Becky Kriger's Public Library

10 Dec 08

Capacitors, formerly known as “condensers,” are devices that store electric energy and release it needed.
Capacitors can release a lot of power at once, but are poor at storing energy.
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- They consist of two conducting plates (usually made of metals that are capable of being charged) and a thin dielectric (insulating material) as a separator. The plates are charged by a power source and, when the power is needed, they can send out their entire charge almost instantaneously. The amount of capacitance that can be achieved is directly proportional to the area of the plates, and inversely proportional to the distance between the plates.
- Unlike batteries that have high energy capacity and low power, ultracapacitors (electrochemical capacitors or supercapacitors) can deliver high power in short bursts.
- ultracapacitors can improve battery life by handling peak current output.
- Ultracapacitors can be thought of as the bridge between traditional capacitors and batteries, because they have more power than batteries, but also more energy storage than capacitors. An ultracapacitor does not store energy between two plates like a traditional capacitor. It stores energy within an electrochemical double-layer that forms at the electrode/electrolyte interface as shown in the figure below.

SolRayo's Ultracapacitor Research

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ultracapacitor

We have developed a new method of fabricating ultracapacitors. We utilize less expensive carbon cloths or papers as our electrode backing material. We then coat these materials with nanoparticles that are able to improve the performance at a lower cost.
Results for two nanoparticle-coated backing materials are shown by the blue and green squares in the figure below. We see that our materials have better energy storage and power delivery compared to typical ultracapacitors (electrochemical capacitors).
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- Ultracapacitors can provide one to two orders of magnitude more charge/discharge cycles than rechargeable batteries. The plot below shows the performance of one of our electrochemical capacitors over 3 million cycles.
- By using different backing materials, particle sizes, coating processes and differing electrolytes we can tailor performance of these electrochemical capacitors for specific application needs.

04 Dec 08

"Elements of Chemistry: Polymers and Plastics"

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Polymers

About plasticizers

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plasticizer plastics

A plasticiser is a substance which when added to a material, usually a plastic,
makes it flexible, resilient and easier to handle.
Today, modern plasticisers are manmade organic chemicals; the majority of which
are esters, such as adipates and phthalates.
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- Importantly, they are not just additives (like pigments or fillers). They are
  major components that determine the physical properties of polymer products.
- They are colourless, odourless liquids produced by a simple chemical
  reaction, whereby molecules of water are eliminated from commercially produced
  petrochemical products.
- The most commonly used plasticisers are phthalates.
- Predominantly, phthalates are used in the plastics industry to soften the
  popular plastic PVC. This is used to make a diverse range of cost effective
  products with various levels of technical performance suited to a wide range of
  applications. Many of these PVC products we use everyday but tend to take for
  granted. They include everything from lifesaving medical devices such as medical
  tubing and blood bags, to footwear, electrical cables; packaging, stationery,
  and toys.

Copolymerization

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copolymers polymerization

The major practical problem, however, is that homopolymers
blend together with difficulty and even where blends are possible, as in some
thermoplastics, phase separation can occur readily.

This problem is often overcome by polymerizing a mixture of
monomers, a process known as copolymerization.
It gives a much greater range of structures than is possible by mixing
homopolymers because of the possibility of branching, structural isomerism
within a single monomer, and the way in which the different repeat units can be
added together.
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- suppose that two monomers, A and B, are copolymerized. The chain could start
  with either a molecule of A or a molecule of B, and at each successive addition
  there are always two possibilities as to which monomer molecule will be
  attached. As shown in Table 7, the number of possible
  chain structures grows rapidly as n increases. Since the number of
  possible structures is proportional to 2ⁿ, it is easy to see
  that even for low degrees of polymerization the number of possible copolymers is
  very large indeed. Some of these molecules are identical however
- Table 7 shows that the composition varies from chains
  of only monomer A (homopolymer A) to chains containing only monomer B
  (homopolymer B).
- In many of the structures no regularity can be detected,
  although there will be short sequences of one type of unit, and the copolymer
  can be regarded as completely random; such copolymers are usually said to be
  ideal copolymers. These possible copolymer structures are shown
  schematically in Table 7.
- It can be shown that the rate of change of monomer
  concentration in any copolymerization is given by the equation
  
  where [M₁] and [M₂] are the
  concentrations of monomers 1 and 2 at any instant and r₁ and
  r₂., are reactivity ratios. The reactivity ratios represent
  the rate at which one type of growing chain end adds on to a monomer of the same
  structure relative to the rate at which it adds on to the alternative monomer.
  The copolymer equation can be used to predict chain structure in the
  three different ways, already mentioned.
- An ideal copolymer will tend to form when each type of
  chain end shows an equal preference for adding on to either monomer. In this
  case,
  
  and the copolymer equation becomes
  
  Hence composition depends on the relative amounts of
  monomer present at any time and the relative reactivities of the two
  monomers.
- Step growth copolymerizations produce ideal (random) copolymers since in this
  special case r ₁ = r ₂ = 1.
- The main reason for copolymerizing different monomers is to adjust the physical
  properties of a given homopolymer to meet a specific demand. SBR elastomer, for
  example (Table 1), based on 24 wt%
  styrene monomer shows better mechanical properties and better resistance to
  degradation than polybutadiene alone
- A second reason for copolymerization is to enhance the chemical reactivity of a
  polymer, particularly to aid crosslinking. Conventional vulcanization in rubbers
  is brought about by forming sulphur crosslinks at or near double bonds in the
  chain
- To show the dramatic effect of copolymer structure on
  physical properties, consider the change from random SBR copolymer to a block
  copolymer of exactly the same chemical composition but where the styrene and
  butadiene parts are effectively homopolymer chains linked at two points:
  
  The material behaves like a vulcanized butadiene rubber
  without the need for chemical crosslinking since the styrene chains segregate
  together to form small islands or domains within the structure. Such so-called
  thermoplastic elastomers (TPEs) today form an important growth area for
  new polymers because of the process savings in manufacture that can be achieved
  with their use.

Effects of Temperature on Polymers

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polymerization

Many polymers have a mixture of ordered (crystalline) regions and random
(amorphous) regions. In the glassy state the tangled chains in the
amorphous region are frozen so movement of chains is not possible. The
polymer is brittle.
If the glassy material is heated, the chains reach a temperature at which they
can move. This temperature is called the glass transition temperature
T_g. Above this temperature the polymer is flexible.
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- The glass transition temperature of a
  polymer can be changed by two different ways:
  
  Copolymerisation. Ethene can be
  polymerised with propene to give a new polymer with different properties.
  
  Plasticisers. PVC is quite
  brittle. Its T_g can be lowered, making it less brittle, by
  introducing a substance between the polymer chains, allowing the chains to slide
  over each other more easily. Such a substance is called a plasticiser.

Turning Plastics Back to Oil

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energy conservation plastics

Key to GRC's process is a machine that uses 1200 different frequencies within
the microwave range, which act on specific hydrocarbon materials. As the
material is zapped at the appropriate wavelength, part of the hydrocarbons that
make up the plastic and rubber in the material are broken down into diesel oil
and combustible gas.
"Anything that has a hydrocarbon base will be affected by our process," says
Jerry Meddick, director of business development at GRC, based in New Jersey. "We
release those hydrocarbon molecules from the material and it then becomes gas
and oil."
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- Whatever does not have a hydrocarbon base is left behind, minus any water it
  contained as this gets evaporated in the microwave.
- Take a piece of copper wiring," says Meddick. "It is encased in plastic - a kind
  of hydrocarbon material. We release all the hydrocarbons, which strips the
  casing off the wire." Not only does the process produce fuel in the form of oil
  and gas, it also makes it easier to extract the copper wire for recycling.
- Autofluff is the stuff that is left over after a car has been shredded and the
  steel extracted. It contains plastics, rubber, wood, paper, fabrics, glass,
  sand, dirt, and various bits of metal. GRC says its Hawk-10 can extract enough
  oil and gas from the left-over fluff to run the Hawk-10 itself and a number of
  other machines used by Gershow.
- Because it makes extracting reusable metal more efficient and evaporates water
  from autofluff, the Hawk-10 should also reduce the amount of end material that
  needs to be deposited in landfill sites.

On oil and plastic

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Plastics polymers Energy conservation

Manufacturers take simple hydrocarbons from whatever source material they're
using -- commonly crude oil, but also natural gas, corn, and other biomass --
and turn them into polymers
In the case of crude oil, they do this by heating it to more than 750 degrees
Fahrenheit, then separating its components. The polymers usually travel onward
in life in the form of pellets, ending up at one plastic factory or another to
be molded into familiar shapes
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- Polyethylene (HDPE
  or LDPE) is the soft one you likely encounter most, in milk jugs, shampoo
  bottles, plastic bags, and so forth. Polystyrene (PS) is
  the hard plastic that makes casings for computers and other appliances
- call Styrofoam. Polypropylene (PP) is used in dishwasher-safe containers
- You'll often find polyethylene terephthalate (PET) in soda bottles, and it is
  sometimes recycled into fleece, upholstery fabrics, and other useful materials.
  And then of course there's polyvinyl
  chloride (PVC)
- about 4 percent of the world's annual oil production of some 84.5 million
  barrels per day is used as feedstock for plastic, and another 4 percent or so
  provides the energy to transform the feedstock into handy plastic.
- drilling. Recycling, however, does cut into energy use. According to the U.S.
  EPA, manufacturing new plastic from recycled plastic requires two-thirds of the
  energy used in virgin plastic manufacture. I have more numbers, too: one ton of
  recycled plastic saves 685 gallons of oil.

How are Plastic Bottles Made ? A Start to Finish Process

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Plastics manufacture

How Is Nylon Made?

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Polymers Nylon Polyamides

nylon was used to make parachutes, clothes, military uniforms, tires,
machine parts and other necessary items
Nylon is made through a complex chemical reaction known as ring opening polymerization. In
this reaction, a molecule with a ring shape such as hydrocarbons found in
petroleum are submitted to various types of acids and bases. The ensuing
chemical reactions cause the ring-shape molecular structure to flatten and
lengthen. These molecules are caused to connect with one another to form
molecular chains by being heated well above 600 degrees Fahrenheit. When done,
what you have is a liquid with a high surface tension. If it cools down it will
harden into a solid useless mass, so while it's still a liquid it is extruded
through a hole with a diameter slightly greater than that of a human hair.
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- There is one problem, however, with this is process called hydrolysis. It's a
  chemical reaction during which the oxygen and hydrogen molecules in nylon's
  molecular chain can be broken away from the chain to produce water. This is the
  primary means by which nylon decays. It does not happen over time, but is
  instead a reaction to contact with certain caustic materials such as sulfuric or
  hydrochloric acid

03 Dec 08

The Science of Nylon - Spinning the Elements

www.chemheritage.org/...chem.html - Preview

Nylon was developed as a synthetic substitute for silk.
Silk is a protein. Like all proteins, it is a polypeptide, and it has a structure something like
this:

How are polymers made? : Scientific American

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polymers

Synthetic polymers are produced by chemical reactions, termed "polymerizations."
but such reactions consist of the repetitive chemical bonding of individual
molecules, or monomers. Assorted combinations of heat, pressure and catalysis
alter the chemical bonds that hold monomers together, causing them to bond with
one another. Most often, they do so in a linear fashion, creating chains of
monomers called polymers.
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- The monomer ethylene is composed of two carbon atoms, each bonded to two
  hydrogen atoms and sharing a double bond with one another. Polyethylene consists
  of a chain of single-bonded carbon atoms, each still carrying its two hydrogen
  atoms.
- One way to produce polyethylene is called "free radical polymerization." As
  in other polymerizations, the process has three stages, known as initiation,
  propagation and termination. To begin, we need to add a catalyst to our supply
  of ethylene. A common catalyst is benzoyl peroxide, which when heated has the
  habit of splitting into two fragments, each with one unpaired electron, or free
  radical. These fragments are known as initiator fragments.
- The unpaired electron naturally seeks another and finds a convenient target
  in the double bond between the carbon atoms in the ethylene molecule. Taking an
  electron from the carbon bond, the initiator fragment bonds itself to one of the
  monomer's carbon atoms.
- The new radical also seeks a partner. And so ethylene monomers begin attaching
  themselves in a chain, creating new radicals each time and lengthening the
  chain. This stage is called propagation.
- Eventually, free radical polymerization stops due to what are called termination
  reactions. For example, instead of stealing an electron from double-bonded
  carbons or a nearby propagating chain, the carbon atom with the free radical
  sometimes steals an entire hydrogen atom from another chain end. The polymer
  end--robbed of its hydrogen--easily forms a double bond with its adjacent carbon
  atom, and polymerization stops.
- Because every part of the ethylene monomer is included in the finished polymer,
  the free radical polymerization of polyethylene is referred to as an addition
  polymerization
- Polymerizations that use only portions of a monomer, however, are known as
  condensation polymerizations. The monomers that condense with each other must
  contain at least two reactive groups in order to form a chain.
- For example, poly(ethyleneterepthalate), a polyester known as PET that is
  commonly found in soda bottles, forms from a reaction of two monomers: ethylene
  glycol and terephthoyl chloride. At the reaction's end, an atom of hydrogen and
  an atom of chlorine are left out of each PET molecular junction, resulting in a
  by-product of hydrogen chloride (HCl) gas.

Carbohydrates and Polysaccharides

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Carbohydrates polymers Polysaccharides

A condensation reaction takes place releasing water. This process
requires energy. A glycosidic bond forms and holds the two monosaccharide
units together.
Disaccharide Monosaccharides
sucrose from α-glucose + α-fructose
maltose from α-glucose + α-glucose
α-lactose * from α-glucose + β-galactose

* Lactose also exists in a beta form, which is made from β-galactose and
β-glucose
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- Carbohydrates (also called saccharides) are molecular compounds made from
  just three elements: carbon, hydrogen and oxygen. Monosaccharides (e.g. glucose)
  and disaccharides (e.g. sucrose) are relatively small molecules.
- a source of energy
- building blocks for polysaccharides (giant carbohydrates
- components of other molecules eg DNA, RNA, glycolipids, glycoproteins, ATP
- Monosaccharides are the simplest carbohydrates and are often called single
  sugars.
- Monosaccharides have the general molecular formula
  (CH₂O)_n, where n can be 3, 5 or 6.
- n = 3
  trioses, e.g. glyceraldehyde
  n = 5
  pentoses, e.g. ribose and deoxyribose ('pent'
  indicates 5)
  n = 6
  hexoses, e.g. fructose, glucose and galactose
  ('hex' indicates 6)
- Molecules that have the same molecular formula but different structural
  formulae are called structural isomers.
- Monosaccharides containing the aldehyde group are classified as aldoses,
  and those with a ketone group are classified as ketoses. Aldoses are
  reducing sugars; ketoses are non-reducing sugars.
- in water pentoses and hexoses exist mainly in the cyclic form, and it is in
  this form that they combine to form larger saccharide molecules.
- There are two forms of the cyclic glucose molecule: α-glucose and β-glucose.
- Two glucose molecules react to form the dissacharide maltose.
  Starch and cellulose are polysaccharides made up of glucose units.
- Galactose molecules look very similar to glucose molecules. They can also
  exist in α and β forms. Galactose reacts with glucose to make the dissacharide
  lactose.
- However, glucose and galactose cannot be easily converted into one another.
  Galactose cannot play the same part in respiration as glucose.
- Fructose reacts with glucose to make the dissacharide sucrose.
- Ribose and deoxyribose are pentoses. The ribose unit forms part of a
  nucleotide of RNA. The deoxyribose unit forms part of the
  nucleotide of DNA.
- Monosaccharides are rare in nature. Most sugars found in nature are
  disaccharides. These form when two monosaccharides react.
- The three most important disaccharides are sucrose, lactose and
  maltose.
- Disaccharides are soluble in water, but they are too big to pass through the
  cell membrane by diffusion.
- This is a hydrolysis reaction and is the reverse of a condensation
  reaction. It releases energy.
- Monosaccharides are converted into disaccharides in the cell by condensation
  reactions. Further condensation reactions result in the formation of
  polysaccharides. These are giant molecules which, importantly, are too
  big to escape from the cell. These are broken down by hydrolysis into
  monosaccharides when energy is needed by the cell.
- Monosaccharides can undergo a series of condensation reactions, adding one
  unit after another to the chain until very large molecules (polysaccharides) are
  formed. This is called condensation polymerisation, and the building
  blocks are called monomers. The properties of a polysaccharide molecule
  depend on:
  
  its length (though they are usually very long)
  the extent of any branching (addition of units to the side of the chain
  rather than one of its ends)
  any folding which results in a more compact molecule
  whether the chain is 'straight' or 'coiled'
- Starch is often produced in plants as a way of storing energy. It exists in two
  forms: amylose and amylopectin
- Amylose is an unbranched polymer of α-glucose. The molecules coil into a helical
  structure. It forms a colloidal suspension in hot water. Amylopectin is a
  branched polymer of α-glucose. It is completely insoluble in water.
- Glycogen is amylopectin with very short distances between the branching
  side-chains.
- Inside the cell, glucose can be polymerised to make glycogen which acts as a
  carbohydrate energy store.
- Cellulose is a third polymer made from glucose. But this time it's made from
  β-glucose molecules and the polymer molecules are 'straight'.
- Cellulose serves a very different purpose in nature to starch and glycogen.
  It makes up the cell walls in plant cells. These are much tougher than cell
  membranes. This toughness is due to the arrangement of glucose units in the
  polymer chain and the hydrogen-bonding between neighbouring chains.
- Cellulose is not hydrolysed easily and, therefore, cannot be digested so it is
  not a source of energy for humans.

Sugars & Polysaccharides

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D and L
designations are based on the configuration about the single asymmetric
carbon in glyceraldehyde.
D &
L sugars are mirror images of one another.
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- Monosaccharides - simple
  sugars, with multiple hydroxyl groups. Based on the number of carbons
  (e.g., 3, 4, 5, or 6) a monosaccharide is a triose, tetrose, pentose, or hexose,
  etc.
  
  Disaccharides - two
  monosaccharides covalently linked
  
  Oligosaccharides - a few
  monosaccharides covalently linked.
  
  Polysaccharides - polymers
  consisting of chains of monosaccharide or disaccharide units.
- For sugars with more than one chiral center, the D or L designation refers to the asymmetric carbon farthest from the aldehyde or keto
  group.
  Most naturally occurring sugars are D isomers.

Rubber Polymers

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Rubber polymers

Rubber is an example of an elastomer type polymer, where the polymer has the
ability to return to its original shape after being stretched or deformed.
The elastic properties arise from the its ability to stretch the chains apart,
but when the tension is released the chains snap back to the original position.
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- Natural rubber is an addition polymer
- Natural rubber is from the monomer isoprene (2-methyl-1,3-butadiene). Since
  isoprene has two double bonds, it still retains one of them after the
  polymerization reaction. Natural rubber has the cis configuration for the methyl
  groups.
- Charles Goodyear accidentally discovered that by mixing sulfur and rubber, the
  properties of the rubber improved in being tougher, resistant to heat and cold,
  and increased in elasticity. This process was later called vulcanization
- Vulcanization causes shorter chains to cross link through the sulfur to longer
  chains.
- Some of the most commercially important addition polymers are the copolymers.
  These are polymers made by polymerizing a
  mixture of two or more monomers. An
  example is styrene-butadiene rubber (SBR) - which is a copolymer of
  1,3-butadiene and styrene which is mixed in a 3 to 1 ratio, respectively.
- More than 40% of the synthetic rubber production is SBR and is used in tire
  production. A tiny amount is used for bubble-gum in the unvulcanized form.
- . At the nipple end of the balloon, there is lots of rubber and therefore many,
  many polymer chains - still loosely coiled. These chains can be pierced without
  popping the balloon because the the chains can still be stretched. This is
  because they allow the skewer in between the chains without breaking the chains
  or the bonds that connect them. But on the sides of the balloon, these chains
  are stretched almost to their limit and very far apart. The piercing is too much
  for the stretched chains and they break apart., and the balloon pops.

Emulsion polymerization - Wikipedia, the free encyclopedia

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Emulsion Polymerization polymers

Emulsion polymerization is a type of radical polymerization that usually
starts with an emulsion
incorporating water, monomer, and surfactant. The most common type of
emulsion polymerization is an oil-in-water emulsion, in which droplets of
monomer (the oil) are emulsified (with surfactants) in a continuous phase of water.
Typical monomers are those that
undergo radical polymerization, are liquid or gaseous at reaction conditions,
and are poorly soluble in water.
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- A dispersion resulting from emulsion polymerization is often called a latex (especially if derived from a synthetic rubber) or
  an emulsion (even though "emulsion" strictly speaking refers to a dispersion of
  a liquid in water). These emulsions find applications in adhesives, paints, paper coating and textile coatings.
- Advantages of emulsion polymerization include:^[1]
  
  High molecular weight polymers can be made at fast
  polymerization rates. By contrast, in bulk and solution free radical polymerization, there
  is a tradeoff between molecular weight and polymerization rate.
  The continuous water phase is an excellent conductor of heat and allows the heat to be
  removed from the system, allowing many reaction methods to increase their rate.
  Since polymer molecules are contained within the
  particles, viscosity remains close
  to that of water and is not dependent on molecular weight.
  The final product can be used as is and does not generally need to be
  altered or processed.
  Surfactants and other polymerization adjuvants remain in the polymer or are difficult to
  remove
  For dry (isolated) polymers, water removal is an energy-intensive process
  Emulsion polymerizations are usually designed to operate at high conversion
  of monomer to polymer. This can result in significant chain transfer to
  polymer.
- The first "true" emulsion polymerizations, which used a surface-active agent and polymerization initiator,
  were conducted in the 1920s to polymerize isoprene.^[6]^[7]
- The Smith-Ewart-Harkins theory for the mechanism of free-radical emulsion
  polymerization is summarized by the following steps:
  
  A monomer is dispersed or emulsified
  in a solution of surfactant and water forming relatively large droplets of
  monomer in water.
  Excess surfactant creates micelles
  in the water.
  Small amounts of monomer diffuse through the water to the micelle.
  A water-soluble initiator is introduced into the water phase where it reacts
  with monomer in the micelles. (This characteristic differs from suspension polymerization where an
  oil-soluble initiator dissolves in the monomer, followed by polymer formation in
  the monomer droplets themselves.) This is considered Smith-Ewart Interval 1.
  The total surface area of the micelles is much greater than the total
  surface area of the fewer, larger monomer droplets; therefore the initiator
  typically reacts in the micelle and not the monomer droplet.
  Monomer in the micelle quickly polymerizes and the growing chain terminates.
  At this point the monomer-swollen micelle has turned into a polymer particle.
  When both monomer droplets and polymer particles are present in the system, this
  is considered Smith-Ewart Interval 2.
  More monomer from the droplets diffuses to the growing particle, where more
  initiators will eventually react.
  Eventually the free monomer droplets disappear and all remaining monomer is
  located in the particles. This is considered Smith-Ewart Interval 3.
  Depending on the particular product and monomer, additional monomer and
  initiator may be continuously and slowly added to maintain their levels in the
  system as the particles grow.
  The final product is a dispersion of polymer particles
  in water. It can also be known as a polymer colloid, a latex, or commonly and inaccurately as an
  'emulsion'.
- Both thermal and redox generation of free radicals have been used in
  emulsion polymerization. Persulfate salts are commonly used in both initiation modes. The persulfate ion
  readily breaks up into sulfate radical ions above about 50°C, providing a
  thermal source of initiation.
- Emulsion polymerizations have been used in batch, semi-batch, and continuous
  processes. The choice depends on the properties desired in the final polymer or
  dispersion and on the economics of the product. Modern process control schemes
  have enabled the development of complex reaction processes, with ingredients
  such as initiator, monomer, and surfactant added at the beginning, during, or at
  the end of the reaction.
- Colloidal stability is a factor in
  design of an emulsion polymerization process. For dry or isolated products, the
  polymer dispersion must be isolated, or converted into solid form. This can be
  accomplished by simple heating of the dispersion until all water evaporates. More
  commonly, the dispersion is destabilized (sometimes called "broken") by addition
  of a multivalent cation. Alternatively, acidification will
  destabilize a dispersion with a carboxylic acid surfactant. These techniques
  may be employed in combination with application of shear to increase the rate of
  destabilization. After isolation of the polymer, it is usually washed, dried,
  and packaged.
- Ethylene and other simple olefins must be
  polymerized at very high pressures (up to 800 bar).
- Copolymerization is common in emulsion
  polymerization. The same rules and comonomer pairs that exist in radical
  polymerization operate in emulsion polymerization.
- Monomers with greater aqueous solubility will tend to partition in the aqueous phase and not
  in the polymer particle. They will not get incorporated as readily in the
  polymer chain as monomers with lower aqueous solubility.
- Ethylene and other olefins are used as minor comonomers in emulsion
  polymerization, notably in vinyl acetate copolymers.
- Redox initiation takes place when an oxidant such as a persulfate salt, a reducing agent such as
  glucose, Rongalite, or sulfite, and a redox catalyst such as an
  iron compound are all included in the polymerization recipe. Redox recipes are
  not limited by temperature and are used for polymerizations that take place
  below 50°C.
- Selection of the correct surfactant is critical to the development of any
  emulsion polymerization process. The surfactant must enable a fast rate of
  polymerization, minimize coagulum or
  fouling in the reactor and other
  process equipment, prevent an unacceptably high viscosity during polymerization
  (which leads to poor heat transfer), and maintain or even improve properties in
  the final product such as tensile strength, gloss, and water absorption
- Anionic, nonionic, and cationic surfactants
  have been used, although anionic surfactants are by far most prevalent.
- Examples of surfactants commonly used in emulsion polymerization include fatty acids,
  sodium
  lauryl sulfate, and alpha olefin sulfonate.
- Some grades of poly(vinyl alcohol) and other water soluble polymers can
  promote emulsion polymerization even though they do not typically form micelles
  and do not act as surfactants (for example, they do not lower surface tension). It is
  believed that these polymers graft onto growing polymer particles and stabilize
  them.^[12]
- Other ingredients found in emulsion polymerization include chain
  transfer agents, buffering agents, and inert salts. Preservatives are added to
  products sold as liquid dispersions to retard bacterial growth. These are
  usually added after polymerization, however.
- Polymers produced by emulsion polymerization can be divided into three rough
  categories.
  
  Synthetic rubber
  Some grades of styrene-butadiene
  (SBR)
  Some grades of Polybutadiene
  Polychloroprene (Neoprene)
  Nitrile rubber
  Acrylic
  rubber
  Fluoroelastomer
  (FKM)
  Plastics
  Some grades of PVC
  Some grades of polystyrene
  
  Some grades of PMMA
  Acrylonitrile-butadiene-styrene terpolymer (ABS)
  Polyvinylidene fluoride
  PTFE
  Dispersions (i.e. polymers sold as aqueous dispersions)
  polyvinyl
  acetate
  polyvinyl acetate copolymers
  latexacrylic paint
  Styrene-butadiene
  VAE (vinyl acetate - ethylene copolymers)

Polymerization catalysts past, present, and future

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Polymers catalysts polymerization

The most common polymers are polyolefins, especially polyethylene (better
known as Polythene, although this is a trade name owned by DuPont) and
polypropylene. However, efficient ways of producing these vital materials are
only the result of recent discoveries and have been dependant on the chemistry
of catalysts.
Since the 1950s, the production of polyolefins has depended on the use of
Ziegler-Natta catalysts.
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- Ziegler-Natta catalysts are based on a mixture of a transition metal, commonly a
  titanium compound, and an alkali metal, most commonly aluminium oxide.
- their products have variable physical properties. To this day, the systems are
  little understood, but the monomers (polymer starting materials) react through a
  number of reaction sites on the catalyst. Unfortunately, this means the polymer
  can grow from many sites and at different rates, leading to a very wide
  distribution in the molecular weight, based on the polymer chain length.
- Modern life has demanded more of the humble polymer. We want polymers that are
  stronger than steel, lighter than aluminium, and can be dyed any colour
  imaginable
- Metallocenes are positively charged metal ions, most commonly Titanium or
  Zirconium, sandwiched between two negatively charged cyclopentadienyl rings (see
  fig). Their big advantage over the Ziegler-Natta systems is that they catalyse
  the reaction of olefins through only one reactive site. Due to this “single
  site” reaction, the polymerization continues in a far more controllable fashion,
  leading to polymers with narrow ranges of molecular weight and, more
  importantly, predictable and desirable properties.
- it has been found that changing the ligands (functional groups attached to the
  metal) upon the metallocene molecule can controllably affect the properties of
  the polymer.
- The drawback of metallocene catalysts is that they are unable to polymerize
  polar molecules, such as common acrylics or vinyl chloride. This is due to the
  metallocenes’ oxophilicity – their propensity for binding to oxygen.
- Catalysts using late transition metals – those metals from groups 6 and higher
  in the Periodic Table – have become increasingly utilized. These compounds have
  good polymerization activity, although slightly less than metallocenes. However,
  crucially they can polymerize reactions with polar monomers.
- The most commercially advanced of this type of catalysts are the Brookhart
  catalysts [6], which are diimine complexes of palladium or nickel (see fig).

What are Ziegler-Natta Catalysts?

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Ziegler-Natta Catalysts Ziegler-Natta Catalysts polymerization

It was discovered that Group IV metals, especially titanium, were effective
polymerization catalysts for ethylene. Following Ziegler’s successful
preparation of linear polyethylene in 1953, Giulio Natta prepared and isolated
isotactic (crystalline) polypropylene at the Milan Polytechnic Institute. This
was immediately recognized for its practical importance. Ziegler and Natta
shared the Nobel Prize in Chemistry in 1963.
A Ziegler-Natta catalyst is composed of at least two parts: a transition metal
component and a main group metal alkyl compound. The transition metal component
is usually either titanium or vanadium. The main group metal alkyl compound is
usually an aluminum alkyl. In common practice, the titanium component is called
"the catalyst’ and the aluminum alkyl is called "the co-catalyst".
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- In some instances, especially for catalyzing the polymerization of propylene, a
  third component is used. This component is used to control stereoregularity
- Today, Ziegler-Natta catalysts are used worldwide to produce the following
  classes of polymers from alpha olefins:
  
  High density polyethylene (HDPE)
  Linear low density polyethylene (LLDPE)
  Ultra-high molecular weight polyethylene (UHMWPE)
  Polypropylene (PP)--homopolymer, random copolymer and high impact copolymers
  
  Thermoplastic polyolefins (TPO’s)
  Ethylene propylene diene monomer polymers (EPDM)
  Polybutene (PB)

Addition Polymers

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Addition Polymerization polymers

Addition polymers are usually made from molecules that have the following
general structure:

Different W, X, Y, and Z groups distinguish one addition polymer from
another.
In the first stage, a substance is split into two identical parts, each with an
unpaired electron. (Peroxides, which contain an O-O bond, are often used in this
role.) A molecule with an unpaired electron is called a free radical. The free
radical then initiates the reaction sequence by forming a bond to one of the
carbon atoms in the double bond of the monomer. One electron for this new bond
comes from the free radical, and the second electron for the new bond comes from
one of the two bonds between the carbon atoms. The remaining electron from the
broken bond shifts to the carbon atom on the far side of the molecule, away from
the newly formed bond, forming a new free radical. Each half-headed arrow
indicates the shift of one electron.
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- The chain begins to grow--propagate, stage two--when the new free radical formed
  in the initiation stage reacts with another monomer to add two more carbon
  atoms. This process repeats over and over again
- It can be terminated--stage three--when any two free radicals combine, thus
  pairing their unpaired electrons and forming a covalent bond that links two
  chains together.
- Polyethylene molecules made with the free radical initiation process tend to
  form branches that keep the molecules from fitting closely together. Techniques
  have been developed that use catalysts, like Cr₂O₃, to
  make polyethylene molecules with very few branches.
- yielding a high-density polyethylene, HDPE, that is more opaque, harder, and
  stronger than the low-density polyethylene, LDPE, made with free radical
  initiation.

Nucleotides, Polymerization of DNA

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polynucleotides DNA

Nucleic acids are linear, unbranched polymers of nucleotides
Nucleotides consist of three parts:
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- two purines, called adenine (A) and guanine
  (G)
  two pyrimidines, called thymine (T) and cytosine
  (C)
  The same purines, adenine (A) and guanine (G).
  RNA also uses the pyrimidine cytosine (C), but instead of
  thymine, it uses the pyrimidine uracil (U).
- A five-carbon sugar (hence a pentose). Two kinds are found:
  Deoxyribose, which has a hydrogen atom attached to its #2 carbon atom
  (designated 2')
  Ribose, which has a hydroxyl group atom there
- A nitrogen-containing ring structure called a base. The base is attached
  to the 1' carbon atom of the pentose. In DNA, four different bases are
  found:
- The combination of a base and a pentose is called a nucleoside.
- One (as shown in the first figure), two, or three phosphate groups. These
  are attached to the 5' carbon atom of the pentose.
- The nucleic acids, both DNA and RNA, consist of polymers of nucleotides. The
  nucleotides are linked covalently between the 3' carbon atom of the pentose and
  the phosphate group attached to the 5' carbon of the adjacent pentose.
- Most intact DNA molecules are made up of two strands of polymer,
  forming a "double helix".
  
  RNA molecules, while single-stranded, usually contain regions where two
  portions of the strand twist around each other to form helical regions.

Becky Kriger's Public Library

General Ultracapacitor Information

SolRayo's Ultracapacitor Research

"Elements of Chemistry: Polymers and Plastics"

About plasticizers

Copolymerization

Effects of Temperature on Polymers

Turning Plastics Back to Oil

On oil and plastic

How are Plastic Bottles Made ? A Start to Finish Process

How Is Nylon Made?

The Science of Nylon - Spinning the Elements

How are polymers made? : Scientific American

Carbohydrates and Polysaccharides

Sugars & Polysaccharides

Rubber Polymers

Emulsion polymerization - Wikipedia, the free encyclopedia

Polymerization catalysts past, present, and future

What are Ziegler-Natta Catalysts?

Addition Polymers

Nucleotides, Polymerization of DNA

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