Mixed Science

The Iron Pagoda of Kaifeng, China, built in 1049 AD

Wooden five-story pagoda of Hōryū-ji in Japan, built in the 7th century, one of the oldest wooden buildings in the world.

Wooden three-story pagoda of Ichijō-ji in Japan, built in 1171 AD

One Pillar Pagoda, Hanoi, Vietnam.

The nine-story Xumi Pagoda, Hebei, China, built in 636 AD

Taipei 101 in Taipei, Taiwan

The Bombardier Pagoda at the Indianapolis Motor Speedway

A pagoda is the general term in the English language for a tiered tower with multiple eaves common in China, Japan, Korea, Vietnam, Nepal and other parts of Asia. Some pagodas are used as Taoist houses of worship. Most pagodas were built to have a religious function, most commonly Buddhist, and were often located in or near temples. This term may refer to other religious structures in some countries. In Vietnam, pagoda is a more generic term referring to a place of worship, although pagoda is not an accurate word to describe a Buddhist temple. The modern pagoda is an evolution of the Ancient Indian stupa, a tomb-like structure where sacred relics could be kept safe and venerated.^[1] The architectural structure of the stupa has spread across Asia, taking on many diverse forms as details specific to d

History

The origin of the pagoda can be traced to the Indian stupa (3rd century BC).^[3] The stupa, a dome shaped monument, was used in India as a commemorative monument associated with storing sacred relics.^[3] The stupa emerged as a distinctive style of Indian architecture and was adopted in Southeast and East Asia,^[4] where it became prominent as a Buddhist monument used for enshrining sacred relics.^[3] In East Asia, the architecture of Chinese towers and Chinese pavilions blended into pagoda architecture, eventually also spreading to Southeast Asia. The pagoda's original purpose was to house relics and sacred writings.^[5] This purpose was popularized due to the efforts of Buddhist missionaries, pilgrims, rulers, and ordinary devotees to seek out, distribute, and extol Buddhist relics.^[6]

[edit] Symbolism

Chinese iconography is noticeable in Chinese pagoda as well as other East Asian pagoda architectures. The image of the Shakyamuni Buddha in the abhaya mudra is also noticeable in some Pagodas. Buddhist iconography can be observed throughout the pagoda symbolism.^[7]
In an article on Buddhist elements in Han art, Wu Hung suggests that in these tombs, Buddhist iconography was so well incorporated into native Chinese traditions that a unique system of symbolism had been developed.^[8]

[edit] Architecture

Pagodas attract lightning strikes because of their height. This tendency may have played a role in their perception as spiritually charged places. Many pagodas have a decorated finial at the top of the structure. The finial is designed in such a way as to have symbolic meaning within Buddhism; for example, it may include designs representing a lotus. The finial also functions as a lightning rod, and thus helps to both attract lightning and protect the pagoda from lightning damage. Early pagodas were constructed out of wood, but steadily progressed to sturdier materials, which helped protect against fires and rot.
Pagodas traditionally have an odd number of levels, a notable exception being the eighteenth century pagoda "folly" designed by Sir William Chambers at Kew Gardens in London.
ifferent regions are incorporated into the overall design.

A polymer is a large molecule (macromolecule) composed of repeating structural units. These subunits are typically connected by covalent chemical bonds. Although the term polymer is sometimes taken to refer to plastics, it actually encompasses a large class of natural and synthetic materials with a wide variety of properties.
Because of the extraordinary range of properties of polymeric materials,^[2] they play an essential and ubiquitous role in everyday life.^[3] This role ranges from familiar synthetic plastics and elastomers to natural biopolymers such as nucleic acids and proteins that are essential for life.
Natural polymeric materials such as shellac, amber, and natural rubber have been used for centuries. A variety of other natural polymers exist, such as cellulose, which is the main constituent of wood and paper. The list of synthetic polymers includes synthetic rubber, Bakelite, neoprene, nylon, PVC, polystyrene, polyethylene, polypropylene, polyacrylonitrile, PVB, silicone, and many more.
Most commonly, the continuously linked backbone of a polymer used for the preparation of plastics consists mainly of carbon atoms. A simple example is polyethylene, whose repeating unit is based on ethylene monomer. However, other structures do exist; for example, elements such as silicon form familiar materials such as silicones, examples being silly putty and waterproof plumbing sealant. Oxygen is also commonly present in polymer backbones, such as those of polyethylene glycol, polysaccharides (in glycosidic bonds), and DNA (in phosphodiester bonds).
Polymers are studied in the fields of polymer chemistry, polymer physics, and polymer science.

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[edit] Etymology

The word polymer is derived from the Greek words πολύ- - poly- meaning "many"; and μέρος - meros meaning "part". The term was coined in 1833 by Jöns Jacob Berzelius, although his definition of a polymer was quite different from the modern definition.

[edit] Historical development

Starting in 1811, Henri Braconnot did pioneering work in derivative cellulose compounds, perhaps the earliest important work in polymer science. The development of vulcanization later in the nineteenth century improved the durability of the natural polymer rubber, signifying the first popularized semi-synthetic polymer. In 1907, Leo Baekeland created the first completely synthetic polymer, Bakelite, by reacting phenol and formaldehyde at precisely controlled temperature and pressure. Bakelite was then publicly introduced in 1909.
Despite significant advances in synthesis and characterization of polymers, a correct understanding of polymer molecular structure did not emerge until the 1920s. Before then, scientists believed that polymers were clusters of small molecules (called colloids), without definite molecular weights, held together by an unknown force, a concept known as association theory. In 1922, Hermann Staudinger proposed that polymers consisted of long chains of atoms held together by covalent bonds, an idea which did not gain wide acceptance for over a decade and for which Staudinger was ultimately awarded the Nobel Prize. Work by Wallace Carothers in the 1920s also demonstrated that polymers could be synthesized rationally from their constituent monomers. An important contribution to synthetic polymer science was made 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,^[4] 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.

[edit] Polymer synthesis

Polymerization is the process of combining many small molecules known as monomers into a covalently bonded chain. During the polymerization process, some chemical groups may be lost from each monomer. This is the case, for example, in the polymerization of PET polyester. The monomers are terephthalic acid (HOOC-C₆H₄-COOH) and ethylene glycol (HO-CH₂-CH₂-OH) but the repeating unit is -OC-C₆H₄-COO-CH₂-CH₂-O-, which corresponds to the combination of the two monomers with the loss of two water molecules. The distinct piece of each monomer that is incorporated into the polymer is known as a repeat unit or monomer residue.

[edit] Laboratory synthesis

Laboratory synthetic methods are generally divided into two categories, step-growth polymerization and chain-growth polymerization.^[5] The essential difference between the two is that in chain growth polymerization, monomers are added to the chain one at a time only,^[6] whereas in step-growth polymerization chains of monomers may combine with one another directly.^[7] However, some newer methods such as plasma polymerization do not fit neatly into either category. Synthetic polymerization reactions may be carried out with or without a catalyst. Laboratory synthesis of biopolymers, especially of proteins, is an area of intensive research.

[edit] Biological synthesis

There are three main classes of biopolymers: polysaccharides, polypeptides, and polynucleotides. In living cells, they may be synthesized by enzyme-mediated processes, such as the formation of DNA catalyzed by DNA polymerase. The synthesis of proteins involves multiple enzyme-mediated processes to transcribe genetic information from the DNA to RNA and subsequently translate that information to synthesize the specified protein from amino acids. The protein may be modified further following translation in order to provide appropriate structure and functioning.

[edit] Modification of natural polymers

Many commercially important polymers are synthesized by chemical modification of naturally occurring polymers. Prominent examples include the reaction of nitric acid and cellulose to form nitrocellulose and the formation of vulcanized rubber by heating natural rubber in the presence of sulfur.

[edit] 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.^[8] 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 macro-scale, they describe how the bulk polymer interacts with other chemicals and solvents.

[edit] Monomers and repeat units

The identity of the monomer residues (repeat units) comprising a polymer is its first and most important attribute. Polymer nomenclature is generally based upon the type of monomer residues comprising the polymer. Polymers that contain only a single type of repeat unit are known as homopolymers, while polymers containing a mixture of repeat units are known as copolymers. Poly(styrene), for example, is composed only of styrene monomer residues, and is therefore classified as a homopolymer. Ethylene-vinyl acetate, on the other hand, contains more than one variety of repeat unit and is thus a copolymer. Some biological polymers are composed of a variety of different but structurally related monomer residues; for example, polynucleotides such as DNA are composed of a variety of nucleotide subunits.
A polymer molecule containing ionizable subunits is known as a polyelectrolyte or ionomer.

[edit] Microstructure

The microstructure of a polymer (sometimes called configuration) relates to the physical arrangement of monomer residues along the backbone of the chain.^[9] These are the elements of polymer structure that require the breaking of a covalent bond in order to change. Structure has a strong influence on the other properties of a polymer. For example, two samples of natural rubber may exhibit different durability, even though their molecules comprise the same monomers.

[edit] Polymer architecture

An important microstructural feature determining polymer properties is the polymer architecture.^[10] The simplest polymer architecture is a linear chain: a single backbone with no branches. A related unbranching architecture is a ring polymer. A branched polymer molecule is composed of a main chain with one or more substituent side chains or branches. Special types of branched polymers include star polymers, comb polymers, brush polymers, dendronized polymers, ladders, and dendrimers.^[10]
Branching of polymer chains affects the ability of chains to slide past one another by altering intermolecular forces, in turn affecting bulk physical polymer properties. Long chain branches may increase polymer strength, toughness, and the glass transition temperature (T_g) due to an increase in the number of entanglements per chain. The effect of such long-chain branches on the size of the polymer in solution is characterized by the branching index. Random length and atactic short chains, on the other hand, may reduce polymer strength due to disruption of organization and may likewise reduce the crystallinity of the polymer.
A good example of this effect is related to the range of physical attributes of polyethylene. High-density polyethylene (HDPE) has a very low degree of branching, is quite stiff, and is used in applications such as milk jugs. Low-density polyethylene (LDPE), on the other hand, has significant numbers of both long and short branches, is quite flexible, and is used in applications such as plastic films.
Dendrimers are a special case of polymer where every monomer unit is branched. This tends to reduce intermolecular chain entanglement and crystallization. Alternatively, dendritic polymers are not perfectly branched but share similar properties to dendrimers due to their high degree of branching.
The architecture of the polymer is often physically determined by the functionality of the monomers from which it is formed.^[11] This property of a monomer is defined as the number of reaction sites at which may form chemical covalent bonds. The basic functionality required for forming even a linear chain is two bonding sites. Higher functionality yields branched or even crosslinked or networked polymer chains.
An effect related to branching is chemical crosslinking - the formation of covalent bonds between chains. Crosslinking tends to increase T_g and increase strength and toughness. Among other applications, this process is used to strengthen rubbers in a process known as vulcanization, which is based on crosslinking by sulfur. Car tires, for example, are highly crosslinked in order to reduce the leaking of air out of the tire and to toughen their durability. Eraser rubber, on the other hand, is not crosslinked to allow flaking of the rubber and prevent damage to the paper. Polymerization of pure sulfur at higher temperatures also explains why sulfur becomes more viscous with elevated temperatures in its molten state.^[12]

A cross-link suggests a branch point from which four or more distinct chains emanate. A polymer molecule with a high degree of crosslinking is referred to as a polymer network.^[13] Sufficiently high crosslink concentrations may lead to the formation of an infinite network, also known as a gel, in which networks of chains are of unlimited extent—essentially all chains have linked into one molecule.^[14]

[edit] Chain length

The physical properties^[15] of a polymer are strongly dependent on the size or length of the polymer chain.^[16] For example, as chain length is increased, melting and boiling temperatures increase quickly.^[16] Impact resistance also tends to increase with chain length, as does the viscosity, or resistance to flow, of the polymer in its melt state.^[17] Chain length is related to melt viscosity roughly as 1:10^3.2, so that a tenfold increase in polymer chain length results in a viscosity increase of over 1000 times^{[citation needed]}. Increasing chain length furthermore tends to decrease chain mobility, increase strength and toughness, and increase the glass transition temperature (T_g)^{[citation needed]}. This is a result of the increase in chain interactions such as Van der Waals attractions and entanglements that come with increased chain length^{[citation needed]}. These interactions tend to fix the individual chains more strongly in position and resist deformations and matrix breakup, both at higher stresses and higher temperatures^{[citation needed]}.
A common means of expressing the length of a chain is the degree of polymerization, which quantifies the number of monomers incorporated into the chain.^[18][19] As with other molecules, a polymer's size may also be expressed in terms of molecular weight. Since synthetic polymerization techniques typically yield a polymer product including a range of molecular weights, the weight is often expressed statistically to describe the distribution of chain lengths present in the same. Common examples are the number average molecular weight and weight average molecular weight.^[20][21] The ratio of these two values is the polydispersity index, commonly used to express the "width" of the molecular weight distribution.^[22] A final measurement is contour length, which can be understood as the length of the chain backbone in its fully extended state.^[23]
The flexibility of an unbranched chain polymer is characterized by its persistence length.

[edit] Monomer arrangement in copolymers

Monomers within a copolymer may be organized along the backbone in a variety of ways.

• Alternating copolymers possess regularly alternating monomer residues:^[24] [AB...]_n (2).
• Periodic copolymers have monomer residue types arranged in a repeating sequence: [A_nB_m...] m being different from n .
• Statistical copolymers have monomer residues arranged according to a known statistical rule. A statistical copolymer in which the probability of finding a particular type of monomer residue at an particular point in the chain is independent of the types of surrounding monomer residue may be referred to as a truly random copolymer^[25][26] (3).
• Block copolymers have two or more homopolymer subunits linked by covalent bonds^[24] (4). Polymers with two or three blocks of two distinct chemical species (e.g., A and B) are called diblock copolymers and triblock copolymers, respectively. Polymers with three blocks, each of a different chemical species (e.g., A, B, and C) are termed triblock terpolymers.
• Graft or grafted copolymers contain side chains that have a different composition or configuration than the main chain.(5)

[edit] Tacticity

Tacticity describes the relative stereochemistry of chiral centers in neighboring structural units within a macromolecule. There are three types: isotactic (all substituents on the same side), atactic (random placement of substituents), and syndiotactic (alternating placement of substituents).

[edit] Polymer morphology

Polymer morphology generally describes the arrangement and microscale ordering of polymer chains in space.

[edit] Crystallinity

When applied to polymers, the term crystalline has a somewhat ambiguous usage. In some cases, the term crystalline finds identical usage to that used in conventional crystallography. For example, the structure of a crystalline protein or polynucleotide, such as a sample prepared for x-ray crystallography, may be defined in terms of a conventional unit cell composed of one or more polymer molecules with cell dimensions of hundreds of angstroms or more.
A synthetic polymer may be lightly described as crystalline if it contains regions of three-dimensional ordering on atomic (rather than macromolecular) length scales, usually arising from intramolecular folding and/or stacking of adjacent chains. Synthetic polymers may consist of both crystalline and amorphous regions; the degree of crystallinity may be expressed in terms of a weight fraction or volume fraction of crystalline material. Few synthetic polymers are entirely crystalline.^[27]
The crystallinity of polymers is characterized by their degree of crystallinity, ranging from zero for a completely non-crystalline polymer to one for a theoretical completely crystalline polymer. Polymers with microcrystalline regions are generally tougher (can be bent more without breaking) and more impact-resistant than totally amorphous polymers.^[28]
Polymers with a degree of crystallinity approaching zero or one will tend to be transparent, while polymers with intermediate degrees of crystallinity will tend to be opaque due to light scattering by crystalline or glassy regions. Thus for many polymers, reduced crystallinity may also be associated with increased transparency.

[edit] Chain conformation

The space occupied by a polymer molecule is generally expressed in terms of radius of gyration, which is an average distance from the center of mass of the chain to the chain itself. Alternatively, it may be expressed in terms of pervaded volume, which is the volume of solution spanned by the polymer chain and scales with the cube of the radius of gyration.^[29]

[edit] Mechanical properties

The bulk properties of a polymer are those most often of end-use interest. These are the properties that dictate how the polymer actually behaves on a macroscopic scale.

[edit] Tensile strength

The tensile strength of a material quantifies how much stress the material will endure before suffering permanent deformation.^[30][31] This is very important in applications that rely upon a polymer's physical strength or durability. For example, a rubber band with a higher tensile strength will hold a greater weight before snapping. In general, tensile strength increases with polymer chain length and crosslinking of polymer chains.

[edit] Young's modulus of elasticity

Young's Modulus quantifies the elasticity of the polymer. It is defined, for small strains, as the ratio of rate of change of stress to strain. Like tensile strength, this is highly relevant in polymer applications involving the physical properties of polymers, such as rubber bands. The modulus is strongly dependent on temperature.

[edit] Transport properties

Transport properties such as diffusivity relate to how rapidly molecules move through the polymer matrix. These are very important in many applications of polymers for films and membranes.

[edit] Phase behavior

[edit] Melting point

The term melting point, when applied to polymers, suggests not a solid-liquid phase transition but a transition from a crystalline or semi-crystalline phase to a solid amorphous phase. Though abbreviated as simply T_m, the property in question is more properly called the crystalline melting temperature. Among synthetic polymers, crystalline melting is only discussed with regards to thermoplastics, as thermosetting polymers will decompose at high temperatures rather than melt.

[edit] Glass transition temperature

A parameter of particular interest in synthetic polymer manufacturing is the glass transition temperature (T_g), which describes the temperature at which amorphous polymers undergo a transition from a rubbery, viscous amorphous solid, to a brittle, glassy amorphous solid. The glass transition temperature may be engineered by altering the degree of branching or crosslinking in the polymer or by the addition of plasticizer.^[32]

[edit] Mixing behavior

In general, polymeric mixtures are far less miscible than mixtures of small molecule materials. This effect results from the fact that the driving force for mixing is usually entropy, not interaction energy. In other words, miscible materials usually form a solution not because their interaction with each other is more favorable than their self-interaction, but because of an increase in entropy and hence free energy associated with increasing the amount of volume available to each component. This increase in entropy scales with the number of particles (or moles) being mixed. Since polymeric molecules are much larger and hence generally have much higher specific volumes than small molecules, the number of molecules involved in a polymeric mixture is far smaller than the number in a small molecule mixture of equal volume. The energetics of mixing, on the other hand, is comparable on a per volume basis for polymeric and small molecule mixtures. This tends to increase the free energy of mixing for polymer solutions and thus make solvation less favorable. Thus, concentrated solutions of polymers are far rarer than those of small molecules.
Furthermore, the phase behavior of polymer solutions and mixtures is more complex than that of small molecule mixtures. Whereas most small molecule solutions exhibit only an upper critical solution temperature phase transition, at which phase separation occurs with cooling, polymer mixtures commonly exhibit a lower critical solution temperature phase transition, at which phase separation occurs with heating.
In dilute solution, the properties of the polymer are characterized by the interaction between the solvent and the polymer. In a good solvent, the polymer appears swollen and occupies a large volume. In this scenario, intermolecular forces between the solvent and monomer subunits dominate over intramolecular interactions. In a bad solvent or poor solvent, intramolecular forces dominate and the chain contracts. In the theta solvent, or the state of the polymer solution where the value of the second virial coefficient becomes 0, the intermolecular polymer-solvent repulsion balances exactly the intramolecular monomer-monomer attraction. Under the theta condition (also called the Flory condition), the polymer behaves like an ideal random coil. The transition between the states is known as a coil-globule transition.

[edit] Inclusion of plasticizers

Inclusion of plasticizers tends to lower T_g and increase polymer flexibility. Plasticizers are generally small molecules that are chemically similar to the polymer and create gaps between polymer chains for greater mobility and reduced interchain interactions. A good example of the action of plasticizers is related to polyvinylchlorides or PVCs. A uPVC, or unplasticized polyvinylchloride, is used for things such as pipes. A pipe has no plasticizers in it, because it needs to remain strong and heat-resistant. Plasticized PVC is used for clothing for a flexible quality. Plasticizers are also put in some types of cling film to make the polymer more flexible.

[edit] 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 polyethylene can have a lower melting temperature compared to other polymers.

[edit] Standardized polymer nomenclature

There are multiple conventions for naming polymer substances. Many commonly used polymers, such as those found in consumer products, are referred to by a common or trivial name. The trivial name is assigned based on historical precedent or popular usage rather than a standardized naming convention. Both the American Chemical Society (ACS)^[33] and IUPAC^[34] have proposed standardized naming conventions; the ACS and IUPAC conventions are similar but not identical.^[35] Examples of the differences between the various naming conventions are given in the table below:

Common name	ACS name	IUPAC name
Poly(ethylene oxide) or PEO	Poly(oxyethylene)	Poly(oxyethene)
Poly(ethylene terephthalate) or PET	Poly(oxy-1,2-ethanediyloxycarbonyl-1,4-phenylenecarbonyl)	Poly(oxyetheneoxyterephthaloyl)
Nylon 6	Poly[amino(1-oxo-1,6-hexanediyl)]	Poly[amino(1-oxohexan-1,6-diyl)]

In both standardized conventions, the polymers' names are intended to reflect the monomer(s) from which they are synthesized rather than the precise nature of the repeating subunit. For example, the polymer synthesized from the simple alkene ethene is called polyethylene, retaining the -ene suffix even though the double bond is removed during the polymerization process:

[edit] Polymer characterization

The characterization of a polymer requires several parameters which need to be specified. This is because a polymer actually consists of a statistical distribution of chains of varying lengths, and each chain consists of monomer residues which affect its properties.
A variety of lab techniques are used to determine the properties of polymers. Techniques such as wide angle X-ray scattering, small angle X-ray scattering, and small angle neutron scattering are used to determine the crystalline structure of polymers. Gel permeation chromatography is used to determine the number average molecular weight, weight average molecular weight, and polydispersity. FTIR, Raman and NMR can be used to determine composition. Thermal properties such as the glass transition temperature and melting point can be determined by differential scanning calorimetry and dynamic mechanical analysis. Pyrolysis followed by analysis of the fragments is one more technique for determining the possible structure of the polymer. Thermogravimetry is a useful technique to evaluate the thermal stability of the polymer. Detailed analyses of TG curves also allow us to know a bit of the phase segregation in polymers. Rheological properties are also commonly used to help determine molecular architecture (molecular weight, molecular weight distribution and branching)as well as to understand how the polymer will process, through measurements of the polymer in the melt phase. Another polymer characterization technique is Automatic Continuous Online Monitoring of Polymerization Reactions (ACOMP) which provides real-time characterization of polymerization reactions. It can be used as an analytical method in R&D, as a tool for reaction optimization at the bench and pilot plant level and, eventually, for feedback control of full-scale reactors. ACOMP measures in a model-independent fashion the evolution of average molar mass and intrinsic viscosity, monomer conversion kinetics and, in the case of copolymers, also the average composition drift and distribution. It is applicable in the areas of free radical and controlled radical homo- and copolymerization, polyelectrolyte synthesis, heterogeneous phase reactions, including emulsion polymerization, adaptation to batch and continuous reactors, and modifications of polymers.^[36][37][38]

[edit] Polymer degradation

Polymer degradation is a change in the properties—tensile strength, color, shape, or molecular weight—of a polymer or polymer-based product under the influence of one or more environmental factors, such as heat, light, chemicals and, in some cases, galvanic action. It is often due to the scission of polymer chain bonds via hydrolysis, leading to a decrease in the molecular mass of the polymer.
Although such changes are frequently undesirable, in some cases, such as biodegradation and recycling, they may be intended to prevent environmental pollution. Degradation can also be useful in biomedical settings. For example, a copolymer of polylactic acid and polyglycolic acid is employed in hydrolysable stitches that slowly degrade after they are applied to a wound.
The susceptibility of a polymer to degradation depends on its structure. Epoxies and chains containing aromatic functionalities are especially susceptible to UV degradation while polyesters are susceptible to degradation by hydrolysis, while polymers containing an unsaturated backbone are especially susceptible to ozone cracking. Carbon based polymers are more susceptible to thermal degradation than inorganic polymers such as polydimethylsiloxane and are therefore not ideal for most high-temperature applications. High-temperature matrices such as bismaleimides (BMI), condensation polyimides (with an O-C-N bond), triazines (with a nitrogen (N) containing ring), and blends thereof are susceptible to polymer degradation in the form of galvanic corrosion when bare carbon fiber reinforced polymer CFRP is in contact with an active metal such as aluminum in salt water environments.
The degradation of polymers to form smaller molecules may proceed by random scission or specific scission. The degradation of polyethylene occurs by random scission—a random breakage of the bonds that hold the atoms of the polymer together. When heated above 450 °C, polyethylene degrades to form a mixture of hydrocarbons. Other polymers, such as poly(alpha-methylstyrene), undergo specific chain scission with breakage occurring only at the ends. They literally unzip or depolymerize back to the constituent monomer.
The sorting of polymer waste for recycling purposes may be facilitated by the use of the Resin identification codes developed by the Society of the Plastics Industry to identify the type of plastic.

[edit] Product failure

In a finished product, such a change is to be prevented or delayed. Failure of safety-critical polymer components can cause serious accidents, such as fire in the case of cracked and degraded polymer fuel lines. Chlorine-induced cracking of acetal resin plumbing joints and polybutylene pipes has caused many serious floods in domestic properties, especially in the USA in the 1990s. Traces of chlorine in the water supply attacked vulnerable polymers in the plastic plumbing, a problem which occurs faster if any of the parts have been poorly extruded or injection molded. Attack of the acetal joint occurred because of faulty molding, leading to cracking along the threads of the fitting which is a serious stress concentration.
Polymer oxidation has caused accidents involving medical devices. One of the oldest known failure modes is ozone cracking caused by chain scission when ozone gas attacks susceptible elastomers, such as natural rubber and nitrile rubber. They possess double bonds in their repeat units which are cleaved during ozonolysis. Cracks in fuel lines can penetrate the bore of the tube and cause fuel leakage. If cracking occurs in the engine compartment, electric sparks can ignite the gasoline and can cause a serious fire.
Fuel lines can also be attacked by another form of degradation: hydrolysis. Nylon 6,6 is susceptible to acid hydrolysis, and in one accident, a fractured fuel line led to a spillage of diesel into the road. If diesel fuel leaks onto the road, accidents to following cars can be caused by the slippery nature of the deposit, which is like black ice.

The Bermuda Triangle, also known as the Devil's Triangle, is a region in the western part of the North Atlantic Ocean where a number of aircraft and surface vessels allegedly disappeared mysteriously. Popular culture has attributed these disappearances to the paranormal or activity by extraterrestrial beings.^[1] Documented evidence indicates that a significant percentage of the incidents were inaccurately reported or embellished by later authors, and numerous official agencies have stated that the number and nature of disappearances in the region is similar to that in any other area of ocean.^[2][3][4]

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The Triangle area

The boundaries of the triangle cover the Straits of Florida, the Bahamas and the entire Caribbean island area and the Atlantic east to the Azores. The more familiar triangular boundary in most written works has as its points somewhere on the Atlantic coast of Miami; San Juan, Puerto Rico; and the mid-Atlantic island of Bermuda, with most of the accidents concentrated along the southern boundary around the Bahamas and the Florida Straits.
The area is one of the most heavily traveled shipping lanes in the world, with ships crossing through it daily for ports in the Americas, Europe, and the Caribbean Islands. Cruise ships are also plentiful, and pleasure craft regularly go back and forth between Florida and the islands. It is also a heavily flown route for commercial and private aircraft heading towards Florida, the Caribbean, and South America from points north.

History

Origins

The earliest allegation of unusual disappearances in the Bermuda area appeared in a September 16, 1950 Associated Press article by Edward Van Winkle Jones.^[5] Two years later, Fate magazine published "Sea Mystery At Our Back Door",^[6] a short article by George X. Sand covering the loss of several planes and ships, including the loss of Flight 19, a group of five U.S. Navy TBM Avenger bombers on a training mission. Sand's article was the first to lay out the now-familiar triangular area where the losses took place. Flight 19 alone would be covered in the April 1962 issue of American Legion Magazine.^[7] It was claimed that the flight leader had been heard saying "We are entering white water, nothing seems right. We don't know where we are, the water is green, no white." It was also claimed that officials at the Navy board of inquiry stated that the planes "flew off to Mars." Sand's article was the first to suggest a supernatural element to the Flight 19 incident. In the February 1964 issue of Argosy, Vincent Gaddis's article "The Deadly Bermuda Triangle" argued that Flight 19 and other disappearances were part of a pattern of strange events in the region.^[8] The next year, Gaddis expanded this article into a book, Invisible Horizons.^[9]
Others would follow with their own works, elaborating on Gaddis's ideas: John Wallace Spencer (Limbo of the Lost, 1969, repr. 1973);^[10] Charles Berlitz (The Bermuda Triangle, 1974);^[11] Richard Winer (The Devil's Triangle, 1974),^[12] and many others, all keeping to some of the same supernatural elements outlined by Eckert.^[13]

Larry Kusche

Lawrence David Kusche, a research librarian from Arizona State University and author of The Bermuda Triangle Mystery: Solved (1975)^[14] argued that many claims of Gaddis and subsequent writers were often exaggerated, dubious or unverifiable. Kusche's research revealed a number of inaccuracies and inconsistencies between Berlitz's accounts and statements from eyewitnesses, participants, and others involved in the initial incidents. Kusche noted cases where pertinent information went unreported, such as the disappearance of round-the-world yachtsman Donald Crowhurst, which Berlitz had presented as a mystery, despite clear evidence to the contrary. Another example was the ore-carrier recounted by Berlitz as lost without trace three days out of an Atlantic port when it had been lost three days out of a port with the same name in the Pacific Ocean. Kusche also argued that a large percentage of the incidents that sparked allegations of the Triangle's mysterious influence actually occurred well outside it. Often his research was simple: he would review period newspapers of the dates of reported incidents and find reports on possibly relevant events like unusual weather, that were never mentioned in the disappearance stories.
Kusche concluded that:

• The number of ships and aircraft reported missing in the area was not significantly greater, proportionally speaking, than in any other part of the ocean.
• In an area frequented by tropical storms, the number of disappearances that did occur were, for the most part, neither disproportionate, unlikely, nor mysterious; furthermore, Berlitz and other writers would often fail to mention such storms.
• The numbers themselves had been exaggerated by sloppy research. A boat's disappearance, for example, would be reported, but its eventual (if belated) return to port may not have been.
• Some disappearances had, in fact, never happened. One plane crash was said to have taken place in 1937 off Daytona Beach, Florida, in front of hundreds of witnesses; a check of the local papers revealed nothing.
• The legend of the Bermuda Triangle is a manufactured mystery, perpetuated by writers who either purposely or unknowingly made use of misconceptions, faulty reasoning, and sensationalism.^[14]

Further responses

When the UK Channel 4 television program "The Bermuda Triangle" (c. 1992) was being produced by John Simmons of Geofilms for the Equinox series, the marine insurer Lloyd's of London was asked if an unusually large number of ships had sunk in the Bermuda Triangle area. Lloyd's of London determined that large numbers of ships had not sunk there.^[15]
United States Coast Guard records confirm their conclusion. In fact, the number of supposed disappearances is relatively insignificant considering the number of ships and aircraft that pass through on a regular basis.^[14]
The Coast Guard is also officially skeptical of the Triangle, noting that they collect and publish, through their inquiries, much documentation contradicting many of the incidents written about by the Triangle authors. In one such incident involving the 1972 explosion and sinking of the tanker SS V. A. Fogg in the Gulf of Mexico, the Coast Guard photographed the wreck and recovered several bodies,^[16] in contrast with one Triangle author's claim that all the bodies had vanished, with the exception of the captain, who was found sitting in his cabin at his desk, clutching a coffee cup.^[10]
The NOVA/Horizon episode The Case of the Bermuda Triangle, aired on June 27, 1976, was highly critical, stating that "When we've gone back to the original sources or the people involved, the mystery evaporates. Science does not have to answer questions about the Triangle because those questions are not valid in the first place... Ships and planes behave in the Triangle the same way they behave everywhere else in the world."^[17]
David Kusche pointed out a common problem with many of the Bermuda Triangle stories and theories: "Say I claim that a parrot has been kidnapped to teach aliens human language and I challenge you to prove that is not true. You can even use Einstein's Theory of Relativity if you like. There is simply no way to prove such a claim untrue. The burden of proof should be on the people who make these statements, to show where they got their information from, to see if their conclusions and interpretations are valid, and if they have left anything out."^[17]
Skeptical researchers, such as Ernest Taves^[18] and Barry Singer,^[19] have noted how mysteries and the paranormal are very popular and profitable. This has led to the production of vast amounts of material on topics such as the Bermuda Triangle. They were able to show that some of the pro-paranormal material is often misleading or inaccurate, but its producers continue to market it. Accordingly, they have claimed that the market is biased in favor of books, TV specials, and other media that support the Triangle mystery, and against well-researched material if it espouses a skeptical viewpoint.
Finally, if the Triangle is assumed to cross land, such as parts of Puerto Rico, the Bahamas, or Bermuda itself, there is no evidence for the disappearance of any land-based vehicles or persons.^{[citation needed]} The city of Freeport, located inside the Triangle, operates a major shipyard and an airport that handles 50,000 flights annually and is visited by over a million tourists a year.^[20]

Supernatural explanations

Triangle writers have used a number of supernatural concepts to explain the events. One explanation pins the blame on leftover technology from the mythical lost continent of Atlantis. Sometimes connected to the Atlantis story is the submerged rock formation known as the Bimini Road off the island of Bimini in the Bahamas, which is in the Triangle by some definitions. Followers of the purported psychic Edgar Cayce take his prediction that evidence of Atlantis would be found in 1968 as referring to the discovery of the Bimini Road. Believers describe the formation as a road, wall, or other structure, though geologists consider it to be of natural origin.^[21]
Other writers attribute the events to UFOs.^[22] This idea was used by Steven Spielberg for his science fiction film Close Encounters of the Third Kind, which features the lost Flight 19 aircrews as alien abductees.
Charles Berlitz, author of various books on anomalous phenomena, lists several theories attributing the losses in the Triangle to anomalous or unexplained forces.^[11]

Natural explanations

Compass variations

Compass problems are one of the cited phrases in many Triangle incidents. While some have theorized that unusual local magnetic anomalies may exist in the area,^[23] such anomalies have not been shown to exist. Compasses have natural magnetic variations in relation to the magnetic poles, a fact which navigators have known for centuries. Magnetic (compass) north and geographic (true) north are only exactly the same for a small number of places - for example, as of 2000 in the United States only those places on a line running from Wisconsin to the Gulf of Mexico.^[24] But the public may not be as informed, and think there is something mysterious about a compass "changing" across an area as large as the Triangle, which it naturally will.^[14]

Deliberate acts of destruction

Deliberate acts of destruction can fall into two categories: acts of war, and acts of piracy. Records in enemy files have been checked for numerous losses. While many sinkings have been attributed to surface raiders or submarines during the World Wars and documented in various command log books, many others suspected as falling in that category have not been proven. It is suspected that the loss of USS Cyclops in 1918, as well as her sister ships Proteus and Nereus in World War II, were attributed to submarines, but no such link has been found in the German records.
Piracy—the illegal capture of a craft on the high seas—continues to this day. While piracy for cargo theft is more common in the western Pacific and Indian oceans, drug smugglers do steal pleasure boats for smuggling operations, and may have been involved in crew and yacht disappearances in the Caribbean. Piracy in the Caribbean was common from about 1560 to the 1760s, and famous pirates included Edward Teach (Blackbeard) and Jean Lafitte.^{[citation needed]}

Gulf Stream

The Gulf Stream is an ocean current that originates in the Gulf of Mexico and then flows through the Straits of Florida into the North Atlantic. In essence, it is a river within an ocean, and, like a river, it can and does carry floating objects. It has a surface velocity of up to about 2.5 metres per second (5.6 mi/h).^[25] A small plane making a water landing or a boat having engine trouble can be carried away from its reported position by the current.

Human error

One of the most cited explanations in official inquiries as to the loss of any aircraft or vessel is human error.^[26] Whether deliberate or accidental, humans have been known to make mistakes resulting in catastrophe, and losses within the Bermuda Triangle are no exception. For example, the Coast Guard cited a lack of proper training for the cleaning of volatile benzene residue as a reason for the loss of the tanker SS V.A. Fogg in 1972^{[citation needed]}. Human stubbornness may have caused businessman Harvey Conover to lose his sailing yacht, the Revonoc, as he sailed into the teeth of a storm south of Florida on January 1, 1958.^[27]

Hurricanes

Hurricanes are powerful storms, which form in tropical waters and have historically cost thousands of lives lost and caused billions of dollars in damage. The sinking of Francisco de Bobadilla's Spanish fleet in 1502 was the first recorded instance of a destructive hurricane. These storms have in the past caused a number of incidents related to the Triangle.

Methane hydrates

An explanation for some of the disappearances has focused on the presence of vast fields of methane hydrates (a form of natural gas) on the continental shelves.^[28] Laboratory experiments carried out in Australia have proven that bubbles can, indeed, sink a scale model ship by decreasing the density of the water;^[29] any wreckage consequently rising to the surface would be rapidly dispersed by the Gulf Stream. It has been hypothesized that periodic methane eruptions (sometimes called "mud volcanoes") may produce regions of frothy water that are no longer capable of providing adequate buoyancy for ships. If this were the case, such an area forming around a ship could cause it to sink very rapidly and without warning.
Publications by the USGS describe large stores of undersea hydrates worldwide, including the Blake Ridge area, off the southeastern United States coast.^[30] However, according to another of their papers, no large releases of gas hydrates are believed to have occurred in the Bermuda Triangle for the past 15,000 years.^[15]

Rogue waves

In various oceans around the world, rogue waves have caused ships to sink^[31] and oil platforms to topple.^[32] These waves, until 1995, were considered to be a mystery and/or a myth.^[33][34]

Notable incidents

Flight 19

Flight 19 was a training flight of TBM Avenger bombers that went missing on December 5, 1945 while over the Atlantic. The squadron's flight path was scheduled to take them due east for 120 miles, north for 73 miles, and then back over a final 120-mile leg that would return them to the naval base, but they never returned. The impression is given^{[citation needed]} that the flight encountered unusual phenomena and anomalous compass readings, and that the flight took place on a calm day under the supervision of an experienced pilot, Lt. Charles Carroll Taylor. Adding to the intrigue is that the Navy's report of the accident ascribed it to "causes or reasons unknown."^{[citation needed]}
Adding to the mystery, a search and rescue Mariner aircraft with a 13-man crew was dispatched to aid the missing squadron, but the Mariner itself was never heard from again. Later, there was a report from a tanker cruising off the coast of Florida of a visible explosion^[35] at about the time the Mariner would have been on patrol.
While the basic facts of this version of the story are essentially accurate, some important details are missing. The weather was becoming stormy by the end of the incident, and naval reports and written recordings of the conversations between Taylor and the other pilots of Flight 19 do not indicate magnetic problems.^[36]

Mary Celeste

The mysterious abandonment in 1872 of the 282-ton brigantine Mary Celeste is often but inaccurately connected to the Triangle, the ship having been abandoned off the coast of Portugal. The event is possibly confused with the loss of a ship with a similar name, the Mari Celeste, a 207-ton paddle steamer that hit a reef and quickly sank off the coast of Bermuda on September 13, 1864.^[37][38] Kusche noted that many of the "facts" about this incident were actually about the Marie Celeste, the fictional ship from Arthur Conan Doyle's short story "J. Habakuk Jephson's Statement" (based on the real Mary Celeste incident, but fictionalised).

Ellen Austin

The Ellen Austin supposedly came across a derelict ship, placed on board a prize crew, and attempted to sail with it to New York in 1881. According to the stories, the derelict disappeared; others elaborating further that the derelict reappeared minus the prize crew, then disappeared again with a second prize crew on board. A check from Lloyd's of London records proved the existence of the Meta, built in 1854 and that in 1880 the Meta was renamed Ellen Austin. There are no casualty listings for this vessel, or any vessel at that time, that would suggest a large number of missing men were placed on board a derelict that later disappeared.^[39]

USS Cyclops

The incident resulting in the single largest loss of life in the history of the US Navy not related to combat occurred when USS Cyclops, under the command of Lt Cdr G.W. Worley, went missing without a trace with a crew of 309 sometime after March 4, 1918, after departing the island of Barbados. Although there is no strong evidence for any single theory, many independent theories exist, some blaming storms, some capsizing, and some suggesting that wartime enemy activity was to blame for the loss.^[40][41]

Theodosia Burr Alston

Theodosia Burr Alston was the daughter of former United States Vice President Aaron Burr. Her disappearance has been cited at least once in relation to the Triangle.^[42] She was a passenger on board the Patriot, which sailed from Charleston, South Carolina to New York City on December 30, 1812, and was never heard from again. The planned route is well outside all but the most extended versions of the Bermuda Triangle. Both piracy and the War of 1812 have been posited as explanations, as well as a theory placing her in Texas, well outside the Triangle.

Carroll A. Deering

A five-masted schooner built in 1919, the Carroll A. Deering was found hard aground and abandoned at Diamond Shoals, near Cape Hatteras, North Carolina on January 31, 1921. Rumors and more at the time indicated the Deering was a victim of piracy, possibly connected with the illegal rum-running trade during Prohibition, and possibly involving another ship, S.S. Hewitt, which disappeared at roughly the same time. Just hours later, an unknown steamer sailed near the lightship along the track of the Deering, and ignored all signals from the lightship. It is speculated that the Hewitt may have been this mystery ship, and possibly involved in the Deering crew's disappearance.^[43]

Douglas DC-3

On December 28, 1948, a Douglas DC-3 aircraft, number NC16002, disappeared while on a flight from San Juan, Puerto Rico, to Miami. No trace of the aircraft or the 32 people onboard was ever found. From the documentation compiled by the Civil Aeronautics Board investigation, a possible key to the plane's disappearance was found, but barely touched upon by the Triangle writers: the plane's batteries were inspected and found to be low on charge, but ordered back into the plane without a recharge by the pilot while in San Juan. Whether or not this led to complete electrical failure will never be known. However, since piston-engined aircraft rely upon magnetos to provide spark to their cylinders rather than a battery powered ignition coil system, this theory is not strongly convincing.^[44]

Star Tiger and Star Ariel

G-AHNP Star Tiger disappeared on January 30, 1948 on a flight from the Azores to Bermuda; G-AGRE Star Ariel disappeared on January 17, 1949, on a flight from Bermuda to Kingston, Jamaica. Both were Avro Tudor IV passenger aircraft operated by British South American Airways.^[45] Both planes were operating at the very limits of their range and the slightest error or fault in the equipment could keep them from reaching the small island. One plane was not heard from long before it would have entered the Triangle.^[14]

KC-135 Stratotankers

On August 28, 1963 a pair of US Air Force KC-135 Stratotanker aircraft collided and crashed into the Atlantic. The Triangle version (Winer, Berlitz, Gaddis^[8][11][12]) of this story specifies that they did collide and crash, but there were two distinct crash sites, separated by over 160 miles (260 km) of water. However, Kusche's research^[14] showed that the unclassified version of the Air Force investigation report stated that the debris field defining the second "crash site" was examined by a search and rescue ship, and found to be a mass of seaweed and driftwood tangled in an old buoy.

SS Marine Sulphur Queen

SS Marine Sulphur Queen, a T2 tanker converted from oil to sulfur carrier, was last heard from on February 4, 1963 with a crew of 39 near the Florida Keys. Marine Sulphur Queen was the first vessel mentioned in Vincent Gaddis' 1964 Argosy Magazine article,^[8] but he left it as having "sailed into the unknown", despite the Coast Guard report, which not only documented the ship's badly-maintained history, but declared that it was an unseaworthy vessel that should never have gone to sea.^[46][47]

Connemara IV

A pleasure yacht was found adrift in the Atlantic south of Bermuda on September 26, 1955; it is usually stated in the stories (Berlitz, Winer^[11][12]) that the crew vanished while the yacht survived being at sea during three hurricanes. The 1955 Atlantic hurricane season shows Hurricane Ione passing nearby between the 14th and 18th of that month, with Bermuda being affected by winds of almost gale force.^[14] It was confirmed that the Connemara IV was empty and in port when Ione may have caused the yacht to slip her moorings and drift out to sea.^{[citation needed]}

Triangle authors

The incidents cited above, apart from the official documentation, come from the following works. Some incidents mentioned as having taken place within the Triangle are found only in these sources:

• Gian J. Quasar (2003). Into the Bermuda Triangle: Pursuing the Truth Behind the World's Greatest Mystery ((Reprinted in paperback (2005) ISBN 0-07-145217-6) ed.). International Marine / Ragged Mountain Press. ISBN 0-07-142640-X.
• ^[11] Charles Berlitz (1974). The Bermuda Triangle (1st ed.). Doubleday. ISBN 0-385-04114-4.
• ^[14] Lawrence David Kusche (1975). The Bermuda Triangle Mystery Solved. Buffalo: Prometheus Books. ISBN 0-87975-971-2.
• ^[10] John Wallace Spencer (1969). Limbo Of The Lost. ISBN 0-686-10658-X.
• David Group (1984). The Evidence for the Bermuda Triangle. Wellingborough, Northamptonshire: Aquarian Press. ISBN 0-85030-413-X.
• ^[38] Daniel Berg (2000). Bermuda Shipwrecks. East Rockaway, N.Y.: Aqua Explorers. ISBN 0-9616167-4-1.
• ^[12] Richard Winer (1974). The Devil's Triangle. ISBN 0553106880.
• Richard Winer (1975). The Devil's Triangle 2. ISBN 0553024647.
• ^[42] Adi-Kent Thomas Jeffrey (1975). The Bermuda Triangle. ISBN 0446599611.

See also

• List of Bermuda Triangle incidents
• Atlantis
• Devil's Sea (or Dragon's Triangle)
• The Michigan Triangle
• Sargasso Sea
• SS Cotopaxi
• The Triangle (TV miniseries)
• Vile Vortices

References

Other sources