Paraffin wax candleParaffin wax candlePlastic milk jugPlastic milk jug Body armorBody armor

CHEMICALLY CHEMICALLY IDENTICALIDENTICALFishing lineFishing line

C C

H

H H

H

n

Polymer Science allowsus to engineer thesematerials and distinguishthem from one another!

Polymer Science allowsus to engineer thesematerials and distinguishthem from one another!

Polymers in BriefPolymers in Brief A polymer is a large (macro) molecule A polymer is a large (macro) molecule

with a specific repeating structurewith a specific repeating structure Polymer properties are dictated byPolymer properties are dictated by

The The bondingbonding within the chains within the chains The The bondingbonding betweenbetween the chains the chains The The sizesize of the chains of the chains The The shapeshape of the chains of the chains

The structure of a polymer is denoted The structure of a polymer is denoted using the smallest repeating unit:using the smallest repeating unit:

X Y Z

n

…-X-Y-Z-X-Y-Z-X-Y-Z-X-Y-Z-X-Y-Z-X-Y-Z-…

Common PolymersCommon Polymers

HHigh igh DDensity ensity PPolyolyEEthylenethylene

LLow ow DDensity ensity PPolyolyEEthylenethylene

Poly(Poly(VVinyl Chloride)inyl Chloride)

PPolyolyPPropyleneropylene

PPoly(oly(EEthylene thylene TTerephthalate erephthalate EEster)ster)

PPolyolySStyrenetyrene

PPoly(oly(MMethyl ethyl MMethethAAcrylate) (crylate) (PlexiglasPlexiglas),),PPolyolyCCarbonate (arbonate (LexanLexan), ), PPolyolyUUrethanes,rethanes,PPolyolyTTetraetraFFluoroluoroEEthylene (thylene (TeflonTeflon),),PPolyolyAAmides (mides (NylonNylon, , KevlarKevlar, , NomexNomex),),PPolyolyIImides, other Polyesters, etc.mides, other Polyesters, etc.

StereoisomerismStereoisomerism(in vinyl polymers)(in vinyl polymers)

Example 1.Example 1.Diads in Poly(vinyl chloride)Diads in Poly(vinyl chloride)

All-Meso = All-Meso = isotacticisotactic

All-Racemic = All-Racemic = syndiotacticsyndiotactic

Random = Random = atacticatactic

Example 2. Stereoregularity in polypropyleneExample 2. Stereoregularity in polypropylene

IsotacticIsotactic polypropylene polypropylene• TTmm = 160-170 °C = 160-170 °C• Strong, hard material with Strong, hard material with good resistance to stress, good resistance to stress, cracks, and chemical reactioncracks, and chemical reaction

SyndiotacticSyndiotactic polypropylenepolypropylene• TTmm = 125-131 °C = 125-131 °C• Softer than isotactic Softer than isotactic polypropylenepolypropylene• Tough, clear, and stable when Tough, clear, and stable when exposed to gamma radiationexposed to gamma radiation

AtacticAtactic polypropylene polypropylene• TTmm < 0 °C < 0 °C• Soft, rubbery polymerSoft, rubbery polymer

StereoisomerismStereoisomerism(in polypropylene)(in polypropylene) WHY THIS MATTERSWHY THIS MATTERS

Structural isomerismStructural isomerism(in polydienes)(in polydienes)

Natural Natural rubberrubber

Diene numbering Diene numbering schemescheme

Example: Structural isomers of Example: Structural isomers of poly(isoprene)poly(isoprene)

WHY THISWHY THISMATTERS:MATTERS:1,2 and 3,41,2 and 3,4units areunits are

more reactivemore reactiveto crosslinkingto crosslinking(vulcanization)(vulcanization)than 1,4 unitsthan 1,4 units

The Effects of Molecular WeightThe Effects of Molecular WeightC C

H

H H

H

n

Low-MW polyethyleneLow-MW polyethylene

Paraffin waxesParaffin waxes

High-MW polyethyleneHigh-MW polyethylene

Solvents / fuels / oilsSolvents / fuels / oils

Gases / fuelsGases / fuels