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Файл:Polimers. Учебное пособие по подготовке к интернет-экзамену по английскому языку
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by the Italian chemist Giulio Natta and the German chemist Karl
Ziegler, who won the Nobel Prize in Chemistry in 1963 for the
development of the Ziegler-Natta catalyst. Further recognition of
the importance of polymers came with the award of the Nobel
Prize in Chemistry in 1974 to Paul Flory, whose extensive work
on polymers included the kinetics of step-growth polymerization
and of addition polymerization, chain transfer, excluded volume,
the Flory-Huggins solution theory, and the Flory convention.
Synthetic polymer materials such as nylon, polyethylene,
Teflon, and silicone have formed the basis for a burgeoning
polymer industry. These years have also shown significant
developments in rational polymer synthesis. Most commercially
important polymers today are entirely synthetic and produced in
high volume on appropriately scaled organic synthetic techniques.
Synthetic polymers today find application in nearly every
industry and area of life. Polymers are widely used as adhesives
and lubricants, as well as structural components for products
ranging from children's toys to aircraft. They have been employed
in a variety of biomedical applications ranging from implantable
devices to controlled drug delivery. Polymers such as poly(methyl
methacrylate) find application as photoresist materials used in
semiconductor manufacturing and low-k dielectrics for use in
high-performance microprocessors. Recently, polymers have also
been employed as flexible substrates in the development of
organic light-emitting diodes for electronic display.
ASSIGNMENTS
1. Give chemical terms to the following definitions:
1. A type of functional group that joins a carbohydrate (sugar)
molecule to another group, which may or may not be another
carbohydrate.
2.A group of strong covalent bonds between a phosphate group
and two 5-carbon ring carbohydrates (pentoses) over two ester
bonds.
3. A large molecule (macromolecule) composed of repeating
structural units typically connected by covalent chemical bonds.
2. Answer the questions:
1. Could you give a definition of a polymer?
2. What is material capable of being shaped into virtually any
form?
3. What do you think is the originof the word “polymer”?
4. What polymers could you name?
3. Translate the following sentences into Russian:
1. It is necessary that this substance should be analysed under
suitable conditions.
2. If they used these materials, the cost of production would not
be expensive.
3. The professor insisted that I should take part in the conference.
4. It is desirable that a chemist should know the structure of a
polymer.
5. Unless synthetic polymers possessed such valuable properties?
they would not be so important for industry.
4. Find the topical sentences and make a shot summurt
using these sentences.
5. Retell the text using the following words:
first of all, in this respect, in particular, taking into account
Polymer properties
Polymer properties are broadly divided into several classes
based on the scale at which the property is defined as well as
upon its physical basis. The most basic property of a polymer is
the identity of its constituent monomers. A second set of
properties, known as microstructure, essentially describe the
arrangement of these monomers within the polymer at the scale of
a single chain. These basic structural properties play a major role
in determining bulk physical properties of the polymer, which
describe how the polymer behaves as a continuous macroscopic
material. Chemical properties, at the nano-scale, describe how the
chains interact through various physical forces. At the macroscale, they describe how the bulk polymer interacts with other
chemicals and solvents
.
Chemical properties
The attractive forces between polymer chains play a large part
in determining a polymer's properties. Because polymer chains
are so long, these interchain forces are amplified far beyond the
attractions between conventional molecules. Different side groups
on the polymer can lend the polymer to ionic bonding or
hydrogen bonding between its own chains. These stronger forces
typically result in higher tensile strength and higher crystalline
melting points.
The intermolecular forces in polymers can be affected by
dipoles in the monomer units. Polymers containing amide or
carbonyl groups can form hydrogen bonds between adjacent
chains; the partially positively charged hydrogen atoms in N-H
groups of one chain are strongly attracted to the partially
negatively charged oxygen atoms in C=O groups on another.
These strong hydrogen bonds, for example, result in the high
tensile strength and melting point of polymers containing
urethane or urea linkages. Polyesters have dipole-dipole bonding
between the oxygen atoms in C=O groups and the hydrogen
atoms in H-C groups. Dipole bonding is not as strong as hydrogen
bonding, so a polyester's melting point and strength are lower
than Kevlar's (Twaron), but polyesters have greater flexibility.
Ethene, however, has no permanent dipole. The attractive
forces between polyethylene chains arise from weak van der
Waals forces. Molecules can be thought of as being surrounded
by a cloud of negative electrons. As two polymer chains
approach, their electron clouds repel one another. This has the
effect of lowering the electron density on one side of a polymer
chain, creating a slight positive dipole on this side. This charge is
enough to attract the second polymer chain. Van der Waals forces
are quite weak, however, so polyethene can have a lower melting
temperature compared to other polymers.
ASSIGNMENTS
1. What can you tell about properties of polymers?
2. Translate the following sentences into Russian.
1.Polymer properties are broadly divided into several classes
based on the scale at which the property is defined as well as
upon its physical basis
2.Polymers containing amide or carbonyl groups can form
hydrogen bonds between adjacent chains; the partially positively
charged hydrogen atoms in N-H groups of one chain are strongly
attracted to the partially negatively charged oxygen atoms in C=O
groups on another.
3. This charge is enough to attract the second polymer chain.
3. Summarize the general idea developed in all texts
concerning polymers.
Theme: Plastic
1. Give the initial forms of the following words:
materials, strained, molecular, deformation, much, bottles,
deforming, solidified, lassified, hardness, attractive
2. State to what parts of speech these words belong:
general, deforming, example, substances, amorphous, pressed,
use, is applied, electrically, seriously, important, made, from,
balls
3. Translate the following word-groups into Russian:
common term, two types of plastics, a certain point, can also be
classified, many traditional materials, the use of plastics,
classifications are based on
4. Define the tense and voice of the verbs:
is constrained, will break, have already displaced, acquired, finds
5. Check up if you remember the following verbs:
to be, to confuse, to undergo, to rank, to melt, to reduce, to press,
to contain, to give, to assume
6. Guess the meaning of the words in black type:
mean – meaning, form – deforming, class – classifications, ion
– ionizing, relative - relatively, place - displaced
Plastic
Plastic is the general common term for a wide range of
synthetic or semisynthetic organic amorphous solid materials
used in the manufacture of
industrial products. Plastics
are typically polymers of
high molecular mass, and
may contain other
substances to improve
performance and/or reduce
costs.
The word is derived
from the Greek πλαστικός
astikos) meaning fit for
(pl
molding, and πλαστός (plastos) meaning mol
ded. It refers to their
malleability, or plasticity during manufacture, that allows them to
be cast, pressed, or extruded into a variety of shapes—such as
films, fibers, plates, tubes, bottles, boxes, and much more.
The common word plastic should not be confused with the
technical adjective plastic, which is applied to any material which
undergoes a permanent change of shape (plastic deformation)
when strained beyond a certain point. Aluminium, for instance, is
plastic in this sense, but not a plastic in the common sense; in
contrast, in their finished forms, some plastics will break before
deforming and therefore are not plastic in the technical sense.
There are two types of plastics: thermoplastics and
thermosetting polymers. Thermoplastics will soften and melt if
enough heat is applied; examples are polyethylene, polystyrene,
polyvinyl chloride and polytetrafluoroethylene (PTFE).
Thermosets can melt and take shape once; after they have
solidified, they stay solid.
Plastics can be classified by chemical structure, namely the
molecular units that make up the polymer's backbone and side
chains. Some important groups in these classifications are the
acrylics, polyesters, silicones, polyurethanes, and halogenated
plastics. Plastics can also be classified by the chemical process
used in their synthesis; e.g., as condensation, polyaddition, crosslinking, etc.
Other classifications are based on qualities that are relevant
for manufacturing or product design. Examples of such classes
are the thermoplastic and thermoset, elastomer, structural,
biodegradable, electrically conductive, etc. Plastics can also be
ranked by various physical properties, such as density, tensile
strength, glass transition temperature, resistance to various
chemical products, etc.
Due to their relatively low cost, ease of manufacture,
versatility, and imperviousness to water, plastics are used in an
enormous and expanding range of products, from paper clips to
spaceships. They have already displaced many traditional
materials, such as wood; stone; horn and bone; leather; paper;
metal; glass; and ceramic, in most of their former uses.
The use of plastics is constrained chiefly by their organic
chemistry, which seriously limits their hardness, density, and their
ability to resist heat, organic solvents, oxidation, and ionizing
radiation. In particular, most plastics will melt or decompose
when heated to a few hundred degrees celsius. While plastics can
be made electrically conductive to some extent, they are still no
match for metals like copper or aluminium. Plastics are still too
expensive to replace wood, concrete and ceramic in bulky items
like ordinary buildings, bridges, dams, pavement, railroad ties,
etc.
ASSIGNMENTS
1. Answer the questions:
1. How many types of plastic do you know?
2. How can be classified plastics?
3. Are plastics cheap or expensive material?
5. What is the difference between a plastic and polymer?
2. Give your own conclusion to the text.
3. Write out of the text sentences expressing the main
idea.
Chemical structure
Common thermoplastics range from 20,000 to 500,000 in
molecular mass, while thermosets are assumed to have infinite
molecular weight. These chains are made up of many repeating
molecular units, known as repeat units, derived from monomers;
each polymer chain will have several thousand repeating units.
The vast majority of plastics are composed of polymers of carbon
and hydrogen alone or with oxygen, nitrogen, chlorine or sulfur in
the backbone. (Some of commercial interests are silicon based.)
The backbone is that part of the chain on the main "path" linking
a large number of repeat units together. To vary the properties of
plastics, both the repeat unit with different molecular groups
"hanging" or "pendant" from the backbone, (usually they are
"hung" as part of the monomers before linking monomers
together to form the polymer chain). This fine tuning of the
properties of the polymer by repeating unit's molecular structure
has allowed plastics to become such an indispensable part of
twenty first-century world.
Some plastics are partially crystalline and partially
amorphous in molecular structure, giving them both a melting
point (the temperature at which the attractive intermolecular
forces are overcome) and one or more glass transitions
(temperatures above which the extent of localized molecular
flexibility is substantially increased).The so-called semicrystalline plastics include polyethylene, polypropylene, poly
(vinyl chloride), polyamides (nylons), polyesters and some
polyurethanes. Many plastics are completely amorphous, such as
polystyrene and its copolymers, poly (methyl methacrylate), and
all thermosets.
Cellulose-based plastics
In 1855, an Englishman from Birmingham named Alexander
Parkes developed a synthetic replacement for ivory which he
marketed under the trade name Parkesine, and which won a
bronze medal at the 1862 World's fair in London. Parkesine was
made from cellulose (the major component of plant cell walls)
treated with nitric acid and a solvent. The output of the process
(commonly known as cellulose nitrate or pyroxilin) could be
dissolved in alcohol and hardened into a transparent and elastic
material that could be molded when heated.
[8]
By incorporating
pigments into the product, it could be made to resemble ivory.
Bois Durci is a plastic moulding material based on cellulose.
It was patented in Paris by Lepage in 1855. It is made from finely
ground wood flour mixed with a binder, either egg or blood
albumen, or gelatine. The wood is probably either ebony or rose
wood, which gives a black or brown resin. The mixture is dried
and ground into a fine powder. The powder is placed in a steel
mould and compressed in a powerful hydraulic press whilst being
heated by steam. The final product has a highly polished finish
imparted by the surface of the steel mould.
The first plastic based on a synthetic polymer was made from
phenol and formaldehyde, with the first viable and cheap
synthesis methods invented in 1909 by Leo Hendrik Baekeland, a
Belgian-born American living in New York state. Baekeland was
searching for an insulating shellac to coat wires in electric motors
and generators. He found that mixtures of phenol (C6H5OH) and
ormaldehyde (HCOH) formed a sticky mass when mixed
f
together and heated, and the mass became extremely hard if
allowed to cool. He continued his investigations and found that
the material could be mixed with wood flour, asbestos, or slate
dust to create "composite" materials with different properties.
Most of these compositions were strong and fire resistant. The
only problem was that the material tended to foam during
synthesis, and the resulting product was of unacceptable quality.
Baekeland built pressure vessels to force out the bubbles and
provide a smooth, uniform product. He publicly announced his
discovery in 1912, naming it bakelite. It was originally used for
electrical and mechanical parts, finally coming into widespread
use in consumer goods in the 1920s. When the Bakelite patent
expired in 1930, the Catalin Corporation acquired the patent and
began manufacturing Catalin plastic using a different process that
allowed a wider range of coloring.
Bakelite was the first true plastic. It was a purely synthetic
material, not based on any material or even molecule found in
nature. It was also the first thermosetting plastic. Conventional
thermoplastics can be molded and then melted again, but
thermoset plastics form bonds between polymers strands when
cured, creating a tangled matrix that cannot be undone without
destroying the plastic. Thermoset plastics are tough and
temperature resistant.
Bakelite was cheap, strong, and durable. It was molded into
thousands of forms, such as radios, telephones, clocks, and
billiard balls. The U.S. government even considered making onecent coins out of it when World War II caused a copper shortage.
Phenolic plastics have been largely replaced by cheaper and
ess brittle plastics, but they are still used in applications requiring
l
its insulating and heat-resistant properties. For example, some
electronic circuit boards are made of sheets of paper or cloth
impregnated with phenolic resin.
Phenolic sheets, rods and tubes are produced in a wide variety
of grades under various brand names. The most common grades
of industrial phenolic are Canvas, Linen and Paper.
ASSIGNMENTS
1. Answer the questions:
1. What can you say about the first plastic?
2. When was the first plastic invented?
3. What can you say about Leo Hendrik Baekeland ?
4. What is bakelite?
2. Retell this text in 100 words.
Toxicity
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