Polymerization of nitrophenyl and 3-diethylaminophenyl prop-2-yn-1-yl ethers with PdCl2. Polymers and copolymers characterization

Article abstract of DOI:10.1135/cccc19981803

2-, 3- and 4-Nitrophenyl prop-2-yn-1-yl ethers were polymerized with PdCl₂ in N,N-dimethylformamide (DMF) giving brown polymers soluble in DMF. dimethyl sulfoxide and N-methylpyrrolidone. Broad (mostly bimodal) molecular weight distributions we

Full text of DOI:10.1135/cccc19981803

Polymerization of Nitrophenyl
1803
POLYMERIZATION OF NITROPHENYL AND 3-DIETHYLAMINOPHENYL
PROP-2-YN-1-YL ETHERS WITH PdCl2. POLYMERS AND COPOLYMERS
CHARACTERIZATION
a
b
c
d
Hynek BALCAR , Petr HOLLER , Jan SEDLACEK and Vratislav BLECHTA
a J. Heyrovsky Institute of Physical Chemistry, Academy of Sciences of the Czech Republic,
182 23 Prague 8, Czech Republic; e-mail: balcar@jh-inst.cas.cz
b Institute of Macromolecular Chemistry, Academy of Sciences of the Czech Republic,
162 06 Prague 6, Czech Republic; e-mail: holler@imc.cas.cz
c Department of Physical and Macromolecular Chemistry, Faculty of Sciences, Charles University,
128 40 Prague 2, Czech Republic; e-mail: jansedl@prfdec.natur.cuni.cz
d Institute of Chemical Process Fundamentals, Academy of Sciences of the Czech Republic,
165 02 Prague 6-Suchdol, Czech Republic; e-mail: blechta@icpf.cas.cz
Received June 15, 1998
Accepted July 28, 1998
2-, 3- and 4-Nitrophenyl prop-2-yn-1-yl ethers were polymerized with PdCl2 in N,N-dimethylforma-
mide (DMF) giving brown polymers soluble in DMF, dimethyl sulfoxide and N-methylpyrrolidone.
Broad (mostly bimodal) molecular weight distributions were observed by size-exclusion chromato-
graphy (SEC) with maxima at molecular weight of about 4 . 103 and 1 . 105. With the same catalyst,
3-diethylaminophenyl prop-2-yn-1-yl ether gave predominantly low molecular weight homopolymer
(Mn = 4 200) soluble in DMF, N-methylpyrrolidone, CHCl3 and tetrahydrofuran-soluble copolymers
with 4-nitrophenyl prop-2-yn-1-yl ether (Mn about 3 000). IR, NMR and UV-VIS spectra of prepared
polymers and copolymers proved the structure to consist of the polyene-type main chain with
phenoxymethyl pendant groups bearing nitro or diethylamino substituents.
Key words: Propargyl ethers; Palladium dichloride; Polymerization; Copolymerization; Polyace-
tylenes; Homogeneous catalysis.
Synthesis of substituted polyacetylenes has attracted great interest because polyace-
tylenes with suitable substituents offer promising applications in electronics and optoe-
lectronics1,2. Introduction of proper pendant groups into polyacetylene molecules not
only improves polymer solubility, processibility and stability but can also endow
polymers with properties such as photoconductivity, electroluminescence, liquid crys-
tallinity and non-linear optical effects. The importance of the influence of the polarity
of pendant groups on the above listed polymer properties is known2. In spite of that,
polyacetylenes substituted with non-polar substituents have been mostly reported3.
Mainly, this is a consequence of the fact that polymerizations of monomers with polar
groups are complicated by inhibitive interactions of these groups with polymerization-
inducing transition metal catalysts. Therefore, search for catalysts tolerating the
Collect. Czech. Chem. Commun. (Vol. 63) (1998)

1804
Balcar, Holler, Sedlacek, Blechta:
presence of polar groups in acetylenic monomers is of great importance in polyace-
tylene chemistry and may open ways for new polyacetylene-based materials.
Series of polyacetylenes with halogen- or oxygen-containing pendant groups have
been prepared3,4. However, polymerizations of acetylenes with nitrogen-containing
groups still remain rather rare. As to nitro-group containing monomers, only recently
the polymerization of 4-nitrophenylacetylene has been described5,6. From previous re-
ports, a mention on copolymerization of 4-nitrophenylacetylene with 4-dimethylamino-
phenylacetylene is known7. In our preceding paper8, we reported a successful
polymerization of nitrophenyl prop-2-yn-1-yl ethers (2-NPPE, 3-NPPE and 4-NPPE)
with MoCl5- and MoOCl4-based metathesis catalysts. With these catalysts, high-mole-
cular-weight polymers were prepared, of which only poly(4-nitrophenyl prop-2-yn-1-yl
ether), [poly(4-NPPE)] was soluble in solvents such as dimethyl sulfoxide (DMSO) or
N-methylpyrrolidone (NMP). Poly(3-nitrophenyl prop-2-yn-1-yl ether), [poly(3-
NPPE)] and poly(2-nitrophenyl prop-2-yn-1-yl ether), [poly(2-NPPE)] were insoluble
and could not be completely characterized.
In the literature, there are several reports on polymerizations of tertiary and second-
ary prop-2-yn-1-ylamines9–13 with transition metal catalysts. In addition to molybde-
num-based catalysts, PdCl2 showed remarkable activity in these reactions. However, no
attempt to polymerize or copolymerize dialkylaminophenyl prop-2-yn-1-yl ethers has
been made, to our best knowledge.
We have found that PdCl2 in N,N-dimethylformamide (DMF) initiates the polymeri-
zation of 2-NPPE, 3-NPPE and 4-NPPE (Scheme 1) providing soluble polymers suit-
able for further characterization. PdCl2 has been found to be also active in
polymerization of 3-diethylamino phenyl prop-2-yn-1-yl ether (3-DEAPPE) (Scheme 1)
and in copolymerization of 3-DEAPPE with 4-NPPE. The results are presented in this
paper.
5
6
PdCl
2
4
n
O
CH
C CH
2
C
C
1
DMF
n
3
2
CH
O
2
R
R = 2-NO , 3-NO , 4-NO , 3-NEt
2
2
2
2
R
SCHEME 1
EXPERIMENTAL
Materials
PdCl2 (Aldrich, 99%) was used as obtained. N,N-Dimethylformamide (DMF) (Lachema, Czech Re-
public, purum) was dried with P2O5 and distilled under argon. Preparation and characterization of 2-,
3- and 4-nitrophenyl prop-2-yn-1-yl ethers are described elsewhere8.
3-Diethylaminophenyl prop-2-yn-1-yl ether (3-DEAPPE ) was prepared by alkylation of the corre-
sponding phenol with prop-2-yn-1-yl bromide in the presence of excess of NaOH. The amount of 3.3 g
Collect. Czech. Chem. Commun. (Vol. 63) (1998)

Polymerization of Nitrophenyl
1805
(20 mmol) of 3-diethylaminophenol (Aldrich, 97%) was mixed with 1.6 g (40 mmol) of NaOH (pul-
verized), 3.3 g of KI and 17 g of anhydrous Na2CO3 (pulverized) in 40 ml of dry DMF. Then 3 g (20 mmol)
of prop-2-yn-1-yl bromide in toluene (Aldrich, 80 wt.%) was added and the reaction mixture was
stirred at 50 °C for 8 h. After cooling, it was poured into 500 ml of water and organic products were
extracted with diethyl ether. The ether layer was separated, and after washing with 1 M NaOH and
water, dried with anhydrous Na2SO4. After evaporating ether, the dark oil was purified by distillation
in vacuo. Pure product (99%, GC-MS) was obtained as orange liquid (density 1.03 g/ml) soluble in
common organic solvents (aromatics, CHCl3, DMF, methanol). Yield: 14%. IR spectrum (KBr),
1
cm–1: 3 270 (≡C–H), 2 110 (C≡C). H NMR spectrum (CDCl3), ppm (for atom numbering, see
Scheme 1): 1.14 t, 6 H, J(CH3,NCH2) = 7.0 (CH3); 2.48 t, 1 H, J(≡CH,O–CH2) = 2.1 (≡CH); 3.31 q,
4 H (N–CH2); 4.64 d, 2 H (O–CH2); 6.22 dd, 1 H (H-4 or H-6); 6.30 dd, 1 H (H-4 or H-6); 6.26 t,
1 H (H-2); 7.11 t, 1 H, J(H-5,H-4) = 7.9, J(H-5,H-6) = 7.9 (H-5). 13C NMR spectrum (CDCl3), ppm
(for atom numbering, see Scheme 1): 12.50 (CH3), 44.31 (N–CH2), 55.54 (O–CH2), 75.06 (C≡CH),
78.96 (C≡CH), 99. 02 (C-2), 100.63 (C-4 or C-6), 105.63 (C-4 or C-6), 129.75 (C-5), 149.02 (C-3),
158.90 (C-1). Attempts to resolve positions 4 and 6 were not successful.
Polymerization
Polymerizations were performed using the standard vacuum break-seal technique14 and DMF as sol-
vent. The reaction conditions were (unless otherwise stated): initial monomer concentration 0.5 mol/l,
initial molar ratio monomer : catalyst 50, reaction temperature 85 °C, reaction time 24 h. Polymeri-
zations were started by mixing PdCl2 in DMF with DMF solution of monomer (2-NPPE, 3-NPPE,
4-NPPE, 3-DEAPPE) or mixture of comonomers (4-NPPE + 3-DEAPPE). In the time depending ex-
periment, PdCl2 in DMF was mixed with 4-NPPE solution in DMF. After 10 min of stirring at 85 °C,
the reactor was removed from a bath and the orange solution was divided into individual ampoules,
which were, after sealing off, treated separately. The reactions were always quenched by pouring the
reaction mixture into an excess of methanol or water (in the case of homopolymerization of 3-
DEAPPE). The methanol- or water-insoluble product was isolated, washed with methanol and dried
in vacuo at 40 °C to constant weight. The yield of polymer was determined gravimetrically. The super-
natant from the polymer isolation was (after evaporating solvents) analyzed by SEC, IR and GC.
Techniques
IR spectra were recorded on a Specord 75 IR spectrometer in KBr pellets, UV-VIS spectra on a
Hewlett–Packard HP 89500 spectrometer.
1H and 13C NMR spectra of polymers were measured in CDCl3 or in DMSO-d6 solution on a
1
Varian UNITY-500 NMR spectrometer. A basic one-pulse sequence with broad-band H decoupling
for the 13C nucleus were used. The relaxation delay and acquisition time were respectively 5 and 1 s for
13C, 5 or 8 s and 1 or 2 s for 1H. An exponential weighting function (linebroadening 4 Hz for 13C
1
1
and 1 Hz for H NMR spectra) was applied. H NMR spectra measured in CDCl3 solution were ref-
erenced to hexamethyldisilane (HMDS, δ 0.04), used as an internal standard. The remaining spectra
were referenced to a central line of the solvent multiplet: δ 76.99 for CDCl3, δ 39.7 for DMSO-d6,
δ 2.5 for DMSO.
1H and 13C NMR spectra of the 3-DEAPPE monomer were recorded on a Varian UNITY-200
NMR spectrometer in a CDCl3 solution with HMDS added and referenced like in the previous cases.
Homonuclear selective decoupling and chemical shifts were used for the 1H NMR line assignment.
Chemical shifts and line multiplicities found by DEPT (ref.15) editing helped in 13C NMR line as-
signment of NEt2, CH2–O and C≡CH groups. Quaternary C-1 and C-3 carbons were assigned by 13C
Collect. Czech. Chem. Commun. (Vol. 63) (1998)

1806
Balcar, Holler, Sedlacek, Blechta:
proton selective decoupling experiments while tertiary C-2, C-4, C-5 and C-6 were assigned using
HETCOR spectrum.
For SEC analyses, two devices were used: (i) Apparatus train consisting of a high-pressure pump
HPP 5001 (Laboratorní pristroje, Czech Republic), Rheodyne sampling valve 7125 (Rheodyne,
U.S.A.), GM 1000 column (Labio, Czech Republic; exclusion limits 6 . 105 and 1 . 103) or PL 1000
column (Polymer Laboratories, United Kingdom), and UV detector HP1030B (Hewlett–Packard)
operating at 254 or 400 nm. As a mobile phase, N-methylpyrrolidone (NMP) (distilled in vacuo) was
used with Labio column (flow rate 1 ml/min) and tetrahydrofuran (THF) (distilled, dried over mole-
cular sieve) was applied for PL column with the same flow rate. (ii) TSP (Thermo Separation Pro-
ducts, Florida, U.S.A.) chromatograph, series of two PL column (Mixbed B and C), UV detector
operating at 254 nm and THF as a mobil phase (flow rate 0.7 ml/min). In all cases, the analyses were
performed at room temperature and molecular weights relative to polystyrene standards are reported.
RESULTS AND DISCUSSION
Polymerization of 2-, 3- and 4-Nitrophenyl Prop-2-yn-1-yl Ethers
The results of polymerization of 2-, 3- and 4-NPPE are given in Table I. PdCl2 poly-
merizes all three monomers providing brown methanol-insoluble polymers in good
yields. Analyses of supernatants collected after polymer isolation (IR, SEC) revealed
only unreacted monomers accompanied by a small amount (<10%) of low oligomers
TABLE I
Results of polymerization of 2-, 3- and 4-nitrophenyl prop-2-yn-1-yl ethers with PdCl2. Initial cata-
lyst concentration 0.5 mol/l, monomer : catalyst molar ratio 50, DMF, 85 °C
Polymer fraction, %a
No. Monomer
Reaction
time
Polymer
yield, %
MW
1 . 103–1 . 104 1 . 104–5 . 104
>5 . 104
1
2
3
4
5
6
7
8
2-NPPE
3-NPPE
4-NPPE
4-NPPE
4-NPPE
4-NPPE
4-NPPE
4-NPPEb
24 h
24 h
24 h
2 h
41
43
50
5
22
63
46
49
54
46
47
–
16
22
9
62
15
45
20
22
30
33
–
31
24
24
20
–
5 h
17
22
46
0
9 h
24 h
3 days
a SEC record area; b room temperature.
Collect. Czech. Chem. Commun. (Vol. 63) (1998)

Polymerization of Nitrophenyl
1807
(MW < 1 000) and proved that the polymers are strongly prevailing products in all
cases.
Contrary to the results obtained with MoCl5- or MoOCl4-based catalysts8, there are
only small differences in polymer yields in PdCl2 polymerizations of individual
monomers. For 3- and 4-NPPE, the yields achieved with PdCl2 are comparable with
those obtained with Mo-based catalysts; for 2-NPPE, however, the yield achieved with
PdCl2 is significantly higher than the best result obtained with Mo catalyst (24% for the
MoOCl4 + Me4Sn catalyst system8). PdCl2 catalyst does not seem so sensitive to the
steric effect of NO2 group in ortho position. However, PdCl2 requires different reaction
conditions than Mo catalysts, in particular higher temperatures and prolonged reaction
times (cf. 60 °C and 8 h for Mo catalysts8). It is seen from the time dependence experi-
ment (Nos 4–7, Table I), that even at 85 °C the reaction proceeds slowly and prolonged
time is necessary to obtain a good yield. The slight difference in polymer yield and
molecular weight distribution (vide infra) between experiments No. 3 and No. 7 in
Table I may be due to the different regime in the early stages of the reaction (see
Experimental). At room temperature (No. 8, Table I) no methanol-insoluble product
was obtained even after 3 days of reaction.
All poly(nitrophenyl prop-2-yn-1-yl ether)s prepared with PdCl2 catalyst are soluble
in DMF, DMSO and NMP. Their molecular-weight characterization was performed by
SEC in NMP and the results are given in Figs 1 and 2. In Fig. 1, the SEC chromato-
Y, a.u.
1
2
FIG. 1
SEC records (in NMP) of: 1 poly(2-NPPE)
3
(sample No. 1, Table I), 2 poly(3-NPPE)
(sample No. 2, Table I) and 3 poly(4-NPPE)
(sample No. 3, Table I). Y detector response, M
3.0
4.0
5.0
log M
6.0
molecular weight
Collect. Czech. Chem. Commun. (Vol. 63) (1998)

1808
Balcar, Holler, Sedlacek, Blechta:
grams of poly(2-NPPE), poly(3-NPPE) and poly(4-NPPE) (Nos 1, 2 and 3, respec-
tively, Table I) are given. These chromatograms show broad molecular-weight distribu-
tions with two distinct maxima: in the low (3 000–5 000) and high-molecular-weight
region (150 000–270 000). While for poly(2-NPPE) and poly(4-NPPE), the high-mole-
cular-weight maxima are well developed, for poly(3-NPPE) this maximum is only
weak. Time dependence experiments (polymerization of 4-NPPE, Nos 4–7, Table I)
showed an additional (weak) maximum in the central region of molecular weight (at
about 15 000) for the lower reaction times (Fig. 2). It is evident that individual peaks of
chromatograms in Figs 1 and 2 were not baseline-separated. In order to quantify the
individual polymer fractions, we divided the area of each SEC record into three parts
corresponding to low-, medium- and high-molecular-weight regions according to the
limits given in Table I. The percentages of thus obtained polymer fractions are listed in
Table I from which the following conclusions can be drawn: (i) the high-molecular-
weight fraction decreases in the following series: poly(2-NPPE) > poly(4-NPPE) >
poly(3-NPPE); (ii) in the time course of 4-NPPE polymerization, the percentage of
low-molecular-weight polymer fraction in the product remains approximately un-
changed, the medium-molecular-weight fraction decreases, but the high-molecular-
weight fraction continuously rises.
Time evolution of molecular-weight distribution (polymerization of 4-NPPE, Fig. 2)
suggests the presence of at least two different kinds of important catalytic centres in the
polymerization system, responsible for the formation of low- and high-molecular-
weight polymer fractions, respectively. The nature of catalytic species of both types is
not apparent. In olefin polymerizations induced by Pd(II) compounds, monomer inser-
tion in the Pd–C bond is assumed16. For polymerization of substituted acetylenes, the
same reaction mode is very probable. Catalytic centres resulting from the reaction of
PdCl2 with DMF and/or monomers may differ in both the Pd oxidation state and the
Y, a.u.
4
3
FIG. 2
2
SEC records (in NMP) obtained in the course of
polymerization of 4-NPPE. Polymerization
times: 1 2 h, 2 5 h, 3 9 h, 4 24 h (samples Nos
1
4–7, Table I). Y detector response, M molecular
3.0
4.0
5.0
6.0
weight
log M
Collect. Czech. Chem. Commun. (Vol. 63) (1998)

Polymerization of Nitrophenyl
1809
kind of ligands in the Pd coordination sphere. The differences in molecular-weight
distribution of poly(2-NPPE), poly(3-NPPE) and poly(4-NPPE) in Fig. 1 may probably
reflect differences in concentrations of distinct types of catalytic centres formed in the
presence of individual monomers.
Polymers prepared were characterized by IR, UV-VIS and NMR spectroscopy. IR
spectra of poly(2-NPPE), poly(3-NPPE) and poly(4-NPPE) prepared with PdCl2 were
practically identical with IR spectra of corresponding polymers prepared with Mo-
based catalysts, reported previously8. No significant differences were also revealed be-
tween individual poly(4-NPPE) listed in Table I. Always, the absence of bands
corresponding to ν(≡C–H) and ν(C≡C) vibrations (3 270–3 245 cm–1 and about 2 125 cm–1,
respectively) in polymers confirms the complete transformation of monomer triple
bond. On the other hand, the bands characteristic of the CH2 group (2 932, 2 982 cm–1),
NO2 group (1 540–1 522 and about 1 355 cm–1) and phenyl ring affected by NO2
substitution (3 120–3 030 cm–1, about 1 610, 1 585 and 1 490 cm–1 and between 875
and 700 cm–1) give evidence for the presence of nitrophenoxymethyl pendant groups in
polymers. UV-VIS spectra of poly(2-NPPE), poly(3-NPPE) and poly(4-NPPE)
(together with spectra of corresponding monomers) are shown in Fig. 3. Intensive
bands in the UV region take their origin mainly from transitions in substituted phenyl
rings of the pendant groups. The VIS part of spectra must be ascribed to π–π* transition
in polyacetylenic main chain with a broad distribution of effective conjugation length.
1H and 13C NMR spectra of poly(2-NPPE), poly(3-NPPE) and poly(4-NPPE) are
given in Fig. 4. In 1H NMR spectra (Fig. 4a), broad peaks in the region 3.5–5.5 ppm are
ascribed to OCH2 group and broad bands between 6.0 and 8.5 ppm to aromatic protons.
1.5
a
b
c
A
1.0
0.5
0.0
2
2
2
1
1
1
400
600
800 400
600
800 400
600
800
λ, nm
λ, nm
λ, nm
FIG. 3
UV-VIS spectra of: 1 2-NPPE and 2 poly(2-NPPE) (a); 1 3-NPPE and 2 poly(3-NPPE) (b); 1 4-NPPE
and 2 poly(4-NPPE) (sample No. 3, Table I) (c). DMSO, c = 0.3 mg/ml, l = 0.1 cm
Collect. Czech. Chem. Commun. (Vol. 63) (1998)

1810
Balcar, Holler, Sedlacek, Blechta:
Olefinic protons of the main chain are supposed to be very broad and to lie in the last
region overlapped by signals of aromatic protons. The line broadening in these spectra
indicates a high irregularity of all polymers measured (irregularity with respect to head-
to-tail and head-to-head monomer linkages and/or cis/trans configuration of the main-
chain double bonds). 13C NMR spectra (Fig. 4b) consist of OCH2 broad and
low-intensity peaks in the range 63–75 ppm (probably doublets) and peaks of aromatic
carbons assigned according to the corresponding monomers (for numbering the peaks
in Fig. 4b, see the numbering in Scheme 1). The main-chain carbon-atom signals are
less intensive and manifest themselves by base line elevation in the region 130–150 ppm.
1
The splitting of bands corresponding to OCH2 groups is visible in H NMR spectra of
all poly(nitrophenyl prop-2-yn-1-yl ether)s in Fig. 4a and has been also reported for
other poly(phenyl prop-2-yn-1-yl ether)s17. A similar splitting seems to be present also
in 13C NMR spectra. It may be considered as a result of hindered rotation of bulky
phenoxymethyl groups in polymer molecules. However, neither IR nor NMR spectra
allow to draw any reliable detailed information about the conformation of the main
chain giving no data sufficient for construction of any conformation models.
Polymerization and Copolymerization of 3-Diethylaminophenyl Prop-2-yn-1-yl
Ether
Table II shows the results of polymerization experiments with 3-DEAPPE. Its homo-
polymerization provides a very good yield of a black polymer soluble in CHCl3, NMP
3
3
2
2
4
1
1
1
2
3
5
3
4
2
6
3
1
2
3
5
4
2
1
6
2 4, 6
5
2 4 6
3
5
1
4
4
5
5
9
8
7
6
5
4
3
2
ppm
1
160 140 120 100
80
60
40
20
ppm
FIG. 4
1H NMR spectra (a) and 13C NMR spectra (b) of poly(NPPE)s in DMSO-d6, and poly(3-DEAPPE)
and copolymer of 3-DEAPPE with 4-NPPE in CDCl3. 1 Poly(4-NPPE) (sample No. 3 Table I), 2
poly(3-NPPE), 3 poly(2-NPPE), 4 poly(3-DEAPPE), 5 copolymer (sample No. 2, Table II). Solvent
1
and impurities lines (ppm) in: H NMR 2.5; 3.4 (H2O); 7.25; 2.89 and 2.73 (DMF) and 13C NMR 40; 77
Collect. Czech. Chem. Commun. (Vol. 63) (1998)

Polymerization of Nitrophenyl
1811
and in THF. Although insoluble in methanol, this polymer could not be isolated from
the reaction mixture via precipitation into methanol; instead, water had to be used.
According to SEC in NMP, poly(3-diethylaminophenyl prop-2-yn-1-yl ether), [poly(3-
DEAPPE)] (Table II, No. 1) has a bimodal molecular-weight distribution in which the
low-molecular-weight fraction (Mn = 4 200, Mw = 5 400) strongly prevails. High-mole-
cular-weight fraction (MW > 100 000) makes only about 10 wt.% of the polymer.
Poly(3-DEAPPE) spectra (IR (Fig. 5), UV-VIS (Fig. 6) and NMR (Fig. 4)) are consist-
ent with the polymer structure given in Scheme 1. Complete disappearance of IR bands
and NMR signals at 3 270 and 2 110 cm–1, at 2.48 ppm (1H) at 78.96 ppm and at 75.06 ppm
(13C) as a result of polymerization proves the polymerization to proceed by transforma-
tion of the monomer C≡C bond. Enhanced absorbances of polymer at λ > 325 nm due
TABLE II
Results of polymerization and copolymerization of 3-diethylaminophenyl prop-2-yn-1-yl ether with
PdCl2. Initial catalyst concentration 10 mmol/l, DMF, 85 °C (F initial molar fraction of 4-nitrophenyl
prop-2-yn-1-yl ether in the comonomer feed, f molar fraction of 4-nitrophenyl prop-2-yn-1-yl ether
units in copolymer)
Polymer
d
d
No.
Monomer
3-DEAPPEb
3-DEAPPE, 4-NPPEb
3-DEAPPE, 4-NPPEc
F
f
Mn
Mw
yield, %a
1
2
3
0
0
76
40
52
4 200e
3 500f
3 000f
5 400e
9 200f
7 900f
0.5
0.3
0.5
0.75
a
c
b
Relative to the total initial mass of comonomers; initial 3-DEAPPE concentration 0.5 mol/l;
d
initial 3-DEAPPE concentration 0.25 mol/l; without high-molecular-weight (minor) fraction if
any; e in NMP; f in THF.
3
2
A, a.u.
1
FIG. 5
IR spectra: 1 Poly(4-NPPE) (sample
No. 3 Table I), 2 poly(3-DEAPPE),
3 copolymer of 4-NPPE with
3-DEAPPE (sample No. 2, Table II)
3 700 3 200
2 700
2 100 1 600
1 100
λ, cm
600
–1
Collect. Czech. Chem. Commun. (Vol. 63) (1998)

1812
Balcar, Holler, Sedlacek, Blechta:
to the double-bond-conjugated main chain are clear in comparison with UV-VIS spec-
trum of the monomer. The bands characteristic of diethylaminophenoxy groups are evident
in the IR spectrum of polymer (mainly bands of ethyl groups in the 2 800 to 3 000 cm–1
region, aromatic ring vibration at 1 607 and 1 500 cm–1, C–O and C–N vibrations at 1 266
1
and 1 200 cm–1). The signals in H NMR spectra were assigned to the polymer as
follows: signal at 1.14 ppm to CH3, at 3.30 ppm to N–CH2, broad signal at 3.6–5.2 ppm
to O–CH2, and signal at 5.8–7.2 ppm to aromatic protons as indicated by numbers in
the spectrum (Fig. 4a). The olefinic proton signal must be also present in this last
region but, like in the previous cases, it is supposed to be broad and overlapped by the
signals of aromatic protons. In 13C NMR spectrum, CH3 signal is located at 12.6 ppm,
N–CH2 signal at 44.3 ppm, O–CH2 signal at 60–75 ppm, and the positions of signals of
aromatic carbons are indicated by numbers (Fig. 4b). Tertiary and quaternary carbons
of the polymer main chain are expected at about 125 ppm and 135 ppm, respectively,
but they are probably very broad and hardly visible. In 1H NMR as well as in 13C NMR,
the sharp lines and slightly elevated base line in the aliphatic region indicate the
presence of some impurities (probably low oligomers and/or side products of initiation
reactions).
Using mixtures of 3-DEAPPE and 4-NPPE as a comonomer feed (experiment No. 2
and No. 3, Table II) brown copolymers precipitated from methanol after termination
which were completely soluble in NMP and CHCl3. Copolymer from experiment No. 2
is completely soluble in THF, copolymer from No. 3 contains a small amount of THF-
insoluble fraction. Their IR and NMR spectra (Figs 5 and 4) exhibit all bands charac-
teristic of pendant groups of both monomeric units. The spectra together with the
differences in solubility of copolymers and corresponding homopolymers give evidence
that copolymers were really formed in copolymerization experiments. The SEC records
in NMP and THF show bimodal molecular-weight distribution for both copolymers.
The minor, high-molecular-weight fraction has molecular weight about 1 . 106 for both
2.0
A
1.5
4
3
2
1.0
0.5
FIG. 6
1
1 UV-VIS spectra of 3-DEAPPE, 2 poly(3-
DEAPPE), and copolymers of 4-NPPE with 3-
DEAPPE 3 (sample No. 2, Table II), 4 (sample
No. 3, Table II). THF, c = 0.3 mg/ml, l = 0.1 cm
300
400
500
λ, nm
Collect. Czech. Chem. Commun. (Vol. 63) (1998)

Polymerization of Nitrophenyl
1813
samples (SEC in THF). For sample No. 3, this fraction makes about 20% of the whole
SEC record area, while for sample No. 2, its amount is negligible (~2%). Molecular-
weight characteristics of the major, low-molecular-weight fractions (determined in THF
using PL 1000 column) are given in Table II. Composition of copolymers was deter-
mined from 1H NMR spectra (using CH3 bands) and the results are presented in Table II. It
can be seen that both copolymers are enriched in 3-DEAPPE monomeric units compared
with the compositions of comonomer feeds used for copolymerizations, i.e. 3-DEAPPE
is more readily incorporated into copolymer chains. Increasing 4-NPPE fraction in the
comonomer feed from 0.5 to 0.75 leads to an enhanced amount of the high-molecular-
weight copolymer fraction. Therefore, the composition of low- and high-molecular-
weight fractions may differ: the high-molecular-weight fraction may be enriched by
4-NPPE units. UV-VIS spectra of 3-DEAPPE, poly(3-DEAPPE) and both copolymers
are shown in Fig. 6. The long-wavelength tails of UV-VIS spectra of the copolymers
(Fig. 6) do not differ significantly suggesting the approximately same distribution of
effective conjugation length in both copolymers, probably very similar to that of
poly(3-DEAPPE).
In the supernatants, after poly(3-DEAPPE) and copolymers isolation, a mixture of
low-molecular-weight products (MW < 1 000) was revealed by SEC in THF. However,
no monomer(s) were found (IR, GC), contrary to the experiments in which NPPEs were
homopolymerized. This indicates that oligomerization and/or other monomer transfor-
mation reactions take place in considerable extent in the reaction systems containing
3-DEAPPE.
It may be noted that Mo-based catalyst, which showed high activity in 4-NPPE ho-
mopolymerizations8, failed in copolymerization of 4-NPPE with 3-DEAPPE. Using the
MoOCl4/3 Me4Sn catalyst system in benzene (60 °C, 6 h, initial MoOCl4 concentration
3 mmol/l, initial 4-NPPE concentration equal to initial 3-DEAPPE concentration, 80 mmol/l),
only homopolymer of 4-NPPE was obtained in the yield of 5%. Evidently, the used
Mo-based catalyst does not tolerate amino group in 3-DEAPPE.
CONCLUSIONS
PdCl2 in DMF is an active catalyst for homopolymerization of 2-, 3- and 4-NPPEs as
well as 3-DEAPPE. It provides soluble polymers of the polyacetylene type having phe-
noxymethyl pendants groups with nitro or diethylamino substituents. Molecular-weight
distribution is bimodal having the first maximum in the low-molecular-weight region
(3 000–5 000) and the second maximum in the high-molecular-weight region (above
100 000). The ratio of these fractions depends strongly on the starting monomer. Al-
though bimodal molecular-weight distributions of products have already been reported
for olefin polymerizations with alkylpalladium complexes16, to our knowledge, they
have not been observed in acetylene polymerizations.
Collect. Czech. Chem. Commun. (Vol. 63) (1998)

1814
Balcar, Holler, Sedlacek, Blechta:
Copolymers of 3-DEAPPE with 4-NPPE soluble in common solvents such as CHCl3
and THF were prepared with PdCl2 in DMF. The copolymer containing 50% of 4-NPPE
monomeric units has bimodal molecular-weight distribution with major fraction of Mn =
3 000 and minor fraction of molecular weight about 1 . 106; the copolymer containing
30% of 4-NPPE monomeric units has Mn of 3 500. To our knowledge, they are the first
examples of soluble acetylene-type copolymers bearing both nitro and dialkylamino
substituents on pendant groups (the copolymer of 4-nitrophenylacetylene with 4-di-
methylaminophenylacetylene was only partly soluble7). The good solubility of the co-
polymers prepared makes possible a subsequent study of their physical properties (e.g.,
in thin layers).
The authors are indebted to Dr L. Petrusova (J. Heyrovsky Institute of Physical Chemistry, Academy
of Sciences of the Czech Republic, Prague) for IR spectra measurements. Financial support from the
Grant Agency of the Czech Republic (grant No. 203/98/1165) and from the Ministry of Education, Youth
and Physical Training of the Czech Republic (grant No. VS 97103) is gratefully acknowledged.
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