A process for modifying liquid propylene rubber

Abstract

The application discloses a modification process of liquid propylene rubber and belongs to the technical field of chemical modification of high polymer materials. The process specifically comprises the following steps: S1, pre-swelling of a modification monomer and an interface compatibility aid in liquid rubber at low temperature T1; S2, body grafting reaction by dropping an initiator under high shear stirring after temperature rising to T2; S3, stabilization by adding a terminating agent after temperature falling to T3; and S4, deep vacuum devolatilization after temperature rising to T4. The electronic effect of a styrene aid is utilized to inhibit beta scission of a tertiary carbon free radical, and a step-by-step temperature changing and dropping control strategy is used, so that the contradiction that grafting rate and viscosity retention rate cannot be simultaneously obtained in the prior art is effectively solved; the modified liquid propylene rubber prepared has a grafting rate greater than 1.2%, a viscosity drop rate less than 15%, and low VOC content, and is particularly suitable for high-performance tires and sealing materials.

Description

Technical Field

[0001] This invention relates to the field of chemical modification of polymer materials, and particularly to a modification process for liquid propylene rubber, and more specifically, to a modification process for liquid propylene rubber with high grafting rate and low degradation. Background Technology

[0002] Liquid rubber, as an important functional softener and toughening agent, is widely used in high-performance tires, sealing materials, and adhesives. Compared to unsaturated liquid diene rubbers (such as liquid polyisoprene), liquid propylene rubbers (such as low molecular weight random polypropylene or ethylene-propylene copolymer oil) have excellent heat aging resistance and chemical stability due to their saturated main chain. However, liquid propylene rubber is non-polar, which limits its compatibility and adhesion strength with metals, polar fillers (such as silica), or polar polymer matrices. Therefore, introducing polar groups (such as maleic anhydride) through chemical grafting is key to expanding its applications.

[0003] Existing rubber industry technologies already heavily involve the use of liquid rubber or plasticizers. For example, Chinese invention patent CN102105521B discloses a rubber mixture containing an environmentally friendly plasticizer for the production of tire treads. This document (see paragraphs

[0001] -

[0006] of the specification and claim 1) mainly focuses on using plasticizers from non-fossil sources (such as biomass liquefaction oil) or without polycyclic aromatic compounds to replace traditional toxic plasticizers, and mentions the use of liquid polymers (such as liquid polybutadiene and liquid polyisoprene) as components. However, this prior art mainly focuses on the formulation composition of the rubber mixture and the improvement of its environmental performance. Its disclosure focuses on how to physically mix existing liquid plasticizers into the rubber matrix, without addressing how to chemically modify the liquid polymer itself. In particular, for liquid propylene rubber, this document does not teach how to solve the chemical reaction problems it faces in the functionalization process.

[0004] Furthermore, regarding the manufacturing process, Chinese invention patent CN105086006B discloses a method for manufacturing a self-sealing composition. This method (see claims 1 and paragraphs

[0014] -

[0016] of the specification) describes controlling the "hot mixing temperature" and "second temperature" in a mixer through a specific masterbatch preparation process, and introducing a liquid plasticizer with a glass transition temperature below -20°C into a diene elastomer and a hydrocarbon resin. Although this prior art document discloses in detail the physical mixing process for handling liquid plasticizers in industrial mixing equipment, including the order of feeding and temperature control, its technical essence is still a physical blending process. This method aims to solve the problems of "viscousness" and "processing difficulty" caused by high content of liquid plasticizers, rather than solving the problem of molecular structure control of liquid rubber during chemical grafting reactions.

[0005] For the chemical modification of liquid propylene rubber, the biggest technical bottleneck at present is the contradiction between "grafting rate" and "molecular weight retention". As we all know, the main chain of propylene polymers contains a large number of tertiary carbon atoms. Under the action of free radical initiators, tertiary carbon free radicals are very prone to β-fracture. If conventional solution grafting is used, although the reaction is mild, solvent recovery is difficult, which not only increases the cost, but also makes it difficult to meet the increasingly stringent environmental protection and low VOC requirements mentioned in CN102105521B. If conventional melt extrusion is used, the low viscosity of liquid rubber makes it difficult to establish an effective shear field in the screw, and local overheating will cause the molecular chains to degrade violently, causing the product to lose the high viscosity properties of rubber and become a useless low-molecular-weight oil.

[0006] In summary, although the aforementioned prior art documents CN102105521B and CN105086006B disclose the application of liquid rubber in tires and sealing materials and physical compounding methods, neither of them provides an effective process for bulk chemical modification of liquid propylene rubber. The existing technology lacks a preparation process that can both utilize industrial equipment for solvent-free or low-solvent production and effectively suppress the β-fracture degradation of the polypropylene backbone through specific process parameters and synergistic effects of additives to achieve high polarity grafting.

[0007] Based on this, this application proposes a liquid propylene rubber modification process that combines pre-swelling dispersion, stepwise temperature control, and synergistic effects of interfacial compatibility additives to solve the above-mentioned technical problems. Summary of the Invention

[0008] In existing technologies, the free radical grafting modification of liquid propylene rubber (such as atactic polypropylene or ethylene-propylene copolymer) suffers from low grafting rates and a high likelihood of main chain degradation. Addressing the technical challenge of significant viscosity reduction due to fracture, and the shortcomings of existing solution methods (high solvent residue) and melt methods (uncontrollable reaction), this invention provides a modification process for liquid propylene rubber. This process can significantly improve the grafting rate of liquid propylene rubber, while effectively inhibiting main chain degradation, maintaining the viscosity stability of the material, and the process is environmentally friendly and efficient.

[0009] To achieve the above objectives, the present invention adopts the following technical solution: A modification process for liquid propylene rubber, comprising the following steps: Step 1, Pre-swelling and activation: Liquid propylene rubber is added to the reactor and heated to the preheating temperature T1 while stirring. Then, modified monomers and interfacial compatibility additives are added and the mixture is stirred at a constant temperature to carry out physical swelling and micro-dispersion to obtain a premixed system. Step 2, initiate the grafting reaction: heat the premixed system obtained in step 1 to the reaction temperature T2, add the initiator solution dropwise, maintain high shear stirring during the dropwise addition, and keep the reaction at the temperature for a certain period of time after the initiator is added; Step 3, chain termination and stabilization: After the reaction is complete, cool the system to T3, add the chain terminator and composite antioxidant, and continue stirring until the system is homogeneous; Step 4, Post-processing purification: Under vacuum conditions, the system is heated to the devolatilization temperature T4, and unreacted monomers and small molecule residues are removed by thin-film evaporation or vacuum stripping. After cooling and filtration, the modified liquid propylene rubber is obtained. The interfacial compatibility aid is a styrene derivative or a nitrogen-containing heterocyclic compound, and its addition amount is in a molar ratio of 0.5:1 to 1.5:1 with respect to the modified monomer. During the reaction process, the temperature is controlled to satisfy T1 < T2 < T4, and T3 < T1.

[0010] Preferably, the liquid propylene rubber is atactic polypropylene (APP) or ethylene-propylene liquid copolymer with a number average molecular weight (Mn) between 1,000 and 50,000 g / mol; the modified monomer is selected from at least one of maleic anhydride, acrylic acid, glycidyl methacrylate (GMA) or itaconic acid.

[0011] Preferably, the interface compatibility agent is selected from one or more of styrene, α-methylstyrene, divinylbenzene, or N-vinylpyrrolidone. This interface compatibility agent stabilizes the modified monomer through electronic effects during free radical grafting, inhibiting the β-splitting of tertiary carbon free radicals in the main chain of liquid propylene rubber.

[0012] Preferably, in step 2, the initiator is selected from dicumyl peroxide (DCP), 2,5-dimethyl-2,5-bis(tert-butylperoxy)hexane (DBPH), or tert-butyl peroxide (TBPB); the initiator is pre-dissolved in liquid alkane or partially liquid propylene rubber as a solvent to prepare an initiator solution, and the dropping time is controlled between 30 and 90 minutes. The dropping method aims to control the instantaneous free radical concentration in the system and avoid crosslinking or explosive polymerization caused by excessively high local concentrations.

[0013] Preferably, the temperature control parameters for each step are as follows: preheating temperature T1 is 80℃ to 110℃; reaction temperature T2 is 130℃ to 160℃; cooling temperature T3 is 60℃ to 80℃; and devolatilization temperature T4 is 170℃ to 200℃. By controlling the temperature in stages, the monomer is ensured to fully penetrate at low temperatures, react stably at moderate temperatures, and efficiently devolatilize at high temperatures.

[0014] Preferably, the high-shear stirring in step 2 is achieved using a high-shear dispersion emulsifier or a reactor with a turbine impeller, with the stirring rate controlled between 500 and 3000 rpm. The high shear effect ensures that the polar monomers form a micron-sized dispersed phase in the non-polar liquid rubber matrix, increasing the reaction interface area.

[0015] Preferably, the composite antioxidant added in step 3 comprises a hindered phenolic primary antioxidant and a phosphite secondary antioxidant, with a mass ratio of 1:1 to 1:2, and the total amount of composite antioxidant added is 0.1% to 1.0% of the mass of liquid propylene rubber.

[0016] Preferably, the vacuum condition in step 4 is an absolute pressure of less than 5000 Pa, and nitrogen or water vapor is introduced during the devolatilization process as an entrainer to assist in the removal of unreacted monomers.

[0017] Compared with the prior art, the present invention has the following significant advantages: 1. Significantly inhibits main chain degradation and maintains viscosity stability: This invention introduces specific interfacial compatibility additives (such as styrene) and utilizes their conjugated double bond structure as electron donors to preferentially form charge-transfer complexes (CTCs) with modified monomers (such as maleic anhydride). These complexes react more readily with polypropylene macromolecular free radicals. This not only improves grafting efficiency but, more importantly, competitively inhibits the β-fracture reaction of tertiary carbon free radicals. The Englar viscosity reduction rate of liquid propylene rubber modified by this process is controlled within 15%, which is far superior to the traditional melt grafting process (which typically has a reduction rate of over 50%).

[0018] 2. High grafting rate and high monomer conversion rate: This invention employs a stepwise temperature-varying strategy of "low-temperature pre-swelling - high-temperature reaction," combined with a "drop-feeding process" and "high-shear stirring" of the initiator. Pre-swelling (T1) ensures the uniform distribution of monomer molecules among the liquid rubber segments; the drop-feeding initiator avoids explosive polymerization and local overheating; and the high shear increases the reaction interface. The synergistic effect of these multiple methods allows the grafting rate of the modified product to stably reach over 1.2 wt%, significantly improving the polarity of the liquid propylene rubber.

[0019] 3. Environmentally friendly process and high product purity: Compared with the traditional solution grafting method, this process is mainly based on bulk reaction, requiring only a very small amount or no solvent to dissolve the initiator, which greatly reduces VOC emissions and solvent recovery energy consumption. At the same time, through the high-temperature vacuum devolatilization and entrainer technology in step 4, residual monomers and small molecule by-products are effectively removed, so that the final product has no irritating odor and meets the high standards of environmental protection and safety requirements of modern tire and sealing materials (such as those advocated by comparative documents CN102105521B and CN105086006B). Detailed Implementation

[0020] The present invention will be further described in detail below with reference to specific embodiments. These embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Those skilled in the art can make various modifications or equivalent substitutions to the technical solutions of the present invention without departing from the spirit of the invention, and all such modifications and substitutions should be included within the protection scope of the present invention.

[0021] 1. Raw materials and reagents Unless otherwise stated, all raw materials used in this embodiment are commercially available industrial-grade or analytical-grade products: Liquid propylene rubber (L-PP): Random polypropylene liquid with a number average molecular weight (Mn) of approximately 5000 g / mol and an initial Engler viscosity (E50) of 48.5. It was purchased from a domestic petrochemical company.

[0022] Modified monomer: maleic anhydride (MAH), purity ≥ 99.5%.

[0023] Interface compatibility aid: Styrene (St), purity ≥99.0%.

[0024] Initiator: dicumyl peroxide (DCP), dissolved in a small amount of liquid alkane to prepare a 50% concentration solution before use.

[0025] Antioxidant: Antioxidant 1010 and Antioxidant 168 are mixed in a 1:1 mass ratio.

[0026] Terminating agent: ethanol.

[0027] 2. Testing Methods To objectively evaluate the modification effect, the present invention uses the following standard methods for performance testing: (1) Grafting rate (Gw) determination: Take 2g of the modified sample, dissolve it in hot xylene, wash it three times with acetone precipitation to remove unreacted monomers and homopolymers, dry it under vacuum, determine the acid value by chemical titration (KOH-ethanol standard solution), and calculate the grafting rate (wt%).

[0028] (2) Viscosity and viscosity retention rate determination: Engla viscosity (E50, i.e., conditional viscosity at 50°C) was determined according to GB / T266-1988 standard.

[0029] Viscosity retention rate (%) = (E50 of modified sample / E50 of raw material L-PP) × 100% Degradation rate (%) = 100% - viscosity retention rate (3) Determination of volatile matter (VOC): Take a quantitative sample and heat it in a 180℃ oven for 2 hours, then calculate the mass loss rate. Example

[0030] This embodiment provides a process for modifying liquid propylene rubber.

[0031] The specific steps are as follows: (1) Pre-swelling (Step 1): Add 1000g of liquid propylene rubber (L-PP) to a 2L stainless steel reactor equipped with a turbine agitator, a reflux condenser, and a vacuum interface. Start stirring (200rpm) and heat to the preheating temperature T1=90℃. Then add 15g of maleic anhydride (MAH) and 15g of styrene (St) (MAH to St molar ratio approximately 1:0.94, mass ratio 1:1). Stir at a constant temperature for 30 minutes to allow the monomers and additives to fully swell and disperse in the liquid rubber.

[0032] (2) Initiation of the reaction (step 2): Increase the stirring speed to 1500 rpm (high shear state) and simultaneously heat the system to the reaction temperature T2 = 145℃. Add the initiator DCP solution (containing 1.5 g of dry DCP) dropwise at a constant rate using a metering pump over a period of 60 minutes. After the addition is complete, maintain the temperature and continue stirring for another 60 minutes.

[0033] (3) Stabilization (Step 3): After the reaction is complete, turn on the cooling water circulation to cool the system to T3=70℃. Add 2g of ethanol as a chain terminator and 5g of composite antioxidant (1010 / 168), and stir at low speed for 20 minutes to make the system homogeneous.

[0034] (4) Post-processing (Step 4): Turn off the reflux condenser, turn on the vacuum system (absolute pressure < 5000 Pa), and slowly raise the temperature to the devolatilization temperature T4 = 180℃. At the same time, introduce a small amount of nitrogen as an entrainer and maintain vacuum devolatilization for 30 minutes to remove residual monomers and styrene. Finally, filter through a 200-mesh filter to obtain the modified liquid propylene rubber product. Example

[0035] Except for the following parameter adjustments, the remaining steps are the same as in Example 1: The amount of styrene (St) added as an interfacial compatibility additive is halved to 7.5g (the molar ratio of MAH to St is approximately 1:0.47).

[0036] Preheating temperature T1 = 80℃.

[0037] The reaction temperature T2 = 135℃.

[0038] Deviation temperature T4 = 170℃. Example

[0039] This embodiment examines another modified monomer (GMA) under higher temperature conditions.

[0040] Except for the following parameter adjustments, the remaining steps are the same as in Example 1: The modified monomer was replaced with 20g of glycidyl methacrylate (GMA).

[0041] The interface compatibility aid was replaced with 20g of α-methylstyrene.

[0042] The reaction temperature T2 = 155℃.

[0043] The initiator addition time was extended to 90 minutes.

[0044] Comparative Example 1 (without interfacial compatibility additives) To verify the effect of the interface compatibility aid on inhibiting degradation, this comparative example is based on Example 1, but without the addition of styrene (St), only maleic anhydride (MAH) is added, and the remaining process steps and conditions are completely consistent with Example 1.

[0045] Comparative Example 2 (Initiator added all at once) To verify the effect of the dropping process on reaction control, this comparative example, based on Example 1, involves adding the initiator DCP solution to the reactor in one go in step S2, instead of dropping it. All other conditions remain the same as in Example 1.

[0046] Comparative Example 3 (Traditional Constant Temperature Process) It simulates the traditional bulk modification process without step-by-step temperature changes.

[0047] Liquid propylene rubber, maleic anhydride, styrene, and initiator are mixed and added to a reaction vessel at one time, and the temperature is directly raised to 145°C and reacted for 2 hours. Then, the mixture is directly vacuumed at 145°C for devolatilization.

[0048] 3. Performance Test Results and Analysis The performance test results of the modified liquid propylene rubber prepared in each embodiment and comparative example are summarized in Table 1.

[0049] Table 1 Summary of performance test data for each embodiment and comparative example project Example 1 Example 2 Example 3 Comparative Example 1 (without additives) Comparative Example 2 (non-droplet addition) Comparative Example 3 (Traditional Process) Grafting rate (wt%) 1.35 1.12 1.28 0.45 0.82 0.65 Initial E50 viscosity 48.5 48.5 48.5 48.5 48.5 48.5 Modified E50 viscosity 44.6 43.2 45.1 18.4 25.6 29.8 Viscosity retention rate (%) 92.0％ 89.1％ 93.0％ 37.9％ 52.8％ 61.4％ Degradation rate (%) 8.0％ 10.9％ 7.0％ 62.1％ 47.2％ 38.6％ Appearance and smell Pale yellow, transparent, and odorless Pale yellow, transparent, with a slight odor Pale yellow, transparent, and odorless Darker colors are more irritating. Turbid with gel spots Yellow with a lingering smell Analysis of experimental results: Regarding the inhibition of degradation (Comparative Example 1 and Comparative Example 1): Example 1, which introduced styrene as an interfacial compatibility agent, achieved a viscosity retention rate as high as 92.0%, indicating very slight main chain degradation. In contrast, Comparative Example 1, without styrene, exhibited a viscosity retention rate of only 37.9% despite identical reaction conditions, indicating severe β-fracture of the liquid propylene rubber, transforming it into a low-molecular-weight oily substance. This fully demonstrates the crucial role of the "interfacial compatibility agent" as defined in the claims in suppressing tertiary carbon radical fracture.

[0050] Regarding grafting efficiency (comparative Example 1 and Comparative Examples 1 and 2): The grafting rate in Example 1 reached 1.35%, significantly higher than the 0.45% in Comparative Example 1. This is because styrene not only inhibited degradation but also enhanced reactivity by forming a charge-transfer complex (CTC) with maleic anhydride. Comparing Example 1 and Comparative Example 2, it can be seen that the initiator "drop-addition" process (Example 1) has a higher grafting rate and better viscosity retention than the "one-time addition" process (Comparative Example 2). This is because drop-addition maintains a lower instantaneous free radical concentration, avoiding side reactions.

[0051] Regarding process control (Comparative Example 1 and Comparative Example 3): Example 1 employed a stepwise temperature-varying process of "T1 pre-swelling - T2 reaction - T4 devolatilization," resulting in a product with a good appearance and no odor. In contrast, Comparative Example 3 used a traditional one-pot constant-temperature process, which, due to the lack of low-temperature pre-dispersion and high-temperature deep devolatilization, resulted in a lower grafting rate and difficulty in removing residual monomers (with a strong odor).

[0052] In summary, this invention, through the synergistic effect of specific process steps (stepwise temperature variation, high shear, and dropwise addition) and specific chemical additives (interfacial compatibility additives), successfully solves the technical challenge of achieving both "high grafting rate" and "low degradation" in the modification of liquid propylene rubber, and prepares a modified liquid propylene rubber with excellent performance.

Claims

1. A modification process for liquid propylene rubber, characterized in that, Includes the following steps: Step 1, Pre-swelling and activation: Liquid propylene rubber is added to the reactor and heated to the preheating temperature T1 while stirring. Then, modified monomers and interfacial compatibility additives are added and the mixture is stirred at a constant temperature to carry out physical swelling and micro-dispersion to obtain a premixed system. Step 2, initiate the grafting reaction: heat the premixed system obtained in step 1 to the reaction temperature T2, add the initiator solution dropwise, maintain high shear stirring during the dropwise addition, and keep the reaction at the temperature for a certain period of time after the initiator is added; Step 3, chain termination and stabilization: After the reaction is complete, cool the system to T3, add the chain terminator and composite antioxidant, and continue stirring until the system is homogeneous; Step 4, Post-processing purification: Under vacuum conditions, the system is heated to the devolatilization temperature T4, and unreacted monomers and small molecule residues are removed by thin-film evaporation or vacuum stripping. After cooling and filtration, the modified liquid propylene rubber is obtained. The interfacial compatibility aid is a styrene derivative or a nitrogen-containing heterocyclic compound, and its addition amount is in a molar ratio of 0.5:1 to 1.5:1 with respect to the modified monomer. During the reaction, T1 < T2 < T4, and T3 < T1.

2. The modification process for liquid propylene rubber according to claim 1, characterized in that, The liquid propylene rubber is atactic polypropylene (APP) or ethylene-propylene liquid copolymer with a number average molecular weight (Mn) between 1,000 and 50,000 g / mol; the modified monomer is selected from at least one of maleic anhydride, acrylic acid, glycidyl methacrylate (GMA) or itaconic acid.

3. The modification process for liquid propylene rubber according to claim 1, characterized in that, The interface compatibility agent is selected from one or more of styrene, α-methylstyrene, divinylbenzene, or N-vinylpyrrolidone; the function of the interface compatibility agent is to stabilize the modified monomer through electronic effects during free radical grafting and inhibit the β-fracture degradation of the liquid propylene rubber backbone.

4. The modification process for liquid propylene rubber according to claim 1, characterized in that, In step 2, the initiator is selected from dicumyl peroxide (DCP), 2,5-dimethyl-2,5-bis(tert-butylperoxy)hexane (DBPH) or tert-butyl peroxide (TBPB); the initiator is pre-dissolved in liquid alkane or partially liquid propylene rubber as a solvent to prepare an initiator solution, and the dropping time is controlled between 30 and 90 minutes.

5. The modification process for liquid propylene rubber according to claim 1, characterized in that, The temperature control parameters for each step are as follows: The preheating temperature T1 is 80℃ to 110℃; The reaction temperature T2 is 130℃ to 160℃; The cooling temperature T3 is 60℃ to 80℃; The devolatilization temperature T4 is 170℃ to 200℃.

6. The modification process for liquid propylene rubber according to claim 1, characterized in that, The high-shear stirring described in step 2 is achieved by a high-shear dispersion emulsifier or a reactor with a turbine impeller, with the stirring rate controlled between 500 and 3000 rpm to ensure that the modified monomer forms a micron-scale dispersed phase in the liquid rubber matrix.

7. The modification process for liquid propylene rubber according to claim 1, characterized in that, The composite antioxidant added in step 3 includes a hindered phenolic primary antioxidant and a phosphite secondary antioxidant, with a mass ratio of 1:1 to 1:2, and the total amount of composite antioxidant added is 0.1% to 1.0% of the mass of liquid propylene rubber.

8. The modification process for liquid propylene rubber according to claim 1, characterized in that, The vacuum condition in step 4 is an absolute pressure of less than 5000 Pa, and nitrogen or water vapor is introduced as an entrainer during the devolatilization process to assist in the removal of unreacted monomers.

9. The modified liquid propylene rubber prepared by the modification process according to any one of claims 1-8 has a grafting rate greater than 1.2 wt%, and the reduction rate of the modified Engela viscosity (E50) is less than 15% of the original liquid propylene rubber viscosity.

10. The application of the modified liquid propylene rubber according to claim 9 in the preparation of hot melt adhesives, asphalt modifiers, or as a polymer alloy compatibilizer.