Polyester production by polycondensation method. Polyester production technology

PC: 1 – in the melt; 2 - in solution; 3 - in emulsion; 4 - in suspension; 5 - interphase.

Methods 2 - 4 have already been considered in the study of the polymerization reaction. Therefore, we will focus on the remaining 2.

PC in the melt. If the starting materials and the polymer are stable at the melting temperature, then the reaction is carried out in the melt in an inert gas atmosphere at reduced pressure, and finished in a vacuum (to remove by-products).

Interfacial PC. This reaction is carried out between 2 immiscible solutions of monomers or (more rarely) monomers in the liquid and gas state. In this case, the polymer is formed at the interface between the media (from where it is continuously removed), and by-products are dissolved in one of the phases. That's why interfacial PC - irreversible(and removal of by-products is not required) and makes it possible to obtain linear polymers with high MM (up to 500,000).

9. The PC reaction is often carried out in the presence of catalysts that speed up the process and balance the reaction.

Lecture No. 14 - Production of polymeric dielectric material

(on the example of polyethylene)

Let us consider a simplified scheme of the technological cycle for the production of high-pressure polyethylene (LDPE).

raw material initiator ______________________

↓ ↓ ↓

→→→→→→→→ →

1 2 3 4 2 5 6 7 8 9

_________________ 

polyethylene ← ←← ← additives

14 12 11

1 – ethylene shop. The ethylene gas plant is located close to the reactor for the synthesis of PE by the reaction polymerization in a gaseous monomer medium. This technical polymerization method provides a chemically pure polymer suitable for the production of dielectrics. The reaction is carried out at elevated pressure in order to increase the yield of the polymer.

Ethylene gas, through collector - 2, enters low pressure mixer - 3 where it mixes with initiator at low pressure. (Polymerization reaction of high pressure ethylene initiated by oxygen or peroxides).

Then, compressor of the 1st stage - 4, compresses the mixture, after which it through mixer - 5 And 2nd stage compressor - 6 goes to reactor - 8, which is separated from the compressor stages flame arrester - 7.

The reaction takes place at a temperature (200 - 300)˚С and pressure (1.5 - 3) thousand atmospheres. The residence time of the reaction mixture in the reactor no more than 30 sec. This achieves 15% ethylene conversion. unreacted ethylene is separated from the polymer in high separators - 9 And low - 10 pressure, after which, through return ethylene purification units – 13 And collectors - 2 served, respectively, in mixers high – 5 And low - 3 pressure. The PE obtained in the reactor is mixed with additives And granulated V 11 and then through dust collector - 12 goes to packaging - 14. Operations 11 – 14 are called confectioning.

LDPE production dangerous for a number of reasons: the presence of high-pressure equipment, the possibility of an explosion and ignition of ethylene in the event of a leak in the process line; narcotic and toxic effects of ethylene and initiators on humans. the maximum allowable concentration of ethylene in the air is 50 mg/m 3 .

Lecture 16 Transformation of polymers

The electrophysical properties of polymers are influenced not only by the chemical structure of molecules and their flexibility, but also by many other factors, among which the structure of the material is of particular importance. For example, if we talk about mechanical strength, fibrils are stronger than spherulites. Large diameter spherulites are more brittle than small ones. Therefore, a thoughtful choice of crystallization conditions is necessary. But this is a simplified view of the problem, because The morphology of a polymer dielectric depends not only on the supramolecular structure of the polymer. It is influenced by the processing method, modification methods (i.e. intentional impact on the polymer in order to change the properties of the material), temperature, and much more, which can be called the term "polymer transformation" under the influence of external factors during manufacture, storage and use.

This transformation is a spontaneous, often undesirable (destruction, cross-linking) or purposeful (cross-linking, molecular rearrangement, plasticization) change in the composition, structure, and, as a result, the electrophysical, chemical, and mechanical properties of polymers.

Reactions of chemical transformations of polymers can be conditionally divided into 2 main groups:

1 . not affecting the polymer backbone– cross-linking, interaction of functional groups, etc.;

2. Occurring with a change in the polymer backbone –

A. intramolecular rearrangements, block copolymerization, etc.;

b. rupture of the main polymer chain with the formation of macrofragments (destruction) or gradual cleavage of individual links (depolymerization).

In addition, it is worth considering separately the mutual dissolution of solid and liquid dielectrics, which is extremely important in relation to impregnated polymer insulation.

In practice, spontaneously developing chemical reactions can run at the same time:

______ _________ _______________ ____________ _______

___ _______________ __ |____________ ______ |_____________ ______

___________ _______ ___________ |______ ___ ______ |_______________

destruction crosslinking destruction and crosslinking

As a result, spatial and branched structures are formed, which significantly reduces elasticity, increases brittleness, reduces solubility, and also affects the electrical and mechanical properties of polymers.

Condensation is the basis for the creation of polymeric synthetic materials: polyvinyl chloride, olefins. When using the basic variants of monomers, it is possible to obtain millions of tons of new polymeric substances by copolycondensation. Currently, there are various methods that allow not only to create substances, but also to influence the molecular weight distribution of polymers.

Process features

The polycondensation reaction is the process of obtaining a polymer by stepwise addition of molecules of polyfunctional monomers to each other. This results in the release of low molecular weight products.

As the basis of this process can be considered. Due to the isolation of by-products, there are differences in the elemental composition of the polymer and the original monomer.

The amino acid polycondensation reaction is associated with the formation of water molecules during the interaction of the amino and carboxyl groups of neighboring molecules. In this case, the first stage of the reaction is associated with the formation of dimers, then they turn into macromolecular substances.

The polycondensation reaction, an example of which we are considering, is distinguished by the ability to form stable substances at each stage. The dimers, trimers and polymers obtained by the interaction of amino acids can be isolated at all intermediate stages from the reaction mixture.

So, polycondensation is a stepwise process. For its flow, monomer molecules are needed, which include two functional groups that can interact with each other.

The presence of functional groups allows oligomers to react not only with each other, but also with monomers. Such an interaction characterizes the growth of the polymer chain. If the original monomers have two functional groups, the chain grows in one direction, which leads to the formation of linear molecules.

Polycondensation is a reaction that will result in products capable of subsequent interaction.

Classification

The polycondensation reaction, an example of which can be written for many organic substances, gives an idea of ​​the complexity of the ongoing interaction.

Currently, such processes are usually classified according to certain criteria:

• type of connection between links;
• the number of monomers taking part in the reaction;
• process mechanism.

How does the polycondensation reaction differ for different classes of organic substances? For example, in polyamidation, amines and carboxylic acids are used as starting components. During the stepwise interaction between the monomers, the formation of a polymer and water molecules is observed.

In esterification, the starting materials are alcohol and carboxylic acid, and the condition for obtaining an ester is the use of concentrated sulfuric acid as a catalyst.

How does polycondensation take place? Examples of interactions indicate that, depending on the number of monomers, homo- and heteropolycondensation can be distinguished. For example, during homopolycondensation, substances having similar functional groups will act as monomers. In this case, condensation is the combination of the starting substances with the release of water. An example is the reaction between several amino acids, which will form a polypeptide (protein molecule).

Process mechanism

Depending on the characteristics of the flow, reversible (equilibrium) and irreversible (non-equilibrium) polycondensation are distinguished. Such a division can be explained by the presence or absence of destructive reactions, which involve the use of low molecular weight processes, different activities of monomers, and also allow differences in kinetic and thermodynamic factors. Such interactions are characterized by low equilibrium constants, low process rate, reaction time, and high temperatures.

In many cases, irreversible processes are characterized by the use of highly reactive monomers.

High process rates using this type of monomer explain the choice of low-temperature and interfacial polycondensation in solution. The irreversibility of the process is due to the low temperature of the reaction mixture, obtaining a low-active chemical. IN organic chemistry There are also variants of nonequilibrium polycondensation that occur in melts at high temperatures. An example of such a process is the process of obtaining from diols and dihalogen derivatives of polyesters.

Carothers equation

The depth of polycondensation is related to the thoroughness of the removal of low molecular weight products from the reaction medium, which prevent the process from shifting towards the formation of a polymer compound.

There is a relationship between the depth of the process and the degree of polymerization, which has been combined into a mathematical formula. During the polycondensation reaction, two functional groups and one monomer molecule disappear. Since a certain number of molecules are consumed during the process, the depth of the reaction is related to the proportion of reacted functional groups.

The greater the interaction, the higher the degree of polymerization will be. The depth of the process is characterized by the duration of the reaction, the size of the macromolecules. What is the difference between polymerization and polycondensation? First of all, the nature of the flow, as well as the speed of the process.

Reasons for terminating the process

Stopping the growth of the polymer chain is caused by various reasons of a chemical and physical nature. As the main factors that contribute to stopping the process of synthesis of a polymer compound, we single out:

• increasing the viscosity of the medium;
• slowing down the diffusion process;
• decrease in the concentration of interacting substances;
• drop in temperature.

With an increase in the viscosity of the reaction medium, as well as a decrease in the concentration of functional groups, the probability of collision of molecules decreases, followed by a stop in the growth process.

Among the chemical reasons for the inhibition of polycondensation, the leading ones are:

• change chemical composition functional groups;
• disproportionate amount of monomers;
• the presence in the system of a low molecular weight reaction product;
• balance between forward and reverse reactions.

Specificity of kinetics

The reactions of polymerization and polycondensation are associated with a change in the rate of interaction. Let us analyze the main kinetic processes using the example of the polyesterification process.

Acid catalysis proceeds in two stages. First, protonation of the acid, the initial reagent, by the acid acting as a catalyst is observed.

During the attack of the alcohol group by the reagent, the intermediate decomposes to a reaction product. For the direct reaction to proceed, it is important to timely remove water molecules from the reaction mixture. Gradually, a decrease in the rate of the process is observed, caused by an increase in the relative molecular weight polycondensation product.

In the case of using equivalent amounts of functional groups at the ends of molecules, the interaction can be carried out for a long period of time until a giant macromolecule is created.

Process options

Polymerization and polycondensation are important processes used in modern chemical production. There are several laboratory and industrial methods for carrying out the polycondensation process:

• in solution;
• in the melt;
• in the form of an interfacial process;
• in emulsion;
• on matrices.

Melt reactions are necessary to produce polyamides and polyesters. Basically, equilibrium polycondensation in the melt proceeds in two stages. First, the interaction is carried out in a vacuum, which avoids the thermal oxidative degradation of monomers, as well as polycondensation products, guarantees gradual heating of the reaction mixture, and complete removal of low molecular weight products.

Important Facts

Most of the reactions are carried out without the use of a catalyst. Vacuuming the melt in the second stage of the reaction is accompanied by complete purification of the polymer, so there is no need to additionally carry out the laborious process of reprecipitation. A sharp increase in temperature at the first stage of interaction is not allowed, since this can lead to partial evaporation of the monomers, a violation of the quantitative ratio of the interacting reagents.

Polymerization: features and examples

This process is characterized by the use of a single starting monomer. For example, such a reaction can produce polyethylene from a starting alkene.

A feature of polymerization is the formation of large polymer molecules with a given number of repeating structural units.

Conclusion

By polycondensation, you can get a lot of polymers that are in demand in various modern industries. For example, phenol-formaldehyde resins can be isolated during this process. The interaction of formaldehyde and phenol is accompanied by the formation of an intermediate compound (phenol alcohol) at the first stage. Then condensation is observed, leading to the production of a high molecular weight compound - phenol-formaldehyde resin.

The product obtained by polycondensation has found its application in the creation of many modern materials. Phenoplasts based on this compound have excellent thermal insulation characteristics, therefore they are in demand in construction.

Polyesters, polyamides obtained by polycondensation are used in medicine, technology, and chemical production.

The first mention of polyester dates back to 1833, when the scientists Gay-Lussac and Peluza synthesized a polyester based on lactic acid. In 1901, Smith was the first to synthesize polyesters based on phthalic acid and glycerol, and also found their use in molding compositions. In 1941 Winfield and Dixon synthesized polyethylene terephthalate (PET), the production of which in the modern world is 68 million tons per year.

The leading role in the polyurethane industry is occupied by polyethers (80%), despite this, polyesters have specific applications due to their unique properties. The high abrasion resistance of polyester-based polyurethanes as well as the chemical resistance to solvents have led to their extensive use in coatings and shoe soles. The high thermal and oxidative stability of aromatic polyesters is used in the production of rigid isocyanurate foams. The ability to elongate and stretch has led to the use of polyesters in components for the production of flexible foams.

Polyesters are obtained by a polycondensation reaction between dicarboxylic acids (as well as their derivatives - esters and anhydrides) and diols (or polyols), as well as by a polymerization reaction, as a result of opening the rings of cyclic esters - lactones and cyclic carbonates.

Consider the main classes of polyesters:

Linear and lightly branched aliphatic polyesters

Aliphatic polyesters are formed as a result of the polycondensation reaction of a dibasic carboxylic acid (adipic, sebacic, glutaric) with glycols (diethylene glycol, ethylene glycol, propylene glycol, 1,4-butanediol, 1,6-hexanediol) and branching agents (glycerol, trimethylol propane and pentaerythritol). Unlike polyethers, polyesters have a broad molecular weight distribution.

Aliphatic polyesters are most commonly waxy solids with a melting point of approximately 60°C. The exceptions are diethylene glycol and 1,2-propylene glycol, which form liquid polyesters. The resistance to hydrolysis of polyurethanes based on polyesters increases with the lengthening of the polyester chain, as residual acidity and catalyst level decrease, and chain branching and the number of polyester bonds increase. It also reduces the swelling of polyurethanes in solvents and oils.

For thermoplastics, waxy polyesters based on adipic acid, ethylene glycol, 1,4 butanediol and 1,6 hexanediol are used. Due to the presence of hydrogen bonds between molecules, polyesters show higher physical and mechanical properties than simple polyesters. However, there are also disadvantages, at high humidity and temperature, thermoplastics based on polyesters are subjected to microbiological attack. This limits their use in tropical climates. The use of thermoplastics is also limited in cold climates due to low flexibility at sub-zero temperatures.

For elastic foams, liquid polyesters with a molecular weight of 2000 to 3000 g/mol and a functionality of 2.05 - 2.2 based on adipic acid and diethylene glycol are used, and chain splitters are also used - glycerol, trimethylol propane and pentaerythritol. Polyesters have a higher viscosity than polyethers, which helps stabilize the cell during foam growth. Primary hydroxyl groups stimulate early gelation when the foam rises. Therefore, when polyesters are used, fewer amine catalysts are required.

The first industrial grades of flexible PU foams were made from lightly branched polyesters and TDI. Elastic polyurethane foams are currently used in the production of laminated fabrics, suitcases, bags, and car interior trim parts that need to be solvent resistant and have increased strength.

Based on standard grades of polyesters with a molecular weight of 2000 g/mol, materials with a relative elongation of 150-300% are obtained, depending on the density and formulation of the foam. Softer polyurethane foams obtained on the basis of TDI 80/20, with an isocyanate index of 90-98, have an elongation at break of 350-450% and are mainly used for tissue duplication. A typical semi-rigid block PUF is formed by reacting TDI with a 50:50 blend of standard polyester and highly branched polyester.

Polyesters are also used as starting materials for polyurethane adhesives. As hydroxyl-containing compounds, polyester is used, for example, based on sebacic acid, glycerol and glycol. TDI, MDI, reaction products of TDI with trimethylolpropane and other polyhydric alcohols are used as isocyanates.

Aromatic polyesters.

Aromatic polyesters are used in rigid polyurethane and polyisocyanate foams.

The development of highly crosslinked fast polyisocyanate PIR foams has led to the active use of polyesters, since high functionality of the polyester is not required, crosslinking is provided by isocyanurates. Polyisocyanurate foams are hybrid structures containing both polyurethane groups and isocyanurate rings. The isocyanate index is in the range of 200 to 300 and above. PIR foams have a higher operating temperature of 140⁰С versus 100⁰С and a lower flame spread rate.

The main advantage of PIR - resistance to open fire - is due to the formation of a grid of carbonized material under the action of a high flame temperature, which retains the macrostructure of the original foam. This material (foam coke) is destroyed very slowly, playing the role of a barrier that prevents the spread of flame. In addition, due to the formation of coke during combustion, much less heat is released. Urethane structures break down at 200⁰C and coke 20%, while isocyanurate structures break down at 325⁰C and coke 50%.

Thermal stability and coking are also dependent on the polyol structure. Aromatic structures are less combustible than aliphatic ones. All this has led to the proliferation of aromatic polyesters with low functionality, low viscosity and low cost.

PET-based polyesters find use for rigid PUR foams: for example, polyester with an equivalent weight of 181 g/mol, a functionality of 2.3, a hydroxyl value of 295-335 mgKOH/g and a viscosity of 8000-10000mPa.s at 25°C.

For the production of PIR foams, a PET-based polyester with an equivalent weight of 238 g/mol, a functionality of 2, a hydroxyl number of 230-250 mgKOH/g and a viscosity of 2700-5500 mPa.s at 25°C is used.

The use of aromatic polyesters based on phthalic anhydride in fast PIR/PUR foams results in good physical and mechanical properties, low smoke generation, thermal stability and fire resistance. The problem of poor compatibility of polyesters based on phthalic anhydride with foaming agents is solved by introducing vegetable oils into the composition, using emulsifiers, amines and polyethers in systems.

For the production of PIR panels, mainly aromatic polyesters based on FA are used with the following parameters: hydroxyl number from 190 to 320 mg KOH/g, functionality 2 - 2.4, acid number less than 1.0 mg KOH/g, viscosity (25 °C) 2000 to 9000 mPa.s

Polycaprolactones- are formed due to the opening of the rings of ԑ-caprolactones in the presence of initiators and catalysts. Polycaprolactones have a much narrower molecular weight distribution than polyesters based on dibasic carboxylic acids and low viscosity. The introduction of polycaprolactones into the system makes it possible to achieve high hydrolytic stability due to the presence of relatively long repeating hydrophobic segments (CH 2) n and the required elasticity even at low temperatures; however, their use in industry is limited by their high cost.

Polycaprolactones are predominantly used in high solids two-component paints. In this area, they compete with polyester polyols, which are less expensive. Polycaprolactone polyesters also find use as segments in other polymers. For example, they are recommended for use in cationic electrodeposition paint formulation, for plasticizing epoxy, or as soft segments in polyurethane dispersions.

Polycarbonates

Polycarbonates are highly transparent, heat-resistant, have good mechanical properties, are not subject to hydrolysis, since there are no catalytically active carboxyl groups. Polycarbonates at room temperature are solids, depending on the mass, the melting point lies in the range from 40-60⁰С.

High molecular weight polycarbonates are used for painting building parts and structures, car decoration, and in electronics. Low molecular weight polycarbonates 1000-4000 g/mol are of greater interest to the LC industry. They are cured by addition products of aliphatic and cycloaliphatic polyisocyanates. The result is products with high weather resistance.

Oligoetheracrylates

Products based on hydroxyl-terminated polyesters in the presence of acrylic acid. Such double bond products are used in UV curable paints. As a result of radical polymerization in the presence of UV initiators, the products are crosslinked, forming a regular network structure. Coating properties are affected by the size and composition of the polyester segment. Branched polyesters with low molecular weight create a dense network structures, while long aliphatic chains lead to film elasticity.

In contact with

RAW

ethylene glycol
Glycerol
Phthalic anhydride
diethylene glycol
allylene alcohol
1,2-propylene glycol
4,4"-Dihydroxydiphenyl-2-propane
Terephthalic acid
Maleic anhydride
dipropylene glycol
Fumaric acid
Methacrylic acid

Scheme for the production of polyestermaleates:
1 - reactor; 2,3 - refrigerators; 4 - condensate collector; 5 - vacuum pump;
6.11 - filter; 7 - mixer; 8 - mernik-dispenser; 9 - pump; 10 - capacity for
styrene; 12 - container
Ethylene glycol (or other polyhydric alcohol) is poured into
enamelled or stainless steel reactor 1,
equipped with a stirrer, jacket for heating and cooling, reverse
refrigerator 2, and heated to 60-70 °C. Pass carbon dioxide
or nitrogen and gradually, with stirring, load solid acids and
reaction catalyst. The temperature is raised to 160-210 ° C and maintained
it within 6-30 hours, depending on the synthesized brand of NPEF.
The liberated water is carried away by a gas current from the reaction sphere and, having passed
cooler 2, condenses in cooler 3 and is collected in a collector
condensate 4. Together with water vapor, the gas partially carries away glycol, which
after cooling in refrigerator 2, where the temperature is maintained above
100 °C, drained back into reactor 1.
Typically, the polycondensation is terminated at the acid number
reaction mixture 20-45 mg KOH/g. Finished NPEF, cooled to 70 °C,
poured into the mixer 7, where the monomer is preliminarily supplied from the tank
10 in an amount of 30-55% by weight of the resin.
To prevent premature copolymerization in
mixer and during subsequent storage, 0.01-0.02%
hydroquinone. After 2-4 hours of stirring and cooling
a homogeneous transparent mixture is filtered on filter 11 and poured into a container
12.

Polyethylene terephthalate

Dimethyl terephthalate is loaded into reactor 1, heated to 140 °C, and
solution of zinc acetate in ethylene glycol heated to 125 °C.
Interesterification is carried out in a stream of nitrogen or carbon dioxide at 200-230 °C for 4-6 hours. The reactor is equipped with a packed column 2, which
serves to separate vapors of ethylene glycol and methyl alcohol.
Methyl alcohol from refrigerator 3 is collected in receiver 4, and
subliming dimethyl terephthalate is washed off in a column with ethylene glycol
from the nozzle and returned back to the reactor. After distillation of methyl
alcohol, the temperature in the reactor is increased to 260-280 ° C and distilled off
excess ethylene glycol. Molten diglycol terephthalate
poured through a metal strainer 5 into the reactor 6. After it
loading for 0.5-1 h create a vacuum (residual pressure 267 Pa).
Polycondensation is carried out at 280 °C for 3-5 hours until
melt of a given viscosity. The released ethylene glycol is distilled off,
condense in the refrigerator 7 and collect in the receiver 8.
Molten PET is squeezed out of the reactor with pressurized nitrogen.
slotted hole in the form of a film on the drum 9, placed in a bath with
water. The cooled film is chopped on the machine 10 and in the form of crumbs
goes to drying and packaging.
Polyethylene terephthalate production scheme:
1.6 - reactors; 2 - packed column; 3.7 - refrigerators; 4.8-
receivers; 5 - filter; 9 - cooled drum; 10 - crusher

Polycarbonate

Phosgenation method
Interesterification method

Scheme for the production of polycarbonate by the periodic method:
1 - reactor; 2, 6 - refrigerators; 3 - washer; 4 - apparatus
for dehydration; 5 - packed column; 7 - precipitator; 8 -
filter; 9 - dryer; 10 - granulator
In the reactor 1, equipped with a paddle stirrer (8-12 rpm),
load 10% alkaline solution of DFP, methylene chloride,
catalyst (quaternary ammonium salt), and
then phosgene is introduced into the stirred mixture at 20–25°C.
Polycondensation is carried out for 7-8 hours in a nitrogen atmosphere
or argon, since phenolates are oxidized by atmospheric oxygen.
The heat released from the reaction is removed by cold
water supplied to the reactor jacket, and with evaporating
methylene chloride, which after condensation in the refrigerator
2 is returned to the reactor.
The polymer dissolves in methylene chloride as it forms.
A viscous 10% solution enters washer 3, where, at
stirring is neutralized with a solution of hydrochloric acid and
is divided into two phases. The aqueous phase containing
dissolved sodium chloride, separated and poured into a line
Wastewater. The organic phase is washed several times with water
(the aqueous phase is separated after each washing) and fed to
dehydration into the apparatus 4. Water vapor passes through
packed column 5, condense in the refrigerator 6 and
enter the water reservoir. The PC solution is fed into the precipitator 7, in
in which PC is precipitated with methyl alcohol or acetone. From
PC suspensions are separated on filter 8 and in the form of a powder
sent to the dryer 9, and then to the granulator 10 to obtain
granules. The granules are either colorless or have a color to light brown. The mixture of solvent and precipitant enters the
regeneration.

Scheme for the production of polycarbonate by a continuous method:
1,2, 3 - reactors; 4.6 - devices for separation; 5 - extraction
Column; 7 - stripping column; 8, 10 - refrigerators; 9 - precipitation
Column
In the continuous method of PC production, all components are an aqueous solution
sodium diphenolate, obtained by dissolving aqueous alkali bisphenol,
methylene chloride and phosgene - through dispensers continuously flow into the first
reactor 1 of the cascade of reactors. Fast mixing ensures
the course of the reaction. The resulting oligomer flows into reactor 2 and then into
reactor 3. In all reactors, the temperature is maintained within 25-30 °C.
To reactor 3 to deepen the process of polycondensation and obtain a polymer
high molecular weight catalyst is introduced (aqueous solution
ammonium alkylaryl chloride).
The reaction mixture, consisting of aqueous and organic phases, enters the
apparatus 4 for continuous separation. The aqueous phase is fed for purification, and
PC solution in methylene chloride is washed with water in the extraction column 5
and separated from the water in apparatus 6. The washed polymer solution passes
distillation column 7 to separate the remaining water in the form of an azeotropic mixture
water-methylene chloride, the vapors of which are cooled in the refrigerator 8 and enter
for division.
Dehydrated solution of PC in methylene chloride after cooling in
heat exchanger and filtration (the filter is not shown in the diagram) is supplied for
drain into a container (when used as a varnish when receiving films and
coatings) or after heating up to 130 °C under a pressure of 6 MPa using
nozzle is fed into the precipitation column 9. In this column, due to
pressure reduction To atmospheric and evaporation of methylene chloride PC
separated as a powder and precipitated at the bottom of the column. Couples
methylene chloride are condensed into the refrigerator 10, and the powder
polymer - for granulation.

Polyarylates

10.

Scheme for the production of polyarylates by the batch method
1 - apparatus for preparing a solution of dichlorides; 2 - apparatus for
preparation of a solution of bisfepol; 3 - reactor; 4 - suspension collector; 5 -
centrifuge; 6 - wet powder collector
Interfacial polycondensation occurs at the boundary
phase separation formed when the solution is drained
dicarboxylic acid dichloride (or a mixture
dichlorides of various dicarboxylic acids) in
organic solvent (solution I) with an aqueous alkaline
dihydric phenol solution (solution II). IN
industry, this process is carried out as follows
way. In apparatus 1, solution I is prepared from
terephthalic and isophthalic acid dichlorides in
p-xylene, and in apparatus 2 - solution II from DFP, aqueous
sodium hydroxide solution and emulsifier. filtered
solutions are fed into the reactor 3, where at 20-25 ° C and
stirring with a stirrer for 20-40 minutes
going on
reaction
polycondensation,
accompanied by the release of polymer in the form
powder. The suspension is collected in collection 4, powder
polymer is separated in a centrifuge 5, repeatedly
washed with water, transferred to a collection of wet
powder 6 and served for drying in a fluidized bed dryer.
The dried fine powder is fed to
packaging or granulation.

The choice of a method for carrying out polycondensation is determined by the physicochemical properties of the initial substances and the resulting polymers, technological requirements, tasks that are set during the process, etc.

By temperature polycondensation methods are divided into high temperature(not lower than 200С) and low temperature(0-50С), according to the state of aggregation of the reaction system or phase state- for polycondensation in mass(melt), solid phase, solution, emulsions(suspensions), two-phase system(interfacial polycondensation - for example, at the interface of the organic phase with dichloride and water with diamine, a polyamide film is obtained).

Polycondensation in the melt and solid phase occurs at high temperatures; emulsion polycondensation and interfacial polycondensation - at low temperatures; polycondensation in solution - at high and low temperatures.

Low temperature polycondensation is predominantly nonequilibrium, high temperature - mainly equilibrium.

Melt polycondensation, the method of conducting polycondensation (usually equilibrium) in the absence of a solvent or diluent; the resulting polymer is in a molten state. The starting materials (and sometimes the catalyst) are heated at a temperature 10-20°C higher than the melting (softening) temperature of the resulting polymer (usually at 200-400°C). To avoid the oxidation of monomers and thermal-oxidative degradation of the polymer, the process is first carried out in an atmosphere of an inert gas (often dried), and finished in a vacuum to more completely remove low-molecular reaction products and shift the equilibrium towards the formation of a high-molecular polymer.

Advantages of the method: the possibility of using low-reactive monomers, the comparative simplicity of the technological scheme, the high yield and degree of purity of the resulting polymer, the possibility of forming fibers and films from the resulting polymer melt.

Flaws: the need to use thermally stable monomers and the process at high temperatures, the duration of the process, the use of catalysts.

Due to the high viscosity of the melts of most polymers, the rate at the final stages of the process is determined not so much by the activity of the reacting groups as by diffusion factors(mobility of macromolecules).

Melt polycondensation is practically the only industrial method for the synthesis of aliphatic polyamides and polyesters (for example, polyamide-6,6 And polyethylene terephthalate). It is carried out on a periodic and continuous scheme. In the first case, the process is carried out in an autoclave, squeezing the finished polymer out of it with nitrogen through a heated valve. The continuous process is carried out in U- and L-shaped, as well as tubular reactors, equipped with a screw mixer at the polymer outlet, which ensures effective mixing of the melt and its extrusion through a spinneret in the form of a monofilament, tow or film. The tubular apparatus does not need a stirrer, since the process takes place in a thin layer.

In laboratory practice by the method of polycondensation in the melt synthesize polyamides, polyesters, polyheteroarylenes, block and random copolymers.

Solution polycondensation- a method of carrying out polycondensation, in which the monomers and the resulting polymer are in solution in one phase. Various variants of the method are possible when the monomer and (or) polymer are partially soluble in the reaction medium. To obtain polymers of high MW, the monomers and the polymer must, as a rule, be completely dissolved in the reaction medium, which is achieved by using a mixture of two or more solvents or by increasing the reaction temperature. Usually the process is carried out at 25-250°C. The resulting polymer can form thermodynamically unstable (metastable) solutions or lyotropic liquid crystal systems. After the polymer has precipitated from such a solution, it cannot be re-dissolved in this solvent. In the precipitated crystalline polymer, which does not swell in the reaction solution, the growth of macromolecules stops; in an amorphous polymer capable of swelling continues. Precipitation of the polymer from the reaction solution can lead to its crystallization.

Advantages of the method: the possibility of carrying out the process at relatively low temperatures; the ability of the solvent to act as a catalyst; good heat transfer; the possibility of direct use of the resulting polymer solutions for the manufacture of films and fibers.

A distinctive feature is the influence of the nature of the solvent on the pier. mass and structure of the resulting polymer. Examples are known when a solvent (pyridine, tertiary amines, N,N-dimethylacetamide, N-methylpyrrolidone, etc.) binds the acid formed in the reaction, for example. at polyesterification or polyamidation(so-called acceptor catalytic polycondensation). The solvent and impurities contained in it, for example, H 2 O, can cause side reactions leading to the blocking of functional groups. A special place among them is occupied by cyclization, the intensity of which increases with decreasing concentration of the reaction solution.

In laboratory practice by the method of polymerization in solution synthesize various carbo- And heterochain polymers, incl. organoelemental (polyacetylenes, polyamides, polyesters and polyethers, polysulfones, polyheteroarylenes, polysiloxanes, etc.).

Technology and instrumentation depend on the type of polycondensation. With equilibrium (reversible) polycondensation in solution, the process is carried out at 100–250°C and solvents are used that dissolve the resulting polymers well, and low molecular weight reaction products poorly. The boiling point of such solvents should be higher than that of low molecular weight reaction products. Sometimes solvents are used that form an azeotropic mixture with a low molecular weight reaction product, the boiling point of which is lower than that of the solvent ( azeotropic polycondensation). In industry, this process is rarely used. The first stage in the production of a number of polyesters, for example, polyethylene terephthalate, is a kind of equilibrium polycondensation in solution, when one of the monomers (in this example, ethylene glycol), taken in excess, serves as a solvent.

Non-equilibrium (irreversible) polycondensation in solution is subdivided into low- and high-temperature - process temperatures below 100°C and above 100°C, respectively (more often up to 200°C). A variation of low-temperature polycondensation in solution is emulsion polycondensation, when the polymer is formed in the organic phase of a water-organic heterogeneous system. The liberated HNa1 is neutralized in the aqueous phase with alkali metal carbonates or hydroxides. In industry, non-equilibrium solution polycondensation is used in the production of polyamides, polycarbonates, polyarylates, polyheteroarylenes and others and carried out on a periodic basis.

Polycondensation in the solid phase (solid state polycondensation), a method of carrying out polycondensation, when the monomers or oligomers are in a crystalline or glassy state and a solid polymer is formed. A kind of solid-state polycondensation is possible, when during its course the starting materials melt or soften. In many ways (conditions, regularities of the process), solid-state polycondensation is similar to polycondensation in a melt. The solid-state polycondensation of aliphatic (-amino acids), which is characterized by the presence of autocatalysis due to the increase in the monomer-polymer interface during the reaction, on which the monomer molecules are more mobile than in the crystal, has been studied in detail.

The method is used to obtain polyheteroarylenes from highly reactive monomers. Carrying out the process under pressure in a mold, they combine the synthesis of the polymer and the molding of the product. In this way, in particular, monolithic products are obtained from polyimides, poly(aroylen- bis-benzimidazoles).

An important variety of solid-state polycondensation is the second stage in the process of formation of many polyheteroarylenes, carried out in films or fibers formed from pre-obtained intermediate high molecular weight polymers (prepolymers). This is a thermal process of intramolecular polycyclization carried out in an inert gas flow or vacuum at temperatures usually below the glass transition temperature of the intermediate polymer (for example, polyamic acid) or above it, but below the glass transition temperature or softening temperature of the final polyheteroarylene. In some cases (for example, during the transformation of polyhydrazides into poly-1,3,4-oxadiazoles), kinetic inhibition of the process is observed due to an increase in the glass transition temperature during cyclization; then resort to a stepwise increase in temperature. Sometimes polycyclization is accompanied by solid-state polycondensation at the terminal functional groups of macromolecules, leading to an increase in the molecular weight of the polymer.