CN102321198B - A kind of method for preparing bimodal distribution polymer - Google Patents

Abstract

The method discloses a method for preparing a bimodal distribution polymer. The method comprises the following steps of preparing a polymerization system, performing an RAFT (Reversible Addition Fragmentation Chain Transfer) polymerization reaction at 50-90 DEG C for at least one hour, separating and purifying, and obtaining the bimodal distribution polymer, wherein the polymerization system comprises a monomer, a free radical initiating agent, a single head RAFT reagent and a double head RAFT reagent; the free radical initiating agent is one selected from styrene, acrylic, water soluble N-isopropyl acrylamide and the like; the conventional free radical initiating agent is one selected from azobisisobutyronitrile and benzoyl peroxide; and the single and double functional-group RAFT reagent combination is one selected from dithiocarbamate and trithiocarbonates. According to the invention, the bimodal distribution polymer with molecular weights and controllable molecular weight distribution can be synthesized because the used RAFT method has 'active'/controllable polymerization characteristics.

Description

A kind of method for preparing bimodal distribution polymer

technical field

The invention relates to a method for synthesizing a bimodal distribution polymer by using a reversible addition-fragmentation chain transfer (Reversible Addition-Fragmentation Chain Transfer, RAFT) polymerization method.

Background technique

The molecular weight and molecular weight distribution index of a polymer determine its physical properties, mechanical properties and processing properties. Polymers with lower molecular weight have better toughness and flow properties, but the rigidity of the polymer will be reduced. A polymer with a higher molecular weight has better mechanical properties, but its toughness will decrease accordingly. Even though high molecular weight materials exhibit good toughness, they are difficult to process due to their high melt viscosity. For some special applications, it is often required that polymers have good mechanical properties and processing properties at the same time. In order to overcome the shortcomings of incompatibility between use performance and processing performance, by synthesizing bimodal polymers, that is, polymers with high molecular weight and low molecular weight at the same time, the processing performance of the material can be balanced and optimized under many extreme conditions (low molecular weight part ) and performance (high molecular weight part). At the processing temperature, the low molecular weight part of the polymer can improve the fluidity of the polymer material; at the use temperature, the high molecular weight part of the polymer can improve the performance of the material. The preparation methods of bimodal distribution polymers usually include the following:

(1) Physical blending, this method is to mix high and low molecular weight polymers separately (see: Xue Feng, Ma Guangsheng. Two-stage polymerized polyethylene resin with broad peak or bimodal distribution Performance Research. Modern Plastic Processing Applications , 2007 , 19, 13-16.)

(2) two-step reaction, its method refers to first synthesizing the polymer of wherein a kind of relative molecular mass under a kind of polymerization condition, then changes reaction condition to obtain another kind of polymer of relative molecular mass in the second step reaction ( see:

Abedi, S.; Hassanpour, N. Preparation of Bimodal Polypropylene in Two-Step Polymerization. J. Appl. Polym. Sci., 2006 , 101, 1456-1462.).

(3) Use chain transfer agent or cross-linking agent, etc., this method generally synthesizes low molecular weight polymer first, and then adds chain transfer agent or cross-linking agent to the reaction system to synthesize higher molecular weight polymer (see: Tobita, H. Bimodal Molecular Weight Distribution Formed in the Emulsion Polymerization of Ethylene. J. Polym. Sci., Part A: Polym. Chem., 2002 , 40, 3426-3433.).

(4) Using a mixed catalyst or a mixed catalytic system, a composite catalytic system composed of nickel, zirconium, and titanium, activated by a cocatalyst methylaluminoxane (MAO), can make a single ethylene polymerized to prepare bimodal long-chain branched polyethylene. Similarly, iron, cobalt, and chromium compounds can also produce bimodal polyethylene after activation with large amounts of MAO or with Ziegler-Natta catalysts (see: (a) Li, L.; Wang, Q. Synthesis of Polyethylene with Bimodal Molecular Weight Distribution by Supported Iron-Based Catalyst. J. Polym. Sci., Part A: Polym. Chem. , 2004 , 42, 5662-5669. (b) Yamamoto, K.; Ishihama, Y.; Sakata, K. Preparation of Bimodal HDPEs with Metallocene on Cr-Montmorillonite Support . J. Polym. Sci. Part A: Polym. Chem. , 2010 , 48, 3722-3728.).

Although these methods can successfully synthesize bimodal polymers, the two-step reaction method is complicated to operate, the mixed catalyst method system contains toxic metals, and the catalyst synthesis method is complicated and expensive. The most important thing is that the above methods are difficult to synthesize bimodal polymers with controllable molecular weight and molecular weight distribution.

Reversible Addition-Fragmentation Chain Transfer (RAFT, that is, reversible addition-fragmentation chain transfer) polymerization method, as one of the most potential "living"/controllable free radical polymerization methods, was first proposed by Rizzardo et al. in 1998. RAFT polymerization is to add appropriate RAFT reagents to the conventional free radical polymerization system, and the monomers, initiators, solvents and reaction temperatures used are consistent with conventional free radical polymerization. Therefore, like ordinary free radical polymerization, it has the advantages of simple operation and post-treatment and diversified polymerization methods, and is one of the most industrialized "living"/controllable free radical polymerization methods. Judging from the existing reports, there is no literature report on the application of RAFT method to synthesize bimodal distribution polymers.

Contents of the invention

The inventive object of the present invention is to provide a method for preparing bimodal distribution polymers.

In order to achieve the purpose of the above invention, the technical solution adopted in the present invention is: a method for preparing a bimodal distribution polymer, comprising the following steps: preparing a polymerization system, performing RAFT polymerization reaction at 50-90°C for at least 1 hour, separating and purifying , to obtain a bimodal distribution polymer;

The polymerization system includes a monomer, a free radical initiator, a single-head RAFT reagent, and a double-head RAFT reagent, wherein, n (monomer): n (initiator): n (single-head RAFT reagent): n (double-head RAFT Reagent) = 200~100000: 1~30: 1~150: 1~150;

Wherein, the monomer is a free radical polymerizable monomer, selected from: one of styrene, acrylates, water-soluble N -isopropylacrylamide, etc.; the acrylate is preferably: acrylic acid Methyl acrylate, ethyl acrylate, propyl acrylate, butyl acrylate, methyl methacrylate, ethyl methacrylate, propyl methacrylate, or butyl methacrylate;

The initiator is a conventional free radical initiator, selected from one of azobisisobutyronitrile (AIBN) and dibenzoyl peroxide (BPO);

或三硫代碳酸酯类

中的一种；  The single head RAFT reagent is selected from: dithiocarbamate

or trithiocarbonates

one of

或三硫代碳酸酯类

中的一种； The double-headed RAFT reagent is selected from: dithiocarbamates

or trithiocarbonates

one of

、、或

中的一种，其中n＝7～23。 Wherein R, R ₁ , R ₂ are each selected from one of: -Ph, -Ph-OCH ₃ , -(CH ₃ ) ₂ CC≡N, C1-C4 alkyl, naphthalene or carbazole groups ; _R is selected from

, , or

One of them, wherein n=7～23.

In the above technical solution, the molecular weight of the polymer can be controlled by adjusting the reaction time.

In the above technical scheme, the mass fraction of high and low molecular weight polymers in the polymer can be controlled by adjusting the molar ratio of the single-head and double-head RAFT reagents. For example, it is necessary to obtain a higher proportion of high molecular weight polymers, which can be achieved by increasing the proportion of double-headed RAFT agents, and vice versa.

In the above technical solution, the molecular weight distribution of the obtained polymer is narrow (PDI<1.2), and the actual molecular weight of the obtained polymer is consistent with the theoretical molecular weight.

In the above technical solution, the RAFT polymerization reaction can be carried out in bulk or solution polymerization.

Due to the use of the above-mentioned technical solutions, the present invention has the following advantages compared with the prior art:

1. This invention proposes for the first time the use of "living"/controllable free radical polymerization to synthesize bimodal distribution polymers, and the molecular weight and molecular weight distribution of the two polymers can be controlled at the same time, which is a bimodal distribution polymer material mixed at the molecular level Provide a new method.

2. Since the present invention adopts the RAFT polymerization method, it has a wide range of polymerized monomers, various polymerization methods and simple operation, and does not require complicated post-treatment processes. The chemical reagents used in the present invention are stable in the air and the reaction can be carried out in the air. Operate under atmospheric conditions, which is convenient for industrialized production.

3. Because in the polymerization system of the present invention, the ratio of single-head and double-head RAFT reagents is adjustable, it is possible to synthesize bimodal polymers with adjustable mass fractions of high and low molecular weights.

4. Since the present invention adopts the RAFT polymerization system, the molecular weight of the obtained polymer can be easily designed, and the end group of the polymer is still active, which can be used to synthesize some active/controllable block and graft copolymerization with topological structure things.

Description of drawings

Fig. 1 is the reaction kinetic diagram (1a) and conversion rate and molecular weight relation diagram (1b) of synthesizing bimodal distribution polymer with dithiocarbamate mono- and double-headed RAFT reagent combination in embodiment 1;

Fig. 2 is the NMR image of the bimodal distribution polymer in Example 4;

Figure 3 is the reaction kinetics diagram (3a) and the relationship diagram (3b) between conversion rate and molecular weight for the synthesis of bimodal distribution polymers by combining trithiocarbonate single- and double-headed RAFT reagents in Example 5.

Detailed ways

The present invention will be further described below in conjunction with accompanying drawing and embodiment:

Chemical reagents used in the examples: styrene (St), 99%, China National Pharmaceutical (Group) Shanghai Chemical Reagent Company; Carbazole, 99%, China National Pharmaceutical (Group) Shanghai Chemical Reagent Company; Azobisisobutyronitrile ( AIBN), 99%, China Pharmaceutical (Group) Shanghai Chemical Reagent Company; hydroquinone, 99%, China National Pharmaceutical (Group) Shanghai Chemical Reagent Company; carbon disulfide, 99%, China National Pharmaceutical (Group) Shanghai Chemical Reagent Company; two Methyl sulfoxide, 99%, China National Pharmaceutical (Group) Shanghai Chemical Reagent Company; tetrahydrofuran (THF), dichloromethane and methanol, analytically pure, Changshu Yangyuan Chemical Reagent Co., Ltd.; triethylamine, 99%, China National Pharmaceutical (Group) ) Shanghai Chemical Reagent Company; Benzylmercaptan, propanethiol, 99%, China Pharmaceutical (Group) Shanghai Chemical Reagent Company; 1,4-chloromethylbenzene, benzyl bromide, 99%, China National Pharmaceutical (Group) Shanghai Chemical Reagent company.

Test equipment and conditions:

Gel permeation chromatography: GPC 1515 from Waters, USA; measurement conditions: HR1, HR3 and HR4 three columns used in series, differential detector, mobile phase tetrahydrofuran (1mL/min), column temperature 30°C, Calibrate with polymethyl methacrylate or polystyrene standards.

Nuclear magnetic resonance instrument: 400 MHz; measurement conditions: use _CDCl3 as solvent, tetramethylsilane as internal standard, and test temperature as room temperature.

Example 1: Bimodal distribution polystyrene (PS) was synthesized by combining dithiocarbamate monofunctional and bifunctional RAFT reagents in an equimolar ratio

According to the ratio n(St) : n (AIBN) : n (single-head RAFT reagent) : n (double-head RAFT reagent) = 200~2000: 1: 1~20: 1~10, add single-head RAFT reagent in turn, double-head RAFT reagent The first RAFT reagent, AIBN, St was placed in a 5 mL ampoule, and after 15 minutes of nitrogen gas flow, the tube was sealed under an oxygen-free atmosphere (bulk polymerization). The sealed ampoule was placed in an oil bath at a constant temperature (75°C) for a predetermined time to react. After the reaction, take out the sealed tube, cool it with cold water immediately, open the sealed tube, dissolve it with 2~5 mL of tetrahydrofuran, pour it into 250 mL of methanol, leave it overnight, filter it with suction, wash it with water, and dry it to get the "activity" polystyrene;

Among them, the representative single-head RAFT reagent structure in dithiocarbamate is

；

;

The structure of a representative difunctional RAFT agent in dithiocarbamate class is:

。

.

Figure 1 is the reaction kinetic diagram of bimodal distribution polymer synthesized by RAFT method; the polymerization conditions are: St = 3mL, [St] ₀ /[AIBN] ₀ /[single-head RAFT reagent] ₀ /[double-head RAFT reagent] ₀ = 1200:1:2.5:2.5, T = 75°C, no oxygen. It can be seen from Figure 2a and Figure 2b that the concentration of derived free radicals remains constant during the reaction, the high and low molecular weight polymers are consistent with the corresponding theoretical molecular weights, and the molecular weight distribution is narrow. Both high and low molecular weight polymers increase linearly with the increase of polymerization time, and the polymerization process can better control the molecular weight of the polymer. At the same time, it can also be seen that the polymer with bimodal distribution can be obtained no matter under the condition of high or low monomer conversion rate.

Example 2: Combination of dithiocarbamate single-head and double-head RAFT reagents at different molar ratios (the types of RAFT reagents are the same as in Example 1) to synthesize polystyrene (PS) with bimodal distribution

According to the ratio n(St) : n(AIBN) : n (single-head RAFT reagent) : n (double-head RAFT reagent) = 200~10000: 1~30: 1~150: 150~1, add single-head RAFT reagent in sequence , double-ended RAFT reagent, AIBN, St in a 5 mL ampoule, after 15 minutes of nitrogen gas, the tube was sealed under an oxygen-free atmosphere (bulk polymerization). The sealed ampoule was placed in an oil bath at a constant temperature (75°C) for a predetermined time to react. After the reaction, take out the sealed tube, cool it with cold water immediately, open the sealed tube, dissolve it with 2~5 mL of tetrahydrofuran, pour it into 250 mL of methanol, leave it overnight, filter it with suction, wash it with water, and dry it to get the "activity" of polystyrene.

The data of embodiment two are shown in table 1.

Table 1. The results of the synthesis of polystyrene with bimodal distribution by combining single-headed and double-headed RAFT reagents in different molar ratios

Reaction conditions: 3.0 mL styrene, bulk polymerization, reaction temperature 75°C.

^a) R = [St] ₀ /[AIBN] ₀ /[single-head RAFT agent] ₀ /[double-head RAFT agent] ₀ ;

^b) Low molecular weight polymer/high molecular weight polymer; M _n,th is the theoretically calculated molecular weight, the molecular weight of low molecular weight polymer = ([St] ₀ /[RAFT group] ₀ ) × M _w,St × Conversion % + Mw _{, single-head RAFT reagent} , high molecular weight polymer molecular weight = 2 × ([St] ₀ /[RAFT group] ₀ ) × M _{w, St} × conversion % + M _{w, double-head RAFT reagent} ; Mn _{, GPC} is the molecular weight obtained by gel permeation chromatography (GPC) test;

^c) low molecular weight polymer/high molecular weight polymer; M _w / M _n is the molecular weight distribution index obtained by gel permeation chromatography (GPC) test.

It can be seen from the data in Table 1 that when different molar ratios of monofunctional and bifunctional RAFT reagents are added to the system, the reaction is still controllable. For example, when single-head RAFT reagent: double-head RAFT reagent = 1:100, bimodal distribution polymers can still be obtained, and the PDI of the reaction system is still very low.

Example 3: Combination of dithiocarbamate single-head and double-head RAFT reagents (the types of RAFT reagents are the same as in Example 1) to synthesize high molecular weight polystyrene with bimodal distribution.

According to the ratio n(St) : n(AIBN) : n (single-head RAFT reagent) : n (double-head RAFT reagent) = 10000~100000: 1: 2-10: 2-10, add single-head RAFT reagent in turn, double-head RAFT reagent The first RAFT reagent, AIBN, St was placed in a 5 mL ampoule, and after 15 minutes of nitrogen gas flow, the tube was sealed under an oxygen-free atmosphere (bulk polymerization). The sealed ampoule was placed in an oil bath at a constant temperature (75°C) for a predetermined time to react. After the reaction, take out the sealed tube, cool it with cold water immediately, open the sealed tube, dissolve it with 2~5 mL of tetrahydrofuran, pour it into 250 mL of methanol, leave it overnight, filter it with suction, wash it with water, and dry it to get the "activity" of polystyrene.

The data of embodiment three are shown in table 2.

Table 2. Polymerization results for the synthesis of high molecular weight bimodal polystyrene

Reaction conditions: 12.0 mL styrene, bulk polymerization, reaction temperature 75°C.

^a) R = [St] ₀ /[AIBN] ₀ /[single-head RAFT agent] ₀ /[double-head RAFT agent] ₀ ;

^b) Low molecular weight polymer/high molecular weight polymer; M _n,th is the theoretically calculated molecular weight, the molecular weight of low molecular weight polymer = ([St] ₀ /[RAFT group] ₀ ) × M _w,St × Conversion % + Mw _{, single-head RAFT reagent} , high molecular weight polymer molecular weight = 2 × ([St] ₀ /[RAFT group] ₀ ) × M _{w, St} × conversion % + M _{w, double-head RAFT reagent} ; M _{n, GPC} is the molecular weight obtained by gel permeation chromatography (GPC) test;

^c) Low molecular weight polymer/high molecular weight polymer; M _w/ M _n is the molecular weight distribution index obtained from gel permeation chromatography (GPC) test.

It can be seen from the data in Table 2 that when using the RAFT method to synthesize high molecular weight bimodal polymers, when the molecular weight is high, the reaction is still controllable, and the PDI of the reaction system is still very low.

Example 4: The NMR spectrum of polystyrene with bimodal distribution synthesized by dithiocarbamate-based single- and double-headed RAFT reagent combinations (the types of RAFT reagents are the same as in Example 1).

In living polymerization, the NMR spectrum of the polymer is used to analyze the end groups of the polymer to verify the living polymerization characteristics of the polymer.

The NMR test of polystyrene was carried out according to the experimental procedures known to those skilled in the art. The test results are shown in Figure 2, the end of the bimodal distribution polymer has RAFT reagent groups.

Example 5: Combining trithiocarbonate monofunctional and bifunctional RAFT reagents in an equimolar ratio to synthesize bimodal distribution polystyrene (PS)

According to the ratio n(St) : n (AIBN) : n (single-head RAFT reagent) : n (double-head RAFT reagent) = 200~2000: 1: 1~20: 1~10, add single-head RAFT reagent in turn, double-head RAFT reagent The first RAFT reagent, AIBN, St was placed in a 5 mL ampoule, and after 15 minutes of nitrogen gas flow, the tube was sealed under an oxygen-free atmosphere (bulk polymerization). The sealed ampoule was placed in an oil bath at a constant temperature (75°C) for a predetermined time to react. After the reaction, take out the sealed tube, cool it with cold water immediately, open the sealed tube, dissolve it with 2~5 mL of tetrahydrofuran, pour it into 250 mL of methanol, leave it overnight, filter it with suction, wash it with water, and dry it to get the "activity" polystyrene;

Among them, the representative monofunctional RAFT reagent structure among trithiocarbonates is:

；

;

。 The structure of a representative bifunctional RAFT agent in the class of trithiocarbonates is:

.

Fig. 3 is the ln([M] ₀ /[M])-time kinetic curve of St polymerization by RAFT method at 75 ℃. Shown is the first-order kinetics of the monomer concentration, showing that the derived radical concentration is constant during the polymerization. At the same time, the induction period (≈7.5 h) can also be observed in Figure 3a. According to the polymerization mechanism of the RAFT system, the free radicals generated by the decomposition of AIBN in the early stage of the reaction may combine with the trithiocarbonate RAFT reagent, and the decomposition rate of the formed intermediate is relatively slow, resulting in a long induction period. However, as the reaction proceeds, a reversible dynamic equilibrium is finally established between the derived free radicals and the RAFT reagent in the system. It can also be clearly seen from Figure 3b that the molecular weight of the polymer increases linearly with the monomer conversion rate, while the prepared PS still has a narrow molecular weight distribution index ( M _w / M _n ) (<1.4). The molecular weight is close to the theoretical molecular weight calculated from the molar ratio of the starting concentration of St to the RAFT agent. All of the above indicate that bimodal distribution polymers can be synthesized using single- and double-headed trithiocarbonate RAFT reagents.

Claims (3)

1. a method for preparing bimodal distribution polymer is characterized in that, may further comprise the steps: the preparation polymerization system, under 50～90 ℃, carried out the RAFT polyreaction at least 1 hour, and separating-purifying obtains bimodal distribution polymer;

Described polymerization system comprises monomer, radical initiator, single head RAFT reagent, double end RAFT reagent, wherein, with molar ratio computing, Dan Ti ﹕ Yin Fa Ji ﹕ single head RAFT Shi Ji ﹕ double end RAFT reagent=200～100000 ﹕, 1～30 ﹕, 1～150 ﹕ 1～150;

Wherein, described monomer is the monomer of free redical polymerization, and described initiator is the conventional free radical initiator;

Described single head RAFT reagent is

,

Described double end RAFT reagent is

Perhaps, described single head RAFT reagent is

,

Described double end RAFT reagent is

2. the described method for preparing bimodal distribution polymer according to claim 1 is characterized in that described monomer is selected from: vinylbenzene, esters of acrylic acid, water miscible NA kind of in the-N-isopropylacrylamide.

3. the described method for preparing bimodal distribution polymer according to claim 1 is characterized in that described initiator is the conventional free radical initiator, is selected from: a kind of in Diisopropyl azodicarboxylate, the dibenzoyl peroxide.

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