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23 -- Part 1: CARBOHYDRATES AND NUCLEIC ACIDS
Determine the structure of the monomers.
Predict the structure of the material with the help of the monomers.
If you propose mechanisms for the formation of addition and condensation, you will be able to explain why the polymers have observed structures.
The bones of a human foot are created by extruding a molten filament of a thermoplastic.
The strength and resilience of prehistoric tools and shelters can be found in the biopolymer of glucose.
The hides and hair of animals can be used to make clothing that is strong and supple.
After people learned how to use fire, they made this polyester which has a convenient melting ceramic and pottery glass.
The first synthetic organic polymer was made in the 19th century.
Polystyrene was discovered in the 19th century.
Unless a stabilizer is added, the discovery of polystyrene was inevitable.
The inventor of tire and blimp fame discovered how to make a stretchy material out of the rubber tree by heating it with sulfur.
This was the first time that a natural biopolymer had been artificially cross-linked to give it more strength and stability.
We have become surrounded by synthetic materials in less than 150 years.
Our toys, computers, and pens are all made of plastic.
The articles that are not made from synthetic polymers are often held together.
A bookcase may be made from wood, but the wood is painted with latex and phenol-formaldehyde.
Many organic chemists are employed to develop and produce these polymers.
Some of the fundamental principles of chemistry are discussed in this chapter.
Some of the structural characteristics that determine the physical properties of apolymer are discussed.
The two major classes of synthetic materials are step-growth and chain-growth.
The rapid addition of one monomer at a time to a reactive intermediate at the growing end of the chain occurs.
Chain-growth polymerization involves successive additions across the double bonds.
Poly(vinylchloride) is a chain-growth addition that is often made by free-radical polymerization.
Amides and esters are formed in the most common condensations.
Dacron is a step-growth condensation polymer.
Many alkenes are treated with small amounts of suitable initiators.
Repeated additions across the double bonds of the monomers lead to the products.
The table shows some of the most common additions made from substituted alkenes.
Adding the end of the growing chain across the double bond is called F mechanism.
The reactive intermediates may be free radicals or carbanions.
The three types of chain-growth polymerizations are not the same.
When it is heated to 100 degrees, styrene becomes polystyrene.
This is a chain reaction.
Benzoyl peroxide cleaves when heated to give two carboxyl radicals.
A resonance-stabilized benzylic radical is given by a phenyl radical.
The growth of the chain is started by this reaction.
Styrene is added to the growing chain by each propagation step.
The orientation gives another resonance-stabilized benzylic radical.
The chain may continue to grow with the addition of more units.
The length of a chain depends on the number of additions that occur before the process is stopped.
There are conditions that favor fast chain growth and minimize termination steps.
The chain reaction stops when the two chains are in contact with each other or when there is an impurity.
The catalyst forms a radical that starts the chain.
A molecule adds to the chain.
The free-radical intermediates are less stable than the polypropylene, so stronger reaction condi ties are required.
Ethylene can be obtained from sures around 3000 atm and temperatures of 200 degC.
There is a mechanism for reaction of the first three units in the polymerization of propylene.
Low-density polyethylene is soft and flimsy because it has a branched structure.
Chain branching occurs when a hydrogen atom is removed from the middle of a chain.
A new branch grows off the chain.
Figure 26-1 is a guide for showing chain branching during the free-radical polymerization of styrene.
There are two types of hydrogens in the chain.
Strongly acidic catalysts are used.
The catalyst requires a trace of water or Methanol as a co-catalyst.
There is enough water for the first step of the mechanism when the reagents are dried.
The catalyst starts the chain.
The cationic end of the chain is added by another molecule of monomer.
The cat ionic process requires a stable carbocation when it reacts with the cationic end of the growing chain.
Some monomers form intermediates that are stable.
Under these conditions, styrene and isobutylene can be easily converted into cationic polymerization.
Suggestions on which of the following might work well on treatment with BF3.
Cationic polymerization and free-radical polymerization both have chain branching.
There is a mechanism to show how branching occurs.
Isobutylene might be a better monomer for cationic polymerization.
A stabilizing carbanion is required when an anionic end of a growing chain is reacted with a stabilizing carbanion.
A good monomer should have at least one strong electron-drawing group such as a carbonyl group, a cyano group, or a nitro group.
The chain-lengthening step is shown in the reaction.
The chain-growth step of an anionic polymerization is a conjugate addition to a Michael acceptor.
The anion formed in the anionic polymerization of methyl acrylate has important resonance forms.
A strong carbanion-like reagent such as organolithium or Grignard is used to initiate anionic polymerization.
The chain begins to grow when the initiator is added to a molecule.
Many units react before the carbanion is protonsated under the polymerization conditions.
There is a butyllithium-initiated anionic polymerization of acrylonitrile.
An anion is formed when the initiator adds the monomer.
A molecule adds to the chain.
Even by weak bases, it is easy to modify msg a@cyanoacrylate.
Explain why base-catalyzed polymerization goes so quickly and easily.
Chain branching is not as common with anionic polymerization as it is with free-radical polymerization.
There is a mechanism for chain branching.
Compare the relative stabilities of the intermediates in this mechanism with those you drew for chain branching.
A head-to-tail bonding arrangement is usually given by chain-growth polymerization of alkenes.
There is a bonding arrangement for a generic polyalkene.
The most stable all- anti-conjugated version of the polymer backbone is shown, even though it is joined by single bonds.
The side groups in the polymer have a big effect on its properties.
The possibility of millions of stereoisomers is raised by the fact that the polymer has many chiral centers.
In most cases, isotactic and syndiotactic polymers have improved strength, clarity, and thermal properties.
Draw the structures of isotactic poly and syndiotactic polystyrene.
The three stereochemical forms have different properties.
The stereoregular isotactic and syndiotactic polymers are usually stronger and stiffer because of their regular packing arrangement.
The conditions used for polymerization can affect the stereochemistry.
Depending on the nature of the side group, anionic polymerizations give isotactic or syndiotactic polymers.
Depending on the catalysts and conditions used, cationic polymerizations are often stereoselective.
branched, atactic polymers are the result of free-radical polymerization.
The polymerization is very precise.
The isotactic form or the syndiotactic form can be made by selecting the right catalyst.
The catalyst keeps the intermediates stable.
The resulting materials are linear.
The plumbing industry is "aged" by heating it for about an hour.
The titanium atom appears to form a complex with both the growing and rigid PEX pipe, a cross-linked polymer chain and a molecule of monomer, as the active catalyst moves away from copper.
PEX is chain, which remains complexed to the catalyst, leaving the titanium atom with a free durable, flexible, and easy to connect site for complexation to the next molecule of monomer.
Most can be produced with almost no chain branching and with much greater strength than the cracking and leaking that is common low-density polyethylene.
Older PVC plumbing is common with many other polymers.
They received the prize for their work in 1963, which had changed the industry in ten years.
There are many other plants that produce this material as well.
Natural rubber is soft and sticky.
Charles Macintosh discovered that rubber is a good waterproof coating for raincoats.
The use of natural rubber was limited to waterproof cloth and other strong materials.
Natural rubber is composed of isoprene units.
The following figure shows a structure similar to natural rubber.
The cis double bonds in natural rubber force it to assume that the structure may be stretched and still remain the same.
When we pull on a mass of natural rubber, the chains slide by each other and the material splits.
Natural rubber is not suitable for certain uses.
Charles Goodyear accidentally dropped a mixture of natural rubber and sulfur onto a hot stove in 1839.
He was surprised to see that the rubber had grown strong and elastic.
The discovery led to the rubber plantation.
Natural rubber has less elasticity than vulcanized rubber.
It is elastic and flexible when cold.
The casting of rubber tires can be done with gusto.
Natural rubber can be mixed with sulfur and placed into a mold.
The mold is closed and heated, and the rubber and string is vulcanized into a tire carcass.
In rubber, the chains are linked together so they can't slip past each other.
Cross-linking prevents tearing when the material is stressed.
As the rubber snaps back, the chains return to their shortened, kinked conformations.
The amount of sulfur used in vulcanization can affect the physical properties of rubber.
Low-sulfur rubber is soft and stretchy.
It's good for rubber bands.
Good tires are made of medium-sulfur rubber, which is 2% to 5% sulfur.
The number of disulfide cross-links and the number of bridges with three or more sulfur atoms can be increased by using more sulfur.
Gutta-percha is a natural rubber with all its double bonds in the trans configuration.
Gutta-percha is not very elastic even after it is vulcanized.
There are special catalysts that can produce buta-1,3-diene, where 1,4-addition has occurred on each butadiene unit and the remaining double bonds are allcis.
It can be vulcanized in the same way as natural rubber.
Polyisoprene S S chains have disulfide cross-links.
When it is stretched.
In many cases, the monomers are chosen so that they add in an alternating manner.
There are three or more monomers that can give the desired properties.
The material used for bumpers, crash helmets, and other articles that must endure heavy impacts is made from acrylonitrile, butadiene, and styrene.
The structure of the repeating unit in butyl rubber can be drawn.
Styrene and butadiene rubber are used in auto mobile tires.
The structure of the repeating unit can be drawn.
Monomer molecule may react to form a pair of bonds.
The oligomers can form longer chains by adding longer chains at either end.
There is no chain reaction when it comes to each reaction.
Most step-growth polymerizations involve condensations to form acid-derivative linkages.
We will discuss the four most common types of step-growth polymers.
A new age of fibers and textiles was opened by Wallace Carothers when he discovered nylon in 1935.
The thread used for clothing was made from spun animal and plant fibers.
The fibers were weak and subject to unraveling and rotting.
Silk was the strongest fiber known at the time, and Carothers thought that the strength of silk could be achieved by bonding a amide linkage to a scanning electron micrograph.
A nylon stocking proved to be a completely new type of fiber.
It can be melted and made into stockings that are strong and continuous.
It can be made much thinner with thread spun from continuous nylon fibers, which are so strong they can be 888-282-0465 888-282-0465 888-282-0465 888-282-0465 888-282-0465.
The most common nylon is called nylon 6,6 because it is made by reacting a six-carbon diacid with a six-carbon diamine.
When nylon salt is heated to 250 degC, water is driven off as a gas and molten nylon results.
nylon can be cast into a solid shape or spun through a spinneret to produce a fiber.
This reaction is similar to the process of a@amino acids.
This type of nylon 6 is made from six carbons.
The synthesis begins with e@caprolactam.
When caprolactam is heated with water, some of it hydrolyzes.
The nylon 6 is made from condensation and polymerization.
Caprolactam is used to absorb and distribute the impact of stressed fibers.
It's used in making bulletproof vests.
You can draw the structure of Kevlar.
Most of the modern permanent-press fabrics are blended with other fibers.
The use of these blends has reduced the need for ironing clothes to achieve a wrinkled surface that holds its shape.
The diacid and the glycol could be mixed and heated to drive off the water.
A better product can be obtained using a transesterification process.
The dimethyl ester of terephthalic acid is heated to about 150 degrees.
Methanol has evolved as a gas.
Mylar film is used to make magnetic recording tape, and Dacron fiber is used to make fabric and tire cord.
Mylar film is resistant to the sun's harmful rays.
Aluminized Mylar was used to make the huge balloons that were put into space as giant reflectors in the early 1960s.
Billions of plastic soft-drink bottles are sold each year.
The structure of Kodel was drawn.
It is possible to make glyptal from terephthalic acid and glycerol.
Explain the structure of Glyptal by drawing it.
Carbonic acid can be found in equilibrium with carbon dioxide and water.
Carbonic acid is a carbonate ester and can be used for medical purposes.
The synthesis components are shown in the equation.
There is a mechanism for the reaction of phosgene and bisphenol A.
Diethyl carbonate is a less toxic alternative to phosgene.
The mechanism for the transesterification of diethyl carbonate is proposed.
A large scale condensation of phenol with acetone is what makes bisphenol A.
Latex surgical gloves cause a severe catalyst, and propose a mechanism for this reaction.
Some people have an allergy to condensation because three molecules are joined with a loss of water.
COOH, a half Latex-free gloves are often made with carbonic acid.
Less amines and CO2 can be caused by the unstable nature of chloric acids.
Their compounds are quite stable.
R NH R NH C O R' are not as bad in storage.
Normal esterification procedures can't be used to form urethanes because they are unstable.
The yield of the reaction is quantitative.
There is a mechanism for the reaction of phenyl isocyanate.
There is a rapid exothermic reaction when toluene diisocyanate is added.
Butane is often added to the reaction mixture.
The heat evolved by the polymerization creates bubbles that convert the volatile liquid to a frothy mass of foam.
Give the structure of the toluene diisocyanate reaction.
We can explain the physical and chemical properties of polymers in terms of what we already know about smaller molecules.
The fabric is weakened when the base hydrolyzes because of the ester linkages.
Concepts we have already encountered can be used to explain the physical properties of polymers.
Some aspects of thermal behavior and crystallinity are briefly discussed in this section.
Figure 26-5 shows how the chains are arranged in parallel lines.
An example of how crystallinity affects apolymer's physical properties is provided by polyethylene.
There are areas of crystal structure in a solid material.
An unbranched, high-density polyethylene is made using a catalyst.
It is said that high-density polyethylene is denser, stronger, and more rigid than low-density polyethylene.
Stereochemistry affects crystallinity.
Stereoregular isotactic and syndiotactic are usually more dense than atactic polymers.
We can make a linear polymer with either isotactic or syndiotactic stereochemistry.
The individual molecule can slide past one another.
The drug is released when the fibers are cooled in water.
They grow gummier and less solid until they become liquids.
The phase transitions only apply to long-chain polymers.
Cross-linked polymers are more likely to stay rubbery and may not melt until the temperature is high.
A plasticizer is a nonvolatile liquid that can be dissolved in the polymer, which lowers the attractions between the chains and allows them to slide by one another.
Poly(vinylchloride) is a common example of a plasticized material.
"vinyl" is brittle without a plasticizer.
Dibutyl phthalate is gradually evaporates.
The plasticized vinyl becomes brittle as it loses its plasticizer.
Synthetic polymers do not rot, oxidize, or hydrolyze so they are useful in consumer products.
When plastic consumer products are thrown away, they are problematic.
Between 10% and 15% of solid municipal waste is enormous.
Re-melted and recycled polymers can be used to make new plastic products.
Chemical reactions can be used to recycle some of the ones that can't be re-melted, but this process is more expensive than simply re-melting them.
There is always a small amount of impurities in recycled plastic.
Compared to newly made plastic, recycled plastic has less strength and is not used where strength is important.
For example, recycled plastic isn't used for storing food products or aviation components.
In order to recycle plastics economically, there needs to be just one pure polymer.
The plastics are sorted by their types in the most important stage of recycling.
The table shows how plastic is classified.
Most plastic consumer products are molded into these numbers.
The plastic is shredded into small chips after being sorted by type.
The chips are washed and floated in a solution that allows metal fragments to sink.
The chips are shipped to a facility to be re-melted and molded.
Not usually recycled materials.
A chain-growth process forms most additions.
An anion at the end of the growing chain is involved in the process of forming an addition.
A cation at the end of the growing chain is involved in the process of forming an addition.
Alkenes and dienes are added to most chain-growth polymers.
A step-growth process that forms amide linkages between any two molecules is what most condensation polymers are formed by.
There are two or more different monomers.
The size and amount of the crystallites are compared.
The regions are found below the melting temperature.
A free radical at the end of the growing chain is involved in the process of forming an addition.
It's made from the same units.
One of the small molecule that bonds together.
A small chain of up to a few dozen monomer units.
A nonvolatile liquid is added to apolymer to make it more flexible and less brittle.
The repeating units are bonded by carbonate ester linkages.
The repeating monomer units are bonded by carboxylate ester linkages.
A large molecule with many smaller units bonding together.
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