The phenol + formaldehyde rxn The phenol + formaldehyde rxn

Network formationNetwork formationFurther reaction under heat & pressure builds up densely cross-linked network. This is Bakelite, a thermosetting polymer. Once reaction is complete, material cannot be reheated and/or reformed

Further reaction under heat & pressure builds up densely cross-linked network. This is Bakelite, a thermosetting polymer. Once reaction is complete, material cannot be reheated and/or reformed

BakeliteBakelite

Bakelite telephoneBakelite telephone

Bakelite microphoneBakelite microphoneBakelite cameraBakelite camera

Clear Bakelite itemsClear Bakelite items

Bakelite radioBakelite radio

Phenolic resin/celluloid clockPhenolic resin/celluloid clock

Bakelite - Material of a Thousand UsesBakelite - Material of a Thousand Uses

Crosslinking Crosslinking

Take linear polymer chains & link using covalent bondsTake linear polymer chains & link using covalent bonds

Crosslinking Crosslinking

Ex: rxn of natural rubber or poly(isoprene)Ex: rxn of natural rubber or poly(isoprene)

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

(vulcanization)

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

(vulcanization)

H

CH2 -

CH3-

C = C- CH2

--

-H

CH2 -

CH3-

C = C CH2

--

-H

CH2 -

CH3-

C = C CH2

--

-

Crosslinking Crosslinking

3 typesisotacticsyndiotacticatactic

3 typesisotacticsyndiotacticatactic

TacticityTacticity

TacticityTacticity

CH3CH3

propylene monomer: CH2=CHpropylene monomer: CH2=CH

Ex: polypropyleneEx: polypropylene

CH3CH3

upon polymerization: –CH2–C–upon polymerization: –CH2–C–

HH

isotacticisotactic

TacticityTacticity

CH3

propylene: CH2=CH

TacticityTacticity

atacticatactic

syndiotacticsyndiotactic

TacticityTacticity

Polypropylene - largely isotactic

isotactic character of PP allows "crystallization"

as a result, material can be stiffer

Polypropylene - largely isotactic

isotactic character of PP allows "crystallization"

as a result, material can be stiffer

TacticityTacticity

Polystyrene - atactic

Polypropylene - largely isotactic

PVC - largely atactic (some syndiotactic sequences)

PMMA -atactic

Polystyrene - atactic

Polypropylene - largely isotactic

PVC - largely atactic (some syndiotactic sequences)

PMMA -atactic

Copolymers 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-

Blends Blends

miscible immisciblemiscible immiscible

single phase phase separatedsingle phase phase separated

blendblend

Molecular weight Molecular weight

Gases

Liquids

IncreasingMolecular Weight

16

30

44

58

114

450

420030

CH4

CH3 - CH2 _ CH3

CH3 - CH3

CH3 - CH2 - CH2 - CH3

CH3 - (CH2)6 _ CH3

CH3 - (CH2)30 _ CH3

CH3 - (CH2)30000 _ CH3

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

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

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

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

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

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

----------

"Semi-solid"

Solids

increasingmolecular weight

Molecular weight Molecular weight

Chains have different molecular weights

There is a distribution

Molecular weight Molecular weight

Is it important?

Mol. Wt.Mol. Wt.

Melt ViscosityMelt ViscosityTensile StrengthTensile Strength

Mol. Wt.Mol. Wt.

Molecular weight Molecular weight

Is it important?Is it important?

Very important in processing

If viscosity too high, polymer difficult to process

Very important in processing

If viscosity too high, polymer difficult to processIf too low, an extruded material won't hold together until it solidifies

If too low, an extruded material won't hold together until it solidifies

Blow molding Blow molding

Step 1: make preform by extrusion or injection molding

Step 1: make preform by extrusion or injection molding

Blow molding Blow molding

Step 1: make preform by extrusion or injection molding

Step 1: make preform by extrusion or injection molding

Step 2: use air pressure to inflate preform inside closed, hollow mold. Polymer expands to take shape of cooled mold & solidifies under pressure

Step 2: use air pressure to inflate preform inside closed, hollow mold. Polymer expands to take shape of cooled mold & solidifies under pressure

Polymers are different Polymers are different

Polymers are different Polymers are different

• Normal crystalline materials– Either crystalline (~100 %, neglecting defects ) or amorphous at a particular temperature

– Melt at a sharp, well-defined temperature

• 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

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