CN111533836B

CN111533836B - Self-initiated free radical polymerization of N-isopropylacrylamide

Info

Publication number: CN111533836B
Application number: CN202010400248.2A
Authority: CN
Inventors: 孙义文; 翟光群
Original assignee: Changzhou University
Current assignee: Changzhou University
Priority date: 2020-05-13
Filing date: 2020-05-13
Publication date: 2021-11-09
Anticipated expiration: 2040-05-13
Also published as: CN111533836A

Abstract

The invention belongs to the field of preparation of high molecular weight polymers, and relates to aqueous solution free radical polymerization of N-isopropyl acrylamide. The reaction process of the invention is to form a redox initiation system by ultra-high oxidation state copper salt complex and N-isopropyl acrylamide in aqueous solution to initiate the free radical polymerization of the N-isopropyl acrylamide. The viscosity average molecular weight of the obtained polymer ranges from 100 to 300 ten thousand. The invention has the advantages of simple operation, low external requirement and low price of raw materials.

Description

Self-initiated free radical polymerization of N-isopropylacrylamide

Technical Field

The invention belongs to the field of preparation of high molecular weight polymers, relates to free radical polymerization of N-isopropyl acrylamide (NiPAm), and particularly relates to a method for preparing a high molecular weight polymer PNiPAm by initiating free radical polymerization of the high molecular weight polymer PNiPAm by redox NiPAm through an ultrahigh oxidation state copper salt complex (CuIII).

Background

The N-H bond energy of the secondary amide group is relatively large, about 445 kJ mol-1; furthermore, the oxidation potential (vs calomel electrode) is about 1.8V, so that it is difficult to oxidize it into radicals. There is no report in the literature of small molecule secondary amide compounds that undergo free radical initiated free radical polymerization via N-H cleavage. Only the nylon chain or surface is subjected to high-energy radiation, ultra-high oxidation state transition metal salt complex, etc. to cleave the secondary amide group N-H into radicals, and initiate radical polymerization, thereby obtaining a graft polymer (Journal of Macromolecular Science, Part C, 17:2, 267-296).

N-isopropylacrylamide (NiPAm) is one of the common water-soluble monomers, the polymer product of which, PniPAm, exhibits significant phase separation in aqueous solution, with polymer precipitation when the solution temperature exceeds about 31 ℃, and re-dissolution of the polymer at reduced temperatures. The process is fully reversible. This also means that the NiPAm cannot be polymerized in aqueous solution at temperatures exceeding 30 ℃ otherwise the polymerization is difficult to proceed smoothly. Considering that the exothermic heat of polymerization will cause the temperature of the reaction system to rise, the lower the temperature at which polymerization starts to occur, the better, otherwise phase separation or even irreversible macroscopic gelation will occur. This places even greater demands on the polymerization initiated by redox of the N-H covalent bond of NiPAm to a free radical.

In the reaction process of the invention, in an aqueous solution at 25 ℃, an ultrahigh oxidation state copper salt complex (abbreviated as CuIII) initiates self free radical polymerization by NiPAm oxide without an external strengthening means to obtain a high molecular product. The invention has the advantages that: the method is simple to operate, has low requirements on experimental conditions, and uses cheap and easily-obtained raw materials.

The technical scheme adopted by the invention comprises the following specific operation steps:

(1) preparation of CuIII complexes

Copper sulfate pentahydrate (3.54 g), potassium periodate (6.82 g), potassium persulfate (2.20 g), and potassium hydroxide (9.00 g) were added to 200mL of deionized water. The mixture was boiled for 40 minutes. After cooling to room temperature, the mixture was filtered and the filtrate was diluted to 250mL with deionized water. The final solution contained 0.056 mol/L CuIII and 0.55 mol/L KOH. (Journal of Polymer Science Part A: Polymer Chemistry, 2006, 44(6):1952-

(2) Preparing a reaction solution

According to different reaction conditions, a certain amount of NiPAm and CuIII are measured and added into a self-sealing bag in batches, deionized water is added to the corresponding total volume, and the components are uniformly mixed by stirring.

(3) Reaction of

And introducing argon into the prepared reaction liquid to remove oxygen for 20min, sealing, and heating in a water bath at a certain temperature to start the reaction. Heating to react for different time to obtain a polymer according to requirements, dissolving the obtained polymer with water, precipitating and separating out the polymer by using ethanol, and placing a separated molecular weight sample in an oven for drying.

(4) Testing

The viscosity-average molecular weight of the polymer is measured by a viscosity method. The molecular weight of the obtained copolymer sample is measured by a single-point viscosity method, and the method comprises the following specific steps: the dried polymer was weighed at 0.50-0.70 g L-1, dissolved in deionized water to prepare 100 mL of an aqueous polymer solution, and the flow-out times of the deionized water and the polymer solution were measured at a water bath temperature of 20 ℃ using an Ubbelohde viscometer, respectively.

(5) Computing

The intrinsic viscosity ([ eta ]) of the polymer was calculated according to the following formula:

[η]=(2η_sp-2lnη_r)^0.5/c (1)

the polymer viscosity average molecular weight was then calculated from the Mark-Houwink equation as follows:

[η] = kM_ν ^α (2)

wherein k = 0.145 mL g^-1，α = 0.5（M. Kurata, X Tsunashima, Viscosity-molecular weight relationships and unperturbed dimensions of linear chain molecules, in Polymer Handbook, 4th Edition; Eds.: J. Brandrup, E. H. Immergut, E. A. Grulke; Wiley, Pergamon, 2003; VII/10）。

Detailed description of the invention

The present invention is further described in detail below with reference to specific examples, which are intended to illustrate the invention and not to limit or narrow the scope thereof.

Comparative example 1:

preparing a total volume of 50mL of aqueous solution, wherein the initial concentration of N, N-dimethylacrylamide is 4.87 mol/L, CuIII and the initial concentration is 1.12X 10^-3mol/L. Adding the mixture into a plastic self-sealing bag, uniformly mixing, and introducing argon to remove oxygen. After sealing, the mixture reacts for 6 hours at the temperature of 40 ℃ without polymerization.

Comparative example 2:

a total volume of 50mL of aqueous solution was prepared, with an initial sodium acrylate concentration of 3.6 mol/L, CuIII and an initial concentration of 1.12X 10^-3mol/L. Adding the mixture into a plastic self-sealing bag, uniformly mixing, and introducing argon to remove oxygen. After sealing, the mixture reacts for 6 hours at the temperature of 40 ℃ without polymerization.

Example 1:

preparing a total volume of 50mL of aqueous solution, wherein the initial concentration of NiPAm is 0.88 mol/L, CuIII and the initial concentration is 2.24X 10^-3mol/L. Adding into plastic self-sealing bag, mixing, introducing argon to remove oxygen for 20-30 min. Sealing and reacting at 25 ℃. The conversion rate of 12% in 0.5 h was determined by using N, N-dimethylacetamide as an internal standard. The viscosity-average molecular weight of the obtained polymer is 297 ten thousand by a viscometry.

Example 2:

preparing a total volume of 50mL of aqueous solution, wherein the initial concentration of NiPAm is 0.88 mol/L, CuIII and the initial concentration is 2.24X 10^-3mol/L. Adding into plastic self-sealing bag, mixing, introducing argon to remove oxygen for 20-30 min. Sealing and reacting at 25 ℃. The conversion rate of 92% after 3 h was measured by using N, N-dimethylacetamide as an internal standard. The viscosity average molecular weight of the obtained polymer is 268 ten thousand measured by a viscosity method.

Example 3:

preparing a total volume of 50mL of aqueous solution, wherein the initial concentration of NiPAm is 0.88 mol/L, CuIII and the initial concentration is 2.24X 10^-3mol/L. Adding the mixture into a plastic self-sealing bag and then uniformly mixing,introducing argon to remove oxygen for 20-30 min. Sealing and reacting at 25 ℃. The conversion rate of 96% after 5.5 h is measured by taking N, N-dimethylacetamide as an internal standard. The viscosity-average molecular weight of the obtained polymer is 226 ten thousand by the viscosity method.

Example 4:

preparing a total volume of 50mL of aqueous solution, wherein the initial concentration of NiPAm is 0.88 mol/L, CuIII and the initial concentration is 4.48X 10^-3mol/L. Adding into plastic self-sealing bag, mixing, introducing argon to remove oxygen for 20-30 min. Sealing and reacting at 25 ℃. The conversion rate of 5% at 0.5 h was determined using N, N-dimethylacetamide as an internal standard. The viscosity-average molecular weight of the obtained polymer is 154 ten thousand measured by a viscosity method.

Example 5:

preparing a total volume of 50mL of aqueous solution, wherein the initial concentration of NiPAm is 0.88 mol/L, CuIII and the initial concentration is 4.48X 10^-3mol/L. Adding into plastic self-sealing bag, mixing, introducing argon to remove oxygen for 20-30 min. Sealing and reacting at 25 ℃. The conversion rate of 21% in 1 h was determined by using N, N-dimethylacetamide as an internal standard. The viscosity-average molecular weight of the obtained polymer is 114 ten thousand measured by a viscosity method.

Example 6:

preparing a total volume of 50mL of aqueous solution, wherein the initial concentration of NiPAm is 0.88 mol/L, CuIII and the initial concentration is 4.48X 10^-3mol/L. Adding into plastic self-sealing bag, mixing, introducing argon to remove oxygen for 20-30 min. Sealing and reacting at 25 ℃. The conversion rate of 87% after 3 h was measured by using N, N-dimethylacetamide as an internal standard. The viscosity-average molecular weight of the obtained polymer is 100 ten thousand by the determination of a viscosity method.

Example 7:

preparing a total volume of 50mL of aqueous solution, wherein the initial concentration of NiPAm is 0.88 mol/L, CuIII and the initial concentration is 4.48X 10^-3mol/L. Adding into plastic self-sealing bag, mixing, introducing argon to remove oxygen for 20-30 min. Sealing and reacting at 25 ℃. The conversion rate of 96% after 5.5 h is measured by taking N, N-dimethylacetamide as an internal standard. The viscosity-average molecular weight of the obtained polymer is 102 ten thousand by the determination of a viscosity method.

Claims

1. A method for initiating free radical polymerization by redox of an ultrahigh oxidation state copper salt complex and N-isopropylacrylamide is characterized in that:

(1) oxidizing N-isopropyl acrylamide to generate free radicals to initiate polymerization by using an ultrahigh oxidation state copper salt complex as an oxidant;

(2) adding water and N-isopropyl acrylamide, fully and uniformly mixing, introducing argon to remove oxygen for 20-30 min;

(3) the above radical polymerization was carried out at a reaction temperature of 25 ℃.

2. The method of claim 1 wherein the oxidant concentration is in the range of 1.12 x 10^-3-4.48×10^-3mol/L。

3. The polymer obtained by the process of claim 1, wherein the polymer has a viscosity average molecular weight in the range of from 100 to 300 million.