Truth comes out of error more easily than out of confusion 
 – Francis Bacon

Tacticity 3 types isotactic syndiotactic atactic

Tacticity Ex: polypropylene CH3 propylene monomer: CH2=CH CH3 upon polymerization: –CH2–C– H

Tacticity isotactic CH3 propylene: CH2=CH

Tacticity syndiotactic atactic

Tacticity Polypropylene - largely isotactic isotactic character of PP allows "crystallization" as a result, material can be stiffer

Tacticity Polystyrene - atactic Polypropylene - largely isotactic PVC - largely atactic (some syndiotactic sequences) PMMA -atactic

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

Blends miscible immiscible blend single phase phase separated

Molecular weight molecular weight CH4 CH3 - CH2 _ CH3 CH3 - CH3 Gases Liquids Increasing Molecular 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 increasing molecular weight

Molecular weight Chains have different molecular weights There is a distribution

Molecular weight Is it important? Tensile Strength Melt Viscosity Mol. Wt. Melt Viscosity Tensile Strength

Molecular weight Is it important? Very important in processing If viscosity too high, polymer difficult to process If too low, an extruded material won't hold together until it solidifies

Blow molding Step 1: make preform by extrusion or injection molding

Blow 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

Polymers are different

Normal crystalline materials 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

Assignment: Review today's classnotes a. tacticity - types b. copolymers - types c. blends d. molecular weight e. blow molding f. changes of state in polymers g. crystallization