EN! S.p.A., P.le E. Mattei, 1 - ROMA

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DESCRIPTION

The present invention relates to a photoactive fluorinated conjugated copolymer.

More in particular, the present invention relates to a photoactive fluorinated conjugated copolymer comprising units in which there is a donor group and a benzothiadiazole group, and units in which there is a donor group and a benzotriazole group, at least one of said benzothiadiazole group and said benzotriazole group being fluorinated. The present invention also relates to the use of said photoactive fluorinated conjugated copolymer in the manufacture of photovoltaic devices (or solar devices) such as, for example, photovoltaic cells (or solar cells), photovoltaic modules (or solar modules), either on rigid support, or on flexible support.

Photovoltaic devices (or solar devices) are devices able to convert the energy of light radiation into electrical energy. Currently, most of the photovoltaic devices (or solar devices) that may be used for practical applications exploit, the chemical/physical properties of inorganic photoactive materials, in particular highly pure crystalline silicon. Due to the high production costs of silicon, however, scientific research has long been focusing on the development of alternative organic materials having a conjugated, oligomeric or polymeric structure, for the purpose of obtaining organic photovoltaic devices (or solar devices) such as organic photovoltaic cells (or solar cells). In fact, unlike highly pure crystalline silicon, said organic materials are characterized by their relative ease of synthesis, a low production cost, a reduced weight of the relative photovoltaic devices (or solar devices), as well as allowing said organic materials to be

4 recycled at the end of the life cycle of the organic photovoltaic device (or solar device) in which they are used.

The advantages reported above make the use of said organic materials energetically and economically attractive despite potential lower efficiencies (η) of the organic photovoltaic devices (or solar devices) thus obtained with respect to inorganic photovoltaic devices (or solar devices).

The operation of organic photovoltaic devices (or solar devices) such as, for example, organic photovoltaic cells (or solar cells), is based on the combined use of an electron acceptor compound and an electron donor compound. In the state of the art, the electron acceptor compounds most frequently used in organic photovoltaic devices (or solar devices) are fulierene derivatives, in particular PC61BM (6, 6-phenyf-C61 -butyric acid methyl ester) or PC71 BM (6, 6-phenyl-C71 -butyric acid methyl ester), which have led to the highest efficiencies when mixed with electron donor compounds selected from π-conjugated polymers such as, for example, polythiophenes (η > 5%), polycarbazoles ( > 6%), derivatives of poly(thienothiophene)-benzodithiophene (PTB) (η > 8%).

The elementary conversion process of light into electrical current in an organic photovoltaic cell (or solar cell) takes place through the following stages:

1. absorption of a photon by the electron donor compound with the formation of an exciton, i.e. a pair of "electron-electron hole" charge carriers;

2. diffusion of the exciton in a region of the electron donor compound up to the interface with the electron acceptor compound;

3. disassociation of the exciton in the two charge carriers: electron (-) in the

accepting phase (i.e. in the electron acceptor compound) and electron hole (+) in the donor phase (i.e. in the electron donor compound);

5 4. carrying the charges thus formed at the cathode (electron through the electron acceptor compound) and at the anode [electron hole through the electron donor compound], with the generation of an electric current in the organic photovoltaic cell (or solar cell) circuit.

The photoabsorption process with the formation of the exciton and subsequent loss of an electron to the electron acceptor compound implies the excitation of an electron from the HOMO ("Highest Occupied Molecular Orbital") to the LUMO ("Lowest Unoccupied Molecular Orbital") of the electron donor compound and, subsequently, the passage from this to the LUMO of the electron acceptor compound.

The characteristics of the photovoltaic materials involved in the transformation process of light into energy are therefore:

the amount of light that photovoltaic materials can absorb: the higher said quantity, the higher the currents that could potentially be produced; said property is in turn attributable to the size of the absorption spectrum of the photovoltaic materials used and how intense said absorption is (i.e. how high their molar extinction coefficient is (ε);

the electron transfer efficiency from the donor compound to the acceptor compound and/or the transfer efficiency of electron holes from the acceptor compound to the donor compound;

the efficiency with which the charges can percolate to the electrodes, attributable to the mobility of the electron holes towards the anode through the donor compound and of the electrons towards the cathode through the electron acceptor compound.

in the simplest operating method _r the organic photovoltaic ceils (or solar cells) are made by introducing between two electrodes, usually made of indium tin oxide (ITO)

6 (anode) and aluminium (Al) (cathode), a thin layer (about 100 nanometres) of a mixture of the electron acceptor compound and the electron donor compound (architecture known as "bulk heterojunction"). Generally, for the purpose of creating a layer of this type, a solution of the two compounds is prepared and, subsequently, a photoactive film is created on the anode [indium tin oxide (ITO)] based on said solution, making use of appropriate application techniques, such as "spin-coating", "spray-coating", "ink-jet printing", and the like. Finally, on the dried film, the counter electrode is deposited [i.e. the aluminium (Al) cathode]. Optionally, between the electrodes and the photoactive film, other additional layers may be introduced, which can perform specific electrical, optical or mechanical functions.

Generally, for the purpose of helping the electron holes to reach the anode [indium tin oxide (ITO)] and at the same time stop electrons being carried, hence improving the charge harvesting by the electrode and inhibiting recombination phenomena, before creating the photoactive film starting from the mixture of the acceptor compound and the donor compound as described above, a film is deposited, based on an aqueous suspension of PEDOT:PSS [poly(3,4-ethylenedioxythiophene)polystyrene sulfonate], making use of appropriate application techniques, such as "spin-coating", "spray- coating", "ink-jet printing", and the like. Finally, the counter electrode is deposited [(Al) cathode] on the dried film.

Conjugated copolymers deriving from the copolymerization of donor groups (i.e.

electron-rich groups) and acceptor groups (i.e. electron-poor groups) are known in the state of the art.

For example, Boudreault P.-L. T. et al., in "Chemistry of Materials" (201 1 ), Vol. 23, pag. 456-469, describe processable polymers with a low band-gap useful in photovoltaic applications. In particular, electron-donor polymers are described (type-p) based on

7 thiophene, 1 ,3,2-benzothiadiazo!es, pyrrole[3,4-c]pyrrole-1 ,4-diones, benzo[1 ,2-b;3,4- 6]-dithiophenes.

Fluorinated conjugated polymers are also known that may be used in photovoltaic applications as reported, for example, by: Price S. C. et al., in "Journal of the American Chemical Society' (201 1 ), Vol. 133, pag. 4625-4631 ; Liu Y. et al., in "Nature

Communications" (2014), 5:5293, DOI : 10.1038/ncomms6239; in patent application US 2012/0152357.

However, said conjugated polymers, in particular fluorinated conjugated polymers, can have some drawbacks such as, for example, low processabi!ily as they are not very soluble, and poor interest for industry because of poor scalability due to their high synthetic complexity.

Therefore, the Applicant set out to solve the problem of finding photoactive fluorinated conjugated copolymers able to overcome the aforementioned drawbacks.

The Applicant has now found photoactive fluorinated conjugated copolymers comprising units in which there is a donor group and a benzothiadiazole group, and units in which there is a donor group and a benzotriazoie group, at least one of said benzothiadiazole group and said benzotriazoie group being fluorinated, which have low synthetic complexity, high solubility and high power conversion efficiency (PCE), said power conversion efficiency (PCE) being defined as the ratio between the number of electrons produced and the number of photons with which the surface unit is irradiated. Said photoactive fluorinated copolymers may be advantageously used in the manufacture of photovoltaic devices (or solar devices) such as, for example, photovoltaic cells (or solar cells), photovoltaic modules (or solar modules), either on rigid support, or on flexible support.

Hence, the subject matter of the present invention is a photoactive fluorinated

8 conjugated copolymer comprising units having general formula (I):

-(D-BTD)- (I)

and units having general formula (la):

-(D-BTZ)- (la)

in which:

D represents a d rmulae (II), (III), (IV):

in which:

Ri, R ₂ , R ₃ and R ₄ , the same or different, represent a hydrogen atom; or they are selected from linear or branched, saturated or unsaturated C C ₂ 0 alkyl groups, preferably C ₂ -C ₀ , optionally containing heteroatoms;

n is 1 or 2;

BTD represents a benzothiadiazole group having general formula (V):

9 in which X, and X _2> mutually identical, represent a hydrogen atom; or a fluorine atom; or they are selected from linear or branched, saturated or unsaturated Ci C ₂₀ alkyl groups, preferably C ₂ -C _C , optionally containing heteroatoms, linear or branched, saturated or unsaturated C C ₂₀ alkoxy groups, preferably C ₂ -C ₀ ; BTZ represents a benzotriazole group having general formula (VI):

in which:

R ₅ is selected from linear or branched, saturated or unsaturated C C ₂ o alky! groups, preferably C ₈ -C ₁₈ , optionally containing heteroatoms;

and X ₂ , mutually identical, represent a hydrogen atom; or a fluorine atom; or they are selected from linear or branched, saturated or unsaturated d-C ₂₀ alkyl groups, preferably C ₂ -C ₀ , optionally containing heteroatoms, linear or branched, saturated or unsaturated C C ₂₀ alkoxy groups, preferably C ₂ -C ₁₀ ;

provided that in at least one from the benzothiadiazole group having general formula (V) and the benzotriazole group having general formula (VI), X, and X _Zl mutually identical, represent a fluorine atom.

10 In accordance with a preferred embodiment of the present invention, in said photoactive fluorinated conjugated copolymer, the molar ratio between donor group D, benzothiadiazole group BTD and benzotriazole group BTZ, is ranging from 1:0.2:0.8 to 1 :0.8:0.2, preferably it is 1 :0.5:0.5:

In accordance with a further preferred embodiment of the present invention said photoactive fluorinated conjugated copolymer has the following general formula (lb):

-(D-BTD) _x -(D-BTZ) _y - (lb)

in which:

D represents a donor group having general formula (III):

in which R ₃ and R ₄ , the same or different, are selected from linear or branched, saturated or unsaturated Ci-C ₂ o alky! groups, preferably C ₂ -C ₁₀ , optionally containing heteroatoms;

BTD represents a benzothiadiazole group having general formula (V):

in which and X ₂ , mutually identical, represent a hydrogen atom; or a fluorine atom; or they are selected from linear or branched, saturated or unsaturated C _r C ₂ o alkyl groups, preferably C ₂ -Ci ₀ , optionally containing heteroatoms, linear or branched, saturated or unsaturated d-C ₂ o alkoxy groups, preferably C ₂ -Ci ₀ ;

11 BTZ represents a benzotriazole group having general formula (VI):

in which:

R ₅ is selected from linear or branched, saturated or unsaturated C ₁ -C ₂₀ aikyi groups, preferably C ₈ C _ia> optionally containing heteroatoms;

X-i and X ₂ , mutually identical, represent a hydrogen atom; or a fluorine atom; or they are selected from linear or branched, saturated or unsaturated Ci-C _2Q alkyi groups, preferably C ₂ -C ₁₀ , optionally containing heteroatoms, linear or branched, saturated or unsaturated CrC ₂₀ alkoxy groups, preferably C ₂ -C ₁₀ ;

provided that in at least one from the benzothiadiazole group having general formula (V) and the benzotriazole group having general formula (VI), X ₁ and X ₂ , mutually identical, represent a fluorine atom;

x is a number ranging from 0.2 to 100, preferably ranging from 0.4 to 20;

y is a number ranging from 0.2 to 100, preferably ranging from 0.4 to 20.

For the purpose of the present description and of the following claims, the definitions of the numeric ranges always include the extremes unless specified otherwise.

For the purpose of the present description and of the following claims, the term

"comprising" also includes the terms "which essentially consists of or "which consists of.

For the purpose of the present description and of the following claims, the term "CrC ₂₀

12 a Iky I group" means an alkyl group having from 1 to 20 carbon atoms, linear or branched. Specific examples of C C ₃₂ alkyl groups are: methyl, ethyl, propyl, iso- propyl, butyl, f-butyl, hexyl, heptyl, octyl, decyl, tetradecyl, dodecyl, hexadecyl, octadecyl, eicosyl, 1 -ethyl propyl, 1-butylpentyl, 1-hexylheptyl, 1-octylnonyl, 1- dodecyltridecyl, 1 -hexadecylheptadecyl, 1 -octadecylnonadecyl, 2-ethylhexyl, 2- ethyloctyl, 2-ethyldecyl, 2-ethyldodecyl, 2-butylhexyl, 2-butyldodecyl, 2-hexyloctyl, 2- hexyldecyl, 2-octyldecyl, 2-decyldodecyl, 3-ethyl hexyl, 4-butylhexyl, 4-butyloctyl, 4- butyldecyl, 4-butyldodecyl, 4-hexyldecyl, hexanoyl, octanoyl, decanoyl.

The term "alkyl groups C ₁ -C ₂₀ optionally containing heteroatoms" means alkyl groups having from 1 to 20 carbon atoms, linear or branched, saturated or unsaturated, wherein at least one of the hydrogen atoms is substituted with a heteroatom selected from halogens, for example, fluorine, chlorine, bromine, preferably fluorine; nitrogen; sulfur; oxygen. Specific examples of C C ₂₀ alkyl groups optionally containing heteroatoms are: fluoromethyl, difluoromethyl, trifluoromethyl, trichloromethyl, 2,2,2- trifluoroethyl, 2,2,2-trichloroethyl, 2,2,3,3-tetrafluoropropyl, 2,2,3,3,3-pentafluoropropyl, perfluoropentyl, perfluoroctyl, perfluorodecyl, oxymethyl, thiomethyl, thioethyl, thiohexanoyl, thiooctanoyl, thiodecanyl, dimethylamine, propylamine, dioctylamine. The term "C^C^ alkoxy groups" means groups comprising an oxygen atom to which a linear or branched, saturated or unsaturated C-C ₂₀ alkyl group is bonded. Specific examples of Ci-C ₂₀ alkoxy groups are: methoxyl, ethoxyl, n-propoxyl, so-propoxyl, n- butoxyl, /so-butoxyl, f-butoxyl, pentoxyl, hexyloxyl, 2-ethylhexyloxyl, 3-ethyl hexyloxyl, heptyloxyl, octyloxyl, nonyloxyl, decyloxyl, dodecyloxyl.

In accordance with a preferred embodiment of the present invention, said photoactive fiuorinated conjugated copolymer may have an average molecular weight (Mw) ranging from 20 kDa to 200 kDa, preferably ranging from 30 kDa to 180 kDa. Said average

13 molecular weight ( w) may be calculated as specified below.

In accordance with a preferred embodiment of the present invention, said photoactive fluorinated conjugated copolymer may have a number average molecular weight (Mn) ranging from 10 kDa to 100 kDa, preferably ranging from 12 kDa to 80 kDa. Said number average molecular weight (Mn) may be calculated as specified below.

The photoactive fluorinated conjugated copolymer according to the present invention may be synthesized through processes known in the state of the art such as, for example, the Stiile reaction, the Suzuki reaction, as described, for example, in patent application US 2012/0157357; or by Kotowski D. et al., in "Journal uf Materials

Chemistry A" (2013), 1 , pag. 10736-10744.

Further details relating to the synthesis process of said photoactive fluorinated conjugated copolymer are provided in the examples below.

Said photoactive fluorinated conjugated copolymer may be used in the manufacture of photovoltaic devices (or solar devices) such as, for example, photovoltaic cells (or solar cells), photovoltaic modules (or solar modules), either on rigid support, or on flexible support.

The present invention therefore also relates to the use of said photoactive fluorinated conjugated copolymer in the manufacture of photovoltaic devices (or solar devices) such as, for example, photovoltaic cells (or solar cells), photovoltaic modules (or solar modules), either on rigid support, or on flexible support.

Further subject matter of the present invention is a photovoltaic device (or solar device) thai may be selected, for example, from photovoltaic cells (or solar cells), photovoltaic modules (or solar modules), either on rigid support, or on flexible support, comprising at least one photoactive fluorinated conjugated copolymer described above.

For the purpose of understanding the present invention better and to put it into practice,

14 below are some illustrative and non-limitative examples thereof.

Characterisation of the copgiymers obtained

Determination of the molecular eight

The molecular weight of the copolymers obtained operating in accordance with the following examples, was calculated through Gel Permeation Chromatography (GPC) on Agilent 220 equipment, using HT5432 columns, with trichlorobenzene eluent, at

100°C.

The average molecular weight (Mw) and the number average molecular weight (Mn) are provided.

EXAMPLE 1

The following components were introduced into a 100 ml three-necked flask, equipped with a mechanical stirrer, in a nitrogen atmosphere:

2.782 g (3.6 mmoles) of (4,8-bis(3-ethylhexyloxy)benzo[1 ,2-b;4,5-b']dithiophene-

2,6-diyl)bis(trimethylstannane) having formula (1 ) (Suntech Inc.);

991.2 mg (1.8 mmoles) of 4,7-dibromo-4,6-difluorobenzo[c][1 ,2,5]thiadiazole having formula (2) (Suntech Inc.);

595.1 mg (1.8 mmoles) of 4,7-dibromo-2-(2-nonyloctyl)-5 _> 6-difluoro-2H- benzo[d][1 ,2,3]triazole having formula (3) (Suntech Inc.);

20 ml of distilled toluene (Aldrich).

The reaction mixture obtained was heated to 70°C and subsequently 40 mg (0.032

15 mmol) of tetrakis triphenylphosphine palladium [Pd(PPh ₃ ) ₄ ] (Aldrich) and 5 ml of distilled toluene (Aldrich) were added. Subsequently, the reaction mixture obtained was brought to boiling point and left to react for 40 hours. Subsequently, 1 ml of

bromobenzene (Aldrich) was added and, after 4 hours, 2 ml of

trimethylstannylthiophene (Aldrich): everything was left to react for 4 hours after which methanol (250 ml) (Aldrich) was added, obtaining a precipitate. The precipitate obtained was extracted in a Soxhiet extractor using, in succession, methanol (500 ml) (Aldrich), acetone (500 ml) (Aldrich) and heptane (500 ml) (Aldrich), 8 hours for each extraction, obtaining a solid product. The solid product thus obtained was subjected to further extraction in a Soxhiet extractor with chloroform (500 ml) (Aldrich). The solution obtained was concentrated in a rotary evaporator and precipitated in methanol (250 ml) (Aldrich). The precipitate obtained was dried in the stove, at 55°C, all night, obtaining 510 mg of a blue coloured solid (copolymer P1 ) which was subjected to determination of the molecular weight, obtaining the following values:

average molecular weight (Mw) = 36 kDa;

number average molecular weight (Mn) = 15 kDa.

EXAMPLE 2

The following components were introduced into a 100 ml three-necked flask, equipped with a mechanical stirrer, in a nitrogen atmosphere:

2.4997 g (3.24 mmoles) of (4,8-bis(3-ethy!hexyloxy)benzo[1 ,2-b;4,5-

16 b']dithiophene-2,6-diyl)bis(trimethylstannane) having formula (1 ) (Suntech Inc.); 890.4 mg (1.6178 mmoles) of 4,7-dibromo-5,6-bis(octyloxy)benzo-2,1 ,3- thiadiazole having formula (4) (Suntech Inc.);

892.8 mg (1.6134 mmoles) of 4,7-dibromo-2-(2-nonyloctyl)-5,6-difluoro-2H- benzo[d][1 ,2,3]triazole having formula (3) (Suntech Inc.);

20 ml of distilled toluene (Aldrich).

The reaction mixture obtained was heated to 70°C and subsequently 40 mg (0.032 mmol) of tetrakis triphenylphosphine palladium [Pd(PPh ₃ ) ₄ ] (Aldrich) and 2 ml of distilled toluene (Aldrich) were added. Subsequently, the reaction mixture obtained was brought to boiling point and left to react for 40 hours. Subsequently, 1 ml of

bromobenzene (Aldrich) was added and, after 4 hours, 2 ml of

trimethylstannylthiophene (Aldrich); everything was left to react for 4 hours after which methanol (250 ml) (Aldrich) was added, obtaining a precipitate. The precipitate obtained was extracted in a Soxhiet extractor using, in succession, methanol (500 ml) (Aldrich), acetone (500 ml) (Aldrich) and heptane (500 ml) (Aldrich), 8 hours for each extraction, obtaining a solid product. The solid product thus obtained was subjected to further extraction in a Soxhiet extractor with chloroform (500 ml) (Aldrich). The solution obtained was concentrated in a rotary evaporator and precipitated in methanol (250 ml) (Aldrich). The precipitate obtained was dried in the stove, at 55°C, all night, obtaining 2.5 g of a blue coloured solid (copolymer P2) which was subjected to determination of the molecular weight, obtaining the following values:

average molecular weight (Mw) = 85 kDa;

number average molecular weight (Mn) = 39 kDa.

EXAMPLE 3

Syntiieg g: of copolymer having formu Sa ( P31

17

The following components were introduced into a 100 ml three-necked flask, equipped with a mechanical stirrer, in a nitrogen atmosphere:

2.4735 g (3.20 mmoles) of (4 ₍ 8-bis(3-ethylhexyloxy)benzo[ ,2-b;4,5- b']dithiophene-2,6-diyl)bis(trimethylstannane) having formula (1 ) (Suntech Inc.);

527.9 mg (1.6 mmoles) of 4,7-dibromo 4,6-difluorobenzo[c][1 ,2,5]thiadiazole having formula (2) (Suntech Inc.);

827.8 mg (1.6 mmoles) of 4,7-dibromo-2-(2-nonyloctyl)-benzo[d][1 ,2,3]triazole having formula (5) (Suntech Inc.);

20 ml of distilled toluene (Aldrich).

The reaction mixture obtained was heated to 70°C and subsequently 34 mg (0.029 mmol) of tetrakis triphenylphosphine palladium [Pd(PPh ₃ ) ₄ ] (Aldrich) and 2 ml of distilled toluene (Aldrich) were added. Subsequently, the reaction mixture obtained was brought to boiling point and left to react for 40 hours. Subsequently, 1 ml of

bromobenzene (Aldrich) was added and, after 4 hours, 2 ml of

trimethylstannylthiophene (Aldrich): everything was left to react for 4 hours after which methanol (250 ml) (Aldrich) was added, obtaining a precipitate. The precipitate obtained was extracted in a Soxhiet extractor using, in succession, methanol (500 ml) (Aldrich), acetone (500 ml) (Aldrich) and heptane (500 ml) (Aldrich), 8 hours for each extraction, obtaining a solid product. The solid product thus obtained was subjected to further extraction in a Soxhiet extractor with chloroform (500 ml) (Aldrich). The solution obtained was concentrated in a rotary evaporator and precipitated in methanol (250 ml)

18 (Aldrich). The precipitate obtained was dried in the stove, at 55°C, all night, obtaining 2 g of a blue coloured solid (copolymer P3) which was subjected to determination of the molecular weight, obtaining the following values:

average molecular weight (Mw) = 153 kDa;

number average molecular weight (Mn) = 42 kDa.

EXAMPLE 4

Synthesis gf eogoiymer ha in formula (f¾

(!)

The following components were introduced into a 50 ml three-necked flask, equipped with a mechanical stirrer, in a nitrogen atmosphere:

1.0089 g (1.31 mmoles) of (4,8-bis(3-ethylhexyloxy)benzo[1 ,2-b;4,5- b']dithiophene-2,6-diyl)bis(trimethylstannane) having formula (1 ) (Suntech Inc.);

192.6 mg (0.655 mmoles) of 4,7-dibromo-benzo[c][1 ,2,5]thiadiazole having formula (6) (Suntech Inc.);

361.2 mg (0.655 mmoles) of 4,7-dibromo-2-(2-nonyloctyl)-5,6-difiuoro-2H- benzo[d][1 ,2,3]triazole having formula (3) (Suntech Inc.);

20 ml of distilled toluene (Aldrich).

The reaction mixture obtained was heated to 70°C and subsequently 20 mg (0.017 mmol) of tetrakis triphenylphosphine palladium [Pd(PPh ₃ ) ] (Aldrich) and 2 ml of distilled toluene (Aldrich) were added. Subsequently, the reaction mixture obtained was brought to boiling point and left to react for 40 hours. Subsequently, 1 ml of

bromobenzene (Aldrich) was added and, after 4 hours, 2 ml of

19 trimethy!stannylihsophene (Aldrich): everything was left to react for 4 hours after which methanol (250 ml) (Aldrich) was added, obtaining a precipitate. The precipitate obtained was extracted in a Soxhlet extractor using, in succession, methanol (500 ml) (Aldrich), acetone (500 ml) (Aldrich) and heptane (500 ml) (Aldrich), 8 hours for each extraction, obtaining a solid product. The solid product thus obtained was subjected to further extraction in a Soxhlet extractor with chloroform (500 ml) (Aldrich), the soiuiion obtained was concentrated in a rotary evaporator and precipitated in methanol (250 ml) (Aldrich). The precipitate obtained was dried in the stove, at 55X, all night, obtaining 717 mg of a blue coloured solid (copolymer P4) which was subjected to determination of the molecular weight, obtaining the following values:

average molecular weight (Mw) ~ 92 kDa;

number average molecular weight ( n) ^~ 31 kDa.

20