Characteristic Ratios

• Polyethylene, 6.7
• Vinyl polymers: C depends on the nature of side chain and on tacticity. It is often (but not always) larger than C for polyethylene.
  • Polypropylene, atactic (p_m = 0.5, Bernoullian), 5.4
  • Polystyrene, atactic (p_m = 0.5, Bernoullian), 10.5
  • Poly(vinyl chloride)
    • Isotactic, 9.7
    • Atactic (p_m = 0.5, Bernoullian), 9.6-10.9
    • Syndiotactic, 30 (C is large because strings of racemo diads in this polymer have a strong preference for the propagation of trans states, producing high extension)
• Polybutadiene: C is larger for trans than for cis, but in both cases smaller than C for polyethylene
  • 1,4-cis, 4.9
  • 1,4-trans, 5.8
• Polyethers: C initially decreases as more methylene units are added between successive oxygen atoms. But this decrease must turn around eventually (see polyethylene). It turns around at polyoxytrimethylene. Preferred conformations are gauche at C-O bonds, and trans at C-C bonds.
  • Polyoxymethylene, 10 (the chain tends to propagate runs of gauche placements of the same sign).
  • Polyoxyethylene, 5.1
  • Polyoxytrimethylene, 3.9
  • Polyoxytetramethylene, 5.9
• Polysaccharides: Amylose and cellulose are both constructed from 1,4-strings of D-glucose. These units are alpha for amylose, beta for cellulose, with the latter being much stiffer. The characteristic ratio is defined using a virtual bond for each D-glucose unit.
  • Amylose, 4-5
  • Cellulose trinitrate, 30-40
• Polyalanine: The optically pure forms both have the same unperturded dimensions (as they must), but the racemic form is much more compact. The characteristic ratio is defined using a virtual bond spanning each peptide unit.
  • D, 9.4
  • L, 9.4
  • DL (Racemic), 2

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