A new route to organoboron polymers via highly selective polymer modification reactions

Article abstract of DOI:10.1021/ma035880r

We have developed a highly efficient new method for the introduction of Lewis acidic boron centers into the side chains of organic polymers. Our methodology involves three steps: (i) the controlled polymerization of the functional monomer 4-trimethylsilylstyrene (S-Si), (ii) the exchange of the silyl groups in poly(4-trimethylsilylstyrene) (PS-Si) with BBr₃ to give the reactive polymer poly(4-dibro-moborylstyrene) (PS-BBr), and (iii) the fine-tuning of the Lewis acidity of the individual boron centers through substituent exchange reactions with nucleophiles. Treatment of PS-BBr with ethoxytrimethylsilane and THF respectively yields the moderately Lewis acidic poly(arylboronate)s PS-BOR (R = Et, 4-bromobutyl). The alkoxy groups in PS-BOR have been exchanged with pinacol to form the air-stable polymer PS-BPin (Pin = pinacolato). Treatment of PS-BBr with 2-thienyltrimethyltin and pentafluo-rophenylcopper respectively gives the well-defined highly Lewis acidic triarylborane polymers PS-BTh and PS-BPf (Th = 2-thienyl, Pf = 2,3,4,5,6-pentafluorophenyl), which contain triarylborane moieties at every repeat unit along the polymer chain. All polymers have been studied by multinuclear NMR spectroscopy and differential scanning calorimetry. The molecular weights of the arylboronate polymers PS-BOR have been determined by gel permeation chromatography, and the highly selective formation of polymer PS-BPin has been confirmed by static light scattering.

Full text of DOI:10.1021/ma035880r

Macromolecules 2004, 37, 7123-7131
7123
A New Route to Organoboron Polymers via Highly Selective Polymer
Modification Reactions
Ya n g Qin , Gu a n glou Ch en g, Obia n u ju Ach a r a , Ksh itij P a r a b, a n d F r ied er J a1k le*
Department of Chemistry, Rutgers UniversitysNewark, 73 Warren Street, Newark, New J ersey 07102
Received December 11, 2003; Revised Manuscript Received J une 9, 2004
ABSTRACT: We have developed a highly efficient new method for the introduction of Lewis acidic boron
centers into the side chains of organic polymers. Our methodology involves three steps: (i) the controlled
polymerization of the functional monomer 4-trimethylsilylstyrene (S-Si), (ii) the exchange of the silyl
groups in poly(4-trimethylsilylstyrene) (P S-Si) with BBr3 to give the reactive polymer poly(4-dibro-
moborylstyrene) (P S-BBr ), and (iii) the fine-tuning of the Lewis acidity of the individual boron centers
through substituent exchange reactions with nucleophiles. Treatment of P S-BBr with ethoxytrimeth-
ylsilane and THF respectively yields the moderately Lewis acidic poly(arylboronate)s P S-BOR (R ) Et,
4-bromobutyl). The alkoxy groups in P S-BOR have been exchanged with pinacol to form the air-stable
polymer P S-BP in (Pin ) pinacolato). Treatment of P S-BBr with 2-thienyltrimethyltin and pentafluo-
rophenylcopper respectively gives the well-defined highly Lewis acidic triarylborane polymers P S-BTh
and P S-BP f (Th ) 2-thienyl, Pf ) 2,3,4,5,6-pentafluorophenyl), which contain triarylborane moieties at
every repeat unit along the polymer chain. All polymers have been studied by multinuclear NMR
spectroscopy and differential scanning calorimetry. The molecular weights of the arylboronate polymers
P S-BOR have been determined by gel permeation chromatography, and the highly selective formation
of polymer P S-BP in has been confirmed by static light scattering.
In tr od u ction
procedures6 due to the high reactivity of the monomers.
Notably, Chung and co-workers have recently reported
the homo- and copolymerization of a boron-functional-
ized styrene monomer with styrene using a titanium
catalyst, which yields syndiotactic boron-functionalized
random copolymers with molecular weights ranging
from Mn ) 28 000 to 83 000 and polydispersities be-
tween 2.0 and 2.9.16 The functionalization of organic
polymers or resins in a postpolymerization modification
step represents an alternative to the polymerization of
borylated monomers. Early studies by Paetzold showed
that the direct borylation of polystyrene with halobo-
ranes X2BH under forcing conditions occurs with rela-
tively low selectivity.17 In a recent development, tran-
sition-metal-catalyzed borylation of polyolefins has been
reported by Hartwig and Hillmyer to yield boronate-
functionalized polymers in one step.8 Moreover, Chung
and co-workers showed that the olefin-functionalized
copolymers poly(ethylene-co-1,4-hexadiene) and poly-
(propylene-co-1,4-hexadiene) can be efficiently converted
to boron-functionalized polymers via hydroboration
reactions.18 However, in most instances multistep poly-
mer modification reactions need to be used to introduce
the boron moiety, and often only low degrees of func-
tionalization are realized.19
Inorganic and organometallic polymers have over the
past two decades emerged as an important area of
research in the field of materials chemistry. New devices
have, for example, been developed based on polysilox-
anes and polysilanes, new advances in medical research
have been triggered by the discovery of polyphos-
phazenes, and, more recently, transition-metal-contain-
ing polymers have been developed for nanoscience
applications.1
The incorporation of electron-deficient boron centers
into polymer structures is particularly intriguing as it,
for example, provides an opportunity to take advantage
of the facile and reversible formation of donor acceptor
bonds for the further manipulation and functionaliza-
tion of the polymers.2 Indeed, the binding of nucleophiles
to organoboron polymers has resulted in the design and
development of new supported reagents and immobi-
lized catalysts3 and of highly selective sensor materi-
als.4,5 Boron-containing polymers also play a major role
as intermediates in the synthesis of functionalized
polymers with polar side groups6-8 and are used as
polymeric electrolytes for batteries,9 sophisticated flame
retardants,10 and preceramic11 and photoluminescent
materials.12,13
Our research in this area is aimed at the development
of well-defined soluble organoboron polymers and co-
polymers of controlled architecture, molecular weight,
and degree of functionalization, in which the substitu-
ents on boron can be readily exchanged, and conse-
quently the strength of the Lewis acid centers can be
fine-tuned (Figure 1). We give here full details on the
synthesis and properties of a new family of well-defined
boron-based polymeric Lewis acids.20
However, the selective incorporation of highly Lewis
acidic boron centers into polymer structures remains a
challenging task. While organoboron polymers can be
prepared from organoboron monomers using a variety
of polymerization techniques including condensation
and addition polymerization,11,12 standard free radical
polymerization,5,14 metathesis polymerization,15 and
Ziegler-Natta polymerization,6 the polymerization of
monomers bearing strongly Lewis acidic moieties has
been largely restricted to Ziegler-Natta polymerization
Resu lts a n d Discu ssion
We have developed a new methodology for the syn-
thesis of organoboron polymers that involves three
* To whom correspondence should be addressed. E-mail fjaekle@
rutgers.edu.
10.1021/ma035880r CCC: $27.50 © 2004 American Chemical Society
Published on Web 08/18/2004

7124 Qin et al.
Macromolecules, Vol. 37, No. 19, 2004
F igu r e 1. Schematic representation of Lewis acid function-
alized homopolymers and block copolymers (LA represents a
Lewis acid center and R corresponds to an organic group).
Sch em e 1. Gen er a l Meth od for th e Syn th esis of
Or ga n obor on P olym er s of Va r yin g Lew is Acid ity
F igu r e 2. Dependence of Mn and PDI on monomer conversion
for atom transfer radical polymerization (ATRP) of 4-(tri-
methylsilyl)styrene in anisole (50 wt %) at 110 °C as deter-
mined by GPC relative to polystyrene standards using a
refractive index detector. [M]0 ) 2.6 M and [M]0:[1-PEBr]0:
[CuBr]0:[PMDETA]0 ) 150:1:1:1.
steps: (i) the controlled polymerization of the functional
monomer 4-trimethylsilylstyrene (S-Si), (ii) the selec-
tive exchange of the functional group in poly(4-trimeth-
ylsilylstyrene) (P S-Si) with BBr3 to give the borylated
polymer P S-BBr , and (iii) the fine-tuning of the Lewis
acidity of the individual Lewis acid centers through
substituent exchange reactions with nucleophiles, which
gives access to a series of new well-defined polymers
P S-BR bearing Lewis acidic boron centers (Scheme
1).20
F igu r e 3. Kinetic data for atom transfer radical polymeriza-
tion (ATRP) of 4-(trimethylsilyl)styrene in anisole (50 wt %)
1
at 110 °C as determined by H NMR spectroscopy. [M]0 ) 2.6
M and [M]0:[1-PEBr]0:[CuBr]0:[PMDETA]0 ) 150:1:1:1.
erization (PDI < 1.2), as shown in Figure 2. The slightly
lower molecular weights determined for P S-Si in
comparison to the calculated molecular weights are due
to the difference in hydrodynamic volume between
P S-Si and the polystyrene standards. The initial
linearity of ln([M]0/[M]) vs time (t) in the pseudo-first-
order kinetic plot (Figure 3) indicates that the number
of active species remains constant during this part of
the polymerization reaction, and thus chain termination
is insignificant; i.e., kp[P*] ) constant, where kp stands
for the rate constant and [P*] stands for the concentra-
tion of active propagation chains.24 However, while the
polydispersity remains low and the molecular weight
continues to increase linearly, a deviation from linearity
of ln([M]0/[M]) with time is evident at longer reaction
times. This effect indicates a decrease in active propa-
gation chains and could be due to chain transfer or
termination by radical coupling or elimination reac-
tions.25 A linear dependence of ln([M]0/[M]) vs t2/3 for
living free radical polymerizations as a result of the
persistent radical effect has been derived by Fischer and
has in some instances been experimentally verified.26
In the case of ATRP, typically a linear dependence on t
is observed, which is attributed at least in part to a
decrease in the termination rate constant kt with
increase in chain length and viscosity.26d However, this
effect is less pronounced in solution polymerizations.
Indeed, our data for ln([M0]/[M]) give a significantly
better correlation with t2/3 (R2 ) 0.9902) than with t
(R2 ) 0.9646).
(i) Con t r olled P olym er iza t ion of 4-Tr im et h yl-
silylstyr en e. Poly(4-trimethylsilylstyrene) (P S-Si)21,22
of controlled molecular weight was synthesized accord-
ing to a typical protocol for atom transfer free radical
polymerization (ATRP)23 in anisole (50 wt %) at 110 °C
initiated with 1-phenylethyl bromide (1-PEBr) and
catalyzed by CuBr/N,N,N′N′′,N′′-pentamethyldiethyl-
enetriamine (PMDETA). Different ratios of 4-trimeth-
ylsilylstyrene to initiator were used to obtain polymers
with molecular weights ranging from 5000 to 30 000.
The polymer solutions thus obtained were passed through
a column of neutral alumina and isolated by repeated
precipitation into methanol. Molecular weights were
determined by GPC analysis using a refractive index
and light scattering detector. GPC relative to poly-
styrene standards can provide a rough estimate of the
molecular weight but slightly underestimates the actual
molecular weight by ca. 10-15% as shown by a com-
parison with static light scattering data. For example,
a sample of P S-Si of Mn ) 27 120 according to static
light scattering measurements (GPC-LS) gives a mo-
lecular weight of Mn ) 24 200 when determined by GPC
detection vs polystyrene standards.
A kinetic analysis of the polymerization reaction was
performed using a molar ratio of 4-trimethylsilyl-
styrene:1-PEBr:CuBr:PMDETA ) 150:1:1:1. The mo-
lecular weight of the active propagation chains increases
linearly with increase in monomer conversion, and the
polydispersity remains narrow throughout the polym-

Macromolecules, Vol. 37, No. 19, 2004
Well-Defined Organoboron Polymers 7125
substituent, and two closely spaced signals (δ ) 153.3,
152.9) are observed for the ipso-carbon atom closest to
the polymer backbone. Again, these data correlate well
with those of the molecular model compound 4-dibro-
moborylcumene, which shows signals at δ ) 157.2 and
138.5 for the C4 and C2,6 carbons of the phenyl group,
respectively. Our data do not show any sign of isomer-
ization reactions at the phenyl rings or of polymer
degradation but rather indicate selective and quantita-
tive borylation of P S-Si by BBr3.
The soluble borylated polymer P S-BBr can be iso-
lated in ca. 80% yield as a white solid material after
precipitation into hexanes. However, because of the
extreme sensitivity to moisture, the polymer is most
conveniently used in situ for further exchange of the
bromide substituents with nucleophilic reagents.
(iii) F in e-Tu n in g of Lew is Acid ity. The dibro-
moborylated polymer P S-BBr is ideally suited as a
precursor to other polymers with boron centers of
varying Lewis acidity. While the introduction of alkoxy
substituents on boron should yield moderately Lewis
acidic arylboronate polymers, the exchange of the
bromide substituents for aryl groups should provide
access to highly Lewis acidic triarylborane polymers.
F igu r e 4. Comparison of the 13C NMR spectra of P S-Si (Mn
) 5750, PDI ) 1.13) and the resulting P S-BBr in CD2Cl2.
To confirm the compatibility of the silyl functional
groups with the catalyst system, a model reaction was
performed, in which the compound 4-trimethylsilyl-
cumene was treated with the ATRP components in a
1:1 molar ratio and the resulting mixture heated to 110
°C for 3 h. Analysis of the reaction mixture by GC-MS
showed coupling products of the initiator as previously
reported by Matyjaszewski25a but did not reveal any
products resulting from C-Si bond cleavage. The ob-
served good control of the polymerization and lack of
side reactions with the silyl functional groups thus
indicate the potential applicability of our methodology
to the preparation of a wide variety of well-defined
polymers of different molecular weight and architecture,
including copolymers.27
(a ) Syn th esis a n d Ch a r a cter iza tion of P oly-
(styr en ebor on a te)s. Initially we studied the reactivity
of P S-BBr toward alcohols such as methanol or etha-
nol. However, better exchange selectivity is achieved
with silyl ethers or cyclic ethers, which do not produce
hydrogen bromide upon reaction with P S-BBr .30 Thus,
the polymeric boronate P S-BOEt readily formed upon
treatment with excess of Me3SiOEt and was isolated as
a white solid in ca. 90% yield upon freeze-drying from
benzene (Scheme 2). Similarly, P S-BBr smoothly
reacted with an excess of tetrahydrofuran to give the
gummy polymer P S-BOBu Br in ca. 83% yield upon
precipitation into hexanes. The isolated yield of ca. 83%
for the gummy polymer P S-BOBu Br is slightly lower
due to losses during precipitation into hexanes.31 The
alkoxy substituents in P S-BOEt are readily replaced
upon reaction with pinacol at ambient temperature in
toluene to yield the air-stable pinacol polymer P S-
BP in , which was isolated by precipitation into methanol
(Scheme 2). A relatively high glass transition temper-
ature of Tg ) 228 °C was observed for P S-BP in (Mn )
12 690) in comparison to poly(4-trimethylsilystyrene)
(Tg ) 132 °C, Mn ) 27 120), which may be attributed to
the bulky and rigid nature of the five-membered bor-
onate ring. The gummy appearance of P S-BOBu Br
suggested a significantly lower glass transition temper-
ature relative to that for P S-BP in . Indeed, DSC
analysis revealed Tg ) -52 °C for P S-BOBu Br and Tg
) 20 °C for P S-BOEt. As expected from the high
flexibility of the alkoxy side chains attached to these
polymers, the glass transition temperatures are signifi-
cantly lower than that for P S-BOP in .
(ii) Bor yla tion of P oly(4-tr im eth ylsilyl)styr en e.
A solution of the silylated polymer P S-Si in CH2Cl2
was treated with a slight excess of BBr3 (caution! BBr3
is toxic and highly corrosive), a strong Lewis acid that
cleaves Si-C(sp2) bonds under mild conditions with
nearly quantitative yields, and high selectivity.28 Selec-
tive cleavage of the Si-C(sp2) bonds in P S-Si (>97%)
to form P S-BBr occurred over a period of ca. 12-24 h
at room temperature as confirmed by multinuclear
NMR spectroscopy.29 The signal due to the trimethyl-
silyl substituents of P S-Si in the 29Si NMR spectrum
at δ ) -4.4 completely disappeared, and a new sharp
resonance that may be assigned to Me3SiBr developed
at δ ) 28.0. At the same time a new broad resonance
grew in the 11B NMR spectrum at δ ) 54 in a region
typical of arylboron dibromides. The chemical shift of δ
) 54 compares favorably with that of δ ) 55.8 found
for the molecular model compound 4-dibromoboryl-
i
cumene (4-Br2BC6H4 Pr; see Supporting Information).
The presence of strongly electron-withdrawing substit-
1
All arylboronate polymers P S-BOR (R ) Et, 4-bro-
mobutyl, pinacolato) were fully characterized by 1H, 13C,
and 11B NMR spectroscopy, and the selective attach-
ment of pinacol substituents in P S-BP in was further
confirmed by elemental analysis. Formation of the
arylboronate polymers is reflected in a pronounced
upfield shift of the 11B NMR resonance at δ ) 26 relative
to the precursor polymer P S-BBr (δ ) 54), which is
indicative of significant π-overlap between the alkoxy
substituents and the boron centers (Table 1). The
uents on the phenyl rings is further reflected in the H
and 13C NMR spectra of P S-BBr . Upon borylation, the
protons in the ortho-position to the functional group
experience a pronounced downfield shift from δ ) 7.4-
7.0 in P S-Si to δ ) 8.2-7.6 in P S-BBr (for 4-dibro-
moborylcumene: δ ) 8.08). A similar trend is observed
for the carbon atoms in the ortho-position to the boryl
groups which resonate at δ ) 138.5 (P S-Si: δ ) 133.8/
133.5) (Figure 4). A broad resonance at δ ) 136.4 can
be attributed to the carbon atom bearing the boryl

7126 Qin et al.
Macromolecules, Vol. 37, No. 19, 2004
Sch em e 2. F or m a tion of Ar ylbor on a te P olym er s P S-BOR (R ) Et, 4-Br om obu tyl, P in a cola to) fr om P S-BBr
Ta ble 1. 11B NMR Da ta of P olym er ic Lew is Acid s P S-BR a n d th e Resp ective Mod el Com p ou n d s M-BRa
R groupsb
Br
Pf
Th
OEt
OBuBr
Pin
PS-BR
M-BR
54 (2800)
56 (300)
56 (2500)
62 (1100)
47 (2500)
55 (1000)
26 (1400)
28 (450)
26 (1700)
28 (550)
26 (1600)
31 (400)
a
Chemical shifts are given in ppm relative to BF3‚OEt2; the width of the signal at half-height (reported in Hz) is given in parentheses.
Pf ) 2,3,4,5,6-pentafluorophenyl, Th ) 2-thienyl, BuBr ) 4-bromobutyl, Pin ) pinacolato.
b
Sch em e 3. Selective F or m a tion of Tr ia r ylbor a n e
P olym er s via Tin -Bor on a n d Cop p er -Bor on
Exch a n ge Rea ction s (Th ) 2-Th ien yl)
the structurally related triarylamine polymer poly-
(vinyltriphenylamine) (Tg ) 136 °C for Mn ) 26 200).32
We were interested in attaching electron-withdrawing
pentafluorophenyl (Pf) substituents to boron in order
to access even more highly Lewis acidic polymers such
as P S-BP f. Tin-boron exchange cannot, however, be
applied to the synthesis of P S-BP f because the methyl
group in the respective organotin reagent C6F5SnMe3
is transferred more readily than the pentafluorophenyl
group.33,34 The arylcopper reagent pentafluorophenyl-
copper, [C6F5Cu]4,35 provides a solution to this problem.
We have recently shown that this crystalline, readily
isolable organometallic reagent selectively transfers the
C6F5 moiety to boron halides at low temperature in
aromatic or chlorinated solvents.36 Indeed, treatment
of P S-BBr with 0.5 equiv of [C6F5Cu]4 yielded the
highly Lewis acidic polymer P S-BP f. We found that it
is important in this reaction to avoid any excess of the
copper reagent. We thus applied a slight deficiency of
[C6F5Cu]4 (95-97%) and then treated the crude product
with a small amount of ThSnMe3 (Th ) 2-thienyl) in
order to quench any unreacted B-Br groups.37 The
polymer P S-BP f was obtained as a white solid in ca.
74% yield after repeated precipitation into hexanes
(Scheme 3). The glass transition temperature for P S-
BP f (prepared from P S-Si of Mn ) 27 120, PDI ) 1.11)
of 134 °C (onset) is similar to that of P S-BTh and the
previously reported nitrogen analogue poly(vinyltri-
phenylamine) of Tg ) 136 °C.32
chemical shifts observed are at slightly higher field in
comparison to those recorded for the related model
compounds. This effect, however, is not significant as
the signal is strongly broadened as a result of the
incorporation of the boron centers into the polymer
structure.
(b) Syn th esis a n d Ch a r a cter iza tion of Tr ia r yl-
bor a n e P olym er s. Triarylborane polymers are readily
accessible from P S-BBr via tin-boron exchange reac-
tions. Treatment of a solution of P S-BBr in dichlo-
romethane with a slight excess of the highly selective
aryl transfer reagent 2-trimethylstannylthiophene yielded
polymer P S-BTh (Scheme 3). The polymer thus formed
was obtained as a white solid material in 80% isolated
yield after repeated precipitation from dichloromethane
into hexanes. The glass transition temperature for the
triarylborane polymer P S-BTh (prepared from P S-
Si of Mn ) 27 120, PDI ) 1.11) was determined to be
148 °C (onset), which compares favorably with that of
The triarylborane polymers P S-BAr (Ar ) Th, Pf)
were fully characterized by multinuclear NMR spec-
troscopy, and the selective attachment of the aryl groups
was further confirmed by elemental analysis. The large
chemical shifts of δ ) 47 for P S-BTh and of δ ) 56 for
P S-BP f confirm the expected high Lewis acidity of
these triarylborane polymers (Table 1). Similar to our
observations with the arylboronate polymers, the 11B
NMR resonances appear slightly upfield-shifted and
strongly broadened in comparison to the signals for the
1
cumene model compounds. While the H NMR spectra
for polymers P S-BAr typically show broad signals that

Macromolecules, Vol. 37, No. 19, 2004
Well-Defined Organoboron Polymers 7127
F igu r e 5. Aromatic region of the HMQC spectrum of P S-BTh .
F igu r e 7. Estimation of Lewis acidity of P S-BP f through
formation of crotonaldehyde complex in CD2Cl2.
indicative of highly Lewis acidic centers attached to the
pentafluorophenyl groups.34,38 The resonance due to the
ortho-fluorine atoms is split into two signals at δo )
-130.5/-130.9 as a result of the atactic nature of the
polystyrene backbone. The chemical shifts compare
favorably with those of the molecular model compound
4-isopropylphenylbis(pentafluorophenyl)borane (Figure
6b).36,39
F igu r e 6. (a) 19F NMR spectrum of P S-BP f (Pf ) 2,3,4,5,6-
pentafluorophenyl) in CD2Cl2; ∆δmeta/para represents the chemi-
cal shift difference between the meta- and para-fluorine atoms.
(b) 19F NMR spectrum of 4-isopropylphenylbis(pentafluo-
rophenyl)borane in C6D6.
do not provide much information, the 13C NMR signals
are distinct and can readily be assigned through two-
dimensional NMR spectroscopy as shown for the poly-
mer P S-BTh . The HMQC (heteronuclear multiple
quantum correlation) spectrum of P S-BTh shows in
the aromatic region one set of four relatively sharp
peaks assigned to the pending thienyl substituents and
one set of resonances for the phenyl groups that is
strongly broadened due to the atactic nature of the
polystyrene backbone (Figure 5).
The 13C NMR chemical shifts of the phenyl groups of
the polystyrene backbone also demonstrate the high
Lewis acidity of polymers P S-BAr . For instance, the
carbon atoms in the ortho-position to the boryl group
resonate at δ ) 140.0 and 137.4 for P S-BP f and P S-
BTh , respectively. The chemical shifts are close to that
of the parent compound P S-BBr at δ ) 138.5 and
significantly downfield-shifted relative to the signals
observed for the arylboronate polymers in the range
from δ ) 133.8 to 135.2.
Estim ation of Lewis Acidity Accor din g to Ch ilds’
Meth od . The relative Lewis acidity of the boron centers
in P S-BP f was estimated by complexation with cro-
tonaldehyde in CD2Cl2 at -20 °C according to Childs’
method (Figure 7).40 On a scale from 0 to 1.0 (BBr3
)
1.0) a relative Lewis acidity of 0.60 was determined for
P S-BP f based on the 13C NMR shifts of the complexed
crotonaldehyde relative to those of the free aldehyde.
The determined relative Lewis acidity of P S-BP f is
pronounced, but slightly lower than that found for
B(C6F5)3 (values ranging from 0.68 to 0.77 have been
reported)41,42 as is expected since the phenyl groups of
the polystyrene are not fluorinated. A pronounced Lewis
acidity of P S-BP f is further confirmed by a character-
istic large chemical shift difference between the meta-
and para-fluorine atoms of ∆δm,p ) 13.0 for the free acid
(see Figure 6) that significantly decreases to ∆δm,p
6.4 in the polymeric crotonaldehyde adduct.
)
Molecu la r Weigh t Det er m in a t ion of Bor on -
Con ta in in g P olym er s. The molecular weights of the
alkoxy-substituted polymers were determined by GPC
measurements relative to polystyrene standards.43 The
molecular weight and polydispersity of all polymers
were found to be very close to those of the precursor
polymer P S-Si. Static light scattering measurements
The attachment of pentafluorophenyl groups in P S-
BP f was conveniently followed by 19F NMR spectros-
copy. A large chemical shift difference of ∆δm,p ) 13.0
(Figure 6a) between the meta- and para-fluorine atoms
at δp ) -149.5 and δm ) -162.5, respectively, is

7128 Qin et al.
Macromolecules, Vol. 37, No. 19, 2004
Ta ble 2. Com p a r ison of GP C a n d Ligh t Sca tter in g Da ta
for P S-Si a n d P S-BP in in THF a
solvents were subsequently distilled from CaH2 and degassed
via several freeze-pump-thaw cycles.
The 399.952 MHz 1H and 100.564 MHz 13C NMR spectra
were recorded at ambient temperature on a Varian VXR-S 400
MHz and the 499.893 MHz 1H and 125.681 MHz 13C NMR
spectra on a Varian INOVA 500 MHz spectrometer. The 79.4
MHz 29Si (DEPT mode) and the 376.263 MHz 19F spectra were
recorded on the Varian VXR-S 400 spectrometer, and the 160.4
MHz 11B NMR spectra were recorded on the Varian INOVA
500 spectrometer equipped with a boron-free probe using
boron-free quartz NMR tubes. All solution 1H and 13C NMR
spectra were referenced internally to the solvent peaks. 29Si
and 11B NMR spectra were referenced externally to SiMe4 (δ
) 0) and BF3‚Et2O (δ ) 0) in C6D6, respectively, and 19F NMR
spectra were referenced to R,R′,R′′-trifluorotoluene (0.05% in
C6D6; δ ) -63.73). GPC analyses were performed in THF (1
mL/min) using a Waters Breeze system equipped with a
717plus autosampler, a 1525 binary HPLC pump, a 2487 dual
λ absorbance detector, and a 2414 refractive index detector. A
series of styragel columns (Polymer Laboratories; 5 µm Mix-
D, 5 µm Mix-C, and 10 µm Mix-B), which were kept in a
column heater at 35 °C, were used for separation. The columns
were calibrated with polystyrene standards (Polymer Labo-
ratories). Multiangle laser light scattering (MALLS) experi-
ments were performed at 690 nm (30 mW linear polarized
GaAs laser) using a Wyatt Dawn EOS instrument either in a
batch mode or in-line with the GPC as specified; differential
refractive indices dn/dc were determined using a Wyatt Optilab
at 690 nm. Dynamic light scattering (DLS) studies were
performed using the Wyatt Dawn EOS modified with a Wyatt
QELS attachment. Data were collected at an angle of 108°
using an avalanche photodiode and an optical fiber and
processed with the Wyatt QELS software (regularization
analysis). GC-MS spectra were acquired on a Hewlett-Packard
HP 6890 series GC system equipped with a series 5973 mass
selective detector and a series 7683 injector. A temperature
profile with a heating rate of 20 °C/min from 50 to 280 °C was
used. Mass spectral data (EI mode; direct probe) were obtained
at the Michigan State University Mass Spectrometry Facility
which is supported, in part, by a grant (DRR-00480) from the
Biotechnology Research Technology Program, National Center
for Research Resources, National Institutes of Health. DSC
measurements were performed on a Perkin-Elmer differential
scanning calorimeter Pyris 1 system with ca. 20 mg of polymer
using the specified scan rate. Elemental analyses were per-
formed by Quantitative Technologies Inc. Whitehouse, NJ .
Ca u tion ! BBr3 is toxic and highly corrosive and should be
handled appropriately with great care. Fluorinated grease was
used for ground glass joints in all reactions involving boron
tribromide.
dn/dc
polymer (mL/g)
RH
Mw
PDI DP A2 (mol‚mL/g2) (nm)
PS-Si
PS-BPin
0.157
0.138
10 140 1.08 51
13 830 1.09 53
8.774 × 10-4
2.2
2.4
4.772 × 10-4
a
Differential refractive index (dn/dc) from batch measurements,
molecular weight (Mw), degree of polymerization (DP), and second
virial coefficient A2 from batch mode static light scattering,
polydispersity (PDI) from GPC (LS detector), and hydrodynamic
radius (RH) from dynamic light scattering.
were performed on polymer P S-BP in in order to
further confirm the high selectivity and absence of cross-
linking upon borylation and subsequent functionaliza-
tion of P S-Si. Again, both the experimentally deter-
mined average degree of polymerization and the poly-
dispersity of P S-BP in were similar to those of the
precursor polymer P S-Si (Table 2). This clearly con-
firms that the borylation and subsequent substituent
exchange occur without significant cross-linking or
cleavage of the polymer backbone.
Con clu sion s
We have developed a highly efficient new method for
the attachment of Lewis acidic boron centers to the side
chains of organic polymers. The borylation of the sily-
lated polymer P S-Si with BBr3 occurs nearly quanti-
tatively and with very good selectivity. The resulting
reactive polymer P S-BBr serves as a highly versatile
precursor to a family of new boron-containing polymeric
Lewis acids. Facile substituent exchange reactions on
boron provide access to various poly(arylboronates) P S-
BOR and highly Lewis acidic polymeric triarylboranes
P S-BAr . For example, the introduction of pentafluo-
rophenyl substituents on boron resulted in formation
of P S-BP f, the first polymeric analogue of the impor-
tant class of highly Lewis acidic fluorinated arylboranes,
which play a major role as catalysts in organic synthe-
sis44 and as cocatalysts in olefin polymerization.41,45,46
The organoboron polymers also lend themselves to
further studies with regard to the formation of polymeric
complexes with nucleophiles and their assembly with
donor-functionalized polymers, which is currently un-
derway in our laboratory.
Rep r esen ta tive P r oced u r e for th e Syn th esis of P oly-
(4-tr im eth ysilylstyr en e) (P S-Si). 4-Trimethylsilylstyrene
was distilled from CaH2 and degassed via several freeze-
pump-thaw cycles prior to use. In a glovebox, 4-trimethylsi-
lylstyrene (50 g, 0.284 mol), 1-bromo-1-phenylethane (0.26 g,
1.42 mmol), copper(I) bromide (0.20 g, 1.42 mmol), and
PMDETA (0.25 g, 1.42 mmol) were charged into a 250 mL
Schlenk flask, and 50 g of anisole were added. The flask was
then taken out of the glovebox, degassed by three freeze-
pump-thaw cycles, and subsequently immersed in an oil bath
preset at 110 °C. After stirring for 5 h the flask was cooled to
room temperature, and the reaction mixture was precipitated
into methanol (1 L). The precipitate was collected by filtration
and redissolved in THF. The THF solution was then passed
through a short column packed with ca. 5 g neutral alumina
and concentrated to ca. 15 mL. Poly(4-trimethylsilylstyrene)
(P S-Si) was recovered by precipitation into methanol (1 L)
and dried under vacuum at 50 °C for 24 h (yield: 32.2 g, 64%).
For P S-Si: 1H NMR (399.952 MHz, CD2Cl2) δ ) 7.31, 7.17,
7.04 (br m, 2H, Ph-H2,6), 6.58, 6.38, 6.18 (br m, 2H, Ph-
H3,5), 2.0-1.2 (br, 3H, CH2CH), 0.24 (s, 9H, Si[CH3]3). 1H
NMR (399.952 MHz, CDCl3) δ ) 7.25, 7.11, 6.97 (br m, 2H,
Ph-H2,6), 6.54, 6.33, 6.10 (br m, 2H, Ph-H3,5), 2.0-1.2 (br,
Exp er im en ta l Section
Ma ter ia ls a n d Gen er a l Meth od s. The compounds 4-chlo-
rostyrene (99%), Mg (turnings, 99.9%), Me3SiCl (98%), BBr3
(99.9%), CuBr (98%), 1-bromo-1-phenylethane (97%), anisole
(99%), pinacol (99%), and crotonaldehyde (99+%) were pur-
chased from Acros. The compounds Me3SiOEt (98%) and
N,N,N′,N′′,N′′-pentamethyldiethylenetriamine (PMDETA; 99%)
were purchased from Aldrich, and 4-bromocumene (97%) was
obtained from Lancaster. BBr3 was distilled under vacuum,
and Me3SiCl, Me3SiOEt, PMDETA, anisole, and 1-bromo-1-
phenylethane were distilled from CaH2 prior to use; CuBr was
purified according to a literature procedure.47 All other chemi-
cals were used as received without further purification. The
compounds 4-trimethylsilylstyrene,48 2-trimethylstannyl-
thiophene,49 and [C6F5Cu]4(toluene)235 were prepared according
to literature procedures. Reactions and manipulations involv-
ing boron species were carried out under an atmosphere of
prepurified nitrogen using either Schlenk techniques or an
inert-atmosphere glovebox (Innovative Technologies). Ether
solvents were distilled from Na/benzophenone prior to use.
Hydrocarbon and chlorinated solvents were purified using a
solvent purification system (Innovative Technologies; alumina/
copper columns for hydrocarbon solvents), and the chlorinated
1
3H, CH2CH), 0.21 (s, 9H, Si[CH3]3). H NMR (399.952 MHz,
C6D6) δ ) 7.45, 7.37, 7.29 (br m, 2H, Ph-H2,6), 6.81, 6.63,

Macromolecules, Vol. 37, No. 19, 2004
Well-Defined Organoboron Polymers 7129
6.54 (br m, 2H, Ph-H3,5), 2.27, 2.10 (br m, 1H, CH2CH]), 1.63
(br, 2H, CH2CH), 0.31 (br s, 9H, Si[CH3]3). 13C NMR (100.564
MHz, CD2Cl2) δ ) 146.8 (br, Ph-C4), 137.8, 137.5, 137.3 (Ph-
C1), 133.8, 133.5 (Ph-C2,6), 128.0, 127.8, 127.7, 127.3, (Ph-
C3,5), 48-42 (br, CH2CH), 41.2 (CH2CH) -0.8 (Si[CH3]3). 13C
NMR (100.564 MHz, C6D6) δ ) 146.7 (Ph-C4), 137.4 (Ph-
C1), 133.7 (Ph-C2,6), 128.0 (Ph-C3,5), 48-42 (br, CH2CH),
41.2 (CH2CH), -0.5 (Si[CH3]3). 29Si NMR (79.4 MHz, CD2Cl2)
δ ) -4.4. GPC-LS (in THF): Mn ) 27 120, Mw ) 30 100, PDI
) 1.11; refractive index increment at 25 °C in THF: dn/dc )
PS standards): Mn ) 5470, PDI ) 1.14; DSC (second heating
curve): Tg ) 20 °C (onset, 20 °C/min); repeated elemental
analyses showed consistently low carbon content, which is
likely due to partial hydrolysis of the boronic ester linkages
during analysis.
Tr ea tm en t of P S-BBr w ith THF : Syn th esis of P oly-
[4-bis(4′-br om obu toxy)bor ylstyr en e] (P S-BOBu Br ). A
solution of P S-BBr prepared from BBr3 (0.60 g, 2.4 mmol)
and P S-Si (0.35 g, ca. 2.0 mmol repeat units; Mn ) 5750; PDI
) 1.13) in 15 mL of CH2Cl2 was treated with THF (0.40 g, 5.5
mmol) and stirred for 12 h. The reaction solution was concen-
trated under high vacuum to ca. 2 mL and then precipitated
into a large volume of hexanes (ca. 200 mL). The hexane
solution was decanted from a gummy precipitate. After freeze-
drying, P S-BOBu Br was isolated as a colorless gummy
material (0.69 g, 83%). 1H NMR (399.952 MHz, C6D6): δ )
7.8-7.2 (br m, 2H, Ph-H2,6), 7.1-6.4 (br m, 2H, Ph-H3,5),
3.92 (br, 4H, OCH2), 3.10 (br, 4H, CH2Br), 2.6-1.4 (br m, 14H,
0.161 mL/g; DSC (second heating curve; Mn ) 27 120): Tg
)
132 °C (onset, 20 °C/min). Polymers of different molecular
weight were obtained by variation of the ratio of initiator to
monomer.
Gen er a l P r oced u r e for Kin etic An a lysis of Atom
Tr a n sfer Ra d ica l P olym er iza tion of P S-Si. 4-Trimethyl-
silylstyrene, 1-bromo-1-phenylethane, CuBr, PMDETA (150/
1/1/1), and anisole (50 wt %; used as both solvent and internal
NMR standard) were charged in a glovebox into a Schlenk
flask with a rubber septum, which was then immersed in an
oil bath at 110 °C. At predetermined times, a small amount of
sample was withdrawn from the flask with a nitrogen-flushed
syringe for GPC and NMR analysis.
1
CH2CH2CH2Br, CH2CH). H NMR (399.952 MHz, CDCl3): δ
) 7.8-7.0 (br m, 2H, Ph-H2,6), 7.0-6.2 (br m, 2H, Ph-H3,5),
3.99 (br, 4H, OCH2), 3.41 (br, 4H, CH2Br), 2.1-1.0 (br m, 14H,
CH2CH2CH2Br, CH2CH). 13C NMR (100.564 MHz, C6D6): δ
) 147.7 (Ph-C4), 134.3 (Ph-C2,6), 130.7 (Ph-C1), 128 (Ph-
C3,5), 63.7 (OCH2), 50-42 (br, CH2CH), 41.2 (CH2CH), 33.7
(CH2Br), 30.5, 29.7 (CH2CH2CH2Br). 11B NMR (160.370 MHz,
C6D6): δ ) 26 (w1/2 ) 1700 Hz). GPC (in THF against PS
standards): Mn ) 6300, PDI ) 1.14; DSC (second heating
curve): Tg ) -52 °C (onset, 20 °C/min); elemental analysis
for P S-BOBu (153 repeat units): calcd: C, 45.99; H, 5.54;
found: C, 46.36; H, 5.75.
Rea ction of P S-Si w ith BBr 3: Syn th esis of P oly(4-
d ibr om obor ylstyr en e) (P S-BBr ). Caution: BBr3 is toxic
and highly corrosive! A solution of BBr3 (0.31 mL, 3.3 mmol)
in 5 mL of CH2Cl2 was added dropwise under stirring to P S-
Si (0.48 g; ca. 2.7 mmol repeat units; Mn ) 5750; PDI ) 1.13)
in 10 mL of CH2Cl2. After completion of the addition the
mixture was stirred for 24 h. Complete replacement of the silyl
substituents for dibromoboryl groups was confirmed by 1H
NMR spectroscopy. The reaction solution was concentrated
under high vacuum to ca. 2 mL and then precipitated into a
large volume of hexanes (ca. 200 mL). The hexane solution
was decanted from a white precipitate. The solid was washed
with hexanes and dried under high vacuum for 12 h to give
0.60 g (81%) of P S-BBr . More conveniently, the polymer
solution may be used directly for further reactions with
nucleophiles. 1H NMR (399.952 MHz, CD2Cl2): δ ) 8.2-7.6
(br m, 2H, Ph-H2,6), 7.2-6.4 (br m, 2H, Ph-H3,5), 2.4-1.4
(br m, 3 H, CH2CH). 1H NMR (399.952 MHz, CDCl3) δ ) 8.2-
7.6 (br m, 2H, Ph-H2,6), 7.2-6.4 (br m, 2H, Ph-H3,5), 2.4-
1.4 (br m, 3 H, CH2CH). 13C NMR (100.564 MHz, CD2Cl2): δ
) 153.3, 152.9 (Ph-C4), 138.5 (Ph-C2,6), 136.4 (Ph-C1),
128.1, 127.9 (Ph-C3,5), 45-42 (br, CH2CH), 42.1, 41.7 (CH2-
CH). 11B NMR (160.370 MHz, CDCl3): δ ) 54 (w1/2 ) 2800
Hz). Note: The crude mixture shows the following additional
signals due to Me3SiBr: 1H NMR (399.952 MHz, CD2Cl2): δ
) 0.59 (s, 9 H, BrSi(CH3)3). 13C NMR (100.564 MHz, CD2Cl2):
δ ) 4.5 (BrSi(CH3)3). 29Si DEPT NMR (79.4 MHz, CD2Cl2): δ
) 28.0 ppm; the NMR data for Me3SiBr were confirmed by
comparison with those of a sample of commercial Me3SiBr
(Aldrich) in CD2Cl2.
Tr ea tm en t of P S-BBr w ith Me3SiOEt: Syn th esis of
P oly(4-d ieth oxybor ylstyr en e) (P S-BOEt). A solution of
P S-BBr prepared from BBr3 (0.86 g, 3.4 mmol) and P S-Si
(0.50 g, ca. 2.8 mmol repeat units; Mn ) 5750; PDI ) 1.13) in
15 mL of CH2Cl2 was treated with Me3SiOEt (1.3 mL, 8.3
mmol) and stirred for 12 h. All volatile material was removed
under high vacuum, and the oily residue was redissolved in
benzene (10 mL). After freeze-drying P S-BOEt was isolated
as a white solid (0.52 g, 90%). 1H NMR (399.952 MHz, CD2-
Cl2): δ ) 7.6-7.0 (br m, 2H, Ph-H2,6), 7.0-6.4 (br m, 2H,
Ph-H3,5), 4.13 (br, 4H, OCH2CH3), 2.2-1.4 (br m, 3H,
CH CH2), 1.33 (br, 6H, OCH2CH 3). 1H NMR (399.952 MHz,
CDCl3): δ ) 7.5-7.1 (br m, 2H, Ph-H2,6), 6.8-6.2 (br m, 2H,
Ph-H3,5), 4.00 (br, 4H, OCH2CH3), 2.0-1.4 (br m, 3H,
CH CH2), 1.23 (br, 6H, OCH2CH 3). 1H NMR (399.952 MHz,
C6D6): δ ) 7.8-7.4 (br m, 2H, Ph-H2,6), 7.1-6.5 (br m, 2H,
Ph-H3,5), 4.07 (br, 4H, OCH2CH3), 2.6-1.4 (br m, 3H,
CHCH2), 1.21 (br, 6H, OCH2CH3). 13C NMR (100.564 MHz,
CD2Cl2): δ ) 148.0, 147.1 (Ph-C4), 133.8 (Ph-C2,6), 131.0
(Ph-C1), 127.4 (Ph-C3,5), 60.4 (OCH2CH3), 48-42 (br,
CH2CH]), 41.0 (CH2CH), 17.8 (OCH2CH3). 11B NMR (160.370
MHz, CD2Cl2): δ ) 26 (w1/2 ) 1400 Hz). GPC (in THF against
Tr ea tm en t of P S-BOEt w ith P in a col: Syn th esis of
P S-BP in . Neat pinacol (1.04 g, 8.77 mmol) was added to P S-
BOE t (1.47 g, 7.3 mmol; synthesized from P S-Si of Mn
)
9390, PDI ) 1.08 by GPC-LS) in 20 mL of toluene and stirred
for 12 h. The resulting clear solution was then concentrated
to ca. 5 mL under vacuum and precipitated into methanol (500
mL). The white solid thus obtained was dissolved in 20 mL of
benzene and freeze-dried to give a white powdery material
1
(1.27 g, 77%). H NMR (399.952 MHz, C6D6): δ ) 8.2-7.8 (br
m, 2H, Ph-H2,6), 6.9-6.4 (br m, 2H, Ph-H3,5), 2.4-1.2 (br
m, 3H, CHCH2), 1.4-1.0 (br, 12H, OCMe2CMe2O). 13C NMR
(100.564 MHz, CD2Cl2): δ ) 149.1 (Ph-C4), 135.2 (Ph-C2,6),
127.8 (Ph-C3,5), 127.0 (Ph-C1), 84.0 (OCMe2CMe2O), 48-
42 (br, CH2CH), 41.1 (CH2CH), 25.3 (OCMe2CMe2O). 11B NMR
(160.370 MHz, CD2Cl2): δ ) 26 (w1/2 ) 1600 Hz). GPC (in THF
against PS standards): Mn ) 10 100, PDI ) 1.10; refractive
index increment at 25 °C in THF: dn/dc ) 0.138 mL/g; static
light scattering (Zimm plot): Mw ) 13 830; A2 ) 4.772 × 10-4
mol‚mL/g2; dynamic light scattering: RH ) 2.4 nm (average);
DSC (second heating curve): Tg ) 228 °C (onset, 40 °C/min);
TGA (20 °C/min; under N2): 98% weight loss between 360 °C
and 560 °C; elemental analysis for P S-BP in (51 repeat
units): calcd: C, 72.75; H, 8.27; found: C, 72.63; H, 8.36.
Tr ea t m en t of P S-BBr w it h 2-(Tr im et h ylst a n n yl)-
th iop h en e: Syn th esis of P oly(4-(d i-2-th ien ylbor yl)sty-
r en e) (P S-BTh ). A solution of P S-BBr prepared from BBr3
(3.11 g, 12.4 mmol) and P S-Si (2.0 g, ca. 11.3 mmol repeating
units; Mn ) 27 120; PDI ) 1.11) in 20 mL of CH2Cl2 was
treated with a solution of 2-(trimethylstannyl)thiophene (6.1
g, 28.3 mmol) in CH2Cl2 (10 mL), and the mixture was stirred
for 12 h. The reaction solution was concentrated under high
vacuum to ca. 5 mL, and the polymer was recovered by
repeated precipitation into hexanes. The resulting white solid
was washed with hexanes and dried under high vacuum for
24 h at 50 °C to give 2.5 g (80%) of P S-BTh . 1H NMR (499.893
MHz, CDCl3): δ ) 8.0-7.4 (br, 6H, Ph-H2,6 and Th-H3,5),
7.08 (br, 2H, Th-H4), 6.9-6.7 (br, 2H, Ph-H3,5), 2.6-1.4 (br
m, 3H, CH2CH). 13C NMR (125.681 MHz, CDCl3): δ ) 149.2,
148.4 (br, Ph-C4), 145.1 (Th-C2), 142.3 (Th-C3), 140.9 (br,
Ph-C1), 137.4 (br, Ph-C2,6), 137.0 (Th-C5), 129.0 (Th-C4),
127.1 (br, Ph-C3,5), 47-42 (br, CH2CH), 41 (br, CH2CH). 11
B
NMR (160.370 MHz, CDCl3): δ ) 47 (w1/2 ) 2500 Hz). DSC
(second heating curve): Tg ) 148 °C (onset, 40 °C/min);
elemental analysis for P S-BTh (153 repeat units): calcd: C,
68.51; H, 4.68; S, 22.79; found: C, 68.17; H, 4.50; S, 21.96.

7130 Qin et al.
Macromolecules, Vol. 37, No. 19, 2004
Wiley & Sons: Hoboken, 2003; Vol. 1. (g) Manners, I.
Synthetic Metal-Containing Polymers; Wiley-VCH: Wein-
heim, 2004.
Tr ea tm en t of P S-BBr w ith Cu C6F 5: Syn th esis of
P oly[4-bis(p en ta flu or op h en yl)bor ylstyr en e] (P S-BP f).
A solution of P S-BBr prepared from BBr3 (0.78 g, 3.1 mmol)
and P S-Si (0.50 g, ca. 2.8 mmol repeat units; Mn ) 27 120;
PDI ) 1.11) in 15 mL of CH2Cl2 was treated at -78 °C with a
solution of [CuC6F5]4(toluene)2 (1.80 g, 1.6 mmol) in 10 mL of
CH2Cl2. The mixture was kept stirring for 1 h at -78 °C and
then allowed to slowly warm to room temperature and stirred
for 3 h. A solid precipitate (CuBr) formed and was removed
by filtration through a fritted glass disk. A small amount of
ThSnMe3 was added in order to quench any unreacted B-Br
groups. The reaction solution was concentrated under high
vacuum to ca. 3 mL and then precipitated repeatedly into a
large volume of hexanes (ca. 200 mL). The hexane solution
was decanted from a white precipitate. The solid was washed
with hexanes and dried under high vacuum for 24 h to give
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1
0.94 g (74%) of P S-BP f. H NMR (399.952 MHz, CD2Cl2): δ
) 7.3 (br m, 2H, Ph-H2,6), 6.6 (br m, 2H, Ph-H3,5), 2.2-1.2
(br m, 3H, CH2CH). 13C NMR (125.7 MHz, CD2Cl2): δ ) 154.5
1
1
(br, Ph-C4), 147.2 (d, J CF ) 248 Hz, Pf-C2,6), 143.6 (d, J CF
1
) 256 Hz, Pf-C4), 140.0 (br, Ph-C2,6), 138.1 (d, J CF ) 254
Hz, Pf-C3,5), 137.1 (br, Ph-C1), 128.3, 127.9 (br, Ph-C3,5),
114.2 (br, Pf-C1), 46-42 (br, CH[CH3]2). 19F NMR (376.263
MHz, CD2Cl2): δ ) -130.5, -130.8 (4F, Pf-F2,6), -149.5 (2F,
Pf-F4), -162.5 (4F, Pf-F3,5). 11B NMR (160.370 MHz, CD2-
Cl2): δ ) 56 (w1/2 ) 2500 Hz); DSC (second heating curve): Tg
) 134 °C (onset, 20 °C/min); elemental analysis for P S-BP f
(153 repeat units): calcd: C, 53.61; H, 1.58; found: C, 53.33;
H, 1.75. A sulfur content of 0.14% was found by elemental
analysis, indicating the attachment of a small number of
thiophene groups (average of ca. 3 thiophene groups per
polymer).
Deter m in a tion of th e Rela tive Lew is Acid ity of P S-
BP f. A solution of P S-BP f (ca. 0.3 M) in CD2Cl2 was treated
with a deficiency of crotonaldehyde (ca. 50%) according to
Childs’ method.40 The relative Lewis acidity of the boron
centers was estimated to 0.60 (BBr3 ) 1.0) by comparison of
the chemical shift of the olefinic carbon NMR signals for the
1
free aldehyde and the Lewis acid complex. (Reliable H NMR
data could not be obtained due to signal overlap; furthermore,
neighboring group effects in the polymer may influence the
1H NMR chemical shifts.) Similar treatment of P S-BP f with
a slight excess of crotonaldehyde (1.3 equiv) gave the following
NMR data for the fully complexed polymeric Lewis acid: 19F
NMR (376.263 MHz, C6D6): δ ) -133.0 (4F, Pf-F2,6), -159.4
(2F, Pf-F4), -165.8 (4F, Pf-F3,5).
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Ack n ow led gm en t is made to the National Science
Foundation (CAREER award CHE-0346828 to F.J .), to
the donors of the Petroleum Research Fund, adminis-
tered by the American Chemical Society, and to the
Rutgers Research Council for support of this research.
We thank the National Science Foundation for GPC and
LS instrumentation provided through the NSF-MRI
program (MRI 0116066). We are grateful to Dr. Lazaros
Kakalis for acquisition of 2D NMR spectra.
Su p p or tin g In for m a tion Ava ila ble: Data for model
compounds. This material is available free of charge via the
Internet at http://pubs.acs.org.
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