OF CONTROLLED MOLECULAR WEIGHT

CLAIM OF PRIORITY

This application claims the benefit of priority to U.S. Provisional Patent Application Serial No. 61/901,555, filed on November 8, 2013, which is hereby incorporated by reference herein in its entirety.

BACKGROUND

Polythiophenes are materials showing promise as conductive polymers for use in photovoltaics, flexible circuitry, and other applications where non- metallic substances are needed for weight reduction, flexibility, and other properties possessed by this unique type of polymers.

Methods of preparation of regioregular polythiophenes have been disclosed and claimed; see, for example, U.S. Patent Nos. 7,572,880 and 7,935,781 ; and, U.S. Pub. No. 2010/0004423; the disclosures of which are incorporated by reference herein.

For use in electronics devices, it is desired to retain an adequate degree of solubility in organic solvents and physical flexibility of layers of the

polythiophenes laid down by solvent deposition, while preserving a high conductivity. Control of the physical and electronic properties of

polythiophenes such as but not limited to solubility and flexibility, can be achieved by control of the average molecular weight and molecular weight distribution range of the regioregular polythiophenes.

SUMMARY

The present invention is directed to methods for the preparation of improved regioregular polythiophenes. The improvement concerns control of the average molecular weight and molecular weight range. Embodiments of the present invention can provide methods for controlling and management of the average molecular weight and molecular weight range of a regioregular polythiophene. The embodiments of the inventive method involve controlling and managing the ratio of the number of moles of the Grignard reagent to the number of moles of the 2,5-dihalothiophene substituted by an alkyl group to a range between about 1.00 and about 1.10, preferably 1.00 and about 1.10. According to these embodiments of the invention, a greater ratio of Grignard reagent to -2,5-dihalo thiophene substituted by alkyl yields a regioregular polythiophene of lower average molecular weight than is produced by a lower ratio trending to a ratio of 1.00 or slightly below. Instances of embodiments of the invention also enable control of the polydispersity so that a narrow range of molecular weights of the regioregular polythiophene is achieved.

According to the present invention, embodiments of the invention are based upon a three step method for preparation of a regioregular polythiophene from 2,5-dihalothiophene substituted by alkyl. The first step involves formation of the organogrignard intermediate by reaction of the Grignard reagent and the 2,5-dihalo thiophene substituted by alkyl. The second step involves transmetallation of the organo-Grignard intermediate with a manganese, zinc or nickel salt to form a transmetallated intermediate. The third step involves polymerization of the transmetallated intermediate using a Nickel (II) catalyst. While these steps can be conducted separately by means such as isolating the intermediates from the other substances of the reaction media, preferably, the steps are conducted in a single reaction container without such separation.

The alkyl substituted 2,5-dihalo thiophene starting material has as the halo group chloride, bromide or iodide and may have the same halo group at both positions or be mixed such as 2-chloro-5-bromo-3-alkylthiophene, or the reverse (2-bromo-5-chloro-3-alkyl), or 2-chloro-5-iodo-3-alkylthiophene or the reverse , or 2-bromo-5-iodo-3-alkylthiophene or the reverse. Preferably the halo group is the same at both positions and preferably is chloro or bromo, more preferably is bromo.

The alkyl group of the alkyl substituted-2,5-dihalo thiophene may contain from one to fifteen carbons and may be linear, branched or cyclic. Preferably, the alkyl group is linear or branched, more preferably linear.

Preferably the linear, branched or cyclic alkyl group contains from two to ten carbons, more preferably from three to eight carbons, most preferably from four to six carbons and especially preferably six carbons. The alkyl group may be substituted at the 3 or 4 position of the dihalothiophene. When the halo group is the same at both positions, the 3 and 4 positions of the alkyl group are redundant. In other words, a 2,5-dichloro-3-alkyl thiophene is the same as a 2,5- dichloro-4-alkyl thiophene and IUPAC rules provide that the designation of the alkyl position should be the lower number, eg., 3. However, when the halo groups at positions 2 and 5 differ, positioning the alkyl at the 3 or 4 position does not yield a redundant molecule.

The Grignard reagent used in this first step of the method may be any Grignard reagent known in the art. Linear and branched alkyl magnesium halide, cycloalkyl magnesium halide, arylalkyl magnesium halide and aryl cycloalkyl magnesium halide are examples of suitable Grignard reagents wherein the halide is chloride, bromide, or optionally iodide, preferably chloride or bromide, more preferably chloride. Preferred Grignard reagents include alkyl magnesium halide and cycloalkyl magnesium halide wherein the alkyl group contains one to eight carbons, preferably four to six carbons, more preferably five or six carbons and the cycloalkyl group contains four to eight carbons, preferably five or six carbons.

The transmetallation salt may be a manganese, zinc or nickel salt wherein the gegenion may be any that enables facile transmetallation, including but not limited to halide, sulfate, nitrate. Preferred salts are halide including chloride, bromide and iodide, preferably chloride and bromide, more preferably chloride. The preferred transmetallation salt is the manganese (II) salt. Especially preferred is manganese (II) chloride.

The present invention is also directed to the product polythiophene produced according to the method of invention. This product polythiophene has a average molecular weight that is controlled to be lower than the average molecular weight of a polythiophene of the same monomeric composition which is produced by a molar ratio of Grignard to polythiophene starting material of 1.00 (hereinafter reference polythiophene). Preferably the product

polythiophene also has a controlled polydispersity that is narrower than the reference polythiophene.

The polythiophene product according to the invention can be used a conductive polymer, in a flexible electronic circuit, in a photovoltaic device, in an RFID chip and in electronic applications utilizing conductive and semi- conductive materials. DETAILED DESCRIPTION

In carrying out a polymerization condensation reaction of substituted 2,5- dihalothiophenes, such as 2,5-dibromo-3-n-hexylthiophene, to yield useful regioregular polythiophene polymers, reference is made to the disclosures of U.S. Patent Nos. 7,572,880 and 7,935,781; and, in particular U.S. Pub. No. 2010/0004423, the disclosures of which are incorporated herein by reference.

U.S. Pub. No. 2010/0004423 discloses a method of preparation of regioregular substituted polythiophenes by reaction of a 2,5-dihalothiophene having an additional ring substitutent, such as an n-alkyl substituent, by contacting the dihalothiophene and a Grignard (organomagnesium) reagent, then transmetallating the organomagnesium intermediate with a manganese salt, such as MnCl ₂ , then contacting with a Ni(II) catalyst system, such as Ni(DPPE)C¾ to provide the regioregular polythiophene product. In example 1 therein, it is described that by use of 25 mmole of 2,5-dibromo-3-hexylthiophene and 12.5 mL of a 2.0 M solution of cyclohexylmagnesium chloride in ether, nominally also 25 mmole, followed by the transmetallation with an equivalent of the Μη(¾ reagent and subsequent contact with Ni(DPPE)C¾, a polythiophene having a regioregularity of about 97% and an average molecular weight (i.e., weight average molecular weight) of about 40-60 kDa as determined by gel permeation chromatography (GPC) in tetrahydrofuran using a polystyrene standard, but even higher, about 80- 120 kDa as determined by light scattering analysis.

In carrying out this work, the molar ratio of Grignard reagent to dihalothiophene was fixed by the weight of the 2,5-dibromo-3-hexylthiophene, and the volume of the Grignard solution as measured by a standard laboratory syringe.

It has now been unexpectedly discovered that by precise control of the ratio of Grignard reagent to the thiophene starting material, relatively small variations in the molar ratio of Grignard to 2,5-dihalothiophene substituted by alkyl (hereinafter thiophene starting material) can significantly and reproducibly cause a predictable variation in the average molecular weight of the regioregular polythiophene product obtained from this reaction. By slightly increasing the ratio of Grignard reagent thiophene starting material, a systematic decrease in the average molecular weight of the resulting regioregular polythiophene can be obtained. In the experiments presented below, it is demonstrated that varying the ratio of Grignard reagent to thiophene starting material, in the presence of a slight molar excess of manganese, zinc or nickel salt, preferably manganese salt, can bring about the following results:

1. Use of a ratio of 1.02 equivalents of Grignard per equivalent of

thiophene starting material produces a polythiophene average molecular weight of about 75-90 kDa;

2. When 1.05 equivalents of Grignard per equivalent of thiophene starting material is used, the average polythiophene molecular weight is reduced to about 55-60 kDa;

3. When 1.10 equivalents of Grignard per equivalent of thiophene starting material is used., the average polythiophene molecular weight is reduced to about 20-25 kDa.

The sensitivity of product molecular weight to the relatively small variations in the molar excess of Grignard reagent used in the thiophene starting material / Grignard / Μη(Ι¾ / Ni(DPPE)C¾ polymerization process is not disclosed or inferred by the earlier results.

While an equimolar amount of Grignard reagent (1.00 equivalents) relative to thiophene starting material yields a regioregular polythiophene of relatively high average molecular weight, in excess of 75 kDa, as little as 5 mole % excess of the Grignard reagent (1.05 equivalents) dropped the molecular weight to an intermediate value around 50 kDa, and use of about 10 mole % excess of Grignard (1.10 equivalents) was surprisingly found to yield a regioregular polythiophene of relatively low molecular weight, around 20 kDa.

According, the present invention provides, in various embodiments, a method for controlling the average molecular weight of a regioregular poly (thiophene optionally substituted by alkyl) prepared by condensation of thiophene starting material in the presence of a Grignard reagent, a manganese, zinc or nickel salt, and a nickel catalyst. The method involves controlling the ratio of the number of moles of the Grignard reagent to the number of moles of the 2,5-dihalothiophene starting material to a range between 1.00 and 1.10, wherein a greater ratio of Grignard reagent to thiophene starting material yields a regioregular polythiophene product of lower average molecular weight compared with the average molecular weight of the regioregular polythiophene product produced using a ratio of 1.00 or slightly below, preferably 1.00. The transmetallation salt may be present in a molar ratio relative to the Grignard reagent of 1.00- 1.05. Maintaining the transmetallation salt to Grignard ratio within this range has no effect upon variation of the polythiophene average molecular weight, its range or its polydispersity,

In an embodiment of the method, when the molar ratio of the Grignard reagent to the thiophene starting material is about 1.00 - 1.02, the average molecular weight of the regioregular polythiophene product produced is at least about 75 kDa.

In an embodiment of the method, when the molar ratio of the Grignard reagent to the thiophene starting material is about 1.04 - 1.06, the average molecular weight of the regioregular polythiophene product produced is about 50 kDa to about 60 kDa.

In an embodiment of the method, when the molar ratio of the Grignard reagent to the thiophene starting material is about 1.08 - 1.12 the average molecular weight of the regioregular polythiophene product produced is no greater than about 30 kDa.

A regioregular polythiophene prepared by a method of the invention can have a relatively low polydispersity index (PDI), the ratio of weight average molecular weight to number average molecular weight. For example, a polydispersity index of the polythiophene product is no greater than about 2.5, or preferably is no greater than about 2.3, or more preferably is no greater than about 2.1.

Various embodiments of the invention are exemplified in the following experimental data. Scheme 1 outlines the synthetic chemistry involved. In this scheme, the transmetallation salt shown is manganese chloride. Another manganese salt such as a bromide or iodide as well as a zinc salt or a nickel salt may be substituted in place of the manganese chloride and will produce the same or essentially the same results for the control of average molecular weight of the thiophene polymer. The manganese salt is preferred. Manganese (II) chloride is especially preferred. Scheme 1 :

Example 1 :

A 2L 2-neck round bottom flask was placed under an argon atmosphere after weighing 2,5-dibromo-3-hexylthiophene into it. Tetrahydrofuran (400 mL) was added and the flask was cooled in an ice bath to 4°C. A measured quantity of isopropylmagnesium chloride solution in ether, ranging from about 1.00 to about 1.10 molar equivalents of Grignard reagent relative to dibromothiophene starting material was added, keeping the internal temperature under 15°C. After stirring 5 minutes, an aliquot was removed and quenched with water, which showed formation of the thiophene-magnesium reagent to be complete. A measured weight of manganese(II) chloride was suspended in tetrahydrofuran, and the solution of the thiophene-magnesium reagent added via cannula. The reaction stirred 5 hours and particulate matter was allowed to settle overnight. Then, a measure portion of the nickel catalyst was added to the chilled solution of thiophene-manganese reagent, and the reaction mixture was stirred overnight and allowed to warm to room temperature. The product polymer was obtained by quenching the reaction with methanol, filtering the polythiophene product, washing with additional methanol, and drying under vacuum. The polymer was further purified by extracting the solid in a Sohxlet extractor twice with hexanes and twice with chloroform. Example 2:

Products of reactions outlined in Example 1 were analyzed for average molecular weight using gel permeation chromatography in tetrahydrofuran, versus a polystyrene standard. Table 1 shows the results of the analyses.

Table 1 :

Example 3:

The above reactions were carried out on a scale of about 150 gm polymer product. Results are shown in Table 2.

Table 2:

While the invention has been described and exemplified in sufficient detail for those skilled in this art to make and use it, various alternatives, modifications, and improvements will be apparent to those skilled in the art without departing from the spirit and scope of the claims.

All patents and publications referred to herein are incorporated by reference herein to the same extent as if each individual publication was specifically and individually indicated to be incorporated by reference in its entirety.

The terms and expressions which have been employed are used as terms of description and not of limitation, and there is no intention that in the use of such terms and expressions of excluding any equivalents of the features shown and described or portions thereof, but it is recognized that various modifications are possible within the scope of the invention claimed. Thus, it should be understood that although the present invention has been specifically disclosed by preferred embodiments and optional features, modification and variation of the concepts herein disclosed may be resorted to by those skilled in the art, and that such modifications and variations are considered to be within the scope of this invention as defined by the appended claims.