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The phenol + formaldehyde rxn

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Network formation Further reaction under heat & pressure builds up denselycross-linked network. This is Bakelite, a thermosetting polymer. Once reaction is complete, material cannot bereheated and/or reformed

Bakelite

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Bakelite telephone

Bakelite microphone Bakelite camera

Clear Bakelite items

Bakelite radio

Phenolic resin/celluloid clock

Bakelite - Material of a Thousand Uses

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Crosslinking

Take linear polymer chains & link using covalent bonds

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Crosslinking

Ex: rxn of natural rubber or poly(isoprene)

with sulfur - interconnects the chains by reacting with the double bonds

(vulcanization)

H

CH 2 -

CH 3 C = C

- CH 2

H

CH 2 -

CH 3 C = C

CH 2

H

CH 2 -

CH 3 C = C

CH 2

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Crosslinking

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3 types isotactic syndiotactic

atactic

Tacticity

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Tacticity

CH3

propylene monomer: CH2=CH

Ex: polypropylene

CH3

upon polymerization: CH2C

H

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isotactic

Tacticity

CH3

propylene: CH 2=CH

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Tacticity

atactic

syndiotactic

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Tacticity

Polypropylene - largely isotactic

isotactic character of PP allows "crystallization"

as a result, material can be stiffer

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Tacticity

Polystyrene - atactic

Polypropylene - largely isotactic

PVC - largely atactic(some syndiotactic sequences)

PMMA -atactic

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Copolymers

Graft Copolymers

-B-B-B-B-B-B-B-B-B-B-B-B-B-B-B-B-B-B-B-B-B-B-

A - A - A - A - A - A

- A - A -

A

- A - A - A - A - A - A - A

- A - A -

A - A - A - A

- A - A -

Block Copolymers

-A-A-A-A-A-A-B-B-B-B-B-B-B-B-B-B-A-A-A-A-A-A-

Random Copolymers-A-B-B-B-A-A-B-A-B-A-A-A-B-A-B-B-A-B-B-A-A-A-B-

Alternating Copolymers

-A-B-A-B-A-B-A-B-A-B-A-B-A-B-A-B-A-B-A-B-A-B-

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Blends

miscible immiscible

single phase phase separated

blend

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Molecular weight

Gases

Liquids

Increasing Molecular Weight

16

30

44

58

114

450

420030

CH 4

CH 3 - CH 2 _ CH 3

CH 3 - CH 3

CH 3 - CH 2 - CH 2 - CH 3

CH 3 - (CH 2 )6 _ CH 3

CH 3 - (CH 2 )30 _ CH 3

CH 3 - (CH 2 )30000 _ CH 3

--------------------------------------------------------

-----------------------------------------

---------------

---------------

---------------

----------

"Semi-solid"

Solids

increasing molecular weight

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Molecular weight

Is it important?

Mol. Wt.

Melt ViscosityTensile Strength

Mol. Wt.

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Molecular weight

Is it important?

Very important in processing

If viscosity too high, polymerdifficult to process

If too low, an extruded materialwon't hold together until itsolidifies

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Blow molding

Step 1: make preform byextrusion or injectionmolding

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Blow molding

Step 1: make preform byextrusion or injectionmolding

Step 2: use air pressureto inflate preform inside

closed, hollow mold.Polymer expands to takeshape of cooled mold &solidifies under pressure

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Polymers are different

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Polymers are different

Normal crystalline materials Either crystalline (~100 %, neglecting

defects ) or amorphous at a particular temperature

Melt at a sharp, well-defined temperature

Crystallizable polymers Never 100% crystalline Melt over a range of temperatures

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