Comparison between the electric conductivity of polyhydroxamic acids of different origin

Article abstract of DOI:10.1007/PL00000084

Polyhydroxamic acid (PHA) was prepared from polyacrylamide (PAA) and from polymethacrylamide (PMAA). It was found that PHA from PAA has the properties of a semiconductor when it reacts with some metals. PHA from PMAA has typical semiconducting properties when reacting with 1 mmol of ferric chloride, whereas its electric conductivity is somewhat lower when it contains 0.5 mmol of ferric chloride.

Full text of DOI:10.1007/PL00000084

Monatshefte fuÈr Chemie 129, 245±252 (1998)
Comparison Between the Electric Conductivity
of Polyhydroxamic Acids of Different Origin
Wafaa M. Sayed1;Ã, Yahia M. Abed1, El-Sha®e A. M. Gad1,
and Tousson A. Salem2
1
Petroleum Research Institute, Nasr City, Cairo
2
National Research Center*, El-Dokki, Cairo
Summary. Polyhydroxamic acid (PHA) was prepared from polyacrylamide (PAA) and from
polymethacrylamide (PMAA). It was found that PHA from PAA has the properties of a
semiconductor when it reacts with some metals. PHA from PMAA has typical semiconducting
properties when reacting with 1 mmol of ferric chloride, whereas its electric conductivity is
somewhat lower when it contains 0.5 mmol of ferric chloride.
Keywords. Polyhydroxamic acid; Polyacrylamide; Polymethacrylamide; Electrical properties;
Semiconductors.
È È
Vergleich der elektrischen Leitfahigkeit von Polyhydroxamsauren verschiedenen Ursprungs
È
Zusammenfassung. Polyhydroxamsaure (PHA) wurde aus Polyacrylamid (PAA) und Polymeth-
È
acrylamid (PMAA) hergestellt. Bei der Reaktion mit einigen Salzen verhalt sich PHA aus PAA wie ein
Halbleiter. PHA aus PMAA hat typische Halbleitereigenschaften, wenn sie mit 1 mmol Eisenchlorid
È È
reagiert, wahrend ihre Leitfahigkeit bei einem Eisenchloridgehalt von 0.5 mmol etwas niedriger ist.
Introduction
Some organic compounds show paramagnetic properties, i.e. they behave as
semiconductors. Eley and Par®tt [1,2] have shown that some chelated compounds
like phthalocyanin and copper-phthalocyanin have semiconducting properties.
Organic compounds with paramagnetic properties are found among simple organic
molecules [3,4], proteins [5] dyes [6] and chelated compounds as well as polymers
[7]. Wang, et al. [8] have prepared blends of conducting polymers (polythiophene
and polypyrrole in insulating host polymers like polystyrene and polycarbonate
resins). Yoshino et al. [9] have produced polypyrrole-PMMA composites by hot
pressing of a mixture of polypyrrole coated and non coated PMMA spheres at
appropriate concentrations. Polypyrrole-PE composites have also been prepared by
a similar method. Their electrical conductivity has been controlled over a wide
range (10ꢀ7±10 ꢀꢀ1. cmꢀ1) by changing the concentration of the coated spheres.
Chen et al. [10] have discussed the temperature dependence of the conductivity and
* Corresponding author

246
W. M. Sayed et al.
the structure of the composite. Misra et al. [11] have investigated semiconducting
polymers (polypyrrole and polyaniline).
In this paper, the polymer chosen is polyhydroxamic acid (PHA) from
polyacrylamide. It was found that PHA from polyacrylamide (PAA) has
semiconducting properties when it reacts with some metals. PHA from
polymethacrylamide (PMAA) has semiconducting properties when it contains
higher concentrations of ferric ions.
Results and Discussion
From the introduction and from the above mentioned results it can be seen that
organic compounds with semiconducting properties are either molecules contain-
ing hetero atoms such as oxygen, nitrogen, sulfur, etc. or substances with polar
moieties like NO2, SO3H, SO3Cl, OH, or NH2OH. Polymers of moderate
molecular weight that contain polar groups [17] or are linked to metals, oxides, or
salts can also show semiconducting properties. Accordingly, polyhydroxamic acids
from polyacrylamide and polymethacrylamide which are polymers containing
polar groups (±NHOH) and which can be linked to metals and metal salts (e.g.
Cu2Cl2 or FeCl3) may have paramagnetic properties.
Compounds with semiconducting properties are characterized by speci®c
electric conductivities between 10ꢀ12 and 10ꢀ2 ꢀꢀ1 Á cmꢀ1 and by a linear relation
between log ꢀ and 1/T ꢀ : electric resistivity; (T: absolute temperature).
Scheme 1
Fig. 1. Variation of speci®c resistivity with Tꢀ1 for
polyhydroxamic acid from polyacrylamide ‡ ferrous
oxalate ‡ cuprous chloride ‡ cobalt acetate

Electrical Conductivity of Polyhydroxamic Acid
247
Applying these criteria, it can be seen from Fig. 1 that polyhydroxamic acid
prepared from polyacrylamide is a semiconductor. Its speci®c electric conductivity
is 10ꢀ7ꢀꢀ1 Á cmꢀ1 at 70ꢁC.
PHA from polymethacrylamide exhibits semiconducting properties at higher
concentration of FeCl3 its speci®c electric conductivity ranging between 10ꢀ8 and
10ꢀ6ꢀꢀ1 Á cmꢀ1 at temperatures between 25 and 80ꢁC (Fig. 4) Fig. 3 shows that,
although the relation between logꢀ and 1/T is linear for PHA from PAA, the speci®c
electric conductivity is between10ꢀ10 and 10ꢀ12 at temperatures between 25 and
80ꢁC, due to the lower FeCl3 content of this sample.
Figures 2 and 5 demonstrate that the relation between the electric current and
voltage is ohmic for both PHA from PAA and PMAA.
Figure 6 shows that the relation between logꢀ and 1/T for PHA from a
copolymer of AA and MMA is linear. Since ꢀ ˆ 10ꢀ7 ꢀꢀ1 Á cmꢀ1 only at 80ꢁC and
the activation energy calculated for this compound is 113 kcal, this material shows
semiconducting properties only at high temperatures. In Fig. 7 the relation between
logꢀ and 1/T is linear, and the speci®c electric conductivity between 25 and 85ꢁC
for the copolymer containing ferric chloride is between 10ꢀ7 and 10ꢀ5ꢀꢀ1 Á cmꢀ1;
the activation energy calculated for this compound is 10.4 kcal. Accordingly, this
material is a typical semiconductor. Figures 8 and 9 show that the relation between
current and voltage for the copolymer is ohmic.
Fig. 2. Variation of current with voltage for polyhy-
droxamic acid from polyacrylamide ®lms containing
ferous oxalate, cuprous chloride, and cobalt acetate
Fig. 3. Variation of speci®c resistivity of polyhy-
droxamic acid from polymethacrylamide containing
0.5 m mol ferric chloride with Tꢀ1

248
W. M. Sayed et al.
Fig. 4. Variation of speci®c resistivity with Tꢀ1 for
polyhydroxarmic acid from polymethacrylamide con-
taining lm mol ferric chloride
Fig. 5. Variation of current with voltage for PHA
from polymethacrylamide containing 0.5 m mol ferric
chloride
Fig. 6. Variation speci®c resistivity with Tꢀ1 for
polyhydroxamic acid from a copolymer of acrylamide
and methylmethacrylate

Electrical Conductivity of Polyhydroxamic Acid
249
Fig. 7. Variation of speci®c resistivity for polyhy-
droxamic acid from a copolymer of acrylamide and
methylmethacrylate ‡ ferric chloride with Tꢀ1
Fig. 8. Variation of current with voltage for poly-
hydroxamic acid from acrylamide and methylmetha-
crylate copolymer
Fig. 9. Variation of current with voltage for
polyhydroxamic acid from acrylamide and methyl-
methacrylate copolymer containing ferric chloride
The lower the activation energy, the more easily the substance can be activated
to the semiconducting state. Compounds 2 and 3 demonstrate that the higher the
concentration of FeCl3, the more easily the substance becomes semiconductive.
The values of the activation energies of compounds 4 and 5 show that the activation
energy drops heavily when 1 mmole of FeCl3 is added.

250
W. M. Sayed et al.
Activation energya
Compound
PHA from PAA ‡ Fe(COO)2, Cu2Cl2, and Co(CH3COO)2 (1)
PHA from PMAA ‡ 0.5 mmol FeCl3 (2)
21.3 kcal
21.5 kcal
7.14 kcal
113 kcal
10.4 kcal
PHA from PMAA ‡ 1 mmol FeCl3 (3)
PHA from a copolymer of AA and MMA (4)
PHA from a copolymer of AA and MMA ‡ 1 mmol FeCl3 (5)
a
Calculated according to Arrhenius from ꢀ ˆ ꢀo exp(ꢀE/RT)
Experimental
Preparation of polyhydroxamic acid from polyacrylamide
The method of preparation has been described before [12]. To 20 g of polyacrylamide in 300 ml of
water, 69.5 g (1 mol) of hydroxylamine hydrochloride were added. After stirring for 30 min at room
temperature the pH was adjusted to ꢂ 12 by successive addition of 55±65 g of sodium hydroxide.
After 24 h, during which time ammonia evolves, the solution is rendered acidic by addition of 3 N
HCl (pH ˆ lꢀ3). 0.5 mmol/g of polymer of cuprous chloride, ferrous oxalate, and cobalt acetate were
dissolved in 50 ml of water and added to the prepared mixture. The polymer is separated after
reaction with the salts, washed with water and alcohol, and dried at low temperature. A pellet of
1 mm thickness of the salt was prepared.
Preparation of methacrylamide
50 g (0.5 mol) of methylmethacrylate (MMA) and 90 ml of concentrated ammonia solution (speci®c
gravity 0.88) were mixed in a round bottomed ¯ask. After standing with occasional shaking for 1±2
days (until homogeneity; a longer period of standing is not harmful), the mixture is distilled. The
method described makes use of a procedure for preparing acetamide from ethylacetate [13].
Preparation of polymethacrylamide
25±50 g of MAA were mixed with 100 ml of chloroform and 0.25±0.5 g benzoyl peroxide in a round-
bottomed ¯ask. After re¯ux for 20 min, the polymer was separated by distillation.
Preparation of polyhydroxamic acid from PMAA
The same procedure as for the preparation of PHA from PAA was followed. After acidi®cation of the
mixture to pH 1±3 with 3 N HCl, the polymer was separated by ®ltration. Two fractions of the
Scheme 2

Electrical Conductivity of Polyhydroxamic Acid
251
polymer were dissolved in dichloromethane. To the ®rst fraction, 0.5 mmol of FeCl3 per gram of
polymer were added. To the second fraction, 1 mmol of FeCl3 per gram of polymer was added. The
ferric salt solutions of PHA from PMAA were poured in petri disheds; ®lms of 1 cm diameter and
1 mm thickness were obtained.
Preparation of a copolymer of acrylamide and methylmethacrylate
45 g of acrylamide and 5 g of methylmethacrylate were mixed in a round-bottomed ¯ask. The
contents of the ¯asks were dissolved in 100±200 ml of water, and 3 g of potassium persulfate were
added. After mounting a re¯ux condenser, the contents were heated at 40ꢁC for 15 minutes. The
copolymer was obtained by distillation. The polyhydroxamic acid from the copolymer was prepared
by the same method used for the preparation of PHA from polyacrylamide.
Measurement of the speci®c electric conductivity of the polymers
The speci®c electric conductivity of thin ®lms of the polymers was measured by the method
mentioned of Eley and Par®tt [1,2]1. The thin ®lm of 1 cm diameter and 1 mm thickness was tightly
adjusted between the plates of two copper electrodes of an electric cell. The cell was put in an
electric furnace. This electric cell was connected to a battery and an electrometer, forming an electric
circuit. The electric conductivity was either measured directly by the electrometer, or from the
measurements of the voltage and the electric current through the electric cell. The temperature of the
electric furnace was measured by a thermocouple.
Measurement of molecular weight
ꢁ
The average molecular weights ꢃMn† of polyacrylamide and polymethylmethacrylate were
determined via viscosity measurements employing an Ubbelohde viscosimeter. The following
0:66
0:76
4
4
ꢁ
ꢁ
relations were used: PAA, ‰ꢁꢁŠ ˆ 6:8  10 ‰MnŠ
[14, 15]; PMAA:‰ꢁŠ ˆ 0:94  10 ‰MnŠ
30ꢁ
30ꢁ
ꢁ
ꢁ
[16]. The following values were obtained: PAA, Mn ˆ 735:2; PMMA., Mn ˆ 3880; PMAA,
ꢁ
Mn ˆ 3315:
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1
In the case of polyhydroxamic acid from polycrylamide, a pellet of 1 mm thickness and 1 cm
diameter was adjusted between the plates of the copper electrodes

252
W. M. Sayed et al.: Electrical Conductivity of Polyhydroxamic Acid
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Á
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Received November 20, 1996. Accepted (revised) June 16, 1997