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Polym Int 48 :99–108 (1999)
Polymer International
Anionic synthesis of
x-dimethylamino-functionalized polymers by
functionalization of polymeric organolithiums
with 3-dimethylaminopropyl chloride
Roderic P. Quirk,*,¹ Kwans oo Han and Youngjoon Lee
Maurice Morton Ins titute of Polymer Science , The Univers ity of Akron , Akron , Ohio 44325 -3909 , USA
Abstract : The functionalization reactions of polystyryllithium, polyisoprenyllithium and polybutadienyllithium in benzene with 3-dimethylaminopropyl chloride have been investigated in detail.
The eþ ects of addition mode (normal and inverse addition), added Lewis bases (THF and TMEDA),
temperature and concentration have been investigated. The polymer products were analysed by SEC,
1H and 13C NMR spectroscopy and end-group titration. The pure x-dimethylamino-functionalized
polymers were quantitatively isolated by silica gel column chromatography. The functionalizations of
polystyryllithium, polyisoprenyllithium and polybutadienyllithium by normal addition in benzene
produce the corresponding x-dimethylamino-functionalized polymers in isolated yields of 67% , 85%
and 90% , respectively. Functionalization efficiencies were improved by using the inverse addition procedure and by post-polymerization addition of Lewis bases before functionalization.
( 1999 Society of Chemical Industry
Keywords : anionic polymerization ; functionalization ;
butadienyllithium ; amine functionalization ; end-group
polystyryllithium ;
polyisoprenyllithium ;
poly-
INTRODUCTION
One of the unique aspects of living anionic polymerization is the ability to prepare u-functionalized
polymers by post-polymerization reactions with electrophilic reagents.1h3 Although a variety of functionalization reactions have been reported, many of these
have not been adequately characterized or optimized
for general utility.1 In general, it is necessary to
investigate each speciüc functionalization reaction
individually and to determine optimum experimental
procedures. An alternative to these speciüc functionalization procedures is to ünd general, quantitative
functionalization reactions which are eþective for a
variety of diþerent functional groups.1
The reaction of polymeric organolithium compounds with substituted 1,1-diphenylethylenes and
1-phenyl-1-arylethylenes has been shown to be a
useful, general, living functionalization reaction for
the preparation of polymers functionalized with
amine,
phenol,
carboxyl
and
ýuorescent
groups.1,2,4,5
The
reaction
of
polymeric
organolithium compounds with silyl halides contain-
ing functional groups or protected functional groups
has been shown to proceed efficiently for the perýuoroalkyl group and other functionalization reactions.6,7
Another simple, potentially useful, general functionalization methodology utilizes the reaction of
polymeric organolithium compounds with substituted alkyl halides as shown in eqn (1),
* Corres pondence to : Roderic P Quirk, Maurice Morton Ins titute of
Polymer Science, The Univers ity of Akron, Akron, Ohio 44325-3909,
USA
¹ Vis iting Profes s or, Laboratoire de Chimie des Polymères
Organiques , L’Univers ite Bordeaux I, 1998.
PLi ] ClwCH CH (CH ) CH wX ]
2
2
2n
2
PwCH CH (CH ) CH wX ] LiCl
2
2
2n
2
(1)
where PLi is a polymeric organolithium compound,
and X is a functional group. This Wurtz-couplingtype reaction would be expected to be complicated
by competing elimination reactions (eqn 2)
(Received 2 April 1998 ; revis ed vers ion received 25 May 1998 ;
accepted 2 September 1998 )
( 1999 Society of Chemical Industry. Polym Int 0959-8103/99/$17.50
99
RP Quirk, K Han, Y Lee
and lithium–halogen exchange followed by coupling
to form dimer (eqns 3 and 4).8,9
In addition, it has been reported that free radicals are
formed by single electron transfer during the reaction of organolithium compounds with alkyl halides
under certain conditions.10h14
In spite of these anticipated problems, the reactions of functionalized alkyl halides with polymeric
organolithium compounds have been reported to
proceed in good yields under certain reaction conditions.15h24 For example Nakahama and coworkers15,16 have prepared u-amino-functionalized
polystyrenes and polyisoprenes by reaction of the
corresponding polymeric organolithium compounds
with a-halo-u-aminoalkane derivatives containing a
protected primary amine functionality. The functionalities were greater than 91% ; however, the functionalization reactions were eþected in the presence
of tetrahydrofuran (THF) at [78¡C. Richards et
al.21 reacted polybutadienyllithium with 3dimethylaminopropyl chloride in hexane and reported that the corresponding u-dimethylaminofunctionalized polybutadiene was obtained in
85–95% yield ; however, THF was used in most of
the tabular examples and in the experimental
description for the functionalization reaction. Unfortunately, n-butyllithium was used as the initiator and
the molecular weight distributions were not narrow
(M /M \ 1.17–1.27). Teyssie and co-workers22
w n
reacted
a,u-disodiumpolyisoprene
with
3dimethylaminopropyl chloride in THF at [78¡C
and reported that the amino functionality was 1.9
(95%); however, the molecular weight distributions
were not narrow (M /M \ 1.2–1.3) and the polyw n
isoprene microstructure corresponded to predominantly 3,4-enchainment.
Recently Deffieux and co-workers23 described the
reactions
of
polystyryllithium
and
polybutadienyllithium with chloroalkyl derivatives
bearing oxygen atoms. Reactions of narrow molecular weight distribution polystyryllithium in benzene
with
2-chloroethyl
ethyl
ether
and
3chloropropinonaldehyde diethyl acetal at room temperature produced the corresponding ether- and
acetal-functionalized polystyrenes, respectively, in
93–102% yields.24 Reactions of narrow molecular
weight distribution polybutadienyllithium in toluene
with
2-chloroethyl
ethyl
ether
and
3chloropropionaldehyde diethyl acetal at [30¡C produced the corresponding ether-functionalized
polybutadienes in 92 and 93% yields, respectively.24
These reports of efficient functionalizations of
polymeric organolithium and organosodium compounds by reaction with substituted alkyl halides
100
suggested that these reactions could provide a
general methodology for efficient functionalization
for a variety of diþerent functional groups. Herein is
reported a systematic investigation of the scope and
limitations of the u-dimethylamino functionalization
reaction of polystyryllithium, polyisoprenyllithium
and
polybutadienyllithium
with
3-dimethylaminopropyl chloride in hydrocarbon solution. It
was of interest to develop a useful tertiary amine
functionalization procedure applicable to hydrocarbon solution at room temperature. It was also important to determine the role of amine hetero-atom
complexation on functionalization efficiency with
substituted alkyl chlorides compared to the results of
Deffieux and co-workers23 with an ether oxygen
hetero-atom. The tertiary amine substituent was of
interest because of the ability to form ammonium
salts and ionomers22 as well as the unique ability of
tertiary amines to aid dispersion of üllers such as
carbon black.24
EXPERIMENTAL
Chemicals and solvents
Benzene, tetrahydrofuran, cyclohexane, styrene,
butadiene and isoprene were puriüed as described
previously.25h27 t-Butylbenzene (Aldrich, reagent
grade) was stored over conc H SO (Fisher, 96%)
2 4
for 1 week, followed by separation, washing with distilled water and drying over anhydrous magnesium
sulphate (Fisher, certiüed grade). After stirring over
freshly crushed calcium hydride (Alfa) with intermittent degassing, t-butylbenzene was distilled
under vacuum onto sodium dispersion (Aldrich, 50%
paraffin) with stirring and intermittent degassing. As
required, puriüed t-butylbenzene was distilled
directly into polymerization reactors. Decahydronaphthalene (Aldrich, reagent grade) was puriüed
using the same procedures as described for tbutylbenzene. 3-Dimethylaminopropyl chloride was
formed by neutralization of 1-chloro-3-dimethylaminopropane hydrochloride (Aldrich, 96%) by
sodium hydroxide in distilled water. After drying
sequentially over anhydrous magnesium sulphate
and calcium hydride, followed by several freeze–
degas-thaw sequences on the vacuum line, 3dimethylaminopropyl chloride was distilled into
calibrated ampoules followed by dilution with
benzene.
N,N,N@,N@-Tetramethylethylenediamine
(Aldrich, 98%) was stirred over freshly crushed
calcium hydride for 24 h, followed by several freeze–
degas–thaw cycles and then distillation into calibrated ampoules followed by dilution with benzene.
1,1-Diphenylethylene (Aldrich, 99%) was stirred
over potassium metal at 75¡C and then distilled
under vacuum into calibrated ampoules and diluted
with benzene. sec-Butyllithium (FMC, Lithium
Division, 12 wt% in cyclohexane) was used as
received and titrated using the Gilman double titration method with 1,2-dibromoethane.28
Polym Int 48 :99–108 (1999)
Anionic synthesis of u-dimethylamino-functionalized polymers
Anionic polymerization and functionalization
reactions
All polymerizations and functionalization reactions
were carried out in all-glass, sealed reactors using
breakseals and standard high vacuum techniques.29
Styrene polymerizations were carried out in benzene
(10 vol% styrene) at room temperature using secbutyllithium as initiator. Polymerization and functionalization were monitored using a Quartz UV cell
attached to the polymerization reactor. Functionalization by normal addition was eþected by smashing
the breakseal of a 3-dimethylaminopropyl chloride
ampoule to add the benzene solution directly to the
polystyryllithium solution. Functionalizations using
inverse additions were eþected by smashing the
breakseal of the ampoule containing the benzene
solution of polystyryllithium and addition to a
benzene solution of 3-dimethylaminopropyl chloride.
Conversion of polystyryllithium (j \ 330 nm)30
max
to the corresponding polymeric 1,1-diphenylalkyllithium (j \ 410 nm)31 was eþected by addimax
tion of 1.1 molar equivalents of 1,1-diphenylethylene
via ampoule. The crossover was monitored by UV
spectroscopy and was completed after 2 h.
Butadiene and isoprene polymerizations were
carried out in benzene (3–5 vol% diene) at room
temperature using sec-butyllithium as initiator.
Functionalizations of polybutadienyllithium and
polyisoprenyllithium by 3-dimethylaminopropyl
chloride were eþected using the same procedures as
described for polystyryllithium.
All polymerization and functionalization reactions
were terminated by addition of several millilitres of
degassed methanol via a breakseal. Polymers were
isolated by precipitation of the benzene solutions
into excess methanol. For isolation of polybutadiene
and polyisoprene samples, the methanol solutions
contained 0.5 wt% 2,6-di-tert-butyl-4-methylphenol
(Aldrich, 99%) as stabilizer.
Characterization
Number-average molecular weights were determined
using vapour pressure osmometry (VPO) and sizeexclusion chromatography (SEC). VPO measurements were made using a Knauer Type 11.00
osmometer in toluene (Fisher Scientiüc, Certiüed
ACS) which was distilled from freshly crushed
CaH . Puriüed sucrose octa-acetate (Aldrich) was
2
used as the calibration standard ; it was puriüed by
recrystallization from methanol ; m p 84–85¡C (lit32
m p 83–85¡C). SEC analyses of polymers were performed at a ýow rate of 1.0 ml min~1 in tetrahydrofuran at 30¡C using a Waters HPLC
component system (RI or UV detector) equipped
with six ultra-k-styragel columns (two 500, two 103,
104 and 105 Ó) for low molecular weight samples
(M \ 2 ] 104 g mol~1) and four ultra-k-styragel
n
columns (1 ] 103, 1 ] 104, 1 ] 105 and 1 ] 106 Ó)
for high molecular weight samples (M [ 2
n
Polym Int 48 :99–108 (1999)
] 104 g mol~1) after calibration with either polybutadiene standards from American Polymer Standards Corp. or polystyrene and polyisoprene
standards from Polymer Laboratories.
Thin layer chromatographic (TLC) analyses were
carried out on silica gel plates (Kodak Eastman silica
gel chromatogram sheet 13179 with ýuorescent
indicator) or silica gel coated glass plates (Aldrich,
precoated on glass, Z2,276-6 with ýuorescent
indicator) using toluene as eluent. Silica gel (EM
Science, 220–400 mesh ; dried overnight under
vacuum at 150¡C) column chromatography was used
to separate unfunctionalized polymers from functionalized polymers using toluene as initial eluent
followed by THF to remove the functionalized polymers from the column.
UV–visible spectra of living polymers were
obtained on a Hewlett-Packard 8452 Diode Array
spectrophotometer using a 0.10 cm UV cell attached
to the polymerization reactor. Infrared spectra of
polymers were obtained on a Beckman Instruments
FT-2100 FTIR spectrometer. Polymer ülms were
cast onto KBr plates from CHCl solutions. The
3
microstructures of polybutadienes were calculated
from their infrared absorptions using the modiüed
Kimmer and Schmalz method33 as proposed by
Wang and Peng.34 1H NMR and 13C NMR spectra
were recorded on a Varian Gemini-200 spectrometer
using deuterated chloroform (Aldrich, 99.8%
CDCl ) as solvent. The polymer concentrations were
3
1–5 wt% for 1H NMR and 5–10 wt% for 13C NMR.
1H NMR was used to determine the microstructures
of both polybutadiene and polyisoprene.35
The concentrations of amine chain end groups in
the amine-functionalized polymers were determined
by titration in a 1/1 (v/v) mixture of chloroform and
glacial acetic acid, using perchloric acid (Fisher, 0.1
N in glacial acetic acid) as the titrant and methyl
violet 2B (Aldrich, about 75% dye content) as the
indicator.36
RESULTS
Polystyryllithium functionalization
The amine functionalization of polystyryllithium
(M \ 2.1–5.1 ] 103 g mol~1) with 1.5 molar equivan
lents of 3-dimethylaminopropyl chloride was examined using two diþerent protocols : normal addition
in which 3-dimethylaminopropyl chloride in benzene
was added to polystyryllithium in benzene, and
inverse addition in which polystyryllithium in
benzene was added to 3-dimethylaminopropyl chloride in benzene. In addition, the eþects of chain-end
concentration, temperature, Lewis base additives and
end-capping of the chain end with 1,1diphenylethylene were investigated to optimize the
yield of functionalized polymer. The reaction products were characterized by SEC (see Fig 1); the
dimer fraction was quantitatively determined from
the SEC chromatograms for each procedure. The
101
RP Quirk, K Han, Y Lee
raphy. The results of the complete analysis of the
products of these reactions are shown in Table 1.
The 1H NMR spectrum of the puriüed udimethylamino-functionalized polystyrene (M \
n
2000 g mol~1) (see Fig 2, curve B) exhibited a peak at
d \ 2.21 ppm, which is not observed for the polystyrene base polymer (Fig 2, curve A). This peak was
assigned to the methyl protons in the wN(CH )
32
group by analogy with the corresponding peak
observed at d \ 2.20 ppm for the analogous udimethylamino-functionalized polybutadiene.21 The
13C NMR spectrum of the puriüed udimethylamino-functionalized polystyrene (M \
n
Figure 1. Size exclus ion chromatograms of crude products from
reaction of polys tyryllithium with 3-dimethylaminopropyl chloride
us ing normal addition (curve A) and invers e addition (curve B) ;
the bas e polys tyrene (M \ 2000 g molÉ1, M /M \ 1.05) is
n
w n
s hown in curve C.
amine-functionalized polystyrenes were quantitatively separated and isolated from the non-functional
components (unfunctionalized polystyrene and
dimer) by silica gel column chromatography. The
amine functionalization yield for polystyryllithium
was also determined by amine end-group titration
using perchloric acid36 for samples of the crude
product mixtures. In general, the yield determined
by titration was in good agreement with the isolated
yield obtained by quantitative column chromatog-
Run
Figure 2. 1H NMR s pectra (CDCl ) of bas e polys tyrene (curve A)
3
and purified u-dimethylamino-functionalized polys tyrene (curve
B).
Product Yields (wt %)c
Addition
mode b
PS wH
1
2
3
4
5
6
7
8
9
Table 1. Characterization of the
products from the
functionalization of
polys tyryllithium in benzene with
3-dimethylaminopropyl chloride
at room temperaturea
102
Normal
Invers e
Normalf
Normalg
Normalh
Normali
Normalj
NormalK
Invers el
10
10
16
7
13
12
22
13
7
PS wPS
23
10
24
13
–
–
3
–
4
PS wN (CH ) d
32
67 (65)
80 (77)
60
80
87
88
75
87
89 (91)
PS wN (CH )
32
characterization
M ] 10 É3 e
n
(g mol É1)
M /M
w n
2.2 (2.0)
2.1 (2.0)
2.2
2.2
2.1
2.1
2.0
2.0
5.1
1.05
1.05
1.06
1.06
1.06
1.06
1.05
1.05
1.10
a Functionalizations us ing other chain end s tructures , s olvents and/or temperatures are noted
with footnotes des cribing the s pecific reaction conditions .
b Normal addition corres ponds to addition of 3-dimethylaminopropyl chloride to PSLi ; invers e
addition corres ponds to addition to PSLi to 3-dimethylaminopropyl chloride.
c Dimer wt% from SEC analys is ; quantitative column chromatographic s eparation of nonfunctional polymer fraction (PSwH and PSwPS) from functionalized polymer.
d Yield in parenthes es determined by titration of the crude reaction mixture.
e M determined by SEC us ing polys tyrene s tandards . Values in parenthes es determined by VPO.
n
f t -Butylbenzene as s olvent at 76¡C.
g t -Butylbenzene as s olvent at [21¡C.
h THF added to PSLi before functionalization ([THF]/[PSLi] \ 10).
i TMEDA added to PSLi before functionalization ([TMEDA]/[PSLi] \ 1.2).
j Poly(s tyryl)lithium converted to 1,1-diphenylalkyllithium chain end (DDPELi) by reaction with 1,1diphenylethylene.
k THF added to DDPELi before functionalization ([THF]/DDPELi] \ 10.
l THF added to PSLi before functionalization ([THF]/[PSLi] \ 25).
Polym Int 48 :99–108 (1999)
Anionic synthesis of u-dimethylamino-functionalized polymers
2000 g mol~1) (see Fig 3, curve B) exhibited peaks at
d \ 46 ppm and at d \ 60 ppm, which are not
observed for the polystyrene base polymer (Fig 3,
curve A). The peak at d \ 46 ppm is assigned to the
methyl carbons in the wN(CH ) group ; the corre32
sponding peak was observed at d \ 45.5 ppm for the
analogous u-dimethylamino-functionalized polybutadiene.21 The peak at d \ 60 ppm is assigned to
the methylene carbon adjacent to nitrogen,
CH wN(CH ) ; the corresponding peak was
2
32
observed at d \ 59.7 ppm for the analogous udimethylaminopropyl-functionalized
polybutadiene.21 It is noteworthy that the peak at
d \ 33.7 ppm corresponding to the benzylic carbon
at the terminal chain end of unfunctionalized polystyrene (see Fig 3, curve A, peak a)37 is not observed
in the 13C NMR spectrum of the puriüed functionalized polymer.
The
eþect
of
polystyryllithium
(M \
n
3000 g mol~1) chain-end concentration on this functionalization reaction using the normal addition
mode was examined brieýy and the results are shown
in Fig 4. It was observed that more dimer (28%) was
formed when the chain-end concentration was higher
(6.2 ] 10~3 M) (Fig 4, curve A); only 11% dimer
was formed when the chain end concentration was
1.2 ] 10~3 M (Fig 4, curve B). The eþect of tem-
Figure 3. 13C NMR s pectra (CDCl ) of (A) bas e polys tyrene and
3
(B) purified u-dimethylamino-functionalized polys tyrene (B).
Figure 4. Size exclus ion chromatograms of the functionalization
of polys tyryllithium (M \ 3000 g molÉ1) with
n
3-dimethylaminopropyl chloride us ing PSLi chain-end
concentrations of (curve A) 1.2 ] 10É3 M and 6.2 ] 10É3 M (curve
B).
Polym Int 48 :99–108 (1999)
perature variation on the functionalization of polystyryllithium with 3-dimethylaminopropyl chloride
using the normal addition mode was investigated by
eþecting the functionalizations at both [ 21¡C and
76¡C in t-butylbenzene (Runs 3 and 4 in Table 1).
The size exclusion chromatograms of the products of
these functionalizations are shown in Fig 5.
The eþects of the Lewis bases, THF and
TMEDA, were investigated for both the normal and
inverse modes of addition (Table 1: Runs 5 and 6 for
normal addition ; Run 9 for inverse addition).
Polyisoprenyllithium functionalization
The amine functionalization of well-deüned
polyisoprenyllithiums
(M \ 1.8 ] 103
and
n
4.3 ] 103 g mol~1) in benzene with 1.5 molar equivalents of 3-dimethylaminopropyl chloride in benzene
was examined using the normal and inverse addition
procedures. The eþect of adding stoichiometric
amounts of THF for each addition mode was also
investigated. The amount of dimer formation for
each procedure was determined quantitatively by
SEC analysis as illustrated in Fig 6, curve B. The
amine-functionalized polyisoprenes were quantitatively separated and isolated from the non-functional
Figure 5. Size exclus ion chromatograms of the crude
functionalization products of polys tyryllithium (M \ 2000 g molÉ1)
n
with 3-dimethylaminopropyl chloride at [21¡C (curve B) and at
76¡C (curve C) compared to the bas e polys tyrene (curve A).
Figure 6. Size exclus ion chromatograms of crude products from
reaction of polyis oprenyllithium with 3-dimethylaminopropyl
chloride us ing normal addition (curve B) compared with the bas e
polyis oprene (M \ 1800 g molÉ1, M /M \ 1.08) (curve A).
n
w n
103
RP Quirk, K Han, Y Lee
components (unfunctionalized polyisoprene and
dimer) by silica gel column chromatography. The
amine functionalization yield from polyisoprenyllithium was also determined by amine end-group
titration using perchloric acid36 for samples of the
crude product mixtures. In general, the yield determined by titration was in good agreement with the
yield determined by quantitative column chromatography. The results of complete analysis of the
product mixtures are shown in Table 2.
The 1H NMR spectrum of the puriüed udimethylamino-functionalized polyisoprene (Fig 7,
curve B) shows a peak at d \ 2.22 ppm assigned to
the wN(CH ) protons.21 The polyisoprene micro32
structure was determined to be 92% 1,4-enchainment and 8% 3,4-enchainment by 1H NMR using
the peak integrations at d \ 5.1 and 4.75 ppm.35 The
13C NMR spectrum of the puriüed udimethylamino-functionalized polyisoprene (Fig 8,
curve B) shows peaks at d \ 46 ppm and 60 ppm
Figure 8. 13C NMR s pectra (CDCl ) of (A) bas e polyis oprene and
3
(B) purified u-dimethylamino-functionalized polyis oprene (B).
which are assigned to the CH N(CH ) and
2
32
CH N(CH ) carbons, respectively.21
2
32
Polybutadienyllithium functionalization
The amine functionalization of narrow molecular
weight distribution polybutadienyllithiums (M \
n
1.9 ] 103 and 20 ] 103 g mol~1) in benzene with 1.5
molar equivalents of 3-dimethylaminopropyl chloride in benzene was examined using the normal and
inverse addition procedures. The eþect of adding
stoichiometric amounts of THF for each addition
mode was also investigated. The amount of dimer
formation for each procedure was determined quantitatively by SEC analysis as illustrated in Fig 9,
curve B. The amine-functionalized polybutadienes
were quantitatively separated and isolated from the
non-functional components (unfunctionalized polybutadiene and dimer) by silica gel column chromatography. The yield of amine functionalization of
polybutadienyllithium was also determined by amine
end-group titration using perchloric acid36 for
Figure 7. 1H NMR s pectra (CDCl ) of bas e polyis oprene (A) and
3
purified u-dimethylamino-functionalized polyis oprene (B).
Run
Product Yields (wt %)b
Addition
mode a
PI wH
1
2
3
4
Table 2. Characterization of the
products from the
functionalization of
polyis oprenyllithium (PILi) in
benzene with
3-dimethylaminopropyl chloride
at room temperature
104
Normal
Invers e
Normale
Invers ee
11
6
8
8
PI wPI
(dimer )
PI wN (CH ) c
32
4
1
4
–
85
93 (89)
88 (88)
92 (90)
PI wN (CH )
32
characterization
M ] 10 É3 d
n
(g mol É1)
M /M
w n
(SEC )
1.8
4.3
4.3
4.3
1.08
1.06
1.06
1.06
a Normal addition corres ponds to addition of 3-dimethylaminopropyl chloride to PILi ; invers e
addition corres ponds to addition of PILi to 3-dimethylaminopropyl chloride.
b Dimer wt% from SEC analys is ; quantitative column chromatographic s eparation of nonfunctional polymer fraction (PIwH and PIwPI) from functionalized polymer.
c Yield in parenthes es determined by titration of the crude reaction mixture.
d M determined by SEC us ing polyis oprene s tandards .
n
e THF added to PILi before functionalization ([THF]/[PILi] \ 20).
Polym Int 48 :99–108 (1999)
Anionic synthesis of u-dimethylamino-functionalized polymers
Figure 9. Size exclus ion chromatograms of crude products from
reaction of polybutadienyllithium with 3-dimethylaminopropyl
chloride us ing normal addition (curve B) compared to the bas e
polybutadiene (M \ 1900 g molÉ1, M M \ 1.07) (curve A).
n
w n
samples of the crude product mixture. In general,
the yield determined by titration was in good agreement with the yield determined by quantitative
column chromatography. The results of complete
Product Yields (wt %)b
Addition
mode a
PBD wH
1
2
3
4
Table 3. Characterization of the
products from the
functionalization of
polybutadienyllithium (PBDLi) in
benzene with
3-dimethylaminopropyl chloride
at room temperature
Polym Int 48 :99–108 (1999)
Normal
Invers e
Normale
Invers ee
analysis of the product mixtures are shown in Table
3.
The 1H NMR spectrum of the puriüed udimethylamino-functionalized polybutadiene (Fig
10, curve B) shows a peak at d \ 2.24 ppm assigned
to the wN(CH ) protons.21 The polybutadiene
32
microstructure was determined to be 90% 1,4enchainment and 10% 1,2-enchainment by 1H NMR
using the peak integrations at d \ 5.1–5.7 and 4.8–
5.0 ppm.35 The 13C NMR spectrum of the puriüed
u-dimethylamino-functionalized polybutadiene (Fig
11, curve B) exhibits peaks at d \ 46 ppm and
60 ppm assigned to the CH N(CH )
and
2
32
CH N(CH ) carbons, respectively.21
2
32
DISCUSSION
The reaction of polymeric organolithium compounds
with substituted alkyl halides, especially chlorides
(see eqn 1), may provide a general functionalization
procedure which is independent of the speciüc functional group contained on the alkyl chloride. In order
for this type of nucleophilic substitution reaction to
Figure 10. 1H NMR s pectra (CDCl ) of bas e polybutadiene (A)
3
and purified u-dimethylamino-functionalized polybutadiene (B).
Run
Figure 11. 13C NMR s pectra (CDCl ) of (A) bas e polybutadiene
3
and (B) purified u-dimethylamino-functionalized polybutadiene
(B).
10
6
7
5
PBD wPBD
(dimer )
PBD wN (CH ) c
32
–
\1
1
\1
90
94 (96)
92 (96)
95 (99)
PBD wN (CH )
32
Characterization
M ] 10 É3 d
n
(g mol É1)
M /M
n n
(SEC )
1.9
20
20
20
1.07
1.05
1.05
1.05
a Normal addition corres ponds to addition of 3-dimethylaminopropyl chloride to PBDLi ; invers e
addition corres ponds to addition of PILi to 3-dimethylaminopropyl chloride.
bDimer wt% from SEC analys is ; quantitative column chromatographic s eparation of nonfunctional polymer fraction (PBDwH and PBDwPBD) from functionalized polymer.
c Yield in parenthes es determined by titration of the crude reaction mixture.
d M determined by SEC us ing polyis oprene s tandards .
n
e THF added to PBDLi before functionalization ([THF]/[PBDLi] \ 30).
105
RP Quirk, K Han, Y Lee
be useful as a general functionalization procedure, it
must be possible to obtain the functionalized
polymer in more than 90% yield, preferably using
polymeric organolithiums prepared using alkyllithium initiators in hydrocarbon solution at room
temperature or above. The solvent and counter-ion
requirements are derived from the desire to prepare
well-deüned, functionalized polydienes with high
1,4-microstructure which requires the use of alkyllithium initiators in hydrocarbon solution.2 Thus,
the tertiary amine functionalizations of polystyryllithium, polyisoprenyllithium and polybutadienyllithium
with
3-dimethylaminopropyl
chloride in benzene were investigated as a representative and potentially useful functionalization reaction.
Polystyryllithium functionalization
The results for functionalization of polystyryllithium
are listed in Table 1. In contrast to previous results
by Nakahama and co-workers15 who reported yields
of 99% for functionalization of a,u-dilithiumpolystyrene with a protected primary amine-functionalized
propyl chloride in THF at [78¡C by normal addition, the functionalization of polystyryllithium in
benzene with 3-dimethylaminopropyl chloride by
normal addition yielded the tertiary aminefunctionalized polystyrene in only 67% yield (Run 1,
Table 1). The functionalized polymer was contaminated with signiücant amounts of dimer (23%) (see
Fig 1) and unfunctionalized polystyrene (10%). It is
important to note that the functionalization yield
could not be obtained directly from SEC, because
SEC did not separate the functional and nonfunctional polystyrenes. However, the functional and
non-functional polymers were readily separated by
silica gel column chromatography as described in the
Experimental section.
As
discussed
in
the
Introduction,
the
unfunctionalized polystyrene and dimer were the
expected side products resulting from elimination
(see eqn 2) and lithium–halogen exchange followed
by coupling (see eqns 3 and 4), respectively. It was
anticipated that side reactions such as dimer formation could be minimized by an inverse addition procedure, i.e. addition of polymeric organolithium to
the solution of 3-dimethylaminopropyl chloride.
Using the inverse addition procedure (Run 2, Table
1), the yield of amine-functionalized polystyrene
increased to 80% and the amount of dimer was
decreased to only 10% ; the yield of unfunctionalized
polymer was unaþected by this addition mode.
In an eþort to further increase the efficiency of
this functionalization reaction, and by analogy with
the previous work of Nakahama and co-workers15,16
and Teyssie and co-workers,22 Lewis bases, THF
and N,N,N@N@-tetramethylethylenediamine, were
added to the benzene solution of polystyryllithium
before the functionalization reaction. It is known
that Lewis bases promote dissociation of
106
organolithium
aggregates
to
form
either
unaggregated or less aggregated species which are
generally more reactive than the more aggregated
species.2,8,38h40 Using the normal addition procedure, functionalization of polystyryllithium in the
presence of either THF ([THF]/[Li] \ 10) or
TMEDA ([TMEDA]/[Li] \ 1.2) increased the
yield of u-dimethylamino-functionalized polystyrene
to 87% and 88% (Runs 5 and 6, Table 1), respectively, compared to only 67% in the absence of
Lewis base (Run 1, Table 1). It is interesting to note
that in the presence of THF, inverse addition had
only a modest eþect on the yield of functionalized
polystyrene (89–91%, Run 9, Table 1) compared
with the normal addition procedure in the presence
of THF (87%, Run 5, Table 1). These results are
consistent with previous studies which indicate that
the coupling reactions of alkyl halides with
organolithium compounds are promoted by the addition of Lewis bases.8,9 Although the mechanistic
implications of these eþects are not clear, it is known
that Lewis bases decrease the average degree of
association of the chain-ends2,8,38h40 which suggests
that the functionalization reaction may be favoured
by reaction with the unassociated chain-ends versus
the aggregated species. This is also consistent with
the reduced amount of dimer formation at lower
chain-end concentrations (see Fig. 4); in general,
aggregation of organolithium chain-ends is favoured
by higher chain-end concentrations.2,8
The eþect of temperature on this functionalization
reaction was examined using t-butylbenzene as
solvent. Using the normal addition procedure, functionalization at elevated temperature (76¡C; Run 3,
Table 1) decreased the yield to 60% compared with
67% at room temperature (Run 1, Table 1).
However, functionalization at lower temperature
([21¡C; Run 4, Table 1) increased the yield of functionalized polymer to 80%. It is concluded that the
selectivity for the desired Wurtz-type coupling and
functionalization increases as the temperature is
lowered. This result is in accord with the previous
reports of efficient functionalization of polymeric
organolithiums by alkyl chlorides at low temperatures ([78¡C).15,22
The eþect of chain-end structure on functionalization was investigated by conversion of polystyryllithium to the corresponding polymeric 1,1diphenylalkyllithium by
reaction with 1,1diphenylethylene (DPE) (see eqn 5)
C H
=6 5
PSLi ] CH xC(C H ) ] PSCH C`Li^
2
6 52
2=
C H
6 5
(5)
In general, conversion of polystyryllithium to the
more stable, more sterically hindered, polymeric 1,1diphenylalkyllithium would be expected to increase
selectivity and promote functionalization, as reported
Polym Int 48 :99–108 (1999)
Anionic synthesis of u-dimethylamino-functionalized polymers
for a number of other functionalization reactions
such as carbonation41 and sulphonation.42 Endcapping of polystyryllithium with DPE, however,
using the normal addition procedure only increased
the yield of functionalized polymer to 75% (Run 7,
Table 1), although the yield of dimer decreased signiücantly. Addition of THF ([THF]/[Li] \ 10) to
the polymeric 1,1-diphenylalkyllithium before functionalization with 3-dimethylaminopropyl chloride
increased the functionalization yield for the normal
addition mode to 87% (Run 8, Table 1). This corresponds to an insigniücant eþect of this chain-end
structure, because comparable functionalization
yields are reported for polystyryllithium in the presence of THF (87%, Run 5, Table 1).
It was found that the amount of dimer formation
was increased by increasing the chain-end concentration ; thus the amount of dimer increased from 11%
to 28% by increasing the chain-end concentration
from 1.2 ] 10~3 M to 6.2 ] 10~3 M for functionalization of polystyryllithium with M \ 3000 g mol~1
n
(M /M \ 1.05) (see Fig 4). Since the chain end
w n
concentration decreases for higher molecular weight
polymers at the same monomer concentration, a
beneücial eþect on functionalization efficiency
should be realized with increasing molecular weight.
Thus, for functionalization of polystyryllithium
with 3-dimethylaminopropyl chloride using the
simple normal addition procedure, the highest yields
of u-dimethylaminopolystyrene (87–88%) were
obtained by post-polymerization addition of Lewis
bases such as THF and TMEDA before the functionalization reaction. The functionalized polystyrene was contaminated only with unfunctional
polymer (12–13%) and no dimer using this procedure. Although inverse addition signiücantly
improves functionalization yields in the absence of
Lewis bases, only small improvements (89–91%)
over the normal addition mode (87–88%) are
obtained by inverse addition in the presence of THF.
Lowering the temperature to [ 21¡C also improved
the functionalization yield for the normal addition
mode.
It is important to compare these results with the
studies of Deffieux and co-workers23 for functionalization of polystyryllithium in benzene solution at
room temperature with 2-chloroethyl ethyl ether
(CIE) and 3-chloropropionaldehyde diethyl acetal
(CIAC). In contrast to the results reported herein
(see Table 1), the functionalizations with CIE and
CIAC by the normal addition procedure produced
functionalized polystyrenes in 90–100% yields as
determined by 1H NMR analysis. These authors
invoked complexation of the lithium counter-ion by
the hetero-atom of the chloroalkyl derivative to
explain the high degrees of functionalization
observed. Based on the results reported herein, a
unique role of ether oxygen complexation versus tertiary amine complexation must be involved. If a
complexation with the substituted alkyl halide is
Polym Int 48 :99–108 (1999)
involved before functionalization, the tertiary amine
group appears to be much less eþective in promoting
functionalization of polystyryllithium. This is in
accord with the lower enthalpies of interaction
observed for polystyryllithium interacting with triethylamine (0.3 kcal mol~1 of base) compared with
1,2-dimethoxyethane (9.8 kcal mol~1 of base).39 The
better solvating ability of 1,2-dimethoxyethane is
also manifested in the higher amount of 1,2-polybutadiene obtained in anionic polymerization in the
presence of 1,2-dimethyoxyethane (46% 1,2-microstructure with [1,2-dimethoxyethane]/[PLi] \ 0.6)
compared to triethylamine (33% 1,2-microstructure
with [triethylamine]/[PLi] \ 270), even though
much larger molar ratios of triethylamine were compared.2,43
Polydienyllithium functionalizations
The functionalizations of both polyisoprenyllithium
and polybutadienyllithium (see Tables 2 and 3,
respectively) with 3-dimethylaminopropyl chloride
were much more efficient than the corresponding
functionalizations of polystyryllithium. Even using
the direct addition mode, polyisoprenyllithium was
converted to the u-dimethylaminopolyisoprene in
85% yield, while polybutadienyllithium was functionalized in 90% yield. Richards et al.21 reported
analogous efficient functionalization of polybutadienyllithium ([85%) by 3-dimethylaminopropyl chloride in cyclohexane. Deffieaux and
co-workers23 also reported high functionalization
efficiency (92–93%) for the functionalization of polybutadienyllithium with 2-chloroethyl ethyl ether in
toluene at [30¡C. This dramatic eþect of chain-end
structure was unexpected, especially given the ineffectiveness of the 1,1-diphenylalkyllithium chain end
(see Table 1, Sample 7).
For the functionalization of polyisoprenyllithium,
the inverse addition procedure improved the functionalization efficiency to 93% (Sample 2, Table 2)
from 85% for the normal addition mode (Sample 1,
Table 2). In contrast to the results for functionalization of polystyryllithium, addition of THF
exhibited little inýuence on the efficiency of functionalization of polyisoprenyllithium for either the
normal or the inverse addition mode (compare
Samples 3 and 4 with Samples 1 and 2 in Table 2).
The most efficient functionalization reactions
using
3-dimethylamainopropyl
chloride were
observed for polybutadienyllithium. Even using the
normal addition procedure, a 90% yield of the udimethylamino-functionalized polybutadiene was
obtained (Sample 1, Table 3). Using either an
inverse addition mode or adding THF for the normal
addition mode increased the functionalization yields
to 94% and 92%, respectively (96% for both by endgroup titration) (Samples 2 and 3, Table 3). The
highest functionality (95% by isolation and 99% by
end-group titration) was obtained in the presence of
107
RP Quirk, K Han, Y Lee
THF using the inverse addition procedure (Sample
4, Table 3).
These results and the recent studies of Deffieux
and co-workers23 indicate that reactions of polydienyllithiums with functionalized alkyl halides can
provide useful general functionalization reactions. It
is anticipated that a wide variety of other functional
groups or their protected analogues can be introduced using the corresponding alkyl chloride derivatives. Most importantly, these functionalization
reactions of polymeric organolithiums can be
eþected in hydrocarbon solution at room temperature or above, i.e under conditions which
provide polydienes with high 1,4-microstructure.
CONCLUSIONS
The chain-end functionalizations of polyisoprenyllithium and polybutadienyllithium by normal addition
of 3-dimethylaminopropyl chloride are efficient
functionalization reactions in hydrocarbon solution.
Contrary to previous studies of analogous functionalizations, the reaction of polystyryllithium with 3dimethylaminopropyl chloride is inefficient. Yields
of functionalized polymers were generally improved
by using an inverse addition mode and postpolymerization addition of Lewis bases such as
tetrahydrofuran
and
N,N,N@,N@-tetramethylethylenediamine before functionalization.
ACKNOWLEDGEMENTS
The authors would like to thank FMC, Lithium
Division, for support of this research and for providing samples of sec-butyllithium. RPQ would like to
acknowledge the hospitality of Professor Michelle
Fontanille, Dr Yves Gnanou and Dr Alain Deffieux
at the Laboratoire de Chimie des Polymères
Organiques, L’Universite Bordeaux I, during his
tenure as Visiting Professor during which time this
paper was written.
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Polym Int 48 :99–108 (1999)
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