Polyether polyols with low cyclic oligomer content

Abstract

The present invention relates to a polyether polyol characterized by a low content of cyclic by-products, a method for producing the polyether polyol, and an adhesive composition containing the polyether polyol.

Description

[Technical field]

[0001] The present invention relates to a polyether polyol characterized by a low content of cyclic by-products, a method for producing the polyether polyol, and an adhesive composition containing the same. [Background technology]

[0002] Polyether polyols are well-known compounds suitable for a variety of applications. A common application is the use of polyether polyols in the production of adhesive systems, especially polyurethane adhesives, where the polyether polyol is reacted with an isocyanate component to obtain the desired polyurethane. In particular, when applying polyether polyols to adhesive systems, it is desirable to have a high content of linear OH-terminated polymer chains. However, in most cases, polyether polyols also contain a certain amount of cyclic oligomer by-products that lead to a decrease in the mechanical performance of the adhesive and the thermoplastic polyurethane. Therefore, it is desirable to keep the cyclic oligomer content as low as possible.

[0003] Many attempts have been made to obtain suitable polyether polyols, one of which is the polymerization of cyclic ethers. Three- and four-membered ring ethers undergo easy polymerization reactions due to the large ring strain, but the polymerization of thermodynamically stable five- and six-membered ring systems remains difficult.

[0004] A. Ishigaki, in Die Makromolekulare Chemie 1964, 79, p.170, described the copolymerization of 2-substituted tetrahydrofurans with several cyclic ethers using BF3-(C2H5)2O as an initiator. 2-Methyltetrahydrofuran (MTHF), which was known not to homopolymerize, was found to copolymerize with monomers such as epichlorohydrin and 3,3-bis(chloromethyl)oxacyclobutane (BCMO). In particular, the low reactivity of 2-substituted tetrahydrofurans was emphasized, and they were found to polymerize only with halogenated comonomers. [Prior art documents] [Non-patent literature]

[0005] [Non-Patent Document 1] A.Ishigaki Die Makromolekulare Chemie 1964,79,p.170 Summary of the Invention [Problem to be solved by the invention]

[0006] However, it has been found that polyether polyols produced by known processes contain large amounts of cyclic by-products which impair the performance of products derived from the polyether polyols.

[0007] In view of the above, it is an object of the present invention to provide polyether polyols which are capable of producing products exhibiting good mechanical performance.

[0008] Surprisingly, it has been found that polyether polyols with a low number of cyclic by-products lead to mechanically stable products such as adhesives, coating systems, etc. Surprisingly, it has been found that the amount of undesired cyclic by-products can be significantly reduced if the respective polyether polyols are prepared by polymerization of an epoxy-containing compound with a further compound capable of undergoing a ring-opening reaction in the presence of a Bronsted acid having a weakly coordinating and non-nucleophilic anion. [Means for solving the problem]

[0009] A first object of the present invention is therefore a polyether polyol obtained by copolymerizing a compound A containing at least one epoxide moiety with a compound B capable of a ring-opening reaction, wherein compound A and compound B are different from each other and the copolymerization is carried out in the presence of a Brönsted acid having a weakly coordinating and non-nucleophilic anion.

[0010] Surprisingly, it has been found that the polyether polyols of the present invention can be obtained in good yields and with chain lengths suitable for adhesive applications. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] The presence of cyclic by-products, especially cyclic oligomers, is detrimental to the mechanical performance of final products such as adhesives, sealants, coatings, etc., and is therefore desirably avoided. Surprisingly, little formation of cyclic by-products was observed when preparing the polyether polyols of the present invention. In addition, the difference between the number average molecular weight Mn of the polyether polyols of the present invention determined by gel permeation chromatography (GPC) and the number average molecular weight Mn of the polyether polyols of the present invention determined by end group titration was used as an indicator of the presence of undesirable cyclic by-products. The large difference between the number average molecular weight measured by GPC and the number average molecular weight measured by end group titration was interpreted as being due to the presence of cyclic by-products that are not registered in the end group titration, resulting in a difference in molecular weight. Thus, in one embodiment of the present invention, the difference between the number average molecular weight Mn of the polyether polyols of the present invention determined by GPC and the number average molecular weight Mn of the polyether polyols of the present invention determined by end group titration is less than 50%, preferably less than 40%, particularly less than 20%, based on the number average molecular weight Mn of the polyether polyols of the present invention determined by GPC.

[0012] In a preferred embodiment, compound A is a low molecular weight epoxy compound, in particular having a molecular weight of 40 to 200 g / mol, preferably 50 to 160 g / mol. In a particularly preferred embodiment, compound A is selected from the group consisting of ethylene oxide (EO), propylene oxide (PO) and the compounds shown below.

[0013] [ka]

[0014] In one particularly preferred embodiment, compound A is propylene oxide (PO).

[0015] It has been surprisingly discovered that ring systems that are not normally copolymerized can be employed as comonomers in the polyether polyols of the present invention.

[0016] In a preferred embodiment, compound B is such that it is selected from 5-membered heterocycles and 6-membered heterocycles.In a particularly preferred embodiment, compound B is selected from the group consisting of optionally substituted 5-membered and 6-membered cyclic ethers.In a further preferred embodiment, compound B is selected from the group consisting of substituted 5-membered and 6-membered cyclic ethers, and one or more substituents are independently selected from the group consisting of methyl, ethyl, propyl, iso-propyl, butyl, iso-butyl and tert-butyl.

[0017] In one particularly preferred embodiment, compound B is 2-methyltetrahydrofuran.

[0018] The Bronsted acid having a weakly coordinating and non-nucleophilic anion employed in the present invention is H3PW, where x is 10≦x≦44, preferably 15≦x≦30. 12 O 40 * xH2O, H3PMo 12 O 40 , HBF4, CF3COOH, CF3SO3H, triflimdic acid and HSbF6.

[0019] Conscious of limited resources, there is growing interest in sustainability and in replacing commonly used petroleum-derived compounds with compounds obtained from renewable resources, so-called bio-based compounds. The polyether polyols of the present invention have the advantage that the monomers used in the copolymerization are obtained from renewable resources, such as plants, contributing to the ever-growing field of resource-friendly chemicals. Thus, in a preferred embodiment of the present invention, compound A and / or compound B are obtained from renewable resources.

[0020] Even more surprisingly, it was found that by choosing the appropriate ratio of monomers, the polymer backbone of the polyether polyol can be individually designed. In this way, polyether polyols can be obtained in which the ring-opening units of the monomers in the chain alternate perfectly, and chains terminated with alkenes are formed only in amounts below the quantification limit. In a preferred embodiment, the initial monomer ratio by weight of compound A to compound B is 1:20 to 1:1.3, preferably 1:5 to 1:1.5.

[0021] The molecular weight of the polyether polyol of the present invention can be adjusted according to the specific application. However, considering the application to adhesives in particular, it is advantageous that the molecular weight does not exceed a certain limit. In a preferred embodiment of the present invention, the polyether polyol therefore has an average number molecular weight Mn of 500 to 5000 g / mol, preferably 700 to 3000 g / mol, determined by GPC.

[0022] It is also desirable that the molecular weight distribution is narrow. In a preferred embodiment, the polyether polyol of the present invention therefore has a polydispersity index (PDI) determined according to GPC of 1.1 to 5.0, preferably 1.1 to 2.5. In the present invention, PDI refers to the ratio of the weight average molecular weight to the number average molecular weight (Mw / Mn) of the polyether polyol.

[0023] In a preferred embodiment, the polyether polyols of the invention have a hydroxyl number (OH number), measured according to DIN 53240, of 10 to 200 mg KOH / g, preferably of 50 to 150 mg KOH / g.

[0024] A further object of the invention is a method for the preparation of polyether polyols according to the invention, which comprises providing a reaction vessel filled with compound B and polymerizing compound A and compound B in the presence of a Brönsted acid with a weakly coordinating, non-nucleophilic anion by subsequent addition of compound A over a time tA. Surprisingly, it has been found that the difference between the molecular weight determined by GPC and the molecular weight determined by end group titration is further reduced when compound A is added dropwise over a period of time. The duration of time tA depends on the amount of compound A added and may range from a few minutes to a few hours.

[0025] Surprisingly, it has been found that the presence of compounds having functional groups exhibiting nucleophilic behavior, such as water, alcohols, amines, and thiols, during polymerization also suppresses the formation of cyclic oligomers. These compounds can be called initiators. Therefore, it is preferable to carry out the polymerization in the presence of one or more initiators. However, it has been found that the presence of too much initiator reduces the molecular weight of the polyether polyol. Therefore, in a preferred embodiment, the amount of initiator is 1 to 15 mol-%, preferably 2 to 10 mol-%, relative to compound A.

[0026] The Bronsted acid having a weakly coordinating, non-nucleophilic anion is preferably used in the reaction in an amount of 0.005 to 10 mol-%, preferably 0.01 to 1 mol-%. The Bronsted acid having a weakly coordinating, non-nucleophilic anion is preferably H3PW having 10≦x≦44, preferably 15≦x≦30. 12 O 40 * xH2O, H3PMo 12 O 40 , HBF4, CF3COOH, CF3SO3H, triflimdic acid and HSbF6.

[0027] The polyether polyols of the present invention can be further functionalized with many different reaction partners resulting in acrylates, isocyanates, epoxides, vinyl ethers, thiols, amine ends, etc., making them particularly suitable for applications in the fields of coatings, adhesives, sealings and elastomers (CASE), especially adhesives. A further object of the present invention is therefore an adhesive composition comprising the polyether polyols of the present invention. In a preferred embodiment, the adhesive composition is a polyurethane-based adhesive composition or a silane-based adhesive.

[0028] The subject of the invention is also the use of the polyether polyols according to the invention for the production of adhesives, preferably polyurethane adhesives and silane-based systems.

[0029] The present invention will be described in more detail with reference to the following examples, which should not be construed as limiting the scope and spirit of the present invention in any way. EXAMPLES

[0030] Working Example: Example A (reference) The reaction vessel was charged with 2-methyl-THF and BF3·2H2O was added. Propylene oxide was introduced dropwise into the reaction mixture and the resulting contents were stirred. An aqueous solution of sodium hydroxide was then added. The resulting aqueous phase was extracted with an organic solvent. The resulting organic phase was washed and dried. The organic solvent was removed to yield polyether polyols.

[0031] Example B (according to the invention) The reaction vessel was filled with 2-methyl-THF and phosphotungstic acid (HPW 12 O 40 *24H2O) was added, followed by the addition of alcohol. Propylene oxide was introduced dropwise into the reaction mixture, and the resulting contents were stirred. An aqueous solution of sodium carbonate was then added. Excess 2-methyl THF was evaporated under reduced pressure. The resulting polyether polyol was dissolved in an organic solvent and filtered through a pad of silica. The volatiles in the filtrate were removed to provide the polyether polyol of the present invention.

[0032] The molecular weight of the obtained polyether polyol was measured by GPC-APC and end group titration method, and the results are summarized in Table 1.

[0033] [Table 1]

[0034] GPC analysis was performed using an Acquity Advanced Polymer Chromatography System (Waters, USA) equipped with RI and PDA detectors. THF was used as the eluent at a flow rate of 0.5 ml / min, and the molecular weight was measured based on polystyrene standards (PSS) ranging from 266 to 1,210,000 daltons. The average molecular weight value was evaluated using a 5th order calibration curve ("Streifenmethode").

[0035] The titration of end groups was carried out by acetylating the free hydroxyl groups of the samples with acetic anhydride in pyridine solvent according to the standard procedure described in DIN 53240. After the reaction was completed, water was added to convert the remaining unreacted acetic anhydride to acetic acid, which was then titrated with potassium hydroxide to determine the end group content.

[0036] Polyether polyol of the present invention was reacted with diisocyanate (4,4'-methylenediphenyl diisocyanate) in a ratio of 2.2 (NCO / OH) to obtain a polyurethane adhesive. Films were cast (13 cm x 5 cm, 2 mm thick) and stored at 23°C and 50% relative humidity for 7 days. The same procedure was carried out using PPG 2000 and pTHF as comparative polyether polyols, respectively. The resulting films were characterized by stress-strain tests. The results are summarized in Table 2. Surprisingly, the adhesive using the polyether polyol of the present invention had a higher tensile strength (1.54 n / mm) at 50% elongation than the commonly used PPG. 2 2.18n / mm 2 ) was found to be reached.

[0037] [Table 2]

[0038] Stress-strain tests were performed using a Zwick-Roell Z010 testing system equipped with a probe head of 500 N. The sample extension rate was 50 mm / min according to DIN 535049. Preferred aspects of the invention include the following. [1] A polyether polyol obtained by copolymerization of a compound A containing at least one epoxide moiety with a compound B capable of undergoing a ring-opening reaction, wherein the compounds A and B are different from each other, and the copolymerization is carried out in the presence of a Bronsted acid having a weakly coordinating and non-nucleophilic anion. [2] The polyether polyol according to [1], wherein compound B is selected from 5-membered heterocyclic rings and 6-membered heterocyclic rings, in particular 5-membered cyclic ethers and 6-membered cyclic ethers, and may be optionally substituted. [3] The polyether polyol according to any one of the above items, wherein compound A has a molecular weight of 40 to 200 g / mol, preferably 50 to 160 g / mol. [4] The polyether polyol according to any one of the preceding paragraphs, characterized in that compound A and / or compound B are obtained from renewable resources. [5] The polyether polyol according to any one of the above items, characterized in that the difference between the number average molecular weight Mn of the polyether polyol of the present invention determined by GPC and the number average molecular weight Mn of the polyether polyol of the present invention determined by end group titration is less than 50%, preferably less than 40%, and particularly preferably less than 20%, based on the number average molecular weight Mn of the polyether polyol of the present invention determined by GPC. [6] The Bronsted acid having a weakly coordinating and non-nucleophilic anion is H 3 P.W. 12 O 40 * xH 2 O [wherein 10≦x≦44, preferably 15≦x≦30], H 3 PMo 12 O 40 , H.B.F. 4 , C.F. 3 COOH, CF 3 SO 3 H, triflimdic acid and HSbF 6 2. The polyether polyol according to any one of the preceding claims, characterized in that it is selected from the group consisting of: [7] The polyether polyol according to any one of the preceding claims, characterized in that the polyether polyol has a number-average molecular weight Mn determined by GPC of 500 to 5000 g / mol, preferably 700 to 3000 g / mol. [8] The polyether polyol according to any one of the above items, characterized in that the polyether polyol has a hydroxyl value (OH value) measured in accordance with DIN 53240 of 10 to 200 mg KOH / g, preferably 50 to 150 mg KOH / g. [9] A method for producing the polyether polyol according to any one of [1] to [8], comprising providing a reaction vessel filled with a compound B, and then adding a compound A over a time tA in the presence of a Bronsted acid having a weakly coordinating and non-nucleophilic anion, thereby polymerizing the compound A and the compound B.

[10] The method according to [9], wherein the polymerization is carried out in the presence of a nucleophilic initiator.

[11] The method according to [1], wherein the amount of the initiator is 1 to 15 mol-%, preferably 2 to 10 mol-%, based on compound A.

[12] An adhesive composition comprising the polyether polyol according to any one of [1] to [8].

[13] Use of the polyether polyol according to any one of [1] to [8] for producing an adhesive, preferably a polyurethane-based adhesive and a silane-based adhesive.

Claims

1. 1. An adhesive composition comprising an isocyanate component and a polyether polyol obtained by copolymerization of a compound A containing at least one epoxide moiety and a compound B capable of undergoing a ring-opening reaction, the compounds A and B being different from each other, the copolymerization being carried out in the presence of a Bronsted acid having a weakly coordinating and non-nucleophilic anion, The Bronsted acid having a weakly coordinating and non-nucleophilic anion is H ３ P.W. １２ O ４０ ＊ xH ２ O [in the formula, 10≦x≦44], H ３ PMo １２ O ４０ , H.B.F. ４ , C.F. ３ COOH, C.F. ３ SO ３ H, triflimdic acid and HSbF ６ Characterized in that it is selected from the group consisting of Adhesive composition.

2. 2. The adhesive composition according to claim 1, characterized in that compound B is selected from 5-membered and 6-membered heterocyclic rings, which may be optionally substituted.

3. 3. The adhesive composition according to claim 1, wherein the compound A has a molecular weight of 40 to 200 g / mol.

4. 4. The adhesive composition according to claim 1, wherein compound A and / or compound B is obtained from renewable resources.

5. The adhesive composition according to any one of claims 1 to 4, characterized in that the difference between the number average molecular weight Mn of the polyether polyol of the present invention determined by GPC and the number average molecular weight Mn of the polyether polyol of the present invention determined by end group titration is less than 50% based on the number average molecular weight Mn of the polyether polyol of the present invention determined by GPC.

6. The Bronsted acid having a weakly coordinating and non-nucleophilic anion is H ３ P.W. １２ O ４０ ＊ xH ２ O [in the formula, 15≦x≦30], H ３ PMo １２ O ４０ , H.B.F. ４ , C.F. ３ COOH, C.F. ３ SO ３ H, triflimdic acid and HSbF ６ The adhesive composition according to any one of claims 1 to 5, characterized in that it is selected from the group consisting of:

7. 7. The adhesive composition according to claim 1, wherein the polyether polyol has a number-average molecular weight Mn of 500 to 5,000 g / mol as determined by GPC.

8. 8. The adhesive composition according to claim 1, wherein the polyether polyol has a hydroxyl number (OH number), measured according to DIN 53240, of 10 to 200 mg KOH / g.

9. 9. A method for producing an adhesive composition according to any one of claims 1 to 8, wherein the polyether polyol contained in the adhesive composition is produced by a method comprising providing a reaction vessel filled with compound B, followed by adding compound A over a time tA in the presence of a Bronsted acid having a weakly coordinating and non-nucleophilic anion, thereby polymerizing compound A and compound B.

10. The process according to claim 9, characterized in that the polymerization is carried out in the presence of a nucleophilic initiator.

11. The method according to claim 10, wherein the amount of the initiator is 1 to 15 mol-% based on compound A.

12. The adhesive composition according to any one of claims 1 to 8, which is a polyurethane-based adhesive composition.

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