Thermoplastic polymers processed by a heat-form-cool cycle

1. Thermoplastic polymersprocessed by a heat-form-cool cycle John Summerscales

2. Summary of lecture • basic chemical names • addition polymers • configuration/conformation • stereoregularity/tacticity • crystalline or amorphous • transition temperatures • condensation polymers • ring-opening polymers

3. Naming basic chemicals

4. Basic chemicals Transition temperature data from http://www.elmhurst.edu/~chm/vchembook/501hcboilingpts.html

5. Bond rotation • Movie of rotation about a single bond • file taken from http://plc.cwru.edu/tutorial/enhanced/files/polymers/struct/bond.mov • Movie of rotation with different side groups • file taken fromhttp://plc.cwru.edu/tutorial/enhanced/files/polymers/struct/conform.swf

6. Geometric isomers • cis: • trans:

7. Chemical Groups (reactants) O H C O HO H N H • Acid • Alcohol • Amine • NB: nitrogen in amine has a free p-orbitalwhich can become part of a π-bond

8. Chemical Groups (products) O C O O O C N H • Ester • Amide • Ether

9. Polymers Polymers are class of materials where many small molecules (monomers) are linked together by covalent bonds to form long chains or networks an alternative name for polymers ismacromolecules a homopolymer has only 1 repeating unit a copolymer has 2 different repeating units a terpolymer has 3 different repeating units.

10. Polymers • Thermoplastic - usually long straight chainssometimes with short branches • copolymers AB (and terpolymers ABC) can be • alternating ---ABABABABAB--- • block ---AAABBAAABB--- • graft (type B branches on type A backbone) • random ---AABABBBAAB--- • Thermoset - usually 3-dimensional networks • Elastomers - 3-D networks with sparseinterlinks between chains (e.g. rubber)

11. Addition polymers • reaction by opening double bonds • all atoms from reactants end up in the product • n CH2=CHX reacts to become [- CH2-CHX-]n • if X = H, the polymer is polyethylene • if X = CH3, the polymer is polypropylene • if X = Cl, the polymer is polyvinylchloride • if X = C6H5, the polymer is polystyrene • ... this list is not exhaustive • if monomer is CF2=CF2,the polymer is polytetrafluoroethylene

12. Configuration/Conformation • Configuration • the arrangements of atoms on the polymer chain • fixed relative positions of atoms • Conformation • the arrangement of the atoms in space • regular linear chains can crystallise • branched/bulky side-groups or irregular copolymers have longer repeat units and are thus less likely to crystallisebut more likely to be amorphous

13. Stereoregularity -> tacticity • Isotactic • characteristic groupsall on the same sideof the polymer chain • Syndiotactic • characteristic groupson alternate sidesalong polymer chain • Atactic - characteristic groups located atrandom along the polymer chain • images from http://plc.cwru.edu/tutorial/enhanced/files/polymers/struct/Struct.htm

14. Crystalline vs amorphous • Crystalline polymers • molecules pack more closely leading to: • higher density • better mechanical properties (more bonds/m3) • better resistance to environmental degradation • NB: common polymers are partially crystalline • crystallites distributed in an amorphous matrix • Amorphous polymers • random configuration • reduced properties re. crystalline materials • transparent to white light (e.g. PS, PC, PMMA)

15. Crystallinity • Two model structures have been proposed • Images fromhttp://chem.chem.rochester.edu/~chem421/cryst.htmhttp://www.pslc.ws/mactest/crystal.htm respectively Fringed micelle Folded lamella

16. Transition temperatures • Tg = Glass transition temperature • segmental motion is frozen out • brittle elastic below Tg • tough/viscoelastic above Tg • Tm = Crystalline melting point • only occurs in crystallites • both temperatures may be a rangerather than a specific temperature

17. Transition temperatures Specific volume Liquid Rubbery Amorphous/glassy Crystalline solid Temperature Tg Tm

18. Condensation polymers • XOH + HY  XY + H2O • HOXOH + HYH  HOXYH + H2O • further reactions with HOXOH and HYHwill produce a linear molecule

19. Condensation polymers • Acid + base  salt + water • HCl + NaOH  NaCl + H2O • Acid + alcohol  ester + water • R.C=O.OH + HO.R’  R.C=O.O.R’ + H2O • Acid + amine  amide + water • R.C=O.OH + H2N.R’  R.C=O.HN.R’ + H2O • If two reactive sites on each molecule,then a polymer chain will result

20. Ring-opening polymers • HOXOH + HYH  HOXYH +H2O • further reactions with HOXOH and HYHwill produce a linear molecule • HOXH + HOXH HOXXH +H2O • i.e. both reactants might be on one molecule • but such a system could react with itselfto form a cyclic molecule if X > 4C atoms • such a cyclic molecule can polymerisewithout loss of water(H2O already removed in cyclisation reaction)

21. Ring-opening polymers • Ring-opening polymerisationduring composite manufacture has potential to produce thermoplastic matrix composites from RTM/RIFT • caprolactam to produce polyamide 6 (e.g. DSM Fiber Intermediates APA-6), • laurolactam to produce polyamide 12 (e.g. EMS-Grivory APLC12), and • cyclic butylene terephthalate oligomers to produce PBT polyester (e.g. Cyclics Corporation).

22. Voluntary Plastic Container Coding System abc n • proposed by Society for the Plastics Industry (SPI) in the United States of America • remember Tm = Tg + 200°C (±~50°C) so some common thermoplastics are.....

24. Periodic Table of Thermoplastics(Tangram Technology)http://polymer.w9of.com/wp-content/uploads/2011/01/Polymer-Periodic-Table.pdf

25. Summary of thermoplastics lecture • basic chemical names • addition polymers • configuration/conformation • stereoregularity/tacticity • crystalline or amorphous • transition temperatures • condensation polymers • ring-opening polymers

26. MATS117 continues with thermosetting polymers….

27. Thermosets • generally supplied as a liquid • cross-linked (cured) by chemicals (and heat) • heat increases the rate of cure • heat reduces the instantaneous viscosity • cure decreases the viscosity over time • product is a 3D molecular network • whereas a thermoplastic is usually a 2D chain

28. Summary (key polymers)