Mechanistic Distinctions between Cation Radical and Carbocation Propagated Polymerization

Article abstract of DOI:10.1021/jo972072n

The polymerization of bis[4-(1-propenyl)phenyl] ether in the presence of tris(4-bromophenyl)aminium hexachloroantimonate is found to occur by competing cation radical and carbocation pathways. These pathways involve, respectively, cyclobutanation and linear addition. Methods for favoring each mechanistic type are proposed and explored.

Full text of DOI:10.1021/jo972072n

2586
J . Org. Chem. 1998, 63, 2586-2590
Mech a n istic Distin ction s betw een Ca tion Ra d ica l a n d Ca r boca tion
P r op a ga ted P olym er iza tion
J . Todd Aplin and Nathan L. Bauld*
Department of Chemistry and Biochemistry, The University of Texas at Austin, Austin, Texas 78712
Received November 11, 1997
The polymerization of bis[4-(1-propenyl)phenyl] ether in the presence of tris(4-bromophenyl)aminium
hexachloroantimonate is found to occur by competing cation radical and carbocation pathways.
These pathways involve, respectively, cyclobutanation and linear addition. Methods for favoring
each mechanistic type are proposed and explored.
Although addition polymerization reactions propagated
observation contrasts sharply with poly(1) prepared
under comparable conditions, which is highly soluble in
dichloromethane or chloroform. The solid-state 13C NMR
spectrum of poly(3) has broad absorptions centered at δ
12, 20 (weak), 35, 43, 120, 140, and 155. The insolubility
of the polymer immediately suggested the possibility of
a cross-linked polymer, which is not expected if polym-
erization occurs by a cation radical cycloaddition route.
On the other hand, linear polymerization of 3 via an acid-
catalyzed, carbocation-mediated route would be expected
to yield a cross-linked polymer (Scheme 2). The genera-
tion of strong Bronsted acid under aminium salt induced
reaction conditions is well-established, and instances
have been presented in which carbocation chemistry
prevails over cation radical chemistry.3,4 The extremely
broad 13C NMR absorptions of poly(3) presented difficul-
ties in definitively characterizing the polymer structure
and especially in distinguishing cyclobutapoly(3) from the
similar cross-linked, acyclic structure. A special element
of difficulty arose when the 13C NMR spectrum of poly(3)
was compared with those of the trans-anethole cyclob-
utadimers (Scheme 3),5 which had been projected as NMR
spectroscopic models for cyclobutapoly(3). Whereas the
cyclodimerization of trans-anethole (4) by 2•+ at 0 °C
yields exclusively the trans,anti,trans dimer (13C NMR
δ 18, 43, 52) in the aliphatic region, at -30 °C the
trans,syn,trans cyclodimer (13C NMR δ 15, 34, 49) is
formed in equal amounts. Initially, it was not certain
whether cyclobutapoly(3) should be expected to have
exclusively the anti structure or to be a syn,anti mixture.
Thus the 13C NMR spectrum of poly(3) might have been
considered to be consistent with a mixture of syn and
anti cyclobutapoly(3), especially if the possibility of solid-
state effects on the 13C NMR chemical shifts is consid-
ered. Consequently, a soluble polymer of 3 was sought
in order to permit its characterization by solution phase
by carbocation intermediates are very well-known,1 only
recently have cation radicals been established as viable
intermediates for propagating addition polymerizations.2
The present research describes the polymerization of a
monomer under conditions which were designed to be
conducive to cation radical polymerization but which
result in a competition between cation radical and
carbocation propagated polymerization. As a result of
the present study, criteria are developed for distinguish-
ing between cation radical and carbocation mechanisms
of polymerization, and means for favoring each mecha-
nism are explored.
Resu lts a n d Discu ssion
The cation radical cyclobutanation polymerization of
monomer 1 (Scheme 1) reported recently2 represents the
first instance in which an addition polymerization reac-
tion has been shown to be propagated by cation radical
intermediates. The cation radical chain mechanism
shown in Scheme 1 was proposed and supported for this
unprecedented polymerization. The initiator is tris(4-
bromophenyl)aminium hexachloroantimonate (2•+), a
stable, commercially available cation radical salt. The
polymerization of 1 by 2•+ is also unusual in that it is a
cycloaddition as opposed to a linear (or acyclic) addition
polymerization. Finally, the joining of monomer units
via cyclobutane linkages (i.e. cyclobutanation polymeri-
zation) is especially unprecedented in thermal chemistry.
In the course of our research on cation radical cyclobu-
tanation polymerization, attention was directed to 3
(Scheme 2) as an appropriate monomer for study. Al-
though the oxidation potential of 3 (1.42 V vs SCE) is
somewhat higher than that of 1 (1.33 V), both are well
within the range of oxidizing ability of 2•+ (Eox 1.05 V;
range up to 1.6 V). Monomer 3 was conveniently
prepared by double Friedel-Crafts propionylation of
diphenyl ether, followed by sodium borohydride reduction
and elimination via phosphorus oxychloride/pyridine.
Polymerization of 3 in the presence of 2•+ (5 mol %) in
dichloromethane at 0 °C gave an 81% yield of a polymer
which is highly insoluble in all of a wide variety of
solvents tried, including diphenyl ether at 250 °C. This
1
13C and H NMR spectroscopy. When a dilute solution
of 3 was polymerized by 2•+, a soluble polymer was indeed
obtained which had the same 13C NMR absorptions as
the previously obtained insoluble polymer, but in addition
the 1H NMR spectrum indicated that the poly(3) obtained
has primarily the acyclic structure. In particular, ex-
(3) Gassman, P. G.; Singleton, D. A. J . Am. Chem. Soc. 1994, 106,
7993.
(1) Stevens, M. P. Polymer Chemistry, 2nd ed.; Oxford University
Press: New York, 1990; pp 234-250.
(2) Bauld, N. L.; Aplin, J . T.; Yueh, W.; Sarker, H.; Bellville, D. J .
Macromoclcules 1996, 29, 3661-3662.
(4) Reynolds, D. W.; Lorenz, K. T.; Chiou, H.-S.; Bellville, D. J .;
Pabon, R. A.; Bauld, N. L. J . Am. Chem. Soc. 1987, 109, 4960.
(5) Pabon, R. A.; Bauld, N. L. J . Am. Chem. Soc. 1983, 105, 633-
634.
S0022-3263(97)02072-0 CCC: $15.00 © 1998 American Chemical Society
Published on Web 03/17/1998

Cation Radical and Carbocation Polymerizations
J . Org. Chem., Vol. 63, No. 8, 1998 2587
Sch em e 1. Mech a n ism of Ca tion Ra d ica l Cycloa d d ition P olym er iza tion of 1
Sch em e 2. Ca tion Ra d ica l vs Ca r boca tion P olym er iza tion
Sch em e 3. Ca tion Ra d ica l Cyclod im er iza tion of
NMR spectra, the poly(3) obtained was estimated to have
90% acyclic (acid-catalyzed) linkages and 10% cyclobu-
tane (cation radical) linkages. This analysis was further
supported by the relative 13C NMR peak areas at δ 12
and 20, assuming that the former correspond to acyclic
methyl carbons and the latter to methyl groups attached
to a cyclobutane ring (see the anti dimer of 4).
tr a n s-An eth ole
1
Additional confirmation of the critical 13C and H NMR
absorptions expected for cyclobutapoly(3) were obtained
from model compounds which are structurally even more
closely related to the polymer than the trans-anethole
dimers. First, the monopropenyl analogue of 3 (5) was
treated with 2•+ in order to obtain 6 (Scheme 4). Second,
3 itself was subjected to cyclobutadimerization under
photosensitized electron-transfer conditions, giving 7.
Both of these model compounds exhibit methyl absorp-
tions in their 13C NMR spectra at δ 18, as well as benzylic
tensive previous research has shown that methyl groups
attached to cyclobutane rings absorb at appreciably lower
fields (δ 1.1-1.2) than do typical aliphatic methyl groups
1
(δ 0.7-0.9) in their H NMR spectra.5 The soluble poly(3)
had only very weak methyl absorptions in the range of δ
1.1-1.2 region with much stronger absorptions in the δ
1
0.7-0.9 region. From the relative peak areas in the H

2588 J . Org. Chem., Vol. 63, No. 8, 1998
Aplin and Bauld
Sch em e 4. Ca tion Ra d ica l vs Ca r boca tion
P olym er iza tion
tion of oligomers having Mh w ) 1600 and exclusively the
cyclobutane structure.
Mech a n istic Con sid er a tion s. Although 3 has a
modestly higher oxidation potential than 1 (ca. 0.1 V), it
is still well within the range of oxidizability of 2•+, as
shown by the facile cation radical Diels-Alder and
cyclobutanation reactions of 5. It is therefore a matter
of mechanistic interest that the cation radical cycload-
dition polymerization of 1 is quite efficient but that of 3
is so inefficient as to be overwhelmed by acid-catalyzed
carbocation-mediated polymerization. It has previously
been proposed that the chain mechanism for cation
radical cycloaddition polymerization is far more efficient
than the catalytic mechanism, which represents a step
growth process.2 Further, the maintenance of an efficient
chain process depends critically upon the existence of an
efficient intramolecular transfer of the cation radical
moiety (hole) from its initial location following cycload-
dition (on the cyclobutane long bond) to the terminal
propenyl site required for further cycloaddition (Scheme
1). In the case of 1, this hole transfer is evidently rapid
in comparison to the rate of intermolecular hole transfer
to a neutral, ionizable molecule (1 or 2), which would
convert the chain process into a catalytic, step growth
process. In the case of 3 (Scheme 5), the intramolecular
hole transfer may be less favorable energetically because
the propenyl moiety involved has a higher oxidation
potential than was available in the case of 1. That this
is the case is indicated by the circumstance that the hole
receptor propenyl moiety in the case of 1 is a â-methyl-
styrene moiety having a strongly stabilizing p-alkoxy
substituent (σ+ ) -0.78 for methoxy), while in the case
of 3, the substituent is the less strongly stabilizing
p-phenoxy group (σ+ ) -0.50). The difference in the
oxidation potentials between 4-PhO and 4-MeO â-meth-
ylstyrene is, in fact, 0.14 V or 3.2 kcal/mol.6 Since
intermolecular hole transfer to 2 (see Scheme 5) is highly
exergonic, it is presumably virtually diffusion controlled.
Consequently a diminished rate of intramolecular hole
transfer could easily result in the prevalence of intermo-
lecular hole transfer.
cyclobutane carbon absorption at δ 52, and non-benzylic
cyclobutane carbons at δ 43, but none of the strong ab-
sorptions of poly(3) at δ 12 or 35. In contrast, when the
monopropenyl substrate 5 was subjected to acid-catalyzed
polymerization (triflic acid, 0 °C), the resulting linear
polymer (Scheme 4) exhibited signals at δ 13, 34, and
48, corresponding to the absorptions of poly(3). Finally,
the polymerization of 3 by triflic acid gave a polymer
virtually identical in its 13C NMR spectrum to that
obtained in the aminium salt catalyzed polymerization.
Hindered nitrogen bases such as 2,6-di-tert-butylpyri-
dine are known to suppress acid-catalyzed reactions
completely,3,4 while permitting most cation radical reac-
tions to proceed, albeit with diminished efficiency. Such
bases are known to be able to deprotonate the highly
acidic cation radical intermediates in competition with
their cycloaddition reactions, thus diminishing the ef-
ficiency of the latter reactions. When the polymerization
of 3 via 2•+ was conducted in the presence of a hindered
amine base, the product consisted of a mixture of oligo-
mers up to and including octamers. The 1H and 13C NMR
spectra of these oligomers correspond excellently with the
model cyclobutadimers 6 and 7 and exhibit none of the δ
12 and 35 absorptions of poly(3) prepared in the absence
of base.
The suppression of acid-catalyzed polymerization by
the use of insoluble bases was also studied. When 3 was
polymerized by 2•+ in the presence of solid sodium
carbonate, the product consisted of recovered 3 (40%),
dimers and low oligomers (16%), and higher polymers
(18%). The latter had a 1:1 ratio of cyclic:acyclic linkages.
Finally, the polymerization of 3 was also attempted by
anodic oxidation. Direct oxidation of 3 in acetonitrile at
a reticulated vitreous carbon anode resulted in the
immediate formation of a polymer coating on the anode.
When 2 (the neutral triarylamine) was included in the
reaction mixture, anodic oxidation resulted in the forma-
Con clu sion s
The polymerization of the bispropenyl derivative of
diphenyl ether (3) by tris(4-bromophenyl)aminium hexa-
chloroantimonate (2•+) in dichloromethane at 0 °C pro-
ceeds to give a polymer which consists primarily (9:1) of
acyclic structural units propagated by an acid-catalyzed,
carbocation-mediated mechanism. This polymer is virtu-
ally identical to the one generated by the triflic acid
catalyzed polymerization of 3. Cation radical cyclobu-
tanation polymerization contributes more significantly
(1:1) when sodium carbonate is included in the reaction
medium. When a soluble amine base is included, the
efficiency of polymerization overall is diminished, leading
to oligomers (dimer to octamer) which are exclusively the
result of cation radical cyclobutanation. Anodic oxidation
of the same monomer in the presence of neutral triaryl-
amine 2 also yields an oligomeric mixture which involves
only cyclobutaoligomerization. The greatly diminished
efficiency of the cation radical cyclobutanation polymer-
ization of 3 in comparison to a previously studied
monomer is noted, and a mechanistic rationale for this
is provided.
(6) Yueh, W.; Bauld, N. L. J . Phys. Org. Chem. 1996, 9, 529-538.

Cation Radical and Carbocation Polymerizations
J . Org. Chem., Vol. 63, No. 8, 1998 2589
Sch em e 5. In tr a m olecu la r vs In ter m olecu la r Hole Tr a n sfer
ization mass spectra (CIMS) were recorded on a Finigan MAT
TSQ-70 mass spectrometer. High-resolution mass spectra
(HRMS) were recorded on a Dupont (CEC) 21-110B mass
spectrometer. Cyclic voltammetry (CV) measurements were
performed using a BAS model 100 electrochemical analyzer
at a scan rate of 100 mV/s. The CV measurements were
carried out using a divided cell equipped with a platinum disk
working electrode (anode) and a reticulated vitreous carbon
counter electrode separated by a glass frit. Ag/Ag+ reference
electrode (silver wire immersed in an acetonitrile solution 0.1
M in AgNO3 and LiClO4), calibrated against ferrocene/ferro-
cinium ion, was placed in the anode compartment and sepa-
rated from the bulk solution by a Vycor frit. The peak
oxidation potential (Epox) measurements vs Ag/Ag+ were con-
verted to vs SCE by adding 0.3 V to each value. A blank CV
trace of the electrolyte solution was recorded prior to analyzing
the substrate. The substrate was then added to the cell as a
solution in the electrolyte (concentration ∼4 mM), and its CV
response was recorded. Gel permeation chromatography
(GPC) was carried out in DCM or THF (1 mL/min) using a
Waters 550 HPLC pump, a Waters 410 differential refracto-
meter, and a Waters 745 data module with an Ultrastyragel
Exp er im en ta l Section
Rea gen ts. Dried solvents were obtained by distillation
under nitrogen immediately prior to use. Reagent grade
dichloromethane (DCM) and acetonitrile (AN) were distilled
from phosphorus pentoxide. Pyridine was distilled from
potassium hydroxide. Tetrahydrofuran (THF) and diethyl
ether (Et2O) were distilled from a blue solution of sodium (or
potassium) and benzophenone. All other reagents were used
as received unless otherwise specified. Alumina (neutral) TLC
plates and alumina preparative scale TLC (PTLC) plates
(Analtech, 1.5 mm layer thickness) were washed with a 1:1
solution of ethyl acetate (EtOAc) and DCM and then dried in
a 110 °C oven prior to use. In some instances the PTLC plate
was eluted two or three times in an attempt to obtain better
separation. After identifying the bands, the adsorbent was
scraped from the PTLC plate and was washed with DCM. The
adsorbent was filtered off, and the solvent was removed on a
rotary evaporator. Column chromatography was performed
using neutral or basic alumina. Reagent grade lithium per-
chlorate used for electrochemistry was dried by heating at 180
°C for 24 h under an N2 purge and stored in a desiccator
containing Drierite. All moisture sensitive reactions were
carried out in oven dried glassware which had been flushed
with dry nitrogen. All organic product solutions were dried
over magnesium sulfate unless otherwise indicated. Solvent
removal was performed on a rotary evaporator.
500 Å column connected in series with a µ Styragel 104
Å
column. The GPC analyses were calibrated with a polystyrene
standard. UV-visible spectra were taken on a Hewlett-
Packard 8450A spectrometer. Fourier transform infrared (FT-
IR) spectra were recorded on a Nicolet 205 FT-IR spectrometer
using polystyrene as a standard. Liquid samples were run as
thin films between NaCl plates. Solid samples were run as
thin films on NaCl plates (generated by evaporation of a DCM
solution on the plate) or as solutions in CCl4 using a NaCl
solution cell. Melting points were determined on a Mel-Temp
capillary melting point apparatus and are uncorrected.
An a lysis. Room-temperature 1H NMR and 13C NMR
spectra were recorded on a Bruker AC 250 spectrometer as
solutions in CDCl3. Two-dimensional 1H-1H and 13C-1H
NMR spectra were recorded using a General Electric GN-500
spectrometer as solutions in CDCl3. High-temperature 1H
NMR and 13C NMR spectra of polymers were recorded on a
General Electric G-500 spectrometer as solutions in CDCl3 at
55 °C. Solid-state 13C NMR spectra were recorded on a
Chemagentics CMX-300 spectrometer as fine powders. Chemi-
cal shifts are reported in parts per million (ppm) downfield
from a tetramethylsilane (TMS) reference. Splitting patterns
are designated as follows: s, singlet; d, doublet; t, triplet; q,
quartet; m, multiplet; dd, doublet of doublets; dt, doublet of
Bis(4-p r op ion ylp h en yl) Eth er . To a dry, round-bottom
flask equipped with a magnetic stirrer was added AlCl3 (50.3
g, 0.378 mol) followed by dichloromethane (100 mL). After the
temperature was lowered to -20 °C using a dry ice/acetone
bath, a solution of diphenyl ether (25.6 g, 0.151 mol) in
dichloromethane (50 mL) was added slowly. A solution of
propionyl chloride (30 g, 0.45 mol) in dichloromethane (40 mL)
was then added dropwise over a period of 10-20 min. After
the addition was complete, the dry ice/acetone bath was
replaced with an ice bath and the reaction mixture was stirred
for an additional 3 h and then poured into a separatory funnel
containing crushed ice. The aqueous layer was separated and
extracted twice with dichloromethane (2 × 100 mL). The
combined dichloromethane layers were then washed with
water (500 mL), saturated aqueous NaHCO3 (2 × 500 mL),
and water (2 × 500 mL). The dichloromethane solution was
then dried and the solvent removed by rotary evaporator. The
product (38.1 g, 90%) was obtained as a white solid which was
1
triplets; dq, doublet of quartets; br, broad. Solution-state H,
13C and solid-state 13C NMR spectra of polymer samples gave
broad signals with little fine structure, so chemical shifts of
such samples are reported as the midpoint of the broad signals.
Gas chromatographic (GC) analyses were performed on a
Varian Model 3700 equipped with a flame ionization detector
and a DB-1 (J &W Scientific, 15 m × 0.25 mm, 1 mm film
thickness) capillary column using helium as a carrier gas. Low-
resolution mass spectra (LRMS) were obtained on a Hewlett-
Packard 5890 gas chromatograph equipped with a DB-1 (15
m × 0.25 mm, 1 mm film thickness) capillary column and a
5917A mass selective detector. Low-resolution chemical ion-

2590 J . Org. Chem., Vol. 63, No. 8, 1998
Aplin and Bauld
found to be 99% pure by GC: mp 98.5-99.8 °C; 1H NMR δ 1.2
(t, 6H), 3.0 (q, 4H), 7.1 (d, 4H), 8.0 (d, 4H); 13C NMR δ 8.2,
31.7, 66.3, 118.8, 130.4, 160.2, 199.5; IR (CdO) 1684; LRMS
m/e 282 (M+), 271, 197, 196, 139, 120, 92 (base).
of dimer and low oligomers, and 0.090 g (18.0%) of high
oligomers/polymer were isolated: 1H NMR for polymer methyl
groups δ 0.8 (acid catalysis), 1.1 (cation radical catalysis); the
integrated signals gave an acid:CB linkage ration of 1:1; 13C
NMR for polymer methyl groups δ 13 (acid), 15.5 (tst), and
18.09 (tat); CIMS m/e 1250 (pentamer), 1002 (tetramer + 2
mass units), 751 (trimer + 1), 501 (dimer + 1), 250 (monomer).
P olym er iza t ion of 3 w it h 2,6-Di-ter t-b u t ylp yr id in e
(DTBP ). To 0.382 g (153 mmol) of 3 in 8 mL of dry DCM was
added 0.177 g (0.93 mmol) of DTBP followed by the addition
of 0.595 g (0.73 mmol) of 2•+ dissolved in 5 mL of dry DCM
over 1 min. The reaction was stirred for 15 min and quenched.
After workup and PTLC, 0.208 g (52.4%) of 3, 0.77 g (33.2%)
of dimer and trimer, and 0.080 g (20.9%) of high oligomers/
polymer were isolated. 1H and 13C NMR of the fraction
assigned by TLC to be dimer/trimer gave no resonances for
acid lingages: CIMS m/e 2000 octamer, 1750, 1500, 1250, 751,
501, 250.
P olym er iza tion of 3 a t Low Con cen tr a tion . The po-
lymerization of 3 was performed exactly as above with the
exception that the concentration was 0.02 M lower. This
resulted in the formation of the acid-catalyzed polymer as
before, but the isolated material was soluble.
Acid -Ca ta lyzed P olym er iza tion of 5. To a solution of
triflic acid (0.066 g, 8.7%) in 4 mL of dry DCM at 0 °C was
added 1.057 g (5.03 mmol) of 5 in 8 mL of dry DCM. After 5
min, 10 mL of saturated aqueous NaHCO3 was added along
with 10 mL of additional DCM. The organic layer was isolated,
washed with 20 mL of water, and dried to give 0.976 g (92%
recovery) of solid. Hexane was used to wash the solid, and
0.140 g (13% yield) of insoluble material was isolated by
vacuum filtration. Only the aliphatic resonances are re-
ported: 1H NMR δ 0.8 (methyl), 1.7 (methine), 2.1 (benzyl);
13C NMR δ 13 (methyl), 34 (methine), 48 (benzyl).
P ET Syn th esis of th e tr a n s,syn ,tr a n s-Cyclobu ta n e
Dim er (7) of 3. To a dry Pyrex test tube was added 0.500 g
(2.0 mmol) of 3, 0.025 g (0.19 mmol) of dicyanobenzene, and
10 mL of dry DCM. The test tube was capped with a septum
and the reaction irradiated with a medium-pressure mercury
lamp for 24 h. The solvent was removed, and column chro-
matography was performed (9:1 hexane and DCM). The
trans,syn,trans-cyclobutane dimer (0.200 g, 40% yield) and 2
(0.050 g, 10% recovery) were isolated with no higher oligomers
observed. The assignment of the structure of the dimer is
based on its similarity to the dimer of trans-anethole:6 1H
NMR δ 1.2 (d, 6H), 1.9 (d, 6H), 2.8 (d, 2H), 3.5 (d, 2H), 6.1 (m,
2H), 6.4 (d, 2H), 6.8 (m, 8H), 7.1 (m, 8H); 13C NMR δ 15.1,
18.4, 34.2, 49.6, 117.7, 118.2, 118.8, 125.0, 126.2, 129.3, 130.1,
136.0, 156.5; LRMS m/e 498 (M - 2H), 444, 334, 250 (base),
117.
P r ep a r a tion of 6 by th e Dim er iza tion of 5 Usin g
Tr is(4-b r om op h en yl)a m in iu m H exa ch lor oa n t im on a t e
(2•+). To 1.047 g (4.99 mmol) of 5 in 20 mL of dry DCM at 0
°C was added 0.204 g (0.25 mmol) of 2•+ as a solid. After 5
min of stirring, the reaction was quenched with saturated
K2CO3 in methanol. Excess water and DCM were added, and
the organic layer was isolated. The organic solution was
washed three times with water and dried. TLC analysis of
the crude product mixture showed three spots identified as 5,
the cyclobutane dimer of 5 (6), and polymer. Column chro-
matography (9:1 hexane and DCM) allowed for the isolation
of 5 and 6 as a mixture followed by PTLC (hexane) to separate
5 and 6. After PTLC, 0.67 g (64% recovery) of 5, 0.18 g (36%
yield) of 6, and 0.15 g (15% of recovered material) of polymer
were isolated (95.5% mass balance). The assignment of the
structure of the dimer is based on its similarity to the dimer
of trans-anethole 5. Only the aliphatic resonances are re-
ported: 1H NMR δ 1.2 (6H, d, trans,syn,trans (tst) and
trans,anti,trans (tat) methyl), 1.88 (2H, m, tst benzyl); 13C
NMR of tst δ 15.2, 34, 49, tat δ 18.90, 43.3, 52.4.
Bis[4-(1-h yd r oxyp r op yl)p h en yl] Eth er . The diketone
obtained in the preceding reaction (20 g, 0.071 mole) was
dissolved in 200 mL of a 3:1 ethanol:tetrahydrofuran mixed
solvent, and solid NaBH4 (5.0 g, 0.13 mol) was added. After
1.5 h at room temperature, the reaction was quenched with
excess 10% acetic acid at 0 °C. The aqueous solution was
extracted with dichloromethane (3 × 100 mL), and the
combined organic extracts were washed with saturated aque-
ous NaHCO3 (2 × 100 mL) and water (2 × 100 mL). The
solution was then dried and the solvent removed on a rotary
evaporator, giving 20.5 g of the diol product (99.7%) as an oil
which was used without further purification: 1H NMR δ 0.9
(t, 6H), 1.6-1.9 (m, 4H), 2.6 (br s, 2H), 4.5 (t, 2H). 6.9 (d, 4H),
7.2 (d, 4H); 13C NMR δ 10.2, 31.9, 75.4, 118.6, 127.4, 139.5,
156.5; IR (OdH) 3360.
Bis[4-(1-p r op en yl)p h en yl] Eth er . The diol obtained in
the preceding reduction (6.31 g, 0.02 mol) was dissolved in
pyridine (25 mL) at room temperature, followed by the addition
of POCl3 (7 g, 0.045 mol). The solution was then refluxed for
2 h, cooled in an ice bath, and quenched by adding water
slowly. The quenched reaction mixture was then transferred
to a separatory funnel containing 100 mL of ethyl acetate,
washed with water, and dried, and the solvent was removed
by rotary evaporator. The crude product was chromato-
graphed on alumina, yielding 3.96 g (71.8%) of 3, upon elution
with 1:1 hexane:dichloromethane. The product was found to
be pure (GC), but consisted of a mixture of E,E (87%), Z,E
(11%), and Z,Z (2%) isomers: mp 117-119 °C; λmax 270 nm,
1
log ꢀ 2.4; H NMR δ 1.9 (dd, 6H), 6.1 (dq, 2H, J trans 15.8), 6.4
(d, 2H, J trans 15.8), 6.9 (d, 4H), 7.4 (d, 4H); 13C NMR δ 18.4,
66.8, 118.8, 124.7, 126.9, 130.2, 131.2, 156.1; IR (CdC) 1590.
LRMS m/e 250 (M+), 207, 179, 165, 133, 115 (base), 91; HRMS
m/e calcd for C20H22O2 250.1358, found 250.1369; Eopx 1.36 V
(vs SCE).
Gen er a l P r oced u r e for th e P olym er iza tion of 3 Usin g
2•+. The polymerizations were run at a monomer concentra-
tion of 0.2 M at 0 °C in dry dichloromethane under dry
nitrogen. A catalytic amount of 2•+ (usually 5 mol %) was
added to the reaction mixture as a solid in one portion or as a
solution in 1-5 mL of dry dichloromethane at 0 °C. The
catalyst solution was added slowly over a period of 1-15 min,
and the reaction was stirred for an additional 4-10 min. The
polymerizations were quenched with a saturated solution of
K2CO3 in MeOH, and an aqueous workup was performed by
adding excess DCM and water and then filtering off any solid
that remained. The organic solution was washed three times
with water and dried over magnesium sulfate. The solvent
was removed, and purification was accomplished using PTLC
or column chromatograhy (9:1 hexane and dichloromethane).
TLC was performed to verify the separation, and in some
instances the oligomers, especially the higher ones, were not
cleanly separated. Insoluble material was characterized by
solid-state 13C NMR. Soluble material was characterized by
one or more of the following methods: room- and high-
temperature 1H and 13C NMR, CIMS, TLC, and GPC.
P olym er iza tion of 3 w ith No Ad d ed Ba se. To 0.990 g
(3.96 mmol) of 3 in 8 mL of dry DCM was added 0.170 g (0.21
mmol) of 2•+ dissolved in 5 mL of dry DCM over 15 min. After
10 min of additional reaction time, no further agitation was
observed and the reaction was quenched (the blue-black color
of the reaction mixture was slow to dissipate). After workup,
0.805 g (81.3%) of a tan solid was isolated and found to be
insoluble in common solvents under any conditions, including
diphenyl ether at 250 °C: solid state 13C NMR δ 12, 20, 35,
43, 120, 130, 155.
P olym er iza tion of 3 w ith Sod iu m Ca r bon a te. To 0.501
g (2.00 mmol) of 3 in 8 mL of dry DCM was added 3.05 g (28.8
mmol) of Na2CO3 followed by the addition of 0.166 g (0.020
mmol) of 2•+ for 2 min and quenched. After workup and
column chromatography, 0.198 g (39.5%) of 3, 0.078 g (15.6%)
Ack n ow led gm en t. The authors thank the Robert
A. Welch Foundation (F-149) for supporting this research.
J O972072N