Control of chain ends of polyesters in polycondensation of AA and BB monomers by use of solid-phase reagent

Article abstract of DOI:10.1002/pola.27573

For selective synthesis of linear polyester having a functional group at one end, polycondensation between 1,4-butanediol (1a) and sebacoyl chloride (2a) and between 1,12-dodecanediol (1b) and isophthaloyl chloride (2b) was conducted in the presence of ox

Full text of DOI:10.1002/pola.27573

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Control of Chain Ends of Polyesters in Polycondensation of AA and BB
Monomers by Use of Solid-Phase Reagent
Toshihiko Sugiura, Daisuke Yajima, Kento Shoji, Yoshihiro Ohta, Tsutomu Yokozawa
Department of Material and Life Chemistry, Kanagawa University, 3-27-1 Rokkakubashi, Kanagawa-ku,
Yokohama 221-8686, Japan
Correspondence to: T. Yokozawa (E-mail: yokozt01@kanagawa-u.ac.jp)
Received 31 December 2014; accepted 29 January 2015; published online 3 March 2015
DOI: 10.1002/pola.27573
ABSTRACT: For selective synthesis of linear polyester having a
functional group at one end, polycondensation between 1,4-
butanediol (1a) and sebacoyl chloride (2a) and between 1,12-
dodecanediol (1b) and isophthaloyl chloride (2b) was con-
ducted in the presence of oxime resin or oxime silica gel, fol-
lowed by cleavage of the formed polyester from the solid-
phase support with aniline. Matrix-assisted laser desorption
monomer concentration, feed ratio of monomer to oxime moi-
ety in the support, oxime content in the support, reaction sol-
vent, and the nature of the support. Polyester with a high poly
1/poly
(M 5 1430 g/mol) was obtained by polycondensation of 1b
and 2b in the presence of oxime silica gel in dichloromethane.
2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym.
2 ratio of 81/21 and moderate molecular weight
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ionization time-of-flight mass spectra and H NMR spectra of
Chem. 2015, 53, 1379–1386
the cleaved polyester showed that the products contained not
only polyester with anilide at one end (poly 1), but also polyes-
ter with anilides at both ends (poly 2). The product ratio of
poly 1 to poly 2 (poly 1/poly 2) was dependent on monomers,
KEYWORDS: controlled polymerization; maldi; oxime resin; poly-
condensation; polyesters; silica gel; solid-phase reaction
INTRODUCTION Polycondensation is a fundamental polymer-
ization method, affording polyamides, polyesters, polyimides,
and so on, which are widely used in the manufacture of tex-
tiles, engineering plastics, and other products. As polycon-
densation proceeds in a step-growth polymerization manner,
the obtained polymers possess broad molecular weight dis-
tribution, and controlling the molecular weight is difficult.
However, the polymerization mechanism can be converted
from step-growth to chain-growth if the monomer selectively
reacts with the polymer end group. We have developed
chain-growth condensation polymerization by means of three
approaches: (1) activation of polymer end group due to the
difference in substituent effects between the monomer and
than AB type monomers. Furthermore, physical properties of
the obtained polymers can be easily tuned by appropriate
combination of AA and BB monomers. However, there are only
a few reports of synthesis of polymers with defined molecular
weight and low polydispersity by means of AA 1 BB polycon-
8
densation. Shaffer and Kramer polymerized 1,8-dibromooc-
tane and Na
obtain a polysulfide with high molecular weight and low poly-
dispersity (M 5 683,000 g/mol, M /M 5 1.24). Hay and
coworkers synthesized polyformal with high molecular
weight and low polydispersity (M 5 250,000 g/mol, M
5 1.3) by polymerization of the potassium salt of bisphenol
S with a phase transfer catalyst (PTC) in water to
2
n
w
n
9
/
w
n
M
n
A and an excess amount of dibromomethane in N-methylpyr-
1
–5
the polymer;
(2) activation of polymer end group due to
rolidone with vigorous stirring for only five minutes. Dai and
1
0
successive intramolecular transfer of catalyst to the polymer
coworkers successfully synthesized polyamides with defined
molecular weight and low polydispersity (M 5 3838–
18,860 g/mol, M /M 5 1.1–1.4) by means of a novel, uncon-
6
end; and (3) suppression of self-condensation of monomers
n
7
by dispersion of solid monomers in the reaction mixture.
w
n
However, these approaches are limited to polymerization of
AB type monomers having nucleophilic and electrophilic
sites in the molecule.
ventional condensation polymerization of diisocyanate and
dicarboxylic acid (sequential self-repetitive reaction [SSRR]) in
the presence of a small amount of hindered carbodiimide and
a catalyst for carbodiimide formation.
Most polycondensation is conducted with AA type monomers
having two nucleophilic sites and BB type monomers having
two electrophilic sites; these are generally easier to synthesize
These controlled polycondensations of AA and BB monomers
have been achieved using combinations of specific
Additional Supporting Information may be found in the online version of this article.
2015 Wiley Periodicals, Inc.
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SCHEME 1 Control of chain ends in polycondensation of AA and BB monomers by use of solid-phase reagent.
1
2
monomers under unique conditions. We wanted to open up
a more broadly applicable controlled polymerization method
for polycondensation of conventional AA and BB monomers.
Difficulty of controlling molecular weight in polycondensa-
tion may stem from cyclization of polymers. Kricheldorf
et al. proposed that propagation and cyclization competi-
tively take place during all stages of polycondensation, and
finally only cyclic polymers are obtained, except for some
nucleophile, aniline, after the polycondensation to afford
polyester with anilide at one end.
EXPERIMENTAL
General
1
13
H and C NMR spectra were obtained on JEOL ECA-500
and ECA-600 spectrometers. The internal standard for
1
H
1
1
NMR spectra in CDCl was tetramethylsilane (0.00 ppm), and
rigid monomers. Accordingly, we thought that selective
synthesis of linear polymers by controlling the polymer end
groups would be a way to control polycondensation. It
seemed plausible that a monofunctional reagent added dur-
ing polycondensation of AA and BB monomers would afford
a linear polymer, and the molecular weight of the product
could be controlled by adjusting the feed ratio of monofunc-
tional reagent. However, linear oligomers or polymers
attached to the monofunctional reagent at one end would
not prevent reaction with other oligomers or polymers with
a mono-functional end. Cyclic polymers would also be
included in the products, if the monofunctional reagent did
not have a chance to react with monomer and oligomers. It
occurred to us that attachment of the monofunctional rea-
gent to resin or silica gel would suppress the reaction
between polymers attached to the monofunctional reagent
on the solid-phase support because of the bulkiness of the
support. Cyclic polymers and linear polymers not attached to
the support might be formed in solution, but these polymers
could easily be removed by filtration. The residual support
could then be treated with a cleaving reagent to afford a lin-
ear polymer with a monofunctionalized end (Scheme 1). The
molecular weight would be controlled by the feed ratio of
the monomer to this solid-phase support reagent, and the
molecular weight distribution could be made narrower by
controlling monomer addition to the reaction mixture con-
taining the support reagent.
3
1
3
the internal standard for C NMR spectra in CDCl was the
midpoint of CDCl (77.0 ppm). All melting points were meas-
3
3
ured with a Yanagimoto hot-stage melting point apparatus
without correction. Column chromatography was performed
on silica gel (Kieselgel 60, 230–400 mesh; Merck) with a
specified solvent, and this silica gel was used as the solid-
phase support. Commercially available dehydrated diethyl
ether (Kanto), dehydrated dichloromethane (Kanto), and
dehydrated toluene (Wako) were used as dry solvents.
Oxime resin (cross-linking: 1% DVB; bead size: 200–400
mesh; loading: 0.54 mmol/g; ChemPep) was used as
received. The M and M /M values of polymers were meas-
n
w
n
ured on a Shodex GPC-101 gel permeation chromatography
unit (eluent, THF; calibration, polystyrene standards) with
two Shodex KF-804L columns, Shodex UV-41, and Shodex RI-
1S. Matrix-assisted laser desorption ionization time-of flight
MALDI-TOF) mass spectra were recorded on a Shimadzu/
Kratos AXIMA-CFR plus in the reflectron ion mode by use of
laser (k 5 337 nm). Dithranol (1,8-dihydroxy-9[10H]-
7
(
a
anthracenone) was used as the matrix for the MALDI-TOF
mass measurements.
General Procedure for Polycondensation of 1a and 2a in
the Presence of Solid-Phase Support
All glass apparatus were dried prior to use. Addition of
reagents to a reaction flask was performed via a syringe from
a three-way stopcock under a stream of nitrogen. Oxime resin
(0.5 mmol oxime/g resin, 151.1 mg resin, 0.076 mmol oxime)
was placed in the flask, and the atmosphere in the flask was
replaced with argon. A solution of dry pyridine (0.25 ml, 3.1
mmol) and 1,4-butanediol (1a) (135.3 mg, 1.5 mmol) in dry
dichloromethane (6 ml) was added via a syringe, and the
In this article, we report the first attempt to achieve con-
trolled polycondensation of diol and diacid chloride in the
presence of oxime resin or silica gel. The hydroxyl group in
the oxime reacts with diacid chloride monomer, and the
formed oxime ester moiety is easily cleaved with a weak
1
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ꢀ
mixture was stirred at 0 C. A solution of sebacoyl chloride
2a) (358.7 mg, 1.5 mmol) in dry dichloromethane (3 ml) was
were placed in a round-bottomed flask equipped with a
reflux condenser, and the mixture was refluxed for 3.5 h. The
mixture was then cooled to room temperature, and the pre-
cipitate was collected by filtration, washed with acetone, and
dried under reduced pressure in a vacuum desiccator to
afford 3 as a white solid (4.062 g, 76%).
(
added dropwise to the flask via a syringe over 5–10 min, and
stirring was continued at room temperature for 3–7 days. Dry
ethanol was added via a syringe, and the mixture was stirred
for 30–60 min. Dichloromethane solution in the flask was
removed with a pipette, and the resin was washed in the flask
with six 15 ml portions of dichloromethane with stirring for
1
1
H
N
M
R
(
5
0
0
M
H
z
,
C
D
C
l
)
:
H
N
M
R
(
5
0
0
M
H
z
,
C
D
C
l
)
:
3
3
d 5 7.83–7.76 (m, 9H), 7.72 (d, J 5 8.5 Hz, 2H), 7.64 (td,
J 5 8.2 and 3.6 Hz, 6H), 7.60–7.55 (m, 3H), 7.46 (t, J 5 7.8
Hz, 2H), 7.32 (dd, J 5 8.3 and 2.6 Hz, 2H), 5.72 (d, J 5 14.9
1
0 min for each washing. The combined dichloromethane solu-
tion was washed with 1 M hydrochloric acid and water, dried
over anhydrous MgSO , and concentrated under reduced pres-
sure to afford polyester from the homogeneous solution
4
1
3
Hz, 2H); C NMR (150 MHz, CDCl ): d 5 196.0, 137.1, 136.8,
3
1
3
1
35.0, 134.3, 132.6, 132.3, 131.6, 130.1, 130.0, 129.9, 128.2,
(
246.8 mg, 64.2%). The washed resin was collected and dried
0.3; IR (KBr) 3053, 2870, 2769, 2361, 1648, 1603,
under reduced pressure in a vacuum desiccator. Aniline (5 ml)
and dichloromethane (5 ml) were added to the resin, and stir-
ring was continued at room temperature for 24 h to cleave
polyester from the resin. After filtration of the resin, the fil-
trate was washed with 1 M hydrochloric acid and water, dried
21
438 cm
.
Synthesis of 4-Vinylbenzophenone (4)
An aqueous solution of sodium hydroxide (4 N, 25 ml, 100
ꢀ
mmol) was added dropwise at 0 C to a solution of phospho-
over anhydrous MgSO , and concentrated under reduced pres-
sure to afford polyester cleaved from the resin (23.1 mg,
4
nium salt 3 (687.5 mg, 1.28 mmol) and 37% formaldehyde
(
3.6 ml, 48 mmol). After removal of methanol in vacuo, the
6.0%).
residue was dissolved in dichloromethane, and the solution
was washed with water. The organic layer was dried over
MgSO4 and concentrated. The residue was purified by col-
umn chromatography on silica gel (AcOEt/hexane 5 1/10) to
afford 4 as a slightly yellow liquid (151 mg, 57%).
Polycondensation of 1b and 2b in the Presence
of Resin Containing a Low Concentration of Oxime
Moieties
All glass apparatus were dried prior to use. Addition of
reagents to a reaction flask was performed via a syringe from
a three-way stopcock under a stream of nitrogen. Acetyl chlo-
ride (12 mg, 0.15 mmol) was placed in the flask, and oxime
resin (0.54 mmol oxime/g resin, 416 mg resin, 0.225 mmol
oxime) and dry dichloromethane (4.0 ml) were added to the
flask. Then, dry pyridine (0.1 ml, 1.24 mmol) was added, and
the mixture was stirred at room temperature for 24 h.
Dichloromethane solution in the flask was removed with a pip-
ette, and the resin was washed in the flask with six 15 ml por-
tions of dichloromethane with stirring for 10 min for each
washing. The washed resin was collected and dried under
reduced pressure in a vacuum desiccator to afford a pale yel-
low powder (428 mg). The oxime content in the resin was cal-
culated to be 0.18 mmol/g, assuming that acetyl chloride
reacted quantitatively with the oxime moieties in the resin.
This oxime resin (0.18 mmol/g in resin, 0.428 mg, 0.077
mmol) was placed in the flask, and the atmosphere in the flask
was replaced with argon. A solution of dry pyridine (0.25 ml,
1
H NMR (500 MHz, CDCl ) d 5 7.79 (m, 4H), 7.58 (tt, J 5 7.4
3
and 1.3 Hz, 1H), 7.49 (m, 4H), 6.78 (dd, J 5 10.5 and 17.5
Hz, 1H), 5.89 (d, J 5 17.5 Hz,1H), 5.40 (d, J 510.9 Hz, 1H);
1
3
C NMR (150 MHz, CDCl ): d 5 196.2, 141.5, 137.7, 136.6,
3
1
2
36.0, 132.3, 130.5, 129.9, 128.2, 126.0, 116.6; IR (neat)
2
1
921, 2359, 2342, 1655, 1604 cm
.
Synthesis of 5
A mixture of 4 (1.092 g, 5.24 mmol), (3-mercaptopropyl)tri-
methoxysilane (1.027 g, 5.23 mmol), and 2,2 -azobis(isobu-
tyronitrile) (9.8 mg, 0.060 mmol) in dry toluene (10 ml) was
charged in a glass tube. The tube was degassed by means of
five freeze–pump–thaw cycles, filled with argon, sealed, and
0
ꢀ
heated at 70 C for 26 h. The reaction mixture was concen-
trated in vacuo to give 5 as a slightly yellow viscose liquid
(
2.232 g, 105%).
1
H NMR (500 MHz, CDCl ): d 5 7.81–7.77 (m, 4H), 7.58 (t,
3
3
.1 mmol) and 1,12-dodecanediol (304 mg, 1.5 mmol) in dry
J 5 7.0 Hz, 1H), 7.48 (dd, J 5 7.5 and 1.5 Hz, 2H), 7.33 (dd,
J 5 6.3 and 1.7 Hz, 2H), 3.58 (s, 9H), 2.97 (t, J 5 7.7 Hz, 2H),
dichloromethane (3.5 ml) was added via a syringe, and the
1
3
ꢀ
mixture was stirred at 0 C. A solution of isophthaloyl chloride
305 mg, 1.5 mmol) in dry dichloromethane (1.5 ml) was
2.81 (t, J 5 7.2 Hz, 2H), 2.57 (m, 2H); C NMR (150 MHz,
CDCl ): d 5 191.6, 142.5, 138.4, 133.1, 130.3, 130.2, 128.4,
125.3, 50.5, 36.2, 33.5, 32.9, 25.1, 21.6; IR (neat) 2940,
(
3
added dropwise to the flask via a syringe, and stirring was
continued at room temperature for 7 days. After this, a similar
procedure to that described above was carried out to afford
polyester from the homogeneous solution (356.3 mg, 71.4%)
and polyester cleaved from the resin (32.6 mg, 6.5%).
2
1
2361, 1704, 1657, 1605, 1278 cm
.
Synthesis of 6 (Immobilization of 5 onto SiO
)
2
A suspension of silica gel (1.304 g), dried under reduced
pressure in the presence of P2O5 in a desiccator overnight,
and 5 (407 mg, 1.0 mmol) in dry toluene (12 ml) was
heated under reflux for 24 h. The resulting solid was col-
lected by filtration and dried under reduced pressure in a
vacuum desiccator to afford 6 as a white solid (1.552 g).
Synthesis of [(4-Benzoylphenyl)methyl]triphenyl
phosphonium Bromide (3)
4
-(Bromomethyl)benzophenone (2.766 g, 10.1 mmol), triphe-
nylphosphine (2.628 g, 10.0 mmol), and dry toluene (80 ml)
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SCHEME 2 Polycondensation of diol and diacid chloride in the presence of oxime resin or silica gel.
Synthesis of Oxime Silica Gel 7
presence of commercially available oxime resin ([mono-
A suspension of 6 (507 mg, 0.319 mmol), dry pyridine
mer] /[oxime moiety] 5 20) and pyridine at room tempera-
0
0
(
(
0.45 ml, 5.59 mmol), and hydroxylamine hydrochloride
440 mg, 6.3 mmol) in dry methanol (10 ml) was heated
ture, according to the reported method for homogeneous
1
1
solution polymerization of 1a and 2a. The monomer addi-
tion method was modified as follows: a solution of 2a in
dichloromethane was added dropwise to the reaction mix-
ture of 1a, pyridine, and the resin in dichloromethane. After
stirring, the polymerization mixture was filtered, and the
residual oxime resin was thoroughly washed with dichloro-
methane. The resin was placed in an excess amount of ani-
line and dichloromethane, and stirred for 24 h to cleave
polyester from the resin. The solution was washed with
hydrochloric acid to remove excess aniline and concentrated
to afford polyester in 6.0% yield (Scheme 2; Table 1, Entry
under reflux for 3 days. The resulting solid was collected by
filtration, washed successively with methanol, 50% aqueous
methanol, acetone, and dichloromethane, and dried under
reduced pressure to give 7 as a white solid (476 mg).
RESULTS AND DISCUSSION
Polymerization of 1,4-Butanediol 1a and Sebacoyl
Chloride 2a
Polycondensation of 1,4-butanediol (1a) and sebacoyl chlo-
ride (2a) was first performed in dichloromethane in the
1). The molecular weight was unexpectedly low
TABLE 1 Polymerization of 1a and 2a in the Presence of Oxime Resin
Excess
Amount of
Acid
a
b
M
n
M
n
poly 1 :
b
Chloride
(mol %)
[1a]
0
[1a]
0
/
Reaction
(g/mol)
(GPC)
(g/mol)
(NMR)
poly 2
a
Entry
(mol/L)
[oxime]
0
Time (days)
Yield (%)
M
w
/M
n
(mol %)
1
2
3
4
5
6
7
0
0.33
0.33
0.33
0.33
1.0
20
20
20
20
20
10
6.7
20
7
6.0
6.2
6.5
7.1
4.9
9.4
17.3
2.3
813
572
1.73
1.71
1.97
1.50
1.94
1.76
2.07
2.18
32:68
39:61
18:82
31:69
39:61
52:48
64:36
84:16
2.3
4.4
7.7
0
7
1,210
1,320
1,150
1,410
1,200
1,070
1,330
1,050
1,020
608
9
7
7
1,420
1,360
1,460
1,560
0
1.0
7
0
1.0
7
c)
8
0
1.0
0.21
b
1
Polymerization of 1a and 2a was performed in the presence of 1.03
Estimated from the H NMR spectrum.
c
equiv of pyridine and oxime resin in dichloromethane at rt.
Oxime resin was added to the polymerization mixture after it had
been stirred for 10 min.
a
Estimated by GPC based on polystyrene standards (eluent: THF).
1
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FIGURE 1 MALDI-TOF mass spectra of products cleaved from oxime resin (Table 1, Entry 1): (a) mass/charge range is between
00 and 2800 g/mol, (b) enlargement of a peak around the mass/charge ratio of 1416 g/mol.
9
(
M 5 813 g/mol). Polyester formed in solution, not con-
increased with increasing amount of 2a, and the molecular
weight reached the highest value when a 4.4% excess of 2a
n
nected to the resin, was obtained in 64% yield, and its Mn
was 2140 g/mol. The low yield of polyester on the resin
might be a consequence of the low nucleophilicity of the
hydroxyl group on the oxime resin due to the electron-
withdrawing imino group attached to the hydroxyl group
and the steric hindrance of the resin. These results were dis-
appointing, as we had anticipated that the molecular weight
of the polyester on the resin would be as high as that of the
polyester obtained in solution, because the polymer end
functional groups of the elongated polyester chains on the
resin could react with monomers and oligomers in a similar
manner to that in the case of the polymerization in solution.
was used (M 5 1320 g/mol, Entry 3). However, the selectiv-
n
ity for poly 1 decreased with increasing amount of 2a.
When the monomer concentration was increased from 0.33
to 1.0 mol/L, the M value reached 1410 g/mol, but poly 2
n
became the major product (Entry 5). To decrease formation
of poly 2, polycondensation was performed with increasing
amounts of oxime resin, although the molecular weight
would be decreased under these conditions (Entries 5–7). As
expected, the ratio of poly 2 was decreased from 61% to
36%, and the polymer yield was increased to 17.3%. The
molecular weight was not greatly decreased, implying that
the oxime moieties in the resin are not as reactive as mono-
functional reagent in homogeneous solution.
To establish why the polyester cleaved from the resin had
low molecular weight, we analyzed the polymer end groups
by means of MALDI-TOF mass spectrometry. The spectrum
seemed to show only one series of peaks [Fig. 1(a)], but
when the spectrum was enlarged, it turned out that two
series of peaks were present: the minor peaks are due to the
desired polymers having an anilide at one end and a
hydroxyl group at the other (poly 1), and the major peaks
are due to polymers with anilides at both ends (poly 2) [Fig.
Furthermore, oxime resin was added to the polymerization
mixture after stirring for 10 min, because we expected that
the ratio of poly 1 would be increased if we reacted polyes-
ter that had already been elongated to some degree with the
oxime resin. Indeed, the ratio of poly 1 was increased to
84% (Supporting Information Fig. S1), and the molecular
weight was increased to 1330 g/mol. However, the yield was
decreased, implying that reaction of oxime moiety in the
resin with the terminal acyl chloride moiety of polyester
might be slow because of steric hindrance between resin
and polyester (Entry 8).
1
6
(b)]. The ratio of poly 1 to poly 2 was estimated to be 32/
1
8 from the H NMR spectra. As mentioned in Introduction
section, we had anticipated that the reaction between the
polymer end groups of polymers on the resin would be sup-
pressed because of the bulkiness of the resin. However, poly
Polymerization of 1,12-Dodecanediol 1b
and Isophthaloyl Chloride 2b in the Presence
of Oxime Resin
2
, in which the oxime moieties in the resin had reacted with
both polymer ends, was formed. We speculated that the
oxime moieties in resin beads would have reacted intramo-
lecularly with the acid chloride moiety of polyester to afford
poly 2. This intramolecular reaction in a resin bead might
account for the low molecular weight of the polymer cleaved
from the resin.
As we expected that a rigid polymer backbone would
decrease the probability of reaction of the end groups of
polymers attached on the resin to afford poly 2, the diacid
chloride was changed from sebacoyl chloride (2a) to iso-
phthaloyl chloride (2b). We wanted to use 1,4-butanediol
(1a), but polyester derived from 1a and 2b was not soluble
in dichloromethane. Accordingly, the polycondensation of
1,12-dodecanediol (1b) and 2b was investigated under the
conditions of Entry 5, Table 1. Polyester was not precipitated
1
1
Since Kricheldorf et al. reported that 1% excess of diacid
chloride in polycondensation with diol resulted in the high-
est molecular weight, we conducted polycondensation using
excess 2a (Entries 2–4). The polymer yield was slightly
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TABLE 2 Polymerization of 1b and 2b in the Presence of Oxime Resin
a
b
Oxime
Reaction
Time
M
n
M
n
poly 1 :
b
Content in
(g/mol) (g/mol)
poly 2
a
Entry Resin (mmol/g) Solvent
(days)
Yield (%) (GPC)
(NMR)
M /M
w n
(mol %)
1
2
3
4
5
6
7
0.54
0.54
0.18
0.14
0.11
0.54
0.54
CH
CH
CH
CH
CH
CH
2
2
2
2
2
2
Cl
Cl
Cl
Cl
Cl
Cl
2
2
2
2
2
2
7
8.6
8.4
6.5
3.5
8.5
8.8
9.9
1,820
1,660
888
1,880
1,280
908
2.48
2.50
1.41
1.28
1.42
1.63
2.27
21:79
0:100
66:34
79:21
82:18
39:61
38:62
c
7
7
10
9
654
1,240
1,100
1,720
2,970
561
2
/Et O (2/1 (v/v))
7
2,390
3,000
Et
2
O
9
b
1
Polymerization of 1b and 2b was performed in the presence of 1.03
equiv of pyridine and oxime resin [1b] /[oxime] 5 20 in dry solvent
[1b] 5 1.0 mol/L) at rt.
Estimated by GPC based on polystyrene standards (eluent: THF).
Estimated from the H NMR spectrum.
c
0
0
Reverse addition method: diol 1b was added to the reaction mixture
(
a
0
of acid chloride 2b, pyridine, and resin.
1
1
during the polymerization, and the molecular weight was
higher than that of the polyester from 1a and 2a. Contrary
to our expectation, however, the selectivity for poly 1 was
decreased to 21% (Table 2, Entry 1). When diol 1b was
added to the reaction mixture of 2b, pyridine, and resin,
which is the reverse of the addition method in Table 1, only
poly 2 was obtained (Entry 2).
the polymer chains attached to resin would be less able to
react with each other, resulting in suppression of poly 2 for-
mation. On the basis of this idea, oxime resin was reacted
with a certain amount of acetyl chloride, and then used for
polycondensation. The selectivity for poly 1 increased up to
82% with decreasing oxime content in the resin, although
the molecular weight was decreased (Entries 3–5). Further-
more, polymerization in diethyl ether or a mixed solvent of
diethyl ether and dichloromethane, which does not swell the
resin as much as dichloromethane does, improved the
If the amount of oxime moiety in the resin is decreased (i.e.,
if the concentration of oxime moieties in the resin is low),
SCHEME 3 Synthesis of oxime silica gel 7.
1
384
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TABLE 3 Polymerization of 1b and 2b in the Presence of Oxime Silica Gel
poly 1 :
a
b
b
Oxime Content in
SiO (mmol/g)
Reaction
M
n
(g/mol)
M
n
poly 2
a
Entry
2
Time (days)
Yield (%)
(GPC)
(g/mol) (NMR)
M
w
/M
n
(mol %)
1
2
0.63
0.14
7
7
1.3
1.6
1,320
1,430
1,220
1,520
1.66
1.58
73:27
81:19
a
Polymerization of 1b and 2b was performed in the presence of 1.02
equiv of pyridine and oxime silica gel [1b] /[oxime] 5 10 in dichlorome-
thane ([1b] 5 1.0 mol/L) at rt for 7 days.
Estimated by GPC based on polystyrene standards (eluent: THF).
b
1
0
0
Estimated from the H NMR spectrum.
0
selectivity for poly 1 up to 39% (Entry 6) and increased the
of polyester up to 3000 g/mol (Entry 7), compared to
ear polyester, as an approach to controlling the polymer end
groups and molecular weight in AA 1 BB polycondensation.
We expected that a bulky solid-phase support would prevent
the polyester formed on the support from reacting with
another polyester on the support, so that mono-
functionalized polyester (poly 1) would be formed after
cleavage from the support. However, double-end functional-
ized polyester (poly 2) was also formed. On the basis of the
results that the selectivity for poly 1 was increased when
the oxime content in the support was decreased and when
silica gel support with no mobility was used, poly 2 was
presumably formed intramolecularly on the support. Low
yield of polyester cleaved from the support might be
accounted for by the low nucleophilicity of the hydroxyl
group in the oxime moiety, compared to that of the hydroxyl
group in the diol monomer. We are now investigating poly-
condensation of AA and BB monomers for the synthesis of
mono-end functionalized polyester in the presence of a silica
gel support containing a more nucleophilic hydroxyl group.
M
n
the reaction in dichloromethane (Entry 1). These results
imply that low content of oxime moiety and low mobility of
the solid-phase support would be effective for increasing the
selectivity for poly 1 and the polymer molecular weight. We
next investigated polycondensation of 1b and 2b using
oxime silica gel.
Polymerization of 1,12-Dodecanediol 1b and
Isophthaloyl Chloride 2b in the Presence
of Oxime Silica Gel
1
2
Oxime siilca gel 7 was synthesized as described (Scheme
3
). Commercially available 4-bromomethylbenzophenone
1
3
was converted to phosphonium salt 3,
which was
subjected to Wittig reaction with formaldehyde to give 4-
vinylbenzophenone (4). Radical addition of 3-(trimethoxysi-
0
lyl)propanethiol to 4 was conducted in the presence of 2,2 -
ꢀ
azobis(isobutyronitrile) (AIBN) at 70 C to afford a silane
1
4
coupling agent 5, which was reacted with silica gel in tolu-
ene under reflux for 24 h to give benzophenone silica gel
REFERENCES AND NOTES
1
5
6
.
Finally, the carbonyl group of 6 was converted to oxime
1
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Polycondensation of equimolar 1b and 2b was performed in
the presence of the obtained oxime silica gel in dichlorome-
thane at rt (Table 3). As we had expected, the selectivity for
poly 1 was high even with high-oxime-content silica gel
2
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