Six-membered cyclic carbonate having styrene moiety as a chemically recyclable monomer. Construction of novel cross-linking-de-cross-linking system of network polymers

Article abstract of DOI:10.1021/ma047998t

This article deals with (1) synthesis and anionic polymerization of a six-membered cyclic carbonate having styrene moiety, (2) anionic depolymerization of the obtained polymer, (3) radical cross-linking of the obtained polymer, and (4) anionic de-cross-li

Full text of DOI:10.1021/ma047998t

7944
Macromolecules 2005, 38, 7944-7949
Six-Membered Cyclic Carbonate Having Styrene Moiety as a Chemically
Recyclable Monomer. Construction of Novel
Cross-Linking-De-Cross-Linking System of Network Polymers
,†
Toyoharu Miyagawa, Mie Shimizu,‡ Fumio Sanda,§ and Takeshi Endo*,†
Department of Polymer Science and Engineering, Faculty of Engineering, Yamagata University,
4-3-16 Jonan, Yonezawa, Yamagata 992-8510, Japan; Chemical Resources Laboratory, Tokyo Institute
of Technology, 4259 Nagatsuta-cho, Midori-ku, Yokohama 226-8503, Japan; and Department of
Polymer Chemistry, Graduate School of Engineering, Kyoto University, Kyoto 606-8501, Japan
Received September 28, 2004
ABSTRACT: This article deals with (1) synthesis and anionic polymerization of a six-membered cyclic
carbonate having styrene moiety, (2) anionic depolymerization of the obtained polymer, (3) radical cross-
linking of the obtained polymer, and (4) anionic de-cross-linking of the cross-linked polymer. The monomer
5-ethyl-5-[(p-vinylphenyl) methoxymethyl]-1,3-dioxan-2-one (St6CC) underwent anionic polymerization
with potassium tert-butoxide (t-BuOK) as an initiator in THF to afford the corresponding polycarbonate
[poly(St6CC)]. It was confirmed that this polymerization was equilibrium polymerization by the
relationships between the polymerization temperature and monomer conversion. Poly(St6CC) underwent
anionic depolymerization with t-BuOK (5 mol % vs polymer repeating unit) as a catalyst in THF (0.1 M)
at 20 °C for 24 h to recover St6CC in 60% yield. Treatment of poly(St6CC) with a radical initiator afforded
the cross-linked polymer. Employment of styrene as the comonomer satisfactorily afforded the corre-
sponding cross-linked polymer. It underwent anionic de-cross-linking with t-BuOK (10 mol % vs polymer
repeating unit) in THF at 50 °C for 24 h to afford a THF-soluble polymer. The yield of the THF-soluble
part increased as the styrene composition in the cross-linked polymer increased. It was suggested that
the de-cross-linking efficiency depended on the cross-linking density.
Scheme 1
Introduction
Development of an excellent method for recycling use
of polymeric materials is an issue of great importance
in recent polymer science and technology.1 Chemical
recycling is the most important and essential among a
few recycling methods of used polymers such as thermal
recycling, material recycling, and chemical recycling
because only this method can regenerate the original
monomers from the polymers. Monomers undergoing
equilibrium polymerization is applicable to chemical
recycling of polymeric materials because depolymeriza-
tion of the obtained polymers can afford the starting
monomers. We have recently reported cationic equilib-
rium polymerization behavior of spiro orthoesters2
(SOEs) and bicyclo orthoesters3 (BOEs) and chemical
recycling systems between linear polymers having SOE4
or BOE5 moieties and cross-linked polymers based on
the cationic equilibrium polymerization of SOEs and
BOEs (Scheme 1).
Six-membered cyclic carbonates (6CCs) efficiently
undergo ring-opening polymerization to afford the cor-
responding liner polycarbonates, especially under an-
ionic conditions.6 The most interesting feature of this
polymerization is volume expansion during polymeri-
zation.7 This volume expansion can be accounted for by
the difference in strength of the intermolecular interac-
tion between the monomers and polymers. That is,
strong interactions (dipole-dipole) in the monomers and
weak interactions in the polymers eventually cause the
volume expansion. Ho¨cker et al. have found that this
polymerization shows equilibrium character8 (Scheme
2). We have previously reported the substituent effect
on the anionic equilibrium polymerization of 6CCs,8b i.e.,
the equilibrium between the monomer and polymer
shifts to the monomer side with respect to the bulkiness
of the monomer substituent. 6CCs are also applicable
to chemical recycling of polymeric materials. If we
employed 6CC as a polymerizable group in the side
† Yamagata University.
‡ Tokyo Institute of Technology.
§ Kyoto University.
Present address: JST, ERATO, Yashima Super-structured
Helix Project, 101 Creation Core Nagoya, 2266-22 Aza-Anagahora
Shimoshidami, Moriyama-ku, Nagoya, 463-0003, Japan.
* To whom all correspondence should be addressed: Tel +81-
238-26-3090; Fax +81-238-26-3092; e-mail tendo@poly.yz.yamagata-
u.ac.jp.
10.1021/ma047998t CCC: $30.25 © 2005 American Chemical Society
Published on Web 08/18/2005

Macromolecules, Vol. 38, No. 19, 2005
Six-Membered Cyclic Carbonate 7945
Scheme 2
ether (200 mL × 3). The combined organic layers were dried
over anhydrous magnesium sulfate, filtered, and concentrated
under reduced pressure. Methanol (200 mL) was added to the
residual liquid (121.9 g), and then concentrated HCl (34.8 mL,
420 mmol) was added dropwise to the resulting solution at 10
°C with stirring. Then the reaction mixture was warmed to
room temperature, followed by stirring for 1 h. Then the
reaction mixture was cooled in an ice bath again; triethylamine
(43.6 g, 431 mmol) was added dropwise to the mixture. The
mixture was extracted with benzene (300 mL × 3). The
combined organic layers were evaporated after dryness with
anhydrous magnesium sulfate. The crude solid was recrystal-
lized from diethyl ether to obtain 2 as a white crystal. Yield:
54.7 g (219 mmol, 72%); mp 59-61 °C. 1H NMR (300 MHz,
CDCl3): δ 7.39 (d, J ) 8.1 Hz, 2H, -C6H4-), 7.26 (d, J ) 8.1
Hz, 2H, -C6H4-), 6.70 (dd, J ) 11.0 and 17.6 Hz, 1H, -CHd
CH2), 5.75 (dd, J ) 0.75 and 17.6 Hz, 1H, -CHdCH2), 5.25
(dd, J ) 0.75 and 11.0 Hz, 1H, -CHdCH2), 4.48 (s, 2H,
-OCH2C6H4-), 3.71 (d, J ) 11.0 Hz, 2H, -CH2OH), 3.65 (d,
J ) 11.0 Hz, 2H, -CH2OH), 3.46 (s, 2H, -CH2O-), 2.71 (brs,
2H, -OH), 1.33 (q, J ) 7.5 Hz, 2H, -CH2CH3), 0.82 ppm (t, J
) 7.5 Hz, 3H, -CH2CH3). 13C NMR (75 MHz, CDCl3): δ 137.4,
137.1, 136.4, 127.8, 126.3, 114.0, 73.7, 73.4, 65.9, 42.9, 23.0,
7.48 ppm. IR (KBr): ν (cm-1) ) 3430, 2970, 2935, 2883, 2867,
2250, 1910, 1630, 1570, 1513, 1463, 1406, 1381, 1364, 1090,
1062, 1018, 990, 909, 828, 733. Anal. Calcd for C15H22O3: C,
71.97; H, 8.68. Found: C, 71.78; H, 8.62.
chain, we might obtain a polymer undergoing reversible
cross-linking-de-cross-linking. In this work, we wish to
demonstrate a novel cross-linking-de-cross-linking sys-
tem between linear polymers and network polymers
based on equilibrium polymerization of 5-ethyl-5-[(p-
vinylphenyl)methoxymethyl]-1,3-dioxan-2-one (St6CC).
Experimental Section
Materials. Unless stated otherwise, all chemicals and
reagents were obtained commercially and used without further
purification. Tetrahydrofuran (THF) was dried over sodium
benzophenone and distilled under nitrogen before use. N,N-
Dimethylformamide (DMF) was used after distillation over
calcium hydride and stored over molecular sieves (4A).
Measurements. 1H NMR and 13C NMR spectra were
recorded with a JEOL Lambda-300 spectrometer in chloro-
form-d (CDCl3) using tetramethylsilane as an internal stan-
dard. IR spectra were measured on a Perkin-Elmer Spectrum
One spectrometer. Number-average molecular weights (Mn)
and polydispersities (Mw/Mn) were estimated by size exclusion
chromatography (SEC) on a Tosoh HPLC HLC-8120 system
equipped with two consecutive polystyrene gel columns (TSK
gels G4000HXL and G2500HXL), refractive index, and ultra-
violet detectors using THF as an eluent with a flow rate of
1.0 mL/min, by polystyrene calibration at 30 °C. Thermogravi-
metric analyses (TGA) were performed on a Seiko TG/
DTA6000 (EXSTER 6000) instrument. Differential scan cal-
orimetry (DSC) measurements were performed on a Seiko
DSC-220 instrument under a nitrogen atmosphere.
Monomer Synthesis. Synthesis of 5-Ethyl-5-hydroxym-
ethyl-2,2-dimethyl-1,3-dioxane (1). Trimethylolpropane (53.7
g, 400 mmol), acetone (120 mL, 1.6 mol), petroleum ether (120
mL), and p-toluenesulfonic acid monohydrate (1.8 g) were fed
in a 300 mL flask equipped with a water separator (Dean-
Stark trap). The mixture was refluxed overnight until water
was no more collected in the Dean-Stark trap. The mixture
was cooled in an ice-water bath, and anhydrous sodium
carbonate (1.8 g) was added to the mixture, followed by stirring
for 30 min. The mixture was then filtered, and petroleum ether
and excess amount of acetone were removed from the mixture
by evaporation. The residual liquid was distilled under a
reduced pressure to obtain 1 as a colorless liquid; yield 53.0 g
(76%), bp 117 °C/10 mmHg (lit.9 80-90 °C/0.2 mmHg). 1H
NMR (300 MHz, CDCl3): δ 3.66 (dd, J ) 5.1 and 11.2 Hz, 4H,
-CH2O), 3.60 (s, 2H, -CH2OH), 3.35 (t, J ) 5.1 Hz, 1H,
-CH2OH), 1.41 (d, J ) 11.2 Hz, 6H, -CH3), 1.34 (q, J ) 7.5
Hz, 2H, -CH2CH3), 0.84 ppm (t, J ) 7.5 Hz, 3H -CH2CH3).
13C NMR (75 MHz, CDCl3): δ 98.0, 64.9, 61.9, 36.8, 26.9, 23.5,
20.3, 6.9 ppm. IR (neat): ν (cm-1) ) 3438, 2968, 2881, 2247,
1655, 1477, 1455, 1373, 1348, 1257, 1202, 1155, 1091, 1048,
983, 919, 832, 733.
Synthesis of 5-Ethyl-5-[(p-vinylphenyl)methoxymethyl]-
1,3-dioxan-2-one (St6CC). Ethyl chloroformate (41.6 mL, 437
mmol) and triethylamine (60.7 mL, 437 mmol) were added
dropwise to a solution of 2 (54.7 g, 219 mmol) in THF (500
mL) at 10 °C. After that, the reaction mixture was warmed to
room temperature and stirred overnight. Precipitated triethyl-
amine‚HCl salt was filtered off, and the solvent was removed
from the mixture by distillation under a reduced pressure. The
crude solid was recrystallized from diethyl ether to obtain
St6CC as white crystal. Yield: 39.6 g (143 mmol, 66%); mp
48-50 °C. 1H NMR (300 MHz, CDCl3): δ 7.40 (d, J ) 8.2 Hz,
2H, -C6H4-), 7.25 (d, J ) 8.2 Hz, 2H, -C6H4-), 6.71 (dd, J )
10.9 and 17.6 Hz, 1H, -CHdCH2), 5.76 (d, J ) 17.6 Hz, 1H,
-CHdCH2), 5.26 (d, J ) 10.9 Hz, 1H, -CHdCH2), 4.48 (s,
2H, -OCH2C6H4-), 4.33 (d, J ) 11.0 Hz, 2H, -CH2OCO-),
4.13 (d, J ) 11.0 Hz, 2H, -CH2OCO-), 3.42 (s, 2H, -CH2O-
), 1.53 (q, J ) 7.5 Hz, 2H, -CH2CH3), 0.88 ppm (t, J ) 7.5 Hz,
3H, -CH2CH3). 13C NMR (75 MHz, CDCl3): δ 148.5, 137.3,
136.9, 136.3, 127.8, 126.3, 114.1, 73.7, 72.7, 68.2, 35.4, 23.3,
7.3 ppm. IR (KBr): ν (cm-1) ) 2971, 2926, 1756, 1471, 1405,
1179, 1115, 766. Anal. Calcd for C16H20O4: C, 69.54; H, 7.30.
Found: C, 69.26; H, 7.07.
Anionic Ring-Opening Polymerization of St6CC. Typi-
cal procedure: All glass vessels were heated in vacuo before
use, filled with dry nitrogen, and handled in a stream of dry
nitrogen. A solution of St6CC (276 mg, 1 mmol) in toluene (1
mL) was prepared and stored over molecular sieves (4A)
overnight. 1.0 M solution of potassium tert-butoxide in THF
(10 µL, 0.01 mmol) was quickly added to the monomer solution
in a glass tube equipped with a three-way stopcock, and the
resulting mixture was stirred at a set temperature for 24 h.
The reaction was quenched by the addition of a solution of
methanol/phosphoric acid (v/v ) 9:1, 10 µL). The resulting
mixture was poured into a large amount of methanol to
precipitate the polymer. It was collected as colorless gum by
filtration and dried under vacuum.
Synthesis of 2-Ethyl-2-[(p-vinylphenyl)methoxymethyl]-
1,3-propanediol (2). Sodium hydride (60% dispersion in
mineral oil, 13.5 g) was added to a solution of DMF (40 mL)
and THF (200 mL) with stirring under a nitrogen atmosphere.
A solution of 1 (53.3 g, 306 mmol) in THF (60 mL) was added
dropwise to the resulting mixture at 10 °C. After the addition
was completed, the reaction mixture was warmed to room
temperature and stirred until hydrogen gas was no more
generated (1.5 h). Then the reaction mixture was cooled to 10
°C again, and then p-chloromethylstyrene (46.9 g, 307 mmol)
was added dropwise to the mixture. After the addition was
completed, the reaction mixture was warmed to room temper-
ature, followed by stirring overnight. The mixture was put into
ice-cold water (1 L), and the mixture was extracted by diethyl
1
Poly(St6CC). H NMR (300 MHz, CDCl3): δ 7.34 (d, J )
8.1 Hz, 2H, -C6H4-), 7.22 (d, J ) 8.1 Hz, 2H, -C6H4-), 6.67
(dd, J ) 10.9 and 17.5 Hz, 1H, -CHdCH2), 5.71 (d, J ) 17.5
Hz, 1H, -CHdCH2), 5.21 (d, J ) 10.9 Hz, 1H, -CHdCH2),
4.42 (s, 2H, -OCH2C6H4-), 4.10 (s, 4H, -CH2OCO-), 3.33 (s,
2H, -CH2O-), 1.47 (q, J ) 7.7 Hz, 2H, -CH2CH3), 0.82 ppm
(t, J ) 7.7 Hz, 3H, -CH2CH3). 13C NMR (75 MHz, CDCl3): δ
155.1, 137.8, 136.9, 136.5, 127.6, 126.2, 113.7, 73.1, 69.6, 67.7,
41.9, 22.6, 7.5 ppm. IR (KBr): ν (cm-1) ) 2970, 1750, 1630,
1513, 1462, 1405, 1238, 1110, 989, 827, 788. Anal. Calcd for
C16H20O4: C, 69.54; H, 7.30. Found: C, 69.60; H, 7.10.

7946 Miyagawa et al.
Macromolecules, Vol. 38, No. 19, 2005
Table 1. Radical Cross-Linking of Poly(St6CC) with Styrenea
feed ratio (mol %)
polymer compositiond
run
carbonateb:styrene
yield (%)c
carbonateb:styrene (molar ratio)
Td5e (°C)
Tgf (°C)
1
2
3
4
5
6
7
100:0
50:50
33:67
20:80
11:89
6:94
83
64
85
56
56
82
76
100:0
38:62
29:71
22:78
11:89
7:93
305
333
307
319
325
336
343
g
g
102
112
103
102
97
3:97
5:95
a Conditions: initiator BPO (1 mol %), solvent DMF (2 M), 80 °C, 3 h. b Molar ratio per St6CC repeating unit. c THF-insoluble part.
d Estimated by elemental analysis. e Determined by TGA under nitrogen. f Determined by DSC under nitrogen. g Not determined.
Scheme 3
Anionic Depolymerization of Poly(St6CC). t-BuOK in
THF (1.0 M, 50 µL, 0.05 mmol) was added to a solution of poly-
(St6CC) (276 mg, 1 mmol per repeating unit) in THF (10 mL)
at 20 °C under a nitrogen atmosphere. After the mixture was
stirred at the temperature for 24 h, the reaction was quenched
by the addition of a solution of methanol/phosphoric acid (9:1
) v/v, 20 µL). St6CC was isolated from the mixture by
preparative high-performance liquid chromatography on a
Japan Analytical Industry LC-908 system equipped with two
polystyrene gel columns (JAI gels H1 and H2) with chloroform
as an eluent at a flow rate of 3.8 mL/min. The yield of St6CC
was 166 mg (60%).
Radical Cross-Linking of Poly(St6CC). Typical proce-
dure: Benzoyl peroxide (BPO, 5 mg, 0.02 mmol, 1 mol %) and
subsequently styrene, if required, were introduced to a solution
of poly(St6CC) (552 mg, 2 mmol per repeating unit) in DMF
(1 mL, 2 M) in a polymerization tube. The tube was cooled,
degassed, sealed off, and heated at 80 °C for 3 h. The resulting
residue was rinsed using a Soxhlet extractor and dried under
a reduced pressure. The yield of the cross-linked polymer was
458 mg (83%). Spectral data and elemental analysis of the
cross-linked polymer obtained in run 1 in Table 1 are as
follows. IR (KBr): ν (cm-1) ) 3444, 3083, 3060, 3026, 2919,
2850, 2313, 1943, 1871, 1752, 1602, 1493, 1453, 1365, 1269,
1233, 1096, 1069, 1028, 907, 757, 539. Anal. Calcd for
C16H20O4: C, 69.54; H, 7.30. Found: C, 69.61; H, 7.17.
Anionic De-Cross-Linking of the Cross-Linked Poly-
mer. Typical procedure: The cross-linked polymer (2 mmol
per repeating unit) was fed in a 50 mL flask equipped with a
three-way stopcock and dried under a reduced pressure at 100
°C for 1 h. After it was cooled to 50 °C, THF (20 mL) was added
to the dried cross-linked polymer under a nitrogen atmosphere,
followed by stirring for 1 h to swell the cross-linked polymer.
t-BuOK in THF (10 mol % vs carbonate repeating unit) was
added to the mixture. After the mixture was stirred at 50 °C
for 24 h, the reaction was quenched by the addition of a
solution of methanol/phosphoric acid (9:1 ) v/v, 40 µL). The
reaction mixture was filtered. The filtrate was concentrated
and poured into a large amount of n-hexane to precipitate the
polymer. Spectral data of the polymer obtained in run 2 in
1
Table 1 are as follows. H NMR (300 MHz, CDCl3): δ 7.26-
6.21 (m, 9H, -C6H4- and -C6H5), 4.41 (brs, 2H, -C6H4OCH2-
), 4.30 (brs, 2H, COOCH2), 4.11 (brs, 2H, COOCH2), 3.40 (brs,
2H, OCH2C), 2.17-1.08 (m, 8H, -CH2CHAr- and -CH2CH3),
0.85 ppm (brs, 3H, -CH2CH3). 13C NMR (75 MHz, CDCl3): δ
148.5, 144.8, 134.8, 127.6, 73.4, 72.8, 68.3, 40.4, 35.5, 32.2, 23.4,
7.5 ppm. IR (KBr): ν (cm-1) ) 3084, 3058, 3026, 2970, 2924,
2861, 1758, 1602, 1513, 1494, 1472, 1453, 1406, 1385, 1251,
1177, 1115, 1019, 910, 821, 765, 701.
carried out with 1 mol % potassium tert-butoxide
(t-BuOK) in toluene with an initial monomer concentra-
tion of 1 M at 0 °C for 24 h (Scheme 4) to obtain
polycarbonate [poly(St6CC)] with Mn 14 000 in 80%
yield. The structure of poly(St6CC) was determined by
1H NMR, 13C NMR, and IR spectroscopy. Figure 1
depicts the 1H and 13C NMR spectra of St6CC and poly-
(St6CC). The 1H NMR spectrum of poly(St6CC) (Figure
1B) showed three signals assignable to the vinylic
protons of styrene moiety at 5.21, 5.71, and 6.67 ppm.
The 13C NMR spectrum of poly(St6CC) (Figure 1D)
showed two signals assignable to the vinylic carbon
atoms at 113.7 and 136.9 ppm. It was confirmed that
St6CC selectively underwent anionic ring-opening
polymerization at the 6CC moiety without the polym-
erization of the styrene moiety.
Results and Discussion
Monomer Synthesis. Scheme 3 illustrates the syn-
thetic routes of St6CC, the six-membered cyclic carbon-
ate having a styrene moiety. It was synthesized by the
reaction of ethyl chloroformate with the diol 2, which
was prepared by acetalization of trimethylolpropane
with acetone, etherification of 1 with p-chloromethyl-
styrene, and subsequent alcoholysis catalyzed with HCl.
Anionic Ring-Opening Polymerization of St6CC.
Anionic ring-opening polymerization of St6CC was

Macromolecules, Vol. 38, No. 19, 2005
Six-Membered Cyclic Carbonate 7947
Figure 1. 1H NMR spectra (solvent; CDCl3, 300 MHz) of (A) St6CC and (B) poly(St6CC) obtained in the polymerization with
t-BuOK (1 mol %) as an initiator at 0 °C for 24 h; 13C NMR spectra (solvent; CDCl3, 75 MHz) of (C) St6CC and (D) poly(St6CC)
obtained in the polymerization with t-BuOK (1 mol %) as an initiator at 0 °C for 24 h.
Scheme 4
Figure 2. Time-conversion relationships in the anionic ring-
opening polymerization of St6CC with t-BuOK (1 mol %) in
Equilibrium behavior was examined in the anionic
ring-opening polymerization of St6CC. Figure 2 depicts
the time-conversion relationships in the anionic ring-
opening polymerization of St6CC at 20 °C with the
initial monomer concentration of 0.1, 0.3, and 0.6 M. It
was confirmed that the St6CC conversion reached a
constant after 1 h in every case, whose value decreased
according to the initial monomer concentration ([M]0).
The equilibrium monomer concentrations ([M]e) were
estimated as 0.08 M ([M]0 ) 0.1 M), 0.14 M ([M]0 ) 0.3
M), and 0.15 M ([M]0 ) 0.6 M), respectively. After the
St6CC conversion reached a constant, the monomer was
regenerated by the addition of THF to dilute the
monomer concentration from 0.6 to 0.1 M. These results
THF with the initial monomer concentration of 0.1, 0.3, and
0.6 M at 20 °C.
support strongly that there is an equilibrium between
poly(St6CC) and St6CC.
Figure 3 depicts the time-conversion relationships
in the anionic ring-opening polymerization of St6CC
with the initial monomer concentration of 0.3 M at 0,
20, and 40 °C. The conversions of St6CC reached a
constant after 1 h in every case. It was confirmed that
the monomer conversion decreased with raising the
polymerization temperature, as typically observed in
equilibrium polymerization. Dainton’s equation can be
applied to this type of equilibrium polymerization,

7948 Miyagawa et al.
Macromolecules, Vol. 38, No. 19, 2005
Figure 3. Time-conversion relationships in the anionic ring-
opening polymerization of St6CC with t-BuOK (1 mol %) in
THF with the initial monomer concentration of 0.3 M at 0,
20, and 40 °C.
Figure 5. SEC profiles before and after the depolymerization
of poly(St6CC) (Mn ) 17 000, Mw/Mn ) 1.59). The depolymer-
ization was carried out with t-BuOK (5 mol % vs polymer
repeating unit) as a catalyst in THF (the initial reagent
concentration ) 0.1 M per polymer repeating unit) at 20 °C
for 24 h.
Figure 4. ln [M]e-1/T relationship in the anionic ring-opening
polymerization of St6CC with t-BuOK (1 mol %) in THF for
24 h.
where T, [M]e, ∆HSS, and ∆SSS denote the polymeriza-
tion temperature, monomer concentration at equilibri-
um, standard enthalpy, and standard entropy change
for the polymerization of cyclic carbonate in a solution,
respectively (eq 1).10
Figure 6. Time courses of the formation of St6CC and Mn of
the remaining polymer in the depolymerization of poly(St6CC)
with t-BuOK (5 mol % vs polymer repeating unit) as a catalyst
in THF (the initial reagent concentration ) 0.1 M per polymer
repeating unit) at 20 °C.
ln [M]e ) ∆HSS/RT - ∆SSS/R
(1)
Scheme 5
Figure 4 replots the data in Figure 3 in conjunction with
the logarithm of [M]e vs the reciprocal of the polymer-
ization temperature (1/T). The liner relationships clearly
indicate that the polymerization of St6CC obeys Dain-
ton’s equation, confirming the equilibrium character of
the polymerization. Thermodynamics parameters cal-
culated from the plots were ∆HSS ) -4.99 kcal/mol,
∆SSS ) -12.76 cal/(mol K), and ∆GSS ) -1.25 kcal/mol
(at 20 °C).
Depolymerization of Poly(St6CC). We next exam-
ined the depolymerization of poly(St6CC) with t-BuOK
(5 mol % vs polymer repeating unit) as a catalyst in THF
(reagent concentration ) 0.1 M per polymer repeating
unit) at 20 °C for 24 h. The starting monomer was
recovered in 60% yield (Scheme 5). The original polymer
was completely consumed, producing an oligomer along
with the monomer, as shown in the SEC profiles before
and after depolymerization (Figure 5). Figure 6 shows
the time courses of St6CC formation and Mn of the
remaining polymer in the depolymerization of poly-
(St6CC). The anionic depolymerization of poly(St6CC)
underwent rapidly to form St6CC, and the formation
reached a constant after 1 h. The Mn of the polymer
decreased ≈10% of the initial one for 30 min.
Radical Cross-Linking of Poly(St6CC). Radical
cross-linking of poly(St6CC) was carried out in the
absence and presence of styrene with BPO (1 mol %) as
an initiator in DMF at 80 °C for 3 h to afford the solvent-
insoluble cross-linked polymers in 56-85% yields
(Scheme 6 and Table 1). The compositions of St6CC and

Macromolecules, Vol. 38, No. 19, 2005
Six-Membered Cyclic Carbonate 7949
Table 2. De-Cross-Linking of the Cross-Linked Polymera
Scheme 6
THF-soluble part obtained by
cross-linked
polymer
the de-cross-linking the
cross-linked polymer
run composition ratiob (St6CC: St)
yield (%)
Mn (Mw/Mn)c
1
2
3
4
5
100:0
50:50
37:63
22:78
16:84
23
14
34
50
80
800 (1.10)
1700 (1.97)
5100 (1.58)
14000 (2.43)
11000 (3.19)
a Conditions: initiator t-BuOK (10 mol %), solvent THF (0.1 M:
based on repeating unit of the polymer), 50 °C, 24 h. b Estimated
by elemental analysis. c Estimated by SEC based on polystyrene
standards, eluent THF.
during radical cross-linking process, along with residual
of non-depolymerized 6CC unit, although the amount
should be small.
In summary, we could demonstrate a novel cross-
linking-de-cross-linking system based on the anionic
depolymerization of a novel cyclic carbonate with a
styrene moiety, St6CC. We believe that our approach
will develop a new field of polymer recycling method for
thermosetting resins as well as thermoplastics.
References and Notes
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mined by elementary analysis. There values were in
good agreement with the feed ratios, except for the case
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Anionic De-Cross-Linking of the Cross-Linked
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