A low-polarity system rheological additive based on controllable oxidized polyethylene and a preparation method thereof

Abstract

This invention relates to the field of polymer processing aids, specifically to a rheology modifier for low-polarity organic media such as white oil, mineral oil, and alkane solvents. This invention aims to overcome the technical shortcomings of existing oxidized polyethylene products and provide a synthetic route. This route involves moderate and controllable preliminary oxidation of polyethylene raw materials, followed by quantitative and targeted deep chemical modification of the generated oxygen-containing groups, thereby constructing a "comb-like" polymer structure with both excellent oil compatibility and strong hydrogen bonding ability. Firstly, this invention provides a comb-like structure rheology modifier for low-polarity systems. Secondly, this invention provides a method for preparing the above-mentioned rheology modifier. Thirdly, this invention provides the application of the above-mentioned rheology modifier in compositions using white oil, mineral oil, synthetic alkanes, or mixtures thereof as the continuous phase. Fourthly, this invention provides a low-polarity fluid composition. Through precise secondary chemical design of oxidized polyethylene, this invention successfully transforms a mediocre wax product into a high-performance rheology modifier with a well-defined structure, high efficiency, transparency, and ease of use, perfectly solving the dual requirements of low-polarity systems for excellent rheological properties and appearance quality.

Description

Technical Field

[0001] This invention relates to the field of polymer processing aids, specifically to a rheology modifier for low-polarity organic media such as white oil, mineral oil, and alkane solvents. Particularly, it relates to a functional polymer with a well-defined comb-like structure obtained through controlled oxidation and subsequent precise chemical modification of polyethylene, and its preparation method. Background Technology

[0002] In formulations such as lubricants, creams, and inks that use non-polar media like white oil as a base, rheology modifiers are often added to thicken, prevent sedimentation, and impart thixotropic properties. Traditionally available products include hydrogenated castor oil, polyamide wax, and oxidized polyethylene wax. Among them, oxidized polyethylene wax (OPE-Wax) has been widely tried due to its readily available raw materials and low cost. Commercially available OPE is usually produced by deep oxidation of polyethylene in high-temperature air. The product contains various oxygen-containing groups such as carboxyl, hydroxyl, and carbonyl groups, but it has two inherent drawbacks: 1. Random and uncontrollable polarity distribution: Oxidation reactions occur at random positions in the main chain, resulting in poor uniformity in the number, type, and distribution of polar groups. This makes it weak and unstable in forming a physical cross-linked network in the oil phase, with low rheological efficiency, and it can usually only be used as an inexpensive anti-settling agent or sensory modifier.

[0003] 2. Difficulty in balancing compatibility with oil and polarity: To achieve sufficient thickening effect, the degree of oxidation needs to be increased (increase the content of polar groups), but this will reduce its compatibility with white oil, resulting in a cloudy system, reduced transparency, and even a grainy texture after addition. Therefore, developing a specialized additive based on oxidized polyethylene, but with a well-defined chemical structure, strong and stable rheological properties, and the ability to maintain high transparency of the system, has significant technical and economic value. Summary of the Invention

[0004] This invention aims to overcome the technical shortcomings of existing oxidized polyethylene products and provide a synthetic route. This route involves moderate and controllable preliminary oxidation of polyethylene raw materials, followed by quantitative and targeted deep chemical modification of the generated oxygen-containing groups, thereby constructing a "comb-like" polymer structure that possesses both excellent oil compatibility and strong hydrogen bonding ability. To achieve the above objectives, the present invention adopts the following technical solution: In a first aspect, the present invention provides a comb-shaped rheology modifier for low-polarity systems, characterized in that the modifier has a core structural unit as shown in the following general formula (I): [-(CH2-CH2)_m-CH(COOH)-CH2-]_a - [Other parts of the main chain] - [-(CH2-CH2)_n-]_b In this embodiment, at least a portion of the carboxyl groups (-COOH) are connected to a polar side chain containing a urea group via an amide bond, and the structure of this side chain is shown in formula (II): - CO - NH - R¹ - NH - CO - NH - R² In formula (II) - R¹ is a C2-C6 alkylene group, preferably a residue of ethylenediamine or hexamethylenediamine.

[0005] - R² is a C8-C22 straight-chain or branched alkyl group or alkylaryl group (such as dodecyl, octadecyl, phenyl).

[0006] - a, b, m, n are integers, satisfying that the additive is prepared from polyethylene with a number average molecular weight (Mn) of 2,000-10,000 through controlled oxidation and subsequent reactions, and that the degree of carboxyl functionalization is 10-50 carboxyl groups per 1000 main chain carbon atoms. Secondly, the present invention provides a method for preparing the above-mentioned rheology modifier, characterized by comprising the following steps: Step S1: Preparation of controllable carboxylated polyethylene intermediate - Raw materials: Select polyethylene wax (PE-Wax) or low molecular weight polyethylene with a number average molecular weight (Mn) of 2,000 - 10,000 and a molecular weight distribution (Đ) ≤ 3.0.

[0007] - Oxidation System: Solution oxidation is employed. PE wax is dissolved in a high-temperature inert solvent (such as decahydronaphthalene or xylene), and an ozone-containing air or oxygen mixture is introduced at 120-180°C. Key control points include: the addition of manganese acetate or cobalt stearate as a directional oxidation catalyst, and the addition of a small amount of di-tert-butyl peroxide as an initiator.

[0008] - Control and Termination: The oxidation depth was controlled by online monitoring of the acid value of the reaction mixture. When the acid value reached 20-60 mg KOH / g (corresponding to the target carboxyl content), the aeration was immediately stopped, and a free radical scavenger (such as BHT) was added to terminate the reaction. After cooling, the precipitate was washed and dried to obtain a pale yellow, controllable carboxylated polyethylene intermediate (CCP-I). This product is predominantly carboxyl, with lower carbonyl and hydroxyl content, and a relatively homogeneous structure. Step S2: Amidation reaction introduces a bridged diamine. - Dissolve the CCP-I obtained in step S1 in xylene or N-methylpyrrolidone (NMP) and heat to 100-140°C.

[0009] - Add an excess of aliphatic diamine, preferably ethylenediamine or hexamethylenediamine. The amount of diamine used is 1.5 to 3 times the molar number of carboxyl groups in CCP-I.

[0010] - Under nitrogen protection, the reaction lasts for 4-8 hours, causing the carboxyl group to react with one amino group of the diamine to form an amide bond, generating a polymer CCP-NH2 with a primary amino group at the end. Azeotropic reaction can be used to remove the generated water during the reaction.

[0011] - After the reaction is complete, the mixture is poured into a large amount of cold acetone to precipitate and remove unreacted diamine. After filtration and drying, an amino-terminated intermediate is obtained. Step S3: Urelation reaction to construct polar side chains - Dissolve the CCP-NH2 obtained in step S2 again in anhydrous toluene.

[0012] - At room temperature to 60°C, a long-chain monoisocyanate, which is equimolar in amount of the amino groups in CCP-NH2, is slowly added dropwise. The monoisocyanate is octadecyl isocyanate, dodecyl isocyanate, or phenyl isocyanate.

[0013] - After the addition is complete, raise the temperature to 70-90℃ and react for 2-4 hours. The completeness of the reaction is determined by monitoring the disappearance of the -NCO characteristic peak at 2250 cm⁻¹ using infrared spectroscopy.

[0014] - After precipitation and drying, the reaction solution yields the final product - oxidized polyvinyl comb rheology modifier (OPE-g-urea). Thirdly, the present invention provides the application of the above-mentioned rheology modifier in compositions in which white oil, mineral oil, synthetic alkanes, or mixtures thereof serve as the continuous phase. Fourthly, the present invention provides a low-polarity fluid composition comprising: - Continuous phase: selected from at least one of white oil, mineral oil, and synthetic alkane solvents; - Rheology modifier: The comb-shaped rheology modifier as described in the first aspect is added in an amount of 0.5% to 5.0% of the total weight of the composition. The beneficial effects of this invention are: 1. Well-defined structure and highly efficient and controllable performance: Through a "controlled oxidation + two-step precise modification" approach, random oxygen-containing groups are transformed into strong hydrogen bond sites (amide-urea structure) regularly distributed along the polyethylene backbone. This structure can efficiently form a three-dimensional physical cross-linked network in non-polar media, providing thickening and thixotropic capabilities far exceeding those of traditional OPE.

[0015] 2. Excellent transparency: The main chain is polyethylene, which has excellent intrinsic compatibility with white oil; by controlling the oxidation depth and introducing long-chain R², the solubility of additive molecules in the oil phase is further optimized, which can achieve nanoscale dispersion, thereby ensuring the clarity and transparency of the final system.

[0016] 3. Easy to disperse at room temperature and process-friendly: The resulting product is a powder or granules, which can be fully swollen and dispersed in white oil at room temperature through moderate shear (such as homogenization), eliminating the need for the high-temperature (>80℃) "activation process" required for traditional wax products, simplifying the production process and saving energy.

[0017] 4. Excellent thixotropic recovery: The multiple hydrogen bonds between amide-urea groups are stronger than the van der Waals forces between traditional wax crystals, and exhibit faster reconstruction kinetics. Therefore, the viscosity of the system recovers rapidly after shearing, demonstrating excellent anti-settling and workability.

[0018] 5. Raw material and cost advantages: Using inexpensive polyethylene wax as a starting material, high-performance products are obtained through relatively simple chemical modification, resulting in significant cost benefits and market competitiveness. Detailed implementation methods and effect examples (the following are exemplary descriptions; actual applications require specific experimental data). Example 1: Synthesis of OPE-g-urea (C18) 1. Dissolve 100g of polyethylene wax with Mn=5000 in 500g of decahydronaphthalene. Introduce oxygen containing ozone (3wt%) at 160℃, then add 0.5g of manganese acetate and 0.3g of di-tert-butyl peroxide. Stop the reaction when the acid value reaches 45 mg KOH / g. This yields CCP-I.

[0019] 2. Take 50g of the above CCP-I (containing approximately 16 mmol of carboxyl groups), dissolve it in 200g of NMP, add 4.8g (80mmol) of ethylenediamine, and react at 130℃ for 6 hours. Dry the precipitate to obtain CCP-NH2.

[0020] 3. Dissolve 40g of CCP-NH2 (containing approximately 12 mmol of amino groups) in toluene, add 3.4g (12 mmol) of octadecyl isocyanate dropwise, and react at 80°C for 3 hours. Dry the precipitate to obtain 45g of the final product. Application testing: A comparison was made between adding 2 wt% of the product of this invention to No. 100 white oil (Example 1) and adding 2 wt% of commercially available oxidized polyethylene wax (acid value ~15) and 2 wt% hydrogenated castor oil.

[0021] - Dispersibility: The product of this invention forms a uniform and transparent gel after stirring at room temperature for 30 minutes; commercially available OPE wax needs to be heated to 90°C and kept at that temperature for 30 minutes, and becomes translucent after cooling; hydrogenated castor oil needs to be melted and then cooled to crystallize.

[0022] - Transparency: The transmittance (600nm) of the system of this invention is >85%; the transmittance of commercially available OPE systems is about 60%.

[0023] - Rheological properties (25℃): - Zero shear viscosity: This invention > 10,000 Pa·s; commercially available OPE ~ 500 Pa·s; hydrogenated castor oil ~ 3,000 Pa·s.

[0024] - Thixotropic recovery rate (the percentage of viscosity recovered within 10 seconds at 3 rpm) This invention contains >90%; commercially available OPE ~40%; hydrogenated castor oil ~75%. in conclusion This invention, through precise secondary chemical design of oxidized polyethylene, successfully transforms a mediocre wax product into a high-performance rheology modifier with a well-defined structure, high efficiency and transparency, and easy use, perfectly solving the dual requirements of low-polarity systems for excellent rheological properties and appearance quality.

Claims

1. A rheology modifier for low-polarity systems, which is a comb-like polymer, characterized in that, The main chain of the polymer is carboxylated polyethylene, and the carboxyl group is connected by an amide bond to a side chain with the structure shown in formula (II): `-CO-NH-R¹-NH-CO-NH-R²`, where R¹ is a C2-C6 alkylene group and R² is a C8-C22 alkyl or alkylaryl group.

2. The rheology modifier according to claim 1, characterized in that, The carboxylated polyethylene backbone has a number average molecular weight of 2,000-10,000, and its carboxyl functionalization degree is 10-50 carboxyl groups per 1,000 carbon atoms in the backbone.

3. A method for preparing the rheology modifier as described in claim 1 or 2, characterized in that, Includes the following steps: (1) In the presence of a directional oxidation catalyst and a free radical initiator, polyethylene wax is controlled to be oxidized in a solvent to obtain a carboxylated polyethylene intermediate; (2) React the intermediate obtained in step (1) with an excess of aliphatic diamine to perform amidation, and obtain an amino-terminated intermediate; (3) React the amino-terminated intermediate obtained in step (2) with a long-chain monoisocyanate to ureate it, and obtain the rheology modifier.

4. The method according to claim 3, characterized in that, The directional oxidation catalyst in step (1) is manganese acetate or cobalt stearate, and the free radical initiator is di-tert-butyl peroxide; the oxidation reaction endpoint is controlled by monitoring the acid value.

5. The method according to claim 3, characterized in that, The aliphatic diamine mentioned in step (2) is ethylenediamine or hexamethylenediamine.

6. The method according to claim 3, characterized in that, The long-chain monoisocyanate mentioned in step (3) is octadecyl isocyanate or dodecyl isocyanate.

7. The application of the rheology modifier as described in claim 1 or 2 in a low-polarity medium selected from white oil, mineral oil, and synthetic alkanes.

8. A low-polarity fluid composition comprising a continuous phase and a rheology modifier, characterized in that, The continuous phase is white oil, mineral oil, or synthetic alkane, and the rheology modifier is the comb-like polymer as described in claim 1 or 2.

9. The composition according to claim 8, characterized in that, The amount of the rheology modifier added is 0.5% - 5.0% based on the total weight of the composition.