# Patent

## Title
Comb copolymer and process for the preparation thereof

## Abstract

A comb copolymer having a backbone of 2-acrylamido-2-methylpropanesulfonic acid, with grafted lateral side segments of poly(N-alkylacrylamide) or poly(N,N-dialkylacrylamide), is provided. A process for the preparation of the comb copolymer includes reacting a compound of formula (II) with a compound of formula (III) in a (tert-butanol)-water mixture, to obtain a poly(N-alkylacrylamide) or poly(N,N-dialkylacrylamide) telomere of formula (I); reacting in tert-butanol the telomer of formula (I) with an acid chloride of formula (IV) to obtain a solution of the macromonomer of formula (V); and copolymerizing in tert-butanol the macromonomer of formula (V) with an ammonium salt of 2-acrylamido-2-methylpropanesulfonic acid.

## Background
The present patent application has as subject matter a novel process for the preparation of water-soluble grafted copolymers.
Heat-thickening polymers are polymers, the viscosity of which varies considerably as a function of the temperature. They are characterized in particular by a “critical” temperature, above which the viscosity of their aqueous solution very markedly increases, generally by a factor of several tens.
International application WO 00/40958 describes a process for the preparation of copolymers of acrylamide and of poly(N-isopropylacrylamide) which includes the following successive stages:

    (a) the synthesis of an N-isopropylacrylamide (NIPAM) telomer by radical polymerization;
    (b) isolation of the telomer obtained, (PNIPAM)x-NH2, by precipitation from ether, filtration and then drying;
    (c) the reaction in methylene chloride of (PNIPAM)x-NH2 with a large excess acrylic acid in the presence of cyclohexylcarbodiimide to result in the poly(NIPAM) macromonomer carrying an acryloyl functional group at the (PNIPAM)x chain end;
    (d) the isolation of the macromonomer obtained by precipitation from ether, filtration and then drying;
    (e) the copolymerization of the macromonomer obtained with acrylamide (AM) or dimethylacrylamide (DMA) in water, in order to obtain the grafted copolymers comprising a (PNIPAM)x segment, AM-g-(PNIPAM)x or DMA-g-(PNIPAM)x;
    (f) the purification by precipitation from water for DMA/(PNIPAM)x or from acetone for AM/(PNIPAM)x, followed by ultrafiltration.


The international application published under the number WO 2007/000535 discloses a process for the preparation of grafted polymers, while limiting as much as can be done the use of organic solvents, and more particularly a process for the preparation of a comb copolymer, the backbone of which is of the acrylamide, acrylic acid, acryloylaminoethanol or dimethylacrylamide type, to which poly(N-alkylacrylamide) or poly(N,N-dialkylacrylamide) side segments are grafted, comprising the following successive stages:
(a) the preparation of a poly(N-alkylacrylamide) or poly(N,N-dialkylacrylamide) telomer, of formula (I):

H2N—R1—Z—{CH2—C(R2)[C(═O)N(R3)(R4)]—}n—H  (I)

in which n represents an integer greater than or equal to 2 and less than or equal to 100, Z represents a functional group capable of acting as radical transfer agent, R1 represents a divalent radical comprising from 1 to 4 carbon atoms, R2 represents a hydrogen atom or a methyl radical, R3 represents a hydrogen atom or a linear or branched alkyl radical comprising from 1 to 4 carbon atoms and R4, which is identical to or different from R3, represents a linear or branched alkyl radical comprising from 1 to 4 carbon atoms, by reaction in water of a compound of formula (II):

CH2═C(R2)—C(═O)N(R3)(R4)  (II)

in which R2, R3 and R4 are as defined above, with a chain-limiting compound of formula (III):

—R1—NH2  (III)

in which Z represents a functional group capable of acting as radical transfer agent, in a (II)/(III) molar ratio of less than or equal to n and greater than or equal to n/10, in the presence of a polymerization initiator;

(b) the isolation of the telomer of formula (I) obtained in stage (a);
(c) the reaction in water of the telomer of formula (I) obtained in stage (b) with the acid chloride of formula (IV):

CH2═C(R5)—C(═O)—Cl  (IV)

in which R5 represents a hydrogen atom or a methyl radical and in a (IV)/(III) molar ratio of less than or equal to 10 and greater than or equal to 1, while maintaining the pH of the reaction medium at a value of between 6 and 13 and preferably between 7 and 8, in order to obtain a macromonomer of formula (V):

CH2═C(R5)—C(═O)NH—R1—Z—{CH2—C(R2)[C(═O)N(R3)(R4)]—}n—H  (V)

(d) the isolation of the macromonomer of formula (V) obtained in stage (c);
(e) the copolymerization in water of the macromonomer of formula (V) isolated in stage (d) with a monomer chosen from acrylamide, acrylic acid, acryloylaminoethanol or dimethylacrylamide and, if desired;
(f) the purification of the comb copolymer obtained.
In point of fact, while the process thus disclosed operates perfectly when the main backbone is composed of a sequence of neutral monomers, it is not the same when it is desired to replace these neutral monomers with ionic monomers, such as acrylic acid or 2-acrylamido-2-methylpropanesulfonic acid (ATBS). This is because a salting out phenomenon occurs, which results in the polymerization of the macromonomer intended to form the pendant chains, such as the poly(N-isopropylacrylamide) macromonomer.
The inventors have thus attempted to develop a process which does not exhibit the disadvantage set out above.


For this reason, according to a first aspect, a subject matter of the invention is a process for the preparation of a comb copolymer, the backbone of which is of the 2-acrylamido-2-methylpropanesulfonic acid (ATBS) type, to which poly(N-alkylacrylamide) or poly(N,N-dialkylacrylamide) side segments are grafted, characterized in that it comprises the following successive stages:

    
    
        a stage (a) of reaction of a compound of formula (II):

CH2═C(R2)—C(═O)—N(R3)(R4)  (II)

in which R2 represents a hydrogen atom or a methyl group, R3 represents a hydrogen atom or a linear or branched alkyl radical comprising from 1 to 4 carbon atoms and R4, which is identical to or different from R3, represents a linear or branched alkyl radical comprising from 1 to 4 carbon atoms, with a chain-limiting compound of formula (III):

Z—R1—NH2  (III)

in which R1 represents a divalent radical comprising from 1 to 4 carbon atoms and Z represents a functional group capable of acting as radical transfer agent, in the presence of a polymerization initiator, in a tert-butanol/water mixture, in order to obtain a poly(N-alkylacrylamide) or poly(N,N-dialkylacrylamide) telomer of formula (I):

H2N—R1—Z—{CH2—C(R2)[C(═O)N(R3)(R4)]—}n—H  (I)

in which n represents an integer greater than or equal to 2 and less than or equal to 100 and Z represents a functional group capable of acting as radical transfer agent; optionally

        a stage (b) of isolation and/or of drying of said telomer of formula (I) obtained in stage (a);
        a stage (c) of reaction in tert-butanol of the telomer of formula (I) obtained in stage (a) or optionally in stage (b) with an acid chloride of formula (IV):

CH2═C(R5)—C(═O)—Cl  (IV)

in which R5 represents a hydrogen atom or a methyl radical, in a (IV)/(III) molar ratio of less than or equal to 10 and greater than or equal to 1, while maintaining the pH of the reaction medium at a value of between 8 and 10, in order to obtain a solution of the macromonomer of formula (V):

CH2═C(R5)—C(═O)NH—R1—Z—{CH2—C(R2)[C(═O)N(R3)(R4)]—}n—H  (V)

optionally

        a stage (d) of isolation and/or of drying of said macromonomer of formula (V) obtained in stage (c);
        a stage (e) of copolymerization in tert-butanol of the macromonomer of formula (V) resulting from stage (c) or from stage (d) with the ammonium salt of 2-acrylamido-2-methylpropanesulfonic acid and, if desired;
        a stage (f) of purification of the comb copolymer obtained in stage (e).
    
    


tert-Butanol/water mixture denotes, in the process as defined above, a mixture for which the proportion by volume of water is less than or equal to 50%.
According to a specific aspect of the process as defined above, in the formula (II), R2 and R3 each represent a hydrogen atom and R4 represents an isopropyl radical.
Another subject matter of the invention is a comb copolymer, the backbone of which is of the 2-acrylamido-2-methylpropanesulfonic acid type, to which poly(N-alkyl(meth)acrylamide) or poly(N,N-dialkyl(meth)acrylamide) side segments are grafted, said side segments being chosen from the following side segments:

    
    
        poly(N-methylmethacrylamide) side segments,
        poly(N-ethylmethacrylamide) side segments,
        poly(N-propylmethacrylamide) side segments,
        poly(N-isopropylmethacrylamide) side segments,
        poly[N-(2-hydroxyethyl)methacrylamide] side segments,
        poly(N,N-dimethylmethacrylamide) side segments,
        poly(N,N-diethylmethacrylamide) side segments,
        poly(N-methylacrylamide) side segments,
        poly(N-ethylacrylamide) side segments,
        poly(N-propylacrylamide) side segments,
        poly(N-isopropylacrylamide) side segments,
        poly[N-(2-hydroxyethyl) acrylamide] side segments,
        poly(N,N-dimethylacrylamide) side segments,
        poly(N,N-diethylacrylamide) side segments,

and more particularly a comb copolymer as defined above in which said side segments are chosen from the following side segments:

        poly(N-isopropylacrylamide) side segments,
        poly[N-(2-hydroxyethyl)acrylamide] side segments,
        poly(N,N-dimethylacrylamide) side segments and
        poly(N,N-diethylacrylamide) side segments.
    
    


The following example illustrates the invention without, however, limiting it. It demonstrates that it is possible to prepare comb polymers without an acrylamide backbone comprising side segments of N-alkylacrylamide type which are heat-thickening.
Preparation of a Comb Copolymer Comprising a Backbone of ATBS Type, to which Poly(N-Isopropylacrylamide) Side Segments are Grafted ATBS-g-NIPAM
(1) Preparation of a poly(N-isopropyl acrylamide) telomer
435 g of N-isopropylacrylamide (NIPAM) are dissolved in a tert-butanol/water mixture (50/50 by volume) in a thermostatically controlled reactor until 1000 g are reached, and stirring is carried out under nitrogen sparging for approximately one and a half hours. 2-Aminoethanethiol hydrochloride (AET.HCl) is subsequently added in a predetermined NIPAM/AET.HCl molar ratio of approximately 48/1. The polymerization is initiated with dilauroyl peroxide by bringing the temperature to 60° C. and then the reaction medium is left stirring and under nitrogen sparging for a further 2 hours. A white and pasty final reaction mixture is obtained.
(2) Preparation of the Macromonomer
A solution of potassium hydroxide (0.16 N) in tert-butanol and acryloyl chloride are added to the reaction medium obtained in stage (1) maintained at a temperature of 10° C., while maintaining the pH in the vicinity of 9. At the end of the reaction, the content of NIPAM macromonomer is 17.8% by weight and the water content is 10.7% by weight.
(3) Synthesis of the Copolymer
61.8 g of the reaction medium obtained in stage (2) are diluted in 170 g of tert-butanol in the reactor thermostatically controlled at 15° C. 77 g of the ammonium salt of 2-acrylamido-2-methylpropanesulfonic acid and then 0.44 g of trimethylolpropane triacrylate are added thereto. The polymerization is initiated with dilauroyl peroxide and the medium is left stirring for four hours while maintaining the temperature at 60° C.
The polymer which precipitated during the polymerization is recovered by filtration. After drying, the desired copolymer is obtained in the powder form.
It is found that a 1% by weight solution of the polymer in water is slightly viscous. After heating above 80° C., there is formation of a gel, which is characteristic of a heat-thickening polymer.

## Claims

1. A method for the preparation of a comb copolymer, the comb copolymer comprising a backbone comprising 2-acrylamido-2-methylpropanesulfonic acid, with grafted poly(N-alkylacrylamide) or poly(N,N-dialkylacrylamide) side segments, the method comprising the following successive stages:
(a) reaction of a compound of formula (II):


CH2═C(R2)—C(═O)—N(R3)(R4)  (II)



in which
R2 represents a hydrogen atom or a methyl group,
R3 represents a hydrogen atom or a linear or branched alkyl radical comprising from 1 to 4 carbon atoms, and
R4, which is identical to or different from R3, represents a linear or branched alkyl radical comprising from 1 to 4 carbon atoms,
with a chain-limiting compound of formula (III):


Z—R1—NH2  (III)



in which
R1 represents a divalent radical comprising from 1 to 4 carbon atoms and Z represents a functional group capable of acting as radical transfer agent,
in the presence of a polymerization initiator, in a tert-butanol/water mixture, to obtain a poly(N-alkylacrylamide) or poly(N,N-dialkylacrylamide) telomer of formula (I):


H2N—R1—Z—{CH2—C(R2)[C(═O)N(R3)(R4)]—}n'H  (I)



in which
n represents an integer greater than or equal to 2 and less than or equal to 100 and Z represents a functional group capable of acting as radical transfer agent; optionally
(b) isolation and/or of drying of said telomer of formula (I) obtained in stage (a);
(c) reaction in tert-butanol of the telomer of formula (I) obtained in stage (a) or optionally in stage (b) with an acid chloride of formula (IV):


CH2═C(R5)—C(═O)—Cl  (IV)



in which R5 represents a hydrogen atom or a methyl radical,
in a (IV)/(III) molar ratio of 1 to 10 inclusive, while maintaining the pH of the reaction medium at a value of between 8 and 10, to obtain a solution of a macromonomer of formula (V):


CH2═C(R5)—C(═O)NH—R1—Z—{CH2—C(R2)[C(═O)N(R3)(R4)]—}n—H  (V),



optionally
(d) isolation and/or of drying of said macromonomer of formula (V) obtained in stage (c);
(e) copolymerization in tert-butanol of the macromonomer of formula (V) resulting from stage (c) or from stage (d) with an ammonium salt of 2-acrylamido-2-methylpropanesulfonic acid, and optionally
(f) purification of the comb copolymer obtained in stage (e).

2. The method as defined in claim 1, wherein in the formula (II), R2 and R3 each represent a hydrogen atom and R4 represents an isopropyl radical.

3. The method as defined in claim 1, wherein said side segments are selected from the group consisting of
poly(N-methylmethacrylamide) side segments,
poly(N-ethylmethacrylamide) side segments,
poly(N-propylmethacrylamide) side segments,
poly(N-isopropylmethacrylamide) side segments,
poly[N-(2-hydroxyethyl)methacrylamide] side segments,
poly(N,N-dimethylmethacrylamide) side segments,
poly(N,N-diethylmethacrylamide) side segments,
poly(N-methylacrylamide) side segments,
poly(N-ethylacrylamide) side segments,
poly(N-propylacrylamide) side segments,
poly(N-isopropylacrylamide) side segments,
poly[N-(2-hydroxyethyl) acrylamide] side segments,
poly(N,N-dimethylacrylamide) side segments, and
poly(N,N-diethylacrylamide) side segments.

4. The method as defined in claim 1, wherein said side segments are selected from the group consisting of
poly(N-isopropylacrylamide) side segments,
poly[N-(2-hydroxyethyl)acrylamide] side segments,
poly(N,N-dimethylacrylamide) side segments, and
poly(N,N-diethylacrylamide) side segments.