Draw up a scheme for the polycondensation of aminocaproic acid. High molecular weight compounds

Task 433
What compounds are called amines? Draw up a scheme for the polycondensation of adipic acid and hexamethylenediamine. Name the resulting polymer.
Solution:
Aminami hydrocarbon derivatives are called formed by replacing the last hydrogen atoms with groups -NH 2, -NHR or -NR" :

Depending on the number of hydrogen atoms at the nitrogen atom substituted by radicals ( R ), amines are called primary, secondary or tertiary.

Group -NH 2 , which is part of primary amines, is called an amino group. Group of atoms >NH in secondary amines it is called imino group.

Polycondensation scheme adipic acid And hexamethylenediamine:

Anid (nylon) is a polycondensation product of adipic acid and hexamethylenediamine.

Task 442
What compounds are called amino acids? Write the formula for the simplest amino acid. Draw up a scheme for the polycondensation of aminocaproic acid. What is the name of the resulting polymer?
Solution:
Amino acids compounds are called compounds whose molecule simultaneously contains amine(-NH2) and carboxyl groups(-COOH). Their simplest representative is aminoacetic acid (glycine): NH2-CH2-COOH.

Scheme of polycondensation of aminocaproic acid:

The polycondensation product of aminocaproic acid is called nylon (perlon). From nylon fibers are obtained that are superior in strength to natural fibers. These fibers are used in the production of clothing, car and aircraft tire cords, for the manufacture of durable and rot-resistant fishing nets and gear, rope products, etc.

This is a crystalline substance with Tm = 68.5 – 690 C. It is highly soluble in water, alcohol, ether and other organic solvents. Aqueous solutions of acids cause hydrolysis to ε-ami-

nocaproic acid. When heated to 230 - 2600 C in the presence of small amounts of water, alcohol, amines, organic acids, it polymerizes to form a polyamide resin.

ly. It is a product of large-scale production.

ω-Dodecalactam (laurin lactam) is obtained by multi-step synthesis from 1,3-butadiene.

3CH2

Laurinlactam is a crystalline substance with melting point = 153 – 1540 C, highly soluble in alcohol, benzene, acetone, poorly soluble in water. When heated, it polymerizes into polyamide, however,

polymerization proceeds worse than that of ε-caprolactam. (Lauric or dodecanoic acid - CH3 (CH2)10 COOH.)

4.2. Methods for producing polyamides Polyamides are usually classified as polycondensation polymers, i.e. polymers, according to

resulting from polycondensation reactions. Such an attribution is not very correct,

since polymers of this type can be obtained both by polycondensation and polymer-

ation of monomers. Polyamides are obtained from ω-aminocarboxylic acids by polycondensation

(or their esters), as well as from dicarboxylic acids (or their esters) and diamines. The main polymerization methods are hydrolytic and catalytic polymerization of lactate

mov ω-amino acids. The choice of method is determined by the capabilities of the raw material base and requirements -

to the properties of the corresponding polyamide.

In industry, polyamides are produced in four main ways:

Heteropolycondensation of dicarboxylic acids or their esters with organic diami-

n HOOCRCOOH + n H2 NR"NH2

NH2O

- heteropolycondensation of dicarboxylic acid chlorides with organic di-

- homopolycondensationω-aminocarboxylic acids (amino acids) or their esters;

										NH2O

- polymerization of amino acid lactams.

catalyst

n(CH2)n

HN(CH2)nCO

4.3. Labeling of polyamides The polyamides labeling system is based on the method of their production and chemical

structure. A number of polyamides, especially aromatic ones, have their own names,

supplied by manufacturing companies.

For aliphatic polyamides, after the word “polyamide” (“nylon” in foreign literature)

round) are followed by one or two numbers separated by a comma (or period). If the polyamide is synthesized from one monomer (amino acid or lactam), one number is given,

corresponding to the number of carbon atoms in the monomer. For example, polyamide obtained from

ε-caprolactam or from ε-aminocaproic acid, designated as "polyamide 6"; polymer from aminoenanthic acid - “polyamide 7”, polymer from aminoundecanoic acid -

"Polyamide 11". In technical literature, the word “polyamide” is often replaced by the abbreviation “PA” or the letter “P”. Then the above designations are represented as “PA-6”, “PA-11”, “P-7”. The composition of two numbers separated by a comma indicates that the polyamide is obtained by polycondensation of a diamine with a dicarboxylic acid or its derivatives.

The number (digit) before the decimal point shows the number of carbon atoms in the diamine; the number (digit) after the decimal point is the number of carbon atoms in the acid or its derivative used. For example, "Polyamide 6,6" is obtained from hexamethylenediamine and adipic acid; "Polyamide 6.10" -

from hexamethylenediamine and sebacic acid. It should be noted that the comma (or period)

separating two numbers may be missing. Thus, State Standard 10539 – 87

it is prescribed to designate the polyamide obtained from hexamethylenediamine and sebacic acid in poly, ka kmida "Polyamide obtained 610". from aliphatic amines and aromatic acids, the linear structural element is designated by a number indicating the number of carbon atoms in the mol.

cule, and the acid link is designated by the initial letter of their names. For example, polyamide,

made from hexamethylenediamine and terephthalic acid, designated as “Polyamide

The names of polyamide copolymers are composed of the names of individual polymers indicating

the percentage composition is indicated in brackets (in the literature, a hyphen is used instead of brackets). The polyamide of which there is more in the copolymer is indicated first. For example, the name

The words “Polyamide 6.10/6.6 (65:35)” or “Polyamide 6.10/6.6 - 65/35” mean that the copolymer is co-

Made from 65% polyamide 6.10 and 35% polyamide 6.6. In some cases, simplified notation is used. For example, the notation P-AK-93/7 means that the copolymer is prepared from 93% AG salt and 7% ω-caprolactam (here “A” denotes AG salt, “K” - caprolactam).

In addition to these designations standardized in Russia, in the technical and reference literature there may be proper names of individual types and brands introduced by companies.

lyamides. For example, “Technamid”, “Zytel-1147” and others.

4.4. Production of aliphatic polyamides Of the many polyamides synthesized to date, the largest is practically

Of interest are:

Polyamide 6 (poly-ε-caproamide, polycaproamide, nylon, nylon resin, nylon-6,

caprolon B, caprolit),

Polyamide 12 (poly-ω-dodecanamide),

Polyamide 6,6 (polyhexamethylene adipamide, anide, nylon 6,6),

Polyamide 6,8 (polyhexamethylene suberinamide),

Polyamide 6,10 (polyhexamethylene sebacinamide),

Polyamides 6 and 12 are produced technically by polymerization of the corresponding lactams. Os-

tal polyamides are formed by the polycondensation of hexamethylenediamine and dibasic acids

4.4.1. By polymerization of lactams, this method produces mainly polyamide 6 and polyamide 12.

4.4.1.1. Polyamide 6

Polyamide 6 or polycaproamide is obtained by polymerization of ε-caprolactam in the process

the presence of hydrolytic agents or catalysts that promote the opening of the lactam cycle. The process of polymerization under the influence of water is called hydrolytic polymerization.

tion. Catalytic (anionic or cationic) polymerization of ε-caprolactam occurs in the presence of alkaline or acid catalysts. The main amount of PA-6 is obtained by hydrolytic polymerization of caprolactam.

Hydrolytic polymerization of ε-caprolactam proceeds under the influence of water, dissolved

acids, salts or other compounds that cause hydrolysis of the lactam cycle. Education

The synthesis of polyamide occurs in two stages. The chemistry of the process can be represented by the diagram:

H2 N(CH2 )5 COOH

HN(CH2)5CO

The first stage of the process - hydrolysis of caprolactam to aminocaproic acid - is the slowest stage of the process, limiting its overall speed. Therefore, in production

In industry, polymerization of caprolactam is carried out in the presence of catalysts. These most often are aminocaproic acid itself or a salt of AG (hexamethylene adipate, adi-

pinic acid and hexamethylenediamine - HOOC(CH2)4 COOH · H2 N(CH2)6 NH2), in which the reagents are in strictly equimolecular ratios.

The macromolecule of the resulting polyamide contains free terminal carboxyl and amino groups, which is why it is prone to destructive reactions and further polycondensation.

tions when heated during processing. To obtain a more stable product, these groups can be blocked by introducing monofunctional substances - alcohols, acids or amines - into the reaction mass. Such compounds, called stabilizers or regulators,

viscosity, react with end groups and thereby stabilize the polymer, limiting its ability to enter into further reactions. This provides the opportunity to

produce a polymer with a given molecular weight and viscosity by changing the amount of stabilizer

congestion Acetic and benzoic acids are often used as stabilizers.

Hydrolytic polymerization is a reversible process and the equilibrium state depends on temperature. When carrying out the reaction in the temperature range 230 – 2600 C, the content of mo-

numbers and oligomers in the resulting polyamide is 8 – 10%. At such temperatures, all reagents and polyamide are able to be actively oxidized by atmospheric oxygen. Therefore, the process is carried out in an inert atmosphere of dry nitrogen with a high degree of purification.

The polymerization process can be carried out according to batch or continuous schemes using equipment of different designs. In Fig. Figure 3 shows a diagram of the production of PA 6 by a continuous method in a column-type reactor. The technological process is folding

comes from the stages of preparation of raw materials, polymerization of ε-caprolactam, cooling of the polymer, its grinding, washing and drying.

Preparation of raw materials consists of melting caprolactam at 90 - 1000 C in a separate apparatus

rate 3 with stirring. In apparatus 6, a 50% aqueous solution of salt AG is prepared. Prigo-

The fueled liquids are supplied continuously by dosing pumps 1 and 4 through filters 2 and 5

into the upper part of reactor 7 (a column about 6 m high with horizontal perforated

with metal partitions that promote turbulence of the flow of reagents as they move from top to bottom). The reactor is heated through jacket sections with dinyl (a eutectic mixture of diphenyl and diphenyl ether). The temperature in the middle part of the column is about 2500 C,

in the bottom - up to 2700 C. The pressure in the column (1.5 - 2.5 MPa) is ensured by the supply of nitrogen and pas-

frames of the resulting water.

Polymerization begins immediately after mixing the components. Released during the reaction

tion and the water introduced with the AG salt evaporates. Its vapors, rising along the column, contribute to turbulization and mixing of the reaction mass and carry caprolactam vapors with them.

Upon exiting the column, the vapor mixture sequentially enters reflux condensers 8

and 9. In the first, caprolactam is condensed and returned to the column. Condensed-

In the second, water vapor is removed for purification. Monomer conversion in the column is about 90%.

	Caprolactam

for cleaning

Rice. 3. Scheme for the production of polyamide 6 (polycaproamide) by a continuous method:

1, 4 - dosing pumps; 2, 5 - filters; 3 - caprolactam melter; 6 - apparatus for dissolving salt AG; 7 - reactor column; 8, 9, - refrigerators; 10 - cutting machine; 11 - washer-extractor; 12 - filter; 13 - vacuum dryer; 14 - rotating watering drum.

The resulting molten polymer is squeezed out through a slotted die into a co-

the lower part of the column in the form of a tape on the cold surface of a rotating

fine water of the watering drum 14, is cooled and, with the help of guide and pulling rollers, is fed into the cutting machine 10 for grinding. The resulting polymer crumbs are washed with hot water in a washer to separate them from the remaining monomer and oligomers.

extractor 11. The content of low molecular weight compounds after washing is less

1.5%. The washed crumbs are separated from the water on filter 12 and dried in a vacuum dryer

13 at 125 – 1300 C until the moisture content does not exceed 0.2%.

Anionic polymerizationε-caprolactam can be carried out in a solution or melt of mo-

numbers at temperatures below the melting point of the polymer.

catalyst

n(CH2)5

HN(CH2)5CO

Polymerization is carried out in the presence of a catalytic system consisting of a mixture of

Talizer and activator. Alkali metals, their hydroxides,

carbonates, other compounds. The technique uses mainly sodium salt ε - capro-

lactam, formed when sodium reacts with lactam.

									(CH2)5		1/2 H2
										N-Na+

This salt easily reacts with lactam to form an N-acyl derivative, which
connects to the lactam, giving rise to the polyamide chain and remaining at its end until complete
monomer consumption.
	(CH2)5		(CH2)5	(CH2)5
		N-Na+
					N-CO-(CH2)5 - NH
Activators (cocatalysts) help speed up the reaction. In their capacity
N-acyl derivatives of lactam or compounds capable of acylating lac-
there under polymerization conditions (carboxylic acid anhydrides, esters, isocyanates, etc.). Under
under the influence of such a system, the polymerization of ε-caprolactam occurs without an induction period
at atmospheric pressure and ends at 140 –
1800 C for 1 – 1.5 hours with monomer conversion of 97 – 99%.					Caprolactam
Such “soft” conditions and rapid polymerization
allow it to be carried out not in reactors, but in forms,
having the configuration and dimensions of future products.
Another advantage of anionic polymerization is
the possibility of obtaining polyamides with uniform distribution							caprolactam
twisted spherulite structure, without shrinkage shells
wines, pores, cracks and other defects.
Method of anionic polymerization of ε-caprolactam in
melt in the presence of sodium salt of ε-caprolactam
and activator was called “high-speed polymer-
cation”, and the resulting polymer is called ka-							In the heating cabinet
spilled or caprolon B. It is also used for							caprolite production:
				1 - dosing pump; 2 - reactor prepared
title “block polyamide” Assignment of own				combustion of sodium salt of caprolactam; 3 -
				filter; 4 - melter; 5 - capro mixer
the names of the poly-ε- obtained by this method				lactam with N-acetylcaprolactam; 6 - up to
				sizing pump; 7 - mixer; 8 - form
caproamide, is explained by the fact that caprolon B, having the same chemical structure as poly-
amide 6 has noticeably different properties. It exhibits (Table 5) higher strength
strength, hardness, heat resistance, has less water absorption, etc.							This is explained by
	slightly higher molecular weight of caprolite, secondly, more ordered
new structure. The production of caprolon B includes (Fig. 4)					stages of preparation of raw materials, mixing
tion of components and polymerization.			At the stage of raw material preparation, caprolactam melts and
thoroughly dried under negative pressure in a nitrogen atmosphere in a container-
new type with stirrer 4.		Half of this melt, after filtration, is mixed in a
	with the calculated amount of sodium metal for the preparation of sodium salt
ε-caprolactam, and the other half is mixed in apparatus 5 with a cocatalyst (N - ace-

tilcaprolactam). Both melts (solutions) with a temperature of 135 - 140 0 C are dosed by the pump -

mi 1 and 6 in the required proportions into a high-speed mixer 7, from where the mixture enters pouring molds, the capacity of which can reach 0.4 - 0.6 m3. Filled forms are installed for 1.0 - 1.5 hours in ovens for polymerization at a gradual increase

temperature from 140 to 1800 C. Then the molds with the polymer are slowly cooled to room

temperature and polymer castings are extracted from them. In washing from the monomer it is necessary -

There is no truth here, since its content does not exceed 1.5 - 2.5%.

High-speed polymerization of ε-caprolactam is used to produce large-sized and thick-walled or non-standard finished products, as well as castings, products from which are prepared by mechanical processing.

4.4.1.2. Polyamide 12

Polyamide 12 (poly-ω-dodecanamide or nylon 12) is produced industrially using methods

hydrolytic and anionic polymerization of ω-dodecalactam.

NH2O

Hydrolytic polymerization is carried out in the presence of water and acid (adipic,

ortho-phosphorus). The technology for producing nylon 12 by this method is similar to the technology for synthesizing polyamide 6. The properties of polyamide 12 are shown in Table 5.

The anionic polymerization of ω-dodecalactam is also similar to that of ε-caprolactam.

At lower temperatures, a polymer is formed with a higher molecular weight, a more uniformly developed spherulitic structure and, as a consequence, with increased physical properties.

mechanical properties.

4.4.2. By polycondensation of hexamethylenediamine and dicarboxylic acids, polyamides from dicarboxylic acids and diamines or from amino acids are obtained by the method

equilibrium polycondensation. To synthesize a polymer with a high molecular weight, it is necessary to

we must fulfill several main conditions. One of them is due to the reversibility of polycondensation reactions. Because of this, the formation of a fairly high molecular weight polymer is possible.

is possible only with timely and complete removal of water, which is achieved by carrying out

process in a vacuum or with a continuous flow of dry inert gas through the reaction mass.

In addition, it should be taken into account that as the reaction progresses, the concentrations of the reactants and the rate of the process decrease. A typical technique for increasing the rate of reactions is to increase the temperature. However, above 3000 C, polyamides begin to noticeably degrade.

get out. Therefore, to achieve sufficient conversion it is necessary to increase the duration

contact rate of reagents. Thus, the molecular weight of the resulting polyamides can be controlled during their formation by the duration of the process.

In addition to temperature and time factors for obtaining high molecular weight

Liamide requires ensuring strict equimolecularity of the reagents. An excess of one of them, even within 1%, leads to the formation of polymer chains, at the ends of which there will be

identical functional groups of the excess reagent. If there is an excess of diamine, the end groups will be NH2 groups, and if there is an excess of acid, the end groups will be COOH groups. This will stop the chain propagation reaction. Equimolecularity is achieved by using

lycondensation of not the acids and diamines themselves, but their acid salts. The preparation of such salts is

is an independent stage in the processes of polyamide synthesis by polycondensation. Used

The solution for the polycondensation of salts has a number of other advantages: the salts are non-toxic, easily crystalline

lyse, practically do not change, unlike diamines, properties during long-term storage -

nii, do not require special storage conditions.

Ensuring the equimolecularity of the reagents should theoretically lead to

the formation of a polymer with an infinitely large molecular weight. However, in industrial practice, due to the inevitable loss of some reagents and the occurrence of side reactions, in which

Although functional groups can enter, the molecular weight of polymers ranges from 10,000 to 50,000.

4.4.2.1. Polyamide 6.6

Polyamide 6,6 (polyhexamethylene adipamide, P-66, nylon 6,6, anide) is formed by poly-

condensation of hexamethylenediamine and adipic acid.

HN(CH) NHCO(CH) CO

NH2O

.... .... ..........

... .

. . ... .. . ... .. .... ..

hot... .. .. ...... ..... . .... .............

. .. ................................ .

..... ..

...... .

..... ....

cold

Polyamide

Fig.5. Scheme for the production of polyhexamethylenediadiamide (polyamide 6.6):

1 - centrifuge; 2 - apparatus for separating salt from solution; 3 - salt production apparatus; 4 - autoclave reactor; 5 - refrigerator; 6 - condensate collector; 7 - cutting machine; 8 - dryer; 9 - cooling bath

The first stage of the process is the synthesis of adipic acid salt and hexamethylenediamine

on (AG salts). A salt solution is formed in a heated apparatus 3 by mixing 20% ​​me-

a tanol solution of adipic acid with a 50–60% solution of hexamethylenediamine in methanol. In apparatus 2, when the mass is cooled, the AG salt, which is poorly soluble in methanol, is released from the solution. Its crystals are separated from the mother liquor in centrifuge 1, dried and used.

used for polycondensation. Salt is a white crystalline powder with melting point = 190 – 1910 C,

Easily soluble in water, stable when stored dry and in the form of aqueous solutions.

The process of synthesis of polyamide 6,6 from the salt of AG is not much different from the process of polymerization

tions of ε-caprolactam. The most significant feature is the increased temperature of polycon-

densation. The optimal reaction rate is achieved at 270 – 2800 C. In this case, the reaction proceeds almost to completion and, upon reaching equilibrium, a polymer is formed containing less than 1% of monomers and low molecular weight compounds. The molecular weight distribution is quite narrow. The reason for the lack of significant polydispersity is by-products

structural processes taking place under the influence of temperature and low molecular weight fractions. First of all, high-molecular fractions are subject to destruction. For bo-

To actively limit their presence in the commercial polymer, add -

There are monofunctional compounds capable of reacting with the terminal groups of polyamide

Yes. As in the synthesis of polyamide 6, such stabilizer compounds (viscosity regulators)

bones) can be acetic, benzoic acid. These compounds not only limit the molecular

cular mass of the polymer during its formation, but also contribute to the constancy of the viscosity of the dis-

melt of the polymer during its processing, i.e. upon re-melting, which may cause continued polycondensation.

Polycondensation is carried out in an autoclave under a pressure of 1.5 - 1.9 MPa in a nitrogen atmosphere.

Autoclave 4 is loaded with AG salt, an addition of acetic acid (0.1 - 0.2 mol per mole of salt) and

The apparatus is heated through the jacket with dinil to 2200 C. Then, for 1.5 - 2 hours, the temperature

the temperature gradually rises to 270 - 2800 C. Then the pressure decreases to atmospheric pressure and after a short exposure rises again. Such pressure changes are repeated

occur several times. When the pressure decreases, the water formed during polycondensation boils

solders and its vapors additionally mix the polymer melt. The water vapor leaving the autoclave is condensed in refrigerator 5, collected in collection 6 and discharged into purification systems.

sewage effluents. At the end of the process (6 - 8 hours), the remaining water is removed under vacuum,

and the polyamide melt from the apparatus through a die is extruded in the form of a tape into bath 9 with a pro-

4.4.2.2. Polyamides 6.8 and 6.10

These polyamides are obtained by polycondensation of hexamethylenediamine and the corresponding ki-

slot (suberin and sebacine) using technologies similar to the production technology of

Liamide 6.6.

Acids and diamine are reacted in the form of their salts.

Of these polyamides, only polyamide 610 is of practical interest so far;

since the production of suberic acid is limited by its complexity.

The properties of polyamides 6.8 and 6.10 are given in Table 5.

Mixed polyamides are produced in a similar way when various components are introduced into the polycondensation, for example, salts of AG and caprolactam, salts of AG, SG and caprolactam.

4.4.3. Polycondensation of diamines and dicarboxylic acid chlorides

This method is not widely used in the industry for aliphatic polyamides due to the increased cost of carboxylic acid chlorides. Nevertheless,

it is the only one for the synthesis of most aromatic polyamides, in particular phenylone and Kevlar.

4.5. Properties and application of aliphatic polyamides Aliphatic polyamides are solid horn-like products from white to light cre-

light-colored, melting in a narrow temperature range (Table 5). Narrow intervals

melting point changes indicate low polydispersity and high concentration

trations in crystalline phase polymers. Its content can reach 60 – 80% and depends

sieve on the structure of macromolecules. Regular aliphatic compounds have the highest crystallinity.

chemical homopolyamides, the distinctive feature of which is their content in macro-

a molecule of radicals of only one acid and one diamine. These are, for example, polyamide 6,

polyamide 6.6, polyamide 6.10. The degree of crystallinity of the material in products is influenced by the conditions

Via its processing, heat treatment mode, moisture content and special additives. Ste-

The crystallinity of mixed (obtained from two or more monomers) polyamides is smaller. They are less durable, but have increased elasticity and are transparent.

The high melting temperatures of polyamides are explained by strong hydrogen bonds between macromolecules. The number of these bonds directly depends on the number of amide groups in the macromolecule and, therefore, is inversely related to the number of methylene groups. Hydrogen bonds determine to a large extent all other properties. From-

here: the ratio of methylene and amide groups affects both solubility and water resistance

bone, and physical-mechanical, and other indicators.

5.3. POLYCONDENSATION

Polycondensation is the reaction of the formation of macromolecules when monomers combine with each other, accompanied by the elimination of simple substances - water, alcohol, ammonia, hydrogen chloride, etc. During polycondensation, a series of kinetically unrelated bimolecular reactions occur. Features of the polycondensation reaction:

• 1) the elemental composition of the polymer unit differs from the composition of the original monomer;
• 2) monomer units in a polymer molecule are connected to each other by a covalent or semipolar bond;
• 3) as a result of the reaction, polymer chains of various lengths are formed, i.e. the product is polydisperse;
• 4) polycondensation is a stepwise process.

Table 5.4. Types of compounds formed during polycondensation, depending on the nature of the functional groups

First functional group(s)	Second functional group (b)	Starting material	Type of compound formed
-H	H-	Hydrocarbon	Polyhydrocarbon
-H	Cl-	Halogen derivative	Same
-Br	Br-	Dihalogen derivative	"
-HE	BUT-	Polyhydric alcohol	Polyester
-OH	HOOC-	Hydroxy acid	Polyester
-OH	ROOC-	Hydroxy acid ester	Same
-NH 2	NOOS-	Amino acid	Polyamide
-NH 2	ROOC-	Amino acid ester	Same
-NH 2	СlОC-	Amino acid chloride	"

Both homogeneous and dissimilar molecules can participate in the process of polycondensation. In general, these reactions are depicted by the following diagrams:

• X a-A-b → a-(A) X-b + ( X- 1)ab;
• X a-a-a + x b-B-b → a-(A-B)-b + 2( X- 1)ab,

where a and b are functional groups.

The properties of the product formed during polycondensation are determined by the functionality of the monomer, i.e. number of reactive functional groups. The polycondensation reaction can be used to synthesize various classes of both carbon chain and heterochain polymers.

During polycondensation of bifunctional compounds, linear polymers are formed (Table 5.4). If the monomer functionality is greater than two, then branched and three-dimensional polymers are formed. The number of functional groups in the macromolecule increases as the reaction deepens. For the synthesis of fiber-forming polymers, bifunctional compounds are of greatest interest.

Depending on the nature of the functional groups and the structure of the resulting polymer, various classes of chemical reactions can be represented in the polycondensation reaction: polyesterification, polyanhydridization, polyamidation, etc. In table 5.5 provides examples of various types of compounds formed during polycondensation.

The interaction of the functional groups of the monomer can lead to the formation of a polymer or low-molecular products of a cyclic structure. For example, γ-aminobutyric

Table 5.5. Functional groups and types of compounds formed during polycondensation

Table 5.5. (continuation)

Table 5.5. (ending)

the acid is incapable of polycondensation due to the formation of a stable five-membered cycle - lactam:

However, ζ-aminoenanthic acid forms a linear polymer as a result of dehydration:

Increasing the distance between functional groups increases the likelihood of macromolecule formation. Cyclization as the main direction of the reaction occurs only in those cases when low-tension five- and six-membered cycles should be formed.

Question. Glycine (aminoacetic acid) is incapable of condensation under normal conditions. Explain the probable cause of this phenomenon.

Answer. When two glycine molecules interact, a relaxed six-membered diketipiperazine ring is obtained according to the scheme

In this case, under normal synthesis conditions, a polymer is not formed.

Depending on the structure of the starting substances and the method of carrying out the reaction, two variants of polycondensation processes are possible: equilibrium and nonequilibrium polycondensation.

Equilibrium polycondensation is a polymer synthesis process characterized by low rate constants and a reversible nature of transformations. Polycondensation is a multi-stage process, each stage of which is an elementary reaction of the interaction of functional groups. As a postulate, it is generally accepted that the reactivity of terminal functional groups does not change with the growth of the polymer chain. The process of equilibrium polycondensation is a complex system of exchange, synthesis and destruction reactions, which is called polycondensation equilibrium. In general, polycondensation reactions can be represented as reactions of functional groups, for example:

~COOH + HO~ ~COO~ + H 2 O.

Accordingly, the equilibrium constant is expressed as follows:

K n p =

.

Meaning TO P p is constant at all stages of polycondensation, i.e. does not depend on the degree of polymerization. Thus, for the synthesis of polyethylene terephthalate at 280°C TO P p = 4.9, and polyhexamethylene adipamide at 260°C TO P p = 305.

Factors affecting the molecular weight and polydispersity of polycondensation polymers. The overall rate of the polycondensation process can be estimated by determining the number of functional groups in samples taken from the reaction mixture at various time intervals. The result is expressed by the degree of completion of the reaction X m, which is defined as the proportion of functional groups that have reacted at the time of sampling.

If N 0 is the initial number of functional groups of one type, a Nt- number of groups that did not react at the time of sampling t, That

Task. Calculate the degree of completion of the polycondensation reactions of 8-aminocaproic acid if the initial content of carboxyl groups was N 0 = 8.5 10 -3 eq/g, and the final - Nt= 2.4 · 10 -4 eq/g.

Solution. The reaction scheme is as follows:

Using formula (5.56) we find that X m = 0.971.

To obtain polymers with maximum molecular weight, monomers are taken in strictly equivalent quantities. Each functional group of one starting substance can react with a functional group of another starting substance during polycondensation.

However, the synthesis reaction of polyamides or polyesters is usually catalyzed by H +. The process of protonation of the reacting carboxyl group can be carried out due to the second NOOC- group. Therefore, the reaction rate between a diamine and a diacid or a diol and a diacid can be described respectively as

• -dC/dt = Kn;
• -dC/dt = Kn[COOH][COOH][OH].

Assuming the equivalence of the reacting functional groups and taking into account that = [OH] = [HOOC] = WITH, we have

Where WITH- concentration of functional groups; K p- reaction rate constant.

After integration at t= 0 and WITH = WITH 0 we have

Task. Calculate the rate constant for the polycondensation reaction of sebacic acid ( M 0 = 202) and 2,5-toluenediamine ( M 0 = 122), if after 40 min of reaction at 260°C the concentration of carboxyl groups was Nt= 1.7 · 10 -4 eq/g.

Solution. The reaction scheme is as follows:

n HOOS(CH 2) 6 COOH + n H 2 NC 6 H 3 (CH 3)NH 2 HO n H+2( n- 1)H 2 O.

We calculate the initial concentration of carboxyl groups in the initial mixture, taking into account that 2 moles of monomers participate in the reaction:

WITH 0 = 2/(202 + 122) = 0.61 · 10 -3 eq/g.

Using formula (5.58), we determine the reaction rate constant:

Considering that no significant system volume is removed when water is removed [i.e. we can assume that With t = C 0 (1 - X m)], we have

Task. Determine the rate constant for the polycondensation reaction of adipic acid and ethylene glycol K p and find out whether it changes with increasing size of the molecules of the reacting substances, if the substances are taken in equivalent

Rice. 5.7. Addiction (1 - X m) -2 from the duration of polycondensation t

quantities and the following values ​​of the degree of completion of the reaction were obtained at certain time intervals:

t, min	20	40	60	120	180
X m	0,90	0,95	0,96	0,98	0,99

Solution. According to equation (5.59), if K p does not change with changes in the size of the reacting molecules, then the dependence 1/(1 - X m) 2 = f(t) must be linear. We build a dependence graph (Fig. 5.7), having previously calculated the values ​​1/(1 - X m) 2:

100; 400; 625; 2500; 1000.

A linear dependence (see Fig. 5.7) is observed only at low degrees of reaction completion. The reaction scheme is as follows:

Using equation (5.59) we calculate K p For t= 40 min:

= 5.4 · 10 4 .

The total rate of the polycondensation process can be described by the equation

Where K p- rate constant of the polycondensation reaction; X m is the proportion of functional groups of the monomer that reacted during the time t; a- the amount of low molecular weight product formed over time t; TO P p is the polycondensation equilibrium constant.

In order for the polycondensation reaction to be directed towards the formation of a polymer, the amount of low molecular weight product present in the reaction mixture must be less

Task. Determine the polycondensation equilibrium constant "polycondensation - hydrolysis" if during the polycondensation of benzidine and suberic acid in 30 minutes, the proportion of carboxyl groups that entered into the reaction was 0.84; water content in the system is 0.1 · 10 -3 mol/g; K n = 400; V= 1.3 · 10 -2 mol/(g · min).

Solution. The reaction scheme is as follows:

n H 2 N(C 6 H 4) 2 NH 2 + n HOOC(CH 2) 6 COOH H n OH+ n H2O.

K n p =

= 3.3 · 10 -3 .

The average degree of polymerization of the polycondensation product depends on the content of the low molecular weight reaction product, changing in accordance with the polycondensation equilibrium equation, similar to (6.49). But

Where p a- mole fraction of low molecular weight product released during polycondensation.

Task. Determine the maximum permissible residual amount of ethylene glycol dg in % (wt.) during the polycondensation reaction of diethylene glycol terephthalate in the process of producing a polymer with a molecular weight of 20000, if TO P p = 4.9.

Solution. The reaction scheme is as follows:

R p = 20000/192 = 104.

Using formula (5.61) we find n a:

p a = TO n p/ R 2 = 4.9/104 2 = 4.5 10 -4 mol/mol,

X= 4.5 · 10 -4 · 62 · 100/192 = 0.008% (wt.).

Task. Calculate the number average and weight average molecular weights of the polymer obtained from the polycondensation of 4-amino-2-chloroethylbenzene if the degree of completion of the reaction was 99.35%. Assess the polydispersity of the reaction product.

Solution. It is easy to show that

Where X m is the degree of completion of the reaction; M 0 - molecular weight of the monomer unit.

The reaction scheme is as follows:

According to equation (1.70)

U = M w/M n - 1 = 1,0.

If N 0 is the initial number of functional groups of one type, then the degree of completion of the polycondensation reaction can be expressed as follows:

Solution. The polycondensation reaction scheme is as follows:

We find X m according to equation (5.64):

X m = 0.0054 · 436 · 30/(2 + 0.0054 · 436 · 30) = 0.971.

To calculate the fractional composition of polycondensation products of linear bifunctional compounds, one can use the Flory equation as a first approximation

Where W p- mass fraction of polymer fraction with degree of polymerization P n.

In Fig. Figure 5.8 shows differential MWD curves characterizing the polydispersity of polycondensation products at various degrees of reaction completion X m. It is obvious that as the degree of conversion of the original polymers increases, the degree of polydispersity increases.

However, as a result of reactions that contribute to the establishment of polycondensation equilibrium, in many cases the MWD, even at high degrees of conversion, is characterized by relatively small values U(U

Fig.5.8. Differential MMD curves calculated using the Flory equation (5.60) for various degrees of completion X m of the polycondensation reaction (numbers on the curves)

Solution. The reaction scheme for the synthesis of this polymer is as follows:

Using equation (5.65) we calculate W p:

• A) W p= 40 · 0.9 40-1 (1 - 0.9) 2 = 0.065;
• b) W p= 40 · 0.99 40-1 (1 - 0.99) 2 = 0.0034.

Thus, as the reaction deepens, the content of fractions with a molecular weight of 9000 decreases.

As the content of one type of functional group in the reaction mixture increases, the molecular weight of the polymer decreases (Fig. 5.9).

The influence of an excess of one type of functional group in the reaction medium can be assessed using Korshak's non-equivalence rule. According to this rule,

Where n’ is the number of moles of a bifunctional compound; T’ is the number of moles of a monofunctional compound.

Polycondensation processes can be carried out in a melt (if the monomers and polymer are sufficiently stable at the melting temperature of the polymer), in solution, in the solid phase, as well as at the interface between two phases (immiscible liquids, liquid - solid, etc.). Under conditions of high vacuum, ensuring the removal of low molecular weight reaction products, at temperatures below or above T pl you can carry out the pre-polycondensation reaction (respectively in the solid or liquid phase).

Examples of problem solving

There are two main methods for obtaining high molecular weight compounds: polymerization And polycondensation

Polymerization– reaction of joining of monomer molecules, occurring due to the breaking of multiple bonds.

Polymerization can be represented by a general diagram:

where R is a substituent, for example, R = H, – CH 3, Cl, C 6 H 5, etc.

n – degree of polymerization.

Polymerization of alkadienes with conjugated double bonds (1,3 alkadienes) occurs due to the opening of double bonds in positions 1,4 or 1,2, for example:

The most valuable polymers (rubbers) are obtained by stereoregular polymerization at the 1,4-position in the presence of Ziegler-Natta catalysts:

To improve the properties of rubbers, polymerization of 1,3-butadiene and isoprene is carried out together with styrene, acrylonitrile, and isobutylene. Such reactions are called copolymerizations. For example,

where R = – (butadiene – styrene rubber),

R = -C º N (butadiene – nitrile rubber).

Polycondensation is the reaction of the formation of macromolecules from di or polyfunctional compounds, accompanied by the elimination of low molecular weight products (water, ammonia, hydrogen chloride, etc.).

Polycondensation in which only one monomer is involved is called homopolycondensation. For example,

nHO – (CH 2) 6 – COOH (n-1)H 2 O + H – [–O – (CH 2) 6 – CO –]n – OH

7-hydroxyheptane polymer

acid (monomer)

As a result of homopolycondensation of 6-aminohexanoic acid

(e-aminocaproic acid) the polymer capron is obtained.

Polycondensation involving two monomers containing different functional groups is called heteropolycondensation. For example, polycondensation between dibasic acids and dihydric alcohols leads to the production of polyesters:

nHOOC – R – COOH + nHO – R¢– OH [– OC – R – COOR¢– O –]n + (2n-1) H 2 O

As a result of heteropolycondensation of adipic acid and hexamethylenediamine, polyamide (nylon) is obtained

Example 1.

How many structural units (n) are included in a polyvinyl chloride macromolecule with a molecular weight of 350,000?

M m polymer = 350000

Determine the number of structural links – (n).

1. Reaction scheme:

2. Find the molecular mass of the elementary unit

the addition of the atomic masses of the elements included in its composition - 62.5.

3. Find (n). Divide the molecular weight of the elementary unit: 3500: 62.5 = 5600

Answer: n = 5600

Example 2.

Write a scheme for the formation of isobutylene dimer and trimer under the action of sulfuric acid, taking into account the mechanism of this reaction (cationic polymerization).

Such a polymerization process was observed for the first time by A.M. Butlerov under the action of sulfuric acid on isobutylene.

Chain termination in this case occurs as a result of the abstraction of a proton (H +).

The reaction occurs in the presence of water, which captures a proton, forming a hydronium cation

Test tasks

191. What polymers are called thermoplastic, thermosetting?

192. Write an equation for the copolymerization reaction of styrene

C6H5–CH=CH2 and butadiene CH2=CH–CH=CH2. What properties does the copolymerization product have and where is it used?

193. Write down the equations for the polymerization reaction of propylene

СH2=СH–CH3 and isobutylene H2C=C–CH3.

194. Write the equation for the polycondensation reaction of adipic acid HOOC(СH2)4COOH and hexamethylenediamine NH2(СH2)6NH2. What product is formed, what properties does it have and where is it used?

195. What hydrocarbons are called diene hydrocarbons? Give examples. What general formula expresses the composition of diene hydrocarbons? Draw up a scheme for the polymerization of one of the diene hydrocarbons.

196. What compounds are called amines? Draw up a scheme for the poly-condensation of adipic acid and hexamethylenediamine. What is the name of the polymer formed as a result of this reaction?

197. Calculate the molecular weight of polyvinyl chloride if the degree of polymerization is 200. Write the equation for the polymerization reaction of vinyl chloride.

198. What compounds are called amino acids? Write the formula for the simplest amino acid. Draw up a scheme for the polycondensation of aminocaproic acid. What is the name of the polymer formed as a result of this reaction?

199. Write the reaction equations for the production of nylon from aminocaproic acid NH2(CH2)5COOH and nylon from adipic acid COOH(CH2)4COOH and hexamethylenediamine NH2(CH2)6NH2.

200. What are the names of hydrocarbons of which isoprene is a representative? Draw up a scheme for the copolymerization of isoprene and isobutylene.

HOOC–CH 2 –NH 2 + HOOC–CH–NH 2 HOOC–CH 2 –NH–CO–CH–NH 2

CH 3 –H 2 O CH 3

glycine alanine glycylalanine peptide bond

(gli-ala)

Di-, tri-, .... polypeptides are named by the name of the amino acids that make up the polypeptide, in which all included amino acids as radicals end in - silt, and the last amino acid sounds unchanged in the name.

Resin is obtained by polycondensation of ε - aminocaproic acid or polymerization of caprolactam (ε - caproic acid lactam) nylon:

N CH 2 CH 2 [– NH – (CH 2) 5 – CO – NH – (CH 2) 5 – CO –] m

caprolactam polycaprolactam (kapron)

This resin is used in the production of synthetic nylon fiber.

Another example of synthetic fiber is enant.

Enanth is an enanthic acid polyamide. The enant is obtained by polycondensation of 7-aminoheptanoic acid, which reacts as an internal salt:

N N + H 3 – (CH 2) 6 – COO – [ – NH – (CH 2) 6 – CO – ] n + n H 2 O

Enanth is used for the manufacture of synthetic fibers, in the production of “faux” fur, leather, plastics, etc. Enanth fibers are characterized by great strength, lightness and elasticity.

Tests for self-testing of knowledge on the topic: “Amino acids”

1. Name the compound using systematic nomenclature

CH 3 – CH – COOH

A) 2-aminopropanoic acid

B) a-aminopropionic acid

C) a-alanine

D) 2-aminopropionic acid

2. Name the compound using historical nomenclature

CH 3 – CH – CH – COOH

A) a–amino - b–methylbutyric acid

B) a–methyl - b– aminobutyric acid

C) 2-amino-3-methylbutanoic acid

D) 2-methyl – 3 – aminobutanoic acid

3. Alanine H NH 2 belongs to the series

4. The reaction products are

CH 2 – COOH PCL 5 B

NH 2 NH 3 C

A) A: CH 2 – COONa; B: CH 2 – COCl; C: CH 2 – CONH 2

B) A: CH 2 – COONa; B: CH 2 – COCl 2; C: CH 2 – CONH 4

C) A: CH 2 – COONa; B: CH 2 – COOH; C: CH – NH 2

D) A: CH 2 – COONa; B: CH 2 – COOH; C: CH 2 – CONH 2

NH 2 N + H 3 Cl – NH 2

5. The reaction products are

CH 2 – COOH CH3Br B

NH 2 CH3COCl C

HNO2 D

A) A: CH 2 – COOH; B: CH 2 – COOH; C: CH 2 – COOH; D: CH 2 - COOH

N + H 3 Cl – NHCH 3 NH – COCH 3 OH

B) A: CH 2 – COOCl; B: CH 2 – COOCH 3; C: CH 2 – COOH; D: CH 2 - COOH

NH 2 NH 2 NH-COCH 3 ; OH

C) A: CH 2 – COCl 2; B: CH 2 – COOH; C: CH 2 – COOH; D: CH 2 - COOH

NH 2 NH-CH 3 NH – COCH 3 NH-N = O

D) A: CH 2 – COCl 2; B: CH 2 – COBr; C: CH 2 – COOH; D: CH 2 - COOH

NH 2 NH 2 NH – COCH 3 OH

6. a-Amino acids form when heated

A) lactams

B) ketopiperazines

C) lactones

D) lactides

7. b-amino acids form when heated

A) unsaturated acids

B) ketopiperazines

C) lactams

D) lactones

8. g-amino acids form when heated

A) lactams

B) unsaturated acids

C) lactides

D) lactones

9. Polycondensation of amino acids produces

A) peptides

C) piperazines

D) polyenes

10. Peptide bond in protein molecules is

11. Polycondensation differs from polymerization:

A) No formation of low molecular weight by-products

B) Formation of low molecular weight by-products

C) Oxidation

D) Decomposition

12. A qualitative reaction to a-amino acids is reaction c:

A) ninhydrin

B) a-naphthol

13. The reaction products in the Strecker-Zelinsky synthesis are named:

CH 3 HCN NH 3 2 HOH (HCl)

CH = O A B C

A) A-α-hydroxynitrile butyric acid; B- α-aminonitrile butyric acid; C-

D, L – alanine;

B) A-α-hydroxynitrile propionic acid; B- α-aminonitrile of aminopropionic acid; C-D, L – alanine;

C) A-α-hydroxynitrile valeric acid; B-α-aminonitrile of valeric acid;

C-D, L – threonine;

D) A-α-hydroxynitrile propionic acid; B- α-aminonitrile of propionic acid; C-

D, L – alanine.

14. Name the substances in the chain of transformations:

COOC 2 H 5 O=N-OH [H] (CH 3 CO) 2 O C 2 H 5 ONa

CH 2 – H2O A - H2O IN - CH3COOH WITH - C2H5OH D

malonic ester

Cl-CH 2 -CH(CH 3) 2 H 2 O (HCl) t 0

–NaCl E – CH3COOH, AND - CO2 Z

–2C2H5OH

A) A-nitrosomalon ester; B – oxymalonic ester; C-N-acetyloxymmalone ester; D-Na-N-acetyloxymmalonic ester; E-isobutyl-N-acetyloxymmalonic ester; F-isobutyloxymmalone ether; Z-isoleucine;

B) A-nitrosomalon ester; B – iminomalonic ester; C-N-acetyliminomalone ester; D-Na-N-acetyliminomalonic ester; E-isobutyl-N-acetyliminomalone ester; F - isobutyl aminomalonic ether; Z-threonine;

C) A-nitrosomalon ester; B – aminomalonic ester; C-N-acetylaminomalone ester; D-Na-N-acetylaminomalonic ester; E-isobutyl-N-acetylaminomalonic ester; F-isobutylaminomalone ether; Z-leucine;

D) A-oxymalonic ester; B – nitrosomalon ester; C-N-acetylnitrosomalonic ester; D-Na-N-acetylnitrosomalon ester; E-isobutyl-N-acetylnitrosomalone ester; F-isobutylnitrosomalon ether; Z-valine.

CARBOHYDRATES

Carbohydrates are a large group of organic substances widely distributed in nature. These are glucose, sucrose, starch, cellulose and so on.

Every year, plants on our planet create a huge mass of carbohydrates, which is estimated to contain 4 * 10 10 tons of carbon. About 80% of plant dry matter comes from carbohydrates and 20–30% from animal organisms.

The term “carbohydrates” was proposed in 1844 by K. Schmidt, since most of these substances correspond to the formula Сn(H2O)m. For example, a glucose molecule has the formula C 6 H 12 O 6 and is equal to 6 carbon atoms and 6 water molecules. Later, carbohydrates were found that did not correspond to this composition, for example, deoxyhexose (C 6 H 10 O 5), but the term has been preserved to this day.

Carbohydrates are divided into two large groups - these are simple carbohydrates or monosaccharides (monoses), substances that do not undergo hydrolysis, for example, glucose, fructose. Pentoses and hexoses are more common in nature. The second group is complex carbohydrates, which upon hydrolysis produce monosaccharides. Complex carbohydrates, in turn, are divided into oligosaccharides and polysaccharides. Oligosaccharides consist of two to ten monosaccharide residues. "Oligos" literally means "few". The simplest oligosaccharides are disaccharides (bioses), consisting of two monosaccharide residues. For example, sucrose C 6 H 12 O 6 consists of residues of two monosaccharides: glucose and fructose. Oligosaccharides consisting of residues of three monooses are called trioses, those of four are called tetraoses, and so on. Polysaccharides (polyoses) are formed from monosaccharides as a result of their polycondensation, that is, polyoses are heterochain polymers or biopolymers, the monomers of which are monosaccharides. Heterochain polymers contain in their chain not only carbon atoms, but also oxygen atoms, for example:

NC 6 H 12 O 6 (C 6 H 10 O 5) n + (n-1) H 2 O or (-C 6 H 10 O 4 – O -) n

Carbohydrates