FACTOID # 9: The bookmobile capital of America is Kentucky.
 
 Home   Encyclopedia   Statistics   States A-Z   Flags   Maps   FAQ   About 
 
WHAT'S NEW
RELATED ARTICLES
People who viewed "Polymer" also viewed:
 

SEARCH ALL

FACTS & STATISTICS    Advanced view

Search encyclopedia, statistics and forums:

 

 

(* = Graphable)

 

 


Encyclopedia > Polymer

A polymer (from Greek: πολυ, polu, "many"; and μέρος, meros, "part") is a substance composed of molecules with large molecular mass composed of repeating structural units, or monomers, connected by covalent chemical bonds. Well known examples of polymers include plastics and DNA. Image File history File links Broom_icon. ... The molecular mass (abbreviated Mr) of a substance, formerly also called molecular weight and abbreviated as MW, is the mass of one molecule of that substance, relative to the unified atomic mass unit u (equal to 1/12 the mass of one atom of carbon-12). ... ... In chemistry, a monomer (from Greek mono one and meros part) is a small molecule that may become chemically bonded to other monomers to form a polymer. ... Covalent bonding is a form of chemical bonding characterized by the sharing of one or more pairs of electrons between atoms, in order to produce a mutual attraction, which holds the resultant molecule together. ... A chemical bond is the physical process responsible for the attractive interactions between atoms and molecules, and that which confers stability to diatomic and polyatomic chemical compounds. ... The term plastics covers a range of synthetic or semi-synthetic organic condensation or polymerization products that can be molded or extruded into objects or films or fibers. ... The structure of part of a DNA double helix Deoxyribonucleic acid, or DNA, is a nucleic acid molecule that contains the genetic instructions used in the development and functioning of all known living organisms. ...

Contents

Overview

While the term polymer in popular usage suggests "plastic", polymers comprise a large class of natural and synthetic materials with a variety of properties and purposes. Natural polymer materials such as shellac and amber have been in use for centuries. Paper is manufactured from cellulose, a naturally occurring polysaccharide found in plants. Biopolymers such as proteins and nucleic acids play important roles in biological processes. This article or section does not cite any references or sources. ... Look up shellac in Wiktionary, the free dictionary. ... This article or section is in need of attention from an expert on the subject. ... A blank sheet of paper Paper is a commodity of thin material produced by the amalgamation of fibers, typically vegetable fibers composed of cellulose, which are subsequently held together by hydrogen bonding. ... Cellulose as polymer of β-D-glucose Cellulose in 3D Cellulose (C6H10O5)n is a polysaccharide of beta-glucose. ... Polysaccharides (sometimes called glycans) are relatively complex carbohydrates. ... A representation of the 3D structure of myoglobin, showing coloured alpha helices. ... Highly simplified diagram of a double-stranded nucleic acid. ...


Historical development

The term polymer was coined in 1833 by Jöns Jakob Berzelius. Around the same time 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. The first wholly synthetic polymer, Bakelite, was introduced in 1909. Friherre Jöns Jakob Berzelius (August 20, 1779 – August 7, 1848) was a Swedish chemist. ... Henri Braconnot Henri Braconnot (Commercy May 29, 1780 - Nancy January 15, 1855) was a French chemist and pharmacist. ... Vulcanization refers to a specific curing process of rubber involving high heat and the addition of sulfur. ... This does not cite any references or sources. ... Bakelite is a material based on the thermosetting phenol formaldehyde resin, polyoxybenzylmethylenglycolanhydride developed in 1907–1909 by Dr. Leo Baekeland. ... Year 1909 (MCMIX) was a common year starting on Friday (link will display full calendar) of the Gregorian calendar (or a common year starting on Thursday of the 13-day-slower Julian calendar). ...


Despite significant advances in synthesis and characterization of polymers, a proper understanding of polymer molecular structure did not come until the 1920s. Before that, 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. In the intervening century, synthetic polymer materials such as Nylon, polyethylene, Teflon, and silicone have formed the basis for a burgeoning polymer industry. 1920 (MCMXX) was a leap year starting on Thursday. ... Association theory (also aggregate theory) is a discredited theory first advanced by chemist Thomas Graham in 1861 to describe the molecular structure of substances such as cellulose and starch, now understood to be polymers. ... Hermann Staudinger (March 23, 1881 in Worms- Sept. ... The Nobel Prizes (Swedish: ) are awarded for Physics, Chemistry, Literature, Peace, and Physiology or Medicine. ... Nylon is a generic designation for a family of synthetic polymers first produced on February 28, 1935 by Wallace Carothers at DuPont. ... This article does not cite any references or sources. ... Teflon is polytetrafluoroethylene (PTFE), a polymer of fluorinated ethylene. ... Silicones (more accurately called polymerized siloxanes or polysiloxanes) are inorganic-organic polymers with the chemical formula [R2SiO]n, where R = organic groups such as methyl, ethyl, and phenyl. ...


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 childrens' toys to aircraft. 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. Future applications include flexible polymer-based substrates for electronic displays and improved time-released and targeted drug delivery. A Low-K dielectric is one with a small dielectric constant. ...


Polymer science

Main article: Polymer science

Most polymer research may be categorized as polymer science, a sub-discipline of materials science which includes researchers in chemistry (especially organic chemistry), physics, and engineering. Polymer science may be roughly divided into two subdisciplines: Polymer chemistry or macromolecular chemistry is a multidisciplinary science that deals with the chemical synthesis and chemical properties of polymers or macromolecules. ... Polymer chemistry or macromolecular chemistry is a multidisciplinary science that deals with the chemical synthesis and chemical properties of polymers or macromolecules. ... The Materials Science Tetrahedron, which often also includes Characterization at the center Materials science or Materials Engineering is an interdisciplinary field involving the properties of matter and its applications to various areas of science and engineering. ... For other uses, see Chemistry (disambiguation). ... Organic chemistry is a specific discipline within chemistry which involves the scientific study of the structure, properties, composition, reactions, and preparation (by synthesis or by other means) of chemical compounds consisting of primarily carbon and hydrogen, which may contain any number of other elements, including nitrogen, oxygen, halogens as well... This is a discussion of a present category of science. ... Engineering is the applied science of acquiring and applying knowledge to design, analysis, and/or construction of works for practical purposes. ...

The field of polymer science is generally concerned with synthetic polymers, such as plastics, or chemical treatment and modification of natural polymers. Polymer chemistry or macromolecular chemistry is a multidisciplinary science that deals with the chemical synthesis and chemical properties of polymers or macromolecules. ... Polymer chemistry or macromolecular chemistry is a multidisciplinary science that deals with the chemical synthesis and chemical properties of polymers or macromolecules. ... Polymer physics is the field of physics associated to the study of polymers, their fluctuations, mechanical properties, as well as the kinetics of reactions involving degradation and polymerisation of polymers and monomers respectively. ...


The study of biological polymers, their structure, function, and method of synthesis is generally the purview of biology, biochemistry, and biophysics. These disciplines share some of the terminology familiar to polymer science, especially when describing the synthesis of biopolymers such as DNA or polysaccharides. However, usage differences persist, such as the practice of using the term macromolecule to describe large non-polymer molecules and complexes of multiple molecular components, such as hemoglobin. Substances with distinct biological function are rarely described in the terminology of polymer science. For example, a protein is rarely referred to as a copolymer. This article needs additional references or sources for verification. ... Biochemistry is the study of the chemical processes and transformations in living organisms. ... Biophysics (also biological physics) is an interdisciplinary science that applies the theories and methods of physics, to questions of biology. ... A macromolecule is a large molecule with a large molecular mass bonded covalently, but generally the use of the term is restricted to polymers and molecules which structurally include polymers. ... Structure of hemoglobin. ... A representation of the 3D structure of myoglobin, showing coloured alpha helices. ... A heteropolymer, also called a copolymer, is a polymer formed when two different types of monomer are linked in the same polymer chain. ...


Polymer synthesis

Polymers are synthesized by three primary methods: organic synthesis in a laboratory or factory, biological synthesis in living cells and organisms, or by chemical modification of naturally occurring polymers.


Organic synthesis

Main article: Polymerization

In 1907, Leo Baekeland created the first completely synthetic polymer, Bakelite, by reacting phenol and formaldehyde at precisely controlled temperature and pressure. Subsequent work by Wallace Carothers in the 1920s demonstrated that polymers could be synthesized rationally from their constituent monomers. The intervening years have 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. An example of alkene polymerisation, in which each Styrene monomer units double bond reforms as a single bond with another styrene monomer and forms polystyrene. ... Leo Hendrik Baekeland (1863-1944) Leo Hendrik Baekeland (Ghent, November 14, 1863 - February 23, 1944) was a Belgian-American chemist who invented Velox photographic paper (1893) and Bakelite (1907), an inexpensive, nonflammable, versatile, and popular plastic. ... Bakelite is a material based on the thermosetting phenol formaldehyde resin, polyoxybenzylmethylenglycolanhydride developed in 1907–1909 by Dr. Leo Baekeland. ... Wallace Hume Carothers (April 27, 1896 – April 29, 1937) was an American chemist, inventor, and the leader of organic chemistry at DuPont, who is credited with the invention of nylon. ...


Laboratory synthetic methods are generally divided into two categories, condensation polymerization and addition polymerization. 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. Efforts towards rational synthesis of biopolymers via laboratory synthetic methods, especially artificial synthesis of proteins, is an area of intense research. Step-growth polymerization is a polymerization process that involves a chemical reaction between multifunctional monomer molecules. ... Addition polymerization,also called polyaddition or chain growth polymerization, is a polymerization technique where monomer molecules add on to a growing polymer chain one at a time. ... Plasma polymerization uses plasma sources to generate a gas discharge that provides energy to activate or fragment gaseous or liquid monomer, often containing a vinyl group, in order to initiate polymerization. ... It has been suggested that solid phase peptide synthesis be merged into this article or section. ...


Biological synthesis

Natural polymers and biopolymers formed in living cells 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 and subsequently translate that information to synthesize the specified protein. The protein may be modified further following translation in order to provide appropriate structure and function. The structure of part of a DNA double helix Deoxyribonucleic acid, or DNA, is a nucleic acid molecule that contains the genetic instructions used in the development and functioning of all known living organisms. ... 3D structure of the DNA-binding helix-hairpin-helix motifs in human DNA polymerase beta A DNA polymerase is an enzyme that assists in DNA replication. ... An overview of protein synthesis. ... A micrograph of ongoing gene transcription of ribosomal RNA illustrating the growing primary transcripts. ... Translation is the second process of protein biosynthesis (part of the overall process of gene expression). ... Posttranslational modification is the chemical modification of a protein after its translation. ...


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. Skeletal formula of nitrocellulose Ball-and-stick model of a section of nitrocellulose Nitrocellulose (also: cellulose nitrate, flash paper) is a highly flammable compound formed by nitrating cellulose through, for example, exposure to nitric acid or another powerful nitrating agent. ...


Polymer Structure and Properties

Types of polymer 'properties' can be broadly divided into several categories based upon scale. At the nano-micro scale are properties that directly describe the chain itself. These can be thought of as polymer structure. At an intermediate mesoscopic level are properties that describe the morphology of the polymer matrix in space. At the macroscopic level are properties that describe the bulk behavior of the polymer.


Structure

The structural properties of a polymer relate to the physical arrangement of monomers along the backbone of the chain. Structure has a strong influence on the other properties of a polymer. For example, a linear chain polymer may be soluble or insoluble in water depending on whether it is composed of polar monomers (such as ethylene oxide) or nonpolar monomers (such as styrene). On the other hand, two samples of natural rubber may exhibit different durability even though their molecules comprise the same monomers. Polymer scientists have developed terminology to precisely describe both the nature of the monomers as well as their relative arrangement:


Monomer identity

The identity of the monomers comprising the polymer is generally the first and most important attribute of a polymer. Polymer nomenclature is generally based upon the type of monomers comprising the polymer. Polymers that contain only a single type of monomer are known as homopolymers, while polymers containing a mixture of monomers are known as copolymers. Poly(styrene), for example, is composed only of styrene monomers, and is therefore is classifed as a homopolymer. Ethylene-vinyl acetate, on the other hand, contains more than one variety of monomer and is thus a copolymer. Some biological polymers are composed of a variety of different but structurally related monomers, such as polynucleotides composed of nucleotide subunits. The introduction of this article does not provide enough context for readers unfamiliar with the subject. ... Ethylene-vinyl acetate (also known as EVA or sometimes simply as acetate) is the copolymer of ethylene and vinyl acetate. ... A heteropolymer, also called a copolymer, is a polymer formed when two different types of monomer are linked in the same polymer chain. ... Polynucleotide literally means many nucleotides. ... A nucleotide is a chemical compound that consists of a heterocyclic base, a sugar, and one or more phosphate groups. ...


A polymer molecule containing ionizable subunits is known as a polyelectrolyte. An ionomer is a subclass of polyelectrolyte with a low fraction of ionizable subunits.t78og78g89o Polyelectrolytes combine the properties of electrolytes (salts) and polymers (high MW compounds). ... An ionomer is a polyelectrolyte that comprises copolymers containing both electrically neutral repeating units and a fraction of ionic units (usually no more than 15%). Categories: Chemistry stubs | Polymers | Plastics ...


Chain linearity

The simplest form of polymer molecule is a straight chain or linear polymer, composed of a single main chain. The flexibility of an unbranched chain polymer is characterized by its persistence length. 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, and brush polymers. If the polymer contains a side chain that has a different composition or configuration than the main chain the polymer is called a graft or grafted polymer. 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.[1] 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 extend - there is essentially all chains have linked into one molecule.[2] The persistence length is a basic mechanical property quantifying the stiffness of a fibre. ... In polymer chemistry, branching occurs by the replacement of a substituent, e. ... A graft copolymer has polymer chains of one kind growing out of the sides of polymer chains with a different chemical composition. ...


Chain size

Polymer bulk properties may be strongly dependent on the size of the polymer chain. Like any molecule, a polymer molecule's size may be described in terms of molecular weight or mass. In polymers, however, the molecular mass may be expressed in terms of degree of polymerization, essentially the number of monomer units which comprise the polymer. For synthetic polymers, the molecular weight is expressed statistically to describe the distribution of molecular weights in the sample. This is because of the fact that almost all industrial processes produce a distribution of polymer chain sizes. Examples of such statistics include the number average molecular weight and weight average molecular weight. The ratio of these two values is the polydispersity index, commonly used to express the "width" of the molecular weight. The molecular mass of a substance (less accurately called molecular weight and abbreviated as MW) is the mass of one molecule of that substance, relative to the unified atomic mass unit u (equal to 1/12 the mass of one atom of carbon-12). ... The degree of polymerization, or DP, is the number of repeat units in an average polymer chain at time t in a polymerization reaction. ... The number average molecular weight is a way of determining the molecular weight of a polymer. ... The weight average molecular weight is a way of describing the molecular weight of a polymer. ... In organic chemistry, the polydispersity index (PDI), is a measure of the distribution of molecular weights in a given polymer sample. ...


The space occupied by a polymer molecule is generally expressed in terms of radius of gyration or excluded volume. The radius of gyration is a defined measure for the dimension of an object, a surface, or an ensemble of points. ...


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
  • Periodic copolymers have monomer residue types arranged in a repeating sequence
  • Random copolymers have a random sequence of monomer residue types
  • Statistical copolymers have monomer residues arranged according to a known statistical rule
  • Block copolymers have two or more homopolymer subunits linked by covalent bonds. Block copolymers with two or three distinct blocks are called diblock copolymers and triblock copolymers, respectively.

Tacticity in polymers with chiral centers

Main article: Tacticity

This property describes the relative stereochemistry of chiral centers in neighboring structural units within a macromolecule. There are three types: isotactic, atactic, and syndiotactic. Tacticity (from Greek taktikos: of or relating to arrangement or order) is the relative stereochemistry of adjacent chiral centers within a macromolecule. ... The different types of isomers. ... The term chiral (pronounced ) is used to describe an object which is non-superimposable on its mirror image. ... Isotactic polymers refer to those polymers formed by branched monomers that have the characteristic of having all the branch groups on the same side of the polymeric chain. ... In atactic macromolecules every substituent belonging to a repeating unit is placed randomly at either side of the backbone. ... A syndiotactic macromolecule in polymer chemistry is a tactic macromolecule essentially comprising alternating enantiomeric configurational base units which have chiral or prochiral atoms in the main chain in a unique arrangement with respect to their adjacent constitutional units. ...


Morphological Properties

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. Crystallography (from the Greek words crystallon = cold drop / frozen drop, with its meaning extending to all solids with some degree of transparency, and graphein = write) is the experimental science of determining the arrangement of atoms in solids. ... X-ray crystallography, also known as single-crystal X-ray diffraction, is the oldest and most common crystallographic method for determining the structure of molecules. ...


A synthetic polymer may be 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.[3]


Bulk 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.


Tensile strength

The tensile strength of a material quantifies how much stress the material will endure before failing. This is very important in applications that rely upon polymer's physical strength or durability. For example, a rubber band with a higher tensile strength will hold a greater weigh before snapping. In general tensile strength increases with polymer chain length. Tensile strength isthe measures the force required to pull something such as rope, wire, or a structural beam to the point where it breaks. ...


Young's Modulus of elasticity

This parameter 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. In solid mechanics, Youngs modulus (E) is a measure of the stiffness of a given material. ...


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.


Pure component phase behavior

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 "Tm", 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. The melting point of a crystalline solid is the temperature at which it changes state from solid to liquid. ... A thermoplastic is a plastic that softens when heated and hardens again when cooled. ... Thermosetting plastics (thermosets) refer to a range of polymer materials that cure, through the addition of energy, to a stronger form. ...


Boiling point

The boiling point of a polymer substance is never defined due to the fact that polymers will decompose before reaching theoretical boiling temperatures. Italic text This article is about the boiling point of liquids. ...


Glass transition temperature (Tg)

A parameter of particular interest in synthetic polymer manufacturing is the glass transition temperature (Tg), which describes the temperature at which amorphous polymers undergo a second order phase 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 cross-linking in the polymer or by the addition of plasticizer.[4] A material’s glass transition temperature, Tg, is the temperature below which molecules have little relative mobility. ... A material’s glass transition temperature, Tg, is the temperature below which molecules have little relative mobility. ... Plasticizers are additives that soften the materials (usually a plastic or a concrete mix) they are added to. ...


Polymer solution behavior

In general, polymeric mixtures are far less miscible than mixtures of small molecule materials. This effect is a result of the fact that the driving force for mixing is usually entropics, not energetics. 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 are far less than the number in a small molecule mixture of equal volume. The energetics of mixing, on the other hand, are 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.


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. ... Illustration of a 3-dimensional polypeptide A random coil is a polymer conformation where the monomer subunits are oriented randomly while still being bonded to adjacent units. ...


Polymer Structure/Property relationships

Polymer bulk properties are strongly dependent upon their structure and mesoscopic behavior. A number of qualitative relationships between structure and properties are known.


Chain Length

Increasing chain length tends to decrease chain mobility, increase strength and toughness, and increase the glass transition temperature (Tg). This is a result of the increase in chain interactions such as Van der Waals attractions and entanglements that come with increased chain length. 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.


Branching

Branching of polymer chains also affect the bulk properties of polymers. Long chain branches may increase polymer strength, toughness, and Tg due to an increase in the number of entanglements per chain. Random length and atactic short chains, on the other hand, may reduce polymer strength due to disruption of organization. Short side chains may likewise reduce crystallinity due to disruption of the crystal structure. Reduced crystallinity may also be associated with increased transparency due to light scattering by small crystalline regions. 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 short branches, is quite flexible, and is used in applications such as plastic films. The branching index of the polymer is a parameter that characterizes the effect of long-chain branches on the size of a branched macromolecule in solution. This article does not cite any references or sources. ... Polyethylene or polyethene is one of the simplest and most inexpensive polymers. ... Polyethylene or polyethene is one of the simplest and most inexpensive polymers. ...


Chemical Cross-linking

Cross linking tends to increase Tg and increase strength and toughness. Cross linking consists of the formation of chemical bonds between chains. 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 the tires durability. Eraser rubber, on the other hand, is not cross linked to allow flaking of the rubber and prevent damage to the paper.


Inclusion of plasticizers

Inclusion of Plasticizers tends to lower Tg 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 unplastiscized 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. Plasticizers are additives that soften the materials (usually a plastic or a concrete mix) they are added to. ... Plasticizers are additives that soften the materials (usually a plastic or a concrete mix) they are added to. ...


Degree of Crystallinity

Increasing degree of crystallinity tends to make a polymer more rigid. It can also lead to greater brittlness. Polymers with 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 / glassy regions.


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[5] and IUPAC[6] have proposed standardized naming conventions; the ACS and IUPAC conventions are similar but not identical.[7] Examples of the difference between the various naming conventions are given in the table below: The American Chemical Society (ACS) is a learned society (professional association) based in the United States that supports scientific inquiry in the field of chemistry. ... The International Union of Pure and Applied Chemistry (IUPAC) is an international non-governmental organization devoted to the advancement of chemistry. ... ACS is a three-letter acronym that may refer to: // American Cancer Society, an American medical organization American Chemical Society, an American professional association American Colonization Society American Community Survey, a project of the U.S. Census Bureau American Constitution Society for Law and Policy, or simply American Constitution Society...

Common Name ACS Name IUPAC Name
Poly(ethylene oxide) or (PEO) poly(oxyethylene) poly(oxyethylene)
Poly(ethylene terephthalate) or (PET) poly(oxy-1,2-ethanediyloxycarbonyl -1,4-phenylenecarbonyl) poly(oxyethyleneoxyterephth= aloyl)
Nylon poly[imino(1-oxo-1,6-hexanediyl)] poly[imino(1-oxohexane-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: Ethylene or ethene is the simplest alkene hydrocarbon, consisting of two carbon atoms and four hydrogens. ... This article does not cite any references or sources. ...


Image File history File links File history Legend: (cur) = this is the current file, (del) = delete this old version, (rev) = revert to this old version. ...


Wikipedia does not have an article with this exact name. ...


Chemical properties of polymers

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 melting points. An ionic bond can be formed after two or more atoms give up (or gain) electrons, so as to become ions. ... In chemistry, a hydrogen bond is a type of attractive intermolecular force that exists between two partial electric charges of opposite polarity. ...


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 containg 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, but polyesters have greater flexibility. The Earths magnetic field, which is approximately a dipole. ... Amide functional group Amides possess a conjugated system spread over the O, C and N atoms, consisting of molecular orbitals occupied by delocalized electrons. ... Carbonyl group In organic chemistry, a carbonyl group is a functional group composed of a carbon atom double-bonded to an oxygen atom : C=O. The term carbonyl can also refer to carbon monoxide as a ligand in an inorganic or organometallic complex (a metal carbonyl, e. ... An example of a quadruple hydrogen bond between a self-assembled dimer complex reported by Meijer and coworkers. ... Urethane (also called ethyl carbamate) 1. ... Urea is an organic compound with the chemical formula (NH2)2CO. Urea is also known as carbamide, especially in the recommended International Nonproprietary Names (rINN) in use in Europe. ... SEM picture of a bend in a high surface area polyester fiber with a seven-lobed cross section Polyester is a category of polymers, or, more specifically condensation polymers, which contain the ester functional group in their main chain. ... This article or section is in need of attention from an expert on the subject. ... Chemical structure of Kevlar. ...


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 actually attract the second polymer chain. Van der Waals forces are quite weak, however, so polyethene can have a lower melting temperature compared to other polymers. In chemistry, the term van der Waals force originally referred to all forms of intermolecular forces; however, in modern usage it tends to refer to intermolecular forces that deal with forces due to the polarization of molecules. ...


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 graph of a normal bell curve showing statistics used in educational assessment and comparing various grading methods. ...


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. Wide angle X-ray scattering (WAXS) is an X-ray diffraction technique that is often used to determine the crystalline structure of polymers. ... SAXS (small-angle X-ray scattering) is a small-angle scattering (SAS) technique where the elastic scattering of X-rays (wavelength 0. ... This article or section is in need of attention from an expert on the subject. ... Gel permeation chromatography (GPC) also known as size exclusion chromatography (SEC) is a chromatographic method in which molecules are separated based on their size. ... The number average molecular weight is a way of determining the molecular weight of a polymer. ... The weight average molecular weight is a way of describing the molecular weight of a polymer. ... The polydispersity index, or PDI, is the ratio of the weight average molecular weight to the number average molecular weight. ... FTIR of a thin film of ethanol in the liquid phase. ... This article or section does not cite any references or sources. ... Pacific Northwest National Laboratorys high magnetic field (800 MHz, 18. ... A material’s glass transition temperature, Tg, is the temperature below which molecules have little relative mobility. ... The melting point of a crystalline solid is the temperature at which it changes state from solid to liquid. ... Differential scanning calorimetry or DSC is a thermoanalytical technique in which the difference in the amount of heat required to increase the temperature of a sample and reference are measured as a function of temperature. ... Dynamic mechanical analysis (DMA) or dynamic mechanical thermal analysis (DMTA) is a technique used to study and characterize materials. ... Simple sketch of pyrolysis chemistry Pyrolysis usually means the chemical decomposition of organic materials by heating in the absence of oxygen or any other reagents, except possibly steam. ...


Polymer degradation

Polymer degradation is a change in the properties - tensile strength, colour, shape, etc - of a polymer or polymer based product under the influence of one or more environmental factors such as heat, light or chemicals. It is often due to the hydrolysis of the bonds connecting the polymer chain, which in turn leads to a decrease in the molecular mass of the polymer. These changes may be undesirable, such as changes during use, or desirable, as in biodegradation or deliberately lowering the molecular mass of a polymer. Such changes occur primarily because of the effect of these factors on the chemical composition of the polymer. Tensile strength isthe measures the force required to pull something such as rope, wire, or a structural beam to the point where it breaks. ... Color is an important part of the visual arts. ... For other uses, see Heat (disambiguation) In physics, heat, symbolized by Q, is energy transferred from one body or system to another as a result of a difference in temperature. ... This article does not cite any references or sources. ... A chemical substance is any material substance used in or obtained by a process in chemistry: A chemical compound is a substance consisting of two or more chemical elements that are chemically combined in fixed proportions. ... Hydrolysis is a chemical reaction or process in which a chemical compound reacts with water. ... Biodegradation is the process by which organic substances are broken down by living organisms. ...


The degradation of polymers to form smaller moleculars may proceed by random scission or specific scission. The degradation of polyethylene occurs by random scission - that is by a random breakage of the linkages (bonds) that hold the atoms of the polymer together. When heated above 450 Celsius it degrades to form a mixture of hydrocarbons. Other polymers - like polyalphamethylstyrene - undergo 'specific' chain scission with breakage occurring only at the ends. They literally unzip or depolymerize to become the constituent monomer. Properties For alternative meanings see atom (disambiguation). ... Celsius is, or relates to, the Celsius temperature scale (previously known as the centigrade scale). ... In chemistry, a monomer (from Greek mono one and meros part) is a small molecule that may become chemically bonded to other monomers to form a polymer. ...


In a finished product such a change is to be prevented or delayed. However the degradation process can be useful from the view points of understanding the structure of a polymer or recycling/reusing the polymer waste to prevent or reduce environmental pollution. Polylactic acid and Polyglycolic acid, for example, are two polymers that are useful for their ability to degrade under aqueous conditions. A copolymer of these polymers is used for biomedical applications such as hydrolysable stitches that degrade over time after they are applied to a wound. These materials can also be used for plastics that will degrade over time after they are used and will therefore not remain as litter. This article needs additional references or sources to facilitate its verification. ... It has been suggested that Pollutant be merged into this article or section. ... This article does not cite any references or sources. ... Polyglycolide or Polyglycolic acid (PGA) is a biodegradable, thermoplastic polymer and the simplest linear, aliphatic polyester. ...


Industry

Today there are primarily six commodity polymers in use, namely polyethylene, polypropylene, polyvinyl chloride, polyethylene terephthalate, polystyrene and polycarbonate. These make up nearly 98% of all polymers and plastics encountered in daily life. This article does not cite any references or sources. ... Polypropylene lid of a Tic Tacs box, with a living hinge and the resin identification code under its flap Micrograph of polypropylene Polypropylene or polypropene (PP) is a thermoplastic polymer, made by the chemical industry and used in a wide variety of applications, including food packaging, ropes, textiles, plastic parts... Polyvinyl chloride Polyvinyl chloride, (IUPAC Polychloroethene) commonly abbreviated PVC, is a widely used thermoplastic polymer. ... Polyethylene terephthalate (aka PET, PETE or the obsolete PETP or PET-P) is a thermoplastic polymer resin of the polyester family that produced by the chemical industry and is used in synthetic fibers; beverage, food and other liquid containers; thermoforming applications; and engineering resins often in combination with glass fiber. ... Polystyrene (IPA: ) is a polymer made from the monomer styrene, a liquid hydrocarbon that is commercially manufactured from petroleum by the chemical industry. ... Polycarbonates are a particular group of thermoplastic polyesters. ...


Each of these polymers has its own characteristic modes of degradation and resistances to heat, light and chemicals.


Cracking of polymers

Cracking is the process by which a polymer is divided into its subcomponents or monomers. The resulting subcomponents are more viscous than the original polymer.


References

  1. ^ IUPAC. "Glossary of Basic Terms in Polymer Science". Pure Appl. Chem. 1996, 68, 2287-2311.
  2. ^ Painter, P and Coleman, M. "Fundamentals of Polymer Science". 1997, 96-100.
  3. ^ http://www.iupac.org/publications/books/pbook/PurpleBook-C4.pdf
  4. ^ Brandrup, J.; Immergut, E.H.; Grulke, E.A.; eds Polymer Handbook 4th Ed. New York: Wiley-Interscience, 1999.
  5. ^ CAS: Index Guide, Appendix IV (© 1998).
  6. ^ IUPAC. "Nomenclature of Regular Single-Strand Organic Polymers". Pure Appl. Chem. 1976, 48, 373-385.
  7. ^ [1]
  • Ashby, Michael and Jones, David. Engineering Materials. p. 191-195. Oxford: Butterworth-Heinermann, 1996. Ed. 2.
  • Meyers and Chawla. Mechanical Behavior of Materials. pg. 41. Prentice Hall, Inc. 1999.

See also

This article does not cite any references or sources. ... A heteropolymer, also called a copolymer, is a polymer formed when two different types of monomer are linked in the same polymer chain. ... Electroactive Polymers or EAPs are polymers whose shape is modified when a voltage is applied to them. ... An example of alkene polymerisation, in which each Styrene monomer units double bond reforms as a single bond with another styrene monomer and forms polystyrene. ... This is a list of important publications in chemistry, organized by field. ... In chemistry, a monomer (from Greek mono one and meros part) is a small molecule that may become chemically bonded to other monomers to form a polymer. ... Polyanhydrides are a class of biodegradable polymers used in the medical device and pharmaceutical industry. ... Smart materials are materials that have one or more properties that can be significantly altered in a controlled fashion by external stimuli, such as stress, temperature, moisture, pH, electric or magnetic fields. ...

External links


  Results from FactBites:
 
Polymer banknote - Wikipedia, the free encyclopedia (1108 words)
Polymer banknotes were developed by the Reserve Bank of Australia (RBA) and the Commonwealth Scientific and Industrial Research Organisation (CSIRO) and were first issued as currency in Australia in 1988.
The complexities of counterfeiting polymer banknotes are proposed to act as a deterrent to counterfeiters.
Although the 5 pound Northern Bank polymer banknote was a one-off commemorative issued, unconventionally, in portrait orientation to mark the year 2000, it was in general circulation.
AllRefer.com - polymer (Chemistry) - Encyclopedia (426 words)
An addition polymer is one in which the molecular formula of the repeating structural unit is identical to that of the monomer, e.g., polyethylene and polystyrene.
A condensation polymer is one in which the repeating structural unit contains fewer atoms than that of the monomer or monomers because of the splitting off of water or some other substance, e.g., polyesters and polycarbonates.
Polymerization, the chemical process of forming polymers from their component monomers, is often a complex process that may be initiated or sustained by heat, pressure, or the presence of one or more catalysts.
  More results at FactBites »

 
 

COMMENTARY     


Share your thoughts, questions and commentary here
Your name
Your comments

Want to know more?
Search encyclopedia, statistics and forums:

 


Press Releases |  Feeds | Contact
The Wikipedia article included on this page is licensed under the GFDL.
Images may be subject to relevant owners' copyright.
All other elements are (c) copyright NationMaster.com 2003-5. All Rights Reserved.
Usage implies agreement with terms, 1022, m