2. Say whether the statements below are true or false. Prove your point of view.

1. The process of polymerization can be called as the process, under which the individual molecules of carbon compounds are capable of separating themselves one from another, thereby forming a network or chain.

2. Co-polymer is a compound with a fixed unchangeable set of clusters.

3. Homopolymer is a start product of a single monomer.

4. Straightforward polymerization involves substitution at the carbonyl atom.

5. Complex reactions of polymerization require more complex synthesis.

6. Polymers such as PVC consist of repeated long chains of structures.

7. Polymers that consist of less than two molecules are called “singular”.

8. Compounds consisting of more than 4-monomer units are called oligomers.

2. Answer the questions given.

   1. How can you describe the process of polymerization?

   2. What is a monomer? What part does it play in the process of polymerization?

   3. What is the difference between synthetic polymers and biopolymers?

   4. What are the two generic groups of synthetic polymers?

   5. Can you describe special characteristics polymers have in solution?

   6. Can you name the chemical characteristics of polymers?

   7. What is the degree of clustering?

   8. What are the physical characteristics of polymers?

   9. What polymers and what aliphatic compounds form in the simple polymerization reaction. How can you call such a polymerization reaction in this case?

   10. What do complex reactions of polymerization involve and require?

   11. What compounds do alkenes form?

   12. In what way are polyethylene and polyvinylchloride useful in manufacturing processes?

   13. What is the difference between singular polymers and co-polymers.

   14. What are trimers? How are they formed?

   15. What are tetramers? How are they formed?

9. Find the proper definition for each of the words given.

monomer; polymer; thermoplastic; thermosetting plastics; thermoplastic elastomer;

heteropolymer (copolymer); glass transition temperature; polyethelene; crosslink; solubility;

viscosity; tensile strength; oligomer; PVC.

1. A polymer derived from two (or more) monomeric species, as opposed to a homopolymer where only one monomer is used.

2. A large molecule (macromolecule) composed of repeating structural units typically connected by covalent chemical bonds. While the term in popular usage suggests plastic, it actually refers to a large class of natural and synthetic materials with a variety of properties and purposes.

3. A plastic that melts to a liquid when heated and freezes to a brittle, very glassy state when cooled sufficiently (достаточно).

4. A small molecule that may become chemically bonded to other monomers to form a polymer.

5. Polymer materials that irreversibly (необратимо) cure form. The cure may be done through heat (generally above 200 degrees Celsius).

6. The temperature at which an amorphous solid, such as glass or a polymer, becomes brittle on cooling, or soft on heating.

7. The characteristic physical property referring to the ability of a given substance, the solute, to dissolve in a solvent.

8. In chemistry, it consists of a limited number of monomer units, in contrast to a polymer which, at least in principle, consists of an unbounded number of monomers.

9. A measure of the resistance of a fluid which is being deformed by either shear stress or extensional stress. In general terms it is the resistance of a liquid to flow, or its "thickness". It describes a fluid’s internal resistance to flow and may be thought of as a measure of fluid friction.

10. The stress at which a material breaks or permanently deforms. Along with elastic modulus and corrosion resistance, it is an important parameter of engineering materials that are used in structures and mechanical devices. It is specified for materials such as alloys, composite materials, ceramics, plastics and wood.

11. A synthetic thermoplastic material made by polymerizing vinyl chloride. The properties depend on the added plasticizer. The flexible forms are used in hosepipes, insulation, shoes, garments, etc.

12. A class of copolymers or a physical mix of polymers (usually a plastic and a rubber) which consist of materials with both thermoplastic and elastomeric properties.

13. A polymer consisting of long chains of the monomer ethylene (IUPAC name ethene). The recommended scientific name polyethene is systematically derived from the scientific name of the monomer. In the polymer industry the name is sometimes shortened to PE in a manner similar to that by which other polymers like polypropylene and polystyrene are shortened to PP and PS respectively. In the United Kingdom the polymer is commonly called polythene, although this is not recognized scientifically.

14. A chemical bond, atom, or group of atoms that connects two adjacent chains of atoms in a large molecule such as a polymer or protein.

TEXT 9. CHAIN-GROWTH AND STEP-GROWTH POLYMERIZATION

Chain-growth. Chain-growth polymerization or addition polymerization involves the linking together of molecules incorporating double or triple chemical bonds. These unsaturated monomers (the identical molecules which make up the polymers) have extra internal bonds which are able to break and link up with other monomers to form the repeating chain. Addition polymerization is involved in the manufacture of polymers such as polyethylene, polypropylene and polyvinyl chloride (PVC).

In the polymerization of ethylene, its pi bond is broken and these two electrons rearrange to create a new propagating center like the one that attacked it. The form this propagating center takes depends on the specific type of addition mechanism. There are several mechanisms through which this can be initiated. The free radical mechanism was one of the first methods to be used. Free radicals are very reactive atoms or molecules which have unpaired electrons. Taking the polymerization of ethylene as an example, the free radical mechanism can be divided into three stages: chain initiation, chain propagation and chain termination.

Free radical addition polymerization of ethylene must take place at high temperatures and pressures, approximately 300°C and 2000 At (atmosphere). While most other free radical polymerizations do not require such extreme temperatures and pressures, they do tend to lack control. One effect of this lack of control is a high degree of branching. Also, as termination occurs randomly, when two chains collide, it is impossible to control the length of individual chains. A newer method of coordination polymerization similar to free radical, but allowing more control involves the Ziegler-Natta catalyst especially with respect to polymer branching.

Other forms of addition polymerization include cationic addition polymerization and anionic addition polymerization. While not used to a large extent in industry yet due to stringent reaction conditions such as lack of water and oxygen, these methods provide ways to polymerize some monomers that cannot be polymerized by free radical methods such as polypropylene.

Step-growth. Step growth polymers are defined as polymers formed by the stepwise reaction between functional groups of monomers. Most step growth polymers are also classified as condensation polymers, but not all step growth polymers (like polyurethanes formed from isocyanate and alcohol bifunctional monomers) release condensates. Step growth polymers increase in molecular weight at a very slow rate at lower conversions and only reach moderately high molecular weights at very high conversion (i.e. >95%).

To solve inconsistencies in these naming methods, adjusted definitions for condensation and addition polymers have been developed. A condensation polymer is defined as a polymer that involves elimination of small molecules during its synthesis, or contains functional groups as part of its backbone chain, or its repeat unit does not contain all the atoms present in the hypothetical monomer to which it can be degraded.

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