Water-soluble nitroxide radical bimolecular initiation system, preparation method and application thereof

Abstract

The application discloses a water-soluble nitroxide radical bimolecular initiation system, a preparation method and application thereof, and belongs to the technical field of radical polymerization, wherein the bimolecular initiation system comprises a water-soluble nitroxide radical and a water-soluble azo initiator; the water-soluble nitroxide radical is di-tert-butyl nitroxide radical; and the water-soluble azo initiator is 2,2'-azobis (isobutylamidine) dihydrochloride. The bimolecular initiation system can control the polymerization process of acrylamide and sodium 4-vinylbenzenesulfonate in neutral water phase, realizes high monomer conversion rate in a short time, makes the actual molecular weight of the obtained polymer basically consistent with the theoretical molecular weight, and keeps good molecular weight distribution control. Compared with common radical polymerization using only the water-soluble azo initiator, the application establishes a reversible activation / deactivation balance mediated by the nitroxide radical by introducing the di-tert-butyl nitroxide radical, so that the polymer molecular weight control is obviously improved.

Description

Technical Field

[0001] This invention relates to the field of free radical polymerization technology, specifically to a water-soluble nitric oxide radical bimolecular initiation system, its preparation method, and its application. Background Technology

[0002] Nitrogen oxide-mediated polymerization (NMP) is an important method for reversibly deactivated radical polymerization. This method typically does not require transition metal catalysts or sulfur-containing chain transfer reagents, has a relatively simple system composition, and facilitates product post-processing, making it suitable for the preparation of functional polymers and water-soluble polymers.

[0003] The NMP system mainly includes unimolecular initiation systems and bimolecular initiation systems. Unimolecular initiation systems typically use alkoxyamines as initiators, whose C-ON bonds cleave upon heating, simultaneously generating carbon-center radicals and nitroxide radicals, thus exhibiting good chain-end control capabilities; however, alkoxyamines usually require multi-step synthesis, resulting in high costs for structural design and purification. Bimolecular initiation systems typically consist of a radical initiator and a nitroxide radical regulator; the initiator decomposes upon heating to generate primary radicals, which initiate monomer polymerization to form growing radicals; the nitroxide radicals capture the growing radicals to form dormant species, which then reversibly cleave to release the growing radicals and nitroxide radicals again; through this reversible activation / deactivation balance, the concentration of radicals in the system is maintained at a low level, thereby reducing the bimolecular termination reaction and achieving control over molecular weight and molecular weight distribution.

[0004] Aqueous NMP polymerization offers advantages such as being environmentally friendly, safe, low-cost, and easy to process, making it suitable for preparing water-soluble polymers like polyacrylamide and sodium poly(4-vinylbenzenesulfonate). Existing bimolecular NMP systems primarily utilize oil-soluble or organic initiators such as BPO and AIBN, as well as modifiers like TEMPO, and are rarely directly applicable to homogeneous pure water systems. The main shortcomings of existing technologies are as follows:

[0005] First, there are few bimolecular initiation and control systems suitable for pure aqueous NMP. Traditional bimolecular NMP is mostly used in organic or heterogeneous systems, and it is difficult to directly use it for homogeneous aqueous solution polymerization of strongly water-soluble monomers such as acrylamide (AM) and sodium 4-vinylbenzenesulfonate (SS).

[0006] Second, although common water-soluble azo initiators can rapidly initiate AM and SS polymerization, they are essentially ordinary free radical polymerizations, making it difficult to control the polymer molecular weight and molecular weight distribution. For example, when using only V50 (2,2'-azobisisobutylamidine dihydrochloride), AM and SS can quickly achieve high conversion rates, but the resulting polymer molecular weight deviates from the theoretical value, and the molecular weight distribution becomes significantly wider.

[0007] Third, existing aqueous NMP systems often struggle to simultaneously achieve rapid polymerization and controllable molecular weight. If only high conversion rates are pursued, molecular weight control is easily lost; if controllability is emphasized, it is often accompanied by a long induction period and low polymerization efficiency.

[0008] Fourth, existing methods for improving the efficiency of aqueous NMP rely heavily on the covalent synthesis of novel alkoxyamines or nitroxide radicals, which involves many synthetic steps and has limited system scalability. There is a lack of a bimolecular aqueous NMP system composed of simple water-soluble components that can be further regulated through host-guest interactions with cucurbitacin.

[0009] Therefore, developing a bimolecular initiation system composed of a water-soluble initiator and a water-soluble nitroxide radical is of great significance for expanding aqueous NMP. Summary of the Invention

[0010] The purpose of this invention is to provide a water-soluble nitric oxide radical bimolecular initiation system, its preparation method, and its application, so as to solve the problems mentioned in the background art.

[0011] To achieve the above objectives, the present invention provides the following technical solution:

[0012] A water-soluble nitroxide radical bimolecular initiation system, wherein the bimolecular initiation system comprises a water-soluble nitroxide radical and a water-soluble azo initiator; the water-soluble nitroxide radical is a di-tert-butyl nitroxide radical; and the water-soluble azo initiator is 2,2'-azobisisobutylamidine dihydrochloride.

[0013] Furthermore, in the bimolecular initiation system, the molar ratio of the water-soluble nitric oxide radical to the water-soluble azo initiator is (1–3):1.

[0014] Furthermore, the bimolecular initiation system also includes cucurbituril; the cucurbituril forms a host-guest complex with water-soluble nitric oxide radicals.

[0015] Furthermore, the cucurbituril is cucurbituril[7] urea.

[0016] Furthermore, the molar ratio of cucurbituril to water-soluble nitric oxide radicals is (0.5–1.5):1.

[0017] Another object of the present invention is to provide a method for preparing the above-mentioned water-soluble nitric oxide radical bimolecular initiation system, comprising the following steps:

[0018] A bimolecular initiation system is obtained by mixing water-soluble nitric oxide radicals and water-soluble azo initiators in water, with or without the addition of cucurbituril.

[0019] Another object of the present invention is to provide the application of the above-mentioned water-soluble nitric oxide radical bimolecular initiation system in regulating aqueous phase nitric oxide stable radical polymerization.

[0020] Furthermore, the method for regulating aqueous nitrogen-oxygen stable free radical polymerization is as follows: the water-soluble nitrogen-oxygen free radical bimolecular initiation system is mixed with the water-soluble vinyl monomer in water, and after deoxygenation treatment, the mixture is heated to carry out the polymerization reaction.

[0021] Furthermore, the water-soluble vinyl monomer includes acrylamide or sodium 4-vinylbenzenesulfonate; the molar ratio of the water-soluble vinyl monomer to the water-soluble nitroxide radical is 500:(1–3).

[0022] Furthermore, the polymerization reaction is carried out at a temperature of 80–100°C.

[0023] The water-soluble nitroxide radical bimolecular initiation system provided by this invention can regulate the polymerization process of acrylamide and sodium 4-vinylbenzenesulfonate in a neutral aqueous phase, achieving high monomer conversion in a short time while ensuring that the actual molecular weight of the resulting polymer closely matches the theoretical molecular weight and maintains good molecular weight distribution control. Compared with conventional free radical polymerization using only water-soluble azo initiators, this invention significantly improves polymer molecular weight control by introducing di-tert-butyl nitroxide radicals to establish a nitroxide radical-mediated reversible activation / deactivation balance.

[0024] Furthermore, this invention introduces cucurbituril into the bimolecular initiation system. Cucurbituril can form a host-guest complex with di-tert-butyl nitroxide radicals. Adding cucurbituril to the polymerization system can shorten the polymerization induction period, accelerate the overall polymerization process, and at the same time maintain the actual molecular weight of the polymer in good agreement with the theoretical molecular weight, without destroying the molecular weight control characteristics of the original bimolecular initiation system. Attached Figure Description

[0025] Figure 1 This is a schematic diagram illustrating the DTBN / V50 bimolecular initiation system's role in regulating the participation of AM and SS in aqueous NMP polymerization.

[0026] Figure 2 The figures show the molecular weight characterization results of AM and SS aqueous NMP initiated by DTBN / V50; in the figure, A represents AM and B represents SS.

[0027] Figure 3 The isothermal titration thermogram of DTBN combined with CB[7].

[0028] Figure 4 The figure shows the EPR characterization results of cucurbituril combined with DTBN; in the figure, A is the EPR characterization result of CB[7] combined with DTBN, and B is the EPR characterization result of CB[8] combined with DTBN.

[0029] Figure 5The results show the kinetic characterization of AM aqueous NMP regulated by the CB[7]-DTBN / V50 bimolecular initiation system; in the figure, A is the change of conversion rate with time, and B is the kinetic data fitted by the first-order kinetic equation.

[0030] Figure 6 The results show the kinetic characterization of the SS aqueous phase NMP controlled by the CB[7]-DTBN / V50 bimolecular initiation system; in the figure, A is the change of conversion rate with time, and B is the kinetic data fitted by the first-order kinetic equation.

[0031] Figure 7 The molecular weight characterization results of AM and SS aqueous NMP initiated by CB[7]-DTBN / V50 are shown in the figure; A is AM and B is SS. Detailed Implementation

[0032] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0033] In one embodiment of the present invention, addressing the problems of limited bimolecular initiation systems in existing aqueous nitroxide-stable radical polymerization (NMP), the difficulty in controlling polymer molecular weight and molecular weight distribution despite the rapid polymerization achieved by common water-soluble azo initiators, and the difficulty in achieving both high conversion rate and controllable molecular weight in aqueous NMP, a water-soluble nitroxide radical bimolecular initiation system is proposed. Specifically, it includes a water-soluble nitroxide radical and a water-soluble azo initiator; wherein the water-soluble nitroxide radical is di-tert-butyl nitroxide radical (DTBN); the water-soluble azo initiator is 2,2'-azobisisobutylamidine dihydrochloride (V50); and the molar ratio of the water-soluble nitroxide radical to the water-soluble azo initiator is (1–3):1.

[0034] DTBN is a structurally stable and water-soluble nitroxide radical; V50 is a water-soluble azo initiator suitable for medium- and high-temperature aqueous radical polymerization; the combination of the two can form an initiation control system (DTBN / V50) suitable for aqueous NMP, which can be used for aqueous polymerization of water-soluble monomers such as acrylamide (AM) and sodium 4-vinylbenzenesulfonate (SS), and achieve high conversion rate, good consistency between actual and theoretical molecular weight and good molecular weight distribution control.

[0035] In a preferred embodiment of the present invention, the above-mentioned bimolecular initiation system may further include cucurbituril; cucurbituril forms a host-guest complex with water-soluble nitric oxide radicals; the molar ratio of cucurbituril to water-soluble nitric oxide radicals is (0.5–1.5):1. Preferably, cucurbituril is cucurbituril[7] (CB[7]).

[0036] It should be noted that cucurbituril is a class of water-soluble macrocyclic molecules, in which CB[7] can form a host-guest complex with DTBN, placing nitric oxide radicals in a confined microenvironment; based on this, by introducing CB[7] into DTBN-involved NMP, a new method can be provided for the regulation of NMP polymerization kinetics in aqueous phase. Specifically, by adding CB[7] to the DTBN / V50 system, a CB[7]-DTBN / V50 supramolecular initiation regulation system is constructed, which can shorten the polymerization induction period and accelerate the polymerization process, while maintaining the molecular weight control characteristics of the polymer, thus providing a supramolecular regulation method that is simple to operate, has readily available components, and is suitable for aqueous phase systems.

[0037] In another embodiment of the present invention, the application of the above-mentioned water-soluble nitroxide radical bimolecular initiation system in regulating aqueous nitroxide stable radical polymerization is also provided. Specifically, the method for regulating aqueous nitroxide stable radical polymerization is as follows: the above-mentioned water-soluble nitroxide radical bimolecular initiation system (DTBN / V50 or CB[7]-DTBN / V50) is mixed with water-soluble vinyl monomers (such as AM or SS) in water to obtain a polymerization system (the system pH is neutral), and then nitrogen gas is passed through for deoxygenation for 20–40 min, followed by heating to 80–100°C and stirring at 200–400 rpm to carry out the polymerization reaction. The molar ratio of water-soluble vinyl monomers to water-soluble nitroxide radicals is 500:(1–3).

[0038] Unless otherwise specified, all raw materials used in the following embodiments are commercially available products and can be purchased through commercial channels. The invention will be described in detail below through specific embodiments in practical applications.

[0039] Example 1: As Figure 1 As shown, this embodiment provides a DTBN / V50 bimolecular initiation system and a method for regulating the aqueous NMP polymerization of AM and SS, as detailed below:

[0040] DTBN was prepared into a 10.18 mM aqueous solution, and V50 was prepared into a 10.12 mM aqueous solution. In the AM polymerization, 180 mg of AM was weighed into a 4 mL glass vial, and 547 μL of the above DTBN aqueous solution, 250 μL of V50 aqueous solution, and 1.35 mL of pure water were added. In the SS polymerization, 206 mg of SS was weighed into a 4 mL glass vial, and 236 μL of DTBN aqueous solution, 99 μL of V50 aqueous solution, and 487 μL of pure water were added. All systems were confirmed to be nearly neutral using a pH meter. After sealing, nitrogen gas was bubbled through the system for 30 min to remove oxygen, and then the mixture was placed in a 95°C oil bath and stirred at 300 rpm to obtain the reaction solution. At different time points, 50 μL of the reaction solution was added to deuterium water, and the reaction was carried out... 1 The monomer conversion rate was calculated by ¹H NMR; the polymerized sample was lyophilized and then reconstituted in water to prepare a 4 mg / mL solution, and the molecular weight and molecular weight distribution were determined by aqueous phase GPC.

[0041] Effects: The DTBN / V50 bimolecular initiation system allows for the control of AM and SS in aqueous NMP. AM conversion exceeds 90% at 55 min, and the resulting PAM exhibits high molecular weight dispersion (…). The value is less than 1.2, and the molecular weight characterization results are as follows: Figure 2 As shown in A; the conversion rate of SS exceeded 90% at 55 min, and the resulting PSS... The value ranged from 1.3 to 1.4, and the molecular weight characterization results are as follows: Figure 2 As shown in B.

[0042] Example 2: This example provides a method for preparing a CB[7]-DTBN host-guest complex, as follows:

[0043] Dissolve DTBN and CB[7] in water respectively, mix them at a molar ratio of DTBN:CB[7]=1:1, and mix thoroughly at room temperature to obtain the CB[7]-DTBN host-guest complex.

[0044] The binding constant K can be determined by isothermal titration calorimetry. A 1.5 mM DTBN aqueous solution was titrated into a 0.15 mM CB[7] aqueous solution at a test temperature of 25 °C, with each titration volume being 1.5 μL. For example... Figure 3 As shown, the results indicate that DTBN binds to CB[7] in a 1:1 stoichiometric ratio, with a binding constant K of 2.1 × 10⁻⁶. 4 M -1 .

[0045] In addition, for EPR characterization, 100 μM DTBN aqueous solution and 100 μM CB[7] aqueous solution can be prepared separately, and the two are mixed in equal volumes or equimolar amounts before testing. Figure 4As shown in Figure A, the results show that after adding CB[7], the high-field EPR signal intensity of DTBN decreased and the spectral lines broadened, and the peak shape became shorter and blunter, indicating that the molecular motion of DTBN was restricted, suggesting that DTBN was partially or completely encapsulated in the CB[7] cavity. As a control, as shown in Figure A. Figure 4 As shown in Figure B, after adding an equimolar amount of cucurbita[8]urea (CB[8]) to DTBN, the peak shape of the EPR signal remained basically unchanged, indicating that there was no significant interaction between DTBN and CB[8].

[0046] Example 3: This example provides a CB[7]-DTBN / V50 bimolecular initiation system and a method for regulating AM and SS in aqueous NMP, as follows:

[0047] In Example 1, CB[7] was added to the bimolecular initiation system in an equimolar amount with DTBN to construct a CB[7]-DTBN / V50 bimolecular initiation system. In AM polymerization, the molar ratio of CB[7]:DTBN:V50:AM was 2.2:2.2:1:500; in SS polymerization, the molar ratio of CB[7]:DTBN:V50:SS was 2.2:2.2:1:500. The polymerization temperature, deoxygenation method, sampling method, and GPC characterization method were the same as in Example 1.

[0048] Effects: such as Figure 5 and Figure 7 As shown, for AM polymerization, the AM conversion rate of the CB[7]-DTBN / V50 bimolecular initiation system exceeded 30% at 10 min and reached 94% at 35 min, with an apparent rate constant of 0.098 min. -1 The obtained PAM It is still less than 1.2, and has a good molecular weight distribution control effect. Compared with the DTBN / V50 system without CB[7], CB[7] mainly shortens the polymerization induction period and accelerates the overall polymerization process. In addition, when only CB[7]-DTBN is used without adding V50, no effective polymerization occurs, indicating that CB[7]-DTBN cannot be used as an initiator alone; when only V50 or CB[7]-V50 is used, explosive polymerization is likely to occur. Although the monomer conversion rate can reach about 99% within 1 hour, the molecular weight distribution of the obtained PAM is poor. The value is approximately 1.53, which is insufficient to achieve effective molecular weight control in the NMP sense.

[0049] For SS aggregation, such as Figure 6 and Figure 7 As shown, the CB[7]-DTBN / V50 bimolecular initiation system achieved an SS conversion rate exceeding 20% ​​at 10 min, exceeding 80% at 25 min, and reaching 96% at 35 min; the apparent rate constant of the system was 0.11 min. -1The resulting PSS The value was 1.3 to 1.4. Furthermore, when only CB[7]-DTBN was used without the addition of V50, effective polymerization did not occur, indicating that CB[7]-DTBN cannot be used alone as an initiator; when only V50 or CB[7]-V50 was used, the monomer conversion rate could reach approximately 98% within 1 hour, but the molecular weight distribution of the resulting PSS was... A value greater than 2.5 cannot achieve effective molecular weight control in the NMP sense.

[0050] The above results indicate that adding CB[7] to the DTBN / V50 bimolecular initiation system can significantly shorten the polymerization induction period and accelerate the polymerization process without destroying the molecular weight control characteristics.

[0051] In summary, the embodiments of the present invention utilize commercially available or readily available DTBN and V50, achieving aqueous NMP without the need to synthesize complex alkoxyamines. A bimolecular initiation system suitable for aqueous NMP is constructed using DTBN / V50, and a supramolecular regulatory system is further formed through the host-guest interaction between CB[7] and DTBN. This system can achieve high conversion polymerization of AM and SS in the aqueous phase in a short time, while maintaining the polymer molecular weight basically consistent with the theoretical molecular weight, indicating that the system has good application value for aqueous NMP.

[0052] Based on the above-described preferred embodiments of the present invention, and through the foregoing description, those skilled in the art can make various changes and modifications without departing from the inventive concept. The technical scope of this invention is not limited to the contents of the specification.

Claims

1. A water-soluble nitric oxide radical bimolecular initiation system, characterized in that, The bimolecular initiation system comprises a water-soluble nitroxide radical and a water-soluble azo initiator; the water-soluble nitroxide radical is a di-tert-butyl nitroxide radical; and the water-soluble azo initiator is 2,2'-azobisisobutylamidine dihydrochloride.

2. The water-soluble nitric oxide radical bimolecular initiation system according to claim 1, characterized in that, In the bimolecular initiation system, the molar ratio of the water-soluble nitric oxide radical to the water-soluble azo initiator is (1–3):

1.

3. The water-soluble nitric oxide radical bimolecular initiation system according to claim 1, characterized in that, The bimolecular initiation system also includes cucurbituril; the cucurbituril forms a host-guest complex with water-soluble nitric oxide radicals.

4. The water-soluble nitric oxide radical bimolecular initiation system according to claim 3, characterized in that, The cucurbituril is cucurbituril[7] urea.

5. The water-soluble nitric oxide radical bimolecular initiation system according to claim 3, characterized in that, The molar ratio of cucurbituril to water-soluble nitric oxide radicals is (0.5–1.5):

1.

6. The method for preparing the water-soluble nitric oxide radical bimolecular initiation system according to any one of claims 1 to 5, characterized in that, Includes the following steps: A bimolecular initiation system is obtained by mixing water-soluble nitric oxide radicals and water-soluble azo initiators in water, with or without the addition of cucurbituril.

7. The application of the water-soluble nitric oxide radical bimolecular initiation system as described in any one of claims 1 to 5 in regulating aqueous phase nitric oxide stable radical polymerization.

8. The application according to claim 7, characterized in that, The method for regulating aqueous nitrogen-oxygen stable free radical polymerization is as follows: the water-soluble nitrogen-oxygen free radical bimolecular initiation system is mixed with water-soluble vinyl monomers in water, and after deoxygenation treatment, the mixture is heated to carry out the polymerization reaction.

9. The application according to claim 8, characterized in that, The water-soluble vinyl monomer includes acrylamide or sodium 4-vinylbenzenesulfonate; the molar ratio of the water-soluble vinyl monomer to the water-soluble nitric oxide radical is 500:(1–3).

10. The application according to claim 8, characterized in that, The polymerization reaction is carried out at a temperature of 80–100°C.

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