Chemistry of Materials Lesson 24 by Owen Borville 11.8.2025
Polymers are molecules containing many smaller parts linked together known as monomers. Thermoplastic polymers can be melted and reshaped. Thermosetting polymers have their shape determined as part of the chemical process that formed the polymer.
Addition polymerization is the simplest type of polymerization reaction and it includes the bonding of monomer molecules by the movement of electrons from a multiple bond into new single bonds between molecules. A free radical initiator molecule attaches to one of the ethylene carbon atoms and breaks the pi bond between the two carbon atoms in ethylene. In the addition reaction, monomers join together to form a polymer without the loss of any atoms. The double bonds in the monomers are broken, and rearranged into single bonds to create a long, repeating chain. Steps involved in the reaction are catalyzed and include initiation, propagation, and termination.
Polyethylene structure: (-CH2-CH2-)n, where n is the number of ethylene monomer molecules that reacted. Depending on reaction conditions, branches can form off the main polyethylene chain during polymerization. Branched chain polyethylene is more flexible and lower density than straight-chain polyethylene.
Natural rubber formed from latex is also an addition polymer and the monomer unit is isoprene. Rubber is an elastomer, a material that can stretch or bend and return to its original shape as long as the limits of its elasticity are not exceeded.
Industrial vulcanization was developed by Charles Goodyear in 1839, a process in which sulfur is used to create linkages between individual polymer chains in the rubber.
Molecules containing carbon=carbon double bonds can form addition polymers:
Styrene-polystyrene is used in disposable cups and plates as well as styrofoam insulation and craft materials.
Vinyl chloride-poly (vinyl chloride) PVC is used in pipes and fittings, some plastic wraps, and the classic "vinyl" records.
Tetrafluoroethylene-polytet rafluoroethylene (Teflon)
Polystyrene is made of a chain of styrene (C8H8) monomers (benzene ring attached to a vinyl ethylene group).
Polyacrylonitrile and polybutadiene are also addition polymers.
Copolymers are polymers made from two or more different monomers. Different combinations of the two or more monomers give rise to different types of copolymers. Examples of copolymers are acylonitrile butadiene styrene (ABS)(strong plastic) and styrene-butadiene rubber (SBR)(tires).
Copolymers formed from butadiene and styrene: SBS rubber-poly(styrene-butadiene-styrene) and HIPS-(high impact polystyrene)
Polymers with a vinyl group can be optical isomers:
Tacticity describes the relative arrangements of such chiral carbon atoms within a polymer.
Isotactic polymers-all the substituents are in the same relative orientation or same side of the chain.
Syndiotactic polymers- the substituents alternate positions along the polymer chain.
Atactic polymers- the substituents are oriented randomly along the polymer chain.
Condensation polymers form when monomers with two different functional groups combine, resulting in the elimination of a small molecule (usually water).
For example, proteins form between amino acid monomers. Each amino acid contains an amino group (-NH2) and a carboxyl group (-COOH). One water molecule is produced as each new C-N bond is formed. The C-N bond formed between an amino group and a carboxyl group is called an amide bond. Polyamides are polymers in which the monomers are connected by amide linkages. Nylon 6,6 is an example of a synthetic condensation polymer. Polyester is also a condensation polymer, along with Kevlar, polycarbonate, and polyurethane. Natural condensation polymers are proteins, starch, and cellulose.
Dacron is the trade name for the condensation copolymer formed from the ethylene glycol and para-terephthalic acid. The bond that forms from the ethylene glycol monomer and each para-terephthalic acid monomer is called an ester linkage.
Polyesters are polymers in which the monomers are connected by ester linkages.
Deoxyribonucleic acid (DNA) is a biological condensation copolymer of the five carbon sugar deoxyribose. Four bases of DNA: adenine, thymine, guanine, and cytosine. Ribonucleic acid (RNA) is also a biological copolymer analogous to DNA. It is made from the five carbon sugar ribose. Four bases of RNA: adenine, uracil, guanine, and cytosine.
The polymerization of acetylene (C2H2) results in electrically conductive polyacetylene, where its carbon triple bonds become alternating double bonds and hydrogens are attached non-linearly instead of horizontally. The presence of electrons in the delocalized p electrons are key to the electrical conductivity in polyacetylene.
Ceramics are polymeric inorganic compounds that share the properties of hardness, strength, and high melting points. Ceramics are usually formed by melting and then solidifying inorganic substances (including clays).
Ceramics are prepared by a process called sintering in which a slurry of a powder of the inorganic substance in water is heated to a very high temperature under high pressure. To avoid imperfections and cracks, the sol-gel process is used to produce particles of nearly uniform size. The first step in the sol-gel process is the preparation of alkoxide of the metal or metalloid
metal + alkoxide => metal alkoxide + nH+
Next, the metal alkoxide is dissolved in alcohol. Water is then added to generate the metal hydroxide and regenerate the alcohol.
metal alkoxide + 3H2O => metal hydroxide (OH) + alcohol
Once the metal hydroxide is formed, it undergoes a condensation polymerization.
Composite materials are made from two or more substances with different properties that remain separate in the bulk material. Polymer matrix composites in modern composite materials commonly including reinforcing fibers in a polymer matrix called resin.
Metal matrix composites are made from a metal and a ceramic, organic polymer, or another metal. Ceramic matrix composites use ceramic as the primary reinforcing material accompanied by organic polymers.
Liquid Crystals have properties of liquids (ability to flow and take shape of container) and those of crystals (regular arrangement of particles in a lattice).
Liquids are isotropic, because particles are free to rotate in every direction. Thus, their properties are independent of the direction of testing. Liquid crystals are anisotropic because their properties depend on the direction of measurement.
Frederick Reinitzer discovered the first compound to exhibit liquid crystal behavior in 1888.
There are three (3) different types of ordering that a liquid crystal can adopt. Nematic is ordered in only one dimension. Smectic is ordered in two dimensions. Cholesteric is molecules that are parallel to each other within each layer, but each layer is rotated with respect to the layers above and below it.
Liquid crystal displays (LCDs) allow polarized light to be transmitted through liquid crystals in one phase, but not transmitted through in another. When a voltage is applied, the plane polarized light can be rotated by a twisted liquid crystal such that it is allowed to pass through.
Liquid crystals can be used in thermometers. Spacing between crystal layers depends on temperature, and the wavelength of light reflected by the crystal depends on spacing.
Biomedical materials include replacement joints, dental implants, and artificial organs. All of these contain modern polymers. All must be designed with enough similarity to the body's own systems that the body will accept the material for its own. Substances used as biomedical materials must be as pure as possible.
Dental implants and dental composite materials have several advantages over traditional amalgams: They can be made in a wide range of colors and they avoid destroying the healthy portion of the tooth to be held in place.
A material used in dentistry must have properties that maximize both patient comfort and the lifetime of the implant. The material must be resistant to acids, must have low thermal conductivity, and must resist wear and resist expansion and contraction as temperature fluctuates.
The best artificial skin material today is based on a polymer of lactic acid and glycolic acid: Sutures, (stitches), are made of the same lactic acid-glycolic acid copolymer as the structural mesh of artificial skin. Researchers today use electrospinning to place nanofibers directly onto wounds.
Artificial joints: Polymethyl methacrylate (PMMA) and polyethylene have been used in many total joint replacements. Ultrahigh-molecular-weight polyethylene is now commonly used in many joint replacements, with the expectation of improved wear. Other surfaces have been researched to reduce wear including metal-on-metal and ceramic-on-ceramic surfaces.
Nanotechnology is the development and study of small-scale materials and objects that have sizes on the order of a tenth of a nanometer. An atomic force microscope can be used to image the surface of a material at the atomic or molecular level. From differences in deflection of a laser beam, electronics attached to a probe can create an image of the surface of an object. The scanning tunneling microscope (STM) measures the peak and valley heights of the sample from the flow of electric current.
Carbon exists as several allotropes, such as graphite, which contains sheets of carbon atoms that are all sp2 hybridized. Graphite is an electrical conductor within its sheets, but not between them.
C60 molecule, also known as buckminsterfullerene or buckyball, is a spherical molecule of 60 carbon atoms arranged in a structure of 12 pentagons and 20 hexagons, and it resembles a soccer ball. C60 was discovered in 1985 when it was isolated from graphite rods. It is the third major allotrope of carbon, after diamond and graphite. C60 has high symmetry, antioxidant properties, and applications in nanotechnology, biomedicine, and electronics.
Fullerenes are elongated and elliptical cages of 60 to 70 carbon atoms discovered after the C60 molecule in 1985.
Graphene is a single sheet of graphite and it is a two-dimensional carbon crystal containing an array of six-membered rings.
Carbon nanotubes are graphene sheets which wrap around themselves forming cylinders with diameters on the scale of nanometers.
Semiconductors: The band energy gaps (or lack of gaps) between the bonding band (valence band) and the antibonding band (conduction band) make it possible to classify a substance's electrical conductivity. Metals have no band gap, so they are good conductors of electricity.
Semiconductors have a band gap, but it is relatively small, so there is limited movement of electrons from valence band to the conduction band. The only elemental semiconductors are silicon, germanium, and carbon in the form of graphite. All three have four valence electrons.
Nonconductors have large band gaps, so it is nearly impossible to promote electrons from the valence band to the conduction band.
The conductivity of a semiconductor can be enhanced greatly by doping, the addition of very small quantities of an element with one more or one fewer valence electrons than the natural semi-conductor.
An n-type semiconductor is a type of doped semiconductor with enhanced semi-conductivity by the addition of negative particles, extra electrons.
A p-type semiconductor is a type of doped semiconductor with enhanced semi-conductivity because of holes (which are in the valence band) moving through the semiconductor rather than electrons.
Diodes are electronic devices that restrict the flow of electrons in a circuit to one direction. A light-emitting diode (LED) contains n-type and p-type semiconductor layers placed in contact.
Superconductors have no resistance to the flow of electrons. The temperature below which an element, compound, or material becomes superconducting is called the superconducting transition temperature.
Yttrium barium copper oxide is considered to be the first high-temperature superconductor.
Superconductors at or below their superconducting transition temperature exhibit the Meisner effect, the exclusion of magnetic fields.
Polymers are molecules containing many smaller parts linked together known as monomers. Thermoplastic polymers can be melted and reshaped. Thermosetting polymers have their shape determined as part of the chemical process that formed the polymer.
Addition polymerization is the simplest type of polymerization reaction and it includes the bonding of monomer molecules by the movement of electrons from a multiple bond into new single bonds between molecules. A free radical initiator molecule attaches to one of the ethylene carbon atoms and breaks the pi bond between the two carbon atoms in ethylene. In the addition reaction, monomers join together to form a polymer without the loss of any atoms. The double bonds in the monomers are broken, and rearranged into single bonds to create a long, repeating chain. Steps involved in the reaction are catalyzed and include initiation, propagation, and termination.
Polyethylene structure: (-CH2-CH2-)n, where n is the number of ethylene monomer molecules that reacted. Depending on reaction conditions, branches can form off the main polyethylene chain during polymerization. Branched chain polyethylene is more flexible and lower density than straight-chain polyethylene.
Natural rubber formed from latex is also an addition polymer and the monomer unit is isoprene. Rubber is an elastomer, a material that can stretch or bend and return to its original shape as long as the limits of its elasticity are not exceeded.
Industrial vulcanization was developed by Charles Goodyear in 1839, a process in which sulfur is used to create linkages between individual polymer chains in the rubber.
Molecules containing carbon=carbon double bonds can form addition polymers:
Styrene-polystyrene is used in disposable cups and plates as well as styrofoam insulation and craft materials.
Vinyl chloride-poly (vinyl chloride) PVC is used in pipes and fittings, some plastic wraps, and the classic "vinyl" records.
Tetrafluoroethylene-polytet rafluoroethylene (Teflon)
Polystyrene is made of a chain of styrene (C8H8) monomers (benzene ring attached to a vinyl ethylene group).
Polyacrylonitrile and polybutadiene are also addition polymers.
Copolymers are polymers made from two or more different monomers. Different combinations of the two or more monomers give rise to different types of copolymers. Examples of copolymers are acylonitrile butadiene styrene (ABS)(strong plastic) and styrene-butadiene rubber (SBR)(tires).
Copolymers formed from butadiene and styrene: SBS rubber-poly(styrene-butadiene-styrene) and HIPS-(high impact polystyrene)
Polymers with a vinyl group can be optical isomers:
Tacticity describes the relative arrangements of such chiral carbon atoms within a polymer.
Isotactic polymers-all the substituents are in the same relative orientation or same side of the chain.
Syndiotactic polymers- the substituents alternate positions along the polymer chain.
Atactic polymers- the substituents are oriented randomly along the polymer chain.
Condensation polymers form when monomers with two different functional groups combine, resulting in the elimination of a small molecule (usually water).
For example, proteins form between amino acid monomers. Each amino acid contains an amino group (-NH2) and a carboxyl group (-COOH). One water molecule is produced as each new C-N bond is formed. The C-N bond formed between an amino group and a carboxyl group is called an amide bond. Polyamides are polymers in which the monomers are connected by amide linkages. Nylon 6,6 is an example of a synthetic condensation polymer. Polyester is also a condensation polymer, along with Kevlar, polycarbonate, and polyurethane. Natural condensation polymers are proteins, starch, and cellulose.
Dacron is the trade name for the condensation copolymer formed from the ethylene glycol and para-terephthalic acid. The bond that forms from the ethylene glycol monomer and each para-terephthalic acid monomer is called an ester linkage.
Polyesters are polymers in which the monomers are connected by ester linkages.
Deoxyribonucleic acid (DNA) is a biological condensation copolymer of the five carbon sugar deoxyribose. Four bases of DNA: adenine, thymine, guanine, and cytosine. Ribonucleic acid (RNA) is also a biological copolymer analogous to DNA. It is made from the five carbon sugar ribose. Four bases of RNA: adenine, uracil, guanine, and cytosine.
The polymerization of acetylene (C2H2) results in electrically conductive polyacetylene, where its carbon triple bonds become alternating double bonds and hydrogens are attached non-linearly instead of horizontally. The presence of electrons in the delocalized p electrons are key to the electrical conductivity in polyacetylene.
Ceramics are polymeric inorganic compounds that share the properties of hardness, strength, and high melting points. Ceramics are usually formed by melting and then solidifying inorganic substances (including clays).
Ceramics are prepared by a process called sintering in which a slurry of a powder of the inorganic substance in water is heated to a very high temperature under high pressure. To avoid imperfections and cracks, the sol-gel process is used to produce particles of nearly uniform size. The first step in the sol-gel process is the preparation of alkoxide of the metal or metalloid
metal + alkoxide => metal alkoxide + nH+
Next, the metal alkoxide is dissolved in alcohol. Water is then added to generate the metal hydroxide and regenerate the alcohol.
metal alkoxide + 3H2O => metal hydroxide (OH) + alcohol
Once the metal hydroxide is formed, it undergoes a condensation polymerization.
Composite materials are made from two or more substances with different properties that remain separate in the bulk material. Polymer matrix composites in modern composite materials commonly including reinforcing fibers in a polymer matrix called resin.
Metal matrix composites are made from a metal and a ceramic, organic polymer, or another metal. Ceramic matrix composites use ceramic as the primary reinforcing material accompanied by organic polymers.
Liquid Crystals have properties of liquids (ability to flow and take shape of container) and those of crystals (regular arrangement of particles in a lattice).
Liquids are isotropic, because particles are free to rotate in every direction. Thus, their properties are independent of the direction of testing. Liquid crystals are anisotropic because their properties depend on the direction of measurement.
Frederick Reinitzer discovered the first compound to exhibit liquid crystal behavior in 1888.
There are three (3) different types of ordering that a liquid crystal can adopt. Nematic is ordered in only one dimension. Smectic is ordered in two dimensions. Cholesteric is molecules that are parallel to each other within each layer, but each layer is rotated with respect to the layers above and below it.
Liquid crystal displays (LCDs) allow polarized light to be transmitted through liquid crystals in one phase, but not transmitted through in another. When a voltage is applied, the plane polarized light can be rotated by a twisted liquid crystal such that it is allowed to pass through.
Liquid crystals can be used in thermometers. Spacing between crystal layers depends on temperature, and the wavelength of light reflected by the crystal depends on spacing.
Biomedical materials include replacement joints, dental implants, and artificial organs. All of these contain modern polymers. All must be designed with enough similarity to the body's own systems that the body will accept the material for its own. Substances used as biomedical materials must be as pure as possible.
Dental implants and dental composite materials have several advantages over traditional amalgams: They can be made in a wide range of colors and they avoid destroying the healthy portion of the tooth to be held in place.
A material used in dentistry must have properties that maximize both patient comfort and the lifetime of the implant. The material must be resistant to acids, must have low thermal conductivity, and must resist wear and resist expansion and contraction as temperature fluctuates.
The best artificial skin material today is based on a polymer of lactic acid and glycolic acid: Sutures, (stitches), are made of the same lactic acid-glycolic acid copolymer as the structural mesh of artificial skin. Researchers today use electrospinning to place nanofibers directly onto wounds.
Artificial joints: Polymethyl methacrylate (PMMA) and polyethylene have been used in many total joint replacements. Ultrahigh-molecular-weight polyethylene is now commonly used in many joint replacements, with the expectation of improved wear. Other surfaces have been researched to reduce wear including metal-on-metal and ceramic-on-ceramic surfaces.
Nanotechnology is the development and study of small-scale materials and objects that have sizes on the order of a tenth of a nanometer. An atomic force microscope can be used to image the surface of a material at the atomic or molecular level. From differences in deflection of a laser beam, electronics attached to a probe can create an image of the surface of an object. The scanning tunneling microscope (STM) measures the peak and valley heights of the sample from the flow of electric current.
Carbon exists as several allotropes, such as graphite, which contains sheets of carbon atoms that are all sp2 hybridized. Graphite is an electrical conductor within its sheets, but not between them.
C60 molecule, also known as buckminsterfullerene or buckyball, is a spherical molecule of 60 carbon atoms arranged in a structure of 12 pentagons and 20 hexagons, and it resembles a soccer ball. C60 was discovered in 1985 when it was isolated from graphite rods. It is the third major allotrope of carbon, after diamond and graphite. C60 has high symmetry, antioxidant properties, and applications in nanotechnology, biomedicine, and electronics.
Fullerenes are elongated and elliptical cages of 60 to 70 carbon atoms discovered after the C60 molecule in 1985.
Graphene is a single sheet of graphite and it is a two-dimensional carbon crystal containing an array of six-membered rings.
Carbon nanotubes are graphene sheets which wrap around themselves forming cylinders with diameters on the scale of nanometers.
Semiconductors: The band energy gaps (or lack of gaps) between the bonding band (valence band) and the antibonding band (conduction band) make it possible to classify a substance's electrical conductivity. Metals have no band gap, so they are good conductors of electricity.
Semiconductors have a band gap, but it is relatively small, so there is limited movement of electrons from valence band to the conduction band. The only elemental semiconductors are silicon, germanium, and carbon in the form of graphite. All three have four valence electrons.
Nonconductors have large band gaps, so it is nearly impossible to promote electrons from the valence band to the conduction band.
The conductivity of a semiconductor can be enhanced greatly by doping, the addition of very small quantities of an element with one more or one fewer valence electrons than the natural semi-conductor.
An n-type semiconductor is a type of doped semiconductor with enhanced semi-conductivity by the addition of negative particles, extra electrons.
A p-type semiconductor is a type of doped semiconductor with enhanced semi-conductivity because of holes (which are in the valence band) moving through the semiconductor rather than electrons.
Diodes are electronic devices that restrict the flow of electrons in a circuit to one direction. A light-emitting diode (LED) contains n-type and p-type semiconductor layers placed in contact.
Superconductors have no resistance to the flow of electrons. The temperature below which an element, compound, or material becomes superconducting is called the superconducting transition temperature.
Yttrium barium copper oxide is considered to be the first high-temperature superconductor.
Superconductors at or below their superconducting transition temperature exhibit the Meisner effect, the exclusion of magnetic fields.