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Polymeric MaterialsChapter 2

Professor Joe Greene

CSU, CHICO

September 8, 1999

MFGT 041

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Chapter 2 Objectives

• Objectives– Fundamentals of Matter– Bonding– Solid, Liquids, and Gases– Basic Organic Chemistry– Polymers– Formation of Polymers– Thermoplastics and Thermosets– Copolymers

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Atomic Theory• Material classification

– Matter is anything that has weight and occupies space– All gases, liquids, and solids are matter.– Heat, light, and electricity are not matter; but energy.– Conversion of matter (mass) to energy releases enormous amounts of energy. E=mc2

• Elements: materials consisting of one kind of atom– All material is composed of various combinations of atoms– Scientists have found over 100 types of atoms; 90 of which are occur naturally; the remaining are synthetic.

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Atomic Terms• Mass is a property of a body, expressed in Kg• Weight is the gravitational force exerted on a body by the earth,

expressed in lbs or N. Remember: F = ma• Isotopes are atoms that vary from the normal atomic mass found in

naturally occurring forms of the element, e.g., an atom may contain more or fewer neutrons in the nucleus.

• Some isotopes are unstable and reactive. These are used in chemical tracers and nuclear fuels.

• Neutrons are neutral particles that do not have electrical charge, and hence do not alter the atomic number or chemical properties of the element.

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Atomic Structure• Atoms are made up of complex subatomic particles.

– Protons are positively charged identical particles.

– Neutrons remain at the nucleus or center of the atom and are neutral identical particles.

– Electrons are negatively charged particles that orbit the nucleus at speeds approaching the speed of light.

• Variations in combinations of protons, neutrons, and electrons make up difference between atom types. – The most fundamental difference between atoms is the number of protons.

– Atoms which differ in the number of neutrons are called isotopes.• e.g., H has 3 isotropic forms: (1) one proton and one neutron, atomic wt 1; (2) one proton and two neutrons, atomic wt

2; (3) one proton and three neutrons, atomic wt 3. Final atomic weight = weighted average of the 3.

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Atomic Structure• The periodic table is a sequential listing of the number of protons from 1 to 110. H has 1 proton, He has 2, Li has

3…– The number of protons is the atomic number.– The sum of protons and neutrons is the atomic weight.– Atomic weight is not a whole number due to the isotopes that have a different number of neutrons.

• Periodic table has Groups in columns and Periods in Rows– Group I elements are most likely to give up electrons– Group II elements are 2nd most likely to give up electrons– Group VIII are stable and do not accept electrons– Group VII are very reactive and accept one electron

• Valence– the number that reflects the number of electrons the atom will usually give up (+1 for H, Li, Na, etc.) or receive (-1 for F, Cl,etc)

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Quantum Mechanics• Electrons orbit the nucleus of the atom. The tiny solar

system behaves in ways that cannot be predicted by common laws of physics. Need quantum mechanics.

• Quantum Mechanics is a field of study that uses energy levels, motion analysis, and probability theories to study atoms.

• In Quantum Mechanics electrons behave in a wavelike fashion rather than individual particles. Waves can be diverted by reflection or diffraction.

• The location of the electron is described by energy levels rather than by individual positions. The higher the energy level the further away from the nucleus.

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Periodic Chart Organization• Elements are divided into two groups- metals and nonmetals

– Of the 120 known elements (including synthesize), approximately 81 are metals. 92 occur naturally in the earth.

• Metals have the following characteristics to varying degrees– High electrical conductivity and High thermal conductivity– Luster- ability to reflext light. Ductility, maleability– Loose electrons (low ionization energy) readily when they react with nonmetals– Metallic character should decrease as we move across the Periodic Table and increase as we

move down.

• Nonmetals tend to be insulators (solid, liquid, or gas)– Gain electrons in chemical reactions

• Noble gases are inert• Metalloids are semiconductors

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Quantum Levels • Electrons exist in orbits around the nucleus. More than one electron can be in

each orbit due to alternating spins.• Energy levels appear at predictable intervals in disctict orbits or shells, e.g., 1s

(2 electrons), 2s (2 electrons) and 2p (6 electrons), 3s, 3p, etc.• s, p, f, and d are Quantum Levels 1, 2, 3, and 4• Vertical groupings in periodic table are based upon similar electron

configuration and similarities in both chemical and physical properties– Group 1A alklai metals; Group IIA are alkaline-earth metals– Group B subgroups- transition elements– Group IIIA through VA and VIIA are mostly non-metals– Group VIII- Noble or Inert Gases– Octet rule- accept/give electrons to fill s and p orbitals (2+6=8)

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Periodic Table• Invented by Dmitri Medeleyev in the late 1800’s• Many of the elements in the table were not discovered until

long after the table was invented• All elements are in their most basic form and cannot be

simplified• Table lists the atomic number and atomic mass• The atomic number is the number of protons in the nucleus

or the center of the atom• The atomic mass is the sum of the masses of the protons and

neutrons. Electrons weigh about 1/2000 as a proton.• Carbon (C) has atomic number 6 because there are 6 protons

in the nucleus.

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Periodic TableIA IIA ….Groups… IIIA IVA VA VIA VIIA VIIIA

Excellent Reference: http://www-tech.mit.edu/Chemicool/

Atm #SymbolWgt

Lanthanides

Actinides

1H

1.01

B Groups

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Periodic Table• Groups

– I: Group 1 is also called the alkali metal group. These are strong metals that are unusually soft and very reactive toward Oxygen forming Oxides and water forming hydroxides of the metal.

– II: Group 2 is called the alkaline earth metals. These metals are not as soft as Group 1 metals. Theyalso react more mildly with Oxygen to produce oxides of the metals and only react with water at temperatures where the water is steam.

– Groups 3-12 are referred to as the transition metal groups. These metals are not as predictable

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Periodic Table• Groups 3B- are referred to as the transition metal groups.

– These metals are not as predictable because of the shielding effect of the inner electrons. As for the "shielding effect" this refers to the inner electrons found in the transition state elements and the inner transition (rare earth)elements. These electrons had a tendency to block the electrical effect of the positive nucleus upon the outer valence electrons of those atoms. This shielding effect helps to partially explain the erratic placement of the electrons in the d and f orbitals relative to the s and p orbitals.

• Groups 1A-2A and 3A-8A are referred to as the representative elements

• Group 7A is referred to as the halogen group • Group 8A is referred to as the Noble gas group previously known

as the inert gas group.

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Periodic Table• The metals which tend to have their atoms losing electrons

during a chemical change are roughly found to the left Group 3

• Non-metals which tend to have their atoms gaining electrons during chemical change are roughly found in Group 6A-7A with some elements in the lower parts of Groups 5A.

• Metalloids which tend to have their atoms sometimes losing and sometimes gaining electrons during chemical change are generally found in Groups 4A-6A

• The Noble gases really belong to their own category since their atoms tend neither to lose or gain electrons. There are only a handful of compounds involving the Noble Gases (mostly involving Xenon).

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Periodic Table Properties

• As you proceed to the left in a period or as you proceed down within a group:

– The metallic strengths increase (non-metallic strengths decrease).

– The atomic radius of atoms (distance from the nucleus to the outermost occupied region) increases. Atomic radii are the distance between the outermost occupied probability region of an atom and its nucleus.

– The ionization potential (energy required to remove an electron from an atom) decreases. Ionization Potential is energy required to remove electron from atom.

– The electron affinity (energy released as electron is picked up by an atom) decreases. – The electronegativity (the electron attracting ability of an atom) decreases.

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Bonding• Bonding occurs when two or more atoms come into close

proximity resulting in an attraction between atoms. • If atoms are large distance from each other, there is little

interaction.

– As the distance between the atoms decreases, the energy begins to decrease and the system becomes more stable.

– Eventually, the atoms reach an optimal separation which is the bottom of the energy curve. The separation is the bond length. Bond energy is depth of well.

– Atoms too close have repulsive energy.

• Bonding is attributed to interactions between the electrons.

Figure 2.3SystemEnergy

Distance between atoms

Repulsive energy

Separated atomsBondEnergyStable

unstable

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Bonding• Ionic bonding (ceramics, e.g., salt and clay)

– Forms when an atoms that has a strong tendency to give up electrons (a metal) is in close proximity to an atom that has a strong tendency to accept electrons (nonmetal).

• Transfer of one or more electrons from the outer shell of one atom to the outer shell of the other atom depending on the valence of the atoms.

• Results in an electron arrangement when many ions (+ and -) are in close proximity, e.g., NaCl, that has a polar arrangement of the ions similar to a magnet.

• Forms crystalline structure

Na e-

e- e-

Cl e-

e- e-

e- e-

Na+

e- e-

Cl- e-

e- e-

e- e-

e-

atoms ions

Na+ Na+ Na+

Na+ Na+ Na+

Cl- Cl- Cl-

Cl-

Cl- Cl- Cl-

Na+ Na+ Na+Cl- Cl-

Metal ion Non-metal ion

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Bonding• Metallic bonding– Occurs when two metal atoms are in close proximity.Both atoms have tendency

to give up electrons. Electrons are free to move about entire atoms structure

– Releasing electrons yields a lower energy state.

– The metal atoms approach each other and give up electrons when in close proximity to a sea of electrons.

– Charged metal ions cancel the repulsive forces due to the electron movement.

– Crystal structures can form in some atoms but the forces are not as strong as ionic bonds in ceramics.

– Metallic alloys can form when each gives up electrons and form a positively charged ion.

Fe Fe e-

e-

e-

e-

Fe++ e-

e- Fe++ e-

e-

Fe atomFe atom

Electrons (free to move)

Fe++ e-

e- Fe++ e-

e- Fe++ e-

e- Fe++ e-

e-

Fe++ e-

e-

Fe++ e-

e-Fe++ e-

e-Fe++ e-

e-Fe++ e-

e-

Fe++ e-

e-Fe++ e-

e- Fe++ e-

e-

Metal ions Sea of electrons

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Bonding• Covalent bonding (most important for plastics)

– Occurs when two nonmetal atoms are in close proximity.

– Both atoms have a tendency to accept electrons, which results in shared outer electron shells of the two atoms.

– Number of shared electrons is usually to satisfy the octet rule.

– Resulting structure is substantially different that the individual atoms, e.g., C and H4 make CH4, a new and distinct molecule.

– Atoms is covalent bonds are not ions since the electrons are shared rather than transferred as in ionic or metallic bonds.

H e-

H e-

H e-

H e-

e-

C

e-

e- e-C e-

e- e-

e-H

e-

H

H

H

e- e-

e-

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Bonding• Secondary bonding: weaker than ionic, metallic, covalent

– Hydrogen bonding• Occurs between the positive end of a bond and the negative end of another

bond.

• Example, water the positive end is the H and the negative end is O.

– van der Waals• Occurs due to the attraction of all molecules have for each other, e.g.

gravitational. Forces are weak since masses are small

– induced dipole• Occurs when one end of a polar bond approaches a non-polar portion of

another molecule.

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Bonding in Polymers• Polymer chains with atoms other than carbon

– Usually polymer chains with C and N, O, S, F, and Cl• PVC has Cl; Nylon has O and N; Polyurethane has O and N• PET has O and benzene ring; PC has O and benzene ring

• Bonding in Plastics (No metallic or Ionic bonds_ Just Covalent)– Covalent bonds are dominate bonding between C and other atoms.

• Secondary bonding and Intermolecular Forces• Van der Waal’s Forces- weak attraction not in plastics• Dipole interactions- Part of molecule is more electronegative than other part causing

one side to be partially negative and the other partially positive.

• Hydrogen bonding- Very important for some plastics- Like Nylon– Causes physical properties to change. Like tensile strength and melting point– Nylon 6 has higher tensile strength and melting point than Nylon 12 because

» Nylon 6 has 1 dipole + 1 hydrogen bond for every 6 Carbon atoms » Nylon 12 has 1 dipole and 1 hydrogen bond every 12 Carbon atoms

– Dipole induces polarity and occurs if» C-Cl single bond (like PVC); C-Fl single bond (Like PTFE); C=O double

bond (like Nylon, PET, PU, PC)– Hydrogen bonds induces polarity and occurs if

» C-OH single bond (like PU-polyurethane); N-H Single bond (PU, Nylon)

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Solids, Liquids, and Gases• States of matter

– Solid: fixed volume and fixed shape• Example, ice cube has fixed shape regardless of which container it is

placed in.

– Liquid: fixed volume and variable shape• Example, water will take the shape of the container

– Gas: matter has neither fixed volume or shape• Example, steam will take the shape of the container and occupy the

entire volume of the container

• Most types of matter can be converted from state to another by changing the temperature.– Example, ice goes from ice to water to steam.

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Thermal Induced Change of State• Single most important property that controls the state of a

material is the freedom of movement of the atoms or molecules.– Solid: particles are highly restricted in their movements

– Liquid: some movement of molecules

– Gas: particles are not restricted in movement

• As heat is applied, the solid material melts– the solid atoms gain energy and vibrate until the the molecules have

more energy than the bonding energy of the structure (secondary bonds in 3 dimensions), melting point.

• As more heat is applied the material evaporates– the liquid continues to vibrate, move and rotate about secondary bonds

until they are broken at the boiling point.

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Basic Concepts of Organic Chemistry• Organic chemistry

– Study of carbon chemistry because of the carbon basis for organic cells and organisms.

– Plastics area based upon carbon and thus are part of organic chemistry.

• Carbon atom bonding– C has atomic number 6. Thus, has 6 protons and 6 electrons surrounding

the nucleus. • Two in the first (s) shell not used in bonding.

• Four in p shell and available for bonding.

• C will always form 4 bonds and has a valance of 4.

– Bonding of Carbon with 4 H, as in CH4, must satisfy 2 conditions• Each hydrogen must bond with one electron in the carbon cloud thus forming 4

bonds. This will satisfy octet rule for the p shell.

• The four H atoms must be as far away as possible to achieve lowest energy.

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Basic Concepts of Organic Chemistry• Figure 2.10. C atom bonding with 4 H atoms to form CH4.

• Figure 2.11. Carbon atoms bound by covalent bonds.

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Basic Concepts of Organic Chemistry• Many other atoms can combine with carbon in

configurations similar to H and Cl to form various molecules.– Each has a characteristic bonding pattern that is dictated by the

number of electrons in outer shell (valence of atom).

• Table 2.2 Number of bonds for typical atoms

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Carbon-Carbon Molecular Orbitals• Key to large complexity of carbon-containing molecules is that

Carbon can form bonds with itself.• Figure 2.12 Bonding in Carbon molecules

• C=C Double bond is 2 different types of bonds– Sigma bond: is more stable due to closer to nucleus.

– Pi bond.

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Functional Groups• Certain chemical characteristics associated with various

groups of atoms, called functional groups.• Particular groups of atoms occur in a large molecule, the

characteristic chemistry is anticipated.– Example, CH3Cl

• Functional groups can be attached to basic groups of carbon atoms by replacing on H atom.

• Table 2.14. – Functional groups in organic chemistry

– Common functional groups

– Differences in Various molecules of carbon, hydrogen

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Functional Groups• Table 2.15. Various molecules of carbon, hydrogen and oxygen

illustrating the differences properties with different atomic arrangements

• isopropyl alcohol- rubbing alcohol• methylethyl ether- anesthetic• acetone- common solvent• methyl acetate- sweet chemical perfume• propionaldehyde- sharp smelling chemical• propanoic acid= related to vinegar

• Aromatic group– 6 carbon atoms bonded together with double bonds

– Highly aromatic if have several aromatic groups

• Aliphatic group– single and double bonded carbons with other atoms

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Naming Organic Compounds• Basis for naming organic compounds

– Indicate the family of organic compounds to which a molecule belongs (importance to polymers)

• Dependent upon functional group, e.g. alcohol group, methanol or methyl alcohol.

• Dependent upon the number of carbon atoms in the repeating molecule.Number Counting Carbons Counting functional groups

– 1 C Meth mono

– 2 C Eth Di

– 3 C Pro Tri

– 4 C But Tetra

– 5 C Pent Penta

• Example,– CH4 has one carbon and no functional groups (alkane), thus is meth ‘ane.

– C2H2 has 2 carbons and has a double bond (alkene), thus is eth ‘ene.

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Polymers• Just as 2 carbons atoms are bonded together in ethane, three,

four, or more carbons can be bonded in chain-like arrangement, sometimes thousands of atoms long.

• Long chains of atoms are polymers (many mers or units)• Figure 2.16. Polyethylene

• Figure 2.17 Polymer chain notations

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Polymers• Polymer chains with atoms other than carbon

• Bonds can have different electronegativities, sharing of electrons may be unequal.– Covalent bonds have some ionic character.– Example,

• Figure 2.19. Pendent oxygen is more electronegative than the carbon which is double bonded to it and so the oxygen would be partially negative and the carbon partially positive.

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Formation of Polymers• Chain-Growth or Addition Polymerization

– Instantaneously, the polymer chain forms with no by-products– Chain-reaction mechanism that proceeds by several sequential steps as shown in

Figure 2.20. Polymerization begins at one location on the monomer by an initiator1. Introduce the monomer containing C=C into reaction vessel.

2. Inject an initiator (small amount) into vessel, e.g.,peroxides.• Note: peroxides are initiators and not catalysts because initiators participate in the reaction and are consumed,

whereas catalysts participate in the reaction but are NOT consumed

3. Initiation step between the peroxide and the C=C.

4. Peroxide free radical extracts one of the two electrons in the bonds and forming a new bond with the C atom. The other electron becomes a free radical.

5. The new free radical from the bond is available to form other bonds.

6. The new free radical from the bond forms bonds with other bond electrons.

7. Process continues of creating bonds and creating polymer chain.

8. Polymer chain ends. Chain termination reaction occurs when two free radicals join or two C atom

free radicals joins that can link two or more polymer chains.

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Carbon Chain Polymers • Homopolymers

– Simplest plastic containing one basic structure– If X = H then Polyethylene– If X = Cl the PVC

– If X = CH3 then PP

– If X = Benzene Ring then Polystyrene

• Through Addition Polymerization from monomer

C C

H X

H H

n

C C

H X

H H

Heat, Pressure, Initiator

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Addition Polymerization Monomers• Figure 2.22

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Formation of Polymers• Polymers from Addition reaction

– LDPE HDPE PP

– PVC PS

C C

H H

H H

n

C C

H H

H H

n

C C

H CH3

H H

n

C C

H Cl

H H

n

C C

H

H H

n

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Other Addition Polymers• Polyphenylene

• Polyphenylene oxide

• Poly(phenylene sulfide)

• PolymonochloroparaxylyeneS S S

O OO

CH2 CH2

Cl Cl

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Other Addition Polymers• Vinyl- Large group of addition polymers

with the formula:– Radicals (X,Y) may be attached to this repeating

vinyl group as side groups to form several related polymers.

• Polyvinyls– Polyvinyl chloride– Polyvinyl dichloride

(polyvinylidene chloride)

– Polyvinyl Acetate (PVAc)

C C

H X

H Y

orC C

H X

H H

CC

H Cl

H H

C C

H Cl

H Cl

C C

H OCOCH3

H H

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Formation of Polymers• Condensation Polymerization

– Step-growth polymerization proceeds by several steps which result in by-products.

• Step-wise (Condensation) Polymerization– Monomers combine to form blocks 2 units long

– 2 unit blocks form 4, which intern form 8 and son on until the process is terminated.

– Results in by-products (CO2, H2O, Acetic acid, HCl etc.)

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Common Polymer Synthesis• Polyamides

– Condensation Polymerization• Nylon 6/6 because both the acid and amine contain 6

carbon atoms

NH2(CH2)6NH2 + COOH(CH2)4COOHHexamethylene diamene Adipic acid

n[NH2(CH2)6NH2 ·CO(CH2)4COOH] (heat)

Nylon salt

[NH(CH2)4NH · CO(CH2)4CO]n + nH2O Nylon 6,6 polymer chain

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Nylon Family

• The repeating -CONH- (amide) link is present in a series of linear, thermoplastic Nylons– Nylon 6- Polycaprolactam:

• [NH(CH2)5CO]x

– Nylon 6,6- Polyhexamethyleneadipamide:• [NH(CH2)6NHCO (CH2)4CO]x

– Nylon 12- Poly(12-aminododecanoic acid)• [NH(CH2)11CO]x

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Polycarbonate• Polycarbonates are linear, amorphous polyesters

because they contain esters of carbonic acid and an aromatic bisphenol (C6H5OH)

• Polymerized with condensation reaction

Phenol + Acetone Bisphenol-A + water

2

OH

+H2O+

C CH2CH3

OC

CH2

CH2

OHOH

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Polycarbonate

Bisphenol-A + Phosgene Polycarbonate + salt

NaCl+

C

CH2

CH2

OHOH + nCOCl2

O C

CH2

CH2

C

O

O

n

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Condensation Polymerization• Polyhydroxyethers (Phenoxy)- Reaction of Bisphenol A

and epichlorohydrin. Similar to polycarbonate. Sold as thermoplastic epoxide resins.

n

O C

CH2

CH2

C

OH

O

H

H

C C

H H

H

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Other Condensation Polymers

• Polyetheretherketone (PEEK)– Wholly aromatic structure– Highly crystalline– High temperature resistance

O O O C

O

n

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Chemical Synthesis• Synthesis of polyketones

– PEK: Formation of the carbonyl link by polyaroylation from low cost starting materials. Requires solvents such as liquid HF. Excessive solvents and catalyst cause the high material cost.

– PEEK: Formation of ether link using phenoxide anions to displace activated halogen.

O

C ClOHF, catalyst

O

nO C + HCl + CO2 +H20

PEK

K2CO3, DPS

O

C FF OHOH+ PEEK + CO2 +H20 +KF

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Other Condensation Polymers• Thermoplastic Polyesters

– Saturated polyesters (Dacron). • Linear polymers with high MW and no crosslinking.• Polyethylene Terephthalate (PET). Controlled crystallinity.• Polybutylene Terephthalate (PBT).

– Aromatic polyesters (Mylar)

O C

O

R O C

O

R

C

O

C

O

R R

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Other Condensation Polymers

• Polysulfones- Repeating unit is benzene rings joined by sulfone groups (SO2), an isopropylidene group (CH3CH3C), and an ether linkage (O).

n

C

CH3

CH3

OO SO2

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Characteristics of Addition and Condensation

• Table 2.4

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Polymerization by other than Addition or Condensation

• Ring opening– Epoxy is created via ring opening to generate active

species and initiate polymerization.– Epoxy plus amine produces epoxy polymerization– Nylon 6 is formed when caprolactam ring is opened.– Acetal polymer is made by the opening of the trioxane

ring.

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Homopolymers• Table 3-2 Plastics Involving Single Substitutions

X Position Material Name AbbreviationH Polyethylene PECl Polyvinyl chloride PVCMethyl group Polypropylene PPBenzene ring Polystyrene PSCN Polyacrylonitrile PANOOCCH3 Polyvinyl acetate PvaCOH Polyvinyl alcohol PVACOOCH3 Polymethyl acrylate PMAF Polyvinyl fluoride PVF

Note:Methyl Group is:

|H – C – H | H

Benzene ring is:

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Homopolymers• Plastics Involving Two Substitutions

C C

H X

H Y

n

X Position Y Position Material Name AbbreviationF F Polyvinylidene fluoride PVDFCl Cl Polyvinyl dichloride PVDCCH3 (Methyl group) CH3 Polyisobutylene PBCOOCH3 CH3 Polymethyl methacrylate PMMA

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Homopolymers• Plastics Involving Three+ Substitutions (use Table 3.2)

C C

W X

Z Y

n

C C

F F

F F

n

e.g. PTFEpolytetrafluoroethylene(Teflon)

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Copolymers• Plastics Involving Two mers in chain (use Table 3-2)

C C

H X1

H H

n

C C

H X2

H H

m

e.g. SAN styrene acronitrile

C C

H

H H

n

C C

H C:::N

H H

m

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Copolymers• Structure of two mers can be

– Alternating- ABABABABABABAB– Random copolymer- AABBABBBAABABBBAB– Block copolymer- AABBBAABBBAABBBAABBB– Graft copolymer- AAAAAAAAAAAAAAAA

B B B

B B B

B B B

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Terpolymers• Plastics Involving Three mers in chain (use Table 3-2)

C C

H X3

H H

k

e.g. ABS acronitrilebutadiene styrene

C C

H

H H

km

C C

H X1

H H

n

C C

H X2

H H

m

C C

H C:::N

H H

n

C C

CH2 CH2

H H

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Terpolymers• Structure of three mers can be

– Alternating- ABCABCABCABCABCABCABC– Random copolymer- AABCBABCBBCAABCABCB– Block copolymer- AABBCAABBCAABBCAABBC– Graft copolymer- C C C C

C C C C

AAAAAAAAAAAAAAAA B B B

B B B

B B B

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Thermoplastics and Thermosets• All polymers made from either condensation or addition

polymerization are either– Thermoplastic, heat forming

– Thermoset, heat setting

• Thermoplastic bonds are covalent• Thermoset bonds are covalent and crosslinked (Fig2.26)

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Epoxy Chemistry

Thermoset Chemistry

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Thermoset Polyesters• Crosslinking of thermoset polyester

– Produced via condensation reaction. • The H on one monomer (alcohol) reacts with the OH on the other (acid) to form water

byproduct and a new bond is formed linking the monomers.

• This repeats because each of the monomers has two reactive sites.

• The second site is a C=C double bond that is only active in addition reactions and is not involved in the initial reaction that forms the basic polymer.

• The basic polymer is a liquid allowing it to be poured into a mold for the crosslinking reaction to occur.

• Crosslinking occurs when styrene and an initiator in added to crosslink and polymerize the polyester.

• The resulting structure is characterized by principle chains of polyesters that were formed by condensation polymerization and then subsequently crosslinked using addition reaction often using bridge monomer (styrene).

• Analogy to this type of reaction is baking a cake. The cake batter is liquid polymer of low chain length and placed in mold (oven). As the cake heats up the liquid is converted to solid cake due to crosslinking. Demold and cools.

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Thermosets and Crosslinking• Melamine formaldehyde (Formica)

– Produced via condensation reaction with multiple reactive sites for crosslinking (required to have multiple sites in monomer)

• Active site on one monomer reacts with active site on another monomer to produce polymer with water as a by-product.

• Melamine monomer has 3 active sites plus formaldehyde with two reactive sites produces a polymer with crosslinking in several directions.

– Figure 2.27 Polymerization and crosslinking of melamine formaldehyde