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Polymerization of methyl methacrylate by copper-chelate of polyacrylic hydrazide.

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Die Angewandte Makromolekulare Clzemie 35 ( 1 9 7 4 ) 85-99 ( N r . 492)
From the Chemical Laboratory of Textile Fibres, Kyoto University of Industrial
Arts and Textile Fibres, Matsugasaki, Sakyo-ku, Kyoto, Japan
Polymerization of Methyl Methacrylate by
Copper-chelate of Polyacrylic Hydrazide *
By SEISHIMACHIDA,
MIKIO ARAKI,HIROSHINARITA,and YOSHIAKI
TAKENAKA
(Received 22 May 1973)
SUMMARY:
Copper-chelate of polyacrylic hydrazide was prepared, and its structure and properties were investigated. It was found that the chelate-polymer initiates radical
polymerization of methyl methacrylate in aqueous dioxane a t room temperature.
The rate of polymerization initiated by the chelate-polymer was much higher
than that by monomeric model-chelate of such as acethydrazide. The catalytic
activity found in the copper-chelate of polyacrylic hydrazide is perhaps caused by
the polyelectrolyte-behaviour of the polymer. The influences of the concentration
of copper ion, molecular weight of polymer-ligand, ionic strength, hydrogen ion
concentration and composition of solvent on the polymerization were investigated.
It was considered that the polymerization is affected not only by stability but also
by conformation of the chelate-polymer. The tacticity of the polymethyl methacrylate obtained is also discussed.
ZUSAMMENFASSUNG :
Das Kupfer-Chelat aus Polyacrylhydrazid wurde hergestellt, und seine Struktur
und Eigenschaften wurden untersucht . Es wurde gefunden, dalj das Chelat-Polymere bei Raumtemperatur in waariger Dioxanlosung die radikalische Polymerisation von Methylmethacrylat initiiert. Die Geschwindigkeit der durch das polymere
Chelat initiierten Polymerisation ist vielgroljerals die durchmonomere Modell-Chelate
wie z. B. Essigsaiirehydrazidausgelosten. Die katalytische Aktivitiit des Chelates aus
Polyacrylhydrazid beruht wahrscheinlich auf dessen Polyelektrolyt-Charakter.Die
Einflusse der Konzentration an Kupfer-Ionen, des Molekulargewichts des Polymerliganden, der Ionenstarke, der Konzentration an Wasserstoff-Ionen und der Zusammensetzung des Losungsrnittels auf die Polymerisation wurden untersucht. Es
wurde geschlossen,daB die Polymerisation nicht nur von der Stabilitiit des polymeren
Chelats sondern auch von seiner Konformation beeinfluat wird. Die Taktizitat des
erhaltenen Polymethylmethacrylates wurde untersucht.
Introduction
Recently there has been interest in the catalytic action of chelate-polymersin
connection with chemical reactions in biological materialsl. As part of the
* Studies of water-soluble polymers, part
27.
85
S. MACHIDA,M. ARAKI,H. NARITA,and Y . TAKENAKA
studies of water-soluble polymers, our attention was called t o the precipitation
produced by reaction of polyacrylic hydrazidez with metallic salt. Since the
precipitation was found to be a chelate-polymer, structure and properties of
the chelate-polymer were investigated. It was found t h a t the copper-chelate
of polyacrylic hydrazide has the ability of a n initiator for radical polymerization of vinyl monomers a t ordinary temperature. The present paper deals with
the polymerization of methyl methacrylate by the chelate-polymer. As the
corresponding monomeric model, copper-chelates of acethydazide, propiohydrazide and benzhydrazide were also investigated for comparison.
Experimental
Preparation of hydrazides
Polyacrylic hydrazide was prepared by the reaction of polyacrylamide with
hydrazine hydrate in aqueous solution. The procedure followed that reported
earlierz. The polyacrylic hydrazide was reprecipiteted with methanol and freezedried. The degree of conversion to hydrazide was determined by the modified iodometric method reported previouslyz.
Acethydazide, propiohydrazide and benzhydrazide were prepared by the usual
methods3.
Preparation of copper-chelates
The chelate-polymer was prepared by adding 1% solution of cupric chloride
into lo/o aqueous solution of polyacrylic hydrazide a t room temperature. The precipitation was filtered after a day, washed with water and dried a t room temperature under reduced pressure. The copper-chelate was used without isolation
when it was used as an initiator of polymerization.
The copper-chelates of acethydrazide, propiohydrazide and benzhydrazide were
prepared respectively by adding 1% solution of cupric chloride into 5% solutions
of the ligands.
Polymerization of methyl methacrylate by chelate compound
Polymerizations were carried out in the reaction vessel reported in the previous
papers4. Solution of monomer and cupric chloride was placed in one side, and s o h tion of hydrazide-ligand was placed in another. Ths vessel was sealed under nitrogen after being frozen in freezing mixture and degassed. After the vessel was
thermostated a t a desired temperature, the two solutions were mixed to polymerize. The mixed solvent of water and dioxane (2: 1 ) was used for the sake of homogeneous reaction. The polymer was separated by pouring the reaction mixture
into methanol, and purified by extraction with organic solvent. The conversion
was determined by weighing the polymer. Fearing that the graft copolymerization
of the monomer onto the polyacrylic hydrazide might occur as a side-reaction, the
extraction was carried out by use of a SOXHLET
extractor, if necessary.
Measurements of absorption spectra
Visible spectrum was taken with a Hitachi 124 type double beam spectrophotometer.
86
Polymerization of Methyl Methacrylate
I R spectrum was taken with a Nihon Bunko D S - 4 0 3 G type recording infrared
spectrophotometer, using the KBr disk method.
NMR spectrum was recorded at 100 MHz in DzO or CDC13 solution by means
of a Nihon Denshi JNM-4H-100 type photometer. The chemical shifts were quoted
as values relative to tetramethylsilan.
Results and Discussion
Preparation of polyacrylic hydrazide
The experimental results are summarized in Table 1
Table
Preparation of polyacrylic hydrazide.
1.
I
Exp.
Polyacryl-
No.
amide
1
2
3
4
5
6
7
8
a
b
Reaction conditions
Hydrazine
hydrateb
Water
(R)
[rll"
(mu
(ml)
0.5
1.0
0.5
1.0
0.5
0.5
0.5
1.5
0.4
0.4
0.4
0.4
0.4
0.4
0.67
0.07
10
20
20
10
10
20
10
20
10
20
10
10
20
10
so
so
Degree of
Reaction Reaction
conversion to
tempera- time
hydrazide (%)
t u r e ("C)
(h)
60
60
60
60
70
80
60
60
1.o
2.5
4.0
6.0
6.0
5.0
5.0
6.0
11.7
30.1
37.3
50.4
67.5
72.7
42.2
42.7
In aqueous solution at 30°C.
80% aqueous solution.
Formation of copper-chelates
The copper-chelate of polyacrylic hydrazide is insoluble in water and organic
solvents, except when the concentration of the polymer-ligand is less than
about 10-2 mole/l. The copper-chelates of acethydrazide, propiohydrazide and
benzhydrazide are, on the contrary, soluble in water.
I n the region of visible light, a single absorption band was observed in the
a t the wavelength of
monomeric copper-chelate. As shown in Fig. 1 the,,A
the absorption spectrum of the chelate is shifted from t h a t of cupric ion by
the interaction between ligand and cupric ion.
The NMR spectra of acethydrazide and its copper-chelate are compared i n
Fig. 2. It is shown in Fig. 2 t h a t the absorption of methyl proton a t 7.7 t is
spread t o 7.6 t and the absorption at 4.78 t vanishes on addition of copper ion
to the ligand.
87
S. MACHIDA,M. ARAKI,H. NARITA,
and Y. TAKENAKA
700
780
740
Wave length
~ J J ]
Fig. 1. Visible spectra of cupric chloride ( I ) , its chelates of benzhydrazide (11),
and acethydrazide (111).
I : i l m a x = 7 7 0 m p ; II:ilm,x=760 m p ; 11I:ilmax
=730 m p .
A
Fig. 2.
88
11
NMR spectra of acethydrazide ( I ) and its copper-chelate (11) in DzO at
20°C (100 Mc).
Polymerization of Methyl Methacrylate
I
1
It
Q)
0
E
0
c
c
.-
E
c
v)
J
2
t-
I700
1600
1500
1200 1100 1000 900
number
Wave
[cm-I]
Fig. 3. IR spectra of polyacrylic hydrazide (I)and its copper-chelate (11) in KBr
disk.
The IR absorption spectra of polyacrylic hydrazide and its copper-chelate are
shown in Fig. 3. As shown, the absorption a t 1000 em-1 assigned to the hydrazide group is extinguished by the chelation, the absorption is produced a t
1100
1200 em-1, and the absorption a t 1540 cm-1 assigned to N-H deformation vibration of hydrazide group is weakened. On the basis of these data,
one might propose for the copper-chelate of polyacrylic hydrazide the following structura :
-
-CH-CHz-
I
-CHs-CH-
I
89
S. MACHIDA,M. ARAKI,H. NARITA,
and Y . TAKENAKA
Polymerization of methyl methacrylate by copper-chelate
Polymerization of methyl methacrylate was initiated by the copper-chelate
of polyacrylic hydrazide, acethydrazide or propiohydrazide a t room temperature. The polyacrylic hydrazide of sample No. 4 in Table 1 was used in the
experiments.
-
o\"
U
20
15
c
.-0
Q)
>
lo
c
G 5
0
Fig. 4.
Polymerizations of methyl methacrylate by copper-chelates of polyacrylic hydrazide (I)and propiohydrazide (11)at 20°C. Ligand: 2.5 * 10-3
mole/l, copper ion: 1 . 10-4 mole/l, monomer 0.27 mole/l.
The plot of conversion against reaction time in the polymerization is shown in
Fig. 4.As shown in Fig. 4 the polymerizations proceed linearly with the reac-
Concentration of cupric c h l o r i d e
Fig. 5 .
[
mole / I ]
Effect of concentration of copper ion on polymerization of methyl methacrylate by copper-chelate of polyacrylic hydrazide at 20 "C. Ligand:
2.5
90
. 10-3
mole/l, monomer 0.27 mole/l.
Polymerization of Methyl Methacrylate
tion time, and the rate of polymerization by the polymeric chelate is about
three times t h a t by the monomeric chelate. The polymerization was found t o
proceed by radical mechanism, because it was inhibited by hydroqninone.
The polymerization rate is affected by the concentration of cupric ion, as shown
in Fig. 5. The decrease in the polymerization rate in high concentra.tion range
of cupric ion is probably due t o termination reaction by the cuprin ions.
Concentration of ligand
[ 1 0 - ~ r n o l e /11
Effect of concentration of ligand on polymerization of methyl methacrylate by copper-chelate of polyacrylic hydrazide in 1.66 .
(I) and
5.5 . 10-4 mole/l (11)of cupric ion concentrations at 20°C; monomer:
0.27 mole/l.
The relations between the polymerization rate and the concentration of the
polymer-ligand in t,he high and low concentration ranges of cupric ion are
shown in Fig. 6.
Fig. 6.
5
I
I
I
10
15
20
25
Molar r a t i o of ligand t o cupric ion
Fig. 7.
Effect of ratio of ligand to cupric ion on polymerization of methyl methacrylate by copper-chelate of polyacrylic hydrazide at 20 "C.
Cupric ion: 1.66 . 10-4 mole/l (I), 5.5 .
mole/l (11).
91
S. MACHIDA,M. ARAKI,H. NARITA,and Y . TAKENAKA
The plot ofthe polymerization rate against the ratio of molar concentration of
polymer-ligand to that of cupric ion is shown in Fig. 7. These results show
that the polymerization rate is maximum when the molar concentration of
polyacrylic hydrazide is about ten times that of cupric ion. Number of ligands
coordinated with a copper atom in polymer-complex is generally smaller than
that in monomeric model-complex under the same condition6. As the methyl
methacrylate is coordinated to the vacant seat of coordination in the complex
to polymerize, the polymerization occurs more readily by the polymer-chelate
than the model-chelate. When the molar concentration of polyacrylic hydrazide
goes up to over about ten times that of cupric ion under the present condition,
however, an excess of the polymer-ligands is coordinated a t the cupric ion to
reduce the vacancies of coordination and the polymerization rate decreases.
30 -
._
c
E
.
-
20-
a,
0
E
?
9
en
10 -
[ M I [mo1e/11
Fig. 8. Effect of monomer concentration on polymerization of methyl methacrylate by copper-chelate of polyacrylic hydrazide at 20°C in 1.66 . 10-4
(I)and 5.5 . 10-4 mole/l (11)of cupric ion concentrations at 20°C; ligand:
2.5 . 10-3 mole/l.
The influence of the concentration of methyl methacrylate on the rate of polymerization by the polymeric chelate is shown in Fig. 8. From the data shown
it is found that the polymerization rates are proportional to 1.7 and 2.5
powers of the monomer concentration in cupric chloride concentrations of
5.5 10-4 and 1.66 . 10-4 mole/l respectively. Such a high rate is probably due
to the initiation of polymerization of methyl methacrylate adsorbed a t the
polymeric catalyst.
92
Polymerization of Methyl Methacrylate
3'5/----------------
I/T
1.
.8
lo3]
plots on polymerization of methyl methacrylate by copperFig. 9. ARRHENIUS
chelates of polyacrylic hydrazide (I)and propiohydrazide (11).
Apparent activation energy calculated from the ARRHENIUS
plots for the
polymerization initiated by the polymeric chelate was 8.75 kcal/mole (Fig. 9).
The value is lower than that of peroxide-initiated polymerization, and it is
close to 8.90 kcal/mole, that is the value for the polymerization by the monomeric chelate. Accordingly the difference in the catalytic activity between
polymeric and monomeric chelates is attributed t o frequency factor rather
than activation energy.
It is considered that the concentration of methyl methacrylate increases
locally in the neighbourhood of the polymeric chelate during the polymerization.
Table 2. Conversion of polymerization of methyl methacrylate by copper-chelate
of polyacrylic hydrazide of various molecular weights. Ligand: 2.5 .
mole/l, cupric ion: 5.0 .
mole/l, monomer: 0.27 mole/l, temperature:
20°C.
Ligand
Polyacrylic hydrazide
I
[q]"
(dl/g)
a
Reaction time
(min)
0.07
0.07
0.40
20
25
20
0.40
25
25
39
0.67
0.67
Propiohydrazide
I
6.7
9.7
15.2
23.0
19.0
30
29.0
2.3
60
4.9
In 0.01 N KC1 solution at 30°C.
93
S. MACHIDA,
M. ARAKI,H. NARITA,
and Y. TAKENAKA
Raising the molecular weight of the ligand-polymer therefore increases the
polymerization rat'e of methyl methacrylate as shown in Table 2.
A certain electrostatic or a special polyfunctional effect may be also considered.
Influence of neutral salt on the polymerizations of methyl methacrylate by
monomeric and polymeric chelates are shown in Tables 3 and 4.
1 . 10-2
11.2
KCl (mole/l)
Conversion ( 9 6 )
Table
4.
I . 10-4
8.3
1 . 10-5
8.8
Polymerization of methyl methacrylate by copper-chelateof polyacrylic
hydrazide in the presence of neutral salt. LigandE: 2.5 . 10-3 mole/l,
cupric ion: 4.0 . 10-4 mole/l, monomer: 0.27 mole/l, temperature: 20°C,
reaction time : 25 min.
KCI (mole/l)
1
1
8
6
4
2
1
i
a
.
1 10-3
9.4
. 10-2
. 10-3
. 10-4
. 10-4
. 10-4
. 10-4
. 10-4
. 10-5
Conversion (yo)
5.35
9.70
7.30
12.7
15.4
28.0
39.0
40.0
Sample No. 4 in Table 1.
It was found that the polymerization by monomeric chelate is not affected by
the ionic strength in the solution but the polymerization by polymeric chelate
is influenced by it. The ionic strength presumably has influence on both conformation and stability of the chelate-polymer. Increase in the ionic strength
would lead to a certain contraction of the polymer shape in the solution and
the active species for the initiation of polymerization is made difficult to be
generated in the chelate-polymer chain.
Hydrogen ion concentration of the solution, however, affects the polymerizations initiated with both monomeric and polymeric chelates, as shown in Fig. 10.
Although the polymerizations are, on the whole, decreased by such high ionic
strength of the system as 0.01 mole/l under the present condition, the conversion reaches a maximum a t pH 5 and 6 in the polymerizations by polymeric and
monomeric chelates respectively. The polymerization is perhaps hindered in
94
Polymerization of Methyl Methacrylate
I
2
0
Fig. 10.
4
8
6
10
Effect of hydrogen ion concentration on polymerization of methyl methacrylate by copper-chelates of polyacrylic hydrazide (I) and propiomole/l, cupric ion: 4 . 10-4 mole/l,
hydrazide (11).Ligand: 2.5 .
monomer: 0.27 mole/l, temperature: 20°C, reaction time: 30 min.
alkaline solution by copper hydroxide produced, whereas it is also hindered a t
the acidic solution by decreasing in chelate-formation because of the protonized hydrazide groups.
n
8
U
20
.-E
c
0
Q
>
c
10
0
0
0
30 4 0 50
Content of dioxane
Fig. 11.
60 70
[%]
Effect of composition of solvent on polymerization of methyl methacrylate by copper-chelate of polyacrylic hydrazide. Ligand: 2.5 . 10-3
mole/l, cupric ion : 5 . 10-4 mole/l, temperature : 20 "C, time : 45 min.
95
S. MACHIDA,
M. ARAKI,H. NARITA,
and Y. TAKENAKA
I n the present polymerizations the mixed solvent of water and dioxane (2 : 1)
was used. The relation between the conversion and the composition of solvent
is shown in Fig. 11 which shows that about 40% aqueous solution of dioxane is
suited for the polymerization. These data would also support the consideration
that the initiation of polymerization is affected by the conformation of the
polymeric chelate in the solution.
Polymethyl methucrybte prepared by copper-chebte
Some experimental data on the polymerization of methyl methacrylate by
the copper-chelate of polyacrylic hydrazide are summarized in Table 5. Graft
copolymerization onto the chelate-polymer as a side reaction is found t o occur
t o some extent. However, it was confirmed by elementary analysis that the
polymethyl methacrylate purified by extraction does not contain nitrogen
atoms.
Table 5. Fractionation of polymethyl methacrylate prepared by copper-chelate
of polyacrylic hydrazide. Polymer ligand (sample No. 4 in Table 1):
2.5 . 10-3 mole/l, temperature: 2 0 ° C , reaction time: 60 min.
Ligandpolymer
(mg)
Cupric
chloride
(10-4 mole/l)
Total
polymer
Extracted
polymer
Grafting
efficiency
(mg)
(mg)
(YO)
Chelate- initiator
Ligand
96
Polymer
CllPric ion
(10-4 mole/l)
Average degree
(dl/g) of polymerization
[q]b
Polymerization of Methyl Methacrylate
The NMR spectra of the polymethyl methacrylate prepared by polymeric
and monomeric chelates are shown in Fig. 12. In the a-methyl region there are
8
10
9
7
Fig. 12. NMR spectra of polymethyl methacrylates prepared by copper-chelates
of propiohydrazide (I)and polyacrylic hydrazide (11) in CDCl3 at 5OoC
(100 Me).
three peaks at 8.78, 8.95 and 9.09 t corresponding t o isotactic, heterotactic and
syndiotactic triads. The fractions of tactic triads and diads were calculated
from the relative area of the charts, and the results are summarized inTable 7.
Table 7.
Tacticity of polymethyl methacrylate prepared by copper-chelate.
Ligand: 2.5 * 10-3 mole/l, cupric ion: 1.5 . 10-4 mole/l, monomer: 0.27
mole/l, temperature: 20°C, time: 60 min.
Tacticity
1
Propiohydrazide
Polyacry lie
hydrazidea
a
diad (oh)
1
triad (o/)
H
S
4
36
5
40
Ligand
l
i
S
60
22
78
55
25
75
Sample No. 4 in Table 1.
97
S. MACHIDA,
M. ARAKI,H. NARITA,
and Y . TAKENAKA
1
4000
3200
2400
1700
1500
Wave number
1300
1100
900
[cm-11
Fig. 13. IR spectrum of polymethyl methacrylate prepared by copper-chelate
of polyacrylic hydrazide in KBr disk.
The I R spectra of the same samples show absorptions a t 1481,1266,1237,
1058 and 909 cm-1, as shown in Fig. 13. These results show that the polymer
prepared has a predominantly syndiotactic structure7. Isotacticity of the polymer obtained by the polymeric chelate is a little higher than that of the polymer obtained by the monomeric chelate.
Conclusion
Copper-chelate of polyacrylic hydrazide initiates radical polymerization of
methyl methacrylate a t room temperature. The catalytic activity of the copper-chelate is perhaps caused by the polyelectrolyte-behaviourof the polymer.
The concentration of copper ion, molecular weight of polymer ligand, ionic
strength, hydrogen ion concentration and composition of solvent affect the
polymerization. It was considered that the polymerization is influenced by
stability and conformation of the chelate-polymer. It would be interesting to
investigate the polymerizations of other vinyl monomers initiated by the
chelate-polymer a t room temperature.
1
2
3
4
T. C. BRUICEand R. M. TOPPING,
J . Amer. Chem. Soc. 84 (1962) 2448; H. SIEGEL
and D. B. Mc CORMICK,
Accounts. Chem. Res. 3 (1970) 201; D. D. ULMER
and
B. L. VALLEE,
Advan. Chem. Ser. 1971, 187
S. MACHIDA,
Tappi 52 (1969) 1734
P. FALCIOLA,
Gazz. Chim. Ital. [l] 50 (1920) 162; L. GATTERMANN,
Die Praxis des
Organischen Chemikers, 26. Aufl., Walter De Gruyter u. Co, Berlin 1939, S. 158
H. NARITA,S. OKAMOTO,
and S. MACHIDA,
Makromol. Chem. 126 (1969) 15;
H. NARITA,
T. OKIMOTO,
and S. MACHIDA,
J. Polym. Sci. A-1 8 (1970) 2725
98
Polymerization of Methyl Methacrylate
5
6
7
8
W. I. BENGOUGH
and W. H. FAIRSERVICE,
Trans. Faraday SOC.61 (1965) 1206
R. YAMAMOTO,
T. NOZAWA,
M. HATANO,
and S. KAMBARA,
J. Chem. SOC.Jap.,
Ind. Chem. See. (Kogyo Kagaku Zasshi) 70 (1967) 760
J. H. BAXENDALE,
S. BYWATER,
and M. G. EVANS,J. Polym. Sci. 1 (1946) 237;
F. J. WELCH,
J. Polym. Sci. 61 (1962) 243
F. A. BOVEYand G. V. D. TIERS,J. Polym. Sci. 44 (1960) 173; S. MURAHASHI,
S. NOZAKURA,
M. SUMI,H. YUKI,and K. HARADA,
J. Polym. Sci. B 4 (1966) 65;
K. HARADA,
Y. TERAWAKI,
H. OKUDA, T. NIINOMI,
and H. YUKI,Chem. High
Polym. [Tokyo] (Kobunshi Kagaku) 28 (1971) 293
U. BAUMANN,
H. SCHREIBER,
and K. TESSMAR,
Makromol. Chem. 36 (1959) 81
99
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