MSE 201-Polymers 1

General Overview of General Overview of Polymers (Unit 1Polymers (Unit 1––5b)5b)

• Polymer Classifications• Concept of Mole. Wt.• Polymerization routes• Polymer crystallinity

IntroductionIntroduction•• Recall polymer (macromolecular) Recall polymer (macromolecular)

definitiondefinition–– Covalent linkages of many repeating Covalent linkages of many repeating

monomer units. (polymer or chain monomer units. (polymer or chain molecules or polymer chains)molecules or polymer chains)

–– Very high MW (e.g., MW of PS = 300,000 Very high MW (e.g., MW of PS = 300,000 (cf. MW of small molecules)(cf. MW of small molecules)

–– Recall Lecture 1Recall Lecture 1

MSE 201-Polymers 2

IntroductionIntroduction

•• Chemical properties defined by Chemical properties defined by monomer propertiesmonomer properties

•• Physical properties are UNIQUE Physical properties are UNIQUE and changeable (large size, and changeable (large size, interactions, chain flexibility, interactions, chain flexibility, M M == xxMoMo).).

Degree of Degree of PolymerizationPolymerization

•• D.P. = polymer chain length (# D.P. = polymer chain length (# repeating units)repeating units)–– e.g., D.P. (PVC) = 1000e.g., D.P. (PVC) = 1000–– M(PVC) =M(PVC) = xxMoMo = 1000 x 62.5= 1000 x 62.5

•• x (or D.P.) is more convenient than x (or D.P.) is more convenient than MW for polymersMW for polymers

•• 1000 < MW < 1,000,000 (typical 1000 < MW < 1,000,000 (typical values)values)

•• 10 < n, 10 < n, xx, D.P. < 10,000 (where , D.P. < 10,000 (where MMoo == 100)100)

MSE 201-Polymers 3

Concept of Molecular Concept of Molecular Weight DistributionWeight Distribution•• ExplainExplain

Class Practice ProblemClass Practice Problem

•• If a particular type of PE has a If a particular type of PE has a degree of polymerization of 10 degree of polymerization of 10 000, what is its molecular 000, what is its molecular weight? (atomic masses of C weight? (atomic masses of C and H are 12 & 1)and H are 12 & 1)

MSE 201-Polymers 4

Molecular vs.Molecular vs. MicrostructuralMicrostructuralEngineeringEngineering

•• Different properties by joining Different properties by joining monomers in different ways (cf. monomers in different ways (cf. metals)metals)–– cfcf: Metals can only be heat: Metals can only be heat--treated or treated or

workwork--treated but their molecules (& treated but their molecules (& crystals) are fixed forever crystals) are fixed forever ((microstructuralmicrostructural engineering)engineering)

–– MicrostructuralMicrostructural eng. also possible eng. also possible with polymer (structurewith polymer (structure––property property relations to be discussed later)relations to be discussed later)

–– Illustrate overIllustrate over

Schematic of Polymer Schematic of Polymer ChainsChains

Linear Branched

CrosslinkedNetwork

MSE 201-Polymers 5

Molecular Molecular ClassificationsClassifications

•• USAGE USAGE –– Plastics, rubber, fiber, coatings & filmsPlastics, rubber, fiber, coatings & films

•• POLYMERIZATION ROUTESPOLYMERIZATION ROUTES–– Condensation vs. addition (or step vs. Condensation vs. addition (or step vs.

chain)chain)–– CopolymerizationCopolymerization (alternating, random, (alternating, random,

block, graft)block, graft)

Molecular Molecular ClassificationsClassifications

•• NATURALNATURAL (silk, wool, DNA, (silk, wool, DNA, cellulose) vs. cellulose) vs. SYNTHETICSYNTHETIC** **

•• ARCHITECTUREARCHITECTURE–– FINITEFINITE (thermoplastics, may be (thermoplastics, may be

"linear" or "branched")"linear" or "branched")–– INFINITEINFINITE ((thermosetsthermosets, usually, usually

crosslinkedcrosslinked))

MSE 201-Polymers 6

UsageUsage

•• PLASTICS (pure polymers + PLASTICS (pure polymers + additives**)additives**)–– Traditionally excludes rubber (NOT Traditionally excludes rubber (NOT

synonymous with polymers), synonymous with polymers), –– e.g., PE, PS, PVCe.g., PE, PS, PVC–– Construction, packaging, Construction, packaging,

automobiles, furniture,dishware, etcautomobiles, furniture,dishware, etc..

Def. - “serves to introduce concepts of chemical structure and terminology [poly (name of monomer) ]"

Examples ofExamples ofPlasticsPlastics

MSE 201-Polymers 7

Usage, Usage, cont’dcont’d•• ELASTOMERS/SYNTHETIC RUBBERSELASTOMERS/SYNTHETIC RUBBERS

–– Emphasize double bond reactivityEmphasize double bond reactivity–– PBD,PBD, PIsoPPIsoP (natural), PCP (neoprene), (natural), PCP (neoprene),

SBRSBR–– Tires & tire products, gaskets, seals, etc.Tires & tire products, gaskets, seals, etc.

Usage, Usage, cont’dcont’d

•• FIBERS (explain high strength FIBERS (explain high strength & stiffness**)& stiffness**)–– Nylon or PA; Polyester (PET); Nylon or PA; Polyester (PET);

Rayon (modified cellulose**)Rayon (modified cellulose**)–– Clothing, upholstery, etc.Clothing, upholstery, etc.

MSE 201-Polymers 8

Usage, Usage, cont’dcont’d

•• COATINGS & FILMS (many types)COATINGS & FILMS (many types)–– Paints, structural adhesives,Paints, structural adhesives, HMPSA'sHMPSA's, ,

varnish, lacquers)varnish, lacquers)–– typically polymer typically polymer emulsionsemulsions

•• Emphasize complex structure of Emphasize complex structure of polymers/ benefits (fortuitously polymers/ benefits (fortuitously polymers can be used without inpolymers can be used without in--depth knowledge of structure)depth knowledge of structure)

•• OptionalOptional Reading (Chap. 1, Rodriguez,1996)Reading (Chap. 1, Rodriguez,1996)–– (Importance & other e.g.s)(Importance & other e.g.s)

Polymerization RoutesPolymerization Routes

•• 2 broad classifications 2 broad classifications (chain vs. step) W.J.(chain vs. step) W.J. CarothersCarothers et alet al–– ADDITION (or "Chain")ADDITION (or "Chain")

�� Chain reactions involving an Chain reactions involving an unpaired electron or an ionunpaired electron or an ion

�� Common with DOUBLECommon with DOUBLE––BONDED compounds, e.g., PEBONDED compounds, e.g., PE

MSE 201-Polymers 9

Addition reactionAddition reaction(VMS 2, J.C. Russ 1994)(VMS 2, J.C. Russ 1994)

Polymerization Routes, Polymerization Routes, cont’dcont’d

ØØ CONDENSATION (or CONDENSATION (or “Step")“Step")ØØ Reaction b/w TWOReaction b/w TWOpolyfunctional polyfunctional molecules (cf. molecules (cf. condensation reactions of condensation reactions of lower MW materials)lower MW materials)

MSE 201-Polymers 10

Example ofExample ofCondensationCondensation RxnRxn

ethylene glycol +ethylene glycol + terephathalicterephathalic acidacid

bifunctionalbifunctionalbifunctionalbifunctional product + product + product + product + waterwaterwaterwater

Linear PETLinear PETLinear PETLinear PET

Chain or Step used to produce Chain or Step used to produce linear & branched polymers linear & branched polymers

Condensation reactionCondensation reaction(VMS 2, J.C. Russ 1994)(VMS 2, J.C. Russ 1994)

MSE 201-Polymers 11

CondensationCondensation RxnRxnDemo (Nylon 66)Demo (Nylon 66)

W h i t e = H

R e d = C

Blue=N

Yel low=Odiaciddiamine

InterfacialInterfacialPolycondensationPolycondensation

MSE 201-Polymers 12

••COPOLYMERIZATION (A,B or C)COPOLYMERIZATION (A,B or C)–– EMPHASIZE technological importance EMPHASIZE technological importance –– SBR, LIPS, HIPS, etcSBR, LIPS, HIPS, etc

••Types of Copolymers:Types of Copolymers:–– AlternatingAlternating–– RandomRandom–– BlockBlock–– GraftGraft

Polymerization Routes, cont’d

Natural vs. SyntheticNatural vs. Synthetic•• Plant sourcesPlant sources

–– CellulosicCellulosic fibers (linen, jute, hemp), corn fibers (linen, jute, hemp), corn starch**starch**

–– SoySoy––protein** (Emphasize protein** (Emphasize biodegradability*)biodegradability*)

•• Animal sourcesAnimal sources–– Silk, wool, chemically known as proteins)Silk, wool, chemically known as proteins)

•• Human tissuesHuman tissues–– Muscle fiber, living organisms (DNA, Muscle fiber, living organisms (DNA,

RNA)RNA)

MSE 201-Polymers 13

ArchitectureArchitecture

•• Bond RotationBond Rotation–– Fixed bond angles (109°28') & random Fixed bond angles (109°28') & random

chain conformationschain conformations–– Random Conformation of carbon Random Conformation of carbon

backbonebackbone

Chain EntanglementChain Entanglement

–– Note bending, kinking, coiling (real case)Note bending, kinking, coiling (real case)–– RepetitionalRepetitional motions overheadmotions overhead

MSE 201-Polymers 14

StereoisomerismStereoisomerism

Crystalline vs. Amorphous

Details in MatE 351

MSE 201-Polymers 15

Chain Molecules are Chain Molecules are Analogous to SpaghettiAnalogous to Spaghetti

–– Random arrangementRandom arrangement–– Thermal motion in real Thermal motion in real

polymerspolymers–– Sliding/AlignmentSliding/Alignment

–– D.P. ( lengths)D.P. ( lengths)

–– Stiffness (dried)Stiffness (dried)

•• Polymers crystallize differently Polymers crystallize differently from simplefrom simple cystallinecystalline solidssolids–– XRD patterns are less sharpXRD patterns are less sharp–– Small crystallite size (100 A)Small crystallite size (100 A)–– Polymer chains much larger than Polymer chains much larger than

100 A100 A–– Hence chain foldingHence chain folding

Polymer CrystallinityPolymer Crystallinity

MSE 201-Polymers 16

Unit Cell of PEUnit Cell of PE

Top ViewTop View7.40 A

4.93

2.54 A Side View

PolymerPolymer CrystallinityCrystallinity

32

MSE 201-Polymers 17

Partially crystallizedPartially crystallizedpolymerpolymer

•• Regions of Regions of crystallinitycrystallinity

•• Amorphous Amorphous regionsregions

Structure of Polymer Structure of Polymer MoleculesMolecules

•• Ethylene (CEthylene (C22HH44) ) -- gasgas•• Polyethylene (PE) Polyethylene (PE) -- solid polymeric solid polymeric

materialmaterial–– carbons are 109° to each other (tetrahedral bond carbons are 109° to each other (tetrahedral bond

angle for spangle for sp33 hybridizationhybridization–– “zigzag” structure“zigzag” structure

34

MSE 201-Polymers 18

Polymer Crystal ModelsPolymer Crystal Models

•• Chain folded Chain folded Chain folded Chain folded modelmodelmodelmodel -- crystals crystals are actually small are actually small platelets of platelets of interwoven interwoven polymer chainspolymer chains

35

Polymer Crystal ModelsPolymer Crystal Models•• In many bulk In many bulk

polymers polymers crystallized crystallized from the melt, from the melt, these platelets these platelets often arrange often arrange themselves in themselves in radiating radiating patterns to formpatterns to formspherulitesspherulitesspherulitesspherulites..

•• PE, PP, PE, PP, PVC,PTFE, PVC,PTFE, nylon crystallize nylon crystallize in this mannerin this manner

36

MSE 201-Polymers 19

Melting and Glass Melting and Glass Transition Transition TemperaturesTemperatures

•• Temperature at which melting (or glass Temperature at which melting (or glass transition) occurs is determined as it is for transition) occurs is determined as it is for glasses: Specific. vol. vs. T.glasses: Specific. vol. vs. T.

Tm

Spec

ific V

olum

e

TgTemperature

A. Amorphous B. Semicrystalline C. Crystalline

AB

C

End of Lecture, Unit 1–4b

• READ • Class notes and Callister 2000, • pp. 446-469, 482-486, 496-512

• Optional Reading• Shackelford 2000, Chap. 13• www.mse.iastate.edu/mate271• www.mse.iastate.edu/mate351