RU2734242C1 - Method of producing copolymers of acrylonitrile in mass - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: present invention relates to a method of producing composition-homogeneous copolymers of acrylonitrile of specified composition with narrow molecular weight distribution in mass in the presence of radical polymerization initiators. Method involves adding a polymerization regulator (OPC-agent) to a polymerization system consisting of a mixture of an acrylonitrile monomer with a comonomer and an initiator. Polymerization regulator used is organo-sulfur compounds of general structure R-S-C(=S)-S-R', where R and R' – alkyl and aryl substitutes of the same or different structure, which may additionally contain carboxyl, nitrile or ester groups. Polymerization is carried out in the temperature range from 50 to 80 °C. Polymerization method is carried out in an atmosphere of inert gas or in a vacuum at low pressure.

EFFECT: present method enables to obtain a directly-finished product which does not require polymer extraction and purification.

8 cl, 3 ex

Description

FIELD OF TECHNOLOGY

The present invention relates to a method for producing acrylonitrile copolymer by radical polymerization using organosulfur compounds of the general structure RSC (= S) -S-R ', where R and R' are alkyl and aryl substituents of the same or different structure, which may additionally contain carboxyl, nitrile, ester and other groups.

LEVEL OF TECHNOLOGY

Acrylonitrile copolymers are used for the production of textile fibers and as a precursor for the production of carbon fibers. The latter are used in the production of reinforced composite materials for the aviation, automotive industry, in construction, etc. Traditional copolymers of acrylonitrile include one or two comonomers that act as a plasticizer and / or an accelerator for the cyclization of nitrile units. Methyl acrylate, methyl methacrylate, acrylic, methacrylic or itaconic acid, acrylamide and others are usually used as comonomers (CA 1281498; TW 201612205, etc.).

The main method for obtaining acrylonitrile copolymers is radical polymerization, which is carried out in an organic solvent (US 2010273952; KR 20190038322), an aqueous salt solution of sodium thiocyanate or zinc chloride (GB 950878, EP 0824111; JP 2004211047 A), in an emulsion (RU 2412966; EP 2851377; US 7098280; RU 2467021) or suspension (JP 0310651B2), as well as precipitation polymerization (RU 2017865 C1; RU 94036404 A1). The main disadvantages of these methods are the impossibility of controlling the molecular weight distribution and the homogeneity of copolymer macromolecules in composition. These disadvantages lead to the formation of defects in the production of the PAN precursor. These problems can be overcome by using radical polymerization with reversible chain deactivation, which allows you to control the molecular weight characteristics of copolymers, obtain copolymers with a narrow molecular weight distribution, and prevent the formation of compositionally inhomogeneous copolymers.

An example of the application of radical polymerization with reversible chain deactivation to the synthesis of acrylonitrile copolymers includes copolymerization of acrylonitrile with methyl acrylate and dimethyl itaconate in a dimethyl sulfoxide solution using carbon tetrachloride, copper (I) bromide, tris- (2-pyridylmethyl) amine and glucose glucose. This process, proceeding by the atom transfer mechanism, requires elevated temperatures, long reaction times (more than 100 h) and is not applicable to monomers with acidic or amide groups (RU 2697882 C1).

One of the most popular variants of polymerization with reversible chain deactivation is polymerization with reversible chain transfer under the action of sulfur-containing compounds of the general formula Z-C (= S) - S-R, where Z and R can be an aryl, alkyl, aroxy, alkoxy substituent or a disubstituted amino group. A number of examples of the use of this method for the synthesis of acrylonitrile copolymers is known from the prior art (RU 2647861 C2; RU 2627264 C1; US 2014271442), all of them based on copolymerization in an organic solvent solution. The main advantage of this copolymerization is that it can be applied to any monomers polymerizing by a radical mechanism over a wide temperature range. The disadvantages of the methods for implementing this method described in patents are reduced to a low polymerization rate due to the use of dithiobenzoates (Z = Ph) or due to a low concentration of the initiator.

The closest analogue to the proposed invention is patent US 3345350A Polymerization of acrylonitrile, 03.10.1967, which describes a method for producing acrylonitrile copolymer in bulk by the method of radical polymerization in the presence of an acrylonitrile polymerization initiator, which includes mechanical stirring of a mixture of acrylonitrile monomer with the said initiator in the polymerization liquid monomer; stopping stirring of the reaction mixture at least at the beginning of the solidification of said mixture and maintaining the reaction mixture free from mechanical stirring.

The main disadvantage of the prototype method is that the polymerization reaction takes a long time (from three days to 4 weeks). In addition, the patent does not contain information on the number average molecular weight of the obtained polymers and on the polydispersity index.

SHORT DESCRIPTION

The method according to this invention allows to obtain copolymers of acrylonitrile with a molecular weight in the range of 5-50 kg / mol, as well as with a narrow molecular weight distribution (polydispersity index does not exceed 1.5). This method is based on the use of radical polymerization with reversible chain deactivation, but differs from the known methods by the presence of additional regulation of the molecular weight of the resulting copolymer by controlling the concentration of the sulfur-containing compound.

The practical significance of low molecular weight AN copolymers is that they can be used to obtain PAN precursors by melt spinning either on their own or as a plasticizer additive to a copolymer with a higher molecular weight.

In the present invention, the copolymerization is carried out in bulk, i.e. in the absence of a solvent, with a comonomer content of 10 to 80 mol. %;

Under the conditions of the method without using a solvent and controlling the molecular weight of the polymer by the concentration of the sulfur-containing compound, it is possible to obtain a compositionally homogeneous copolymer at a high rate (10-16 hours) and high yield in the form of an optically transparent monolithic block.

This method allows you to directly obtain a finished product that does not require polymer isolation and purification.

The objective of the invention is to develop a new method for obtaining compositionally homogeneous acrylonitrile copolymers of a given composition, molecular weight and chemical nature with a controlled distribution of links in the chain, applicable for any functional monomers polymerizing by a radical mechanism, using symmetric (R = R ') and asymmetric ( R Ф R ') tritiocarbonates of the general structure RSC (= S) -S-R', where R and R 'are alkyl and aryl substituents of the same or different structure, which may additionally contain carboxyl, nitrile, ester and other groups.

The technical result from the use of the present invention is to obtain double and ternary copolymers with a number average molecular weight in the range of 5-50 kg / mol, a narrow molecular weight distribution (Mw / Mn up to 1.5), a comonomer content from 10 to 80 mol. % and controlled distribution of units in the copolymer chain. This result is achieved in the following way.

In the method of obtaining a copolymer of acrylonitrile with a number-average molecular weight in the range of 5-50 kg / mol with a second monomer, which can be alkyl acrylate, styrene, vinyl acetate, etc., trithiocarbonate is used (in an amount of 0.3 to 2 mol.%, Based on monomers) , in which the R group includes a benzyl group, a secondary or tertiary alkyl group with functional substituents (hydroxyl, nitrile, carboxyl group, aryl), R 'is chemically identical or identical to the R group or includes n-alkyl. The composition of the monomer mixture can be from 10 to 80 mol%. Copolymerization is carried out in the absence of a solvent (in bulk) using a radical initiator from 0.05 to 0.1 mol. % in terms of monomers in an inert atmosphere (argon or nitrogen) or in vacuum (at reduced pressure). The mixture is heated to a temperature of 50-80 ° C, the polymerization is carried out for 10-16 hours. At the end of the polymerization, a monolithic block of the copolymer is obtained, which can be dissolved in dimethyl sulfoxide to the desired concentration and used as a spinning solution or converted into a viscous state with a comonomer content not lower 20 mol. %.

In accordance with the proposed invention, the synthesis of copolymers is carried out as follows.

The reactor is purged with argon, the radical initiator, tritiocarbonate, monomers are charged and filled with argon or the listed components are loaded into the reactor and the mixture is degassed. An inert atmosphere or reduced pressure is necessary to prevent inhibition of polymerization and to control the molecular weights of the copolymers. Then the reaction mixture is heated to 50-80 ° C and polymerization is carried out for 10-16 hours. Temperatures below 50 ° C do not provide an acceptable polymerization rate; temperatures above 80 ° C lead to a decrease in the ultimate yield of the polymer. The molecular weight of the polymer during bulk polymerization is controlled by the tritiocarbonate concentration and the polymerization time, i.e. conversion of monomers. General scheme of the copolymerization reaction; a step-by-step scheme for obtaining a copolymer with all reaction parameters.

The general scheme of the copolymerization reaction can be represented as follows:

At the end of the polymerization, a finished monolithic product or solution is obtained, suitable for molding after dilution of dimethyl sulfoxide solutions of the required concentration.

The acrylonitrile copolymer obtained by the proposed method has a structure from statistical to gradient, in which the order of distribution of links in the chain is set by the rate of introduction of monomers into polymerization:

The resulting copolymers are characterized by a number average molecular weight in the range of 5-50 kg / mol, Mw / Mn up to 1.5, comonomer content from 10 to 80 mol. % and controlled distribution of units in the copolymer chain.

The key points of the invention is the possibility of synthesizing compositionally homogeneous copolymers of a given composition and with a narrow molecular weight distribution by copolymerization in bulk, which provides a high polymerization rate, suppression of the gel effect and, as a result, the possibility of obtaining a monolithic product without the need for a stage of isolation and purification of the copolymer. and also the possibility of obtaining a higher molecular weight copolymer with a narrow molecular weight distribution and high compositional uniformity with a given distribution of comonomers in the chain by using a controlled rate of introduction of monomers into the copolymerization.

Below are examples of specific implementation of the invention. These examples are not intended to limit the scope of protection of the present invention.

Example 1.

Copolymerization of acrylonitrile with methyl acrylate in bulk is carried out in glass ampoules. For this, a solution is prepared containing 7.3 mg of dinitrile-azo-bis-isobutyric acid (DAA), 18.5 mg of dibenzyl trithiocarbonate (BTK), 9 g of freshly distilled acrylonitrile, 1.55 g of freshly distilled methyl acrylate.

The molar ratio between initiator and RAFT agent in the resulting mixture is 3.5: 5, respectively. The composition of the monomer mixture AN: MA - 90:10 mol. %, respectively.

The solution is poured into ampoules, and after degassing by repeating freeze-thaw cycles, the ampoules were sealed off. (Cycle: freezing with liquid nitrogen, degassing, defrosting to room temperature. Not more than 4 cycles.) Polymerization is carried out at 60 ° C. At the end of polymerization, the samples are cooled with liquid nitrogen, opened, diluted with dimethyl sulfoxide, if necessary, and planted in a 10-fold excess of water. Then the samples are filtered on a glass filter, washed with distilled water, methanol and dried under vacuum to constant weight.

The copolymerization yield is 75%. According to the analysis carried out by the method of gel permeation chromatography, the obtained polymer is characterized by Mn = 49000, Mw / Mn = 1.40.

Example 2.

Copolymerization of acrylonitrile with vinyl acetate in bulk is carried out in glass ampoules. For this, a solution is prepared containing 7.2 mg of dinitrile-azo-bis-isobutyric acid (DAA), 31.9 mg of S- (2-cyano-2-propyl) -8-dodecyltrithiocarbonate (CTA), 8 g of freshly distilled acrylonitrile, 3.2 g of freshly distilled vinyl acetate.

The molar ratio between the initiator and RAFT agent in the resulting mixture is 1: 2, respectively. The composition of the monomer mixture AN: VA - 80:20 mol. %, respectively.

The solution is poured into ampoules, and after degassing by repeating freeze-thaw cycles, the ampoules were sealed off. (Cycle: freezing with liquid nitrogen, degassing, defrosting to room temperature. Not more than 4 cycles.) Polymerization is carried out at 70 ° C. At the end of polymerization, the samples are cooled with liquid nitrogen, opened, diluted with dimethyl sulfoxide, if necessary, and planted in a 10-fold excess of water. Then the samples are filtered on a glass filter, washed with distilled water, methanol and dried under vacuum to constant weight.

The copolymerization yield is 65%. According to the analysis carried out by the method of gel permeation chromatography, the obtained polymer is characterized by Mn = 40,000, Mw / Mn = 1.45.

Example 3.

Copolymerization of acrylonitrile with styrene in bulk is carried out in glass ampoules. For this, a solution is prepared containing 20 mg of dinitrile-azo-bis-isobutyric acid (DAA), 88.4 mg of dibenzyltritiocarbonate (BTK), 10 g of freshly distilled acrylonitrile, 2.18 g of freshly distilled styrene.

The molar ratio between the initiator and RAFT agent in the resulting mixture is 1: 2.5, respectively. The composition of the monomer mixture AN: St - 90:10 mol. %, respectively.

The solution is poured into ampoules, and after degassing by repeating freeze-thaw cycles, the ampoules were sealed off. (Cycle: freezing with liquid nitrogen, degassing, defrosting to room temperature. Not more than 4 cycles.) Polymerization is carried out at 70 ° C. At the end of polymerization, the samples are cooled with liquid nitrogen, opened, diluted with dimethyl sulfoxide, if necessary, and planted in a 10-fold excess of water. Then the samples are filtered on a glass filter, washed with distilled water, methanol and dried under vacuum to constant weight.

The copolymerization yield is 75%. According to the analysis carried out by the method of gel permeation chromatography, the obtained polymer is characterized by Mn = 27000, Mw / Mn = 1.32.

Claims (8)

1. A method of obtaining compositionally homogeneous copolymers of acrylonitrile of a given composition with a narrow molecular weight distribution in the mass in the presence of radical polymerization initiators, characterized in that a polymerization regulator (OPC- agent), which are organosulfur compounds of the general structure RSC (= S) -S-R ', where R and R' are alkyl and aryl substituents of the same or different structure, which may additionally contain carboxyl, nitrile or ester groups, and polymerization carried out in the temperature range from 50 to 80 ° C, while the method is carried out in an atmosphere of an inert gas or in vacuum under reduced pressure. 2. The method according to claim 1, characterized in that copolymers of acrylonitrile with a number average molecular weight in the range from 5 to 50 kg / mol are obtained. 3. The method according to p. 1, characterized in that as a polymerization regulator (RAFT agent), tritiocarbonate is used in an amount of 0.3 to 2 mol. % based on monomers. 4. A method according to claim 1, characterized in that azo compounds, including azobisisobutyronitrile, are used as the polymerization initiator. 5. The method according to claim 1, characterized in that the amount of the radical initiator used is from 0.05 to 0.1 mol. % based on monomers. 6. A method according to claim 1, characterized in that the polymerization proceeds at a high speed from 10 to 16 hours without a gel effect. 7. A method according to claim 1, characterized in that alkyl acrylates, styrene, vinyl acetate are used as copolymers. 8. The method according to claim 1, characterized in that the resulting copolymer is characterized by a molecular weight distribution (Mw / Mn) not exceeding 1.5.