In-chain multi-functionalized polystyrene by living anionic copolymerization with 1,1-bis(4-dimethylaminophenyl)ethylene: Synthesis and effect on the dispersity of carbon black in polymer-based composites

Article abstract of DOI:10.1016/j.polymer.2013.04.011

In-chain multi-functionalized polystyrene possessing definite geminal dimethylamino groups along the polymer backbone, poly(styrene-co-1,1-bis(4- dimethylaminophenyl)ethylene) (poly(styrene-co-BDADPE)), has been designed and synthesized via living anionic copolymerization of styrene with 1,1-bis(4-dimethylanimophenyl)ethylene in benzene at 50 C, using sec-butyllithium as initiator. The amine functionality was readily controlled by the monomer feed ratio and molecular weight. Compositions of styrene/BDADPE were 9.0-57.9 when ratios of styrene/BDADPE = 0.45-7.79 and Mn = 4.7-15.5 kg/mol. The incorporation of 1,1-bis(4-dimethylanimophenyl)ethylene unit resulted in an increase in glass transition temperature of copolymer and was hindered in the presence of Lewis base. The monomer reactivity ratio for styrene, r₁ = 53.4, was obtained. Such in-chain multi-functionalized polystyrene significantly improved the dispersity of carbon black in the corresponding composites, as verified by SEM observation. This in-chain multi-functionalization of matrix polymer via anionic copolymerization employing 1,1-bis(4-dimethylaminophenyl)ethylene as comonomer provides a facile and effective method to prepare carbon black-based polymer composites with good dispersity.

Full text of DOI:10.1016/j.polymer.2013.04.011

Polymer 54 (2013) 2958e2965
Contents lists available at SciVerse ScienceDirect
Polymer
journal homepage: www.elsevier.com/locate/polymer
In-chain multi-functionalized polystyrene by living anionic copolymerization
with 1,1-bis(4-dimethylaminophenyl)ethylene: Synthesis and effect
on the dispersity of carbon black in polymer-based composites
Lingling Wu, Yanshai Wang, Yurong Wang, Kaihua Shen, Yang Li*
State Key Laboratory of Fine Chemicals, Department of Polymer Science and Engineering, School of Chemical Engineering, Dalian University of Technology, No. 2 Linggong Road,
Dalian, Liaoning 116024, China
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 7 December 2012
Received in revised form
In-chain multi-functionalized polystyrene possessing definite geminal dimethylamino groups along the
polymer
backbone,
poly(styrene-co-1,1-bis(4-dimethylaminophenyl)ethylene)
(poly(styrene-co-
BDADPE)), has been designed and synthesized via living anionic copolymerization of styrene with 1,1-
29 March 2013
ꢀ
bis(4-dimethylanimophenyl)ethylene in benzene at 50 C, using sec-butyllithium as initiator. The
Accepted 1 April 2013
Available online 12 April 2013
amine functionality was readily controlled by the monomer feed ratio and molecular weight. Compo-
sitions of styrene/BDADPE were 9.0e57.9 when ratios of styrene/BDADPE ¼ 0.45e7.79 and Mn ¼ 4.7
e15.5 kg/mol. The incorporation of 1,1-bis(4-dimethylanimophenyl)ethylene unit resulted in an increase
in glass transition temperature of copolymer and was hindered in the presence of Lewis base. The
Keywords:
In-chain multi-functionalized polymer
monomer reactivity ratio for styrene, r
1
¼ 53.4, was obtained. Such in-chain multi-functionalized
1,1-Bis(4-dimethylaminophenyl)ethylene
Dispersed polymer composite filler
polystyrene significantly improved the dispersity of carbon black in the corresponding composites, as
verified by SEM observation. This in-chain multi-functionalization of matrix polymer via anionic copo-
lymerization employing 1,1-bis(4-dimethylaminophenyl)ethylene as comonomer provides a facile and
effective method to prepare carbon black-based polymer composites with good dispersity.
Ó 2013 Elsevier Ltd. All rights reserved.
1. Introduction
butadiene [23]. Then Hayashi [24] described the preparation of
styrene-butadiene copolymer with dimethylamino functional
1
,1-Diphenylethylene, especially its substituted derivatives have
groups at both the initiating and terminating chain ends, as well as
within the chain in a one-step anionic polymerization. Furthermore,
Hutchings and his coworkers [25] reported the monomer sequence
distribution in anionic copolymerization of 1,1-diphenylethylene
and its derivatives with styrene. Recently, Ding [26] successfully
synthesized well-defined in-chain multi-functionalized polymers
with a large number of silyl hydride functional groups.
Although the dimethylamino bis-substituted 1,1-diphenyl-
ethylene, 1,1-bis(4-dimethylanimophenyl)ethylene (BDADPE), has
been investigated as functionalization agent to prepare functional
polymers with geminal dimethylamino groups at the chain ends
[27,28] and/or within chains [29], few studies have been focused on
the in-chain multi-functionalization of polymers via anionic copo-
lymerization employing BDADPE as copolymerizable monomer. Such
geminal dimethylamino in-chain multi-functionalized polymers
bear twice functional groups than the dimethylamino-substituted
analogues with the same content of 1,1-diphenylethylene unit, and
thus have extensive application prospect in the fields of sensors,
rubber reinforcement, antibacterial agents, catalysts and the like
[30e33].
been intensely investigated as a general and versatile functionali-
zation adjuvant for anionic synthesis of specialty polymers in terms
of function and branched architecture [1e12].
Particularly, the methodology of alkyllithium-initiated copoly-
merization of substituted 1,1-diphenylethylene derivatives with
other appropriate monomers is quite suitable for the synthesis of in-
chain multi-functionalized polymers with predictable well-defined
functionalityand structures. Yuki and Okamoto first investigated the
anionic copolymerization of the unsubstituted 1,1-diphenylethylene
with styrene [13], ring-substituted styrenes [14e17], isoprene [18],
butadiene [19], and 2,3-dimethylbutadiene [20,21]. Quirk et al.
further demonstrated the anionic copolymerization of
dimethylamino-substituted 1,1-diphenylethylene, i.e., 1-(4-
dimethylaminophenyl)-1-phenylethylene, with styrene [22] and
*
Corresponding author. Tel.: þ86 411 84986106; fax: þ86 411 84986105.
E-mail addresses: leafemma@mail.dlut.edu.cn (L. Wu), wangyanshai2003@
yahoo.com.cn (Y. Wang), wangyurong@dlut.edu.cn (Y. Wang), shen_kh@
yahoo.com.cn (K. Shen), liyang@dlut.edu.cn (Y. Li).
0
032-3861/$ e see front matter Ó 2013 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.polymer.2013.04.011

L. Wu et al. / Polymer 54 (2013) 2958e2965
2959
Carbon black-based polymer composites have attracted
increasing interest because of their unique mechanical, electrical,
optical, and chemical properties [34e37]. The ultimate perfor-
mance of these advanced materials depends greatly on the dis-
persibility of carbon black (CB) in the polymer matrix [38e42].
Hence, interest in the modification with the object of improving the
compatibility between fillers and polymer matrix has been intense,
including modifications in the bulk or confined to the interface.
One of the most widely used methodologies is the modification
of CB and at the same time, various chemical and physical methods
for the surface modification of CB have been developed [43], such as
plasma treatment [44], ultrasonic treatment [45], chemical-deposit
Methyltriphenylphosphonium bromide (Aldrich, 98%), potassium
tert-butoxide (Aldrich, 1.0 M solution in THF), and 4,4 -bis(dime-
thylamino)benzophenone (Aldrich, 98%) were used as received.
0
Carbon black (N550) was purchased from Cabot Company (specific
2
surface area: 40 ꢁ 4 m /g, DPB value: 121 ꢁ 5 mL/100 g, average
particle size: 40 nm, pour density: 360 ꢁ 40 g/L).
2.2. Measurements
1H NMR (5 wt%, CDCl
3 4
AvanceⅡ 400M NMR spectrometer with (CH )
) spectra were recorded on a Bruker
Si (tetramethylsi-
3
lane) as the internal standard. Size exclusion chromatographic
(SEC) analyses of the copolymers were performed on a Waters
HPLC component system (2414 refractive index detector) at a flow
[
46], surface oxidation [47,48] reaction with diazonium salts [49],
polymer grafting [47,50,51], reaction with silane coupling agents
52], and addition of modifier, e.g., hindered amine light stabilizer
LA-57 [32], resorcinol [53], polyvinyl alcohol [54], and oleic acid
55]. In order to make the carbon surface more compatible with the
ꢀ
[
rate of 1.0 mL/min in THF at 30 C after calibration using poly-
g
styrene standard polymers. Glass transition temperatures (T ) of
[
the polymers were measured under nitrogen atmosphere using a
TA Instruments Universal Analysis 2000 differential scanning
polymer matrix, however, some complicated pretreatments and/or
multi steps are required. The compatibility between CB and the
polymer matrix can also be improved by enhancing fillerematrix
interactions either through covalent bridging, ionic bonds and
hydrogen bonds [39,56] or by addition of modifier compatible with
immiscible components in these composites [57,58]. The third
dramatic method of improving the CB dispersity for polymer-based
composites is the functionalization of matrix polymer, i.e., to
directly introduce functional groups such as carboxyl and epoxy
groups into the matrix polymer which then react with the func-
tional groups present on the carbon surface. For example, Ban-
dyopadhyay and his coworkers [59] reported the better dispersity
of surface oxidized CB in carboxylated nitrile rubber matrix with
high temperature extrusion in presence of (3-aminopropyl)trie-
thoxysilane. Similarly, Jong investigated the effect of carboxylated
styrene-butadiene rubber on the dispersion of CB blended with soy
spent flakes [60] and defatted soy flour [61]. In addition, Manna
et al. [62] demonstrated the strong interactions between surfaced
oxidized CB and epoxidized natural rubber during high-
temperature molding. This functionalization of matrix polymer is
comparatively simple and flexible; however, little research has
been carried out with respect to functionalization of matrix poly-
mer by introducing multiple geminal dimethylamino groups.
In this paper, we report investigations into in-chain multi-
functionalization of polystyrene via anionic copolymerization using
ꢀ
calorimeter (DSC) at a heating rate of 10.0 C/min. Sample sizes
were 10 mg and investigated under nitrogen. Scanning electronic
microscopy (SEM) observations were carried out using a FEI Quanta
200F at an acceleration voltage of 20 kV. Samples were fractured
under ambient condition, and the fracture surfaces were covered
with a layer of gold by sputtering treatment before SEM observa-
tion. Contents of bound polymer were determined by extracting
unbound polymer with toluene for 3 days at room temperature and
drying in a vacuum oven to a constant weight. Weights of the
samples before and after the extraction were measured and the
bound polymer contents were calculated [64].
2.3. Synthesis of 1,1-bis(4-dimethylaminophenyl)ethylene
The synthesis of BDADPE was conducted by the classic Wittig
0
reaction using 4,4 -bis(dimethylamino)benzophenone as substrate
under an argon atmosphere (described in detail by Hirao [29]).
Typically, methyltriphenylphosphonium bromide (45.58 g,
127.6 mmol) and freshly distilled THF (500 mL) were added into a
round bottom flask equipped with a reflux condenser and a mag-
netic bar. Potassium tert-butoxide (138.4 mL of a 1.0 M solution in
THF, 138.4 mmol) was then added dropwise to the reaction flask via
constant pressure funnel. The reaction mixture was stirred for 2 h
ꢀ
0
at 0 C. Then the solution of 4,4 -bis(dimethylamino)benzophenone
(21.4 g, 79.75 mmol) in dry THF (690 mL) was dropped to the re-
1,1-bis(4-dimethylaminophenyl)ethylene as comonomer. Further-
ꢀ
more, we study the impact of such geminal dimethylamino groups
along the polystyrene backbone upon the dispersity of CB in the
corresponding composites.
action mixture via constant pressure funnel at 0 C. The orangee
brown reaction mixture was heated to reflux for 7 h with stirring
and then quenched with distilled water. The resultant mixture was
extracted with ether three times. Such ethereal layer was washed
2
. Experimental
with aqueous NaHCO
tion and then dried over MgSO
3
solution and saturated aqueous NaCl solu-
. After filtration, the ethereal layer
4
2.1. Materials
was poured into hexane to precipitate triphenylphosphine oxide.
Flash column chromatography (petroleum ether/ethyl acetate 2:1
The reagents were purchased from Sinopharm Chemical Re-
agent Company and used as received unless otherwise stated.
Benzene was purified by stirring over concentrated sulfuric acid for
weeks, followed by overnight drying with ground calcium hy-
v/v) gave BDADPE in 92% yield (19.52 g, 73.37 mmol) and R
f
¼ 0.76.
), 5.19 (s, 2H,
¼ C), 6.68e6.70 (d, 4H, aromatic proton ortho to N(CH ), 7.25-
7.28 (d, 4H, aromatic proton meta to N(CH ).
1
H NMR (CDCl
CH
3
, 400 MHz):
d
2.96 (s, 12H, 2 ꢂ N(CH
3 2
)
2
3 2
)
2
3 2
)
dride and distillation. Tetrahydrofuran (THF) was dried by reflux
over a Na-benzophenone complex under an argon atmosphere and
then distilled. Lewis bases, e.g., anisole, tert-butyl methyl ether,
tetramethylethylenediamine (TMEDA), and hexamethylphosphoric
triamide (HMPTA) were stirred over freshly crushed calcium hy-
dride for 12 h, followed by degassing distillation. Sec-butyllithium
2.4. Synthesis of poly(styrene-co-1,1-bis(4-dimethylaminophenyl)
ethylene)
ꢀ
Copolymerizations were carried out at 50 C in ampoule under
an argon atmosphere. Styrene and 1,1-bis(4-dimethylaminophenyl)
ethylene were first dissolved in benzene in the same ampoule with
or without addition of the required Lewis base. Samples were then
prepared by adding a solution of s-BuLi to the comonomer solution.
The copolymerization was proceeding under stirring for 24 h and
(s-BuLi) was synthesized from Li and sec-butyl chloride in benzene,
and analyzed using the double titration method with 1,2-
dibromoethane [63]. Styrene monomer was purified by dying
over CaH
2
followed by vacuum distillation from its s-BuLi solution.

2960
L. Wu et al. / Polymer 54 (2013) 2958e2965
then quenched with degassed isopropanol. The resultant co-
polymers were precipitated into excess methanol three times to
remove unreacted BDADPE from the polymer and then dried in a
vacuum oven to constant weight.
2.5. Preparation of CB/poly(styrene-co-1,1-bis(4-
dimethylaminophenyl)ethylene) composites
The composites were fabricated by the solution method. First,
the copolymer powders were dissolved in THF under stirring for 2 h
at ambient temperature to obtain solutions at 0.033 g/mL. In the
second step, CB pellets were introduced into these solutions with
stirring for 6 h to obtain homogeneous solutions with a CB/polymer
weight ratio of about 5.22/94.78. Then the CB/polymer solutions
were deposited onto glass slides cleaned in methanol and THF was
ꢀ
slowly evaporated at 30e40 C.
3
. Results and discussion
3.1. Copolymerization of styrene and 1,1-bis(4-
dimethylaminophenyl)ethylene
3.1.1. Preparation of styrene-co-BDADPE copolymers
The copolymerization of styrene and excess BDADPE was initi-
ꢀ
ated by s-BuLi in benzene at 50 C, as shown in Scheme 1. To
explicitly characterize the structure, the product was purified by
precipitating into excess methanol three times to remove the
unreacted BDADPE from the polymer.
Fig. 1. 1H NMR spectra (CDCl
BDADPE) (c).
The products were collected and characterized by 1H NMR
3
) of BDADPE (a), polystyrene (b), and poly(styrene-co-
1
spectrometry. As seen in the H NMR spectra in Fig. 1, the complete
disappearance of the peak around
the appearance of the peak about
evidence that the crossover reaction take place by nucleophilic
attack of poly(styryl)lithium on the double bond of BDADPE
monomer. And the dimethylamino protons at
show splittings ascribed to different diastereomeric arrangements
of the functional groups as observed previously [65].
d
5.19 ppm simultaneously with
2.6e3.0 ppm is unambiguous
d
Â
Ã
12n
8n
þ 5n
Area ꢃ NðCH Þ
3 2
2
¼
(1)
(2)
Area½aromatic regionꢄ
2
1
d
¼ 2.6e3.0 ppm
M n þ M n ¼ Mn
1
1
2 2
The purified product was further analyzed by SEC using poly-
styrene standards for calibration. The molecular weights and mo-
lecular weight distributions are listed in Table 1. Somewhat broader
molecular weight distributions were obtained for these purified
products compared to homopolystyrene because of the slower rate
of crossover relative to propagation [66]. The SEC overlay of puri-
fied product and polystyrene with the same number of styrene unit
is shown in Fig. 2. The trace of the purified product shows a shift to
smaller retention volume in comparison with that of polystyrene.
Therefore, the above evidence has explicitly verified the chem-
ical structure of styrene-co-BDADPE copolymer.
where n
porated into the copolymer, M
i
refers to the average number of monomer i unit incor-
and Mn are the molecular weight of
monomer i and the number average molecular weight of the
i
copolymer, respectively. The copolymer compositions were also
1
calculated from H NMR integration ratios.
The functionalities and copolymer compositions are summa-
rized in Table 1 and shown in Fig. 3. The molar content of geminal
dimethylamino groups along the polymer chain increased from
1.7% to 10.0% as the monomer feed molar ratio decreased from 7.79
to 0.45 with Mn in range of 4.7e15.5 kg/mol. This is in accord with
the general trend of styrene anionic copolymerization with 1,1-
diphenylethylene [13] and its amino-substituted derivative [22].
Thus, the number of geminal dimethylamino groups along poly-
styrene backbone could be controlled by the monomer feed ratio
and the molecular weight.
3.1.2. Copolymer compositions
The amine functionality, F, corresponding to the number of
geminal dimethylamino groups per polymer chain, was calculated
1
from the H NMR spectra of the copolymers using Eqs. (1) and (2):
Scheme 1. Synthesis of in-chain multi-functionalized polystyrene using BDADPE as comonomer.

L. Wu et al. / Polymer 54 (2013) 2958e2965
2961
Table 1
Monomer feed ratio, composition and glass transition temperature data for styrene
)-BDADPE (M ) copolymers.
(
M
1
2
a
]b Fc
ꢀ
Sample [M
1
0
] /[M
]
2 0
Mn (kg/mol) Mw (kg/mol) Mw/Mn [M
1
]/[ M
2
T
g
( C)
1d
e
11.6
4.7
7.6
10.3
15.5
12.4
9.9
12.1
13.6
12.9
5.6
9.2
12.3
19.3
15.1
12.2
14.5
14.7
1.11
1.19
1.21
1.19
1.25
1.22
1.23
1.20
1.08
e
e
89.9
2
3
4
5
6
7
8
9
0.45
0.56
0.79
2.30
2.40
3.70
4.76
7.79
9.0
11.0
13.6
26.5
27.2
37.6
41.2
57.9
3.9 106.6
5.4 104.3
6.1 103.9
5.1 101.8
4.0 99.7
2.4 97.3
2.7 93.2
2.2 93.0
a
Molar concentration ratio of the two monomers at the beginning of polymeri-
zation, which is the same as the monomer molar feed ratio.
b
Copolymer composition, i.e., the molar ratio of the two monomer units in the
1
copolymer, calculated from the H NMR spectra of the copolymers using Eqs. (1) and
(
2).
c
Amine functionality corresponding to the number of geminal dimethylamino
1
groups per polymer chain calculated from the H NMR spectra of the copolymers
using Eqs. (1) and (2).
d
Homopolystyrene.
Fig. 3. Molar content of geminal dimethylamino groups in styrene-co-BDADPE co-
polymers as a function of the monomer feed molar ratio of styrene to BDADPE.
On the basis of above results, it is concluded that this in-chain
multi-functionalization procedure via anionic copolymerization
employing BDADPE as comonomer can be utilized to prepare
functionalized polymers with multiple geminal dimethylamino
groups along the polymer backbone.
higher than homopolystyrene with the same molecular weight
[
67]. Relative to dimethylamino-substituted analogues [22], the
geminal dimethylamino-substituted copolymers obtained in the
present study exhibited lower T values with the similar copolymer
g
composition and Mn values. This may be due to the decrease of the
dipole moment which results from the symmetrical dimethylamino
bis-substitution in the phenyl rings of 1,1-diphenylethylene
molecule.
The characterization by thermal analysis indicates that copoly-
merization of styrene with BDADPE is an effective means of
increasing the glass transition temperature as well as increasing the
polar interaction between the polymer chains.
3.1.3. Thermal properties of copolymers
The copolymers possessing multiple geminal dimethylamino
groups were tested for their thermal properties by DSC. The rele-
vant data is collected in Table 1 and the corresponding DSC curves
are shown in Fig. 4.
It appears that each random copolymer had only one glass
transition temperature, as expected. Furthermore, an increasing
ꢀ
ꢀ
trend in T
g
from 89.9 C to 106.6 C was observed as the decreasing
is attributed to
3.1.4. Monomer reactivity ratio for styrene
value of monomer feed ratio. Such an increase in T
g
If it is assumed that the styrene monomer is completely
the increasing molar content of polar geminal dimethylamino
diphenyl functional groups incorporated into the polymer which
increase the polar interaction between the polymer chains. It is
interesting to note that the incorporation of modest amounts of 1,1-
bis(4-dimethylaminophenyl)ethylene units (10.0 mol-%) resulted in
consumed at the end of the polymerization, the Mayo-Lewis
copolymerization equation [68] for our system takes the inte-
grated form as shown in Eq. (3):
relatively large increase in T
in Table 1; Mn ¼ 4.7 kg/mol; T
g
of the resulting copolymer (Sample 2
ꢀ
ꢀ
C
g
¼ 106.6 C), more than 24.6
Fig. 2. SEC overlay of poly(styrene-co-BDADPE) (a) and polystyrene with the same
Fig. 4. DSC curves of poly(styrene-co-BDADPE). Each bracket indicates the corre-
number of styrene unit (b).
sponding monomer feed ratio.

2962
L. Wu et al. / Polymer 54 (2013) 2958e2965
Table 3
ꢀ
ꢁ
½
M ꢄ
1
½M ꢄ
Effect of Lewis base on composition of styrene-BDADPE copolymers.
2
1 0
ln
þ
ln
ðr ꢃ 1Þ þ 1 ¼ 0
(3)
]/
1
½
M ꢄ
2
r1 ꢃ 1
½M ꢄ
0
2 0
Lewis base
n(LB/s-BuLi) Mn
Mw
Mw/Mn [M ]/[M ] F [M2]
1
2
(kg/mol) (kg/mol)
(%)
where [M
can be determined from the final copolymer composition.
Thus the value of r can be solved by trial and error from Eq. (3).
1
]
0
/[M
2
]
0
is known from the monomer feed and [M
2
e
0.0
14.0
5.3
14.3
22.5
27.1
17.2
28.3
32.5
1.20
1.26
1.20
29.5
36.7
98.0
4.3 3.3
5.5 2.7
2.6 1.0
[
M
2
]
0
Anisole
tert-Butyl
Methyl Ether
THF
TMEDA
HMPTA
l
When styrene was copolymerized with BDADPE in benzene at
0 C with s-BuLi as initiator, the values of monomer reactivity ratio
2.5
0.1
0.1
18.4
9.6
11.8
20.9
11.6
13.2
1.14
1.21
1.12
60.5
45.2
68.8
2.8 1.6
1.9 2.2
1.6 1.4
ꢀ
5
for styrene, r
1
, are listed in Table 2. The average value of r
1
was
calculated to be 53.4. This means that styrene is 53.4 times more
reactive than BDADPE towards the poly(styryl)lithium anion. In the
Conditions: [M
1
] /[M
0 2
]
0
¼ 2.65; reaction time ¼ 24 h at 50 ꢀC.
1
previous studies, r is reported to be 5.6 for styrene in copoly-
merization with 1-(4-dimethylaminophenyl)-1-phenylethylene in
benzene at 25 C [22]. These results are consistent, since the
addition reaction of 1,1-diphenylethylene derivatives to poly(-
styryl)lithium is accelerated by electron-withdrawing substituents
and retarded by electron-donating substituents in the phenyl rings
work is twice the normal s constant reported by Quirk [22], which
ꢀ
is consistent with expectations in the literature [73]. With a sub-
stituent constant of ꢃ1.04, the geminal dimethylamino groups
strongly retard the nucleophilic attack by a carbanion on the double
bond of the BDADPE monomer in comparison to 1,1-
[69]. In our system both phenyl groups of 1,1-diphenylethylene
diphenylethylene
and
1-(4-dimethylaminophenyl)-1-
molecule were equally substituted by strong electron-donating
dimethylamino groups [70]. Thus, the crossover reaction rate of
poly(styryl)lithium to BDADPE is much less than that of poly(styryl)
lithium to 1-(4-dimethylaminophenyl)-1-phenylethylene. There-
phenylethylene. Thus the much larger value of the monomer
reactivity ratio for styrene in copolymerization with BDADPE is in
accord with expectations based on the electronic properties of the
geminal dimethylamino groups.
fore, the monomer reactivity ratio, r
much larger in copolymerization with BDADPE than that with 1-(4-
dimethylaminophenyl)-1-phenylethylene.
1
(r
1
¼ k11/k12), is expected to be
3.1.5. Effect of Lewis base
Because of such unfavorable monomer reactivity ratio, it was
anticipated that the addition of Lewis base would be necessary to
promote significant incorporation of BDADPE units. Therefore, the
effect of several Lewis base on the final copolymer composition was
The Hammett relationship for the addition reaction of poly(-
styryl)lithium to the 1,1-diphenylethylene system can be described
by Eq. (4):
1
investigated. The copolymers were collected for H NMR and SEC
k12
analyses.
log
¼
rs
(4)
0
k
The results are presented in Table 3. When styrene was copo-
lymerized with BDADPE in the presence of Lewis base ranging in
polarity from weak anisole to mild THF and further to strong
HMPTA, less BDADPE units were incorporated into the copolymers
in the molar ratio range studied here. This is the opposite of that for
the butadiene-1-(4-dimethylaminophenyl)-1-phenylethylene sys-
tem [23]. It would be reasonable to expect that the complex,
formed by Lewis base and living polymer chain, would tend to
hinder sterically approach of the coming BDADPE monomer rela-
tive to attach at the hindered terminal chain end in absence of
Lewis base. This could explain the decrease in incorporation of
BDADPE unit in the presence of Lewis base.
1
2
where
r
¼ þ1.8 [69], k0 and k12 are the crossover reaction rates of
12
poly(styryl)lithium to 1,1-diphenylethylene and a substituted 1,1-
diphenylethylene, respectively.while
0
k11=k0
k11=k12
r
k12
1
12
¼
¼
(5)
0
r1
k
1
2
where k11 is the homopropagation of styrene. Upon substituting the
0
value of k12/k from Eq. (5) into Eq. (4), then Eq. (6) is obtained:
1
2
0
1
r1
r
log
¼
rs
(6)
3.2. CB/poly(styrene-co-BDADPE) composites
A
s
value of ꢃ1.04 for the geminal para-dimethylamino sub-
0
stituent could be calculated from Eq. (6) using r ¼ 0.71 [13],
1
3.2.1. Composite morphologies
r
1
¼ 53.7, and
the para-dimethylamino substituent are ꢃ0.44, ꢃ0.71, ꢃ0.83 [70e
2], and ꢃ0.5 [22]. The substituent constant ( ) obtained in this
r
¼ þ1.8 [69]. Representative literature values of
s for
In order to investigate the effect of such incorporated geminal
dimethylamino functional groups on the dispersity of CB in the
corresponding polymer matrix, three composites, C1, C2 and C3,
with strong deviations in dimethylamino group content but almost
identical in carbon black content, were prepared. The composite
formulation data is given in Table 4. SEM was used to study the
7
s
Table 2
Monomer reactivity ratio for styrene in copolymerization with BDADPE.
/[M Mn Mw Mw/Mn [M ]/[M [M
]a (%)
]
0
F
r
1
b
[
1
M ]
0
2
1
2
]
2
(
kg/mol) (kg/mol)
Table 4
1
1
2
2
2
3
.52
15.3
17.3
15.5
12.4
14.3
9.9
19.1
21.8
19.3
15.1
17.2
12.2
1.25
1.26
1.25
1.22
1.20
1.24
18.6
20.0
26.5
27.2
29.5
37.6
6.9 5.1
7.4 4.8
5.1 3.6
4.0 3.5
4.3 3.3
2.4 2.6
52.2
55.8
54.0
53.4
53.5
51.5
Composite formulation with varied dimethylamino group content and similar CB
content.
.56
.30
.40
.65
.70
Composite CB
content (kg/mol) (kg/mol)
wt%)
Mn
Mw
Mw/Mn [M
1
]/[M
2
] F
2
[M ] Bound
(%) polymer
content
(
(
%)
2.1
2.4 2.6 6.5
10.0 8.4 8.6
ꢀ
Conditions: reaction time ¼ 24 h at 50 C.
1
2
3
5.22
5.22
5.22
11.6
9.9
14.0
12.9
12.2
16.5
1.11
1.23
1.18
e
e
e
a
Molar content of the geminal dimethylamino groups of styrene-co-BDADPE
copolymers.
37.6
10.9
b
Calculated according Eq. (3).

L. Wu et al. / Polymer 54 (2013) 2958e2965
2963
fracture surface morphology of CB/in-chain multi-functionalized
polystyrene composites.
As shown in Fig. 5, distinct morphologies were observed for
these three composites. For example, when dispersed in pure PS
matrix, CB particle domain had a very broad distribution and there
was an amount of large carbon agglomerates in dimension varying
from 2 to 12 mm. This result may be due to the weak fillerematrix
interaction consisting of Van Der Waals types of forces. As for
functionalized polystyrene-based composites, Composite 2, with
backbone which interact with functional groups present on CB
surface to form strong fillerematrix interaction. Therefore, there
are less carbon agglomerates and meanwhile the domain size of CB
agglomerates is remarkably decreased, as is indicated in the illus-
tration of Fig. 6 (a) and (b). In addition, the degree of improvement
in dispersity of CB greatly depends on the content of geminal
dimethylamino groups of the matrix polymer. It is worth
mentioning here that, with the amine functionality further
increasing to 8.4 mol-%, Composite 3 contains uniformly dispersed
CB aggregates (Fig. 6 (c)).
Several works of functionalization of matrix polymer in the
literature employed carboxyl and epoxy functions to interact with
functional groups present on the modified CB surface, which only
form hydrogen bonds [59e62]. By means of functionalization of
matrix polystyrene by incorporating multiple geminal dimethyla-
mino groups we are quite confident to the presumption that, in
addition to the formation of hydrogen bonds, such tert-amino
groups also should react with intrinsic acidic functional groups
present on the carbon surface, and give rise to the formation of
high-energy ionic bonds at ambient condition.
Scheme 2 suggests the strong interaction between CB and in-
chain multi-functionalized polystyrene, illustrating the role of
geminal dimethylamino groups in the fillerematrix interaction. It is
proposed that the geminal dimethylamino groups along the poly-
mer backbone interact with acidic groups on the surface of CB, such
as carboxyl, phenol, and hydroxyl, to form ionic bonds as well as
hydrogen bonds. These high-energy bonds reduce the extent of CB
agglomerate formation and enhance the fillerematrix interaction.
As seen in Table 4, the bound polymer content in CB-filled polymer
composites increased as the content of geminal dimethylamino
groups of the matrix polymer increased, and this is in accord with
expectation based on the strong interaction mechanism presented
above. Therefore, this strong interaction results in good compati-
bility of CB and polymer matrix and thus allows the CB better
dispersion and homogeneity than that in pure PS matrix. The effect
of such incorporated geminal dimethylamnio groups on the CB
2
.6 mol-% geminal dimethylamino groups, contained much less
carbon agglomerates of which the domain size decreased sharply to
e2 m. A similar trend was discovered for Composite 3, with the
1
m
molar content of geminal dimethylamino groups further increasing
to 8.4%, where the composite contained uniformly dispersed CB
aggregates.
It is evident that the incorporation of geminal dimethylamino
groups into the matrix polystyrene backbone changes the
morphology of the corresponding CB-based composite. Thus, the
improvement in dispersity of CB should stem from the strong
interaction between such geminal dimethyamino groups and CB
only. This is not a usual interaction formation process. An expla-
nation for this strong interaction formation is attempted in the next
section.
3.2.2. Mechanism of strong interaction formation
Here we attempt to propose a strong interaction mechanism,
i.e., ionic bonds and hydrogen bonds, for the improvement in
dispersion of CB in such amine-functionalized polystyrene as
illustrated in Scheme 2.
These SEM micrographs reveal more uniformly dispersed CB in
geminal dimethylamine-functionalized polystyrene matrixes
compared with that in unfunctionalized matrix. As unfunctional-
ized PS/CB composite is compounded under similar processing
condition as the functionalized polystyrene/CB composites, such
improvement in dispersity of CB is ascribed to the introduction of
multiple geminal dimethylamino groups along the polystyrene
Fig. 5. SEM micrographs of fracture surface of in-chain multi-functionalized polystyrene filled with 5.22 wt% CB and the molar content of geminal dimethylamino groups: 0 for
Composite 1 (a and d), 2.6% for Composite 2 (b and e) and 8.4% for Composite 3 (c and f).

2964
L. Wu et al. / Polymer 54 (2013) 2958e2965
Scheme 2. Proposed mechanism for the formation of ionic bonds and hydrogen bonds between CB and in-chain multi-functionalized polystyrene with geminal dimethylamino
groups.
dispersion is evident in the light of the SEM studies as shown in
Fig. 5.
application of heating, which should be quite favorable for fillere
matrix interaction. However, this problem could be solved by using
the 1,1-bis(4-aminophenyl)ethylene as comonomer in conjunction
with functional group protection.
Compared with traditional complicated and lengthy methods,
the method developed in this work can be conveniently applied
especially with regard to the rubber reinforcement [35], CB-filled
elastomers and high-performance automotive tires [74], and
sensor arrays [75]. Potential practical applications of this geminal
In summary, functionalization of matrix polymer by introducing
multiple geminal dimthylamino groups into polymer backbone
effectively improves the dispersity of CB in polymer-based com-
posites. It should be noted that this paper has studied only the
effect of tert-amino groups on CB dispersity. In the case of
employing primary amine groups, covalent bonds, i.e., amido
linkage should be formed between CB and polymer matrix upon
2
Fig. 6. Representation of the structure models of CB-based polymer composites as a function of the geminal dimethylamino group content M %: (a) large CB agglomerates
coexisting with aggregates, (b) small and less CB agglomerates along with aggregates, and (c) CB aggregates.

L. Wu et al. / Polymer 54 (2013) 2958e2965
2965
dimethylamino in-chain multi-functionalized polymer are under
investigation.
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