1. The phenol + formaldehyde rxn

2. Network formation 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 Bakelite

3. Bakelite telephone Bakelite microphone Bakelite camera Clear Bakelite items Bakelite radio Phenolic resin/celluloid clock Bakelite - Material of a Thousand Uses

4. Crosslinking Take linear polymer chains & link using covalent bonds

5. Crosslinking 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 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 - - -

6. Crosslinking

7. 3 types isotactic syndiotactic atactic 3 types isotactic syndiotactic atactic Tacticity

8. CH 3 propylene monomer: CH 2 =CH Ex: polypropylene CH 3 upon polymerization: –CH 2 –C– H H

9. isotactic Tacticity CH 3 propylene: CH 2 =CH

10. Tacticity atactic syndiotactic

11. Tacticity 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

12. Tacticity 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

13. 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-

14. Blends miscible immiscible single phase phase separated blend

15. 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

16. Molecular weight Chains have different molecular weights There is a distribution

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

18. Molecular weight 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 process If too low, an extruded material won't hold together until it solidifies

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

20. 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

21. Polymers are different

22. 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