1 / 25

Chapter 31. Synthetic Polymers

Chapter 31. Synthetic Polymers. Based on McMurry’s Organic Chemistry , 6 th edition. Polymers. Large molecules built up by repetitive bonding together of monomers. Drawing Polymers. Indicate repeating unit in parentheses . 31.1 Chain-Growth Polymers.

Télécharger la présentation

Chapter 31. Synthetic Polymers

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.


Presentation Transcript

  1. Chapter 31. Synthetic Polymers Based on McMurry’s Organic Chemistry, 6th edition

  2. Polymers • Large molecules built up by repetitive bonding together of monomers

  3. Drawing Polymers • Indicate repeating unit in parentheses

  4. 31.1 Chain-Growth Polymers • Produced by chain-reaction polymerization • Initiator (radical, acid or anion) adds to a carbon–carbon double bond of an unsaturated substrate (a vinyl monomer) to yield a reactive intermediate that reacts with a second molecule of monomer and so on

  5. Anionic Polymerization • Vinyl monomers with electron-withdrawing substituents (EWG) can be polymerized by anionic catalysts • Chain-carrying step is nucleophilic addition of an anion to the unsaturated monomer by a Michael reaction

  6. Examples of Anionic Polymerization Products • Acrylonitrile (H2C=CHCN), methyl methacrylate [H2C=C(CH3)CO2CH3], and styrene (H2C=CHC6H5) react

  7. 31.2 Stereochemistry of Polymerization: Ziegler–Natta Catalysts • Polymerization of a substituted vinyl monomer can lead to numerous chirality centers on the chain • A polymer having all methyl groups on the same side of the zigzag backbone is called isotactic • If the methyl groups alternate on opposite sides of the backbone, it is called syndiotactic • Randomly oriented methyl groups are on atactic polymers

  8. Ziegler–Natta Catalysts • Allow preparation of isotactic, syndiotactic, and atactic polypropylene • Prepared by treatment of an alkylaluminum with a titanium compound • (CH3CH2)3Al + TiCl4 A Ziegler–Natta catalyst

  9. 31.3 Copolymers • Obtained when two or more different monomers polymerize together • They can be random or alternating

  10. Types of Copolymers • The exact distribution of monomer units depends on the initial proportions of the two reactant monomers and their relative reactivities

  11. Block copolymers • Different blocks of identical monomer units alternate with each other • Prepared by initiating the polymerization of one monomer as if growing a homopolymer chain and then adding an excess of the second monomer to the still-active reaction mix

  12. Graft copolymers • Homopolymer branches of one monomer unit are grafted onto a homopolymer chain of another monomer unit • Made by gamma irradiation of a completed homopolymer chain in the presence of the second monomer generating radical sites that can initiate polymerization of the added monomer

  13. 31.4 Step-Growth Polymers • Produced by reactions in which each bond in the polymer is formed independently, typically by reaction between two difunctional reactants

  14. Step-Growth Polymer from a Lactam • Addition generates new nucleophile • Polyamide from caprolactam is Nylon 6

  15. Polycarbonates • Carbonyl group is linked to two OR groups, [O=C(OR)2]

  16. Polyurethanes • Urethane - carbonyl carbon is bonded to both an OR group and an NR2 group

  17. Preparation of Polyurethanes • Nucleophilic addition of an alcohol to an isocyanate (RN=C=O) gives a urethane • Reaction between a diol and a diisocyanate gives a polyurethane

  18. 31.5 Polymer Structure and Physical Properties • Polymers experience substantially larger van der Waals forces than do small molecules, producing regions that are crystallites

  19. Heat Transitions • Heating at the melt transition temperature,Tm,gives an amorphous material • Heating noncrystalline, amorphous polymers makes the hard amorphous material soft and flexible at the glass transition temperature,Tg

  20. Thermoplastics • Have a high Tg and are hard at room temperature • Become soft and viscous when heated • Can be molded

  21. Plasticizers • Small organic molecules that act as lubricants between chains • Added to thermoplastics to keep them from becoming brittle at room temperature • Dialkyl phthalates are commonly used for this purpose

  22. Fibers • Thin threads produced by extruding a molten polymer through small holes in a die, or spinneret • Fibers are then cooled and drawn out

  23. Elastomers • Amorphous polymers that have the ability to stretch out and spring back to their original shapes • When stretched, the randomly coiled chains straighten out and orient along the direction of the pull

  24. Natural Rubber and Gutta-Percha • The upper structure is rubber, a natural elastomer • The lower structure is the nonelastic gutta-percha

  25. Thermosetting resins • Polymers that become highly cross-linked and solidify into a hard, insoluble mass when heated • Bakelite is from reaction of phenol and formaldehyde, widely used for molded parts, adhesives, coatings

More Related