Secondary Bonding of Polymers

Most common plastics consist of carbon and only a few other elements.  These common 
elements are:








Carbon atoms frequently forms 4 single covalent bonds with other atoms. When bonded 
to another carbon, the bond length is 1.54 x 10E-10 m. The bond energy is 349 kJ/mol. 
That means it takes 348 kiloJoules to break the bonds of 1 mole of C-C bonds.

C-C single bonds are free to rotate and are not straight. The two carbons meet with 
a 109.5 degree included angle. When the carbons rotate, the polymer chains coil 
or kink.

When amorphous polymers melt, the thermal energy causes vibrations that are 
powerful enough to overcome the intermolecular forces.  When a polymer freezes, 
the intermolecular forces must dominate the forces of thermal vibration.  In amorphous 
materials, the switch from the dominance of thermal vibration to intermolecular forces 
is gradual and not sharply defined.

In partially crystalline materials, the intermolecular forces must be great enough 
to drive the ordering, folding, or "cuddling" of the molecules.  This requires greater 
energy than the same transition in amorphous materials.  Conversely, melting 
crystalline materials takes greater energy and occurs at a more definite temperature.

LDPE has short branches, often an ethyl or butyl group. These occur about 15 to 30 
times per 1000 carbon atoms.  In HDPE the branches are less frequent, about 1 to 5 
branches for 1000 carbon atoms.

The relative sizes of atoms and groups effect the characteristics of a polymer.  Large 
atoms or groups cause a...

(Frank’s note: text was not finished)