Chemistry and technology of synthetic rubber. Textbook

8-12 kV); 7 - three-way cock; 8 - ozonation reactor; 9 - trap; 10 - wash bottle with KJ; 11 -column for the ozone decomposition

All connections are made using ground glass joints or polyvinylchloride tubes. Graphite lubricant is used for the lubrication of joints.

Oxygen is fed from a cylinder and passed through two drainage columns (2) filled with calcium chloride or its mixtures with soda lime.

Pressure relief valve (1) is filled with mercury up to 3 - 4 cm in height. Drainage column filled with glass wool (3) prevents the oxygen from the dust-like dryer trapping. Rotameter (4) allows to monitor the consumption of ozone-oxygen mixture. Passing through the discharge tube 5 connected to the high-voltage transformer (6), part of the oxygen (1.5%) is converted into ozone. The three-way cock (7) allows to direct the ozoneoxygen mixture to the atmosphere through a fume hood or a reactor (8). Before the release into the atmosphere, ozone is destroyed in the drainage columns (11) with the ceramic or glass fragments, wet with a 5% solution of sodium hydroxide.

In the simplest case, a twoor three-necked flask with a thermometer, a bubbler and a gas outlet tube can serve as the ozonation reactor. For a better ozone dispersing and the reaction mixture mixing it is recommended to use U-shaped reactor with a porous bottom. The trap (9) cooled with dry ice and acetone mixture (or NaCl and ice), is necessary to trap volatile products of ozonolysis removed from the reactor by stream of oxygen.

Wash bottle (10), filled with 5% solution of potassium iodide is necessary for the absorption of unreacted ozone and to control the completion of the ozonation reaction (by the start of iodine release or obtaining its estimated amounts)

2KJ + O3 + H2O J2 + 2KOH + O2

Attention! Before you start, you should get acquainted with the safety measures when working at the setup for ozone producing.

Operating procedure

10 g of butyl rubber is dissolved in 300 cm3 of chloroform in a round bottom flask of 500 cm3. Reactor 8 (Figure 5.1) is connected to an installation for ozonation, the required gas mixture flow is established and pour the rubber solution is added to the reactor, 2 g of pyridine is added to rubber solution and the transformer (6) is switched on. Ozonation is carried

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out at 20ºC. The progress of the reaction is monitored by sampling and defining the content of carboxyl groups. To do this, 5 cm3 of solution is pipetted. Samples are taken when the ozonolysis of rubber amounts to 25, 50, 75 and 100 %. The sample is transferred to the flat-bottomed flask of 50 cm3, 10 cm3 of chloroform and 2-3 drops of phenolphthalein are added and titrate with 0.1 N alcoholic solution of an alkali until light pink staining. The flask with the solution is then heated using backflow condenser and water bath at 60 - 70ºC for 60 - 80 minutes, and titrated again with a solution of alkali until light pink staining. The measurement results are recorded in the table 5.1.

(Note: The samples should be taken in the reactor volume without gas bubbles. Wear safety goggles and gloves!)

Table 5.1.

Form to record results

The time required to achieve the necessary degree of ozonolysis is defined by the formula

where mr - rubber sample weight, g; Mr - molecular weight of rubber monomer unit; Xoz - the degree of ozonolysis (25, 50, 75 and 100%); Qoz - ozonator output, O3 mol/min.

The content of carboxyl groups in the oligomer is determined according to the formula

where V2 - amount of 0.1 N solution of NaOH, spent on the titration of the control sample; V1 - amount of 0.1 N solution of NaOH, spent on the titration of the control sample; F - correction factor to 0.1 N solution of

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NaOH; 0.0045 - the content of carboxyl groups corresponding to 1 cm3 of 0.1 N NaOH solution; ms - weight of rubber in the sample, which is determined by the formula

ms Vs mr , g,

Vr.m.

where Vs - the volume of the sample, cm3; mr - weight of rubber in the reaction mixture, g; Vr.m. - the volume of the reaction mixture, ml.

The number average molecular weight is found by the equation

where Z - the number of terminal groups in the macromolecule (Z = 1); Mf.g. - molecular weight of the terminal functional group; Cf.g. - the content of the terminal functional groups found experimentally.

According to the tabular data the kinetic curve of accumulation of the carboxyl groups in the synthesized liquid isobutylene rubber is build in the coordinates C(O)OH - toz (Xoz). The IR spectra of the initial and the liquid rubber are read and compared.

Molar mass distribution (MMD) of the synthesized functional liquid isobutyl rubber is determined by liquid - gel chromatography.

Precautions when working with the equipment for the ozone producing

Work with the setup is explosive, flammable and electrical hazardous. In addition, ozone is toxic - the 1st hazard class, MPC 0.1 mg/m3. Irritation of the mucous membranes of the eyes and throat is observed at the concentration of 0.2-1 mg/m3. Concentration of ozone 3-4 mg/m3 for 0.5- 1.5 hours causes irritation of the upper respiratory tracts, dry mouth, inability to concentrate and think, changes in taste, chest pain. Concentration of 2-20 mg/m3 may cause cough, headache, sharp decline in cardiac function. At ozone concentration of 15-20 mg/m3 pulmonary edema develops rapidly.

If you smell ozone immediately switch off the equipment and ventilate the area.

If ozone poisoning it is necessary to take a victim to fresh air, keep a complete rest, warmth, inhalation - 75-80 % of oxygen. By indications the victim can take 20 ml of 40 % CaCl2 and cordials.

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It must be remembered about the voltage up to 10 kV in ozonizer. When using solvents, cautions must be followed according to flammable liquids.

Lab 9. Synthesis of Oligoisoprenediol - Liquid Rubber with Terminal Hydroxyl Groups

Oligoisoprenediol is one of liquid rubbers (reactive oligomers) containing terminal hydroxyl groups. Synthesis of oligoisoprenediol is carried out by using a bifunctional initiator, such as hydrogen peroxide (H2O2). The reaction process involves the following steps:

1) Initiation:

.

3)Material chain termination occurs as a result of chain transfer or combination:

. .

2 HO CH2 CCH CH2CH2 CCH CH2 OHCH2 CCH CH2OH

Objective: acquaintance with the technology of isoprene polymerization in the presence of radical initiator under high pressure, the synthesis of oligoisoprenediol, its separation, evaluation of influence of hydrogen peroxide concentration on the molecular weight of the resulting polymer.

Materials:

1)isoprene, Tm = -145 C, Tb = 34.1 C, d = 0.6809;

2)propyl alcohol, Tm = -126.2 C, Tb = 97.2 C, d = 0,8044;

3)30 % hydrogen peroxide solution;

4)2N aqueous solution of KOH;

5)distilled water.

Apparatus:

Metal stainless steel ampoules of 100 ml with a hermetic stopper; thermostat with automatic temperature control in the range of 100 ± 10°C;

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measuring cylinders of 25 ml (2 pcs.); separating funnel (1 pc.); installation for vacuum degassing of oligomer; installation for isoprene distillation.

Procedure

Before polymerization isoprene is distilled from impurities and inhibitor. Distillation unit consists of round-bottomed flask of 250 ml, fishbone reflux condenser, Liebig condenser with adapter and receiver. The flask, filled to 2/3 with isoprene, is attached to the unit. 3-5 pieces of porous porcelain are placed into the flask. The flask is heated in bain-marie with hot water, the temperature of the bath should not be higher than 45°C.

Attention!!! Do not heat on a hotplate, including the closed one to avoid explosion.

The first portion of distilled isoprene is poured into the sink of organic wastes, the fraction boiling at 34.5 ± 0.5°C is run off for the polymerization. Distilled isoprene is stored when cooling until it is used, the storage life is no more than 6 hours. The distillation is carried out in a fume hood, which is not allowed to have hooked up electrical appliances and open flame.

The polymerization of isoprene is carried out at three different concentrations of hydrogen peroxide.

Clean, dry stainless steel ampoules are loaded with necessary amount of propyl alcohol (by volume) and then the calculated amount of hydrogen peroxide and isoprene is fed. The volumes of the initial reagents are presented in Table 5.2.

Attention!!! Do not allow hydrogen peroxide to come into a contact with the exposed areas of the body, the load is carried out using protective glasses.

Filled ampoule is closed with the stopper, having fluoroplastic gasket and is tightly screwed with a wrench.

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Sealed ampoules are placed in thermostat heated to the desired temperature, filled with oil, are closed with the cover, then a protective screen is placed and the heating starts. The polymerization temperature is 100±2°C, maintained by the relays. The polymerization time is 6 hours. After the polymerization the heating is stopped, ampoules are cooled to room temperature and unsealed with a wrench in a fume hood.

The contents of the ampoule is poured into a separating funnel and washed with distilled water from the propyl alcohol, draining the lower aqueous layer into the sink of organic products. Then oligoisoprenediol is washed of hydrogen peroxide with hot KOH solution (7.5 ml), then washed again with distilled water until neutral. Oligoisoprenediol is then dried under vacuum to constant weight at 50±5°C. In the resulting oligoisoprenediol the content of hydroxyl groups is determined by acetylation (phthalation) or by IR spectroscopy. To do this, a solution of oligoisoprenediol in toluene or CCl4 is prepared at a concentration of 50 g/l and a molecular weight is determined using a calibration curve prepared beforehand.

According to the obtained data the effect of the ratio of components, temperature and duration of the process on the yield and molar mass of oligoisoprenediol is estimated.

Determination of hydroxyl groups in oligoisoprenediol by acetylation (phthalation)

The method is based on the ability of hydroxyl containing compounds to interact with acetic (phthalic) anhydride to form an ester. For acetylation (phthalation), a mixture of acetic (phthalic) anhydride and pyridine is used. Pyridine binds an oozing acetic (phthalic) acid and eliminates the possibility of hydrolysis of the forming ester. The reaction is described by the following scheme:

ROH+(CH3CO)2O+C5H5N ROC(O)CH3+ C5H5N CH3C(O)OH

Pyridine salt is stable in the non-aqueous medium and decomposed by the addition of water. Oozed acetic (phthalic) acid is titrated with alkali.

Materials: acetylating (phthalating) mixture is prepared in 0.5 hours prior to use by mixing 1.2 ml of non-aqueous acetic (phthalic)

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anhydride with 8.8 ml of dried pyridine; 0.5 N solution of NaOH; 1 % alcohol solution of phenolphthalein.

Apparatus: conical flasks of 250 ml; reflux condenser (1 pc.); calcium chloride tubes; pipette of 20 ml; graduated cylinder of 50 ml; microburette; separating funnel of 200 ml.

Methods of analysis

A sample of 0.2-0.5 g (depending on the content of hydroxyl groups) of oligoisoprenediol is placed in a flask weighted with an accuracy of 0.002 g, then 20 ml of dried toluene is added by pipette, oligoisoprenediol is dissolved and then 20 ml of acetylating (phthalating) mixture is pipetted. A condenser closed at the top with a calcium chloride tube is attached to the flask which is then heated in a boiling water bath for 1.5-2 hours. After cooling the flask 50 ml of distilled water is added through the condenser for the hydrolysis of acetic (phthalic) anhydride and pyridine salt. The mixture is then incubated at room temperature for 2-3 hours, or heated in the water bath for 20 minutes. The cooled mixture is poured into a separating funnel, allowing to settle and then the lower layer is taken to a titration flask. Next, the aqueous extract is titrated with an alkali in the presence of phenolphthalein until pink staining.

Three samples are analyzed, two of which have the sample weight of oligoisoprenediol and one contains control sample. The concentration of hydroxyl groups (C, %) is calculated by the formula:

С,% (V1 V2 ) F 0.0085 100 , g

where V1 - the volume of 0.5 N solution of NaOH, spent on titration of control sample, ml; V2 - the volume of 0.5 N NaOH solution, spent on titration of the work sample, ml; F- correction factor of 0.5 N solution of NaOH; 0.0085 - the number of OH-groups corresponding to 1 ml of 0.5 N solution of NaOH, g; g- H the sample weight of oligoisoprenediol, g.

According to the analysis of terminal groups the average molecular weight of the oligomer is determined from the relationship:

Mn , g-mol - X•Y 100 g - C, g

where of the molecular weight is found by Mn = 100•X•Y / C,

where X - the number of terminal hydroxyl groups per macromolecule (2 in case of oligoisoprenediol), Y - the molecular weight of terminal group (17

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for OH group), C - the concentration of hydroxyl groups, defined by one of the methods, %

Safety information

Isoprene - a colorless flammable liquid. Isoprene is readily oxidized when storing to form explosive peroxides and polymerized. Therefore, it is stored in the presence of inhibitors (e.g., hydroquinone). Before using isoprene is freed from inhibitors by distillation. In high concentrations, it acts like a drug, inhibits blood, in small concentrations irritates the mucous membranes, MPC = 0.04 mg/l. Operations must be carried out under the hood, avoid contact with skin.

Propyl alcohol - a solvent, causing poisoning with predominant narcotic effect.

Hydrogen peroxide - an explosion of peroxide compounds can be caused by friction, heat, peroxides cannot be stored in flasks with ground glass stoppers. Be sure to use face shield and rubber gloves.

Lab 10. Obtaining Liquid Thiokol and Sealants

Polysulfide elastomers called thiokols are the rubbers, polymer chain of which contains a significant number of atoms of sulfur. Depending on the molecular weight there are liquid and solid thiokols. Liquid thiokols are reactive due to the terminal mercaptan (SH) groups. By the interaction of different curing agents with terminal SH-groups the liquid thiokols are cured.

The only way to obtain industrial liquid thiokols is the reductive cleaving of high molecular weight polysulfides by sodium hydrosulfide in the presence of sodium sulfite. The process consists of several stages.

1. Polycondensation

Polycondensation of an organic dihalo derivative and sodium dior polysulfide solution is carried out, resulting in a high molecular weight product:

nCl-CH2-CH2-O-CH2-O-CH2-CH2-Cl+(n+1)Na2S4 → NaS4[-CH2-CH2-O-CH2-O-CH2-CH2-S-S-S-S-]nNa+2nNaCl

As the dispersant there are used Mg(OH)2 produced directly in the reaction mixture by reaction of sodium hydroxide and magnesium sulfate according to the following scheme:

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6)dispersant - the reaction product of NaOH and MgSO4;

7)sodium hydrosulfide NaSH and sodium sulfite Na2SO3 (cleaving agents);

8)sodium hydroxide NaOH, 40 % aqueous solution.

Apparatus: four-necked flask, stirrer, thermometer, backflow condenser, heated bath, dropping funnel, beaker, rubber hose.

Synthesis of sodium tetrasulfide

A porcelain dish is filled with 60 ml of water and heating it to boiling, 25 g of sodium hydroxide is carefully added. To this solution 36 g of sulfur is introduced (110 % of the calculated amount) and stirred with a glass rod. The boiling should not be intensive to avoid significant evaporation of water. Brown solution is obtained which is filtered after cooling.

Synthesis should be carried out carefully, avoiding spraying a solution, be sure to work in glasses or face shield.

Procedure

The solution of the calculated amount of sodium tetrasulfide is placed in the four-necked flask of 250 ml equipped with stirrer, thermometer and backflow condenser, the stirrer is turned on and the heating with water bath starts and the solution temperature is raised to 65°C. Then the solution of sodium hydroxide is poured and the solution of magnesium sulfate is added dropwise over 30 minutes through dropping funnel, raising the temperature gradually to 80°C.

Dichloride or a mixture of monomers is placed in the dropping funnel and intensively stirring the contents of the flask is added dropwise over 10-20 minutes at a temperature of 80°C. Thus it is necessary to ensure that the temperature of the reaction system does not exceed 90°C. Upon completion of the dropping, the mixture is kept under stirring at the temperature 90°C for 1 hour. 40 % aqueous NaOH solution is added to the hot solution and kept for 1 hour at 90°C.

The reaction mixture is poured into a beaker filled with water and then repeatedly washed with water by decantation (draining the upper colored aqueous layer through the hose) as long as the upper aqueous layer is colorless. Usually when good settling the polymer dispersion 6-7 washings are needed for this.

The washed dispersion is placed in the same flask, where the polycondensation reaction was carried out. Then, when stirring the dispersion is heated in a water bath to 65°C. To carry out the reductive cleavage of high molecular weight thiokol and to produce the liquid thiokol,

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