Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Nitrogen-containing reactant
Reexamination Certificate
2000-02-07
2001-07-24
Truong, Duc (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Nitrogen-containing reactant
C528S486000, C528S488000, C528S491000, C528S495000, C525S540000, C252S182110, C252S500000
Reexamination Certificate
active
06265532
ABSTRACT:
FIELD OF THE INVENTION
The present invention concerns a process for manufacturing high molecular mass polyaniline in the form of emeraldine.
More precisely, it concerns the manufacturing of polyaniline in the form of protonated emeraldine which is totally-soluble in several organic solvents, particularly meta-cresol, due to greater structural perfection, particularly with regard to rates of chlorination, bridging and branching of the polyaniline obtained.
STATE OF THE ART
Polyanilines can be obtained by oxidation of aniline or aniline derivatives in aqueous solution, and they are valuable because of their electronic conductivity properties and their stability in air.
Polyaniline is a polymer which can appear in different oxidation states according to the formula:
Three distinct oxidation states corresponding to y=0, 0.5 and 1 are known. The corresponding polyanilines are respectively leucoemeraldine base for y=0, emeraldine base for y=0.5 and pernigraniline for y=1.
Polyaniline can be protonated by a strong Bronsted acid such as hydrochloric acid (HCl) to give a protonated polymer (an ionomer salt) with the formula:
with y as defined above and x varying between 0 and ~0.75. The most conductive form is emeraldine salt with y=0.5 and x=0.5, commonly called emeraldine. It has conductivity on the order of 1 to 15 S/cm measured on compressed powder pellets.
The emeraldine base powder, though infusible, can be worked in the form of films or fibres from its soluble fraction in N-methylpyrrolidone (NMP) or di-methylpropylene urea but the films or fibres are not conductive and can only be protonated with great difficulty by very strong acids. It is more soluble in concentrated sulphuric acid, from which conductive fibres can be obtained but which have modest mechanical properties. When protonated by (±)-10-camphor sulphonic acid it is partially soluble in meta-cresol, allowing for the obtaining of films by evaporation of the meta-cresol. For most applications the electrical and mechanical properties of a polymer depend on its average molecular mass in number and in mass, M
n
and M
w
, and on its polydispersion index, P.I.=M
w
/M
n
, the best properties being obtained with a high molecular mass and a reduced polydispersion index. But a high molecular mass polymer is not very valuable unless it has good solubility in its conductive form (protonated).
Document WO-A-93/09175 describes a process for manufacturing polyanilines of high molecular mass by polymerisation using an oxidising agent such as ammonium persulphate, according to which a first solution including aniline, a protonic acid and a salt is mixed with a second solution containing the protonic acid, the salt and at least one compound to start the polymerisation, such as ammonium persulphate. The reaction is carried out at a temperature below −10° C., preferably between −10° C. and about −70° C. The polymerisation reaction can be monitored by continuously measuring the redox potential of the polymerisation solution with respect to a calomel reference electrode. High molecular mass polyanilines can thus be obtained, measured by steric exclusion chromatography (SEC).
The use of this process has some drawbacks such as the monitoring of the polymerisation reaction by measurement of the redox potential at a temperature of −40° C. The measurements of molecular masses done by SEC can also give substantial errors.
The redox potential of the solution equal to the electrochemical potential of the polyaniline being synthesised is measured during the synthesis between a Pt electrode and a calomel reference electrode, both of which are immersed in the reaction bath. With the synthesis temperature of 0 to 3° C. given in example 1Ai of WO-A-93/09715, the end of the synthesis is indicated by the decrease of the potential below 430 mV, this potential corresponding to the oxidation state of emeraldine. But the potential cannot be used to monitor and indicate the end of the synthesis at −40° C., the temperature mentioned in example 1Aii in this document, because the precipitation of aniline chlorhydrate makes potential measurement impossible. This is a major drawback of the process because we cannot monitor the synthesis and control the end of this synthesis which takes place in an uncontrolled manner during the reheating of the suspension before separation of the polyaniline by filtration. The temperature at the end of the synthesis is not controlled either and therefore the syntheses cannot be reproduced.
With regard to molecular masses, the results obtained by SEC on emeraldine base in solution in NMP, even in the presence of 0.5% LiCl, are subject to substantial errors and cannot be taken into consideration quantitatively, especially for determination of high molecular masses due to the partial and colloidal solubility of emeraldine base in NMP and an aggregation equilibrium between the dissolved and aggregated macromolecules which Occurs even in a diluted solution. The best results are obtained by measuring molecular masses on polyaniline in the form of leucoemeraldine in NMP.
The M
w
of various polyanilines can be better compared by determination of their inherent viscosities at 25° C. in concentrated sulphuric acid because most polyanilines are totally soluble in this acid without degradation. This measurement indicates a M
w
which results from an average rotation radius of the macromolecules however. This radius depends on M
w
for a given chain structure. But different synthesis conditions produce chains containing several types of flaws of different rates, among which the most serious are: branching and bridging of chains and chlorination of chains. The comparison of M
w
of various emeraldine bases can only be done by comparison of their inherent viscosities if their chains have the same rates of branching and chlorination. The rate of chlorination is sometimes indicated because it can be determined by elementary analysis, but not the rate of branching and bridging because it cannot be quantitatively determined. It is evaluated with the M
w
by the solubility of the emeraldine base in NMP or in dimethylpropylene urea and of the emeraldine protonated by CSA in meta-cresol and by the speed of gelling of these solutions. Document WO93/09715 gives no indication, neither of the rate of chlorination, nor of the solubility of the polyaniline obtained.
A synthesis of polyaniline done according to the synthesis conditions described in example 1Aii of WO-A-93/09175 at −40° C., in the presence of 5.8M of LiCl, yielded an emeraldine base containing a fraction by weight of insoluble polymer protonated by CSA in meta-cresol of ~15% and a rate of chlorination of ~3%.
This synthesis process therefore cannot produce a high molecular mass polyaniline with a negligible rate of chlorination and a low rate of branching and bridging capable of making the emeraldine protonated by CSA totally soluble in meta-cresol or hexafluoroisopropanol to yield self-supported films with high conductivity.
SUMMARY OF THE INVENTION
This invention precisely involves a process for manufacturing polyanilines which overcomes the drawbacks of the process described above, which gives, in a short time and in a reproducible manner, a high molecular mass polymer with a negligible rate of chlorination and a low rate of branching and bridging, totally soluble in meta-cresol or hexafluoroisopropanol in the form of emeraldine protonated by CSA, this process being in addition suitable for use on an industrial scale
According to the invention, the process for manufacturing a high molecular mass polyaniline in the form of emeraldine includes the following steps:
a) polymerising aniline or an aniline derivative in pernigraniline, doing the polymerisation in a homogeneous aqueous solution including the aniline or the aniline derivative, a protonic acid, a salt, an oxidising agent and ethanol to yield pernigraniline,
b) reducing the pernigraniline obtained in step a) to emeraldine by means of an aq
Beadle Paul
Nicolau Yann-Florent
Commissariat A l'Energie Atomique
Pearne & Gordon LLP
Truong Duc
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