Chemistry and technology of synthetic rubber. Textbook

the required amount of powdered sodium sulfite (Na2SO3) is introduced into the flask. The mixture is stirred and heated to 80°C, then through the dropping or normal funnel the calculated amount of sodium hydrosulfide solution is added to the flask. The flask contents is maintained at 80-85°C for 15 min, after which the dispersion of liquid rubber is moved to the beaker and the polymer is coagulated by 20 % aqueous sulfuric acid solution to pH = 4-5.

Separated polymer with a wooden spatula is taken to the beaker and washed several times with cold water. The washed polymer is taken into the flask of the rotary-film evaporator or the flask with the stirrer and is dried under vacuum at a temperature of about 80°C. At the beginning of the drying the polymer a strong foaming may occur, therefore the temperature should be increased only after the polymer foaming will stop without heating.

The molecular weight of the polymer is determined by the content of terminal HS-groups and the polymer is cured by reacting with inorganic oxidants.

Examples of the calculation of the required amounts of reagents 1. Monomers

Monomers are used individually except 1,2,3-trichloropropane (1,2,3-TCP) or in a mixture with 1,2-dichlorodiethylformal (formal1). The amount of 1,2,3-TCP typically varies from 0.5 to 2.0 mol % of the sum of monomers.

For example, in molar ratio [formal1]: [1,2,3-TCP] = 98:2 "conditional mol" is calculated in accordance with Table 5.3, and then the required amount of monomers is calculated.

If the total amount of monomers is 20 g, the amounts of the individual monomers are calculated as follows:

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Table 5.4 shows the most common monomers ratios in the synthesis of polysulfide polymer.

2. Sodium disulfide and dispersant

Before you calculate the required amount of solution of sodium disulfide, you must check with the teaching staff its concentration in solution.

The molar ratio of [monomer]: [sodium disulfide] is usually 1:1.5. If, for example, 20 g of monomers with the "conditional mole"

172.88 is used, the required amount of sodium disulfide (G1) is:

or considering the concentration of the solution (e.g., at a concentration of 2.5 mol/l) the volume of Na2S2 (V1) is equal to:

V1 20 1.5 1000 69.41ml; 172.88 2.5

The amounts of MgSO4 and NaOH are calculated according to the reaction equation:

MgSO4 +2 NaOHMg(OH)2 + Na2SO4 Molecular masses of the products:

MgSO4 - 120.3

NaOH - 40

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Mg(OH)2 - 58.3.

The amount of Mg(OH)2 is typically equal to 6% wt. of the total weight of monomers. When 20 g of monomer is used, the necessary amount of dispersant (G2) is equal to:

20 6

G2 100 1.2g;

Then to its obtaining it is necessary: magnesium sulfate

G3 120.3 1.2 2.48g; 58.3

or considering the concentration of the solution ( 250 g/l):

V2 1000 120.3 1.2 9.9ml 58.3 250

NaOH

G4 80 1.2 1.64g; 58.3

or considering the concentration of the solution ( 500 g/l):

V3 1000 80 1,2 3.29ml. 500 58.3

3. Cleaving agents

The amount of cleaving agent (NaSH) can regulate the molecular weight of the liquid thiokol. Usually the amount of NaSH is varied within 4-5 g per 100 g of monomers. Optimum is 4.5 g NaSH per 100 g of monomers (cleaving 4.5/100).

When 20 g of monomer is used, then to cleave 4.5/100 it is necessary to have NaSH (G5):

or considering the concentration of the solution NaSH ( 30 % wt.)

V4 4.5 20 100 3.0ml. 100 30

The amount of sodium sulfite is generally 4 mol per 1 mol NaSH, i.e. the required amount of Na2SO3 is:

G6 4.5 20 4 127 8.16g, 100 56

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where 56 and 127 are the molecular weights of NaSH and Na2SO3, respectively.

Determination of the molecular weight of thiokol

The method is based on the interaction of terminal mercaptan groups with a weak iodine solution which excess is determined by titration.

Apparatus:

1)conical flasks with ground glass stoppers of 150-200 ml;

2)chemically pure toluene;

3)0.01 N solution of iodine;

4)0.01 N solution of sodium thiosulfate (Na2S2O3).

Methods of analysis

Thiokol sample weight (0.1 g) is placed in pre-weighed to the nearest 0.0001 g conical flask with ground stopper. Then the sample weight weighted in the flask to the nearest 0.0001 g, is dissolved in 50 ml of toluene. After complete dissolution of thiokol, 35-40 ml of 0.01 N iodine solution is added to the flask. The contents of the flask is shaken vigorously (it is very important!) for 3-5 min. The excess of iodine is titrated with 0.01 N solution sodium thiosulphate. Control titration of iodine in toluene is carried out at the same time.

The molecular weight of thiokol is calculated by the formula:

where g - thiokol sample weight, g; a - the amount of 0.01 N solution sodium thiosulfate, spent on the control titration, ml; b - the amount of 0.01 N solution sodium thiosulphate. spent on the titration of thiokol sample, ml; F- factor of 0.01 N sodium thiosulfate solution (check with the laboratory assistant, typically 1.0); 254 - molecular weight of iodine; 0.00127 - the amount of iodine, corresponding to 1 ml of 0.01 N sodium thiosulphate solution, g.

Vulcanization of liquid thiokol

Sealants based on the liquid thiokol are intended for sealing bolted, rivet or other metal connections which are in contact with air and fuel. The conversion of liquid thiokol to the rubbery solid state is carried out by oxidation of terminal mercaptan groups using various oxidizing agents such as lead and manganese dioxides, sodium dichromate, organic hydroperoxides. Thus, separate molecules are crosslinked to form disulfide bridges, resulting in network structure of the polymer. Titanium dioxide,

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carbon black are most often used as the fillers. Vulcanization accelerator is diphenylguanidine.

Table 5.5 shows one of the mixture composition for vulcanization.

Table 5.5

The mixture composition for vulcanization

Component

Amount, phr

All the ingredients are weighed on an analytical balance.

Thiokol mixing with ingredients is produced in a ceramic mortar. The procedure for the components filing is the following: thiokol, carbon black in portions (in 4 doses), diphenylguanidine, sodium dichromate.

Mixing of liquid thiokol with fillers and accelerator is produced until uniform distribution of the accelerator in thiokol. Uniform mixing is determined visually by the absence of visible grains of accelerators when applying a thin layer of sealant on the glass plate.

Ready paste is applied with a spatula on the glass plate, pre-greased with paraffin, with a layer thickness of 2 mm according to the special pattern. Then the time of the adhesiveness disappearance is determined by contact of the glass rod with the surface. After the disappearance of adhesiveness vulcanizates are heated in a thermostat at 85°C for 4 hours.

Safety rules during the synthesis of liquid thiokols

The synthesis of thiokols is explosive and fire-hazardous. Besides, for this work the range of inorganic and sulfur-containing substances having a toxic and irritating properties are used. Among them are 1,2- dichlorodiethylformal, 1,2,3-trichloropropane, sodium polysulfide, sodium hydrosulphide.

All of them have a depressing effect on the nervous system, respiratory tract, mucous membranes.

Trichloropropane - a drug with a toxic effect on the metabolism and internal organs, especially the liver. Sometimes causes dermatitis, eczema. MAC = 0.02 mg/l.

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Sodium polysulfide and sodium hydrosulphide are readily hydrolyzed in air with the release of hydrogen sulfide, which can be a source of poisoning.

In addition, when hydrolysis of sodium hydrosulphide the caustic soda is produced, which is the cause of skin irritation.

All works are carried out only in a fume hood.

It is forbidden!

1.To leave unattended installation.

2.To be alone in the laboratory.

3.To work without ventilation.

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QUESTIONS FOR THE COLLOQUIUMS

Colloquium 1. Classification of rubbers into groups and methods of producing. The main producers of synthetic rubber in Russia. Russia's role in world production of synthetic rubber. Effect of the chemical nature of catalyst on structure and technological properties of elastomers. Effect of technological properties of rubber on their plasticity and ability to subsequent processing.

Colloquium 2. Solution polymerization technology. Describe the flow sheet of solution polymerization. Requirements for raw materials. Preparation of catalysts, polymerization implementation, solution of the problem of heat removal. Deactivation processes of catalytically active sites and antioxidants introducing. Steam water two-step and four-step degassing. Drying of rubber using screw-drying apparatus. Advantages of the solution polymerization.

Colloquium 3. Resins, obtained by solution polymerization. Obtaining of SKI-3 and SKI-5. Process implementation. Obtaining of modified isoprene rubbers. Butadiene rubbers. Influence of the nature of the catalyst on the technological properties of SKD. Technology for SKD producing. Butadiene-styrene rubbers. Technological solution to the problem of convergence of the relative copolymerization reaction rate constants. Ethylene-propylene rubbers. Influence of the nature of the third monomer on the properties of EPDM. Technology of EPM and EPDM producing in a hydrocarbon solvent and liquid propylene. The types , properties and applications of rubbers obtained by solution polymerization.

Colloquium 4. Process implementation of butyl rubber. Features of the technology using methyl chloride and isopentane as a solvent. Polymerization catalysts, technological approaches to increase the catalyst activity and limit the share of the chain transfer reactions. The types, properties and applications of butyl rubbers. Polyisobutylene. Technology of production, properties and applications of the high and low molecular weight polyisobutylene.

Colloquium 5. Emulsion polymerization. Technical and economic performances of the process. The main and auxiliary components of the

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emulsion polymerization. Mechanism and topography of the process. Implementation of the emulsion polymerization in stages. Degassing and separating of rubber from latex. Obtaining of oil-filled rubbers. Obtaining of butadiene-styrene, nitrile, acrylate, chloroprene, vinyl pyridine and fluoroelastomers. Features of the process. The types, properties and applications of rubbers produced by emulsion polymerization.

Colloquium 6. Synthetic latex. Technology of production. Physical and chemical properties of latexes, their aggregate stability. Methods of latex concentration and agglomeration. The main types of synthetic latexes. Production of artificial latexes from non-emulsion rubbers. Methods of solvent substitution, process flow diagrams and parameters of the latex production. Areas of application of synthetic and artificial latexes.

Colloquium 7. Special purpose rubbers. Polysulfide rubbers. The structure of the polymer chain. The chemistry of the individual steps of thiokols production (liquid and solid). Curing methods of liquid thiokols. Silicone rubbers. Features of the structure of the macromolecular chain of the silicone rubber. The chemistry of the individual process steps. Preparation of octamethylcyclotetrasiloxane, basic monomer for polydimethylsiloxanes production through hydrolysis and dimethyldichlorosilane depolymerization steps. Synthesis of high-molecular and low-molecular silicone rubbers using cationic and anionic initiation. Polyesterurethane rubbers, the chemistry of their production, processing methods. Thermoplastic elastomers. Technology for urethane rubbers producing. The types, properties and applications of special purpose rubbers.

Colloquium 8. Chemical modification of polymers. The chemistry of halogenated butyl rubber producing, production technology chlorinated butyl rubber, modification influence on the properties of elastomers. Obtaining of chlorosulphonated polyethylene, production technology, parameters of the basic process steps.

Colloquium 9. Liquid carbochain rubbers. Classification of liquid carbochain rubbers, methods for their preparation. Differences of the technology of liquid rubbers from their macromolecular counterparts. Obtaining of liquid rubbers with reactive terminal groups, initiators and catalyst systems used in the production of these rubbers. Destructive method of liquid rubbers production with saturated structure.

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REFERENCES

General

1.Averko-Antonovich, L.A., Khimiya i tekhnologiya sinteticheskogo kauchuka: uchebnoye posobie / Averko-Antonovich L.A., AverkoAntonovich Yu.O., Davletbaeva I.M., Kirpichnikov P.A. - Moscow: Chimiya, KolosS. - 2008. - 357 p.

2.Kireev, V.V. Visokomolekulyarniye soedineniya / V.V. Kireev. - M.:Vysshaya shkola - 1992. - 512 p.

3.Reyhsfeld, V.O. Laboratorniy praktikum po sinteticheskim kauchukam / V.O. Reyhsfeld, L.N. Erkova, V.L. Ruban - L.: Chimiya. - 1967. - 228 p.

Additional

1.Schwartz, M. Anionnaya polimerizatsiya / M. Schwartz. - M.: Chimiya, Tr. from English. - 1971. - 669 p.

2.Dolgoplosk, B.A. Organometallicheskiy kataliz v polimerizatsionnikh protsessakh / B.A. Dolgoplosk, E.I. Tinyakova. - M.: Chimiya. - 1982. -

533p.

3.Semchikov, Yu.D. Visokomolekulyarniye soedineniya / Yu.D. Semchikov.-3rd ed. - Moscow: Publishing Center "Academiya". - 2006. -

368p.

4.Toroptseva, A.M. Laboratorniy praktikum po khimii i tekhnologii visokomolekulyarnikh soedineniy / A.M. Toroptseva, K.V. Belgorodskaya, V.M. Bondarenko. - L.: Chimiya. - 1972. - 116 p.

5.Averko-Antonovich Yu.O. Laboratorniy praktikum po khimii i phizike visokomolekulyarnikh soedineniy / Yu.O. Averko-Antonovich. - Kazan: KSTU. - 2001. - 60 p.

6.Sinteticheskiy kauchuk / Ed. Garmonov I.V. - 2nd ed. - L.: Chimiya. - 1983. - 224 p.

7.Dogadkin B.A. Khimiya elastomerov / B.A. Dogadkin, A.A. Dontcov, V.A. Shershnev - 2nd ed., Rev. and add. - M.: Chimiya. - 1981. - 376 p.

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I.M. Davletbaeva, O.R. Gumerova, A.I. Akhmetshina,

Ye.I. Grigoryev

CHEMISTRY AND TECHNOLOGY OF SYNTHETIC RUBBER

Ответственный за выпуск доц. Д. А. Романов

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