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The phenol + formaldehyde rxn

The phenol + formaldehyde rxn. 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. Bakelite - Material of a Thousand Uses.

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The phenol + formaldehyde rxn

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  1. The phenol + formaldehyde rxn

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

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

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

  5. - CH2 CH2 - CH2 CH2 - CH2 CH2 - - - - - - - C = C C = C C = C - - - - - - CH3 H CH3 H CH3 H Crosslinking Ex: rxn of natural rubber or poly(isoprene) with sulfur - interconnects the chains by reacting with the double bonds (vulcanization)

  6. Crosslinking

  7. Tacticity 3 types isotactic syndiotactic atactic

  8. Tacticity Ex:polypropylene CH3 propylenemonomer: CH2=CH CH3 upon polymerization: –CH2–C– H

  9. Tacticity CH3 propylene: CH2=CH isotactic

  10. Tacticity syndiotactic atactic

  11. Tacticity 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

  13. 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 -B-B-B-B-B-B-B-B-B-B-B-B-B-B-B-B-B-B-B-B-B-B- -A-B-A-B-A-B-A-B-A-B-A-B-A-B-A-B-A-B-A-B-A-B- Alternating Copolymers A-A-A-A-A-A- A-A-A-A-A-A-A-A- A-A-A-A-A-A-A-A-A-A- -A-A-A-A-A-A-B-B-B-B-B-B-B-B-B-B-A-A-A-A-A-A- Block Copolymers Graft Copolymers

  14. Blends blend miscible immiscible single phase phase separated

  15. Molecular weight CH4 ----------------------------------------- 16 CH3 - CH3 -------------------------------- 30 Gases CH3 - CH2 _ CH3 ------------------------ 44 CH3 - CH2 -CH2 -CH3 --------------- 58 Liquids CH3 - (CH2)6 _ CH3 --------------- 114 "Semi-solid" CH3 - (CH2)30 _ CH3 --------------- 450 Solids CH3 - (CH2)30000 _ CH3 ---------- 420030 Increasing Molecular Weight increasing molecular weight

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

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

  18. 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

  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. 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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