Macromolecules, Vol. 37, No. 12, 2004
Carbocationic Polymerization of Styrene 4423
tion gave 3a (0.47 g, 98%) as a colorless oil; bp 20 °C/0.007
mbar. 1H and 13C NMR chemical shifts were identical with
those reported in ref 18. MS (EI, 70 eV) m/z (%): 160 (M+, 8),
105 (100), 77 (10).
higher than previously accepted values. Plesch at-
tempted to explain this large discrepancy in a recent
paper4 by proposing first-order propagation on monomer
complexed cations at high monomer concentration and
second-order propagation at monomer concentrations
close to zero. This explanation, however, is not convinc-
ing, as pointed out by Sigwalt,5 who proposed another
interpretation involving a two-step propagation. The
first step is the formation of monomer solvated cations,
which subsequently add monomer. It is clearly apparent
from these papers that the absolute rate constants of
propagation in carbocationic polymerization will remain
a subject of discussion until an agreement is reached.
We now extend our original investigation with iso-
butylene11 to styrene. In this study, the kinetics and
mechanism of capping of 1-phenylethyl cation (1+) with
DTE and 2-PhFu were studied at different temperature
using on-line UV-vis spectroscopy. Competition experi-
ments were also carried out to investigate the effect of
temperature, solvent polarity, and nature of Lewis acid
on the absolute propagation rate constant of the carbo-
cationic polymerization of St. The experimentally de-
termined value is compared to that predicted by the
linear free energy relationship.
Syn th esis of 4-P h en yl-1-p en ten e (3b). A solution of TiCl4
(0.75 mL, 6.8 mmol) in dichloromethane (15 mL) was cooled
to -78 °C. Then a mixture of 1-Cl (703 mg, 5.00 mmol) and
allyltrimethylsilane (2b, 1.14 g, 10.0 mmol) in dichloromethane
(2 mL) was added dropwise. After stirring at -78 °C for 2 h,
the solution was alkalized with concentrated NH3/water (20
mL, 1/1) and filtered through Celite. The layers were sepa-
rated, and the aqueous phase was extracted with dichloro-
methane (2 × 20 mL). The combined organic extracts were
dried over MgSO4, filtered, and concentrated in a vacuum.
Bulb-to-bulb distillation gave 3b (0.60 g, 82%) as a colorless
1
oil; bp 20 °C/0.005 mbar. H NMR (300 MHz, CDCl3) and MS
(EI, 70 eV) spectral data were identical with those reported
in ref 18. 13C NMR (75.5 MHz, CDCl3): δ 21.5 (q, C-5), 39.7
(d, C-4), 42.7 (t, C-3), 115.9 (t, C-1), 126.0, 127.0, 128.3 (3 d,
Ph), 137.1 (d, C-2), 147.0 (s, Ph).
Syn th esis of 2-Meth yl-4,6-d ip h en yl-1-h ep ten e (5a ). A
solution of TiCl4 (948 mg, 5.00 mmol) and DTBP (10 µL) in
dichloromethane (45 mL) was cooled to -78 °C. Then a mixture
of 4-Cl (300 mg, 1.23 mmol) and 2a (316 mg, 2.46 mmol) in
dichloromethane (5 mL) was added dropwise. After stirring
at -78 °C for 2 h, the solution was alkalized with concentrated
NH3/water (50 mL, 1/1) and filtered through Celite. The layers
were separated, and the aqueous phase was extracted with
dichloromethane (2 × 20 mL). The combined organic extracts
Exp er im en ta l Section
Ma ter ia ls. Styrene (St, Aldrich, 99%) and p-methylstyrene
(p-MeSt, Aldrich, 97%) were freed from inhibitor by washing
with 5% NaOH and then repeatedly with water. After drying
overnight over anhydrous Na2SO4, they were distilled from
calcium hydride under reduced pressure. The 1-chloro-1-(4-
methylphenyl)ethane (p-MeStCl),12 2-phenylfuran (2-PhFu),13
and 1,1-di-p-tolylethylene (DTE)14,15 were synthesized accord-
ing to the literature. All other chemicals and solvents were
purified as described previously or used as received.11
were dried over MgSO4, filtered, and concentrated in a
vacuum. Bulb-to-bulb distillation gave 5a (0.18 g, 55%) as a
colorless oil; bp 190-200 °C (oven temperature)/0.08 mbar. 1H
NMR (300 MHz, CDCl3): δ 1.12-2.81 (m, 12 H), 4.55, 4.65 (2
mc, 2 × 1 H, 1-H), 7.06-7.33 (m, 10 H, Ph); MS (EI, 70 eV)
m/z (%): 264 (M+, 4), 105 (100), 91 (19), 77 (15).
Syn th esis of 4,6-Dip h en yl-1-h ep ten e (5b). A solution of
TiCl4 (948 mg, 5.00 mmol) in dichloromethane (45 mL) was
cooled to -78 °C. Then a mixture of 4-Cl (734 mg, 3.00 mmol)
and 2b (686 mg, 6.00 mmol) in dichloromethane (5 mL) was
added dropwise. After stirring at -78 °C for 2 h, the solution
was alkalized with concentrated NH3/water (50 mL, 1/1) and
filtered through Celite. The layers were separated, and the
aqueous phase was extracted with dichloromethane (2 × 20
mL). The combined organic extracts were dried over MgSO4,
filtered, and concentrated in a vacuum. Bulb-to-bulb distilla-
tion gave 5b (0.44 g, 59%) as a mixture of diastereomers; bp
160-170 °C (oven temperature)/0.01 mbar. 1H NMR (300 MHz,
CDCl3): δ 1.13, 1.20 (2 d, each J ) 6.9 Hz, 3 H, 7-H), 1.82-
2.00 (m, 2 H), 2.23-2.70 (m, 4 H), 4.84-4.95 (m, 2 H, 1-H),
5.45-5.69 (m, 1 H, 2-H), 7.01-7.30 (m, 10 H, Ph). 13C NMR
(75.5 MHz, CDCl3): δ 21.0, 23.9 (2 q, C-7), 36.8, 37.4 (2 d, C-6),
41.5, 42.0 (2 t, C-5), 43.2, 43.4 (2 d, C-4), 44.0, 44.7 (2 t, C-3),
115.8, 119 (2 t, C-1), 125.8, 125.9, 126.0, 126.1, 126.4, 126.8,
127.3, 127.6, 127.9, 128.0, 128.2, 128.3 (12 d, Ph), 136.8 (d,
C-2), 144.8, 145.0, 146.8, 148.0 (4 s, Ph). MS (EI, 70 eV) m/z
(%): 250 (M+, 4), 106 (11), 105 (100), 91 (19), 77 (10).
Syn th esis of 1,3-Dip h en ylbu ta n e (5c). A solution of TiCl4
(948 mg, 5.00 mmol) in dichloromethane (30 mL) was cooled
to -78 °C. Then a mixture of 4-Cl (734 mg, 3.00 mmol) and
2c (781 mg, 3.00 mmol) in dichloromethane (5 mL) was added
dropwise. After stirring at -78 °C for 2 h, the solution was
alkalized with concentrated NH3/water (50 mL, 1/1) and
filtered through Celite. The layers were separated, and the
aqueous phase was extracted with dichloromethane (2 × 20
mL). The combined organic extracts were dried over MgSO4,
filtered, and concentrated in a vacuum. Bulb-to-bulb distilla-
tion gave 5c (0.32 g, 51%) as a colorless oil; bp 160-170 °C
(oven temperature)/0.07 mbar. 1H NMR (300 MHz, CDCl3): δ
1.26 (d, J ) 7.0 Hz, 3 H, 4-H), 1.88-1.95 (m, 2 H, 2-H), 2.45-
2.53 (m, 2 H, 1-H), 2.60-2.76 (m, 1 H, 3-H), 7.10-7.30 (m, 10
H, Ph). 13C NMR (75.5 MHz, CDCl3): δ 22.7 (q, C-4), 34.1 (t,
C-1), 39.7 (d, C-3), 40.2 (t, C-2), 125.8, 126.1, 127.3, 128.4, 128.6
(5 d, Ph), 142.7, 147.5 (2 s, Ph).
Ch a r a cter iza tion . Molecular weights were measured using
a Waters HPLC system equipped with a model 510 HPLC
pump, a model 250 dual refractometer/viscometer detector
(Viscotek), a model 486 UV/vis detector, a model 712 sample
processor, and five ultra-Styragel GPC columns connected in
the following series: 500, 103, 104, 105, and 100 Å. THF was
used as eluent at a flow rate of 1.0 mL min-1. The measure-
ments were carried out at room temperature. The molecular
weights and molecular weight distributions (PDI) were deter-
mined using the universal calibration curve and Viscotek
TriSEC GPC software. The 1H and 13C NMR spectra of
solutions in CDCl3 were calibrated to tetramethylsilane as
internal standard (δH 0.00) or to the solvent signal (δC 77.0),
respectively. DEPT-135 experiments were used to obtain
information about the multiplicities of 13C NMR resonances.
Syn th esis of 1-Ch lor o-1-p h en yleth a n e (1-Cl). In Lowell,
1-Cl was synthesized by hydrochlorination of St in CH2Cl2 (1:3
v/v) at 0 °C. In Mu¨nchen 1-Cl was synthesized by reaction of
thionyl chloride (0.25 mol) with 1-phenylethanol (0.20 mol) in
CH2Cl2 (100 mL, room temperature, 86% yield); bp 95-100
1
°C/10 mbar (bp 85 °C/20 Torr).16 The H NMR chemical shifts
(CDCl3) were in accord with those given in ref 15.
1-Ch lor o-1,3-d ip h en ylbu ta n e (4-Cl) was obtained from
St and 1-Cl in the presence of a zinc chloride-etherate catalyst
as a mixture of diastereomers by following a procedure
described in ref 17.
Syn th esis of 2-Meth yl-4-p h en yl-1-p en ten e (3a ). A solu-
tion of TiCl4 (0.50 mL, 4.6 mmol) and DTBP (5 µL) in
dichloromethane (15 mL) was cooled to -78 °C. Then a mixture
of 1-Cl (422 mg, 3.00 mmol) and (2-methylallyl)trimethylsilane
(2a , 2.31 g, 18.0 mmol) in dichloromethane (2 mL) was added
dropwise. After stirring at -78 °C for 2 h, the solution was
alkalized with concentrated NH3/water (20 mL, 1/1) and
filtered through Celite. The layers were separated, and the
aqueous phase was extracted with dichloromethane (2 × 20
mL). The combined organic extracts were dried over MgSO4,
filtered, and concentrated in a vacuum. Bulb-to-bulb distilla-
Com p etition Exp er im en ts. Rela tive Rea ctivities of 2a
a n d 2b tow a r d th e Ca tion 1+. Under an atmosphere of dry