Anionic alternating copolymerization of epoxide and six-membered lactone bearing naphthyl moiety

Article abstract of DOI:10.1002/pola.24470

This article describes the anionic copolymerization of glycidyl phenyl ether (GPE) and 1,2-dihydro-3H-naphtho[2,1-b]pyran-3-one (DHNP), a six-membered aromatic lactone bearing naphthyl moiety. The copolymerization proceeded in a 1:1 alternating manner, to

Full text of DOI:10.1002/pola.24470

Anionic Alternating Copolymerization of Epoxide and Six-Membered
Lactone Bearing Naphthyl Moiety
ATSUSHI SUDO, YUAN ZHANG, TAKESHI ENDO
Molecular Engineering Institute, Kinki University, Kayanomori, Iizuka 820-8555, Japan
Received 31 July 2010; accepted 29 October 2010
DOI: 10.1002/pola.24470
Published online 7 December 2010 in Wiley Online Library (wileyonlinelibrary.com).
ABSTRACT: This article describes the anionic copolymeriza-
networked polymer, of which main chain was endowed with
the DHNP-derived rigid naphthalene moieties, showed
tion of glycidyl phenyl ether (GPE) and 1,2-dihydro-3H-naph-
a
tho[2,1-b]pyran-3-one (DHNP),
a
six-membered aromatic
higher glass transition temperature than that obtained simi-
larly with using 3,4-dihydrocoumarin (DHCM) as a comono-
lactone bearing naphthyl moiety. The copolymerization pro-
ceeded in a 1:1 alternating manner, to afford the correspond-
ing polyester. The ester linkage in the main chain was
cleavable by reduction with lithium aluminum hydride to give
the corresponding diol that inherited the structure of the alter-
nating sequence. The copolymerization ability of DHNP per-
mitted its addition as a comonomer to an imidazole-initiated
polymerization of bisphenol A diglycidyl ether. The resulting
mer, an analogous aromatic lactone bearing phenylene
C
V
moiety instead of naphthalene moiety of DHNP.
2010 Wiley
Periodicals, Inc. J Polym Sci Part A: Polym Chem 49: 619–624,
2011
KEYWORDS: anionic polymerization; copolymerization; polyest-
ers; ring-opening polymerization
INTRODUCTION Lactones have attracted considerable atten-
tion as monomers exhibiting a wide variety of polymerizabil-
ity that can be tuned by choosing plural structural para-
meters such as ring-size, number of unsaturated bonds in
the ring, substituents, and their positions.1 So far, ring-open-
ing polymerizations of simple aliphatic lactones have been
the main focus in this area because of the flexible and bio-
degradable natures of the corresponding polymers.2 In
contrast, aromatic lactones have not been investigated fully
despite their potentiality to afford the corresponding poly-
mers endowed with high thermal stability and mechanical
strength that can not be attained by aliphatic lactones.3
This finding of the successful copolymerization behavior of
DHCM with epoxide has prompted us to develop its analo-
gous systems based on designing new aromatic lactones.9
The monomer highlighted in this article is 1,2-dihydro-3H-
naphtho[2,1-b]pyran-3-one (DHNP),
a six-membered aro-
matic lactone bearing naphthyl moiety, which can be easily
synthesized by the cycloaddition reaction of 2-naphthol and
acrylic acid. This lactone has been known as ‘‘Splitomicin,’’
which is an inhibitor of Sir2p, an NADþ-dependent Sir2 fam-
ily deacetylase required for chromatin-dependent silencing
in yeast.10 What we expected to DHNP were (1) its copoly-
merization behavior with epoxide similar to that of DHCM
and (2) enhancement of thermal stability of the correspond-
ing copolymer because of incorporation of planar and rigid
naphthalene moieties.11
Previously, we have reported the first exploitation of 3,4-
dihydrocoumarin (DHCM) as a monomer (Scheme 1).4 This
aromatic six-membered lactone has been out of the focuses
in polymer chemistry, because it does not undergo anionic
or cationic homopolymerization. However, we discovered
that DHCM underwent 1:1 alternating anionic copolymeriza-
tion with epoxide to afford the corresponding polyester
successfully. This copolymerization ability of DHCM with
epoxide allowed its use as a comonomer in the imidazole-
initiated curing reaction of epoxy resins, which is widely
applied to the bonding of electrodevices,5 coatings,6 struc-
tural adhesives,7 and fabrication of nanocomposite materi-
als.8 By adding DHCM to this conventional curing system,
the resulting cured materials gained remarkably improved
thermal properties and adhesion strength.4(a)
EXPERIMENTAL
Materials
2-Naphthol, acrylic acid, 2-ethyl-4-methylimidazole (EMI),
and solvents were purchased from Wako Pure Chemical
R
Industries and were used as received. AmberystV 15 (acidic
ion exchange resin) and bisphenol A diglycidyl ether (Bis A-
DGE) were purchased from Sigma-Aldrich, Japan.
Equipments and Measurements
1H NMR and 13C NMR spectra were recorded with Lambda-
300 (JEOL) with tetramethylsilane as an internal standard.
Additional Supporting Information may be found in the online version of this article. Correspondence to: T. Endo (E-mail: tendo@mol-eng.fuk.
kindai.ac.jp)
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Journal of Polymer Science: Part A: Polymer Chemistry, Vol. 49, 619–624 (2011) 2010 Wiley Periodicals, Inc.
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JOURNAL OF POLYMER SCIENCE: PART A: POLYMER CHEMISTRY DOI 10.1002/POLA
was removed by decantation, and the sedimentary gummy
residue was dissolved in THF (5 mL) and the solution was
dropped into diethyl ether (200 mL). The supernatant was
removed by decantation, and the residue was dried under
vacuum to afford copolymer 1 (1.45 g, 83%): Mn ¼ 2400;
Mw ¼ 4520; IR (KBr) 1736, 1624, 1597, 808, 752, 692; 1H
NMR (CDCl3, d): 2.5–2.7 (broad, 2H), 3.1–3.4 (broad, 2H),
3.6–4.4 (broad, 4H), 5.0–5.6 (broad, 1H), 6.6–8.0 (broad m,
11H); 13C NMR (CDCl3, d): 20.58, 33.87, 34.24, 65.66, 66.76,
67.08, 68.36, 68.78, 70.23, 70.56, 113.8, 114.4, 114.5, 121.0,
121.1, 121.2, 121.4, 121.6, 122.7, 122.8, 123.4, 126.5, 128.1,
128.2, 128.5, 129.2, 129.4, 132.5, 153.1, 153.2, 158.1, 158.2,
158.3, 172.6.
SCHEME 1 Anionic alternating copolymerization of epoxide
and aromatic lactone.
Reductive Cleavage of Copolymer 1
A solution of 1 (0.664 g; repeating unit 1.91 mmol) in THF
(10 mL) was added to a suspension of LiAlH4 (0.46 g) in
THF (20 mL) at 0 ꢂC, and then the mixture was stirred at
room temperature. After 24 h, the mixture was poured into
Infrared (IR) spectra were obtained on a JASCO model FT-IR-
460 plus. Number average molecular weight (Mn) and weight
average molecular weight (Mw) were estimated from size
exclusion chromatography, performed on a Tosoh model
HLC-8120GPC equipped with Tosoh TSK gel-Super HM-H
styrogel columns (6.0 mm / ꢀ 15 cm), using tetrahydrofu-
ran (THF) as an eluent at the flow rate of 0.6 mL minꢁ1
after calibration with polystyrene standards. Gas chromatog-
raphy (GC) was carried out with a Shimadzu gas chromato-
graph model GC-18A equipped with J&W Scientific DB-WAX-
ꢂ
phosphate buffer (400 mL) at 0 C, and then extracted with
ethyl acetate (200 mL) three times. The organic layers were
combined and washed with distilled water, dried over
MgSO4, filtered, and concentrated under reduced pressure.
The residue was fractionated by column chromatography
[silica gel, eluent ¼ ethyl acetate/hexane (1/2 in v/v)] to
obtain 2 (0.578 g, 1.64 mol, 86%): 1H NMR (DMSO-d6, d)
1.65–1.80 (m, 2H), 3.09 (t, J ¼ 7.7), 3.42–3.50 (m, 2H), 4.11–
4.30 (m, 5H), 4.59 (t, J ¼ 5.1, 1H), 5.49 (d, J ¼ 4.4, 1H),
6.86–7.02 (m, 3H), 7.24–7.53 (m, 5H), 7.79 (d, J ¼ 9.0, 1H),
7.85 (d, J ¼ 7.9, 1H), 7.99 (d, J ¼ 8.6, 1H); 13C NMR (DMSO-
d6, d) 21.05, 22.12, 60.69, 114.47, 114.76, 120.61, 123.06,
123.19, 123.40, 126.27, 127.45, 128.41, 128.91, 129.52,
132.49, 153.32, 158.58.
ETR 125-7332 (0.53 mm
ꢀ
30 m) capillary column.
Thermogravimetric analysis (TG), differential thermal analy-
sis (DTA), and differential scanning calorimetric analysis
(DSC) were performed with a Seiko Instruments model
EXSTAR6000.
Synthesis of DHNP
DHNP was synthesized according to the reported method.10
R
2-Naphthol (4.43 g, 30.4 mmol) and Amberlyst 15V (3.0 g)
Copolymerization of Bis A-DGE and DHNP
were placed in a flask. Toluene (80 mL) and acrylic acid (4.42
g, 60.8 mmol) were added and heated with refluxing for 48 h.
During the reaction, formed water was removed by azeotropic
distillation. After cooling, the mixture was filtered, and the fil-
trate was concentrated under reduced pressure. The residue
was passed through a thin layer of silica gel with using ethyl
acetate/n-hexane (1/7 in v/v) as an eluent, and the eluted
fractions were combined, concentrated under reduced pres-
sure, and dried under vacuum to obtain DHNP (5.25 g; 87%):
Bis A-DGE (6.81 g, 20.0 mmol) and DHNP (1.40 g, 7.06
ꢂ
mmol) were mixed at 80 C under vacuum to obtain a homo-
geneous mixture. To this mixture, EMI (259 mg, 2.35 mmol)
was added at ambient temperature and stirred under vac-
uum to obtain the corresponding mixture. A small portion of
the mixture (ca 10 mg) was taken and used for DSC analysis
(30–200 ꢂC with heating rate of 10 ꢂC minꢁ1) to study the
heat evolution behavior during the curing reaction. The rest
ꢂ
was placed in a silicone vessel and heated at 100 C for 1 h.
1
ꢂ
mp 48–49 C; IR (KBr) 1769, 1515, 1077, 898, 811, 749; H
NMR (CDCl3, d) 2.88 (t, J ¼ 7.4, 2H), 3.30 (t, J ¼ 7.4, 2H),
7.20 (d, J ¼ 8.8, 1H), 7.45 (d, J ¼ 7.5, 1H), 7.55 (d, J ¼ 7.5,
1H), 7.74 (d, J ¼ 8.8, 1H), 7.84 (t, J ¼ 8.3, 2H); 13C NMR
(CDCl3, d) 19.75, 28.47, 115.41, 117.29, 122.69, 125.04,
127.03, 128.62, 128.81, 130.69, 130.99, 149.49, 168.28.
The resulting cured material was analyzed by Fourier Trans-
fer Infrared (FT-IR) to confirm the consumption of DHNP.
Ten milligrams of the mateꢂrial was analyzed by DSC (30–200
ꢂC with heating rate of 10 C minꢁ1) to measure glass transi-
tion temperature (Tg). Five milligrams of the material was
analyzed by TG/DTA (30–500 ꢂC with heating rate of 10 ꢂC
minꢁ1) to study its thermal decomposition behavior and
determine temperature for 10% weight loss (Td10).
Copolymerization of GPE and DHNP
Glycidyl phenyl ether (GPE; 751 mg, 5.00 mmol), DHNP (991
mg, 5.00 mmol), and EMI (11 mg, 0.10 mmol) were placed
in a flask filled with argon gas. By stirring the mixture at
room temperature, it became homogeneous. The resulting
homogeneous mixture was heated at 120 ꢂC for 1 h with
stirring. After cooling to room temperature, the mixture was
dissolved in THF (5 mL) and the resulting solution was
poured into hexane (200 mL). After 1 h, the supernatant
RESULTS AND DISCUSSION
Synthesis of DHNP
DHNP was synthesized from 2-naphthol in a straightforward
manner (Scheme 2).10 By heating 2-naphthol with acylic acid
R
in the presence of AmberystV 15, an acidic ion exchange
resin, the cycloaddition reaction proceeded smoothly to
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ARTICLE
to that of DHCM, which did not undergo the homopolymeri-
zation at all.
On the other hand, DHNP underwent the copolymerization
with GPE successfully (Scheme 3). To an equimolar mixture
of GPE and DHNP, EMI (1 mol % to the total amount of the
two monomers) was added, and the resulting mixture was
heated at 120 ꢂC, with monitoring the progress of the
copolymerization with GC. As shown in Figure 1, both the
monomers were consumed almost in the same rate, implying
the potential alternating character of the copolymerization to
give the corresponding polyester 1.
SCHEME 2 Synthesis of DHNP.
The formed polyester 1 was isolated as an ether-insoluble
achieve the quantitative consumption of 2-naphthol. The
reaction was free from side reaction, and thus removal of
the solid catalyst by filtration and chromatography with a
short silica gel column gave pure DHNP in a high yield. The
spectroscopic features of DHNP involved the strong IR
absorption at 1769 cmꢁ1 and 13C NMR signal at 168 ppm,
which were attributable to the ester carbonyl group. The 1H
NMR and 13C NMR spectra are shown in Figure S1 (in
Supporting Information).
fraction in 83% yield. Its IR analysis revealed the formation
of ester linkage by showing
a strong absorption at
1735 cmꢁ1 (Fig. 2). 13C NMR analysis supported also the for-
mation of ester linkage (Fig. 3). The signal for the ester car-
bonyl group appeared at different positions (173 ppm) to
that for DHNP (168 ppm). In the region from 65 to 70 ppm,
multiple signals appeared, although the ideal structure of the
polymer 1 suggests there would be only three signals in this
region. This multiplicity would be attributable to the pres-
ence of OH-terminated 1. In the 1H NMR spectrum of 1, the
two broad signals at around 2.6 and 3.3 ppm were attri-
butable to the two methylene groups derived from DHNP
(Fig. S2 in Supporting Information). In addition, there was a
signal at 5.4 ppm, which was reasonably assigned to the
methine proton locating on the carbon attached to the acyl-
oxy group in the main chain. The presence of OH-terminated
1, which was suggested by the 13C NMR, was also confirmed
by the signal at 5.2 ppm. These spectroscopic features of 1
were quite similar to those of the 1:1 alternating copolymer
Copolymerization Behavior of DHNP and GPE
Before the investigation on the copolymerization, homopoly-
merization behavior of DHNP was studied. A bulk mixture of
DHNP and EMI (1 mol %) was heated at 120 ꢂC; however,
no reaction took place. This robust nature was quite similar
FIGURE 1 Time-conversion relationships for the copolymeri-
zation of DHNP and GPE ([GPE]0:[DHNP]0:[EMI]0 ¼ 50:50:1, at
120 ꢂC).
SCHEME 3 Anionic alternating copolymerization of GPE and
DHNP.
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JOURNAL OF POLYMER SCIENCE: PART A: POLYMER CHEMISTRY DOI 10.1002/POLA
Scheme 4 shows possible mechanism for the copolymeriza-
tion. The initiation step would involve formation of a 2:1
adduct of epoxide and EMI, which has been reported for the
imidazole-initiated anionic ring-opening polymerization of
epoxide.8 An alkoxide, thus, formed can react both with
epoxide and DHNP; however, the intrinsic nature of the alk-
oxide would force it to choose DHNP rather than epoxide as
a preferable monomer,4(b) leading to the formation of the
corresponding naphthoxide. This ‘‘Step A’’ would be followed
by ‘‘Step B,’’ that is, nucleophilic attack of the naphthoxide to
epoxide. In this step, the naphthoxide would not react with
DHNP at all, but would react exclusively with epoxide to give
the corresponding alkoxide. Alternation of Step A (¼ reaction
of alkoxide with DHNP) and Step B (¼ reaction of naphth-
oxide with epoxide) can afford the alternating copolymer 1.
Application of DHNP as a Comonomer to
Epoxy-Imidazole Curing System
FIGURE 2 IR spectra of (a) a mixture of GPE, DHNP, and EMI
(50:50:1) and (b) the corresponding alternating copolymer 1.
Based on the copolymerization ability of DHNP with GPE, we
next focused on application of DHNP as a comonomer to the
EMI-promoted curing reaction of epoxy resin. As shown in
Scheme 4, the mechanism does not deny the possibility of
formation of epoxide–epoxide sequence, and, therefore,
copolymerizations with feed ratios ([epoxide]0/[DHNP]0) >1
would be performed successfully to give the corresponding
copolymers rich in epoxide–epoxide sequence.4(b) In other
words, a small amount of DHNP can be exploited as an addi-
tive to modify the conventional epoxy–imidazole curing sys-
tem. As was described in Introduction, previously, a similar
system was demonstrated with employing DHCM.4(a)
of GPE and DHCM, suggesting the successful formation of
the 1:1 GPE-DHNP alternating sequence.
The formation of the alternating structure of 1 was con-
firmed further by reductive scission of its polyester-type
main chain (Scheme 3). By treatment of 1 with LiAlH4, its
ester linkages were cleaved readily to give the corresponding
diol 2 as a sole product that was isolated by column chroma-
1
tography in 86%. H NMR and 13C NMR analyses of the diol
supported its structure derived from the repeating unit of
polyester 1 formed by the 1:1 alternating copolymerization
(Fig. S3 in Supporting Information).
To confirm the feasibility of this concept, GPE, DHNP, and
EMI were mixed in a feed ratio of 85:15:5 and the mixture
FIGURE 3 13C NMR spectra of (a)
a
mixture of GPE, DHNP, and
EMI (50:50:1) and (b) the 1:1
alternating copolymer 1.
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SCHEME 4 Mechanism for the alternating copolymerization.
FIGURE 4 IR spectra of (a) a formulation composed of GPE,
DHNP, and EMI (85:15:5), (b) a product obtained by heating the
formulation for 30 min, (c) a product obtained by heating the
formulation for 60 min, and (d) the product obtained by the
copolymerization of Bis A-DGE and DHNP.
was heated at 100 ꢂC for 1 h, with monitoring the progress
of the copolymerization with IR. The set of these parameters
is one of our standard ones.4(a),9(a) Figure 4(a) shows the IR
spectrum of the mixture, which indicated the characterisꢁti1c
absorption of the carbonyl group of DHNP at 1769 cm
.
After 30 min, a new absorption appeared at 1730 cmꢁ1
[Fig. 4(b)], implying the formation of the corresponding co-
polymer having ester linkages in the main chain. After 1 h,
DHNP was completely consumed, as confirmed by the corre-
sponding spectum [Fig. 4(c)]. In addition, GC analysis of the
resulting mixture revealed complete consumptions of both
the monomers.
networked polymer obtained by using DHCM as a comono-
mer in place of DHNP for comparison.4(a) The temperatures
of 10% weight loss (Td10) of the networked polymers were
comparable, as was expected from the similarity in the
chemical bonds that consisted the main chain structures. On
the other hand, the utilization of DHNP as a comonomer
resulted in the higher glass transition (Tg) of the networked
polymer than that obtained by using DHCM, presumably due
Based on the confirmation of the potential of DHNP as a
new comonomer for the epoxy-imidazole system, we investi-
gated its copolymerization with a bifunctional epoxide, Bis
A-DGE (Scheme 5). Bis A-DGE, DHNP, and EMI were mixed in
a feed ratio [epoxy moiety]0:[DHNP]0:[EMI]0 ¼ 85:15:5, and
ꢂ
the resulting homogeneous mixture was heated at 100 C for
1 h to obtain the corresponding networked polymer as a stiff
solid, which was insoluble in any solvent. It was analyzed
with IR to find that DHNP was successfully consumed and
transformed into the corresponding ester linkages in the
main chain [Fig. 4(d)]. The networked polymer was pow-
dered and immersed in chloroform for 24 h; however, DHNP
was not eluted at all to confirm its complete consumption.
In Table 1, some thermal properties of the obtained net-
worked polymer are listed along with those of an analogous
SCHEME 5 Copolymerizations of Bis A-DGE and lactones.
COPOLYMERIZATION OF EPOXIDE AND SIX-MEMBERED LACTONE, SUDO, ZHANG, AND ENDO
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JOURNAL OF POLYMER SCIENCE: PART A: POLYMER CHEMISTRY DOI 10.1002/POLA
molecules 2003, 4, 1466–1486. (e) Lou, X.; Detrembleur, C.; Je´r-
oˆ me, R. Macromol Rapid Commun 2003, 24, 161–172. (f)
Stridsberg, K. M.; Ryner, M.; Albertsson, A.-C. Adv Polym Sci
2002, 157, 41–65.
TABLE 1 Copolymerizations of Bis A-DGE and Aromatic
Lactones
Thermal Properties
of the Networked
2 (a) Martina, M.; Hutmacher, D. W. Polym Int 2007, 56,
145–157. (b) Braunegg, G.; Bona, R.; Koller, M. Polym Plast
Technol Eng 2004, 43, 1779–1793. (c) Vert, M. Biomacromole-
cules 2005, 6, 538–546.
Exothermal Peak
Polymer
Top Temperature
Entry Comonomer of DSC Profile (ꢂC)a Td10 (ꢂC)b Tg (ꢂC)c
1
2
DHCM
DHNP
141
146
410
409
124
135
3 For our recent reports on polymerizations of aromatic lac-
tones, see: (a) Kudoh, R.; Sudo, A.; Endo, T. Macromolecules
2009, 42, 2327–2329. (b) Suzuki, A.; Sudo, A.; Endo, T. J Polym
Sci Part A: Polym Chem 2009, 47, 2214–2218.
a
b
c
Measured by DSC in a dynamic scan mode (10 ꢂC minꢁ1).
Measured by TG/DTA.
Measured by DSC.
4 (a) Sudo, A.; Uenishi, K.; Endo, T. Polym Int 2009, 58,
970–975. (b) Uenishi, K.; Sudo, A.; Endo, T. Macromolecules
2007, 40, 6535–6539. (c) Uenishi, K.; Sudo, A.; Endo, T. J Polym
Sci Part A: Polym Chem 2008, 46, 4092–4102.
to the higher rigidity of the DHNP-derived naphthyl moiety
than the DHCM-derived phenylene moiety.
5 (a) Sumi, H.; Kojima, T. U.S. Patent 2,002,033,275, 2002.
Sumi, H.; Kojima, T. Chem Abstr 136:255, 916; (b) Kim, Y.-S.;
Kim, H.-C.; Shin, D.-R. WO 2,001,096,440, 2001. Kim, Y.-S.; Kim,
H.-C.; Shin, D.-R. Chem Abstr 136:54, 606; (c) Konarski, M.;
Szczepniak, Z. A. WO 9,905,196, 1999. Konarski, M.; Szczepniak,
Z. A. Chem Abstr 130:154, 626.
CONCLUSIONS
In summary, an aromatic six-membered lactone bearing
naphthalene moiety (DHNP) was exploited as a new mono-
mer that copolymerized with epoxide in an imidazole-initi-
ated anionic system. The usefulness of this new lactone-type
monomer was demonstrated by adding it to the conventional
epoxy–imidazole curing system as a comonomer. The basic
chemistry of the system was a copolymerization of a bisphe-
nol A-derived bifunctional epoxide and DHNP, which permit-
ted the incorporation of the DHNP-derived rigid naphthalene
moieties into the main chain of the resulting networked
polymer to achieve the higher glass transition temperature
than that obtained similarly with using DHCM, an analogous
aromatic lactone.
6 (a) Hall-Goulle, V. WO 9,804,531, 1998. Hall-Goulle, V. Chem
Abstr 128:154, 878; (b) Correll, G. D.; Berstler, R. M. U.S. Patent
5,686,185, 1997. Correll, G. D.; Berstler, R. M. Chem Abstr 128:
14, 181.
7 Dearlove, T. J.; Gray, R. K. U.S. Patent 4,383,060, 1983. Dear-
love, T. J.; Gray, R. K. Chem Abstr 99:39, 544.
8 (a) Chen, D.; He, P. Compos Sci Technol 2004, 64, 2501–2507;
(b) Xu, W.-B.; Bao, S.-P.; Shen, S.-J.; Hang, G.-P.; He, P.-S. J Appl
Polym Sci 2003, 88, 2932–2941.
9 (a) Sudo, A.; Uenishi, K.; Endo, T. J Polym Sci Part A: Polym
Chem 2008, 46, 3447–3451. (b) Uenishi, K.; Sudo, A.; Endo, T.
J Polym Sci Part A: Polym Chem 2009, 47, 1661–1672. (c)
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