Functionalized syndiotactic polystyrene polymers prepared by the combination of metallocene catalyst and borane comonomer

Article abstract of DOI:10.1021/ma012215e

This paper discusses an effective route in the functionalization of s-PS polymer that involves the direct copolymerization of styrene with a borane-containing styrenic monomer, i.e., 4-[B-(n-butylene)-9-BBN]styrene (B-styrene). The reactivity ratios of th

Full text of DOI:10.1021/ma012215e

Macromolecules 2002, 35, 3439-3447
3439
Functionalized Syndiotactic Polystyrene Polymers Prepared by the
Combination of Metallocene Catalyst and Borane Comonomer
J . Y. Don g, E. Ma n ia s, a n d T. C. Ch u n g*
Department of Materials Science and Engineering, The Pennsylvania State University,
University Park, Pennsylvania 16802
Received December 20, 2001; Revised Manuscript Received March 4, 2002
ABSTRACT: This paper discusses an effective route in the functionalization of s-PS polymer that involves
the direct copolymerization of styrene with a borane-containing styrenic monomer, i.e., 4-[B-(n-butylene)-
9-BBN]styrene (B-styrene). The reactivity ratios of the two comonomers are quite close, with r1 ) 0.9 for
styrene and r2 ) 1.2 for B-styrene in the Cp*Ti(OMe)3/MAO catalyst system. A broad composition range
of syndiotactic poly(styrene-co-B-styrene) copolymers has been prepared with narrow molecular weight
and composition distributions. The random copolymer structure was further evidenced by DSC and 13C
NMR analyses. With increasing B-styrene concentration, the copolymers show a systematic decrease in
glass transition temperature, melting point, crystallization temperature, and crystallinity. At above 8.4
mol % B-styrene content, the crystallinity of the copolymer completely disappears. In turn, the borane
groups in the copolymer are very versatile and can be quantitatively converted to other functional groups,
such as hydroxy and anhydride groups, or transformed to free radical initiators for in situ free radical
graft polymerization to prepare s-PS-g-PMMA graft copolymers.
Sch em e 1
In tr od u ction
One of the most important advances in metallocene
technology is the preparation of syndiotactic polystyrene
(s-PS)1 that exhibits high melting point (∼270 °C) and
a relatively high crystallization rate that is several
orders of magnitude2 faster than that in isotactic
polystyrene (i-PS). s-PS is a novel engineering plastic
made from an inexpensive commodity monomer.
Despite its unique properties, s-PS polymer also has
several drawbacks that pose serious concerns in many
commercial applications. Because of a high melting
point, the required melt processing temperature at >300
°C (near the polymer decomposition temperature) causes
a major problem in polymer processability. A modified
s-PS polymer with a slightly reduced melting point (to
about 250 °C) would be a very desirable material. In
addition, s-PS polymer has poor impact strength and
low surface energy, similar to traditional atactic poly-
styrene prepared by free radical and anionic processes.
So far, there are only a few reports discussing the
modification of s-PS polymer, including sulfonation3 and
bromination4 of s-PS and hydroxylated s-PS5 prepared
via poly(styrene-co-4-tert-butyldimethylsilyloxystyrene)
precursor. Recently, Xu and Chung also reported a new
method using dialkylborane containing a B-H group
as a chain transfer agent during metallocene-mediated
styrene polymerization to form borane-terminated syn-
diotactic polystyrene,6 which was further engaged in the
free radical chain extension with methyl methacrylate
(MMA) to form s-PS-b-PMMA diblock copolymers.
Several years ago, we developed a very useful method
to functionalize polyolefins, such as polyethylene (PE)
and polypropylene (PP), which involved direct copoly-
merization7 of R-olefin and borane-containing R-olefin
by Ziegler-Natta and metallocene catalysts. Because
of the excellent stability of borane moieties to catalysts
and the good solubility of trialkylborane in hydrocarbon
media, a broad range of borane-containing polyolefin
copolymers with uniform molecular structure were
prepared without sacrificing catalyst activity. In addi-
tion, the incorporated borane groups in the polyolefin
copolymers are very versatile and can be effectively
interconverted to various functional groups under mild
reaction conditions and also transferred to polymeric
radicals for graft reactions8 to prepare polyolefin graft
copolymers, such as PP-g-PMMA and PE-g-PMMA. We
extended this borane monomer approach to s-PS to
prepare functionalized s-PS polymers and s-PS graft
copolymers that not only contain desirable functional
groups but also have lower melting temperatures with
improved processability.
Resu lts a n d Discu ssion
Bor a n e-Con ta in in g Mon om er . As illustrated in
Scheme 1, a new borane-containing monomer of 4-[B-
(n-butylene)-9-BBN]styrene was prepared by a two-step
reaction. After completing a coupling reaction between
allylmagnesium chloride and vinyl benzyl chloride to
form 4-(3-butenyl)styrene, containing a styrenic olefin
and an R-olefin groups, this resulting asymmetrical
diene was selectively monohydroborated by 9-BBN at
the R-olefinic double bond in an anti-Markovnikov
manner.
Both reaction steps are very effective and produce
1
high yields. Figure 1 compares the H NMR spectra of
4-[B-(n-butylene)-9-BBN]styrene (B-styrene) and 4-(3-
butenyl)styrene. After hydroboration reaction by a sto-
ichiometric amount of 9-BBN, all the chemical shifts at
* To whom all correspondence should be addressed.
10.1021/ma012215e CCC: $22.00 © 2002 American Chemical Society
Published on Web 03/27/2002

3440 Dong et al.
Macromolecules, Vol. 35, No. 9, 2002
F igu r e 1. 1H NMR spectra of (a) 4-(3-butenyl)styrene and (b) 4-[B-(n-butylene)-9-BBN]styrene (solvent: d-chloroform).
Ta ble 1. Cop olym er iza tion of Styr en e (S) a n d 4-[B-(n -bu tylen e)-9-BBN]styr en e (B-S) w ith Syn d iosp ecific Tita n ocen e/
MAO Ca ta lystsa
B-S in feed
(mol %)
[S]
[B-S]
yield
(g)
catalyst
B-S content in
Mw × 104 Mn × 104
PDI
Mw/Mn
run no.
catalyst
(mol/L) (mol/L)
activityb copolymer (mol %)
(g/mol)
(g/mol)
A-1
A-2
A-3
A-4
A-5
A-6
A-7
A-8
A-9
B-1
C-1
Cp*Ti(OMe)3
Cp*Ti(OMe)3
Cp*Ti(OMe)3
Cp*Ti(OMe)3
Cp*Ti(OMe)3
Cp*Ti(OMe)3
Cp*Ti(OMe)3
Cp*Ti(OMe)3
Cp*Ti(OMe)3
CpTiCl3
0
1.73
1.73
1.73
1.73
1.59
2.14
2.04
1.13
0
0
3.48
4.44
4.66
5.13
5.36
6.73
6.04
2.98
1.91
3.52
2.98
67.0
85.1
88.3
96.2
106.3
97.3
86.7
66.7
87.3
78.2
66.2
0
20.3
21.5
20.7
15.5
14.4
12.7
9.8
7.0
8.0
8.3
6.7
6.3
5.5
5.2
2.8
2.9
2.7
2.5
2.3
2.3
2.3
2.0
2.0
0.63
1.76
2.59
5.38
7.16
12.2
24.3
100
0.011
0.031
0.046
0.091
0.165
0.284
0.363
0.730
0.091
0.091
1.0
2.1
3.0
6.1
8.4
16.7
32.2
100
6.7
5.4
5.3
6.10
6.10
1.41
1.41
Cp*TiCl3
a
b
Polymerization conditions: [cat] ) 100 µmol /L, Al/Ti ) 2000, temperature ) 50 °C, time ) 3 h, solvent ) 40 mL of toluene. In kg
of polymer/mol Ti‚h‚mol/L.
2.44-2.58, 5.05-5.22, and 5.88-6.10 ppm (correspond-
ing to the three type protons in -CH2-CHdCH2 group)
completely disappear. On the other hand, the chemical
shifts at 5.30-5.37, 5.80-5.88, and 6.75-6.95 ppm (for
the three methylene and methine protons in styrenic
olefin) are unchanged. The big difference in hydrobo-
ration reactivities between the two double bonds toward
9-BBN provides an effective route to the preparation of
B-styrene monomer (I) without forming an undesirable
dihydroborated product.
styrene (B-styrene) was carried out with conventional
half-sandwich metallocene catalysts, including Cp*Ti-
(OMe)3/MAO, Cp*TiCl3/MAO, and CpTiCl3/MAO com-
plexes1 that exhibit high syndiospecificity and good
catalyst activity in styrene polymerization. The result-
ing borane-containing copolymers, poly(styrene-co-4-[B-
(n-butylene)-9-BBN]styrene) (II), were completely soluble
in tetrachloroethane at elevated temperature (110 °C).
Some copolymers with high B-styrene comonomer con-
tents (>8.4 mol %) are soluble in toluene or THF at
ambient temperature. 11B NMR spectra of all copoly-
mers show a single chemical shift at 87 ppm (vs
Cop olym er iza tion of Styr en e w ith 4-[B-(n -bu tyl-
en e)-9-BBN]styr en e. As illustrated in Scheme 2, the
copolymerization of styrene and 4-[B-(n-butene)-9-BBN]-

Macromolecules, Vol. 35, No. 9, 2002
Syndiotactic Polystyrene 3441
Sch em e 2
F igu r e 2. Fineman and Ross plots for copolymerization of
styrene/B-styrene and the least-squares best-fit line (f )
[styrene]/[B-styrene] in feed and F ) d[styrene]/d[B-styrene]
mole ratio in polymer).
ing stable hydroxy-containing s-PS copolymers (s-PS-
OH) for analysis. As will be discussed later, all of the
transformation reactions were quantitative even in
heterogeneous conditions. Table 1 summarizes the
results of styrene/4-[B-(n-butylene)-9-BBN]styrene co-
polymerization reactions under various reaction condi-
tions.
In general, both monomers show similar reactivity.
The para-substituted borane group exhibits almost no
effect on the monomer incorporation, which also indi-
cates the unique advantages of trialkylborane moiety
with excellent stability to the transition-metal catalysts
and good solubility in hydrocarbon reaction media. The
copolymer composition is basically controlled by the
comonomer feed ratio, and we have prepared a whole
composition range of styrene/B-styrene copolymers. In
BF3.OEt2) corresponding to the pendant alky-9-BBN
moieties.
Because of the oxygen sensitivity of the borane
moiety, the borane-containing s-PS copolymers were
usually oxidized by NaOH/H2O2 to form the correspond-
F igu r e 3. GPC curves of (a) s-PS homopolymer (A-1) and several styrene/B-styrene copolymers, including (b) A-2, (c) A-4, (d)
A-5, and (e) A-7 in Table 1 (solvent: trichlorobenzene; temperature: 135 °C).

3442 Dong et al.
Macromolecules, Vol. 35, No. 9, 2002
F igu r e 4. 1H NMR spectra of (a) s-PS and three s-PS-OH copolymers, containing (b) 2.1, (c) 8.4, and (d) 16.7 mol % of OH
groups (solvent: C2D2Cl4; temperature: 110 °C).
general, the catalyst efficiency in the copolymerization
reaction increases somewhat compared to that of ho-
mopolymerization. The better diffusibility of monomers
in the copolymer structures (due to lower crystallinity)
may help provide better polymerization conditions.
The best way to investigate a copolymerization is to
measure the reactivity ratio of the comonomers. A series
of experiments were carried out by varying the monomer
feed ratio and comparing the resulting polymer compo-
sitions at low conversion (<10%). The reactivity ratios
of styrene (r1 ) k11/k12) and B-styrene (r2 ) k22/k21) are
estimated by the Fineman and Ross method.9 Figure 2
shows the plot (1 - F)/f vs F/f 2 and the least-squares
best-fit line, where f ) [styrene]/[B-styrene] in feed and
F ) d[styrene]/d[B-styrene] mole ratio in polymer. The
slope is r2, and the extrapolation to F/f 2 ) 0 gives -r1.
We obtain r1 ) 0.9, r2 ) 1.2, and r1r2 ) 1.08 for styrene/
B-styrene copolymerization by a Cp*Ti(OMe)3/MAO
catalyst.
With r1 and r2 near 1, this styrene/B-styrene copo-
lymerization reaction is close to an ideal case. The
copolymer obtained shall have a narrow composition

Macromolecules, Vol. 35, No. 9, 2002
Syndiotactic Polystyrene 3443
F igu r e 5. 13C NMR spectra of (a) s-PS and three s-PS-OH copolymers, containing (b) 2.1, (c) 8.4, and (d) 16.7 mol % of OH
groups (solvent: C2D2Cl4; temperature: 110 °C).
distribution, and its composition shall be proportional
to the monomer feed ratio, which are consistent with
the DSC results (discussed later) and the experimental
results shown in Table 1 (even with relatively long
reaction time and high monomer conversion).
103 g/mol), even in the copolymer containing a very high
concentration (32.2 mol %) of B-styrene units.
F u n ction a lized s-P S P olym er s. The borane-con-
taining copolymers are stable for long periods of time
(6 months in a drybox) or at elevated temperatures (110
°C during NMR measurement) as long as O2 is excluded.
In this study, the borane groups in the copolymers were
oxidized by NaOH/H2O2 reagents at 40 °C for 3 h. The
borane groups were completely converted to the corre-
sponding hydroxy groups even under the heterogeneous
conditions. The quantitative conversion under mild
reaction conditions may be attributed to the combination
of high reactivity and high surface area of borane groups
in semicrystalline microstructure. Figures 4 and 5
Figure 3 shows several GPC curves of the styrene/B-
styrene copolymers (runs A-1, A-2, A-4, A-5, and A-7 in
Table 1) prepared by the Cp*Ti(OMe)3/MAO complex.
The narrow molecular weight distribution in all samples,
with Mh w/Mh n ) 2-3, implies that the polymerization
follows a single-site reaction mechanism. In fact, the
GPC curves show a slight reduction of molecular weight
distribution in the copolymers, from Mh w/Mh n ) 2.9 in
s-PS to 2.0 in styrene/B-styrene copolymers containing
32.2 mol % of B-styrene. Similar narrow molecular
distributions were also observed in the copolymers
prepared by Cp*TiCl3/MAO and CpTiCl3/MAO com-
plexes. The greater diffusibility of monomers in the
copolymer structures (due to lower crystallinity) may
also help provide the constant polymerization environ-
ment. In general, the copolymers exhibit high molecular
weights that gradually decrease as the B-styrene con-
tent increases. However, they still maintain relatively
high molecular weight (Mw ) 53 × 103 and Mn ) 28 ×
1
compare the H and 13C NMR spectra of s-PS and three
s-PS-OH copolymers containing 2.0, 8.4, and 16.0 mol
% of OH groups, respectively.
In Figure 4, there are two aliphatic proton (Ha and
Hb) peaks at 1.32 and 1.85 ppm and two sharp aromatic
proton (Hc and Hd+e) peaks at 6.68 and 7.15 ppm present
in all compositions, indicating a high syndiotactic ar-
rangement1 of styrene units in all of the polymers. The
borane group in the B-styrene comonomer did not
interfere with the syndiotactic incorporation of styrene
in the polymerization reaction. With increasing hy-

3444 Dong et al.
Macromolecules, Vol. 35, No. 9, 2002
Ch a r t 1
droxylated comonomer units, there are two new aro-
matic proton (Hf and Hg) peaks at 6.50 and 6.92 ppm
and two distinctive proton peaks at 2.55 and 3.68 ppm
corresponding to the protons (Hh and Hk) adjacent to
the aromatic ring (-CH2-Ph) and the primary alcohol
(-CH2-OH) in the hydroxylated B-styrene units. The
combination of integrated intensities at 3.68 and 7.15
ppm and the corresponding protons in each chemical
shift provides the copolymer composition (see Chart 1).
The stereostructure of the polymer was further ex-
amined by 13C NMR. As shown in Figure 5, all peaks
are sharp and assigned to the corresponding carbon
atoms in the polymer structures (shown in the inset).
According to the literature, the presence of a single
resonance10 for the substituted aromatic C1 carbon in
phenyl groups at 145.3 shows that these polymers are
highly syndiotactic. The same conclusion can be reached
by considering two C5 and C6 aliphatic carbons in the
polymer backbone. Two sharp resonances at 44.5 and
41.0 ppm correspond to the methine C5 and methylene
C6 in a highly stereoregular environment. In addition,
a new resonance at 63.2 ppm corresponds to the meth-
ylene carbon atom (C10) in the -CH2-OH group.
Overall, the sharp resonances in the copolymers re-
sembles that of syndiotactic polystyrene and are very
different from several reported atactic polystyrene
derivatives containing chloro and methoxy groups11
prepared with other catalyst systems.
Figure 6 compares the DSC curves of s-PS homopoly-
mer (A-1) and several s-PS-OH copolymers (runs A-2,
A-3, A-5, A-6, A-7, and A-8 in Table 2). As expected, both
the melting point (Tm) and crystallinity (øc) of the
copolymer are affected by the side chains. The higher
the density of the side chain, the lower the Tm and øc.
The detailed results of the melting point (Tm) and
crystallinity (øc) of the copolymers are summarized in
Table 2. The crystallinity (øc) of the copolymer was
calculated from fusion enthalpy according to the follow-
ing equation: øc ) Hf/Hf° × 100, where Hf and Hf° (53
J /g)12 are the fusion enthalpies of the copolymer and the
s-PS homopolymer, respectively. Sample A-3, with an
average of 1 side chain per 50 styrene units, still
possesses >40% crystallinity with a sharp melting peak
at Tm ) 250 °C. In addition to its functionality, this
s-PS-OH copolymer may also benefit from better pro-
cessability at <300 °C. The melting peak in the copoly-
mer completely disappears at >8.4 mol % of B-styrene
concentration. Only a single Tg was observed throughout
the whole composition range, and the Tg systematically
decreases with increasing side-chain density. All of the
experimental results indicate that the copolymer mi-
crostructure is homogeneous and that the copolymer
morphology becomes completely amorphous with more
than 8.4 mol % of B-styrene units.
F igu r e 6. DSC curves of (a) s-PS homopolymer and several
s-PS-OH copolymers, containing (b) 1.0, (c) 2.1, (d) 6.1, (e)
8.4, (f) 16.7, and (g) 32.2 mol % of OH groups.
(III) that are associated with “stable” borinate radicals.8
The polymeric radicals react in situ with maleic anhy-
dride (MA) to produce maleic anhydride grafted s-PS
(s-PS-g-MA) (V) with a single MA unit in each side
chain. Figure 7 shows the IR spectrum of a s-PS-g-MA
copolymer containing 8 mol % of MA units, and the inset
compares the absorption region of the νCdO vibration
modes between s-PS and three s-PS-g-MA copolymers
with 1, 3, and 8 mol % MA contents, respectively.
After the MA graft reaction, several new absorption
peaks were observed at 1860 and 1780 cm-1 corre-
sponding to two υCdO vibrational stretching modes13 in
succinic anhydride. A high concentration of MA groups
has been incorporated in the s-PS copolymers that is
similar to that of the incorporated borane units. The
concentration of incorporated MA units was calculated
by a standard industrial method (discussed in the
Experimental Section), which is based on the IR carbo-
nyl group absorption intensity and sample thickness.
s-P S Gr a ft Cop olym er s. The pending stable poly-
meric radicals associated with dormant borinate radi-
cals in the s-PS copolymer (III) are very useful in the
preparation of s-PS graft copolymers. In the presence
of MMA monomers, the free radical graft polymerization
results in s-PS-g-PMMA (VI) graft copolymers. The
molecular weight of the incorporated PMMA side chain
is proportional to the MMA monomers used, and the
graft density is governed by the incorporated borane
content.
After the graft reaction, the product, isolated by
filtration and washed with boiling MeOH, was then
extracted with acetone in a Soxhlet apparatus for 24 h
to remove PMMA homopolymer (<10%). Figure 8 com-
pares the 1H NMR spectra of a starting styrene/B-
styrene copolymer containing 1 mol % B-styrene units
(after hydroxylation) and two corresponding s-PS-g-
As illustrated in eq 2, the pending borane groups were
selectively oxidized by oxygen to form polymeric radicals

Macromolecules, Vol. 35, No. 9, 2002
Syndiotactic Polystyrene 3445
Ta ble 2. A Su m m a r y of th e Th er m a l P r op er tiesa of Hyd yoxyla ted s-P S Cop olym er s
b
entry
OH- content (mol %)
Tg (°C)
Tm (°C)
Tc (°C)
∆H (J /g)
øcc (%)
A-1
A-2
A-3
A-4
A-5
A-6
A-7
A-8
0
101.5
97.6
94.1
93.1
87.8
87.9
81.3
79.8
272.5
263.0
250.1
247.2
223.9
NDd
233.1
226.9
208.7
197.7
ND
ND
ND
ND
30.1
26.8
21.9
20.2
16.6
56.8
50.5
41.3
38.1
31.3
1.0
2.1
3.0
6.1
8.4
16.7
32.2
ND
ND
a
b
d
Based on DSC measurement with heating and cooling rate of 20 °C/min. Crystallization temperature. c Crystallinity. ND ) not
detected.
F igu r e 7. IR spectrum of a s-PS-g-MA copolymer containing 8 mol % of MA units. The inset compares the absorption region of
νCdO vibration modes between (a) s-PS and three s-PS-g-MA copolymers with (b) 1, (c) 3, and (d) 8 mol % MA content.
reaction process. The first step of the coupling reaction between
allylmagnesium chloride and vinylbenzyl chloride was carried
out in a 1000 mL flask equipped with a magnetic stirring bar
and inert atmosphere. In the flask, 200 mL of allylmagnesium
chloride/THF solution (2 M) was diluted with 150 mL of THF,
and then 50 mL of 4-vinylbenzyl chloride (0.35 mol) diluted
with 50 mL of THF was added dropwise with stirring and
cooling to maintain the reaction temperature at 0 °C. The
reaction mixture was slowly warmed to room temperature and
maintained at room temperature for another 2 h before adding
100 mL of water to destroy the excess allylmagnesium chloride.
The solution was then poured into 500 mL of water, and the
organic layer was separated and dried over anhydrous sodium
sulfate. After removing the THF solvent, about 46 g of the
resulting 4-(3-butenyl)styrene was distilled over calcium hy-
dride under reduced pressure (about 25 Torr) at 60 °C with
about 83% yield.
PMMA graft copolymers with 20 and 59 mol % MMA
contents, respectively. In addition to the major peaks
at 1.32, 1.85, 6.65, and 7.15 ppm for the protons in s-PS
backbone, the distinctive peak at 3.58 ppm corresponds
to methoxyl groups (CH3-O) in PMMA.
Exp er im en ta l Deta ils
In str u m en ta tion a n d Ma ter ia ls. All room- and high-
1
temperature H NMR and 13C NMR spectra were recorded on
a Bruker AM-300 spectrometer. Fourier transform infrared
spectroscopy was performed on a Bio-Rad instrument using
polymer thin film. The molecular weight was determined using
a Waters 150C that was operated at 135 °C. The columns used
were mStyragel HT of 106, 105, 104, and 103 Å. A flow rate of
0.7 mL/min was used, and the mobile phase was trichloroben-
zene. Narrow molecular weight distribution polystyrene samples
were used as standards. Differential scanning calorimetry
(DSC) was measured (with a heating rate of 20 °C/min) on a
Perkin-Elmer DSC-7, TAC-7 instrument controller.
All O2- and moisture-sensitive manipulations were per-
formed inside an argon-filled drybox equipped with a dry train.
Cp*Ti(OMe)3 (95%), Cp*TiCl3 (97%), CpTiCl3 (97%), MAO (10
wt % in toluene), and allylmagnesium chloride (2.0 M in THF)
were purchased from Aldrich and used without further puri-
fication. 9-BBN (0.5 M in THF) from Callery Chemical Co. was
used as received. Styrene (>99%) and vinylbenzyl chloride
(90%) from Aldrich were dried over CaH2 before distillation.
CP grade toluene was deoxygenated by argon purge before
refluxing for 48 h and then distilled over sodium.
The selective mono-hydroboration of 4-(3-butenyl)styrene by
9-BBN (0.3 mol) was carried out in THF (300 mL) at room
temperature. An equal amount (600 mL) of 9-BBN (0.5 M in
THF) was added dropwise into 4-(3-butenyl)styrene/THF solu-
1
tion over a period of 4 h. After another /2 h of stirring at room
temperature, the THF solvent was vacuum-removed. The
reaction mixture was subjected to vacuum distillation (5 Torr)
at 110 °C to obtain about 70 g of 4-[B-(n-butylene)-9-BBN]-
styrene with 90% yield. The 1H NMR spectrum (shown in
Figure 1) confirms the molecular structure.
Cop olym er iza tion of Styr en e a n d 4-[B-(n -bu tylen e)-
9-BBN]styr en e. The copolymerization reactions were carried
out in an argon-filled drybox. In a typical reaction (run 3 in
Table 1), 20 mL of styrene and 0.86 g of B-styrene were mixed
with 100 mL of anhydrous toluene in a 250 mL flask under a
Syn th esis of 4-[B-(n -bu tylen e)-9-BBN]styr en e. 4-[B-(n-
butylene)-9-BBN]styrene monomer was prepared by a two-step

3446 Dong et al.
Macromolecules, Vol. 35, No. 9, 2002
F igu r e 8. 1H NMR spectra of (a) s-PS-OH containing 1 mol % OH units and two corresponding s-PS-g-PMMA graft copolymers
with (b) 20 and (c) 59 mol % MMA contents.
nitrogen atmosphere. 11 mL of MAO (10 wt % in toluene) was
added with stirring. The copolymerization reaction was started
by adding 1 mL (10 µmol) of Cp*Ti(OMe)3/toluene solution.
The polymerization was carried out at 50 °C for 3 h before
terminating with 100 mL of IPA. The precipitated copolymer
was isolated and washed with IPA and dried under vacuum
to yield 4.66 g of polymer solid.
The polymer was isolated by precipitation in MeOH. The
polymer was refluxed in MeOH for 1 h before removing
residual boric acid by distillation of the B(OH)3/MeOH azeo-
trope. The polymer was isolated by filtration and dried under
vacuum to obtain 2.7 g of hydroxylated s-PS copolymer. The
1H NMR spectrum shown in Figure 4a indicates a quantitative
conversion of borane to hydroxy groups.
Hyd r oxyla tion Rea ction . Under a nitrogen atmosphere,
the powder form of styrene/B-styrene copolymer (3 g) contain-
ing 2.1 mol % B-styrene was suspended in 50 mL of THF
solvent in a 200 mL flask equipped with a mechanical stirrer.
Oxidation reaction was carried out by adding NaOH/H2O2
solution (B/NaOH/H2O2 ) 1/2/3) (0.06 g) and 5 mL of methanol
at 0 °C. The reaction mixture was warmed to 40 °C for 4 h.
Ma leic An h yd r id e Rea ction . In a 150 mL flask equipped
with a stirrer and N2 atmosphere, 3 g of styrene/B-styrene
copolymer containing 3.0 mol % of B-styrene was suspended
in 50 mL of THF along with 5 g of maleic anhydride. Under
stirring, a stoichiometric quantity of oxygen (vs borane) was
slowly added to the suspended polymer solution at ambient
temperature. After 2 h, the maleation reaction was terminated

Macromolecules, Vol. 35, No. 9, 2002
Syndiotactic Polystyrene 3447
by precipitating the polymer mixture in 2-propanol. The
maleated s-PS product (2.8 g) was isolated by filtration and
purified by Soxhlet extraction with acetone for 24 h before
drying the resulting polymer under vacuum.
s-PS to the manageable processing temperature and still
maintain high crystallinity. In addition, the pending
borane groups were also transformed to stable radicals
for graft-from polymerization to prepare s-PS-g-PMMA
graft copolymers.
The MA concentration in the polymer was estimated with
-1
the following equation: MA wt % ) kA1780
/d, where d is
cm
-1
the film thickness, A1780
is the peak absorbency, and k is
cm
Ack n ow led gm en t. The authors thank the National
Institute of Standards and Technology for its financial
support.
the absorption constant for anhydride. The k constant is
determined by calibration of the known compounds, assuming
the absorption constant is independent of the incorporated MA
structures.
Gr a ft Rea ction of s-P S w ith P MMA. In nitrogen atmo-
sphere, 3 g of s-PS-B copolymer containing 1 mol % B-styrene
units suspended in 30 mL of THF solvent was mixed with 6 g
of MMA monomer in a septum-capped 250 mL flask equipped
with a magnetic stirring bar. Under agitation, a stoichiometric
quantity (15 mL) of oxygen (vs borane) was slowly added to
the suspended polymer solution. The graft polymerization was
allowed to proceed at room temperature for 12 h before
exposing the solution to air. The suspended polymer solution
was poured into 200 mL of acetone, then filtered, and washed
with acetone several times. The isolated polymer was extracted
with boiling THF to remove PMMA homopolymer. The in-
soluble fraction (soluble in 1,1,2,2-tetrachloroethane, 1,2,4-
trichlorobenzene at elevated temperatures) is s-PS-g-PMMA
graft copolymer (7.3 g). The 1H NMR spectrum of the graft
copolymer shown in Figure 8c indicates 59 mol % MMA
content.
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Con clu sion
This paper has shown a facile route in the preparation
of functional s-PS polymers and s-PS graft copolymers.
The chemistry involves a new 4-[B-(n-butylene)-9-BBN]-
styrene (B-styrene) comonomer and half-sandwich met-
allocene catalysts. The reactivity ratios near to 1 in the
two monomers allow the preparation of a broad com-
position range of s-PS copolymers with narrow molec-
ular weight and composition distributions. The pending
borane groups in the copolymer not only provide the
desirable functional groups, such as hydroxy and an-
hydride, but also reduce the melting temperature of
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