METHOD FOR THE PREPARATION OF COPOLYMERS OF ALKYL METHACRYLATES AND MALEIC ANHYDRIDE

Abstract

A method for the preparation of a sulfur-free copolymer proceeds by solution polymerization in the presence of a radical initiator, wherein the copolymer contains at least one alkyl methacrylate and maleic anhydride having a number average molecular weight of 3000 to 9000 g/mol.

Claims

1. A method for the preparation of a sulfur-free copolymer comprising an alkyl methacrylate monomer unit and a maleic anhydride monomer unit by solution polymerization of one or more alkyl methacrylates and maleic anhydride in a solvent in the presence of a radical initiator, said method comprising: a) providing an initial reaction solution comprising a portion of the one or more alkyl methacrylates, a portion of the maleic anhydride, a portion of the initiator and a portion of the solvent; b) adding a first feed solution comprising a further portion of the maleic anhydride and a further portion of the solvent to the initial reaction solution, and without any initiator; and c) adding a second feed solution comprising a further portion of the one or more alkyl methacrylates, and a portion of the radical initiator to the initial reaction solution, wherein the additions of both first and second feed solutions are started at the same time, and the duration of the additions of the first and second feed solutions are adjusted such that addition of the first feed solution is completed faster than the addition of the second feed solution, and wherein the sulfur-free copolymer has a number average molecular weight of 3000 to 9000 g/mol, being the number average molecular weight determined by gel permeation chromatography against poly(methyl methacrylate) standards, and a polydispersed index in the range of 1 to 5, being the polydispersed index determined by gel permeation chromatography against poly(methyl methacrylate) standards, and wherein a molar ratio of the one or more alkyl methacrylates to the maleic anhydride in the sulfur-free copolymer is in the range of from 10:1 to 1:1, based on the total molar amounts of the one or more alkyl methacrylates and maleic anhydride used for the preparation of the sulfur-free copolymer.

2. The method according to claim 1, wherein the first and second feed solutions are added over the course of 30 minutes to 12 hours.

3. The method according to claim 1, wherein the first feed solution is added to the initial reaction solution over the course of 2 to 4 hours and the second feed solution is added to the initial solution over the course of 5 to 7 hours.

4. The method according to claim 1, wherein the first feed solution is added to the initial reaction solution over the course of 2.5 to 3.5 hours and the second feed solution is added to the initial solution over the course of 5.5 to 6.5 hours.

5. The method according to claim 1, wherein the portion of the one or more alkyl methacrylates in the initial reaction solution is 5 to 25 wt-% based on the total amount of the one or more alkyl methacrylates.

6. The method according to claim 1, wherein the portion of the one or more alkyl methacrylates in the second feed solution is 75 to 95 wt-% based on the total amount of the one or more alkyl methacrylates.

7. The method according to claim 1, wherein the sum of the portions of the one or more alkyl methacrylates in the initial reaction solution and in the second feed solution is 50 to 100 wt-% based on the total amount of the one or more alkyl methacrylates.

8. The method according to claim 1, wherein the portion of the maleic anhydride in the initial reaction solution is 5 to 25 wt-% maleic anhydride based on the total amount of maleic anhydride.

9. The method according to claim 1, wherein the portion of the maleic anhydride in the first feed solution is 75 to 95 wt-% maleic anhydride based on the total amount of maleic anhydride.

10. The method according to claim 1, wherein the sum of the portions of the maleic anhydride in the initial reaction solution and in the first feed solution is 50 to 100 wt-% based on the total amount of the maleic anhydride.

11. The method according to claim 1, wherein the total amount of the one or more alkyl methacrylates and the maleic anhydride is in the range of 10 to 60 wt-% relative to the total weight of the sum of the initial reaction solution and the first feed solution and the second feed solution.

12. The method according to claim 1, wherein at least 80 mol-% of the one or more alkyl methacrylates is selected from the group of C.sub.6 to C.sub.22 alkyl methacrylates, or a mixture thereof.

13. The method according to claim 1, wherein a portion or all of the solvent is selected from the group consisting of methyl ethyl ketone, isobutyl methyl ketone, anisole, n-butanol, dimethylformamide , dimethyl sulfoxide, benzene (petroleum ether), acetone, 1-hexene, ethanol, ortho-xylene, and mixtures thereof.

14. A sulfur-free copolymer obtained by the method as defined in claim 1, wherein the number average molecular weight of the copolymer is in the range of 3000 to 9000 g/mol, wherein the number average molecular weight is determined by gel permeation chromatography against poly(methyl methacrylate) standards, and the polydispersed index of the copolymer is in the range of 1 to 5, wherein the polydispersed index is determined by gel permeation chromatography against poly(methyl methacrylate) standards, and the molar ratio of the one or more alkyl methacrylates to the maleic anhydride in the resulting copolymer is in the range of from 10:1 to 1:1, based on the total molar amounts of the one or more alkyl methacrylates and maleic anhydride used for the preparation of the sulfur-free copolymer.

15. The sulfur-free copolymer according to claim 14, wherein the sulfur-free copolymer comprises equimolar amounts of the one or more alkyl methacrylates and maleic anhydride, based on the total molar amounts of the one or more alkyl methacrylates and maleic anhydride used for the preparation of the sulfur-free copolymer.

Description

EXAMPLES

[0055] The following examples illustrate the present invention. In these examples, the following abbreviations are used:

TABLE-US-00001 MIBK methyl isobutyl ketone LMA lauryl methacrylate, comprising a mixture of linear C12, C14 and C16 methacrylates LA lauryl acrylate, comprising a mixture of linear C12, C14 and C16 acrylates SMA stearyl methacrylate, comprising a mixture of linear C14, C16, and C18 methacrylates SA stearyl acrylate, comprising a mixture of linear C14, C16, and C18 acrylates BeMA behenyl methacrylate, comprising a mixture of C18, C20 and C22 methacrylates BeA behenyl acrylate, comprising a mixture of C18, C20 and C22 acrylates IDMA isodecyl methacrylate DPMA dodecyl pentadecyl methacrylate, comprising a mixture of branched and linear C12, C13, C14 and C15 methacrylates DPA dodecyl pentadecyl acrylate, comprising a mixture of branched and linear C12, C13, C14 and C15 acrylates MSA maleic anhydride

Example 1

[0056] Several copolymers of alkyl methacrylate and maleic anhydride were prepared using the method of the present invention and using different alkyl methacrylates and different comonomer molar ratios according to the following general procedure.

[0057] Solvent (MIBK), a part of the alkyl methacrylate, a part of maleic anhydride and a part of initiator (tert-butyl peroxy-2-ethylhexanoate) were added to the reaction vessel. The mixture was heated to a temperature of 90° C. to dissolve the reactant. A first feed solution comprising the rest of the maleic anhydride was added to the reaction vessel over a period of 3 hours. A second feed solution comprising the rest of the alkyl methacrylate and the free radical initiator in methyl isobutyl ketone was added to the reaction vessel over a period of 6 hours, while stirring. The total amount of MIBK was 50 wt-%, based on the total mass of the monomers and the solvent unless otherwise noted. Addition of the first and second feed solutions was started at the same time. A final additional dosage of initiator was added 2 hours after the feed solutions had been completely added. The copolymerization mixture was stirred over night before the reaction was stopped.

[0058] Copolymer 1 was prepared from a monomer mixture comprising 51 wt-% LMA, 23 wt-% SMA, and 26 wt-% MSA, based on the total amount of monomers. The initial reaction solution comprised 11.1% of the alkyl methacrylates, 11.1% of the MSA, 53.8% of the MIBK. The amount of initiator used was 1.12 wt-% in the initial reaction solution, 1.78 wt-% in the second feed solution, and 0.2 wt-% in the solution of the final additional initiator dosage, based on the total amount of monomers.

[0059] Copolymer 2 was prepared from a monomer mixture comprising 56.9 wt-% SMA, 21.1 wt-% BeMA, and 22 wt-% MSA, based on the total amount of monomers. The initial reaction solution comprised 8.9% of the alkyl methacrylates, 11.1% of the MSA, 60.2% of the MIBK. The amount of initiator used was 2 wt-% in the initial reaction solution, 3.2 wt-% in the second feed solution, and 0.2 wt-% in the solution of the final additional initiator dosage, based on the total amount of monomers.

[0060] Copolymer 3 was prepared from a monomer mixture comprising 82 wt-% IDMA and 18 wt-% MSA, based on the total amount of monomers. The initial reaction solution comprised 10.3% of the alkyl methacrylates, 11.1% of the MSA, 66.6% of the MIBK. The amount of initiator used was 2.3 wt-% in the initial reaction solution, 3.6 wt-% in the second feed solution, and 0.2 wt-% in the solution of the final additional initiator dosage, based on the total amount of monomers.

[0061] Copolymer 4 was prepared from a monomer mixture comprising 22.1 wt-% LMA, 62.9 wt-% SMA, and 15 wt-% MSA, based on the total amount of monomers. The initial reaction solution comprised 11.1% of the alkyl methacrylates, 11.1% of the MSA, 73.5% of the MIBK. The amount of initiator used was 2.5 wt-% in the initial reaction solution, 4 wt-% in the second feed solution, and 0.2 wt-% in the solution of the final additional initiator dosage, based on the total amount of monomers.

[0062] Copolymer 5 was prepared from a monomer mixture comprising 70 wt-% LMA and 30 wt-% MSA, based on the total amount of monomers. The initial reaction solution comprised 3.7% of the alkyl methacrylates, 3.7% of the MSA, 11.7% of the MIBK. The total amount of MIBK was 40 wt-%, based on the total mass of the monomers and the solvent. The amount of initiator used was 0.1 wt-% in the initial reaction solution, 1.3 wt-% in the second feed solution, and 0.2 wt-% in the solution of the final additional initiator dosage, based on the total amount of monomers.

[0063] The crude reaction product containing the copolymers of alkyl methacrylate and maleic anhydride was analyzed by gel permeation chromatography (GPC) against poly(methyl methacrylate) standards to determine the number average molecular weight M.sub.n and the weight average molecular weight M. A mixture of 0.2 wt-% trifluoroacetic acid in tetrahydrofuran (THF) is used as eluent. To determine the conversion rate of maleic anhydride, the residual amount of maleic anhydride in the crude reaction product was determined by high pressure liquid chromatography (HPLC). The residual amount of alkyl methacrylate was also determined by HPLC. HPLC was carried out using tetrahydrofuran as solvent and a Nucleosil 100-7 C.sub.18 column (125×4.6 mm). The eluent was 0.06 to 5 M phosphate buffer at a pH of 2.

[0064] The following table 1 shows the number average molecular weight data of several copolymers (Copolymers No. 1 to 5), and the residual alkyl methacrylate and maleic anhydride contents of the crude reaction products prepared using different alkyl methacrylates and comonomer molar ratios in the monomer mixture.

TABLE-US-00002 TABLE 1 Residual Residual alkyl maleic methacrylates anhydride [weight %, [weight %, Comonomer Alkyl based on based on molar ratio methacrylate the total the total (alkyl composition weight of weight of Reaction methacrylate: based on C M.sub.n M.sub.w the reaction the reaction yield maleic No. alkyl chain [g/mol] [g/mol] PDI solution (*)] solution (*)] [%] anhydride) 1 C12, C14, 6100 17600 2.93 <0.05 0.25 99.4 1:1 C16, C18 linear 2 C14, C16, 6010 15200 2.52 0.08 0.004 99.8 C18, C20, C22 linear 3 C10 5770 14000 2.43 0.11 0.004 99.8 2:1 branched 4 C12, C14, 5560 15200 2.74 0.77 0.001 98.5 C16, C18 linear 5 C12, C14, 5430 19100 3.51 0.75 0.03 98.7 1:1 C16 linear (*) the total weight of the reaction solution corresponds to total weight of the initial reaction solution, the two feed solutions and the solution of the final initiator dosage

[0065] As shown in Table 1, the claimed process for the specific preparation of maleic anhydride-alkyl methacrylate copolymers gives excellent conversions of both monomers maleic anhydride and alkyl methacrylate. Indeed, the residual amount of maleic anhydride according to the claimed process is never higher than 0.25 weight % and the residual amount of alkyl methacrylate according to the claimed process is never higher than 0.77 weight %, based on the total weight of the reaction solution (see Table 1 above). Consequently, the compositions of the copolymers obtained by the claimed process correspond to the compositions of the respective monomers in the reaction mixture.

[0066] Furthermore, the copolymers obtained according to the claimed process have the desired number average molecular weights (all below 9000 g/mol) and are obtained with excellent yields of minimum 98.5%.

Example 2 (Comparative Example)

[0067] The following example illustrates a method for a solution polymerization according to EP 0636637 A2.

[0068] A solution of maleic anhydride in toluene was fed into a reaction vessel and heated to the reaction temperature of 80° C. When the maleic anhydride had dissolved, a radical initiator (AKIN) in toluene was introduced into the reaction vessel. A solution of alkyl methacrylate or alkyl acrylate was added to the reaction vessel over a period of 4 hours.

[0069] Using this general procedure, examples 1, 2 and 3 of EP 0636637 A2 were reproduced to prepare eight different copolymers.

[0070] Copolymer 1 was prepared from 72.7 wt-% DPMA and 27.3 wt-% MSA, based on the total amount of monomers.

[0071] Copolymer 2 was prepared from 73.1 wt-% DPA and 26.9 wt-% MSA, based on the total amount of monomers.

[0072] Copolymer 3 was prepared from 73.7 wt-% DPMA and 26.3 wt-% MSA, based on the total amount of monomers.

[0073] Copolymer 4 was prepared from 76.1 wt-% SA and 23.9 wt-% MSA, based on the total amount of monomers.

[0074] Copolymer 5 was prepared from 76.9 wt-% SMA and 23.1 wt-% MSA, based on the total amount of monomers.

[0075] Copolymer 6 was prepared from 70 wt-% IDMA and 30 wt-% MSA, based on the total amount of monomers.

[0076] Copolymer 7 was prepared from 78.7 wt-% BeA and 26.3 wt-% MSA, based on the total amount of monomers.

[0077] Copolymer 8 was prepared from 78.2 wt-% BeMA and 21.8 wt-% MSA, based on the total amount of monomers.

[0078] The copolymers thus obtained were analyzed using the procedures described above for example 1. The results are shown in the following Table 2 (see Copolymers No.1 to No. 8 in Table 2 below).

TABLE-US-00003 TABLE 2 Residual Residual alkyl maleic (meth)acrylates anhydride [weight %, [weight %, Comonomer Alkyl based on based on molar ratio (meth)acrylate the total the total (alkyl composition weight of weight of Reaction methacrylate: based on C Mn Mw the reaction the reaction yield maleic No. alkyl chain [g/mol] [g/mol] PDI solution (*)] solution (*)] [%] anhydride) 1 C12, C13, 17500 61700 3.53 0.22 3.22 85.5 1:1 C14, C15 linear methacrylate (example 1) 2 C12, C13, 11400 20300 1.79 4.20 5.36 60.3 C14, C15 linear acrylate (example 1) 3 C12, C13, 26800 54100 2.02 1.09 4.29 78.2 C14, C15 linear methacrylate (example 1) 4 C14, C16, 16600 28100 1.69 6.48 5.44 56.1 C18 linear acrylate (example 1) 5 C14, C16, 28100 61000 2.17 1.08 4.31 80.8 C18 linear methacrylate (example 1) 6 C10 branched 17800 64100 3.61 0.04 4.06 25.6 methacrylate (example 2) 7 C18, C20, 45700 92000 2.01 0.01 4.08 89.2 C22 linear acrylate (example 3) 8 C18, C20, 18100 32500 1.80 3.07 5.04 78.2 C22 linear methacrylate (example 3) (*) the total weight of the reaction solution corresponds to total weight of the reaction mixture (solvent, monomers, initiator)

[0079] The data shown in Table 2 demonstrate that the copolymerization of alkyl methacrylate or alkyl acrylate and maleic anhydride according to the process described in EP 0636637 A2 results in a higher residual amount of maleic anhydride as compared to the process of the present invention. Indeed, in the particular case of maleic anhydride-alkyl methacrylate copolymers, the residual amount of maleic anhydride is in the range of 3.22 to 5.04 weight %, based on the total weight of the reaction solution, according to the process of EP 0636637 A2, whereas the residual amount of maleic anhydride according to the claimed process is never higher than 0.25 weight %, based on the total weight of the reaction solution (see Table 1 above). The conversion of maleic anhydride according to the claimed process for the specific preparation of maleic anhydride-alkyl methacrylate copolymers has thus been drastically improved in comparison to the conversions obtained with the prior art process.

[0080] Furthermore, the overall reaction yields of the comparative examples 1 to 8 reproduced according to the process in EP 0636637 A2 are low with values ranging from 25.6% to 89.2%, whereas the claimed process results in yields well above 98% (see Table 1).

Example 3 (Comparative Example)

[0081] In the following comparative example , copolymers of methacrylate and maleic anhydride are prepared under the reaction conditions of the solution copolymerization process disclosed in CN 1302031 C.

[0082] A mixture of maleic anhydride in toluene was charged into a reaction vessel and heated to a reaction temperature of 60° C. The reaction mixture was purged with nitrogen gas for 30 minutes. When the maleic anhydride was completely dissolved, alkyl methacrylate was added and the reaction was started by addition of radical initiator. Instead of AKIN, the radical initiator 2,2′-Azobis-(2-methylbutyronitrile) (AMBN) was used. Both initiators are azo compounds having a similar half-life period.

[0083] Two different copolymers were prepared (Copolymers No.1 and No. 2 in Table 3 below). Copolymer 1 was prepared from 53.3 wt-% LMA; 21.7 wt-% SMA, and 26 wt-% MSA, based on the total amount of monomers. Copolymer 2 was prepared from 56.9 wt-% SMA, 21.1 wt-% BeMA, and 22 wt-% MSA, based on the total amount of monomers.

[0084] The results are given in the following Table 3.

TABLE-US-00004 TABLE 3 Residual Residual alkyl maleic methacrylates anhydride [weight %, [weight %, Monomer Alkyl based on based on molar ratio methacrylate the total the total (alkyl composition weight of weight of Reaction methacrylate: based on C Mn Mw the reaction the reaction yield maleic No. alkyl chain [g/mol] [g/mol] PDI solution (*)] solution (*)] [%] anhydride) 1 C12, C14, 402000 729000 1.82 21.90 5.65 19.2 1:1 C16, C18 linear 2 C12, C14, 370000 796000 2.15 9.20 6.59 53.7 C16, C18 linear (*) the total weight of the reaction solution corresponds to total weight of the reaction mixture (solvent, monomers, initiator)

[0085] The results show that the polymerization process according to CN 1302031 C results in product mixtures containing high amounts of residual monomers, both related to alkyl methacrylate and maleic anhydride and therefore very low yields of 19.2% and 53.7%. Furthermore, the obtained polymers do not comprise number average molecular weights in the desired range of 3000 to 9000 g/mol. In contrast, the resulting copolymers 1 and 2 of Table 3 have a very high number average molecular weight.

[0086] Copolymer No. 2 of Table 3 was prepared according to CN 1302031 C from exactly the same monomer composition as copolymer No. 2 in Table 1, which was synthesized according to the claimed process. In case of the claimed process, a number average molecular weight of 6 010 g/mol was obtained versus a number average molecular weight of 370 000 g/mol in case of the process according to CN 1302031 C. Furthermore, the residual amounts of monomers are very low in case of copolymer 2 prepared according to the claimed process with values of 0.08% residual alkyl methacrylate and 0.004% maleic anhydride, whereas in case of copolymer 2 prepared according to the process of CN 1302031 C, the amounts of residual monomers were high with values of 9.20% residual alkyl methacrylate and 6.59% maleic anhydride. This is also reflected in the yields: copolymer 2 of Table 1, prepared according to the claimed process, was obtained in a yield of 99.8%, whereas copolymer 2 of Table 3, prepared according to CN 1302031 C, was obtained in a yield of 53.7%.

Example 4 (Comparative Example)

[0087] The following example represents a solution polymerization process according to CN 1328392 C.

[0088] A solution of maleic anhydride in xylene was heated to a reaction temperature of 140° C. Subsequently, two separate solutions of radical initiator in xylene and alkyl methacrylate in xylene were added dropwise within 3 hours. The alkyl methacrylate solution also contained n-dodecyl mercaptan as change transfer agent. The mixture was then continuously refluxed for 2 to 4 hours to obtain the alkyl methacrylate/maleic anhydride copolymer. The resulting copolymer composition as analyzed as described above.

[0089] Six different copolymers were prepared (Copolymers No.1 to No.6 in Table 4 below). Copolymer 1 was prepared from 70 wt-% IDMA and 30 wt-% MSA, based on the total amount of monomers. Copolymer 2 was prepared from 52.3 wt-% LMA, 21.7 wt-% SMA, and 26 wt-% MSA, based on the total amount of monomers. Copolymer 3 was prepared from 19.8 wt-% LMA, 56.2 wt-% SMA, and 24 wt-% MSA, based on the total amount of monomers. Copolymer 4 was prepared from 56.9 wt-% SMA, 21.1 wt-% BeMA, and 22 wt-% MSA, based on the total amount of monomers. Copolymer 5 was prepared from 85 wt-% IDMA and 15 wt-% MSA, based on the total amount of monomers. Copolymer 6 was prepared from 22.5 wt-% LMA, 64 wt-% SMA, and 13.5 MSA, based on the total amount of monomers.

[0090] The results are given in the following Table 4.

TABLE-US-00005 TABLE 4 Residual Residual alkyl maleic methacrylates anhydride Alkyl [weight %, [weight %, Comonomer methacrylate based on based on molar ratio composition the total the total (alkyl based on weight of weight of Reaction methacrylate: average C Mn Mw the reaction the reaction Yield maleic No. alkyl chain [g/mol] [g/mol] PDI solution (*)] solution (*)] [%] anhydride) 1 C10 1450 2730 2.13 0.25 0.0001 99.4 1:1 branched 2 C12, C14, 1740 3440 1.98 0.80 0.0002 98.1 C16, C18 linear 3 C12, C14, 2270 4950 2.18 1.10 0.0009 97.4 C16, C18 linear 4 C14, C16, 1990 3780 2.88 0.56 0.0002 98.7 C18, C20, C22 linear 5 C10 1620 3550 2.19 3.20 0.0001 92.5 2:1 branched 6 C12, C14, 2000 5040 2.52 0.54 0.0002 98.7 C16, C18 linear (*) the total weight of the reaction solution corresponds to total weight of the reaction mixture (solvent, monomers, initiator)

[0091] As these results show, the process according to CN 1328392 C results in an excellent conversion rate of maleic anhydride. However, the copolymers do not have the desired number average molecular weight and contain sulfur due to the presence of n-dodecyl mercaptan in the polymerization reaction.

[0092] Copolymer No. 4 of Table 4 was prepared according to CN 1328392 C from exactly the same monomer composition as copolymer No. 2 in Table 1, which was synthesized according to the claimed process. In case of the claimed process, a number average molecular weight of 6010 g/mol was obtained versus a number average molecular weight of 2000 g/mol in case of the process according to CN 1328392 C. The residual amounts of monomers are very low both cases with values of 0.08% residual alkyl methacrylate and 0.004% maleic anhydride in case of the claimed process and 0.54% residual alkyl methacrylate and 0.0002% maleic anhydride in case of the process according to CN 1328392 C. The copolymers obtained with the process according to CN 1328392 C are not sulfur-free copolymers.

[0093] However, the reaction conditions according to CN 1328392 C do not allow controlling the number average molecular weight of the copolymer to produce copolymers with the required number average molecular weight range, while maintaining high conversion of maleic anhydride into the copolymer. The resulting copolymers are also not sulfur-free.

Example 5 (Comparative Example)

[0094] The following example represents the polymerization process according to U.S. Pat. No. 5,178,641A.

[0095] According to the process disclosed in U.S. Pat. No. 5,178,641A, a solution of alkyl acrylate and maleic anhydride in solvent naphtha 150 was heated upon stirring to the reaction temperature in nitrogen flow. After reaching the target reaction temperature, the radical initiator solution was added continuously to the reaction mixture within four hours. Subsequently, a further portion of the radical initiator was added, and the reaction mixture was kept stirring for 1 hour.

[0096] Five different copolymers were prepared according to the above-indicated process of U.S. Pat. No. 5,178,641A, using respectively alkyl methacrylate or alkyl acrylate together with maleic anhydride (Copolymers No.1 to No. 5 in Table 5 below).

[0097] Copolymers No. 1 to 5 were prepared using the reaction conditions of example 1 in US 5178641 A, involving a reaction temperature of 80° C. And AKIN as initiator.

[0098] Copolymer 1 was prepared from 72.7 wt-% LA and 27.3 wt-% MSA, based on the total amount of monomers.

[0099] Copolymer 2 was prepared from 71.6 wt-% LMA and 28.4 wt-% MSA, based on the total amount of monomers.

[0100] Copolymer 3 was prepared from 86.3 wt-% LA and 13.7 wt-% MSA, based on the total amount of monomers.

[0101] Copolymer 4 was prepared from 87.1 wt-% LMA and 12.9 wt-% MSA, based on the total amount of monomers.

[0102] Copolymer 5 was prepared from 89.0 wt-% SA and 11.0 wt-% MSA, based on the total amount of monomers.

[0103] The results are given in the following table 5 (see Copolymers No. 1 to No. 5 in Table 5 below).

TABLE-US-00006 TABLE 5 Residual Residual alkyl maleic (meth)acrylates anhydride Alkyl [weight %, [weight %, Comonomer (meth)acrylate based on based on molar ratio composition the total the total (alkyl based on weight of weight of Reaction methacrylate: average C Mn Mw the reaction the reaction yield maleic No. alkyl chain [g/mol] [g/mol] PDI solution (*)] solution (*)] [%] anhydride) 1 C12, C14 21300 71700 3.37 0.02 6.84 84.0   1:1 linear acrylate 2 C12, C14 8370 17400 2.08 0.58 6.97 82.1 linear methacrylate 3 C12 C14 21700 55100 2.54 2.20 2.73 90.1 linear acrylate 4 C12, C14 64400 324000 5.04 0.01 1.47 97.1 2.5:1 linear methacrylate 5 C14, C16, 25900 84800 3.28 1.74 1.57 94.2 C18 linear acrylate (*) the total weight of the reaction solution corresponds to total weight of the reaction mixture (solvent, monomers, initiator)

[0104] The results show that all copolymers prepared according to the process of U.S. Pat. No. 5,178,641 A do not comprise the full amount of each monomer used in the reaction mixture. For example, in the case of equimolar monomer ratios among alkyl acrylate or alkyl methacrylate versus maleic anhydride as present in copolymers 1 and 2, a very high amount of residual maleic anhydride remains in the product mixture and the yield therefore is low when using the polymerization process according to U.S. Pat. No. 5,178,641A.

[0105] Furthermore, taking into account, on the first hand, the conversion of maleic anhydride, and on the other hand, the residual amount of alkyl acrylate or alkyl methacrylate (0.02 and 0.58 weight % for copolymers 1 and 2, respectively), it can be derived that the composition of the polymer obtained by the process described in U.S. Pat. No. 5,178,641 A is totally different from the copolymers obtained by the claimed process. Indeed, the alkyl methacrylate monomers nearly fully react during the polymerization reaction, whereas the second maleic anhydride monomers only partially react (as shown by the residual amount of maleic anhydride at the end of the reaction). Therefore, the copolymers obtained by the process described in U.S. Pat. No. 5,178,641 A do not comprise an equimolar composition of both repeating units, maleic anhydride versus alkyl acrylate or alkyl methacrylate, whereas the copolymers obtained by the claimed process do.

[0106] Furthermore, the yields obtained with the process of US 5178641 A are lower than the yields obtained with the claimed process.