CN1566165A - Polyvinyl alcohol with high degree of polymerization and its preparing process - Google Patents

Abstract

The invention relates to polyvinyl alcohol with a high degree of polymerization and its synthesis process. The process of the present invention adopts a suspension polymerization method, uses a free radical low-temperature initiation system, and obtains polyvinyl acetate with a high degree of polymerization after 2 to 10 hours of polymerization at 10 to 60 ° C, and performs alcoholysis on the polyvinyl acetate reaction to obtain polyvinyl alcohol with a high degree of polymerization. The synthesis process of the present invention has the characteristics of suitable reaction temperature, simple process control, high polymerization conversion rate, short polymerization time, high product purity, easy industrialization and the like. The degree of polymerization of the high degree of polymerization polyvinyl alcohol of the present invention is more than 5000, the best is 6000-8000, the degree of dispersion is 1.5 to 2.8, the best is 1.8 to 2.5, except that it is particularly suitable for the production of high-strength and high-modulus PVA fibers (intensity greater than 20g/d), it can also be used to process PVA film, PVA sheet, molding parts (such as nozzles and rotating parts) and tire cores.

Description

A kind of polyvinyl alcohol with high degree of polymerization and its synthesis process

technical field

The present invention obtains polyvinyl alcohol with a high degree of polymerization by means of suspension polymerization.

technical background

Polyvinyl alcohol (PVA) is a polymer with excellent performance and wide application. Its main preparation methods include solution polymerization, bulk polymerization, emulsion polymerization and suspension polymerization. The use of high-polymerization polyvinyl alcohol to prepare high-strength and high-modulus fibers can reduce molecular chain terminal defects, increase the draw ratio, shorten the production process, and reduce production costs. The obtained PVA fiber has a strength of up to 20g/d and excellent performance. In addition, polyvinyl alcohol with a high degree of polymerization can also be used to produce PVA film, PVA sheet, molding parts (such as nozzles and rotating parts), and tire cores and other products.

At present, the industrial polyvinyl alcohol polymerization method is solution polymerization, and the obtained polyvinyl alcohol has a maximum degree of polymerization of no more than 3000. The strength of high-strength and high-modulus fibers prepared from it does not exceed 13g/d.

Bulk polymerization is difficult to control because the polymerization reaction conditions are difficult to realize industrialization. Although the obtained product has a high degree of polymerization, its application is limited due to its high degree of branching.

What a large number of patents report to synthesize polyvinyl alcohol with a high degree of polymerization adopts the method of emulsion polymerization to carry out, such as: ① EP255137, 3/1988; ② JP 63, 37106/1988; 1993; ⑥ EP460502 A2/1991.

In the above-mentioned documents, EP255137, 3/1988 discloses that vinyl esters are polymerized in an emulsion containing non-ionic, anionic emulsifiers, peroxides, polyvalent metal ions, and selective reducing agents, and then saponified to obtain high-polymerization degree polymers. vinyl alcohol. However, this method has problems such as difficult operation, poor polymerization stability, complicated post-treatment, and large amount of wastewater treatment. The residual emulsifier in the obtained polyvinyl alcohol causes poor electrical properties of the product, and its application is limited.

JP-A-63, 37106/1988 report adopts low-temperature emulsion polymerization to prepare the method for high degree of polymerization polyvinyl ester, and redox systems such as ferrous sulfate-diaobai powder are used as initiators, and the polymerization temperature of this method is low (at -60～-15 ℃), difficult to control, difficult to wash, and the obtained polyvinyl alcohol has a viscosity of more than 10,000, even higher than 30,000. The product contains metal ions such as iron and sodium, and its purity is poor, so its application is limited. US4818787/1986 and US4818788/1987 report the method for preparing high degree of polymerization by emulsion polymerization, and the intrinsic viscosity of the obtained polyvinyl alcohol is above 1.5dl/g, even higher than 3.2dl/g. Its degree of polymerization is about 10,000 or more, or even more than 20,000. Because the degree of polymerization of the product is too high, it is difficult to dissolve and the solution has poor spinnability, so it is not suitable for fiber spinning.

So far, polyvinyl alcohol has been synthesized by suspension polymerization, and there are some research and patent reports:

JP-A-61-148209/1986 discloses a method for preparing polyvinyl alcohol with a high degree of polymerization by suspension polymerization. The polymerization temperature of this method is below 20°C, the polymerization speed is slow, and the polymerization time is long (more than 48 hours), so it is difficult to realize industrialization . The intrinsic viscosity of the obtained polyvinyl alcohol is above 1.5dl/g, the degree of polymerization is above 10,000, and the product performance and use are not mentioned.

EP250607, 7/1988 discloses a method for preparing polyvinyl alcohol with a high degree of polymerization by suspension polymerization, but the degree of polymerization of polyvinyl alcohol prepared by this method is only 1700, and this method has no industrial value.

"Polymer Processing" (Japan), 44(9) P409-413, 1995; Pollimo ("Polymer"), 20(6), 1004-1013 (Korean) 1996; Colloid Polym.Sci., ("Colloidal State Polymer Science ") 276(11), 951-959,1998; J.KoreaFiber Soc., ("Korea Fiber Association Journal") 36(5), 354-360, 1999 report adopts suspension polymerization method to prepare polyvinyl alcohol or The polymerization time is too long and the polymerization rate is too slow (the polymerization time is more than 47 hours, even more than 100 hours); or the degree of polymerization is low and the conversion rate is not high, so it is difficult to realize industrialization. The degree of polymerization of the obtained polyvinyl alcohol does not exceed 6000, and if it is used to produce high-strength and high-modulus fibers, the strength of the obtained PVA fibers does not exceed 13g/d.

Contents of the invention

The object of the present invention is to provide a method using suspension polymerization, which is suitable for industrial production of polyvinyl alcohol with a high degree of polymerization and its synthesis process.

The degree of polymerization of polyvinyl alcohol obtained by this synthesis process is above 5000, the best is 6000-8000, the degree of dispersion is 1.5-2.8, the best is 1.8-2.5, and it is suitable for the production of high-strength and high-modulus PVA fibers (strength greater than 20g/d) , PVA film, PVA sheet, molding parts (such as nozzles and rotating parts) and tire cores and other products.

Its main process can be expressed as follows:

Monomer preparation → suspension polymerization → separation → alcoholysis → product

The polymerization temperature of the suspension polymerization in the present invention is 10-60°C, preferably 20-50°C, and the polymerization time is 2-10 hours, most preferably 4-8 hours.

The suspension polymerization system of the present invention is composed of a dispersion medium, a monomer, a dispersant, and an initiator, and its weight percentages are as follows: 40% to 80% of the dispersion medium, preferably 50% to 70%; 20% to 70% of the monomer; 60%, the best is 30~50%; the mass ratio of dispersion medium/monomer is between 2:1~1:1; the dispersant is 0~5%, the best is 0.02~2%, and the initiator is 0~4 %, the best is 0.02-2%.

The dispersion medium of the present invention is soft water; the monomer is vinyl acetate; the dispersant is vinyl alcohol-vinyl acetate copolymer with a vinyl acetate molar content of 0-40%, polyacrylic acid alkali metal salt, acrylic acid or methyl Copolymers of acrylic acid or maleic acid and styrene or acrylates or methacrylates, gelatin, carboxymethylcellulose, hydroxyethylcellulose and compositions thereof; initiators are benzoyl peroxide, dodecyl peroxide Acyl, tert-butyl peroxypivalate, diisopropyl peroxydicarbonate, dicyclohexyl peroxydicarbonate, acetylcyclohexanesulfonyl peroxide, azobisisobutyronitrile, azobisisobutyronitrile Heptanonitrile or azobisisonononitrile and combinations thereof.

The reaction temperature of the alcoholysis reaction in the present invention is 0-60° C., preferably 20-40° C., and the reaction time is 0.1-2 hours, most preferably 0.4-1.5 hours.

The alcoholysis solution of the present invention is composed of methanol, sodium hydroxide, soft water and polyvinyl acetate obtained by the above polymerization. The weight percent of alcoholysis liquid is as follows respectively: polyvinyl acetate 2～30%, the best is 4～25%; Methyl alcohol 65～97%, the best is 60～95%; Sodium hydroxide 1～7%, The best is 1.5-6%; soft water is 0-15%, the best is 0.2-10%.

The present invention has the following advantages:

1. The degree of polymerization of polyvinyl alcohol obtained in the present invention is above 5000, preferably 6000-8000, with low dispersion and good linearity.

2. The polymerization time of the present invention is short, the speed is fast, only 2-10 hours, the conversion rate is high, up to 50%, the synthesis process is simple, the operation is convenient, and it is suitable for industrialization.

3, the high degree of polymerization polyvinyl alcohol that the present invention obtains is except being especially suitable for spinning high-strength and high-modulus PVA fibers, and can also be used for the production of PVA films, PVA plates, molding parts such as nozzles and rotating parts, and tire cores, etc. Broad market prospects.

Detailed ways

The present invention is specifically described below through the examples, it is necessary to point out that the following examples are only used to further illustrate the present invention, and can not be interpreted as limiting the protection scope of the present invention, those skilled in the art can according to the above-mentioned SUMMARY OF THE INVENTION Some non-essential improvements and adjustments are made to the present invention.

Example 1:

Introduce nitrogen into the reaction kettle, add 56.1 parts of soft water, and add 42.5 parts of vinyl acetate, 1 part of gelatin, 0.2 parts of azobisisobutyronitrile and 0.2 parts of azobisisononononitrile into the reaction kettle, and the temperature is controlled at 38 ℃, polymerized for 4 hours, then dissolved the polyvinyl acetate obtained in the above reaction in 79.5 parts of methanol and 0.5 parts of soft water to make a 20% solution, and added 1.5% sodium hydroxide for alcoholysis at 30°C for 30 Minutes to obtain a white powdery polyvinyl alcohol product with a degree of polymerization of 6200, a degree of alcoholysis of 99.8%, and a degree of dispersion of 2.41.

Comparative Example 1: According to the operation and conditions of Example 1, except that the temperature during polymerization was changed to 65° C., the degree of polymerization of the obtained PVA was 4800, and the degree of dispersion was 5.10.

Example 2:

Nitrogen gas was introduced into the reaction kettle, 58.6 parts of soft water were added, and 40 parts of vinyl acetate, 0.4 parts of azobisisobutyronitrile and 1 part of hydroxyethyl cellulose were added to the reaction kettle. The temperature is controlled at 40°C, and the polymerization reaction is carried out for 3 hours, then the polyvinyl acetate obtained by the above reaction is dissolved in 78.5 parts of methanol and 3.5 parts of soft water to form an 18% solution, and at a temperature of 30°C, add 2.5% sodium hydroxide After alcoholysis for 35 minutes, a white powdery polyvinyl alcohol product was obtained. The degree of polymerization was 7000, the degree of alcoholysis was 99.9%, and the degree of dispersion was 2.30.

Comparative example 2: according to the operation and condition of embodiment 2, only the consumption of initiator azobisisobutyronitrile is changed to 4.1%, then reaction is violent during polymerization, is difficult to control, and the PVA polymerization degree that obtains is 4200, and dispersion degree is 4.50.

Example 3:

Introduce nitrogen into the reaction kettle, add 61 parts of soft water, 38 parts of vinyl acetate, 0.2 parts of azobisisobutyronitrile, 0.3 parts of acetylcyclohexanesulfonyl peroxide and 0.5 parts of vinyl alcohol-vinyl acetate Add the copolymer into the reactor, control the temperature at 30°C, and polymerize for 3 hours, then dissolve the polyvinyl acetate obtained by the above reaction in 80 parts of methanol and 5 parts of soft water to form a 15% solution, and at 20°C, 3% sodium hydroxide was added for alcoholysis for 80 minutes to obtain a white powdery polyvinyl alcohol product with a degree of polymerization of 6000, a degree of alcoholysis of 99.8%, and a degree of dispersion of 1.80.

Comparative Example 3: According to the operation and conditions of Example 3, only the polymerization time was extended to 11 hours. Although the polymerization yield increased, the obtained PVA had a degree of polymerization of 4200 and a degree of dispersion of 3.83.

Example 4:

Feed nitrogen into the reactor, add 42.1 parts of soft water, and mix 52.7 parts of vinyl acetate, 2.5 parts of vinyl alcohol-vinyl acetate copolymer, 1 part of acrylic acid-acrylate copolymer, 0.5 part of polyacrylic acid alkali metal salt, 0.6 Part of azobisisobutyronitrile, 0.3 part of azobisisononononitrile and 0.3 part of benzoyl peroxide were added to the reaction kettle, the temperature was controlled at 15°C, and the polymerization reaction was carried out for 10 hours, and then the polyvinyl acetate obtained by the above reaction was dissolved Prepare a 6% solution in 88 parts of methanol and 6.0 parts of soft water, and add 3.8% sodium hydroxide for alcoholysis at 55°C for 25 minutes to obtain a white powdery polyvinyl alcohol product with a degree of polymerization of 8000. The degree of alcoholysis is 99.7%, and the degree of dispersion is 1.50.

Example 5:

Introduce nitrogen into the reaction kettle, add 55 parts of soft water, and add 43.6 parts of vinyl acetate, 1.0 parts of acrylic acid-methacrylic acid copolymer, 0.2 parts of dicyclohexyl peroxydicarbonate and 0.2 parts of benzoyl peroxide Reactor, the temperature is controlled at 25°C, react for 5 hours, and then dissolve the polyvinyl acetate obtained in the above reaction in 85 parts of methanol and 3 parts of soft water to make a 12% solution, and add 5% hydrogen at a temperature of 40°C Alkali alcoholysis with sodium oxide for 30 minutes gave a white powdery polyvinyl alcohol product with a degree of polymerization of 7500, a degree of alcoholysis of 99.8%, and a degree of dispersion of 1.80.

Comparative example 4: according to the operation and condition of example 4, the alcoholysis time is shortened to 5 minutes, then the alcoholysis degree of the obtained PVA is only 80%.

Embodiment 6:

Introduce nitrogen into the reaction kettle, add 64.4 parts of soft water, and add 35 parts of vinyl acetate, 0.1 part of hydroxyethyl cellulose, 0.3 part of azobisisoheptanoyl nitrile and 0.2 part of lauryl peroxide into the reaction kettle, the temperature Control at 20°C, polymerize for 6.5 hours, then dissolve the polyvinyl acetate obtained by the above reaction in 65 parts of methanol and 1 part of soft water to make a 35% solution, add 2.0% sodium hydroxide at 25°C for 60 minutes for alcoholysis , to obtain a white powdery polyvinyl alcohol product with a degree of polymerization of 6500, a degree of alcoholysis of 99.9%, and a degree of dispersion of 2.25.

Embodiment 7:

Introduce nitrogen into the reaction kettle, add 72.5 parts of soft water, and add 26.8 parts of vinyl acetate, 0.04 parts of vinyl alcohol-vinyl acetate copolymer, 0.01 part of azobisisonononitrile and 0.02 parts of benzoyl peroxide to the reaction Kettle, the temperature is controlled at 55°C, the polymerization reaction is 2.5 hours, and then the polyvinyl acetate obtained by the above reaction is dissolved in 89 parts of methanol and 7 parts of soft water to make a 4% solution, and 6.8% sodium hydroxide is added at 15°C After alcoholysis for 100 minutes, a white powdery polyvinyl alcohol product was obtained. The degree of polymerization was 8300, the degree of alcoholysis was 99.9%, and the degree of dispersion was 2.80.

Embodiment 8:

Introduce nitrogen into the reaction kettle, add 50 parts of soft water, and add 40 parts of vinyl acetate, 0.8 parts of hydroxymethyl cellulose, 0.01 part of azobisisoheptanonitrile and 0.02 parts of benzoyl peroxide into the reaction kettle, the temperature Control at 45°C, polymerize for 5.5 hours, then dissolve the polyvinyl acetate obtained by the above reaction in 69 parts of methanol and 7.0 parts of soft water to make a 24% solution, add 6.0% sodium hydroxide at 20°C for alcoholysis for 60 Minutes to obtain a white powdery polyvinyl alcohol product with a degree of polymerization of 5000, a degree of alcoholysis of 99.8%, and a degree of dispersion of 2.70.

Claims (5)

1, a kind of polyvinyl alcohol of high-polymerization degree is characterized in that the polymerization degree is more than 5000.

2, the polyvinyl alcohol of high-polymerization degree according to claim 1 is characterized in that polymerization degree the best is 6000～8000, and dispersity is 1.5～2.8.

3, the polyvinyl alcohol of high-polymerization degree according to claim 2 is characterized in that dispersity the best is 1.8～2.5.

4, the synthesis technique of claim 1,2 or 3 described polyvinyl alcohol of high degree of polymerization is characterized in that may further comprise the steps:

(1) vinyl acetate polyisocyanate polyaddition: adopt suspension polymerization to carry out the vinyl acetate polyisocyanate polyaddition, 10～60 ℃ of polymerization temperatures, polymerization time 2～10 hours;

(2) alcoholysis: polyvinyl acetate is carried out alcoholysis reaction, obtain the polyvinyl alcohol of high-polymerization degree;

Wherein, above-mentioned polymerization system and composed as follows:

The polymerization system of described suspension polymerization is made up of dispersion medium, monomer, dispersion agent, initiator, and its weight percentage is as follows respectively: dispersion medium 40～80%, monomer 20～60%, dispersion agent 0～5%, initiator 0～4%.Its dispersion medium is a soft water, monomer is a vinyl-acetic ester, and dispersion agent is that the vinyl-acetic ester molar content is 0～40% vinyl alcohol-vinyl acetate copolymer, polyacrylic acid an alkali metal salt, acrylic or methacrylic acid or toxilic acid and multipolymer, gelatin, carboxymethyl cellulose or Natvosol and the combination thereof of vinylbenzene or acrylate or methacrylic ester; Initiator is benzoyl peroxide, dilauroyl peroxide, peroxidation trimethylacetic acid tertiary butyl, di-isopropyl peroxydicarbonate, di-cyclohexylperoxy dicarbonate, acetyl peroxide hexanaphthene sulphonyl, Diisopropyl azodicarboxylate, 2,2'-Azobis(2,4-dimethylvaleronitrile) or azo two different pelargonitrile and combinations thereof;

Above-mentioned alcoholysis mode and condition:

0～60 ℃ of described alcoholysis reaction temperature, 0.1～2 hour reaction times; Alcoholysis liquid is made up of the polyvinyl acetate of methyl alcohol, sodium hydroxide, soft water and above-mentioned polymerization gained, and its weight percent is as follows respectively: polyvinyl acetate 2～30%, methyl alcohol 97～65%, sodium hydroxide 1～7%, soft water 0～15%.

5,, it is characterized in that this polyvinyl alcohol of high degree of polymerization is suitable for the high strength high modulus PVA fiber of production intensity greater than 20g/d according to claim 1,2 or 3 described polyvinyl alcohol of high degree of polymerization.