Translate the following word combinations into English.

Двойные или тройные химические цепи; механизм присоединения; неспаренные электроны; проходить при крайних температурах и давлениях; использоваться в большой степени; жесткие условия протекания реакции; ступенчатая реакция; увеличиваться в молекулярной массе; разрешить несоответствие.

Answer the following questions.

1) What way does addition polymerization take place?

2) Manufacture of what polymers is addition polymerization involved in?

3) What is a propagating center? What does the form of it depend on?

4) What method is used for polymerization of ethylene?

5) What are the three stages of the free radical mechanism method?

6) What conditions does addition polymerization take place under?

7) Why do most free radical polymerizations tend to lack control?

8) What are other forms of addition polymerization? What are they used for?

9) What are the reaction conditions for cationic addition polymerization and anionic addition polymerization?

10) What are step growth polymers? What are the peculiarities of their reaction of polymerization?

11) How can a condensation polymer be defined?

5. Speak on: a) four methods or forms of chain-growth polymerization;
b) polymerization of ethylene; c) step-growth polymerization.

Find the definition for each of the words given.

a) Ziegler-Natta catalyst; b) condensation polymers; c) chain propagation; d) chain termination;

e) initiation; f) the repeat unit; g) polyurethane;

h) radical polymerization; i) coordination polymerization; j) backbone chain of a polymer.

1. Any class of polymers formed through a condensation reaction, releasing a small molecule by-product such as water or methanol, as opposed to addition polymers which involve the reaction of unsaturated monomers. These polymers include polyamides, polyacetals and polyesters.

2. A chemical reaction that triggers one or more secondary reactions. Often this reaction generates a reactive intermediate from a stable molecule which is then involved in secondary reactions. In polymerization, it is followed by a chain reaction and termination.

3. Any chemical reaction leading to the destruction of a reactive intermediate in a chain propagation step in the course of a polymerization, effectively bringing it to a halt.

4. A form of addition polymerization in which monomer adds to a growing macromolecule through an organometallic active center. The development of this polymerization technique started in the 1950s with heterogeneous Ziegler-Natta catalysts based on titanium tetrachloride and an aluminium co-catalyst such as methylaluminoxane. The polymerization has a great impact on the physical properties of vinyl polymers such as polyethylene and polypropylene compared to the same polymers prepared by other techniques such as free radical polymerization.

5. A reagent or a mixture of reagents used in the production of polymers of 1-alkenes (α-olefins). These catalysts are typically based on titanium compounds and organometallic aluminium compounds. They represent a major breakthrough in polymerization chemistry because they produce a variety of commercially important polymers and can be highly stereoselective.

6. A type of polymerization in which the reactive center of a polymer chain consists of a radical. The polymerization reaction is initiated by three classes of free-radical initiators.

7. The series of covalently-bonded atoms that together create the continuous chain of the molecule.

8. A process in which a reactive intermediate is continuously regenerated during the course of a chemical reaction. In polymerization reaction, the reactive end-groups of a polymer chain react in each propagation step with a new monomer molecule transferring the reactive group to that last unit.

9. An essential concept which defines polymer structure, the simplest structural unit of a polymer chain. So a polymer consists of the units linked together, like the beads of a necklace.

10. Commonly abbreviated PU, any polymer consisting of a chain of organic units joined by urethane links. Such a polymer is formed by reacting a monomer containing at least two isocyanate functional groups with another monomer containing at least two alcohol groups in the presence of a catalyst.

Read the text below to get more information on addition polymerization.

Addition polymerization

Addition polymerization, also called polyaddition or chain growth polymerization, is a polymerization technique where unsaturated monomer molecules add on to a growing polymer chain one at a time.

The process takes place in three distinct steps:

1) chain initiation, usually by means of an initiator which starts the chemical process. Typical initiators include any organic compound with a labile group: e.g. azo (-N=N-), disulfide (-S-S-), or peroxide (-O-O-).

2) chain propagation;

3) chain termination, which occurs either by combination or disproportionation. Termination, in radical polymerization, is when the free radicals combine and is the end of the polymerization process.

Addition polymerization unlike condensation polymerization (also known as step-growth polymerization) is specified by the following:

1) high molecular weight polymer is formed at low conversion;

2) no small molecules, such as H₂O, are eliminated in this process;

3) new monomer adds on the growing polymer chain via the reactive active centre which can be: a) a free radical in free radical addition polymerization; b) a carbocation (an ion with a positively-charged carbon atom) in cationic addition polymerisation; c) a carbanion (an anion in which carbon has an unshared pair of electrons and bears a negative charge) in anionic addition polymerization; d) an organometallic complex in coordination polymerization;

4) above a certain ceiling temperature, no polymerization occurs.

Benzol peroxide and aluminium chloride can serve as examples of reaction initiators. Benzoyl peroxide is a radical initiator for the free radical addition polymerization of styrene to produce polystyrene.

Aluminium chloride is an initiator for the cationic addition polymerization of isobutylene to form isobutyl synthetic rubber.

Memorize the following words and word combinations.

1. labile[`leIbaIl, `leIbIl] – неустойчивый 2. azo – азогруппа, азотная группа 3. disulfide – дисульфид 4. peroxide [pe`rOksaId] – перекись 5. disproportionation–диспропорционирование (перераспределение атомов или групп между двумя одинаковыми/разными соединениями)

6. carbocation – карбкатион 7. carbanion[kR`bxnaIn] – карбанион 8. organometallic – металлоорганический 9. ceiling[`sJlIN]temperature– максимальная температура

Answer the questions given.

1) What are the three distinct steps of addition polymerization?

2) What compounds serve as typical initiators in the chain-initiation step?

3) What are the specific features of addition polymerization?

4) What are the reactive active centers for each of the three types of addition polymerization?

5) What are carbocation and carbanion?

6) Can you guess on the base of information obtained from the previous text, how organometallic complex can be called in other words?

7) Are there any conditions under which no polymerization occurs?

8) What new information have you obtained from the text as compared to the previous one?

Read the text below to get more information on step-growth polymerization.

Step-growth polymerization

Step-growth polymerization involves a chemical reaction between multifunctional monomer molecules. In a step-growth reaction, the growing chains may react with each other to form even longer chains. This applies to chains of all lengths. Thus, a monomer or dimer may react in just the same way as a chain hundreds of monomer units long. This is in contrast to a chain-growth polymerization, where only monomers may react with growing chains (In chain-growth polymerization, two growing chains can’t join together the way they can in a step-growth polymerization).

The most common class of step-growth polymerization is called condensation polymerization and the product a condensation polymer, because the chemical reaction by which the monomer molecules bond is often a condensation reaction that produces a small molecule byproduct. A multifunctional monomer is a molecule that has more than one potential reactive site by which it can form intermolecular chemical bonds. The easiest way to visualize a step growth polymerization is a group of people holding hands to form a human chain: each person has two hands (=reactive sites).

A pioneer in step-growth polymerization is Wallace Carothers who invented nylon, a condensation product of hexamethylene diamine and adipic acid. Each monomer has two functional groups (two amino groups or two carboxyl group) and so each monomer can form an amide link with each of its neighbour.

The functionality of a monomer is the number of reactive sites. A functionality of 2 will yield a linear polymer. For instance, hexamethylene diamine and adipic acid create nylon, terephthalic acid and ethylene glycol create PET (Polyethylene terephthalate).

In theory the polymerization will continue to result in a single macromolecule.

The relationship between the extent of the reaction and the average number of monomer units in a polymer chain is given by the Carothers equation. High molecular weight polymer is formed only at high degrees of conversion (extent of reaction). In practice the average length of the polymer chain is limited by such things as the purity of the reactants and the viscosity of the medium.

A monomer with functionality 3 will introduce branching in a polymer and will ultimately form a cross-linked macrostructure. The point at which this three-dimensional structure is formed is known as the gel point because it is signalled by an abrupt change in viscosity. One of the earliest so-called thermosets is known as bakelite.