Synthesis of refractive star-shaped polysulfide by anionic polymerization of phenoxy propylene sulfide using an initiating system consisting of trifunctional thiol derived from five-membered cyclic dithiocarbonate and amine

Article abstract of DOI:10.1002/pola.23742

Star-shaped poly(phenoxy propylene sulfide) [poly (PPS)] were synthesized by anionic polymerization using a trifunctional initiator (I₁) derived from a trifunctional five-membered cyclic dithiocarbonate and benzyl amine. Conditions for the anio

Full text of DOI:10.1002/pola.23742

Synthesis of Refractive Star-Shaped Polysulfide by Anionic
Polymerization of Phenoxy Propylene Sulfide Using an Initiating System
Consisting of Trifunctional Thiol Derived from Five-Membered Cyclic
Dithiocarbonate and Amine
MITSUHIRO HIRATA,1,2 BUNGO OCHIAI,2 TAKESHI ENDO3
1Yamagata Research Institute of Technology, 2-2-1 Matsuei, Yamagata, Yamagata 990-2473, Japan
2Department of Material Science and Energy Engineering, Graduate School of Science and Engineering, Yamagata University,
4-13-16 Jonan, Yonezawa, Yamagata 992-8510, Japan
3Molecular Engineering Institute, Kinki University, 11-6 Kayanomori, Iizuka, Fukuoka 814-0193, Japan
Received 12 May 2009; accepted 11 September 2009
DOI: 10.1002/pola.23742
Published online in Wiley InterScience (www.interscience.wiley.com).
ABSTRACT: Star-shaped poly(phenoxy propylene sulfide) [poly
(PPS)] were synthesized by anionic polymerization using a tri-
functional initiator (I1) derived from a trifunctional five-mem-
bered cyclic dithiocarbonate and benzyl amine. Conditions for
the anionic polymerization of PPS were optimized to obtain
polymers with desired Mns and narrow Mw/Mns. The best cata-
lyst and solvent were DBU and DMF, respectively. The star-
shaped structure of the resulting star poly(PPS) was supported
by SEC analysis. The refractive indexes (nD) of the star poly
C
V
(PPS) were relatively high (>1.64).
2009 Wiley Periodicals,
Inc. J Polym Sci Part A: Polym Chem 48: 525–531, 2010
KEYWORDS: a five-membered cyclic dithiocarbonate; anionic
polymerization; refractive index; star polymer; thiirane
INTRODUCTION Sulfur-containing polymers are applied for
optic,1,2 metal-scavening,3,4 and adhesive5,6 materials owing
to the high atomic refractivity, the metal complexing ability,
and the high reactivity. Specifically, the application to optics
is very important, and some sulfur-containing polymers have
been applied for precise lithography.7,8 Controlled molecular
size is effective to attain high resolution pattern.9,10
Among them, we preliminary reported a synthesis of star
poly(propylene sulfide)s bearing variable cores and termini
using trifunctional initiators derived from a trifunctional
five-membered cyclic dithiocarbonate with amines.21 The
variety of the cores of the star polymers depends on variable
amines that react with the five-membered cyclic dithiocar-
bonate to give mercapto-thiourethanes by the selective scis-
sion of the SA(C¼¼S) bond.24 It should also be mentioned
that deterioration of the thiols by oxidative coupling, which
is a severe problem for typical multiple thiols, can be
avoided owing to the fast and facile preparation.22
Thiiranes, especially propylene sulfide, are well-investigated
monomers for sulfur-containing polymers with controllable
molecular weights. Examples of the initiating systems for liv-
ing or controlled polymerization of propylene sulfide are car-
banions,11,12 thiolates,13,14 N-substituted porphyrin com-
plexes,15 and thioacetates.16,17 The basicity of the active
species must be lower enough than the nucleophilicity to
attain controlled polymerization, because too high basicity
often leads to sulfur extraction in the initiation step and oxi-
dative coupling of the terminal thiol end groups by forma-
tion of disulfides.18 The thiol/thiolate initiating system with
1,8-diazabicyclo[5.4.0]-undec-7-ene (DBU), in which the
thiol-thiolate equilibrium exists, is one of the most useful
systems, because the polymerization completes rapidly (e.g.,
<5 min) under mild conditions and affords polymers with
controlled molecular weights.19 The control in this polymer-
ization system is good enough for synthesis of star polymers
with controlled molecular weights.20–23
Star-shaped sulfur-containing polymers are expectable as
high-performance optical materials. For example, refractive
indexes of star polysulfides are higher than those of linear
ones due to their compact structures and high segment den-
sities.25–27 Recently, Kudo et al. reported that the nD values
of star polysulfides with calixarenes in the core structure
increase with increasing the number of arms, the length of
arms, and the sulfur content, and with decreasing the size of
the core structure.27 Accordingly, we also investigated the re-
fractive character of our star-shaped polymer with those of
the analogous linear polymer. In addition, we investigated
the solution properties of the star poly(PPS) by SEC with on-
line light scattering and viscometry, based on the fact that
star polymers bearing lower arm-numbers behave as
Correspondence to: T. Endo (E-mail: tendo@me-henkel.fuk.kindai.ac.jp)
C
V
Journal of Polymer Science: Part A: Polymer Chemistry, Vol. 48, 525–531 (2010) 2009 Wiley Periodicals, Inc.
SYNTHESIS OF REFRACTIVE STAR-SHAPED POLYSULFIDE, HIRATA, OCHIAI, AND ENDO
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JOURNAL OF POLYMER SCIENCE: PART A: POLYMER CHEMISTRY DOI 10.1002/POLA
SCHEME 1 Anionic polymerization of PPS with I1 or I2 in the presence of DBU.
Gaussian chain,28,29 owing to the fortunate canceling of
ignored excluded-volume effects by the pronounced excluded
volumes in good solvents.30 For this study, the conditions for
this star polymer synthesis using the trithiol/amine initiating
thioate) (I1) was prepared by the reaction of 1,3,5-tris[(2-
thioxo-1,3-oxathiolan-5-yl)methyl]-1,3,5-triazinane-2,4,6-tri-
one with benzylamine.21 O-Mercapto-3-phenoxypropan-2-yl
benzylcarbamothioate (I2) was prepared by the reaction of
5-phenoxymethyl-1,3-oxathiolane-2-thione with benzyl-
amine.24 Phenoxy propylene sulfide (PPS) was prepared by
the reaction of 2-(phenoxymethyl)oxirane with thiourea.31
system based on
optimized.
a trifunctional dithiocarbonate were
EXPERIMENTAL
Characterization
Materials
Size exclusion chromatograph (SEC) analysis of polymers
were performed using THF at a flow rate of 1.0 mL/min at
40 ꢀC on a system consisting of an Asahi Techneion pump
unit AT-2002, a Viscotek triple detector model 302 [refrac-
tive index (RI), right angle laser light scattering (RALLS),
and differential pressure (DP)] equipped with polystyrene
gel tandem columns (TSKgel G1000HHR, G2500HHR and
G4000HHR, Tosoh) after calibration with standard polysty-
rene samples (Tosoh). Gas chromatography (GC) analysis
was performed at 50–200 C (heating rate: 10 C/min) using
n-tridecane as an internal standard on a Hewlett–Packard
Model HP6890 system equipped with a FID detector and a
poly(dimethyl siloxane) column (DB-5 ms, Agilent technolo-
gies). 1H NMR (620 MHz) and 13C NMR (155 MHz) spectra
of the polymers were measured in CDCl3 containing 0.03
vol % of tetramethylsilane (Acros Organics, 99.8%D) on a
JEOL JNM-A620 spectrometer. Infrared spectra of polymers
were measured on a Perkin–Elmer SYSTEM2000 FTIR spec-
trometer. The ellipsometry analysis of polymer films
was conducted using a ULVAC esm-1 ellipsometer using
0.6328 lm He–Ne laser at 25 ꢀC. The films were prepared
by spin coating at 3000 rpm for 30 s of THF solutions (20
Tetrahydrofran (THF, Kanto Chemical, 99.5%) was refluxed
over lithium aluminum hydride (Kanto Chemical, 92.0%) and
distilled under a nitrogen atmosphere. Triethylamine (Et3N,
Wako Pure Chemical, 99%), toluene (Kanto Chemical, 99.5%)
were dried over calcium hydride (CaH2, Kanto Chemical,
95.0%) and distilled under a nitrogen atmosphere. N,N-
Dimethylformamide (DMF, Kanto, Chemical, 99.5%), dimethyl
sulfoxide (DMSO, Kanto Chemical, 99.0%), benzylamine
(Kanto Chemical, 98.0%), 1-(chloromethyl)naphthalene (To-
kyo Chemical Industry, 95%), N-methyl-2-pyrrolidinone
(NMP, Kanto Chemical, 99.0%), 4-methylimidazole (Acros
organics, 98%), and 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU,
Tokyo Chemical Industry, 98.0%) were dried over CaH2 and
distilled under reduced pressure. 1,4-Diazabicyclo[2.2.2]
octane (DABCO, Tokyo Chemical Industry, 98.0%) was
recrystallized from ethanol. 4-Dimethylaminopyridine (DMAP,
Kanto Chemical, 99%) was recrystallized from toluene.
ꢀ
ꢀ
Initiators and Monomer
The following materials were prepared by the reported
procedures.
O,O0,O00-3,30,300-(2,4,6-Trioxo-1,3,5-triazinane-1,
3,5-triyl)tris(1-mercaptopropane-3,2-diyl)tris(benzylcarbamo-
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ARTICLE
TABLE 1 Anionic Polymerization of PPS with I1 in Various Solventsa
Mn
Run
Solvent
Conv. (%)b
Yield (%)c
Calc.d
NMRe
RALLS (Mw/Mn)f
1
2
3
4
5
a
DMF
>99
>99
>99
15
74
99
87
15
3
12,700
12,900
10,200
3,000
14,600
13,200
13,400
4,400
16,800 (1.07)
14,500 (1.24)
14,300 (1.38)
4,200 (1.52)
3,200 (1.28)
NMP
DMSOg
THF
Toluene
14
2,800
2,900
d
e
f
Conditions; [I1]/[DBU] ¼ 20, PPS ¼ 7.0 mmol, solvent ¼ 2.0 mL, 0 ꢀC,
Mn,calc ¼ 844 þ 166 ꢂ [PPS]0/[SH]0 ꢂ conv. þ 142 ꢂ 3.
Determined by 1H NMR spectroscopy.
N2.
b
Determined by GC analysis.
Methanol insoluble parts.
Estimated by SEC with a triple detector (THF).
Polymerization temperature ¼ rt.
c
g
g/L) of the polymers on silicon-wafers. The refractive
indexes (nD) were determined by the rough thickness data
obtained with Otsuka Electronics optical thickness mea-
surement instrument IMUC-7000, and calibrated with sili-
con wafer. Differential scanning calorimetry (DSC) was mea-
sured from –50 ꢀC to 150 ꢀC at a scanning rate of 10 ꢀC/
min under a nitrogen atmosphere by a Seiko Instruments
DSC6200 instrument. Glass-transition temperatures (Tgs)
were determined in the second heating scans.
(CDCl3, d): 2.60ꢁ2.80 (br, 6H, ACH CH2SA), 2.82ꢁ3.26 (br, 3
ꢂ 57H, ACH2CHSA, ACH2CHSA), 3.86ꢁ4.26 (br, 6H and 2 ꢂ
57H, ANHCH2Ar and ACH2OArA), 4.27ꢁ4.34 (s, 8H,
ACH2Naph), 4.51ꢁ4.71 (br, 6H, ACONCH2CHA), 5.70ꢁ5.99
(br, 3H, ACH2CHOA), 6.71ꢁ6.96, 7.08ꢁ7.27, 7.28ꢁ7.50,
7.68ꢁ7.72, 7.77ꢁ7.81, 8.10ꢁ8.17 (br, Ar) ppm. 13C NMR
(CDCl3, d): 34.34ꢁ34.53 (ACHCH2SA, ACH2CHSA, ACH2
CHSA), 45.58ꢁ46.93 (ACONCH2CHA, ACH2 OAr, ANHCH2Ar,
ASCH2Naph), 69.70ꢁ70.10 (ACONCH2CHA), 113.92ꢁ114.88,
121.21ꢁ121.26, 124.17ꢁ134.16 (Ar), 158.43ꢁ158,47
(AOC¼¼ SNHA), 189.44ꢁ189.42 (ACONA) ppm.
Anionic Polymerization of PPS
The initiator (I1) (84.4 mg, 0.100 mmol) and DMF (1.0 mL)
were added to a flask purged with nitrogen. After degassed
and purged with nitrogen, DBU in DMF (6.7 mM, 1.0 mL)
was injected and degassed again. After purged with nitrogen,
PPS (0.756 g, 4.55 mmol) was added at 0 ꢀC. The mixture
was stirred for 30 min at 0 ꢀC. Then, Et3N (0.10 mL,
0.72 mmol) and 1-(chloromethyl)naphthalene (0.10 mL,
0.67 mmol) were added, and the mixture was stirred over-
night with warming up to room temperature. The conversion
of the monomer was determined by GC analysis of the meth-
anol solution of the crude mixture. The polymer was isolated
as a colorless viscous product by precipitation with methanol
and drying under reduced pressure (82%, 0.88 g). IR (KBr):
3440 (NH), 3040 (aromatic), 2926ꢁ2994 (CH), 1695 and
RESULTS AND DISCUSSION
Anionic Polymerization of PPS with
Trifunctional Initiator (I1)
PPS was polymerized using a trifunctional initiator (I1) in
the presence of DBU in various solvents at 0 ꢀC for 30 min
(Scheme 1, Table 1). The propagating ends were quenched
by 1-(chloromethyl)naphthalene. The polymerization of PPS
proceeded quantitatively in DMF, NMP, and DMSO, and the
polymers were obtained in high yields. The Mns calculated
1
by H NMR (Mn,NMR) and SEC (Mn,RALLS) agreed with the the-
oretical values (Mn,calc). Among them, the polymer obtained
in DMF had the narrowest Mw/Mn, supporting the controlled
polymerization. Contrary to this, the polymerizations in THF
1599 (C¼¼S), 1241 (CAOAC), 753 (CASAC) cmꢁ1
.
1H NMR
TABLE 2 Anionic Polymerization of PPS with I1 in the Presence of Various Catalystsa
Mn
Run
Catalyst
[I1]/[catalyst]
Conv. (%)b
Yield (%)c
Calc.d
NMRe
RALLS (Mw/Mn)f
1
2
3
4
5
6
7
a
DBU
20
20
20
20
20
1
>99
95
74
63
26
27
28
91
67
12,700
12,500
6,400
14,600
13,600
7,100
16,800 (1.07)
15,000 (1.27)
7,800 (1.57)
7,000 (1.63)
6,300 (1.63)
16,600 (2.19)
16,200 (1.30)
DABCO
4-Methyl imidazol
DMAP
44
27
4,500
5,400
Et3N
34
5,220
6,400
DBU
>99
>99
12,900
13,100
21,000
19,500
DBU
2
d
e
f
Conditions; PPS ¼ 7.0 mmol, DMF ¼ 2.0 mL, 0 ꢀC, N2, 30 min.
Determined by GC analysis.
Mn,calc ¼ 844 þ 166 ꢂ [PPS]0/[SH]0 ꢂ conv. þ 142 ꢂ 3.
Determined by 1H NMR spectroscopy.
b
c
Methanol insoluble parts.
Estimated by SEC with a triple detector (THF).
SYNTHESIS OF REFRACTIVE STAR-SHAPED POLYSULFIDE, HIRATA, OCHIAI, AND ENDO
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JOURNAL OF POLYMER SCIENCE: PART A: POLYMER CHEMISTRY DOI 10.1002/POLA
and Mw/Mn. The SEC profiles changed from multidispersed
to monodispersed as increasing the [I1]0/[DBU]0 value (Fig.
1). The higher amounts of DBU would cause the oxidative
coupling of the thiolate propagating ends to produce high
molecular weight products and undesired initiations from
other species (e.g., hydrogen-abstracted PPS) to produce low
molecular weight products.19,20
The polymerization of PPS with the I1/DBU initiating system
was conducted in DMF at 0 ꢀC for 30 min under various
feed ratios of PPS/I1 (Table 3). In every case, PPS was con-
sumed quantitatively, and the purified polymers were
obtained in good yields. Figure 2 shows the relationships
between Mn and [PPS]0/[I1]0. Both the number average mo-
lecular weights estimated by SEC (MnSEC) and NMR (MnNMR
)
increased linearly with [PPS]0/[I1]0, and agreed well with
the theoretical values. The Mw/Mn values were constantly
narrow. These results support the controlled nature of this
polymerization. For comparison, the polymerization using an
analogous monofunctional initiator (I2) was also conducted,
and it also proceeded in a controlled fashion (Scheme 1,
Table 4).
Solution Properties of Star Poly(PPS)
The solution properties of the polymers were analyzed by SEC
equipped with RI, DP, and RALLS detectors in THF, which is a
good solvent for poly (PPS).28,29 Figure 3 shows the plots of the
logarithms of intrinsic viscosity (g) toward log Mw of the star
and linear poly(PPS). Three samples each with close molecular
weights were employed for the comparison. The log g values of
the star poly(PPS) were lower than those of the linear poly
(PPS), supporting the smaller sizes of the star polymer.31,32 The
contraction factor g as the ratio of mean-squared radii of gyra-
tion of the star and linear polymer having the same molecular
weight, on the basis of the assumption that polymer behave as
Gaussian chains,28,29,30,33 is expressed by the eq 1, in which the
f value means the number of arms.34 The g factor of a star poly-
mer with three arms is 0.778.
FIGURE 1 SEC profiles [RI detector, THF of the star poly(PPS)
(Mncalc ¼ 12,700–13,100)] obtained with various [I1]0/[DBU]0; (a)
1/1, (b) 2/1, (c) 20/1.
and toluene were slower, probably due to the low polarities,
which make the equilibrium to thiolate unfavorable.
Various catalysts were examined for the polymerization of
PPS using I1 in DMF at 0 ꢀC for 30 min (Table 2). DABCO
was also a good catalyst, although the Mw/Mn became
slightly broader. However, 4-methyl imidazol, Et3N, and
DMAP were not probably due to the lower basicities. The
feed ratio of I1 to DBU ([I1]0/[DBU]0) also affected both Mn
g ¼ ð3f ꢁ 2Þ=f 2
(1)
TABLE 3 Anionic Polymerization of PPS with I1 in the Presence of DBUa
Mn
Run
PPS/I1
Yield (%)b
Calc.c
NMRd
RALLS (Mw/Mn)e
1
2
3
4
5
6
a
38
57
81
82
70
80
81
82
7,600
10,700
16,500
25,500
36,100
39,300
8,500
10,700
17,000
27,000
33,800
36,000
7,700 (1.22)
9,800 (1.19)
17,700 (1.15)
23,100 (1.22)
34,700 (1.16)
41,900 (1.13)
92
146
210
229
d
e
Conditions; [I1]/[DBU] ¼ 20, [PPS]0 ¼ 2.33 M, 0 ꢀC, N2, 30 min.
Methanol insoluble parts.
Determined by 1H NMR spectroscopy.
Estimated by SEC with a triple detector (THF).
b
c
Mn,calc ¼ 844 þ 166 ꢂ [PPS]0/[SH]0 ꢂ þ 142 ꢂ 3.
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ARTICLE
(Mw,star ¼ 28,300 and Mw,linear ¼ 28,300). From these values,
the e values were calculated as 0.72, 0.61 and 0.62, respec-
tively. The e values higher than 0.50 suppose the underesti-
mated g value, namely the arm-number (f value in eq 1).
The f values for the three sets of the linear and star poly-
mers meeting the eq 3 with e ¼ 0.5 are 3.49, 3.23, and 3.25,
respectively. This calculation suggests that the three thiour-
ethane groups in the core structure behaved as short chains.
Figure 4 shows the plots of the logarithms of radii of gyra-
tion (Rg) toward log Mw of the star and linear poly(PPS). The
Rg values were determined by the Ptitsyn-Eizner eq 4 from
the intrinsic viscosity and the molecular weight determined
by RALLS, in which a is Mark-Houwink exponent.36
ꢀ ꢁ
ꢀ
ꢁ
0:5
0:3
1
Mn;RALLS½gꢃ
Rg ¼
6
U
U ¼ 2:55 ꢂ 1021ð1 ꢁ 2:63j þ 2:86j2Þ
(4)
2a ꢁ 1
j ¼
FIGURE 2 Relationship between Mn and [PPS]/[I1] feed ratio for
the polymerization of PPS in the presence of DBU ([I1]/[DBU] ¼
20). ~: Mn (1H NMR), *: Mn (RALLS), ꢄꢄꢄ: Mn (theoretical value),
ꢂ: Mw/Mn.
3
We employed the three sets of the polymers employed in
Figure 3 as well The log Rg values of the star poly(PPS)
were also lower than those of the linear poly(PPS), further
supporting the smaller sizes of the star polymer.
The contraction factors g0 as the ratio of intrinsic viscosities
of the star and linear polymers having same molecular
weight is defined by the eq 2.
Refractive Indexes (nD) and Thermal Properties
of Star Poly(PPS)
The refractive indexes (nD) of the star and linear poly(PPS)
were measured by ellipsometry. Figure 5 shows the relation-
ships between nD and Mn,NMR of the star and linear poly
(PPS). The nD values of star poly(PPS) (nD,star) were slightly
higher than those of linear poly(PPS) (nD,linear), although the
nD,star values gradually decreased as the increment of Mn,NMR
to approach the nD,linear value. Typical nDs are almost con-
stant regardless of molecular weight except for oligomer
region.37,38 A plausible reason is the higher density of the
arms around the core structure, whose effect decrease as the
increase of the arm lengths.39
g;star
g0 ¼
(2)
g;linear
The relationship between the g and g0 values are expressed
by the eq 3. The equation with e ¼ 0.5 is suitable to the
polymers obeying the Zimm-Kilb assumption,34 but the
appropriate values of the exponent for others are still dis-
cussed.30,35
g0 ¼ ge
(3)
The thermal behaviors of the star and linear poly(PPS) were
The average g0 values of the three sets of the star and linear
polymers were 0.834 (Mw,star ¼ 9300 and Mw,linear ¼ 6400),
0.859 (Mw,star ¼ 11,700 and Mw,linear ¼ 12,100), and 0.856
evaluated with DSC. Figure 6 shows the relationships
between Tg and Mw of star and linear poly(PPS). The Tg val-
ues of the linear poly(PPS) increased as the increase of Mw,
TABLE 4 Anionic Polymerization of PPS with I2 in the Presence of DBUa
Mn
Run
PPS/I2
Yield (%)b
Calc.c
NMRd
RALLS (Mw/Mn)e
1
2
3
4
5
a
34
57
76
75
83
76
70
6,100
9,900
5,500
11,900
17,100
22,200
30,700
5,700 (1.12)
10,400 (1.16)
24,300 (1.17)
27,800 (1.08)
30,400 (1.13)
120
148
179
20,400
25,000
30,200
d
e
Conditions; [I2]/[DBU] ¼ 20, PPS ¼ 2.33 M, 0 ꢀC, N2, 30 min.
Methanol insoluble parts.
Determined by 1H NMR spectroscopy.
b
c
Estimated by SEC with a triple detector (THF).
Mn,calc ¼ 333 þ 166 ꢂ [PPS]0/[SH]0 ꢂ þ 142.
SYNTHESIS OF REFRACTIVE STAR-SHAPED POLYSULFIDE, HIRATA, OCHIAI, AND ENDO
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JOURNAL OF POLYMER SCIENCE: PART A: POLYMER CHEMISTRY DOI 10.1002/POLA
FIGURE 3 Relationships between the logarithm of intrinsic viscos-
ity and the logarithm of weight average molecular weight of star and
linear poly(PPS) in THF. (a) Mw,star ¼ 9300, (a0) Mw,linear ¼ 6400,
(b) Mw,star ¼ 11,700, (b0) Mw,linear ¼ 12,100, (c) Mw,star ¼ 28,300, (c0)
Mw,linear ¼ 28,300. (A), (B), and (C) are g0. The g0s were calculated
from (a) and (a0), (b) and (b0), and (c) and (c0), respectively.
FIGURE 5 Relationships between number average molecular
weight (Mn) and refractive indexes (nD) of the star and linear
poly(PPS). l: star poly(PPS), *: linear poly(PPS).
mers have lower Tg than linear polymers.40 The slightly
higher Tg of the star poly (PPS) at lower molecular weight
region can be ascrꢀibed the rigid core structure, supported by
the Tg of I1 (48.0 C). This effect decreased as the molecular
weight, and hence, the Tg values of the star and linear
and became constant as typical polymers. However, the rela-
tionship of the Tg of the star poly (PPS) differs from typical
ways. The Tg values are higher than those of the linear poly-
mers, and decreased to the Tg of linear polymers as the
increase of the molecular weight, although typical star poly-
FIGURE 4 Relationships between the logarithm of radii of gyra-
tion and the logarithm of weight average molecular weight of
star and linear poly(PPS) in THF. (a) Mw,star ¼ 9300, (a0) Mw,linear
FIGURE 6 Relationships between number average molecular
weight (Mw) and glass-transition temperatures (Tgs) of the star
and linear poly(PPS) determined by DSC (scanning rate: 10 ꢀC/
min, N2, second heating scan). l: star poly(PPS), *: linear
poly(PPS).
¼ 6400, (b) Mw,star ¼ 11,700, (b0) Mw,linear ¼ 12,100, (c) Mw,star
28,300, (c0) Mw,linear ¼ 28,300.
¼
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ARTICLE
15 Aida, T.; Kawaguchi, K.; Inoue, S. Macromolecules 1990, 23,
polymers became almost identical at the examined molecular
weight region.
3887–3892.
16 Kameyama, A.; Shimotsuma, K.; Nishikubo, T. Makromol
Chem Rapid Commun 1994, 15, 335–342.
CONCLUSIONS
17 Kameyama, A.; Shimotsuma, K.; Nishikubo, T. Polym J 1996, 28,
Conditions for synthesis of star poly(PPS) using trithiol/amine
system was optimized. DBU was the best catalyst, and low
amounts of DBU to the initiator was an important factor ([I1]0/
[DBU]0 > 20) for controlled polymerization. The solution prop-
erties of the star poly(PPS) analyzed by SEC supported the
smaller size originating from the star-shaped structure. Both
the refractive indexes and Tg values were higher than the anal-
ogous linear poly(PPS), owing to the higher density around the
core and the hard structure of the core unit. The advantages of
this star polymer synthesis are fast polymerization under mild
conditions, controllable core and terminal structures,21 and
high refractive indexes of the polymers. For this reason, an ex-
pectative application of this star polymer is reactive optical
materials, such as photo-resist materials with high refractivity
and resolution, by introducing curable groups.
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SYNTHESIS OF REFRACTIVE STAR-SHAPED POLYSULFIDE, HIRATA, OCHIAI, AND ENDO
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