Description

The present invention deals with low volatile organic compound anti-oxidation stabilizers for polymeric systems, their production and use, in particular in polyurethane systems.

Currently used phenolic-based AO (antioxidant)-stabilizers are hydrolytically instable due to an ester bond modification (for example, commercial products Irganox® 1 135 & 1076, see also WO 2006/092636 A1 or WO 2017/037204). Cleavage of the ester bond leads to the release of volatile organic compounds, which is undesirable in most applications.

On the other hand, most high-molecular weight AO-stabilizers are solid (like some commercially available stabilizers of the Irganox® series, see also e.g., US 7,262,319 B2) at room temperature and cannot be readily used in PU (polyurethane) formulations.

Layer (J. Org. Chem. 1981 , 46, 5224-5225) describes reactions of epoxides with 2,6-Di-tert-bu- tylphenol. Beside the main product (i. e. 2-hydroxyethyl ether of the phenol), 4-(2-hydroxyethyl)- 2,6-di-tert-butylphenol is generated in a low amount.

Arefiev et al. (Europ. Polym. J. 36, (2000), 857-860) report on sterically hindered phenol-dextran conjugates and their radical scavenging activity in water and water-organic media. Arefiev et al. (Russ. Chem. Bulletin, Int. Ed., Vol. 56, No. 4, 781 -790, April, 2007) also investigated hybrid macromolecular antioxidants based on hydrophilic polymers and sterically hindered phenols.

Krysin et al. (Russ. J. Gen. Chem., 201 1 , Vol. 81 , No. 2, 354-360) report on the β-hydroxyal- kylation of sterically hindered phenols with epoxides in acid medium. Inter alia, 2,6-di-tert-butylphenol was reacted with ethylene oxide (EO) under influence of SnCU, yielding 4-(2-hydroxy- ethyl)-2,6-di-tert-butylphenol.

As mentioned above, some problems and disadvantages remain.

Therefore, it was an aim of this invention to overcome or at least reduce the problems and disadvantages connected with the presently used ways of stabilizing polymeric systems, for example polyols and/or polyurethanes. In particular, it was an objective to provide an anti-oxidation stabilizer, especially for polymeric systems, and a convenient way to produce such an anti-oxidation stabilizer, wherein the stabilizer should preferentially be liquid at room temperature (and thus easy to process) and remain stable also under acidic or basic conditions (therefore stable against hydrolysis), leading to a low emission of volatile compounds. Surprisingly it has now been found that by using a direct alkoxylation approach, readily available precursors could be selectively alkoxylated to gain liquid non-ester bond containing high-molecular weight AO-stabilizers. By using sterically hindered phenols, containing at least one functional group able to form an ether bond, it can be reached that alkoxylation mainly takes place on the non-phenolic OH moiety.

In more detail, for example by using sterically hindered, substituted phenols as educts, in particular 4-(Hydroxymethyl)-2,6-di-tert-butylphenol and/or 4-(2-Hydroxypropyl)-2,6-di-tert-butylphe- nol, alkoxylation can be effected mainly on the non-phenolic OH moiety.

Compared to compounds with an ester bond, such compounds have increased stability towards humidity. As known in the art hydrolysis of ether bonds requires strong alkaline or acidic conditions in contrast to ester bonds.

Furthermore, also by using sterically hindered, substituted phenols as educt, in particular 4- (Aminomethyl)-2,6-di-tert-butylphenol and/or 4-(2-Aminoethyl)-2,6-di-tert-butylphenol, alkoxylation can be effected mainly on the (non-phenolic) amine moiety.

The resulting products do not have ester bonds, but are linked through ether bonds. Therefore, the inventive stabilizers are not susceptible to ester bond cleavage and therefore show a high stability against hydrolysis.

The inventive stabilizers can be used advantageously in PU formulations. Furthermore, the in- ventive stabilizers can be used in other polymeric systems, for example in polyols (for example polyetherols, polyesterols, polymer polyols), polyolefins (for example polyethylene, polypropylene or polystyrene), polyamides, polyesters (for example polyethylene terephthalate or poly- butylene terephthalate), polyethers (for example polyoxymethylene), and/or polycarbonates. Thus, one object of the present invention is an anti-oxidation stabilizer for polymeric systems. Such anti-oxidation stabilizer comprises at least one compound of formula I

R (i);

wherein

R is -(CH ₂ )n-X-[Y-0] _P -H; X is selected from O, NR ¹ ;

Y is selected from the group consisting of -CH ₂ -CH ₂ -, -CH(CH ₃ )-CH ₂ -, -CH ₂ -CH(CH ₃ )-, - CH(CH ₂ -CH ₃ )-CH ₂ -, and -CH ₂ -CH(CH ₂ -CH ₃ )- p is 3 to 50, preferably 3 to 30, more preferably 3 to 20, most preferably 3 to 10;

n is 1 , 2, 3 or 4, preferably 1 , 2 or 3;

R ¹ is hydrogen, [Y-0]r-H or C1-C4 alkyl, preferably [Y-0]r-H or C1-C4 alkyl, more preferably [Y- 0]r-H alkyl, and

The term C1-C4 alkly includes methyl, ethyl, propyl, 1 -methylethyl, butyl, 1 -methylpropyl, 2- methylpropyl and 1 ,1 -dimethylethyl. r is 3 to 50, preferably 3 to 30, more preferably 3 to 20, most preferably 3 to 10

In other words, one preferred embodiment of the anti-oxidation stabilizer comprises a 2,6-di-tert- butylphenol compound substituted by a residue R in 4-position wherein residue R is -(CH ₂ ) _n -X- [Y-0]p-H, wherein X is selected from oxygen (O) or nitrogen-group (NR ¹ ), and Y is selected from the group consisting of -CH ₂ -CH ₂ -, -CH(CH ₃ )-CH ₂ -, -CH ₂ -CH(CH ₃ )- , -CH(CH ₂ -CH ₃ )-CH ₂ -, and -CH ₂ -CH(CH ₂ -CH ₃ )-, and n is selected from the range from 1 to 4, and p is preferably selected from 3 to 10.

In a further preferred embodiment, n is 1 , 2 or 3.

Preference is given to compounds 1-1 to I-20 of formula I of Table 1 , wherein

p is 3 to 50, preferably 3 to 30, more preferably 3 to 20, most preferably 3 to 10;

n is 1 , 2, 3 or 4, preferably 1 , 2 or 3; and

for compounds 1-1 1 to 1-15 r is 3 to 50, preferably 3 to 30, more preferably 3 to 20, most preferably 3 to 10

and the variables R ¹ , X and Y have the meaning as given in table 1 . Table 1

No X Y R ¹

1-1 O -CH ₂ -CH ₂ - (-)

I-2 O -CH(CH ₃ )-CH ₂ - (-)

I-3 O -CH ₂ -CH(CH ₃ )- (-)

I-4 O -CH(CH ₂ -CH ₃ )-CH ₂ - (-)

I-5 O -CH ₂ -CH(CH ₂ -CH ₃ )- (-)

I-6 NR ¹ -CH ₂ -CH ₂ - H

I -7 NR ¹ -CH(CH ₃ )-CH ₂ - H

I-8 NR ¹ -CH ₂ -CH(CH ₃ )- H

I-9 NR ¹ -CH(CH ₂ -CH ₃ )-CH ₂ - H

1-10 NR ¹ -CH ₂ -CH(CH ₂ -CH ₃ )- H

1-1 1 NR ¹ -CH ₂ -CH ₂ - [Y-OJr-H

1-12 NR ¹ -CH(CH ₃ )-CH ₂ - [Y-OJr-H 1-13 NR -CH ₂ -CH(CH ₃ )- [Y-0]r-H

1-14 NR -CH(CH ₂ -CH ₃ )-CH ₂ - [Y-0]r-H

1-15 NR ¹ -CH ₂ -CH(CH ₂ -CH ₃ )- [Y-OJ _r -H

1-16 NR ¹ -CH ₂ -CH ₂ - CH ₃

1-17 NR ¹ -CH(CH ₃ )-CH ₂ - CH ₃

1-18 NR ¹ -CH ₂ -CH(CH ₃ )- CH ₃

1-19 NR ¹ -CH(CH ₂ -CH ₃ )-CH ₂ - CH ₃

I-20 NR ¹ -CH ₂ -CH(CH ₂ -CH ₃ )- CH ₃

More preference is given to compounds 1-1 to I-20 of formula I of Table 1 , wherein

p 3 to 30;

n is 1 , 2 or 3; and

for compounds 1-1 1 to 1-15 r is 3 to 30;

and the variables R ¹ , X and Y have the meaning as given in table 1 .

Most preference is given to compounds 1-1 to I-5, and 1-1 1 to I-20 of formula I of Table 1 , wherein

p is 3 to 20;

n is 1 , 2 or 3; and

for compounds 1-1 1 to 1-15 r is 3 to 20;

and the variables R ¹ , X and Y have the meaning as given in table 1 . Utmost preference is given to compounds 1-1 to I-5, and 1-1 1 to 1-15 of formula I of Table 1 , wherein

p is 3 to 10;

n is 1 , 2 or 3; and

for compounds 1-1 1 to 1-15 r is 3 to 10

and the variables R ¹ , X and Y have the meaning as given in table 1 .

In a particular preferred embodiment the invention comprises compounds 1-1 to I-5 of formula I of Table 1 , wherein

p is 3 to 10;

n is 3.

The term "at least one compound of formula I" in the context of the present invention means that the stabilizer may not only comprise one defined compound of formula I, but also mixtures of mixtures of two or more structurally different compounds of formula I. Such mixtures can be easily produced by the processes as referred to below.

The term "polymeric systems" in the context of this invention refers in particular to synthetic polymers but also polymeric compounds to be used for preparing polymers such as polyols. Mac- romolecular compounds of biological origin, for example DNA, are not aimed at by this inven- tion. Polymeric systems include, without limitation, polyurethanes, thermoplastic polyurethanes, poly- ols (for example polyetherols, polyesterols, polymer polyols), polyolefines (for example polyethylene, polypropylene or polystyrene), polyamides, polyesters (for example polyethylene tereph- thalate or polybutylene terephthalate), polyethers (for example polyoxymethylene), and polycarbonates.

In particular, polymeric systems in this invention comprise polyurethanes, thermoplastic polyurethanes, polyols, polyolefines, polyamides, polyesters, polyethers and/or polycarbonates.

In an embodiment of this invention, polymeric systems contain, preferably consist of, polyole- fins.

In another embodiment of this invention, polymeric systems contain, preferably consist of, polyols. In yet another embodiment of this invention, polymeric systems contain, preferably consist of, polyurethanes.

A further object of the present invention comprises a process for the production of an anti-oxidation stabilizer by reacting at least one Zerewitinoff-active compound Z1 of formula II

wherein

R ^a is (CH ₂ ) _k -R ^b

k is 1 , 2, 3 or 4, preferably 1 , 2 or 3

R ^b is OH or NR ^c R ^d ,

R ^c is H; and

R ^d is H or C1-C4 alkyl

with at least one alkylene oxide under basic catalysis or coordinative catalysis or Lewis acid catalysis.

Preferred compounds of formula II, wherein

R ^a is (CH ₂ ) _k -R ^b

k is 1 , 2 or 3

R ^b is OH; Equally preferred compounds of formula II, wherein

R ^a is (CH ₂ ) _k -R ^b

k is 1 , 2 or 3

R ^b is NR ^c R ^d ,

R ^c is H; and

R ^d is H

Thus, preferably, the Zerewitinoff-active compound Z1 is selected from the group consisting of 4-(Hydroxymethyl)-2,6-di-tert-butylphenol, 4-(2-Hydroxyethyl)-2,6-di-tert-butylphenol, 4-(2-Hy- droxypropyl)-2,6-di-tert-butylphenol, 4-(Aminomethyl)-2,6-di-tert-butylphenol, 4-(2-Aminoethyl)- 2,6-di-tert-butylphenol and 4-(2-Aminopropyl)-2,6-di-tert-butylphenol.

In a particular preferred embodiment the invention comprises compounds of formula II, wherein R ^a is (CH ₂ ) _k -R ^b

k is 3

R ^b is OH;

Equally preferred compounds of formula II, wherein

R ^a is (CH ₂ ) _k -R ^b

k is 3

R is NR ^c R ^d ,

R ^c is H; and

R ^d is H In one embodiment of the inventive process, the coordinative catalyst is selected from the group containing, preferably consisting of, DMC (double metal cyanide) catalysts.

In another embodiment of the invention, the DMC catalyst is selected from the group containing, preferably consisting of, crystalline and amorphous DMCs.

Preferably, the DMC catalyst is non-crystalline.

In one embodiment of the inventive process, the basic catalyst is selected from the group containing, preferably consisting of, alkaline earth metal hydroxides.

In a preferred embodiment of the inventive process, the basic catalyst is selected from KOH or CsOH, more preferably KOH.

In one embodiment, the basic catalyst is selected from the group of phosphazenes.

In another embodiment of the inventive process, the basic catalyst is selected from imidazole and/or dimethylaminoethylamine (DMEA), preferably imidazole. In a further embodiment of the inventive process, a Lewie acid catalyst is used, wherein preferably the Lewis acid catalyst contains, more preferably consists of, BF3.

Regarding the alkylene oxide used in the inventive process, the alkylene oxide is preferably se- lected from ethylene oxide, propylene oxide and/or butylene oxide. More preferably, the alkylene oxide contains propylene oxide. In a further preferred embodiment, the alkylene oxide consists of propylene oxide.

In the process of the present invention, one or more structurally different Zerewitinoff-active compound Z1 of formula II can be used.

Thus, in one embodiment of the inventive process, a mixture of two or more structurally different Zerewitinoff-active compound Z1 of formula II can be used. In a preferred variant of this embodiment of the inventive process, the at least one Zerewitinoff- active compound Z1 is selected from the group containing, preferably consisting of, 4-(Hy- droxymethyl)-2,6-di-tert-butylphenol, 4-(Hydroxyethyl)-2,6-di-tert-butylphenol and 4-(2-Hydrox- propyl)-2,6-di-tert-butylphenol. In a further variant of this embodiment of the inventive process, the at least one Zerewitinoff-active compound Z1 is selected from the group containing, preferably consisting of, 4-(aminome- thyl)-2,6-di-tert-butylphenol, 4-(2-aminoethyl)-2,6-di-tert-butylphenol and 4-(2-aminopropyl)-2,6- di-tert-butylphenol. In another embodiment of the inventive process, only one Zerewitinoff-active compound Z1 of formula II is used. This single Zerewitinoff-active compound Z1 is preferably selected from either 4-(Hydroxymethyl)-2,6-di-tert-butylphenol, 4-(Hydroxyethyl)-2,6-di-tert-butylphenol or 4-(2-Hy- droxpropyl)-2,6-di-tert-butylphenol. In another embodiment of the inventive process, the single Zerewitinoff-active compound Z1 is preferably selected from either 4-(Aminomethyl)-2,6-di-tert-butylphenol, 4-(2-Aminoethyl)-2,6-di- tert-butylphenol or 4-(2-Aminopropyl)-2,6-di-tert-butylphenol.

As to the reaction conditions for the inventive process, the temperature during the reaction is usually in the range of 80 to 180 °C, preferably 90 to 160 °C, more preferably 100 to 140 °C; the pressure during the reaction is usually in the range of 0.01 to 20 bar, preferably 2 to 15 bar, more preferably 3 to 10 bar; and the dosing of the alkylene oxide generally lasts less than 20 h, preferably less than 15 h. The inventive process may be performed in a (additional) solvent and/or (additional) reagent. In one embodiment of the inventive process, the reaction is performed in another Zerewitinoff- active compound Z2. The Zerewitinoff-active compound Z2 may be a polyetherol with an OH value of 15 to 6500 mg KOH/g, preferably 15 to 3000 mg KOH/g, more preferably 15 to 2000 mg.

The Zerewitinoff-active compound Z2 may also be selected from the list containing, preferably consisting of sugars such as sorbitol, sucrose or alcohols with a functionality between 2 to 8 such as glycerol, dipropylene glycol and diethylene glycole, ethylene glycole, propylene gly- cole, 1 ,1 ,1 -trimethylolpropane (TMP), or amines such as ethylendiamin, diethanolamin or tolu- oldiamine or trimethyl or mixtures thereof. The term "in another Zerewitinoff-active compound Z2" in the context of the present invention means that the reagent may not only comprise one reagent Z2, but also mixtures of mixtures of two or more structurally different compounds Z2 can be used.

For example, mixtures of sugars can be used in combination with glycerol.

The inventive process may also be performed in a different solvent, for example an ether bond- containing solvent and/or a solvent inert under the reaction conditions, preferentially polyeth- ylenglycol dimethylethers and/or polypropyleneglycol dimethylethers and/or polytetrahydrofu- rane dimethylethers.

In one embodiment of the inventive process, the reaction is performed in another component and the component is an alkoxylated phenol.

In another embodiment of the invention, the reaction is performed in an inert solvent. Another object of the present invention is the use of the inventive anti-oxidation stabilizer for the stabilization of a polymer, preferably polyolefines, polyols and/or polyurethanes; besides, an object of the present invention is also an anti-oxidation stabilizer, obtainable by the inventive process. The inventive anti-oxidation stabilizer may serve to reduce emissions of volatile organic compounds (VOC) and medium volatile substances (FOG) in the stabilized products, compared to products stabilized with other stabilizers known from the prior art.

The following examples may serve to illustrate some aspects of the present invention, without limiting the scope of the invention.

The OH values were measured according to DIN 53240 and the viscosities in accordance with DIN 51550. Compound A: Synthesis of an ethylene oxide derivative of 3,5-di-tert-butyl-4-hydroxybenzylalco- hol using KOH as a catalyst A mixture of 43 g polyethylene glycol dimethyl ether 500, 98.5 g of 3,5-di-tert-butyl-4-hydroxyben- zylalcohol and 1 ,51 KOH g solution 50% in water were given in a 300 ml. autoclave. The mixture was dried for 60 min at 155° under full vacuum. The reactor was pressurized with 3.5 bar of nitrogen and 91 ,8 g of EO were added within 4 h at 155 °C. After post reaction of 8 h reaction the reaction mixture was cooled to 100 °C and all volatile components were removed under full vacuum. After cooling to 90 °C 5% by weight Macrosorb and 2% water were added for neutralization. The formed suspension was stirred for 3 h. Water was removed and the product was filtered. The product was cooled to temperature and analyzed. 216,1 g (92% yield) of yellow liquid were obtained.

The product had the following characteristics: OH value 151 ,56 mg KOH/g, viscosity 850 mPas at 25 °C.

Compound B: Synthesis of propylene oxide derivates of 3,5-di-tert-butyl-4-hydroxybenzylalcohol using DMC as a catalyst

A mixture of 64.2 g of a two-functional PPG polyol with an OH-value of 100 g/mol , 16,1 g of 3,5- di-tert-butyl-4-hydroxybenzylalcohol and 1 ,1 g DMC suspension (5,5% in a two-functional PPG polyol with an OH-value of 100 g/mol) were given in a 300 ml. autoclave. The mixture was dried for 60 min at 1 10° under full vacuum. 1.95 g of propylene oxide were added at 1 10 °C temperature in one portion and stirred for 15 min. Now the remaining amount of 36,7 g of propylene oxide was added over 80 min at this temperature. The reaction was stirred for another 6 h. The reaction mixture was cooled to 100 °C and all volatile components were removed under full vacuum. The product was cooled to temperature and analyzed. 1 16,1 g (96,7% yield) of yellow liquid were obtained.

The product had the following characteristics: OH value 86.57 mg KOH/g, viscosity 340 mPas at 25 °C. Further Example: Stabilization of polypropylene

The employed mini-extruder, which is commercially available from DSM, enables a flow of the melted polymer in a circle, i.e. two screws in a twin-screw arrangement press the melted polymer to the outlet, which is connected to the inlet zone of the extruder. The temperature of the steel barrel of the mini-extruder can be regulated and the inlet zone of the extruder can be purged with a gas, which allows the removal of entrapped air originating from the loading of the polymer sample. Furthermore, a sensor determines the force, which is exerted by the melted polymer onto the barrel during rotation of the two screws. A change in the viscosity of the melted polymer leads to a change of the force.

The steel housing of the extruder is set at a temperature of 240°C and the inlet zone is set under a nitrogen flow of 20 ml. / min. At a screw speed of 50 rpm, 9 g of a mixture, which consists of 8.955 g of a non pelletized, unstabilized polypropylene homopolymer (Moplen HF 501 N, LyondellBasell Industries; 99.75% by weight of the overall mixture), and 0.1 % by weight of Irgafos® 168FF (phosphor-based antioxidant) and 0.05 % by weight calcium stearate, and 0.1 % or 0.2 % by weight of a compound according to the invention (compound A or B as described above are loaded. In case of the comparative examples, a compound according to the invention is not added.

After loading, the screw speed is set to 100 rpm and the force exerted on the barrel is recorded. The test is conducted for 5 min under nitrogen at a flow rate of 20 mL / min. After a short period, a steady decrease of the force is recorded. The decrease of the force is quantified as slope of the force-to-time curve, wherein the slope is calculated between the time period of 150 and 280 seconds (method A). The curve is rather linear during said period. The decrease of the force with time is taken as degree of melt-degradation of the polymer sample. After 500 seconds, the polymer sample if exposed to air to induce polymer oxidation. Again, the decrease of the force is quantified as slope of the force-to-time curve, wherein the slope is calculated between the time period of 530 and 650 seconds (method B).

Desired is a minimum of degradation, which is expressed by a small value for the slope of the curve. No degradation would mean zero slope.

The results are shown in tables 1 & 2.

Table 1

example tested composition method A [slope] Method B [slope]

1 Base polymer without ad-0.45 -3.10

Polypropylene dition of a compound ac¬

(blank) cording to the invention

2 Base polymer plus 0.1 % -0.42 -2.75

Irgafos® 168 by weight Irgafos® 168

FF FF, 0.05 % by weight Ca- stearate

3 Base polymer plus 0.1 % -0.31 -1 .68

Compound A by weight Irgafos® 168

FF, 0.05 % by weight Ca- stearate + 0.1 % by weight

of compound A

4 Base polymer plus 0.1 % -0.33 -1 .14

Compound A by weight Irgafos® 168

FF, 0.05 % by weight Ca- stearate + 0.2 % by weight

of compound A

Table 2

The examples show that the inventive compounds may be used to stabilize polymeric systems, like, for example, polypropylene.