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Lecture 2, Early History

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Lecture 2, Early History Polymer Science and Engineering "I am inclined to think that the development of polymerization is perhaps the biggest thing that chemistry has done, where it has had the biggest effect on everyday life” —Lord Todd,1980 Ethylene Polyethylene [ -CH - CH -] CH = C H 2 2 n 2 2 Magic ? A Useful Classification USE NATURAL SYNTHETIC Fibers Wool, Silk, Nylon, PET, Cellulose Lycra® Elastomers Natural Rubber, SBR, Silicones, Elastin Polybutadiene Plastics Gutta Percha, Polyethylene, DNA, Polypropylene, Polypeptides Polystyrene Composites Wood, Polyester/Glass, Bone, Carbon Fiber/Epoxy Teeth Formica Adhesives Barnacles! Elmer’s “Glue-All” Super-Glue Paints Shellac Acrylics Historical Background NATURAL POLYMERS - used throughout recorded history SYNTHETIC POLYMERS - initially chemically modified natural polymers RUBBERS OR ELASTOMERS - unique materials, both natural and synthetic HHiissttoorriiccaall BBaacckkggrroouunndd 1845 SCHOENBEIM - nitration reactions 1848 MENARD - collodion films ;nitrated cellulose 1862 PARKES - "Parkesine" ; added camphor (and other stuff) - plasticizers 1870’s HYATT - billiard balls !! 1884 CHARDONNET - extrusion 1890’s CROSS, BEVAN, - regenerated cellulose & BEADLE rayon,cellophane 1905 BAEKELAND - Bakelite, the first thermoset 1920 STAUDINGER - the macromolecular hypothesis > 1920 NEW THERMOPLASTICS - (more on these later) NNaattuurraall PPoollyymmeerrss NATURAL POLYMERS - - used throughout recorded history A natural fiber on the hoof Silk Better hope your garden never looks like this CCoottttoonn NNiittrraatteedd CCeelllluulloossee HO OH O O CH2 OH n Cellulose Schoenbeim EExxpplloossiivvee SSttuuffff!! O O N O O C C C C C C O O O OO Glycerol N N CH OH–CHOH–CH OH O 2 2 O O Nitroglycerin Some Basic Chemistry: Atoms and Bonding H H Cl Na Covalent Ionic – + H H Cl Na Molecule Does not form NaCl molecule! Metallic Some Basic Chemistry: Single and Double Bonds H– C C HH– C– – CH4 H H– H– C C HC– C– – – – H C2H6 H H H– H– – – – C C C – C C2H4 H H Some Basic Chemistry: Functional Groups CH2=CH2 Ethylene O = O = R–OH + R–C–OH R–C–O–R Alcohol Carboxylic Acid Ester O = O = R–NH2 + R–C–OH R–C–NH–R AmineCarboxylic Acid Amide Functional Groups are small groups of atoms held together in a specific arrangement by covalent bonds. They are responsible for the principle chemical properties of the molecule in which they are found. CCoonnddeennssaattiioonn RReeaaccttiioonnss Ester linkage O Reversible O Reaction! CH3 - C - OH + CH3 - CH2 - OH CH3 - C - O - CH2 - CH3 + H2O Acetic Acid Ethyl Alcohol Ethyl Acetate or Ethanol If you don’t know what this is you should be castigated unmercifully WWhhyy ddoo MMoolleeccuulleess RReeaacctt ?? Acetic Acid O CH3 - C - OH kersplat! HO - CH2 - CH3 Ethyl Alcohol or Ethanol WWhhyy ddoo MMoolleeccuulleess RReeaacctt ?? O H:O - CH2 - CH3 CH3 - C:OH . HO + H HO:H ~ H2O OOO . CH3 - C + O - CH2 - CH3 CH3 - C:O - CH2 - CH3 This isn‛t what really happens, but shows you how the valency electrons get rearranged MMaakkiinngg aa PPoollyymmeerr Ester linkage O Reversible O Reaction! CH3 - C - OH + CH3 - CH2 - OH CH3 - C - O - CH2 - CH3 + H2O Acetic Acid Ethyl Alcohol Ethyl Acetate or Ethanol If we heat acetic acid and ethanol up to just over 1000C, to get the reaction going and drive off water, why don‛t we form polymer? EExxpplloossiivvee SSttuuffff!! O O N O O C C C C C C O O O OO Glycerol N N CH OH–CHOH–CH OH O 2 2 O O Nitroglycerin GGuunnccoottttoonn aanndd CCoollllooddiioonn GGuunnccoottttoonn aanndd CCoollllooddiioonn PPaarrkkeess aanndd PPaarrkkeessiinnee He wasn’t this miserable. TThhee CCrryyssttaall PPaallaaccee HHyyaatttt aanndd tthhee EElleepphhaannttss CCeelllluullooiidd What a sales pitch CChhaarrddoonnnneett aanndd MMootthheerr--iinn--LLaaww SSiillkk RReeggeenneerraatteedd CCeelllluulloossee CCeelllloopphhaannee aanndd RRaayyoonn OH HO O O CH2OH NaOH OH HO O O CH2ONa CS2 OH HO O O CH2OCSNa S H+ OH HO O O CH2OH MMoorree CCeelllloopphhaannee RRaayyoonn BBaaeekkeellaanndd aanndd BBaakkeelliittee The first true synthetic plastic BBaakkeelliittee -- MMaatteerriiaall ooff aa TThhoouussaanndd UUsseess Clear Bakelite items Clock made of a phenolic resin A Bakelite telephone and celluloid A Bakelite camera A Bakelite radio A Bakelite microphone NNeettwwoorrkk FFoorrmmaattiioonn The hydrogens in the ortho and para positions to the OH group, which by convention are not OH usually shown but here are indicated by a * , can * * + CH2O react with fomaldehyde to form (initially) oligomers. * OH OH OH CH2 CH2 CH2 OH CH CH2 CH2 2 OH OH OH CH2 OH AA CCoonnddeennssaattiioonn RReeaaccttiioonn!! OH OH HHO HH HH H H H H H H H O H H H H HH OH NNeettwwoorrkk FFoorrmmaattiioonn Continued reaction builds up a densely OH OH OH cross-linked network. CH2 CH2 CH2 CH2 CH2 This is Bakelite, a OH OH HO thermosetting CH2 CH2 CH2 O polymer. Once the OH CH2 reaction is complete, CH2 O CH2 CH2 the material cannot OH H2C H C be reheated and 2 CH2 OH O reformed. So, what do CH2 CH2 HO HO you think the CH2 HO definition of a HO CH2 CH2 thermoplastic is? HO NEXT; Staudinger and the Macromolecular Hypothesis.
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