Polymer Structure

• sources

  natural (starch, cellulose); semisynthetic (rayon); synthetic (nylon, polyester)
• reaction mode of polymerization- additional; condensation (nylon 6,6, polyester)
• not necessary to break chain bonds to alter molecular shape
• copolymers

  two or more monomers polymerized together
• mer

  repeat unit
• natural polymers

  wood, silk, rubber, cotton, wool, leather, teflon, plastic, polyester, sugarcane, dna, rna
• pitch

  a natural polymer used by Noah for the ark
• structure

  linear (nylon, polyester); branched chain (pvc, teflon); cross linked (bakelite, melamine)
• polymers

  hydrocarbon
• unsaturated

  double bond (alkene); triple bond (alkyne)
• polyethylene

  a long-chain hydrocarbon
• molecular weight (M)

  mass of a mole of chains
• there is a distribution of molecular weights
• molecular shape (conformation)

  chain bending and twisting are possible by rotation of carbon atoms around their chain bonds
• chain end-to-end distance

  denoted by r
• stereoisomers

  mirror images; can’t superimpose without breaking a bond
• isotactic

  all R groups on same side of chain
• atactic

  R groups randomly positioned
• trans

  opposite sides of chain
• random

  A and B randomly positioned along chain
• block

  large blocks of A units alternate with large blocks of B units
• crystallinity in polymers

  ordered atomic arrangements involving molecular chains; crystal structures in terms of unit cells (polyethylene unit cell)
• polymers rarely 100% crystalline; difficult for all regions of all chains to become aligned
• some physical properties depend on % crystallinity
• electron micrograph

  multilayered single crystals (chain-folded layers) of polyethylene
• spherulite structures

  formed by some semicrystalline polymers
• cross-polarized light (photomicrograph)

  a maltese cross appears in each spherulite (polyethylene)
• polymer molecules

  macromolecule; composed of repeat units, small structural entities repeated along chain
• polymeric materials

  composed of very large molecular chains with side groups of various atoms or organic groups (methyl/ethyl/phenyl)
• homopolymer

  all repeat units are the same type
• copolymers

  composed of two or more kinds of repeat units
• repeat units

  classified according to number of active bonds
• bifunctional

  produce 2D chainlike structure from monomer; 2 active bonds
• trifunctional monomers

  3 active bonds; form 3D network structures
• chain length

  specified by degree of polymerization
• molecular entanglements

  chains assume twisted, coiled, and kinked shapes or contours as consequence of bond rotations
• rotational flexibility

  diminished when double bonds are present and when bulky side groups are part of repeat unit
• head-to-head and head-to-tail configuration

  repeat units have more than 1 side atom or groups of atoms bonded to main chain
• thermoplastic

  linear and branched structure; soften when heated and hardened when cooled
• thermosetting

  crosslinked and network; once hardened, will not soften upon heating