Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – From boron reactant having at least one boron to hydrogen or...
Reexamination Certificate
2000-03-03
2002-03-05
Dawson, Robert (Department: 1712)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
From boron reactant having at least one boron to hydrogen or...
C528S008000, C528S394000, C528S397000, C252S301160, C252S301350, C323S902000, C430S321000
Reexamination Certificate
active
06353072
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a process for preparing a polymer such as a conjugated polymer for use in an optical device such as an electroluminescent device.
BACKGROUND OF THE INVENTION
Organic electroluminescent devices are known which employ an organic material for lights emission. For example, WO90/13148 describes such a device comprising a semiconductor layer comprising a polymer film which comprises at least one conjugated polymer situated between electrodes. The polymer film in this case comprises a poly(para-phenylene vinylene) (PPV) film which is capable of light emission when electrons and holes are injected therein. Other polymer layers capable of transporting holes or transporting electrons to the emissive layer may be incorporated into such devices. The bandgap of PPV and other poly(arylene vinylene) polymers may be tuned to modulate the wavelength, quantum efficiency and/or refractive index thereof, as described in EP-A-0544795.
Preparation of poly(arylene vinylene)s for use in optical devices has been conveniently carried out by a precursor route where thermal elimination of leaving groups gives rise to a conjugated polymer, or by other routes such as a dehydrohalogenation reaction. However, poly(arylene vinylene)s are not the only class of polymers which are, suitable for use in optical devices. Other aryl-containing polymers may be useful and one route generally useful in the production of conjugated polymers is the Suzuki reaction (Synthetic Communications 11(7), 513, 1981). This reaction involves the use of a palladium-based catalyst, an aqueous alkaline carbonate or bicarbonate inorganic base and a solvent for the reactants and possibly the polymer product. The monomer reactants are typically a diboronic acid or diboronate monomer and a dibromo monomer.
U.S. Pat. No. 5,777,070 is directed to attempts to improve the Suzuki reaction to form conjugated polymers from aromatic monomers. U.S. Pat. No. 5,777,070 indicates that such reactions require as a solvent a non-polar solvent such as toluene. However, such non-polar solvents are acknowledged to slow down the rate of reaction. In order to overcome this disadvantage, U.S. Pat. No. 5,777,070 proposes the use of a phase-transfer catalyst such as tricaprylmethyl ammonium chloride sold under the registered trade mark Alquat to increase the rate of reaction. Accordingly, the reaction mixture contains an iorganic solvent such as toluene, an aqueous solution of an inorganic base such as sodium bicarbonate, a catalytic amount of a palladium complex and a catalytic amount of the phase transfer catalyst.
The inventors of the present invention have identified a number of drawbacks with the process described in U.S. Pat. No. 5,777,070. Firstly, the reaction is very slow; reaction times are typically of the order of 18 hours in order to produce a polymer having a molecular weight of the desired order. Discolouration of the polymer product and decomposition of the catalyst become concerns with such long reaction times. Secondly, the reproducibility of the reaction is somewhat poor. The monomer ratio is generally used in the case of copolymerization to control the molecular weight of the product polymer. However, the present inventors have noticed that the peak molecular weight of polymers produced according to the method disclosed in U.S. Pat. No. 5,777,070 vary considerably from reaction to reaction even when the starting monomer ratio is the same. Experiments conducted by the inventors of the present invention have shown that the peak molecular weight of the product polymer can vary by as much as about 100,000 for the same starting monomer ratio. Thirdly, the inventors of the present invention have also noticed that significant foaming is observed and that side products are produced which complex strongly to the walls of the reaction vessel, when a glass reaction vessel is used. These are difficult to remove, and the reaction thus requires the use of specialized reaction vessels. The above problems also make this a very difficult and expensive process to scale up.
The present invention aims to overcome at least some of the drawbacks mentioned above.
SUMMARY OF THE INVENTION
According to a first aspect of the present invention, there is provided a process for preparing a conjugated polymer, which comprises polymerizing in a reaction mixture (a) an aromatic monomer having at least two boron derivative functional groups selected from a boronic acid group, a boronic ester group and a borane group, and an aromatic monomer having at least two reactive halide functional groups; or (b) an aromatic monomer having one reactive halide functional group and one boron derivative functional group selected from a boronic acid group, a boronic ester group and a borane group, wherein the reaction mixture comprises a catalytic amount of a catalyst suitable for catalysing the polymerisation of the aromatic monomers, and an organic base in an amount sufficient to convert the boron derivative functional groups into —B(X)
3
−
anionic groups, wherein X is independently selected from the group consisting of F and OH.
The polymerisation proceeds by the coupling of the monomers via elimination of a reactive halide group and a boronate anionic group (—B(X)
3
−
).
According to one embodiment of the invention, the conversion of the boron-derivative functional groups to the boronate anionic groups (—B(X)
3
−
) by the organic base to form a salt having an organic cation is carried out under non-polymerisation conditions prior to polymerisation.
The boronate anionic group has the formula —B(OH)
n
F
m
−
, wherein n+m=3 and n and m are each 0, 1, 2 or 3. The boronate anionic group is preferably a —B(OH)
3
−
group. However, the reaction may also proceed, for example, via a —B(OH)
2
F
−
anionic group using, for example, a tetraalkylammonium fluoride as the organic base.
The term conjugated polymer refers to either a fully conjugated polymer i.e. a polymer which is conjugated along the full length of its chain, or a partially conjugated polymer i.e. a polymer which contains conjugated segments together with non-conjugated segments.
The term aromatic monomer refers to any monomer which has the respective functional groups directly substituted on one or more aromatic rings. In the case of monomers having more than one aromatic ring, the functional groups can be substituted on either the same or different aromatic rings. Examples of suitable types of monomers include, but are not limited to, arylenes, heterocylic aromatic monomers, and fused aromatic systems such as biphenylenes, naphthalenes and fluorenes. Each monomer preferably comprises an arylene, a heteroarylene, a triarylamine, or a bisarylene vinylene. Each aromatic group within the monomer may be substituted or unsubstituted. Particularly preferred types of monomers include dialkylphenylenes, dialkoxy phenylenes, substituted and non-substituted thiophenes and benzothiadiazoles, and dialkylfluorenes such as 9,9-di-n-octylfluorenes. One or more of the monomers could also be a pre-formed oligomeric or polymeric chain comprising several smaller units with toe necessary functional groups provided at the desired positions on the chain.
It is also envisaged that under the appropriate reaction conditions, this invention could also be extended to the use of monomers in which some or all of the functional groups are not directly substituted on an aromatic ring, in particular to other kinds of unsaturated monomers.
Monomers particularly useful in the present invention include those which may be polymerised to form a semi-conductive conjugated polymer such as a semiconductive conjugated polymer for use in an optical device such as an electroluminescent device. Such polymers may be used in an emissive layer or as a hole transport or electron transport polymer. Luminescent polymers are particularly useful in such devices. The conjugated polymer may be fully or partially conjugated, perhaps containing conjugated segments and way be a homopo
O'Dell Richard
Towns Robert Carl
Cambridge Display Technology Limited
Finnegan Henderson Farabow Garrett & Dunner
Hendricks Therese
Robertson Jeffrey B.
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