Title of Invention

A PROCESS FOR THE PREPARATION OF CONDUCTING POLYMER HAVING HIGH SENSITIVITY FOR USE IN CHEMICAL SENSOR DEVICES.

Abstract This invention relates to a process for the preparation of conducting polymer having high sensitivity for use in chemical sensor devices. The conducting polymers has functional groups which impart high sensitivity to chemical vapours. Process steps comprises depositing thin films of interdigited gold film electrodes insulating substrates by vacuum evaporation, then subjecting to electrochemical polymerization using electrolyte prepared by adding the nitrogen or sulfur group containing monomer and a macrocyclic compound containing a metal atom complex within it to organic salt containing tetra butyl ammonium group in a polar solvent platinum as counter electrode at 0.5 to 2.0 v with respect to saturated calomel electrode (SCE) for a duration ranging from 60 to 600 seconds, removing the conducting polymer coated electrode, washing and drying the same, connecting two copper wires by means of air drying silver contact paste and drying to obtain conducting polymer film having high sensitivity for use in chemical sensors.
Full Text This invention relates to a process for the preparation of conducting polymer having high sensitivity for use in chemical sensor devices.
In particular it relates to the preparation of conducting polymers having functional groups which impart high sensitivty to chemical vapours.
The various vapours of chemicals and solvents commonly used in the industry such as hydrochloric acid, ammonia, sulfuric acid, benzene, toluene, metha-nol, ethanol, propyl alcohol etc. can often prove to be hazardous because they can be directly toxic or they can cause fire, explosions etc. leading to large scale damage to the industry or health of industrial workers. In order to prevent these, chemical sensors are employed to detect the presence of these chemicals in vapour phase. Currently, the solid state sensor devices are fabricated from ceramic materials such as tin oxide, zinc oxide etc. which have sensitivity to gases but only at high temperature. The ceramic based sensors are stiff, brittle and have to be fabricated using high temperature sintering techniques requiring high energy
inputs. The operation of these sensors also requires
o temperatures exceeding 100 C for high sensitivity. This
renders them to be of fixed geometry, expensive and not easily portable.
In order to overcome the above drawbacks, the sensors based on organic materials or polymers are

finding increasing applications. Phthalocyanine vacuum deposited films have been reported to be sensitive to chemical vapours (Phthalocyanlnes Properties and Applications Vol.3, Edt.C.C.Lenznoff and A.B.Lever, VCH Publ. New York, 1993 ). However, this process is not
very amenable for industrial production since the films
-6
have to be deposited under high vacuum ( 10 mbar) and
9 as such the films have very high resistivity (>10
ohm-cm) which causes very high impedance /low currents in the supporting electronic circuit. Hence, there is a need for materials having low resistance and at the same time high sensitivity to chemicals and which can be easily formed into various desirable sizes, shapes etc. Conducting polymers have low resistivity (0.1 to 10 ohms-cm) but by themselves these are only slightly sensitive to chemical vapours with slow response characteristics.
The object of the present invention is to provide a process for preparation of conducting polymers having high sensitivity for use in chemical sensor devices.
Accordingly, the present invention provides a process for the preparation of conducting polymer having high sensitivity for use in chemical sensor devices comprises depositing thin films of interdigited gold film electrodes insulating substrates by vacuum evaporation, then subjecting to electrochemical poly-

merisation using electrolyte prepared by adding the nitrogen or sulfur group containing monomer and a macrocyclic compound containing a metal atom complexed within it to organic salt containing tetrabutyl ammonium group in a polar solvent, platinum as counter electrode at 0.5 to 2.0 V with respect to saturated calomel electrode (SCE) for a duration ranging from 60 to 600 seconds, removing the conducting polymer coated electrode, washing and drying the same, connecting two
copper wires by means of air drying silver contact
o paste and drying the same for 10 hrs at 25 C to obtain
conducting polymer film having high sensitivity for use in chemical sensors.
In an embodiment of the present invention, the organic salt containing tetrabutyl ammonium group may be such as perchlorate, fluoroborate, sulfate and fluorosulfonate.
In another embodiment of the present invention, the polar solvent used may be such as those having high dielectric constant ranging from 12 to 56 and may be selected from dimethylformaraide, nitrobenzene, n-methyl pyrrolidone or its mixture with water.
In another embodiment of the present invention, the monomer used for polymerization contains nitrogen or sulfur groups and may be chosen from pyrrole, thio-phene or aniline or their substituted derivatives.

In yet another embodiment of the present invention, the macrocylic compounds used may be selected from phthalocyanines, porphyrines or crown ethers.
In another embodiment of the present invention, the concentration of the macrocylic compound ranges from 0.001 to 0.5 mole % of the monomer.
In a feature of the present invention, in the preferred range of composition, the conducting polymer prepared according to the present invention exhibits 500 times more sensitivity to nitric oxide and 10 times more sensitivity to ammonia than the original polymer.
The invention is described hereinbelow by the following examples which are illustrative only and should not be construed to limit the scope of the invention in any manner.
EXAMPLE * 1
The salt tetrabutylammonium perchlorate (3.42 gns) was dissolved in 100 ml of nitrobenzene to which were added 0.25 gms of copper phthalocyanine. The solution was thoroughly mixed for 15 win and placed in an electrochemical cell. The 3.36 gm of thiophene were added to the solution and dry nitrogen was bubbled through the same for 30 man. Glass substrates ( microscopic grade) having thin films of gold electrodes in the interdigited comblike pattern deposited on them were used as working electrodes. Platinum was the counter

electrode and saturated calomel (SCE) was used as the reference electrode. Electorchemical polymerization was carried out by applying 1.8 V vs SCE for 600 s. The polymer films obtained were rinsed in pure solvent and then dried thoroughly. Two copper leads were attached to the gold films by means of air drying type silver paste. The whole assembly was placed in an evacuated glass chamber and the leads connected to an electrometer to monitor the conductivity before and after exposure to nitric oxide and ammonia which were introduced into the chamber in measured quantity. The sensitivity of this polymer is indicated in Table -1.
EXAMPLE - 2
The tetrabuty1ammonium perchlorate salt (3.42 gms) were added to nitrobenzene ( 100 ml) and thoroughly dissolved. Copper phthalocyanine ( 0.5 gms) were added to the solution and thoroughly mixed for 15 min. Thio-phene (3.36 gm) was added to the above mixture and dry nitrogen bubbled for 30 min. The electrochemical polymerization was carried out in the same manner as in example-1 with interdigited gold film coated glass substrates as the working electrode and platinum foil counter electrode. The chemical sensitivity of these polymer films was tested in the manner described in example - 1 and the values are indicated in Table -1

TABLE – 1
(Table Removed)
* polymer synthesised under same conditions as Example 1 & 2 but without addition of macrocylcles
It is seen from the above data that there is considerable increase in the sensitivity factor in the conducting polymers synthesised by the process described in the present invention as compared to that obtained in original polymer.







We claim:
1. A process for the preparation of conducting poly
mer having high sensitivity for use in chemical
sensor devices comprises depositing thin films of
interdigited gold film electrodes insulating
substrates by vacuum evaporation, then subjecting
to electrochemical polymerisation using electro
lyte prepared by adding the nitrogen or sulfur
group containing monomer and a macrocyclic com
pound containing a metal atom complexed within it
to organic salt containing tetrabutyl ammonium
group in a polar solvent platinum as counter
electrode at 0.5 to 2.0 V with respect to saturat
ed calomel electrode (SCE) for a duration ranging
from 60 to 600 seconds, removing the conducting
polymer coated electrode, washing and drying the
same, connecting two copper wires by means of air
drying silver contact paste and drying the same
o for 10 hrs at 25 C to obtain conducting polymer
film having high sensitivity for use in chemical sensors.
2. A process as claimed in claim one wherein, the
organic salt containing tetrabutyl ammonium group
is selected from perchlorate, fluoroborate, sul-
fate and fluorosulfonate.

3. A process as claimed in claims 1 and 2 wherein,
the polar solvent used is selected from those
having high dielectric constant ranging from 12 to
56 and may be selected from dimethyl formaramide,
nitrobenzene, n-methyl pyrrolidone or its mixture
with water.
4. A process as claimed in claims 1 to 3 wherein, the
nitrogen or sulfur group containing monomer used
are chosen from pyrrole, thiophene or aniline or
their substituted derivatives.
5. A process as claimed in claims 1 to 4 wherein,
the macrocylic compounds are selected from
phthalocyanines, porphyrines or crown ethers.
6. A process as claimed in claims 1 to 5 wherein, the
concentration of the macrocylic compound ranges
from 0.001 to 0.5 mole % of the monomer.
7. A process for the preparation of conducting poly
mer having high sensitivity for use in chemical
sensor devices substantially as herein described
with reference to the examples.

Documents:

281-del-1999-abstract.pdf

281-del-1999-claims.pdf

281-del-1999-correspondence-others.pdf

281-del-1999-correspondence-po.pdf

281-del-1999-description (complete).pdf

281-del-1999-form-1.pdf

281-del-1999-form-19.pdf

281-del-1999-form-2.pdf

281-del-1999-form-3.pdf


Patent Number 199537
Indian Patent Application Number 281/DEL/1999
PG Journal Number 38/2008
Publication Date 19-Sep-2008
Grant Date 15-Dec-2006
Date of Filing 19-Feb-1999
Name of Patentee COUNCIL OF SCIENTIFIC AND INDUSTRIAL RESEARCH
Applicant Address RAFI MARG, NEW DELHI - 110 001., INDIA
Inventors:
# Inventor's Name Inventor's Address
1 SUBRAMANIAM RADHAKRISHNAN NATIONAL CHEMICAL LABORATORY, PUNE-8.
2 SHRIPAD DAGADOPANT DESPHANDE NATIONAL CHEMICAL LABORATORY, PUNE-8.
PCT International Classification Number G01N 27/327
PCT International Application Number N/A
PCT International Filing date
PCT Conventions:
# PCT Application Number Date of Convention Priority Country
1 NA