polymers are not foam like materials

can often be shaped (molded, extruded, stretched)

as a rule, strength occurs at surfaces

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to bend, need to lengthen top surface

need to compress lower surface

corrugated cardboard is strong

can cut out most of the middle of a 2x6" floor joist

bubbles are strong

trapped gas-- maintains volume

Foamed Polymers; polystyrene

polymer begins as liquid (density 0.6 g/ml)

then sets into a solid (about same density)

whipped cream or eggs

substance is a liquid (no rigidity)

foam is fairly stiff, firm

(eggs or cream have not become solid)

whip a polymer as if forms and sets

get a rigid foam

very low density

yet still relatively strong

whipping is typically impractical

blowing in bubbles

with a nozzle

creating bubbles internally

reactants that produce CO₂ or N₂

if hot, steam can form bubbles

dissolved fluorocarbons

example: canned foam insulation

(reacts with moisture)

Polymer Chemistry

Polymer starts with a subunit or monomer

must be capable of reacting at two locations on the molecule

otherwise--- can't grow long sequence

sequences are thousands of subunits

Molecule reacts at one end

produces a longer sequence

this must still contain a reactive region

that can in turn react again

(may grow in one or two directions)

As a rule polymers are not made by joining up moderate length segments

Linear Polymers

simple A-A-A-A-A..........-A

repeating unit

also A-B - A-B - A-B - ......A-B

(think of a bowl of spaghetti)

Branched Polymers

usually an occasional change

A-A-A-A-A-O-A-A-A-A-A

\-A-A-A-A-A

Cross Linked Polymers

A-A-A-A-A-O-A-A-A-A-A A-A-A-A-A-O-A-A-A-A-A

A-A-A-A-A-O-A-A-A-O-A A-A-A-A-A-O-A-A-A-O-A-A-A-A-A-A-A

A-A-A-A-A-O-A-A-A-A-A A-A-A-A-A-O-A-A-A-A-A

The Chemistry of Polymerization

1. simple addition, generally at a double bond

polyethylene, polypropylene, polystyrene, PVC

2. condensation-- eliminating a small molecule (usually water)

all of the polyesters

all polyamides (nylon, proteins)

Organic Chemistry and Functional Groups

Backbone-- typically C-C-C

single or multiple bonds

default-- other bonds (4 per carbon) are hydrogen

often abbreviate as R-

some other patterns that occur often

are given a name

contribute specific properties

chemical- reactions

physical-- strength, spectra, color, ...

Alcohols -O-H

Carbonyls =O

with -H, an aldehyde

with -R' a ketone

Amine -N -

Carboxylic acid RCO₂H

an acid RCO₂H + H₂O --> H₃O⁺ + RCO₂-

acetic acid acetate

R=H

.

Alcohol _______ + -ol (ethanol, propanol)

dio = glycol

ethyleneglycol CH₂OH - CH₂OH

triol (glycerol is best known case0

Diamine

H₂N- (C₆H₁₂)-NH₂

Ester: R- CO-O -R'

Let an alcohol react with a carboxylic acid

loss of water

Terphthalic acid

(CO₂H) - (C₆H₄) (CO₂H)

Generally can divide reactions into __ types