Synthesis of diverse well-defined functional polymers based on hydrozirconation and subsequent anti-Markovnikov halogenation of 1,2-polybutadiene

Article abstract of DOI:10.1021/ma202628p

For the first time, hydrozirconation and halogenolysis of 1,2-polybutadiene (1,2-PBD, by living anionic polymerization) were studied to synthesize reactive polyhalohydrocarbons, which provide a platform for preparing well-defined functional polymers via macromolecular substitution. Hydrozirconation and halogenolysis afforded quite convenience for anti-Markovnikov hydrohalogenation of 1,2-PBD with controllable degree of functionalization. Diverse functional polymers and branched polymers were synthesized after macromolecular substitution reaction with a broad range of commercially available nucleophiles (amines, phenols, alcohols, carbanions, carboxylates, and azide) or macromolecular nucleophiles. NMR and GPC characterizations confirmed high conversion in substitution reaction and narrow molecular weight distribution of the resultant functional polymers, respectively. The methodology utilizing Schwartz's reagent for hydrozirconation of macromolecules could greatly facilitate the modification of vinyl groups containing polymers with high efficiency.

Full text of DOI:10.1021/ma202628p

Article
pubs.acs.org/Macromolecules
Synthesis of Diverse Well-Defined Functional Polymers Based on
Hydrozirconation and Subsequent Anti-Markovnikov Halogenation
of 1,2-Polybutadiene
Jun Zheng, Feng Liu, Yichao Lin,†,‡ Zhijie Zhang,†,‡ Guangchun Zhang,†,‡ Lu Wang,†,‡ Yan Liu,†
†
,‡
†,‡
,†
and Tao Tang*
†State Key Laboratory of Polymer Physics and Chemistry, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences,
Changchun 130022, China
‡
Graduate School of the Chinese Academy of Sciences, Beijing 100039, China
*
S Supporting Information
ABSTRACT: For the first time, hydrozirconation and
halogenolysis of 1,2-polybutadiene (1,2-PBD, by living anionic
polymerization) were studied to synthesize reactive poly-
halohydrocarbons, which provide a platform for preparing
well-defined functional polymers via macromolecular sub-
stitution. Hydrozirconation and halogenolysis afforded quite
convenience for anti-Markovnikov hydrohalogenation of 1,2-
PBD with controllable degree of functionalization. Diverse
functional polymers and branched polymers were synthesized after macromolecular substitution reaction with a broad range of
commercially available nucleophiles (amines, phenols, alcohols, carbanions, carboxylates, and azide) or macromolecular
nucleophiles. NMR and GPC characterizations confirmed high conversion in substitution reaction and narrow molecular weight
distribution of the resultant functional polymers, respectively. The methodology utilizing Schwartz’s reagent for hydrozirconation
of macromolecules could greatly facilitate the modification of vinyl groups containing polymers with high efficiency.
1
. INTRODUCTION
polybutadiene (PBD) backbone or side chain offers oppor-
tunities for various modification reactions. Plenty of functional
groups (e.g., hydroxyl, carbonyl, silyl, epoxy, etc.) were
successfully introduced onto PBD chains via reactions with
double bonds. A pioneering research has been reported on
hydroboration of 1,2-PBD followed by oxidation and hydrolysis
Living polymerization methods (living radical and ionic
polymerization) have widely been used to achieve a high
degree of control over the resultant polymers and provide
1
,2
polymers with the narrowest molecular weight distribution.
But relatively low functional groups tolerance restricts the
synthesis of functional polymers directly by living polymer-
ization methods. To overcome such obstacles, a combination of
living radical polymerization (of monomers bearing reactive
5
for synthesis of well-defined polyalcohol without gelation. By
means of hydrocarboxylation and hydroacylation, PBD could
be transformed to poly(carbonyl acid) or polyaldehyde, using
6
3
,4
palladium catalyst in CO pressure or by radical addition of
moieties) and subsequent postmodification approaches
7
aliphatic aldehydes. Thiol−ene click chemistry was employed
provides possibilities for preparation of various functional
polymers with control over molecular weight, functionality, and
tailored properties. However, living anionic polymerization
seems to be extremely incompatible with most functional
groups. Therefore, it is still a key challenge to prepare
functional polymers directly or indirectly by living anionic
polymerization. Instead of synthesis of monomers bearing
reactive groups for living anionic polymerization, we try to
introduce versatile reactive moieties with high efficiency into
polymers for subsequent modification. By this way, a family of
diverse well-defined functional polymers would be prepared
indirectly by anionic polymerization, when incorporation of
reactive groups was performed on an appropriate polymer
precursor from living anionic polymerization.
to introduce functional groups onto 1,2-PBD homopolymer or
8
,10
block polymer.
The recently reported cyclopropanation of
PBD for the preparation of poly(cyclopropanyl acid) or ester
would be feasible with controllable degree of functionaliza-
11
tion. Epoxidation and hydrosilylation seem to be the most
1
2,13
popular methods used in practice due to reactive epoxy ring
and functional hydrosilanes
1
4,15
for possible further trans-
formation. Different postmodification methods selectively or
nonselectively toward 1,4- or 1,2-PBD successfully afford
various reactive groups grafted PBDs accompanied by side
reactions in some cases. Although most of grafted groups vastly
expand the properties of PBD, they are not suitable for later
It is known that butadiene, one of common monomers, can
be polymerized by living anionic polymerization with tunable
,4- or 1,2-microstructure. The nature of unsaturated bonds in
Received: December 4, 2011
Revised: January 10, 2012
Published: January 24, 2012
1
©
2012 American Chemical Society
1190
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polymer-analogous modification due to limited reactivity
toward few substrates.
with yield 85% and stored in nitrogen-filled glovebox (used within 1
month).
2.2. Synthesis of N,N-Dipiperidine Ethane (DPE). Piperidine
24
14
It will be needed to incorporate a versatile group that can
be highly reactive toward a broad range of substrates for the
conversion into functional groups. Halogen groups, considered
as versatile groups, are quite reactive toward abundant
nucleophiles (e.g., alkoxy, azide, nitrile, organometallics for
C−C coupling, and so forth). Introduction of halogen onto
polymers, especially primary halogen groups (in favor of
substitution than elimination), would be an excellent choice for
subsequent transformation of halogens into diverse functional
moieties via substitution reaction. Classical hydrohalogenation
by hydrogen halides usually shows limited control over anti-
Markovnikov halogenation although it has been applied
(
17.2 g, 0.2 mol) and 1,2-dichloroethane (9.4 g, 0.1 mol) were mixed
in 60 mL of H O with 8.8 g of sodium hydroxide. The mixture was
2
vigorously stirred in 80 °C oil bath for 12 h. Upper organic layer of the
final immiscible mixture was separated and washed with water, vacuum
distilled in the presence of sodium hydride to afford transparent oil-
like liquid with yield of 70% (purity >98% GC). δ (300 M, CDCl ):
H
3
2.48 (s, 4H, N−CH
−CH
−N), 2.40 (br, 8H, 2N (CH )5), δ 1.6−1.48
2 2
2
2
2
(
m, 8H, 2N(CH CH ) ), δ 1.46−1.32 (m, 4H, 2CH ).
2
2
2
2
2
.3. Polymerization of Butadiene. 1,2-Polybutadiene (1,2-PBD,
with vinyl content (Cv) of 98%) was prepared in hexane with DPE at
10 °C under an argon atmosphere using sec-butyllithium (BuLi) as
initiator ([DPE]/[BuLi] > 5 (mol/mol)), while 1,2-PBD with Cv of
8% was synthesized in THF at −10 °C without DPE.
.4. Hydrozirconation of PBD and Halogenolysis. PBD
−
8
16
industrially for rubber materials. Hydrozirconation and later
halogenolysis are highly efficient for halogenation of alkene/
alkyne in anti-Markovnikov form (high reaction rate and mild
condition compared to electrophilic addition reaction with
2
(∼0.15 g) was dissolved in 20 mL of THF and stirred overnight in
a N -filled Mbraun glovebox. Cp ZrHCl powder was added and
vigorously stirred. The solution became dark red after all the powder
dissolved, to which solid halogenation reagent (NBS, NCS, NIS, or I2)
2
2
17,18
hazardous hydrohalide
). However, hydrozirconation of
was added for halogenolysis. The mixture was stirred for 1 h, and
macromolecules with unsaturated carbon−carbon bond in the
drops of degassed methanol were added to finish the reaction. After
concentrating by rotary evaporator, the viscous product was washed
with methanol and purified by dissolution−precipitation using
methane dichloride/methanol for 3−5 cycles. Isolated halogenated
polymers were in ca. 80% yield after dried under vacuum at 40 °C
overnight.
2.5. Synthesis of Functional Polymers by Macromolecular
Substitution Reaction. A typical procedure for all the selected
nucleophiles was as follows: 0.18 g of iodinated PBD (92% or 80%)
was dissolved in 15 mL of THF with 400−500 mol % nucleophiles and
sufficient base (NaH or K CO ). Tetrabutylammonium bromide was
backbone or pendent chains is rarely reported to our best
1
9,20
knowledge.
The named hydrozirconation reagent, generally
referred to as “Schwartz’s reagent”, i.e., bis(cyclopentadienyl)-
zirconium hydrochloride (Cp ZrHCl), is a well-known and
2
convenient reagent in organic chemistry for functionalization of
2
1,22
alkenes.
In this study, we demonstrate successful hydro-
halogenation of 1,2-PBD (prepared by anionic polymerization)
with anti-Markovnikov form by hydrozirconation and sub-
sequent halogenolysis (Scheme 1). The synthesized well-
2
3
used as phase-transfer catalyst when alcohols or phenols acted as
nucleophiles. The mixture was stirred at 60 °C for 24 h under an argon
atmosphere, and then the mixture was filtrated and concentrated. The
synthesized functional polymers were isolated by precipitation with
methanol and dried at 40 °C under vacuum.
Scheme 1. Hydrozirconation of 1,2-Polybutadiene and
Halogenolysis Methods to Preparation of
Polyhalohydrocarbon as a Platform for Diverse Functional
Polymers
2.6. Characterization. NMR spectra were performed on a Bruker
AV300 (400) spectrometer by using CDCl as a solvent. Relative
3
molecular weights were determined by gel permeation chromatog-
raphy (GPC) on TOSOH HLC 8220 GPC at 40 °C using THF as an
eluent against linear polystyrene standards. Differential scanning
calorimetry (DSC, Perkin-Elmer 7 DSC instrument) was carried out in
the range from −30 to 100 °C at a heating rate of 30 °C/min and then
cooled down to −30 °C at a cooling rate of 30 °C/min. The secondary
heating rate was 10 °C/min for glass transition temperature (T )
g
determination. Thermogravimetric analysis (TGA) was performed on
SDTQ600 (TA Instruments) under nitrogen flow at a heating rate of
1
0 °C/min.
defined halogenated 1,2-PBD was used as a platform for the
preparation of diverse functional or grafted polymers via
macromolecular substitution. Importantly, this method would
not only produce novel well-defined polymers which could not
be prepared directly by classical polymerization but also
develop alternative applications of Schwartz’s reagent in
polymer chemistry.
3
. RESULTS AND DISCUSSION
3.1. Hydrozirconation of 1,2-Polybutadiene. Figure 1a
1
shows H NMR spectra of 1,2-PBD (Cv = 88%) and
hydrozirconated 1,2-PBD. It could be seen that the hydro-
zirconation of 1,2-PBD was realized with high conversion by
using Schwartz’s reagent (ZrH) in equivalent molar amount of
double bonds of 1,2-PBD. The typical resonance peak at 4.9
2. EXPERIMENTAL SECTION
ppm ascribed to terminal protons of CHCH almost
2
2.1. Materials. All the solvents (tetrahydrofuran (THF), hexane)
disappeared, and a new sharp single peak at 6.0 ppm assigned
to protons of Cp rings was observed. In practice, when ZrH was
added to THF solution of PBD, the transparent solution turned
to yellow in a minute, and ZrH was completely dissolved after
were distilled from sodium/potassium alloy with benzophenone.
Bis(cyclopentadienyl)zirconium dichloride (99%) was purchased from
Alfa Aesar. N-Bromosuccinimide (NBS) was recrystallized from hot
water, washed with alcohol, and vacuum-dried as white flakelike
crystals, while N-chlorosuccinimide (NCS) (98+%) and N-iodosucci-
nimide (NIS) (97%) were used as received from Alfa Aesar. The
commercially available nucleophiles and other reagents used in this
1
0 min when 30% of ZrH (molar ratio of [ZrH] to [CC])
was added. If the loading of ZrH was high (70% or 100%), the
solution color turned to dark red, and the reaction finished
within 4 h at 30 °C (Figure 1b). Because of high reactivity of
Schwartz’s reagent toward terminal alkenes, quantitative
work were in chemically pure grade. Schwartz’s reagent (Cp ZrHCl)
2
23
was prepared using diisobutylaluminum hydride (1 M in hexane)
1
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bromo-, and N-iodosuccinimide (NCS, NBS, and NIS,
respectively) or molecular iodine. All of the halogens (Cl, Br,
I) could be successfully incorporated onto pendent groups of
1
PBD in anti-Markovnikov form. Figure 2 shows the H NMR
1
Figure 2. H NMR spectra of halogenated (PBD-I, PBD-Cl, PBD-Br)
and hydrogenated (PBD-H) of PBD with 30% degree of
functionalization and pristine PBD (Cv = 88%).
spectra of chlorinated (PBD-Cl, by NCS), brominated (PBD-
Br, by NBS), and iodinated (PBD-I, by NIS) PBD with about
3
0% degree of functionalization. The new resonance peaks
centered at 3.5 (PBD-Cl), 3.4 (PBD-Br), and 3.2 ppm (PBD-I)
were assigned to methylene protons of CH −Cl, CH −Br, and
2
2
CH −I, respectively. The chemical shifts are in the order of
2
halogen electronegativity. When hydrozirconated 1,2-PBD was
treated with acidified methanol instead of succinimide, pendent
vinyl groups was hydrogenated (PBD-H), resulting in the
formation of methyl groups (δ 0.8 ppm in H NMR). The
functionalization degree (halogenation and hydrogenation) of
1
1
Figure 1. H NMR (300 MHz) spectra of (a) 1,2-PBD (Cv = 88%)
(
in CDCl ) and hydrozirconated 1,2-PBD (in C D ) and (b)
3
6
6
brominated PBDs from hydrozirconation (various reaction time)
and then halogenolysis (quenched with NBS) of 1,2-PBD (Cv = 88%)
at 30 °C.
3
0% is consistent with the feed amount ([ZrH]/[CC] = 0.3)
of ZrH and succinimide, indicating that these reactions are
almost quantitative.
3
.2.2. Degree of Halogenation with Controllable Fashion.
conversion could take place successfully. All of the pendent
vinyl groups could be hydrozircnoated, meaning no steric
hindrance effect was observed. It should be mentioned that the
use of THF as solvent is an important factor for such high
reaction efficiency. The insolubility of Schwartz’s reagent would
bring kinetic hindrance for the reactions with macromolecules.
Comparatively, hydrozirconation was much faster in THF than
It is an interesting question whether hydrozirconation and
halogenolysis were quantitatively controllable for halogenated
PBDs with various functionalization degrees. Figure 3a shows
H NMR spectra of isolated brominated PBDs from varied
feeding of ZrH. As the feed ratio increased, the relative intensity
1
of peak at 3.4 ppm (CH −Br) increased while the intensities of
2
peaks at 5.5 and 5.0 ppm decreased, indicating that the degree
of bromination was gradually enhanced. In addition, an
unexpected peak (at 0.8 ppm) was also observed, the intensity
22
in hydrocarbon solvents due to donor capability of THF.
Therefore, the dissociation of ZrH cluster by THF greatly
promoted the rate of hydrozirconation reaction with 1,2-PBD.
Hence, hydrozirconation of PBD macromolecules is kinetically
favorable in THF. Such hydrozirconated polymers are
thermally stable in solution at room temperature, but sensitive
to oxygen or moisture, and they can react with a variety of
electrophiles including protons and halides or undergo
of which was increased with the intensity of CH −Br. This peak
2
was assigned to protons from hydrogenated unit, meaning that
the resultant polymers are a kind of copolymers of butadiene, 4-
bromo-1-butene, and 1-butene. Figure 3b shows the plot of the
content of each structural unit versus the feeding ratio. The
formation of 1-butene structural unit was attributed to
hydrolysis (with methanol in work-up) of residual alkylzirco-
nium from incomplete halogenolysis (Figure 4 and Figure S1 in
the Supporting Information). With the increase of bromination
2
2
transmetalation reactions for functional polymers. (For
example, our preliminary study has demonstrated that this
polyorganozirconium could be reactive for initiating ethylene
polymerization.) Halogenolysis is one of the examples
discussed in this work for preparing reactive polymers.
degree, glass transition temperatures (T ) of the resultant
polymers were increased according to DSC results (Table 1 and
Figure S2).
g
3.2. Halogenolysis of Hydrozirconated 1,2-PBD for
Preparing Reactive Polyhalohydrocarbons. 3.2.1. Incor-
poration of Halogen Atoms (Chlorine, Bromine, Iodine) via
Halogenolysis. Halogenolysis reaction was carried out with
different sources of cationic halogen, such as N-chloro-, N-
Additionally, different halogenolysis reagents showed differ-
ent ceiling degree of halogenations under the same reaction
conditions (Figure S3). Only 50% chloronation or 77%
bromination was achieved when NCS or NBS was used,
1
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Table 1. Molecular Weights of Halogenated 1,2-PBDs (Cv of
98%)
PDI
w
a
a
a
b
polymers
,2-PBD
M (g/mol) M (g/mol)
(M /M )
Tg (°C)
n
w
n
1
15800
15400
13500
11900
11600
10300
10300
10200
7700
16500
16300
14900
13700
13300
11700
11500
11700
8300
1.04
1.06
1.10
1.15
1.15
1.13
1.12
1.15
1.09
1.07
−7.4
−3.1
1.7
c
PBD-Br(8% )
c
PBD-Br(30% )
c
PBD-Br(51% )
4.2
c
PBD-Br(66% )
4.4
c
PBD-Br(77% )
8.0
c
PBD-H(99% )
−24
19
c
PBD-I(92% )
c d
PBD-I(92% )
c e
PBD-I(80% )
2000
2200
a
b
Determined by GPC in THF vs linear PS standards. Determined by
c
1
DSC (Figure S2). Degree of functionalization determined by H
NMR spectroscopy. The number molecular weights of parental PBD
was about 9600 g/mol. The number molecular weights of parental
d
e
PBD was about 2200 g/mol.
incomplete halogenolysis, especially when NCS is used. The
low degree of chlorination was also observed in hydro-
26
zirconation of small molecular alkenes. Fortunately, using
molecular iodine indeed promotes halogenolysis, which leads to
the formation of almost complete iodinated PBD. Moreover,
another great advantage of using molecular halogen is the
regeneration of bis(cyclopentadienyl)zirconium dihalide, which
2
6,27
could be separated and reused.
Owing to the existence of unreacted zirconium moieties on
polymer chains, additional care was required for purification.
Deoxygenated methanol should be used to convert all the
unreacted organic zirconiums to methyl groups before exposed
28
in air. Otherwise, possible oxygen-induced radical coupling
1
Figure 3. (a) H NMR (300 MHz, CDCl ) spectra of brominated
3
would bring a shoulder peak in GPC trace of halogenated
polymer (Figure S4). Highly halogenated 1,2-PBDs were slight
yellow (PBD-Br) or brown (PBD-I) solid, which were stable at
room temperature in desiccator for several months (GPC traces
polybutadiene from varied feeding addition and starting polybutadiene
(
Cv = 98%). (b) Microstructure content of brominated PBDs plotted
1
with varied feeding addition (calculated from H NMR (a)).
1
and H NMR spectra did not change).
3
.2.3. Molecular Weight and Polydispersity of the
Resulting Polyhalohydrocarbons. It is crucial to maintain
lengths of parental polymers after postpolymerization mod-
ification. Thus, side reactions, such as chain-scission and cross-
linking, should be avoided during polymer modification.
Unfortunately, chain-scission reaction indeed happened during
the hydrozirconation of 1,2-PBD with Cv of 88%. However, the
chain-scission could be greatly alleviated when 1,2-PBD with
Cv of 98% was used as parental materials (Figure 5), which
gave the viability of the halogenation methodology based on
hydrozirconation and encouraged us to make deep inves-
tigation. As we know, carbon−carbon double bond of the
backbone is a key factor causing chain-scission; i.e., internal
double bonds hydrozirconated compounds undergo β-alky
elimination, which resulted in chain cleavage. A similar
depolymerization process has been reported in hydrogenolysis
Figure 4. 13C{H} NMR (CDCl , 100 MHz) spectra of brominated
3
(
77%) and iodinated (92%) PBD and DEPT135 NMR spectrum of
iodinated PBD (92%).
29
of polyethylene and polypropylene. Only increasing Cv
content could the degree of chain scission be reduced.
Increasing molecular weight of parental PBDs was useless for
PBD with Cv of 88% to maintain high molecular weight after
hydrozirconation and halogenolysis. The new generated end-
groups from chain scission would be halogens after
halogenolysis. (Systematical work related to chain scission
behavior and possible mechanism will be discussed particularly
in another paper.) Therefore, this method is only suitable for
respectively. It was helpless solely by extending halogenolysis
time when succinimide was used as electrophilic halogenation
reagent. However, when I was used, iodinated PBD with a
2
higher degree of halogenation (92%) was obtained. Con-
sequently, the incomplete halogenolysis limited the complete
halogenation. It is possible that the reactivity of grafted
zirconium is weakened as the halogenolysis goes, resulting in
1
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Table 2. Summary of Molecular Weights of Starting 1,2-
PBDs (Cv of 98%) and the Corresponding Iodinated PBDs
a
a
a
polymers
M (g/mol)
n
Mw (g/mol)
PDI (M /M )
w
n
b
PBD2K
2200
2400
1.07
1.07
1.04
1.09
1.04
1.15
1.05
1.27
c
d
d
PBD2K-0.8I
5800
6200
b
PBD10K
9700
10000
c
c
c
d
d
PBD10K-0.9I
24400
26200
b
PBD15K
15900
16600
d
d
PBD15K-0.9I
32400
37900
b
PBD30K
28100
29600
d
d
PBD30K-0.3I
21000
26600
a
b
Determined by GPC in THF vs linear PS standards. Parental PBDs
with different molecular weights (2K, 10K, 15K, 30K) for hydro-
c
zirconation. Iodinated polymers from corresponding PBD with
d
certain degree of halogenation (0.8, 0.9, 0.9, and 0.3). Calculated
according to molecular weights from GPC after considering degree of
halogenation.
Figure 5. GPC traces of brominated 1,2-PBDs (Cv of 88% and 98%)
from hydrozirconation with varied feeding ratios ([ZrH]).
the halogenation of PBDs with high Cv (>98%) for
preservation of molecular weights. Although DPE is a powerful
agent for synthesizing 1,2-PBD with high Cv by living anionic
3
0
polymerization, it failed in preparing 100% 1,2-PBD with high
molecular weight. However, high iodinated PBD with preserved
molecular weights and PDI would be prepared after hydro-
zirconation of 1,2-PBD (Cv of 98%, M < 15 kg/mol) and
n
halogenolysis (Figure 6 and Table 2). In the case of 1,2-PBD
Figure 7. Hydrohalogenation of poly(p-(3-butenyl)styrene) by
1
hydrozirconation and halogenolysis: H NMR (300 MHz, CDCl )
3
and GPC results of parental polymer (PVSt) and brominated polymer
(PSt-Br).
reagent mediated hydrogenation of polybutadiene or poly-
31
Figure 6. GPC traces of iodinated PBDs and corresponding parental
PBDs.
isoprene. However, it is believed that this chain scission will
be useful on polymer recycling.
Although chain-scission took place, the halogenated polymer
from 98% 1,2-PBD retained relatively high molecular weights
and low polydispersity index (Tables 1 and 2). Such
halogenated 1,2-PBDs could be used as reactive building
blocks for functional materials and polymer architecture design
with high molecular weight (30 kg/mol), the changes of PDI
and molecular weights restricted the application of hydro-
zirconation of PBD (Cv = 98%) due to the existence of 1,4
structure. We speculated that hydrozirconation of 100% 1,2-
PBD would be free of such molecular weight limitation and
chain-scission reaction. For a special example, no chain-scission
happened in the hydrozirconation of poly(p-(3-butenyl)-
styrene) (60 kg/mol, PDI = 1.2, from living anionic
polymerization) and its subsequent halogenolysis due to free
double bonds in the backbone (Figure 7). As we can see,
Schwartz’s reagent was quite sensitive to backbone double
although it was thought that terminal vinyl groups were favored
(
grafted or polymer brush) via macromolecular substitution
3
2−37
reaction,
which would facilitate the preparation of
polymers with low PDI described in following section.
3.3. Preparation of Functional Polymers by Macro-
molecular Substitution. Versatile reactivity of incorporated
halogens toward various nucleophiles facilitates abundant
functionality of synthesized polyhalohydrocarbon after macro-
molecular substitution. Typical chemical reagents (Figure 8)
available in our laboratory were used to demonstrate this idea.
As summarized in Table 3, the experiments with all the selected
nucleophiles indicated the success of substitution reaction on
versatile halogen groups to form a diverse of functional
2
6
for hydrozirconation than internal double bonds. This
phenomenon would be helpful for microstructure character-
ization of PBD and diagnosis of microstructure change in
polymerization. Chain scission was also observed in Schwartz’s
1
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perfluoro-1-octanol into side chains of PBD. Cyclopentadiene
containing PBD could be a kind of self-vulcanized rubber
materials with thermoreversible cross-linking−de-cross-linking
properties (Diels−Alder and retro-Diels−Alder reaction of
grafted cyclopentadienes). Azobenzene-functionalized polymer
39
is a kind of photoresponsive polymer and also would be used
40
in host−guest supermolecular chemistry, while carbazole-
modified polymers have been demonstrated to photoconduc-
41
tive or electric conductive polymers. Alkyne, furan, and azide
substituted polymers are perfect candidates for “click” reactions,
especially in the combination of living anionic polymerization
and click chemistry for synthesis of well-defined polymer brush
42
or comb polymers.
It is possible to use mono-end-functional polymers as
43−45
macronucleophiles,
which provides a method to synthesize
grafted (or branched) polymers via substitution reaction. For
example, methoxypoly(ethylene glycol)s (MPEGOH) were
grafted onto halogenated PBD in the presence of sodium
hydride by the Williamson ether approach. PBD-g-PEG was
synthesized with low PDI (1.05), and the graft ratio determined
by GPC was about 20 mol % (Figure S6). When living
polybutadienyllithium (1,4-PB-Li) was used as a macro-
molecular nucleophile to react with iodinated PBD, mono-
dispersed PBD-I grafted 1,4-PBD (PBDI-g-PBD) was prepared
with the graft ratio of 40 mol %, although dimeric products
Figure 8. Chemical structures of various nucleophiles used in
macromolecular substitution for functional and branched polymers.
1
polymers. As confirmed by H NMR (Figure S5a and Table
S1), the macromolecular substitution reaction proceeds with
good conversion. Both molecular weight and molecular weight
distribution were well preserved as elucidated by GPC
measurement (Figure S5b). These results verified the success
of the mentioned-above proposal, i.e., to prepare diverse
functional polymers with controlled structure by incorporation
of versatile reactive groups on well-defined polymer chains and
subsequent polymer-analogy modification.
46
were formed (Figure S7a). The length of branch chains and
density of grafting would be easily adjusted by controlling the
molecular weight of PB-Li and PB-Li/PBD-I ratio (Figure S7b).
Hence, monohydroxyl, carboxyl, or other nucleophilic moieties
terminated polymers could undoubtedly undergo similar
approach to form branched or comb polymers. In these
situations, living anionic macromolecular species were utilized
to graft onto a well-defined polymer chain, which would be
fascinating for synthesizing well-defined nonlinear polymer by
living anionic polymerization. This feasibility should be
attributed to the high reactivity of halogen groups toward
various nucleophiles. Therefore, well-defined polyhydrohalo-
The resultant functional moieties on the 1,2-PBD would
provide a potential as advanced materials. For example,
poly(ionic liquid) was formed by the incorporation of
methylimidazole, which could be applied in full cell alkaline
38
anion exchange membranes and antibacterial or antistatic
materials. Fluororubber was made by incorporation of
Table 3. Summary of Nucleophiles in Experiments and Degree of Conversion, Molecular Weight, and Molecular Weight
Distribution of the Resultant Functional Polymers (PBD-Nu) after Macromolecular Substitution
a
b
c
n
nucleophiles (Nu)
imide or amines
conv (%)
M (g/mol) (PBD-I)
Mn (g/mol) (PBD-Nu)
M /M
n
w
d
phthalimide
-methylimidazole
80
32400
24400
5 800
24400
24400
24400
24400
5800
35700
18400
7000
1.26
e
1
100
100
100
100
100
carbazole
1.07
1.12
phenols
phenol
19500
33600
12900
h
hydroxyazobenzene
allylmagnesium chloride
f
carbanions
1.15
h
f
g
cyclopentadienyl sodium
>90
j
1
1
,4-polybutadienyllithium (M = 2200 g/mol)
40
25000
863000
3000
1.05
1.20
1.10
1.22
e
n
j
,4-polybutadienyllithium (M = 14300 g/mol)
47
24400
5800
n
i
alcohols
propargyl alcohol
furfuryl alcohol
47 (48 )
i
41 (59 )
32400
5800
17200
7100
i
1
H,1H-perfluorooctanol
39 (51 )
j
MPEG-OH (M = 2000 g/mol)
20
24400
24400
24400
68000
20600
13300
1.05
1.07
1.08
n
carboxylates
azide
sodium acetate
sodium azide
50
k
100
a
1
b
Determined from H NMR (Figure S4a); 100% for all the halogen was substituted and converted to functional groups by nucleophiles. Calculated
c
from the conversion and the characteristics of the parental polymers. Determined from GPC in THF against linear PS standards (Figure S4b).
d
e
f
g
Phthalimide potassium was used. Not measured due to insolubility of polymer in THF. Reaction was carried out below 0 °C. Estimated by TGA.
After purification, insoluble solid polymer was obtained because of D−A cross-linking. Ratio of elimination reaction. Graft ratio determined from
h
i
j
k
GPC (Figures S6 and S7). THF/DMF (v/v 4:1) was used.
1
195
dx.doi.org/10.1021/ma202628p | Macromolecules 2012, 45, 1190−1197

Macromolecules
Article
carbons provide an excellent platform for synthesis of diverse
functional polymers as well as nonlinear polymers.
51073149) and the Fund for Creative Research Groups (no.
50921062).
However, it should be noted that phase separation would
happen in some case during postpolymerization reaction. For
example, when 1-methylimidazole and perfluoro-1-octanol were
used as nucleophiles, the precipitation of polymers was
observed, which usually results in a low conversion. Despite
precipitation, high conversion was still obtained for the reaction
of 1-methylimidazole with polyhalohydrocarbon. Optimizing
reaction conditions (such as solvents and reaction temperature)
would be possible to avoid such problem. It is easy to remove
excess small molecules by precipitation in methanol in most of
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