituted acetylene monomers via the coordination–
insertion mechanism to give the corresponding cis–stereoreg-
5
,6
ular substituted polyacetylenes.
The solid state Raman
spectra of the polymers were measured before and after
heating at 250 8C to obtain information on the structures.
Poly(1) and poly(2) exhibited Raman scattering peaks
2
1
around 1560 cm assignable to the vibration of C@C at the
21
main chain and benzene ring, and around 1330 cm assign-
able to the vibration of cis C–C at the main chain as shown
in Figure 3. The Raman scattering peaks around 1200–
2
1
1280 cm
are assignable to the vibration of trans C–C at
the main chain. It is therefore considered that poly(1) and
1
9
poly(2) consist both of cis and trans stereostructures.
It should be noted that the cis polyacetylene backbone possi-
bly isomerizes into trans due to the heat caused by laser
2
0
light irradiation during Raman spectroscopic measurement.
In fact, the cis contents of poly(1) and poly(2) were almost
quantitative judging from the integration ratio of the cis
vinyl protons at the main chain appeared around 5.7 ppm in
1
0
the H NMR spectra as shown in Figure 4. Poly(1) exhibited
21
broad Raman scattering peaks around 1600 and 1350 cm
,
indicating the existence of polyacetylene backbone after ther-
0
mal curing at 250 8C. The stereostructure of poly(1) was
unclear due to the broadness of the absorption peaks. The
0
Raman spectroscopic measurement of poly(2) was unsuc-
cessful due to the emission of luminescence from the sample.
Figure 5 shows the UV–vis absorption spectra of 1 and
poly(1) measured in THF. Poly(1) exhibited absorption peak
assignable to the p–p* transition of the conjugated polyacety-
lene backbone at 350–530 nm, while 1 did not show such
0
FIGURE 2 IR spectra of (a) 1, poly(1), and poly(1) ; (b) 2,
0
poly(2), and poly(2) . [Color figure can be viewed at wileyonli-
nelibrary.com]
J OJ OU UR RN NA AL LO OF FP PO OL LY YMM E ER RS SC CI EI ENN C CE E, ,P PAA RR TT AA :: PP OO LL YY MM EE RR CC HH EE MM II SS TT RR YY 22 00 11 88 ,, 55 66 ,, 11 88 44 –– 11 88 99 33
1 18 88 89 9

JJ OO UU RR NN AA LL OO FF
PP OO LL YY MM EE RR SS CC II EE NN CC EE
AA RR TT II CC LL EE
WW WW WW . .PP OO LL YY MM EE RR CC HH EE MM II SS TT RR YY .. OO RR GG
the endo and exothermic peaks at 97 8C and 150–280 8C cor-
responding to the mp and ring-opening reaction, respectively
[
Fig. 6(c)]. Poly(1) exhibited exothermic peaks around 140–
180 8C possibly assignable to the glass transition, and 200–
2
80 8C assignable to the ring-opening reaction of benzoxa-
0
zine rings [Fig. 6(a,b)] Poly(1) exhibited a exothermic peak
around 290–370 8C, which may be attributable to thermal
decomposition behavior [Fig. 6(a,b)].
1
f
0
Poly(2) poly(2)
exhibited the exothermic peaks [Fig. 6(c,d)] in a manner sim-
0
ilar to poly(1) poly(1) .
Figure 7 shows the TGA traces of the polymers before and
0
0
after heating at 250 8C. Poly(1) and poly(2) were thermally
more stable than poly(1) and poly(2) judging from the 5%
weight loss temperatures (T ) and weight residues at
d5
500 8C. It is likely that the weight loss at the first stage was
caused by the cleavage of the unreacted side chains from the
polyacetylene backbone. At higher temperatures, the poly-
mers underwent decomposition irrespective of prior thermal
treatment at 250 8C. The polymers kept their weights 78–
87% at 500 8C, indicating the enhancement of thermal
FF II GG UU RR EE 44 11 HH NN MM RR (( 44 00 00 MM HH zz )) ss pp ee cc tt rr aa oo ff (( aa )) pp o ll yy (( 11 )) aa nn dd (( bb ))
3
3
pp oo ll y (( 22 )) mm ee aa ss uu rr ee dd ii nn CC DD CC ll .. [[ CC oo ll oo rr ffii gg uu rr ee cc aa nn bb ee vv ii ee ww ee dd aa tt
ww ii ll e yy oo nn ll ii nn ee ll ii bb rr aa rr yy . .cc oo mm ]]
stability compared with poly(PA) derivatives without benzox-
2
1
azine moieties. It is reported that aniline is eliminated
2
2
from benzoxazine moiety upon curing in some cases. The
0
0
FF II GG UU RR EE 33 RR aa mm aa nn ss pp ee cc tt rr aa oo ff (( aa )) 11 ,, pp oo ll yy (( 11 )) ,, aa nn dd pp oo ll yy (( 11 )) ;; (( bb )) 22
aa nn dd pp oo ll yy (( 22 )) .. [[ CC oo ll oo rr ffii gg uu rr ee cc aa nn bb ee v vi ei eww e edd a at tw wi l iel ey yo on nl il ni n ee l li ibb rr aa rr yy ..
cc oo mm ]]
FIGURE 5 UV–vis spectra of 1 and poly(1) measured in THF
(c 5 0.04 mM). [Color figure can be viewed at wileyonlineli-
brary.com]
1
81 98 09 0
JJ OO UU RR NN AA LL OO FF PP OO LL YY MM EE RR SS CC II EE NN C EE ,, PP AA RR TT AA :: PP OO LL YY MM EE RR CC HH EE MM I ISS TT RR YY 2 20 01 18 8, ,5 56 6, ,1 18 88 84 4– –1 18 89 93 3

JJ OO UU RR NN AA LL OO FF
PP OO LL YY MM EE RR SS CC II EE NN CC EE
WW WW WW .. PP OO LL YY MM EE RR CC HH EE MM II SS TT RR YY .. OO RR GG
AA RR TT II CC LL EE
0
0
FIGURE 6 DSC thermograms of (a, b): 1, poly(1), and poly(1) ; (c, d): 2, poly(2), and poly(2) measured at a heating rate5 10 8C/min.
[Color figure can be viewed at wileyonlinelibrary.com]
0
nitrogen contents of poly(1) and poly(1) were 5.79% and
.55%, slightly lower than the theoretical value (6.00%). It is
5
therefore considered that aniline was eliminated only slightly
during the curing process of the present polymers.
The static water contact angle (h) values of the polymers
were measured in order to get information about the hydro-
philicity before and after thermal curing. The h values of
0
poly(1) samples were 48.4–54.48 smaller than those of
poly(1) as listed in Table 3 and the photographs of the rep-
resentative samples as shown in Figure 8. The h values of
the polymers carrying benzoxazine moieties are commonly
not so different before and after curing (ring-opening of ben-
zoxazine moieties), or rather increase after thermal curing,
that is, the sample surface tends to become hydrophobic
after ring-opening reaction of the benzoxaine moieties due to
the formation intra- and intermolecular hydrogen bonding
0
0
FF II GG UU RR EE 77 TT GG AA t tr raa cc ee ss o of f( a( a) )1 1, ,p op loy l (y1 ( )1, ) a, na dn dp op l oy (l 1y () 1; )( ;b )( b2 ), pp oo ll yy (( 22 ))
FF II GG UU RR EE 88 PP hh oo t too gg r raa pp hh ss oo ff ww aa t tee rr dd r roo pp l lee t tss oo nn t thh ee ffiil lmm ss oo ff (( aa ))
0
0
ꢀ
0
aa nn d pp oo ll yy (( 22 )) (( hh ee aa tt ii nn gg rr aa tt ee 5= 11 00 8 CC / /mm i inn ,, uu nn dd ee rr NN
2
2 )) .. [[ CC oo ll oo rr ffii gg uu rr ee
pp oo ll yy (( 11 )) p pr er ep pa ar er ed dbyb sy pi ns p ci no at ci no ga t mi n eg th mo de,t 1h 0o 0d 0, r p1 0m 0;0(b r) pp mo l; y( (1 b) );
0
0
0
cc aa nn bb ee vv ii ee ww ee dd aa tt ww i il lee yy oo nn l li inn ee l li ibb rr aa rr yy . .cc oo mm ]]
p( co )l yp (o1 l )y ;( 2( c) )p pr eo pl ya (r2e )dp br ey p da r roe pd cba ys td mr o ep t hc oa ds t; (md )e pt ho ol yd (; 2 () d.) poly(2) .
J OJ OU UR RN NA AL LO OF FP PO OL LY YMM E ER RS SC CI EI ENN C CE E, ,P PAA RR TT AA :: PP OO LL YY MM EE RR CC HH EE MM II SS TT RR YY 22 00 11 88 ,, 55 66 ,, 11 88 44 –– 11 88 99 33
1 18 89 91 1

JJ OO UU RR NN AA LL OO FF
PP OO LL YY MM EE RR SS CC II EE NN CC EE
AA RR TT II CC LL EE
WW WW WW . .PP OO LL YY MM EE RR CC HH EE MM II SS TT RR YY .. OO RR GG
between amino and hydroxy groups formed, leading to the
similar to common pre- and cured benzoxazine resins. Thus,
we developed novel thermally highly stable benzoxazine res-
ins bearing polyacetylene backbones. The refractive indices
of the cured resins were rather smaller than those of the
prepolymers, showing the possibility of the present polymers
as nonvolume shrinkage thermosetting resins. Further study
such as mechanical properties are now in progress.
2
3
decrease of surface energy. On the contrary, the h values of
poly(1) decreased after thermal curing, indicating the hydro-
0
philicity of the surface of poly(1) larger than that of poly(1)
[
Fig. 8(a,b)]. It is speculated that the hydroxy groups of
0
poly(1) are orientated toward the film surface, and this ori-
entation is not retarded by such hydrogen bonding so much.
On the other hand, no remarkable difference was observed
0
between the h value of poly(2) and poly(2) films, which is
explainable by the formation of hydrogen bonding between
the amino and hydroxy groups formed by ring opening of
the benzoxazine moieties [Fig. 8(c,d)]. This is reasonable
ACKNOWLEDGMENT
The authors are grateful to Prof. Masashi Ishikawa, Prof. Masaki
Yamagata, Mr. Hirofumi Yamamoto (Kansai University), and
Prof. Kayo Terada (Nara Institute of Science and Technology)
for measurement of Raman spectra, Prof. Hideya Kawasaki
(Kansai University) for measurement of diffuse reflectance UV–
vis spectra, Prof. Miyuki Harada and Mr. Takuya Matsumoto
(Kansai University) for measurement of DSC, Prof. Takashi
Miyata and Mr. Takato Senzaki (Kansai University) for measure-
ment of static contact angles, and Prof. Hiroto Kudoh (Kansai
University) for measurement of refractive indices.
0
because the hydroxy groups of poly(1) are located at the
benzene rings directly connected to the rigid polyacetylene
0
backbone, while those of poly(2) are located at the benzene
rings through phenylene–nitrogen–methylene spacer. It is
0
therefore likely that the hydroxy groups of poly(2) are more
0
movable compared to those of poly(1) , and form hydrogen
bonding more efficiently.
Table 4 lists the thickness and refractive indices of the poly-
mer films before and after curing. The thickness and refrac-
tive indices of the four polymer films were in the ranges of
28–41 nm and 1.68–1.80. Poly(1) and poly(2) became thin
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–
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7
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0
0
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0
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81 98 29 2
JJ OO UU RR NN AA LL OO FF PP OO LL YY MM EE RR SS CC II EE NN C EE ,, PP AA RR TT AA :: PP OO LL YY MM EE RR CC HH EE MM I ISS TT RR YY 2 20 01 18 8, ,5 56 6, ,1 18 88 84 4– –1 18 89 93 3

JJ OO UU RR NN AA LL OO FF
PP OO LL YY MM EE RR SS CC II EE NN CC EE
WW WW WW .. PP OO LL YY MM EE RR CC HH EE MM II SS TT RR YY .. OO RR GG
AA RR TT II CC LL EE
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J OJ OU UR RN NA AL LO OF FP PO OL LY YMM E ER RS SC CI EI ENN C CE E, ,P PAA RR TT AA :: PP OO LL YY MM EE RR CC HH EE MM II SS TT RR YY 22 00 11 88 ,, 55 66 ,, 11 88 44 –– 11 88 99 33
1 18 89 93 3