Application of high para-isomer content methylstyrene mixtures in the preparation of polystyrene substitute copolymers

Abstract

This invention provides the application of a mixture of methylstyrene with high para-isomer content in the preparation of polystyrene substitute copolymers, belonging to the field of polymer material synthesis technology. This invention is the first to directly utilize a low-cost mixture of methylstyrene isomers to replace high-purity styrene. Through a "boiling-condensation" cycle in the fluidized bed polymerization process, efficient and constant-temperature heat dissipation is achieved, effectively overcoming the heat transfer difficulties and temperature runaway risks of traditional bulk polymerization. This facilitates control of the polymerization mechanism and yields random copolymers with a narrow molecular weight distribution and mechanical properties comparable to general-purpose polystyrene. This method is simple and controllable, significantly reduces raw material costs, and combines economic benefits with environmental value. The resulting copolymers can be used in general plastics, packaging materials, and other fields.

Description

Technical Field

[0001] This invention belongs to the field of polymer material synthesis technology, and relates to polymer compounds obtained by reacting only carbon-carbon unsaturated bonds, specifically the application of methylstyrene mixtures with high para-isomer content in the preparation of polystyrene substitute copolymers. Background Technology

[0002] Polystyrene copolymers are a class of widely used thermoplastic resins, commonly used in the manufacture of plastic products, coatings, packaging materials, and appliance housings. Current industrial production of polystyrene copolymers heavily relies on high-purity styrene monomers. However, styrene is derived from non-renewable petroleum resources, and its market price fluctuates significantly but generally shows an upward trend. Furthermore, the refining and purification processes for high-purity monomers are complex, leading to high production costs. Therefore, developing alternative monomers and polymerization processes with similar performance but lower costs is of great significance.

[0003] Among many potential alternative monomers, poly(p-methylstyrene) has outstanding characteristics such as light weight, high heat resistance, good transparency, and excellent processing fluidity. However, the high cost of separating and purifying high-purity p-methylstyrene monomer limits the economic viability of using high-purity p-methylstyrene directly as a raw material monomer.

[0004] In contrast, a more cost-effective solution is to use a mixture of isomers of methylstyrene (ortho-, meta-, and para-methylstyrene). Currently, these are petrochemical derivatives, with wider availability, easier access, and significantly lower costs than high-purity styrene or high-purity para-methylstyrene (currently, the low-cost mixture of methylstyrene isomers is often treated as low-grade fuels or waste, failing to realize its high-value utilization). After research, the inventors believe that if the aforementioned inexpensive "mixture of isomers" of methylstyrene could be directly used as comonomers to replace part or all of the styrene, raw material costs could be greatly reduced, turning waste into treasure. This aligns with the development direction of green chemistry and the "dual carbon goals" of energy conservation and emission reduction, promoting the recyclable use of resources.

[0005] However, directly using this complex mixture of isomers of methylstyrene to synthesize copolymers presents significant technical challenges. If conventional polymerization is carried out using a mixture of isomers with a near-equilibrium para-position content (40%), the varying reactivity of the isomers often leads to poor controllability, low yields, and an excessively wide molecular weight distribution in the product. Consequently, the mechanical and thermal properties of the final material are unstable, and batch stability is poor, making it difficult to meet the requirements of high-end applications. The differences in reactivity of the different isomers in the mixture and the control of sequence distribution during the copolymerization process are the core reasons for these problems.

[0006] From the perspective of polymer structure, general-purpose styrene polymers are mainly divided into random copolymers and syndiotactic (or isotactic) copolymers. Random copolymers account for the vast majority of the market (over 95%), such as GPPS, HIPS, EPS, AS, SBS, ABS, and MBS. Their chain segment sequences are randomly distributed, and the materials are usually amorphous, exhibiting high transparency and good processing flowability. Syndiotactic polystyrene (SPS), on the other hand, is a crystalline polymer, and its industrialization technology is still under development and refinement. Therefore, achieving a direct synthesis of qualified random copolymer polystyrene copolymers from inexpensive "isomeric mixtures" of methylstyrene is a key technological breakthrough.

[0007] Currently, there are some technical reports on the copolymerization of styrene and methylstyrene, but none of them have solved the problem of the direct and efficient utilization of the aforementioned "isomeric mixture". Directly using this complex mixture of isomers for controlled polymerization to synthesize random copolymers with qualified performance faces a series of technical challenges:

[0008] (1) At the polymerization process level, the industrial production of general-purpose polystyrene mainly adopts solvent-free bulk polymerization. Although it has advantages such as simple post-processing, it has a fundamental drawback: as the conversion rate increases, the viscosity of the system increases sharply, and the heat of polymerization is difficult to remove quickly. This easily leads to uneven temperature distribution and local overheating in the reactor. From the perspective of polymerization mechanism, the chain termination mode of styrene free radical polymerization is significantly affected by temperature. Studies have shown that although styrene polymerization is mainly terminated by coupling, the proportion of disproportionation termination increases significantly with increasing temperature (for example, at 60℃, the proportion of disproportionation termination can reach about 23%). Coupling termination doubles the molecular weight, which helps to obtain products with a narrow molecular weight distribution; while the increase in the proportion of disproportionation termination leads to a decrease in the average molecular weight of the product and a widening of the molecular weight distribution (PDI), which directly affects the mechanical properties and processing stability of the material. Due to the difficulty of heat dissipation, traditional bulk polymerization is often forced to adopt a programmed temperature increase strategy (such as gradually increasing from 100℃ to 160℃), which undoubtedly exacerbates the change in termination mode and is not conducive to obtaining products with uniform molecular weight and stable performance. When using a mixture of isomers of methylstyrene with varying reactivity, heat dissipation and reaction control issues become more prominent.

[0009] (2) Regarding monomer characteristics and utilization, existing technologies mostly focus on using high-purity, single-structure methylstyrene monomers. For example, Chinese patent application CN119955003A discloses a copolymerization of styrene and α-methylstyrene and its hydrogenation method. Due to the large steric hindrance of the α-methyl group, α-methylstyrene has a significant upper temperature limit (approximately 130-140℃) for homopolymerization and a low enthalpy change in polymerization, which limits its homopolymerization application. However, it can improve heat resistance as a comonomer. However, this patent application uses high-purity α-methylstyrene monomers and does not involve the utilization of low-cost isomer mixtures of methylstyrene. Furthermore, its anionic polymerization process still needs to be carried out within a relatively wide temperature range (30℃~150℃). For mixture systems containing different active monomers, it is difficult to accurately control the reaction process and product uniformity. In the aforementioned mixture of isomers, the methyl substitution on the benzene ring of p-methylstyrene is mainly due to electron-donating effects, and its steric hindrance is much smaller than that of α-methyl. Their polymerization behavior is closer to that of styrene, and there is no obvious upper limit temperature limitation. This makes it possible for them to copolymerize in a wider process window, but it also places higher demands on the uniformity of the copolymerization sequence.

[0010] (3) At the material system design level, US patent application US4352908A discloses blends of poly(p-methylstyrene) or polystyrene with specific styrene-diene-styrene block copolymers, aiming to improve the impact properties of materials, etc. This technology focuses on the physical blending modification of polymer products, rather than the chemical synthesis process starting from monomers, and does not involve any method of directly preparing random copolymers from isomer mixtures.

[0011] (4) At the level of connecting basic research with industrial applications, the early research paper "Phillips, BD, TL Hanlon, and AV Tobolsky. Ionic copolymerization of styrene and p-methylstyrene. Journal of Polymer Science Part A: General Papers 2.9 (1964): 4231-4245." systematically investigated the copolymerization behavior of styrene and p-methylstyrene in different ionic initiators and solvents, revealing the law of variation of copolymer composition with initiation system and solvent polarity. This study focused on copolymerization mechanism and basic scientific issues, but did not explore a large-scale free radical polymerization method applicable to complex isomer mixtures (containing ortho-, meta-, and p-methylstyrene) with simple and controllable processes, and did not solve the heat dissipation control problem that is common in such polymerizations.

[0012] In summary, there is a long-standing lack and an urgent need in this field to develop an industrially feasible method that can directly and efficiently utilize isomer mixtures, achieve efficient heat dissipation and precise temperature control during polymerization, thereby effectively regulating the polymerization mechanism (such as controlling the proportion of termination methods), and ultimately preparing random copolymers with comprehensive performance comparable to general polystyrene. Summary of the Invention

[0013] This invention was made to solve the above-mentioned problems, and its purpose is to provide the application of methylstyrene mixtures with high para-isomer content in the preparation of polystyrene alternative copolymers.

[0014] This invention provides the application of a high para-isomer content methylstyrene mixture in the preparation of polystyrene substitute copolymers. The high para-isomer content methylstyrene mixture includes o-methylstyrene, m-methylstyrene, and p-methylstyrene, with molar fraction ratios ranging from (0%, 10%) to [90%, 100%] and [100%]. The application steps are as follows: Under an inert atmosphere, the high para-isomer content methylstyrene mixture and styrene are added to solvent A at a molar fraction ratio of (10~100):(90~0). Using a peroxide compound as an initiator, the mixture is heated to boiling and refluxed for 1~10 hours. After precipitation in an alcohol solvent B, the mixture is filtered, washed, and dried to obtain the polystyrene substitute copolymer.

[0015] Preferably, the molar fraction of p-methylstyrene in the high para-isomer content methylstyrene mixture is greater than 95%.

[0016] Preferably, the molar ratio of the high para-isomer content methylstyrene mixture to styrene is (50~75):(50~25).

[0017] In the application provided by this invention, it may also have the following characteristics: wherein solvent A is a ketone solvent, ester solvent, ether solvent, or aromatic hydrocarbon solvent with a boiling point higher than 100°C and miscible with peroxide initiators. The ketone solvent includes methyl n-propyl ketone, methyl n-butyl ketone, methyl isobutyl ketone, cyclohexanone, and isophorone; the ester solvent includes n-butyl acetate and isobutyl acetate; the ether solvent includes diethylene glycol dimethyl ether; and the aromatic hydrocarbon solvent includes toluene, p-xylene, and mesitylene.

[0018] In the applications provided by this invention, the following features may also be included: the peroxide compounds include tert-butyl peroxide-2-ethylhexanoate, 1,1-di(tert-butylperoxy)cyclohexane, dicumyl peroxide, ditert-butyl peroxide, and ditert-pentyl peroxide.

[0019] In the applications provided by this invention, it may also have the following feature: wherein the alcohol solvent B includes any one or more of methanol, ethanol, and water.

[0020] The present invention also provides a performance-comparable alternative to polystyrene copolymers, having the characteristics of being prepared by the steps of any of the preceding applications.

[0021] The alternatives provided by this invention may also have the following characteristics: the number average molecular weight of the alternative is 20,000 to 100,000, the weight average molecular weight is 40,000 to 300,000, the density is 0.9 g / cm3 to 1.2 g / cm3, the tensile strength of the alternative is 35 MPa to 45 MPa, the tensile modulus is 2.5 GPa to 4.0 GPa, the elongation at break is 1.0% to 4.0%, and the flexural modulus is 2.5 GPa to 4.0 GPa.

[0022] The present invention also provides the aforementioned alternatives for use in thermoplastic resins.

[0023] The present invention has the following beneficial effects:

[0024] (1) For the first time, the mixture of methylstyrene isomers rich in p-methylstyrene was used directly as the main comonomer, which significantly reduced the cost of raw materials and realized the high-value utilization of low-value raw materials, thus achieving both economic and environmental benefits.

[0025] (2) The process is simple and reliable. By selecting a solvent system with a specific boiling point, boiling polymerization is carried out, which ensures the heat dissipation stability and reaction sufficiency of the reaction system containing complex monomer components under reflux conditions. The process is simple, easy to control and scale up.

[0026] (3) By matching the unique initiator system with the process parameters, the reaction temperature of boiling polymerization was reduced to about 120°C. The polymerization reaction was carried out under conditions far below the industrial polymerization temperature, which reduced energy consumption and equipment requirements.

[0027] (4) The copolymer prepared by this method has a molecular weight that can be effectively controlled within the applicable range, and its key mechanical properties such as density, tensile strength, tensile modulus, elongation at break and flexural modulus are comparable to those of general polystyrene resin prepared from high-purity styrene, which can meet the needs of various application scenarios.

[0028] (5) This invention utilizes monomer boiling vaporization to efficiently remove the heat of reaction, fundamentally solving the heat dissipation problem of traditional bulk polymerization. This process has low requirements for monomer purity and is particularly suitable for direct application to mixture systems containing ortho- and meta-isomers. Furthermore, this invention discovers that when a specific mixture with a significantly higher p-methylstyrene content (>90%) than conventional equilibrium mixtures is used as the main raw material, the heat resistance of the polymer can be significantly optimized while maintaining a cost advantage. Attached Figure Description

[0029] Figure 1 The above is the 1H NMR spectrum result of sample 2 in an embodiment of the present invention.

[0030] Figure 2 This is a gel permeation chromatography result of sample 2 in an embodiment of the present invention.

[0031] Figure 3 This is a graph showing the bending mechanical properties test results of sample 2 according to an embodiment of the present invention.

[0032] Figure 4 This is a comparison chart of the DSC results of sample 2 and the control sample in an embodiment of the present invention. Detailed Implementation

[0033] To make the technical means, creative features, objectives and effects of the present invention easy to understand, the following embodiments, in conjunction with the accompanying drawings, specifically illustrate the application of the high para-isomer content methylstyrene mixture of the present invention in the preparation of polystyrene substitute copolymers.

[0034] Example

[0035] This embodiment provides the application of methylstyrene mixtures with high para-isomer content in the preparation of polystyrene substitute copolymers.

[0036] The high para-isomer content methylstyrene mixture includes o-methylstyrene, m-methylstyrene, and p-methylstyrene, with molar fraction ratios ranging from (0%, 10%) to [90%, 100%]. Preferably, the molar fraction ratio of p-methylstyrene in the high para-isomer content methylstyrene mixture is greater than 95%.

[0037] The application provided in this embodiment specifically includes the following steps:

[0038] First, random copolymerization was carried out under boiling reflux conditions, and the specific operation was as follows:

[0039] Under nitrogen protection, a mixture of methylstyrene with high para-isomer content, styrene, initiator, and solvent A were added sequentially to a 250 mL three-necked flask equipped with a condenser, thermometer, and stirrer. After thorough stirring, the mixture was heated to the boiling point of solvent A and kept under reflux for 1 to 10 hours.

[0040] in:

[0041] (1) The molar ratio of the high para-isomer content methylstyrene mixture to styrene is (10~100):(90~0). Preferably, the molar ratio of the high para-isomer content methylstyrene mixture to styrene is (50~75):(50~25).

[0042] (2) The initiator is a peroxide compound or an azo compound. Peroxide compounds include tert-butyl peroxide-2-ethylhexanoate, 1,1-di(tert-butylperoxy)cyclohexane, dicumyl peroxide, ditert-butyl peroxide, and ditert-pentyl peroxide.

[0043] (3) Solvent A includes ketone solvents, ester solvents, ether solvents, and aromatic hydrocarbon solvents that are miscible with peroxide initiators. Ketone solvents include methyl n-propyl ketone, methyl n-butyl ketone, methyl isobutyl ketone, cyclohexanone, and isophorone; ester solvents include n-butyl acetate and isobutyl acetate; ether solvents include diethylene glycol dimethyl ether; and aromatic hydrocarbon solvents include toluene, p-xylene, and mesitylene.

[0044] Subsequently, the polystyrene-substituted copolymer was separated, and the specific operation was as follows:

[0045] The refluxed reaction system was poured hot into a beaker containing alcohol solvent B for precipitation, resulting in a white flocculent precipitate. The precipitate was then filtered and washed three times with ethanol. The precipitate was placed in a vacuum oven and dried at 60°C–120°C for 12–24 h to obtain a white solid powder of the polystyrene-substituted copolymer.

[0046] Alcohol solvent B includes any one or more of methanol, ethanol, and water. Specifically, in this embodiment, 400 mL of ethanol is selected as alcohol solvent B.

[0047] This embodiment also provides a polystyrene copolymer with comparable performance, namely the polystyrene substitute copolymer prepared above.

[0048] Specifically, in this embodiment, a total of 6 samples were prepared, which were designated as Sample 1, Sample 2, Sample 3, Sample 4, Sample 5 and Sample 6, respectively. Homopolymer styrene was prepared in accordance with the existing homopolymer preparation route for styrene to obtain a comparative sample.

[0049] The parameters for the preparation process of the aforementioned samples are shown in Table 1 below.

[0050] Table 1 (Parameters during the preparation of Sample 1, Sample 2, Sample 3, Sample 4, Sample 5, Sample 6, and control sample)

[0051]

[0052] Figure 1 The above is the 1H NMR spectrum result of sample 2 in an embodiment of the present invention.

[0053] like Figure 1 As shown, in this embodiment, the broad peak with a chemical shift around 2.3 ppm in sample 2 is a characteristic peak of the para-methyl group on the benzene ring; the broad peaks with chemical shifts around 7.10 ppm and 6.51 ppm are characteristic peaks of hydrogen atoms on the aromatic benzene ring; the single peak with a chemical shift around 1.85 ppm is a characteristic peak of the methine group on the polymer backbone; and the single peak with a chemical shift around 1.42 ppm is a characteristic peak of the methylene group on the polymer backbone. The integral area ratio demonstrates that this embodiment successfully prepared the product.

[0054] This embodiment also performed gel permeation chromatography (GPC), thermal property testing (DSC), density testing, and mechanical property testing (tensile and bending) on ​​samples 1, 2, 3, 4, 5, 6, and the control sample. The test results are shown in Table 2 below. The gel permeation chromatography results for sample 2 are shown below. Figure 2 As shown, the bending mechanical properties test results of sample 2 are as follows: Figure 3 As shown, the thermal performance test results of sample 2 and the control sample are as follows: Figure 4 As shown.

[0055] Table 2 (Test results of Sample 1, Sample 2, Sample 3, Sample 4, Sample 5, Sample 6, and control sample)

[0056]

[0057] As shown in Tables 1 and 2, the solvent / initiator system of this invention exhibits good versatility. Using ketone, ether, ester, and aromatic hydrocarbon solvents, combined with medium-to-high temperature peroxide initiators, copolymer products with excellent mechanical properties and good process stability were successfully obtained at reaction temperatures ranging from 115 to 128°C. Comparison with comparative sample data revealed that samples incorporating methylstyrene copolymer units (samples 1-6) exhibited better mechanical properties.

[0058] As shown in Table 2 and Figure 2As shown, Sample 2 has a weight-average molecular weight of 77,000, a number-average molecular weight of 30,000, and a molecular weight distribution width of approximately 2.57, which conforms to the typical characteristics of free radical polymerization. Furthermore, under the high-temperature reaction conditions of this invention, the molecular weight distribution did not become excessively broad due to rapid initiator decomposition or solvent chain transfer, proving that the solvent / initiator combination selected in this invention is well-matched with the reaction conditions.

[0059] As shown in Table 2 and Figure 3 As shown, the introduction of methylstyrene copolymer units significantly enhances the material's resistance to flexural deformation. Taking sample 2 as an example, its flexural modulus is 3.40 GPa, while the control sample is only 2.05 GPa, representing an improvement of approximately 66%.

[0060] As shown in Table 2 and Figure 4 As shown, the glass transition temperatures of all samples were significantly increased compared to the control sample after the introduction of methylstyrene copolymer units. Taking sample 2 as an example, its glass transition temperature was 107.14℃, an increase of 41.4℃ compared to the control sample. The DSC curve showed a single glass transition peak without multiple Tg, proving that the obtained product is a homogeneous random copolymer, rather than a physical blend of homopolymers. The thermal performance data demonstrates that when a specific mixture with a significantly higher p-methylstyrene content than conventional equilibrium mixtures (content >85%, preferably >90% or 95%) is used as the main raw material, the heat resistance of the polymer can be significantly optimized while maintaining a cost advantage.

[0061] Those skilled in the art should understand that this invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to this invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the invention as claimed. The scope of protection of this invention is defined by the appended claims and their equivalents.

Claims

1. The application of high para-isomer content methylstyrene mixtures in the preparation of polystyrene substitute copolymers, characterized in that, The high para-isomer content methylstyrene mixture includes o-methylstyrene, m-methylstyrene, and p-methylstyrene, with molar fraction ratios ranging from (0%, 10%), (0%, 10%), and [90%, 100%), respectively. The steps for the application are as follows: Under an inert atmosphere, the methylstyrene mixture with high para-isomer content and styrene are added to solvent A at a molar ratio of (10~100):(90~0). Using a peroxide compound as an initiator, the mixture is heated to boiling and refluxed for 1~10 hours. After precipitation in an alcohol solvent B, the mixture is filtered, washed, and dried to obtain a polystyrene-substituted copolymer.

2. The application according to claim 1, characterized in that: in, The molar fraction of p-methylstyrene in the high para-isomer content methylstyrene mixture is greater than 95%.

3. The application according to claim 1, characterized in that: in, The molar ratio of the high para-isomer content methylstyrene mixture to styrene feed is (50~75):(50~25).

4. The application according to claim 1, characterized in that: in, Solvent A includes ketone solvents, ester solvents, ether solvents, and aromatic hydrocarbon solvents. The ketone solvents include methyl n-propyl ketone, methyl n-butyl ketone, methyl isobutyl ketone, cyclohexanone, and isophorone. The ester solvents include n-butyl acetate and isobutyl acetate. The ether solvent includes diethylene glycol dimethyl ether. The aromatic hydrocarbon solvents include toluene, p-xylene, and mesitylene.

5. The application according to claim 1, characterized in that: in, The peroxide compounds include tert-butyl peroxide-2-ethylhexanoate, 1,1-di(tert-butylperoxy)cyclohexane, dicumyl peroxide, ditert-butyl peroxide, and ditert-pentyl peroxide.

6. The application according to claim 1, characterized in that: in, The alcohol solvent B includes any one or more of methanol, ethanol, and water.

7. A performance-comparable alternative to polystyrene copolymers, characterized in that, It is prepared by the steps of the application described in any one of claims 1 to 6.

8. The alternative according to claim 7, characterized in that: in, The substitute has a number-average molecular weight of 20,000 to 100,000, a weight-average molecular weight of 40,000 to 300,000, and a density of 0.9 g / cm³. 3 ~1.2g / cm 3 , The alternative has a tensile strength of 35 MPa to 45 MPa, a tensile modulus of 2.5 GPa to 4.0 GPa, an elongation at break of 1.0% to 4.0%, and a flexural modulus of 2.5 GPa to 4.0 GPa.

9. The use of the alternative as described in claim 7 or 8 as a thermoplastic resin.

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